2.A.1 The Major Facilitator Superfamily (MFS)

The MFS is a very old, large and diverse superfamily that includes over 1 million sequenced members. They catalyze uniport, solute:cation (H+, but seldom Na+) symport and/or solute:H+ or solute:solute antiport. Most are of 400-600 amino acyl residues in length and possess either 12, 14, or occasionally, 24 transmembrane α-helical spanners (TMSs). The mechanistic principles applicable to all MFS carriers have been summarized by Law et al (2008), while Zhang et al. 2015 considered the interaction between protonation and the negative-inside membrane potential. Functional roles of the conserved sequence motifs were also discussed in the context of the 3D structures.

The 24 TMS MFS permease, NarK, of Paracoccus pantotrophus has two 12 TMS domains, NarK1 and NarK2, both of which are required for normal nitrate uptake. NarK1 catalyzes NO3-:H+ symport, dependent on the pmf, while NarK2 catalyzes NO3-:NO2- antiport, independently of the pmf (Wood et al., 2002). Thus, the protein is a fusion protein of two homologous but distinct MFS permeases.

MFS permeases exhibit specificity for sugars, polyols, drugs, neurotransmitters, Krebs cycle metabolites, phosphorylated glycolytic intermediates, amino acids, peptides, osmolites, siderophores (efflux), iron-siderophores (uptake), nucleosides, organic anions, inorganic anions, etc. They are found ubiquitously in all three kingdoms of living organisms. One member of the DHA2 family with 14 TMSs, the TetL Me2+ · tetracycline:H+ antiporter of B. subtilis (TC #2.A.1.3.16), which also exhibits monovalent ion antiport activity, can be converted to a monovalent cation (Na+, K+, H+) antiporter with no tetracycline transport activity by deletion of TMSs 7 and 8, the two central and extra TMSs (Jin et al., 2001). Genome analyses of MFS permeases have been published (Lorca et al., 2007).

A 6.5 Å resolution structure for the MFS permease, OxlT (TC #2.A.1.11.1) was obtained in early studies (Heymann et al., 2001; Hirai et al., 2002) which shows the positions of the transmembrane α-helices but does not allow assignment of the TMS # to these helices. Molecular modeling (Hirai et al., 2003) led to the suggestion that the 12 TMS protein arose from a 3 TMS element by two successive duplication events. The same suggestion resulted from sequence comparisons showing that the primordial 3 TMS element may have arisen from a VIC family (TC #1.A.1) 2 TMS channel-forming unit Hvorup & Saier, (2002).This conclusion has been extensively confirmed in several more recent studies.

The high-resolution 3-dimensional structures (3.3 and 3.5 Å resolution) of the glycerol-3-P:P antiporter (GlpT; TC #2.A.1.4.3) and the lactose:H+ symporter (LacY; TC #2.A.1.5.1), respectively (Huang et al., 2003 and Abramson et al., 2003, respectively; see also Locher et al., 2003; Guan et al., 2007) have been determined. These structures reveal the 2-fold symmetry expected, based on sequence similarity of the two halves. The substrate pathway is predicted to exist between the two halves of the permeases using an alternating access mechanism with a single substrate binding site (Huang et al., 2003). This mechanism is termed a 'rocker switch' type of movement.

As suggested above, MFS antiporters are believed to operate via a single binding site, alternating-access mechanism that involves a rocker-switch type movement of the two halves of the protein (Law et al., 2008). In the sn-glycerol-3-phosphate transporter (GlpT) from Escherichia coli, the substrate-binding site is formed by several charged residues and a histidine that can be protonated. Salt-bridge formation and breakage are involved in the conformational changes of the protein during transport (Law et al., 2008).

Vesicular glutamate transporters (VGLUTs [2.A.1.14.13 and 2.A.1.14.16]) are responsible for the vesicular storage of L-glutamate and play an essential role in glutamatergic signal transmission in the central nervous system. VGLUT2 facilitates L-glutamate uptake in a membrane potential (ΔΨ)-dependent fashion. Uptake exhibited an absolute requirement for ~4 mM Cl- and was sensitive to Evans blue, but was insensitive to D,L-aspartate. VGLUT2s with mutations in the transmembrane-located residues Arg184, His128, and Glu191 showed a dramatic loss in L-glutamate transport activity. VGLUT2 appears to possess two intrinsic transport machineries that are independent of each other: a ΔΨ-dependent L-glutamate uptake and a Na+-dependent Pi uptake (Juge et al., 2006). 

Trichoderma spp. are avirulent, fungal, opportunistic plant symbionts present in nearly all climatic soils. These Trichoderma strains produce secondary metabolites that are potent bio-control agents against microbial pathogens and also can be plant growth promoters. The MFS includes a large proportion of efflux-pumps which are linked with membrane transport of these secondary metabolites in T. reesei (Chaudhary et al. 2016).

The generalized transport reactions catalyzed by MFS porters are:

(1) Uniport: S (out) ⇌ S (in).

(2) Symport: S (out) + [H+ (or Na+)] (out) ⇌ S (in) + [H+ (or Na+)] (in).

(3) Antiport: S1 (out) + S2 (in) ⇌ S1 (in) + S2 (out) (S1 may be H+ or a solute).


This family belongs to the MFS Superfamily.



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2.A.1.1 The Sugar Porter (SP) Family


TC#NameOrganismal TypeExample

Galactose:H+ symporter, GalP (also transports xylose) (Hernández-Montalvo et al., 2001). Relative substrate affinities of wild-type and mutant forms of the E. coli sugar transporter GalP have been determined by solid-state NMR (Patching et al., 2008).


GalP of E. coli (P0AEP1)


Maltotriose/maltose:H+ symporter, Mal6T or Mal61 (Dietvorst et al. 2005).  The ortholog (90% identical) in Saccharomyces pastorianus (Lager yeast) (Saccharomyces cerevisiae x Saccharomyces eubayanus), MTT1 or Mty1 of 615 aas, has higher affinity for maltotriose than maltose (Magalhães et al. 2016).


MAL6 of Saccharomyces cerevisiae

2.A.1.1.100Probable metabolite transport protein YFL040WFungiYFL040W of Saccharomyces cerevisiae
2.A.1.1.101Probable metabolite transport protein YDR387CFungiYDR387C of Saccharomyces cerevisiae
2.A.1.1.102Plastidic glucose transporter 4 (AtpGlcT)PlantsAt5g16150 of Arabidopsis thaliana
2.A.1.1.103D-xylose-proton symporter-like 3, chloroplasticPlantsAt5g59250 of Arabidopsis thaliana
2.A.1.1.104Myo-inositol transporter 2FungiITR2 of Saccharomyces cerevisiae
2.A.1.1.105Hexose transporter HXT11 (Low-affinity glucose transporter LGT3)FungiHXT11 of Saccharomyces cerevisiae
2.A.1.1.106Probable metabolite transport protein CsbCBacilliCsbC of Bacillus subtilis
2.A.1.1.107Hexose transporter HXT15FungiHXT15 of Saccharomyces cerevisiae
2.A.1.1.108Low-affinity glucose transporter HXT1FungiHXT1 of Saccharomyces cerevisiae
2.A.1.1.109Hexose transporter HXT14FungiHXT14 of Saccharomyces cerevisiae

General α-glucoside:H+ symporter, Gtr3, Mal11,Mal1T, Mtp1 or Agt1 . (Substrates include trehalose, maltotriose, maltose, turanose, isomaltose, α-methyl-glucoside, maltotriose, palatinose, and melezitose) (Smit et al., 2008).  Maltotriose is transported with higher affinity than maltose (Magalhães et al. 2016).


AGT1 of Saccharomyces cerevisiae

2.A.1.1.110Hexose transporter HXT13FungiHXT13 of Saccharomyces cerevisiae

High-affinity glucose transporter HXT2.  Asp340 and Asn331 in part determine the high glucose affinity (Kasahara et al. 2007; Kasahara and Kasahara 2010).


HXT2 of Saccharomyces cerevisiae

2.A.1.1.112High-affinity glucose transporter Ght1 (Hexose transporter 1)YeastGht1 of Schizosaccharomyces pombe

Putative metabolite transport protein YyaJ


YyaJ of Bacillus subtilis


Putative metabolite transport protein YaaU


YaaU of Escherichia coli


Putative metabolite transport protein YdjK


YdjK of Escherichia coli


Arabinose/xylose transporter, AraE (Wang et al. 2013).


AraE of Coynebacterium glutamicum


Glucose transporter Rco-3 or MoST1. MoST1 plays a specific role in conidiation and mycelial melanization which is not shared by other hexose transporter family members in M. oryzae (Saitoh et al. 2013).


MoST1 of Magnaporthe oryzae


MFS porter of 435 aas


MFS porter of Sulfolobus solfataricus


The galacturonic acid (galacturonate) uptake porter, GatA, of 518 aas and 12 TMSs (Sloothaak et al. 2014).


GatA of Aspergillus niger



Glucose uniporter, Glut3 (also transports dehydro-ascorbate; Maulén et al., 2003). Down-regulated in the brains of Alzheimer's disease patients (Liu et al., 2008b).  The structure of the human orthologue with D-glucose bound was solved at 1.5 Å resolution in the outward occluded conformation (Deng et al. 2015).  Sugars are predominantly coordinated by polar residues in the C-terminal domain. The conformational transition from the outward-open to the outward-occluded states entails a prominent local rearrangement of the extracellular part of  TMS 7. Comparison of the outward-facing GLUT3 structures with inward-open GLUT1 provides insight into the alternating access cycle for GLUTs, whereby the C-terminal domain provides the primary substrate-binding site and the N-terminal domain undergoes rigid-body rotation with respect to the C-terminal domain (Deng et al. 2015).


Gtr3 (Glut3) of Rattus norvegicus (rat)


Major myo-inositol transporter, IolT1, of 456 aas (Kröger et al. 2010).


IolT1 of Samonella enterica


Minor myo-inositol transporter, IolT2, of 478 aas (Kröger et al. 2010).


IolT2 of Salmonella enterica


Sorbitol (glucitol) transporter SOT2 of 491 aas (Liu D and Teng Y, unpublished)


SOT2 of Pyrus pyrifolia (Chinese pear) (Pyrus serotina)


Sorbitol transporter of 535 aas


SOT1 of Pyrus pyrifolia (Chinese pear) (Pyrus serotina)


The sugar uptake porter of 514 aas and 12 TMSs, STP10.  Transports glucose, galactose and mannose, and is therefore a hexose transporter (Rottmann et al. 2016).

STP10 of Arabidopsis thaliana


Glycerol:H+ symporter of 530 aas and 12 TMSs, GT1.  It is essnetial for the glycerol repression of the alcohol oxidase 1 (AOX1 gene (Zhan et al. 2016).

GT1 of Komagataella pastoris (Yeast) (Pichia pastoris)


Myo inositol uptake porter of 574 aas and 12 TMSs, Fst1.  Also takes up the polyketide mycotoxin produced by Fusarium verticillioides during the colonization of maize kernels, Fumonisin B1 (FB1).  The activity was demonstrated with the ortholog in Weissella verticillioides (Niu et al. 2016). 

Fst1 of Weissella confusa


Hexose:proton symporter of 525 aas and 12 TMSs, Hxt5. Takes up D-glucose, D-fructose, D-xylose, D-mannose, D-galactose with decreasing affinity in this order (Rani et al. 2016).

Hxt5 of Piriformospora indica


Facilitative (Na+-independent) glucose-specific transporter (Km = 3 mM) of 486 aas and 12 TMSs, HT1; inhibited by cytochalasin B and localized to the midgut (Price et al. 2007).

HT1 of Nilaparvata lugens (Brown planthopper)


High-capacity facilitative transporter for trehalose, TRET1, required to induce anhydrobiosis. Anhydrobiotic larvae can survive almost complete dehydration. Does not transport maltose, sucrose or lactose. Transports trehalose synthesized in the fat body and incorporates trehalose into other tissues that require a carbon source, thereby regulating trehalose levels in the hemolymph (Kikawada et al. 2007; Kanamori et al. 2010).  70% identical to the Drosophila homologue, TC# 2.a.1.1.99.

TRET1 of Polypedilum vanderplanki (Sleeping chironomid)


Fructose uniporter, GLUT5.  The proteins from rat and cow have been crystalized and their structures have been determined in the open outward- and open inward-facing conformations, respectively. On the basis of comparisons of the inward-facing structures of GLUT5 and human GLUT1, a ubiquitous glucose transporter, a single point mutation proved to be enough to switch the substrate-binding preference from fructose to glucose. A comparison of the substrate-free structures of GLUT5 with occluded substrate-bound structures of E. coli XylE suggested that, in addition to a global rocker-switch-like re-orientation of the bundles, local asymmetric rearrangements of carboxy-terminal transmembrane bundle helices, TM7 and TM10, underlie a 'gated-pore' transport mechanism (Nomura et al. 2015).


SLC2A5 of Homo sapiens


Glucose transporter 1, GLUT1 or Slc2A1 of 491 aas and 12 TMSs.  Expression occurs in the mesodermal region of Xenopus embryos, especially in the dorsal blastopore lip at the gastrula stage.  It is an important player during gastrulation cell movement (Suzawa et al. 2007).

GLUT1 of Xenopus laevis (African clawed frog)


Myo-inositol-specific uptake transporter, ITR1 of 509 aas and 12 TMSs.  The Km for myo-inositol is about 1 mM; glucose and other inositols are apparently not transported (Cushion et al. 2016).

ITR1 of Pneumocystis carinii

2.A.1.1.14Hexose:H+ symporterPlantsHup1 of Chlorella kessleri
2.A.1.1.15Putative sugar transporterArchaeaPorter of Sulfolobus solfataricus

Low-affinity hexose (glucose, fructose, mannose, 2-deoxyglucose) uniporter.  The evolution of hexose transporters in kinetoplastid protozoans has been studied (Pereira and Silber 2012).


Gtr2 (D2) of Leishmania donovani

2.A.1.1.17Glucose transporterProtozoaTh2A of Trypanosoma brucei

Glucose/mannose/fructose transporter and high affinity sensor, Snf3p (regulates glucose transport via other systems).  Residues involved in ligand preference are similar to those involved in transport (Dietvorst et al. 2010).  Snf3p in Candida glabrata is essential for growth in low glucose media but not high glucose media, and plays a role in the induction of severall hexose transporters (Ng et al. 2015).


Snf3p of Saccharomyces cerevisiae


Glucose transporter and low affinity sensor, Rgt2p (regulates glucose transport in conjunction with Snf3p)

YeastRgt2p of Saccharomyces cerevisiae

Arabinose (xylose; galactose):H+ symporter, AraE (low affinity high capacity) (Khlebnikov et al. 2001).


AraE of E. coli (P0AE24)

2.A.1.1.20Myoinositol:H+ symporter, MITProtozoaMIT of Leishmania donovani; most similar to ITRI of Saccharomyces cerevisiae
2.A.1.1.21Hexose:H+ symporter, Ght2 (Glucose > Fructose)YeastGht2 of Schizosaccharomyces pombe
2.A.1.1.22Hexose:H+ symporter, Ght6 (Fructose > Glucose)YeastGht6 of Schizosaccharomyces pombe
2.A.1.1.23Gluconate:H+ symporter, Ght3YeastGht3 of Schizosaccharomyces pombe
2.A.1.1.24Hexose (Glucose and Fructose) transporter, PfHT1ProtozoaPfHT1 of Plasmodium falciparum

Myoinositol:H+ symporter, HMIT (also transport other inositols including scyllo-, muco- and chiro-, but not allo-inositol) (Aouameur et al., 2007). Expressed in the golgi of the hippocampus and cortex. May also transport inositoltriphosphate (Di Daniel et al., 2009). Interacts directly with γ-secretase (9.B.47.1.1) to regulate its activity and the production of Abeta production, important in Alzheimer's disease (Teranishi et al. 2015).


SLC2A13 of Homo sapiens

2.A.1.1.26Major myoinositol:H+ symporter, IolTBacteriaIolT (YdjK) of Bacillus subtilis
2.A.1.1.27Minor myoinositol:H+ symporter, IolFBacteriaIolF of Bacillus subtilis

The erythrocyte/brain hexose facilitator, glucose transporter-1, Gtr1 or Glut1. Transports D-glucose, dehydroascorbate, arsenite and the flavonone, quercetin, via one pathway and water via a distinct channel. Sugar transport has been suggested to function via a sliding mechanism involving several sugar binding sites (Cunningham et al., 2006). Glut1 is the receptor for human T-cell leukemia virus (HTLV)) (Manel et al., 2003). It is regulated by stomatin (TC# 8.A.21) to take up dehydroascorbate (Montel-Hagen et al., 2008). Mutations cause Glut1 deficiency syndrome, a human encephalopathy that results from decreased glucose flux through the blood brain barrier (Pascual et al., 2008).  Mueckler and Makepeace (2009) have presented a model of the exofacial substrate-binding site and helical folding of Glut1. Glut1, 2, 4 and 9 are functional both in the plasma membrane and the endoplasmic reticulum (Takanaga and Frommer, 2010). Glut1 is down-regulated in the brains of Alzheimer's disease patients (Liu et al., 2008b). Metabolic stress rapidly stimulates blood-brain barrier endothelial cell sugar transport by acute up-regulation of plasma membrane GLUT1 levels, possibly involving an AMP-activated kinase activity (Cura and Carruthers, 2010). Serves as a receptor for neuropilin-1 (923aas; 2 TMSs; O14786) and heparan sulfate proteoglycans (HSPGs) (Hoshino, 2012). Glut1 has a nucleotide binding site, and nucleotide binding affects transport activity (Yao and Bajjalieh 2009).  The protein serves as a receptor for dermatin and β-adducin which help link the spectrin-actin junctional complex to the erythrocyte plasma membrane (Khan et al. 2008).  May play a role in paroxysmal dyskinesias (Erro et al. 2017).


SLC2A1 of Homo sapiens


Glucosamine/glucose uniporter, Glut-2 (may also transport dehydroascorbate (Mardones et al., 2011Maulén et al., 2003), and cotransport water against an osmotic gradient (Naftalin, 2008))

AnimalsSLC2A2 of Homo sapiens

Xylose:H+ symporter.  Also transports and binds D-glucose and 6-bromo-6-deoxy-D-glucose.  The 3-d structure is known in three conformers, outward occluded, inward occluded and inward open (Sun et al. 2012: Quistgaard et al. 2013).  Most of the sugar-binding residues are conserved with the human Glut-1, 2, 3 and 4 homologues.  The coalescence of intramolecular tunnels and cavities has been postulated to account for facilitated diffusion of sugars (Cunningham and Naftalin 2014).


XylE of E. coli (P0AGF4)

2.A.1.1.30Low affinity, constitutive, glucose (hexose; xylose) uniporter, Hxt4 (LGT1) (also transports arsenic trioxide [As(OH)3] as do Hxtl, 3, 5, 7 and 9) (Liu et al., 2004)YeastHxt4 of Saccharomyces cerevisiae

High affinity, glucose-repressible, glucose (hexose) uniporter (Hxt6/Hxt7). Asn331 and hydrophobic residue side chains in TMS5 determine substrate affinity (Kasahara et al., 2011; Kasahara and Kasahara 2010).  Also transports xylose (Wang et al. 2013).


Hxt6/Hxt7 of Saccharomyces cerevisiae
Hxt6 (P39003)

2.A.1.1.32Glucose/fructose:H+ symporter, GlcP (Zhang et al., 1989)BacteriaGlcP of Synechocystis sp. (P15729)
2.A.1.1.33Fructose:H+ symporter, Frt1 (Diezemann and Boles, 2003)YeastFrt1 of Kluyveromyces lactis (CAC79614)
2.A.1.1.34The broad specificity sugar/sugar alcohol (myo-inositol, glycerol, ribose, sorbitol, mannitol, xylitol, erythritol, etc) H+ symporter, AtPLT5 (transports a wide range of hexoses, pentoses, tetroses, sugar alcohols and a sugar acid, but not disaccharides) (Reinders et al., 2005) (expressed in roots, leaves and floral organs) (Klepek et al., 2004)PlantsAtPLT5 of Arabidopsis thaliana (Q8VZ80)
2.A.1.1.35The major glucose (or 2-deoxyglucose) uptake transporter, GlcP (van Wezel et al., 2005)BacteriaGlcP of Streptomyces coelicolor (Q7BEC4)

The low affinity, glucose-inducible glucose transporter, MstE (Forment et al., 2006)


MstE of Aspergillus nidulans (Q400D8)

2.A.1.1.37The glucose/fructose facilitator, Glut7 (SLC2A7) (a single mutation, I314V, results in loss of fructose transport but retention of glucose transport (Manolescu et al., 2005)AnimalsSLC2A7 of Homo sapiens
2.A.1.1.38The glycerol:H+ symporter, Stl1p (Ferreira et al., 2005)YeastStl1p of Saccharomyces cerevisiae (NP_010825)
2.A.1.1.39The high affinity glucose transporter, Hgt1 (Baruffini et al., 2006)YeastHgt1 of Kluyveromyces lactis (P49374)
2.A.1.1.4Glucose uniporterBacteriaGlf of Zymomonas mobilis
2.A.1.1.40The xylose facilitator, Xylhp (Nobre et al., 1999)YeastXylhp of Debaryomyces hansenii (AAR06925)
2.A.1.1.41The D-xylose:H+ symporter, XylT (Km=220 μM; inhibited competitively by 6-deoxyglucose (Ki=220 μM), but not by other sugars tested) (Chaillou et al., 1998)BacteriaXylT of Lactobacillus brevis (O52733)
2.A.1.1.42The D-glucose:H+ symporter, GlcP (glucose uptake is inhibited by 2-deoxyglucose, mannose and galactose) (Parche et al., 2006)BacteriaGlcP of Bifidobacterium longum (AAN25419)

The monosaccharide (MST) (glucose > mannose > galactose > fructose):H+ symporter, MST1 (Schussler et al., 2006).


MST1 of Geosiphon pyriformis (A0ZXK6)

2.A.1.1.44The hexose (glucose and fructose but not galactose) transporter (Glut11; SLC2A11) (Scheepers et al., 2005)AnimalsSLC2A11 of Homo sapiens

Vacuolar (tonoplast) glucose transporter1, Vgt1 (important for seed germination and flowering) (Aluri and Büttner, 2007)


Vgt1 of Arabidopsis thaliana (Q8L6Z8)


The blastocyst/testis glucose transporter, Glut8 (Doege et al., 2000) (insulin stimulated in blastocysts) (Carayannopoulos et al., 2000).


Glut8 of Mus musculus (Q9JIF3)


The embryonic liver, kidney, and other tissue uric acid (urate) transporter, Glut9 (SLC2A9) (Wright et al. 2010). Mutations in this transporter cause severe renal hyperuricemia.  It transports hexoses as well as urate, the latter by an electrogenic uniport mechanism.  It's transcription is regulated by a hepatocyte nuclear factor, HNF4α (Prestin et al. 2014).


Glut9 of Mus musculus (Q5ERC7)

2.A.1.1.48The pentose/hexose transporter (sugar transport protein 2), STP2. (Expressed during pollen maturation and early stages of gametophyte development) (Truernit et al., 1999) Plants STP2 of Arabidopsis thaliana (Q9LNV3)
2.A.1.1.49The sink-specific, stress-regulated monosaccharide uptake porter, STP4. (Induced upon wounding or infection with bacteria or fungi; expressed in roots and flowers) (Truernit et al., 1996)PlantsSTP4 of Arabidopsis thaliana (Q39228)
2.A.1.1.5Hexose uniporterYeastHxtO of Saccharomyces cerevisiae

The glucose/fructose:H+ symporter, STP13 (sugar transport protein 13). Expressed in vascular tissues and induced during programmed cell death (Norholm et al., 2006).  Used to combat bacterial infection by competing with them for sugars by phosphorylation of STP13 by the BAK1 receptor kinase (Yamada et al. 2016).


STP13 of Arabidopsis thaliana (Q94AZ2)

2.A.1.1.51Glucose/xylose: H+ symporter, Gsx1 (Leandro et al., 2006)yeastGsx1 of Candida intermedia (Q2MEV7)
2.A.1.1.52The glucose transport protein, GTP1 (Skelly et al., 1994)AnimalsGTP1 of Schistosoma mansoni (Q26579)

Myo-Inositol uptake porter, IolT1 (Km=0.2mM) (Krings et al., 2006).  Can also transport D-glucose (Ikeda et al. 2011).


IolT1 of Corynebacterium glutamicum (Q8NTX0)


Myo-Inositol (Km=0.45mM) uptake porter, IolT2 (Krings et al., 2006).  Can not transport D-glucose (Ikeda et al. 2011).


IolT2 of Corynebacterium glutamicum (Q8NL90)


L-arabinose:proton symporter, AraE (Sa-Nogueira and Ramos, 1997). Also transports xylose, galactose and α-1,5 arabinobiose (Ferreira and Sá-Nogueira, 2010).


AraE of Bacillus subtilis (P96710)

2.A.1.1.56High affinity monosaccharide (KM ≈ 20 µM):H+ symporter, Stp6 (takes up glucose, 3-O-methylglucose, mannose, fructose, galactose and to a lesser extent, xylose and ribulose. (Scholz-Starke et al., 2003)PlantsStp6 of Arabidopsis thaliana (Q9SFG0)

High affinity (15 μM) glucose (monosaccharides including xylose):H+ symporter, MstA (Jørgensen et al., 2007).


MstA of Aspergillus niger


Low affinity glucose:H+ symporter, MstC (Jørgensen et al., 2007).


MstC of Aspergillus niger

2.A.1.1.59The glucose transporter, GLUT10, was originally believed to be responsible for Type 2 diabetes. It is now believed to be responsible for arterial tortuosity, a rare autosomal recessive connective tissue disease (Callewaert et al., 2007). GLUT10 transports glucose and 2-deoxy glucose (Km=0.3 mM), and is inhibited by galactose and phloretin (Coucke et al., 2006). AnimalsSLC2A10 of Homo sapiens

Galactose, glucose uniporter, Gal2. Also transports xylose (Wang et al. 2013).  This transporter has been engineered by mutation (N376F) to transport xylose without being inhibited by glucose or transporting other hexoses (Farwick et al. 2014).  The 3-d structure is known (Wang et al. 2015).


Gal2 of Saccharomyces cerevisiae

2.A.1.1.60The major hexose transporter, Htr1 (mediates the active uptake of hexoses by sugar:H+ symport. Can transport glucose, 3-O-methylglucose, fructose, xylose, mannose, galactose, fucose, 2-deoxyglucose and arabinose. Confers sensitivity to galactose in seedlings. Km=20 uM for glucose) (Stadler et al., 2003; Boorer et al., 1994)PlantsHtr1 of Arabidopsis thaliana (P23586)
2.A.1.1.61High affinity monosaccharide (Km = 25 µM) transporter (takes up glucose, galactose, mannose, xylose and 3-O-methylglucose, but not fructose and ribose), STP11 (expressed in pollen tubes) (Schneidereit et al., 2005) PlantsSTP11 of Arabidopsis thaliana (Q9FMX3)
2.A.1.1.62High affinity (0.24mM) plasma membrane myoinositol-specific H+ symporter, INT4 (Schneider et al., 2006) PlantsINT4 of Arabidopsis thaliana (O23492)
2.A.1.1.63Low affinity inositol (myoinsoitol (Km = 1 mM), scylloinositol, d-chiroinositol and mucoinositol):H+ symporter (expressed in the anther tapetum, the vasculature, and the leaf mesophyll (Schneider et al., 2007)PlantsINT2 of Arabidopsis thaliana (Q9C757)
2.A.1.1.64The hexose sensor, Hxs1 (believed to be non-transporting) (Stasyk et al., 2008)YeastHxs1 of Hansenula polymorpha (B1PM37)
2.A.1.1.65Glucose permease GlcP (Pimentel-Schmitt et al., 2008) (most similar to 2.A.1.1.32)BacteriaGlcP of Mycobacterium smegmatis (A0QZX3)

The tonoplast H+:Inositol symporter 1, Int1 (mediates efflux from the tonoplast to the cytoplasm (Schneider et al., 2008) (most similar to 2.A.1.1.63 and 2.A.1.1.62).


Int1 of Arabidopsis thaliana (Q8VZR6)

2.A.1.1.67Glucose/xylose facilitator-1, GXF1 (functions by sugar uniport; low affinity (Leandro et al., 2008)YeastGXF1 of Candida intermedia (Q2MDH1)

The Glucose Transporter/Sensor Rgt2


Rgt2 Pichia stipitis (A3M0N3)

2.A.1.1.69Sugar & polyol transporter 1 (SPT1): broad specificity; takes up glucose (Schilling and Oesterhelt, 2007). Loss of the first 3 TMSs of the 12 TMSs does not prevent sugar uptake or sugar recognition but lowers substrate affinity & transport rate, and abolished H+ symport (Schilling and Oesterhelt, 2007).Red algaeSPT1 of Galdieria sulphuraria (A1Z264)
2.A.1.1.7Quinate:H+ symporterFungiQay of Neurospora crassa

MFS Permease


MFS Permease of Phaeosphaeria nodurum

2.A.1.1.71Hexose (glucose) transporter, GT4 (D2) (almost identical to 2.A.1.1.16)


Hexose transporter, GT4 of Leishmania mexicana (B1PLM1)


The kidney basolateral voltage-driven urate efflux transporter (URATv1) (orthologue of 2.A.1.1.47) (Anzai et al., 2008). Human SLC2A9a and SLC2A9b isoforms mediate electrogenic transport of urate with different characteristics in the presence of hexoses (Witkowska et al., 2012).  It transports hexoses as well as urate, the latter by a uniport mechanism.  It's transcription is regulated by a hepatocyte nuclear factor, HNF4α (Prestin et al. 2014). Residues involved in urate transport have been identified (Long et al. 2017).


SLC2A9 of Homo sapiens

2.A.1.1.73Glycerol uptake permease (Glycerol:H+ symporter) Stl1. (Involved in salt stress relief) (Kayingo et al. 2009) (similar to Stl1 of S. cerevisiae (2.A.1.1.38))


Stl1 of Candida albicans (Q5A8J5)


The putative L-rhamnose porter, RhaY

Firmicutes, Actinobacteria

RhaY of Listeria monocytogenes (Q926Q9)


The fructose/xylose:H+ symporter, PMT1 (polyol monosaccharide transporter-1). Also transports other substrates at lower rates. PMT2 is largely of the same sequence and function. Both are present in pollen and young xylem cells (Klepek et al., 2005).


PMT1 of Arabidopsis thaliana (Q9XIH7)


Glucose transporter, GT1. GT1, 2, and 3 are homologues. GT2 and GT3 transport ribose as well as glucose at different rates. GT3 transports ribose with 6-fold lower efficiency due to two threonines in GT3 that are alanines in GT2. They are in two loops between TMSs 3, 4, and 7, 8 (Naula et al., 2010). GT1 is expressed in the flagellar membrane and may be both a glucose transporter and sensor, allowing the parasites to enter the stationary phase when they deplete glucose although in the absence of the sensor, they lose viability (Rodriguez-Contreras et al. 2015).


GT1 of Leishmania mexicana (Q9F315)


The D-glucose/D-ribose transporter, LmGT2 (Most similar to 1.A.1.1.18) (Naula et al., 2010).


LmGT2 of Leishmania mexicana (O61059)


The glucose transporter, LmGT3 (homologous to LmGT2 (1.A.1.1.75)). Two threonine residues located in the hydrophilic loops connecting TMSs 3 & 4 and 7 & 8 of GT3 prevent transport of D-ribose. Changing these two residues to alanine (as in GT2) allows transport of ribose. Thus, loops 3-4 and 7-8 partially determine substrate specificity (Naula et al., 2010).


LmGT3 of Leishmania mexicana (O61060)


Polyol (xylitol):H+ symporter, PLT4 (Kalliampakou et al., 2011)



PLT4 of Lotus japonicus (Q1XF07)


Myoinositol:H+ symporter




ITR1 of Saccharomyces cerevisiae


Insulin-responsive facilitative glucose transporter in skeletal and cardiac muscle, adipose, and other tissues, Glut4 (GTR4; SLC2A4; 509aas). Defects in Glut4 cause noninsulin-dependent diabetes mellitus (NIDDM). Hyperinsulinemia leads to uncoupled insulin regulation of the GLUT4 glucose transporter and the FoxO1 transcription factor (Gonzalez et al., 2011). The first luminal loop confers insulin responsiveness to GLUT4 (Kim and Kandror, 2012). Exercise increases Glut4 synthesis in a process involving several protein kinases, the Glut4 enhancer factor (GEF; SLC2A4 regulator; Q9NR83), and the myocyte enhancing factor 2 (MEF2; NP_001139257). (McGee and Hargreaves 2006; Wright 2007; Zorzano et al. 2005)

AnimalsSLC2A4 of Homo sapiens

The glucose uptake porter, GluP (Araki et al., 2011).


GluP of Rhodococcus jostii (Q0SE66)


The cellobiose/cellodextrin transporter, Cdt-1 (Galazka et al., 2010)


Cdt-1 of Neurospora crassa (Q7SCU1)


The cellobiose/cellodextrin transporter, Cdt-2


Cdt2 of Neurospora crassa (Q7SD12)


The heteromeric TMT1/TMT2 glucose/sucrose:H+ antiporter. Catalyzes glucose/sucrose antiport into vacuoles (Schulz et al., 2011).


The TMT1/2 sugar:H+ anti-porter of Arabidopsis thaliana. TMT1 (Q96290). TMT2 (Q8LPQ8).


Zebrafish Slc2A10 (Glut10) facilitative glucose transporter.


Zebrafish Glut10 of Danio rerio (A8KB28)


The sea bream facilitative glucose transporter 1 (GLUT1) (Balmaceda-Aguilera et al., 2012).


Glut1 of Sparus aurata (H9BPB6)

2.A.1.1.87 solute carrier family 2 (facilitated glucose transporter), member 12AnimalsSLC2A12 of Homo sapiens
2.A.1.1.88 solute carrier family 2 (facilitated glucose transporter), member 6AnimalsSLC2A6 of Homo sapiens
2.A.1.1.89Solute carrier family 2, facilitated glucose transporter member 8 (Glucose transporter type 8) (GLUT-8) (Glucose transporter type X1)AnimalsSLC2A8 of Homo sapiens
2.A.1.1.9Lactose, galactose:H+ symporterYeastLacP of Kluyveromyces lactis
2.A.1.1.90Solute carrier family 2, facilitated glucose transporter member 14 (Glucose transporter type 14) (GLUT-14)AnimalsSLC2A14 of Homo sapiens
2.A.1.1.91Solute carrier family 2, facilitated glucose transporter member 3 (Glucose transporter type 3, brain) (GLUT-3)AnimalsSLC2A3 of Homo sapiens

Inner membrane metabolite transport protein YdjE


YdjE of E. coli

2.A.1.1.93Vacuolar protein sorting-associated protein 73FungiVPS73 of Saccharomyces cerevisiae
2.A.1.1.94Putative metabolite transport protein YDL199CFungiYDL199C of Saccharomyces cerevisiae

Inner membrane metabolite transport protein YgcS



YgcS of E. coli

2.A.1.1.96Probable metabolite transport protein YBR241CFungiYBR241C of Saccharomyces cerevisiae
2.A.1.1.97Sugar transporter ERD6 (Early-responsive to dehydration protein 6) (Sugar transporter-like protein 1)PlantsERD6 of Arabidopsis thaliana
2.A.1.1.98Sugar transporter ERD6-like 6PlantsAt1g75220 of Arabidopsis thaliana
2.A.1.1.99Facilitated trehalose transporter Tret1-1 (DmTret1-1)AnimalsTret1-1 of Drosophila melanogaster

2.A.1.10 The Nucleoside: H+ Symporter (NHS) Family


TC#NameOrganismal TypeExample

Nucleoside porter, NupG.  Guanosine, inosine, cytidine and thymidine but not uridine, adenosine and xanthosine are transported (Patching et al. 2005).


NupG of E. coli (P0AFF4)


Xanthosine porter, XapB.  Xanthosine, inosine, adenosine, cytidine and thymidine but not guanosine and uridine are transported (Seeger et al. 1995; Nørholm and Dandanell 2001).


XapB of E. coli

2.A.1.10.3Dol-P-Glc:Glc(2)Man(9)GlcNAc(2)-PP-Dol alpha-1,2-glucosyltransferase (EC (Alpha-1,2-glucosyltransferase ALG10-A) (Alpha-2-glucosyltransferase ALG10) (Asparagine-linked glycosylation protein 10) (Dolichyl-phosphoglucose-dependent glucosyltransferase ALG10)FungiDIE2 of Saccharomyces cerevisiae

Putative ribonucleoside transporter, YegT, of 450 aas and 12 TM


YegT of Escherichia coli


2.A.1.11 The Oxalate:Formate Antiporter (OFA) Family


TC#NameOrganismal TypeExample

The oxalate:formate antiporter.  Residues and TMSs involved in the translocation pathway and substrate binding have been identified (Fu and Maloney 1998; Fu et al. 2001; Ye and Maloney 2002; Wang et al. 2006).


OxlT of Oxalobacter formigenes


Putative MFS transporter of 399 aas; 12 TMSs.


MFS porter of Pseudomonas aeruginosa (Q9I458)


Inner membrane protein yhjX.  Regulated by Crp as well as the LytS-like histidine sensor kinase, YehU, and the corresponding LytTR-like response regulator, YehT.  Possibly induced by peptides as cells enter the stationary growth phase.  Forms a complex with the csiA transporter, YjiY (TC# 2.A.114.1.9) and two sensor kinase/response regulator pairs, YehU/YehT and YdpA/YdpB (Behr et al. 2014).  The carbon storage regulator A (CsrA) is involved in posttranscriptional regulation of both yjiY and yhjX (Behr et al. 2014).


yhjX of Escherichia coli

2.A.1.11.4Uncharacterized membrane protein YJL163CFungiYJL163C of Saccharomyces cerevisiae

MFS-type transporter YcxA (ORF5) of 408 aas and 12 TMSs.  Capable of exporting the peptide antibiotic, surfactin, synthsized by a non-ribosome mechanism in B. subtilis (Li et al. 2015).


YcxA of Bacillus subtilis


Uncharacterized MFS-type transporter YbfB


YbfB of Bacillus subtilis


Uncharacterized protein of 512 aas and 12 TMSs.


UP of Chondrus crispus


Uncharacterized protein of 404 aas


UP of Pseudomonas aeruginosa


2.A.1.12 The Sialate:H+ Symporter (SHS) Family


TC#NameOrganismal TypeExample

The sialic acid porter, NanT.  N-acetylneuraminic acid (Neu5Ac) serves as a sole source of carbon and nitrogen for E. coli.  It is a mucus-derived carbon source in the mammalian gut. NanT can also take up and allow efficient growth on the related sialic acids, N-glycolylneuraminic acid (Neu5Gc) and 3-keto-3-deoxy-d-glycero-d-galactonononic acid (KDN) (Hopkins et al. 2013).


NanT of E. coli


The lactate/pyruvate:H+ symporter. Residues in the substrate translocation pathway have been reported (Soares-Silva et al., 2011).


Jen1 (YKL217w) of Saccharomyces cerevisiae


2.A.1.13 The Monocarboxylate Transporter (MCT) Family (Halestrap, 2011)

MCTs play roles in the absorption, tissue distribution, and clearance of both endogenous and exogenous compounds. MCTs are required for the transport of essential cell nutrients and for cellular metabolic and pH regulation (Jones and Morris 2016).


TC#NameOrganismal TypeExample

The proton-linked monocarboxylate (lactate, pyruvate, mevalonate, branched chain oxo acids, β-hydroxybutyrate, γ-hydroxybutyrate, butyrate, acetoacetate acetate and formate) uptake/efflux porter (Moschen et al. 2012). Also transports anti-tumor agents, 3-bromopyruvate and dichloroacetate (Cooper et al. 1989; Su et al. 2016). Activity is stimulated by direct interaction with carbonic anhydrase isoform II (Becker et al., 2005). This transporter interacts physically with the chaperone protein Basigin (CD147; TC #8.A.23.1.1) which is required both for targetting to the plasma membrane and for activity. Mct-2 uses a different chaperone protein, GP70. Mct-1 also transports the methionine hydroxy analogue 2-hydroxy (4-methylthio) butanate (Martin-Venegas et al., 2007; Becker and Deitmer, 2008). MCT1, 3 and 4 require the ancillary protein, basigin (P35613; 8.A.23.1.1) for plasma membrane localization (Ovens et al., 2010).  Partially localizes to the peroxysomal membrane (Visser et al. 2007). MCT1 is regulated by CD147 proteins, and this association is important for lactate export and cell proliferation in certain cancer cells (Walters et al. 2013).  Upregulated in some cancers and maintains the metabolic phenotype of these cancer cells by mediating lactate efflux together with a proton, promoting pH homeostasis (PMID 24921258). 


MCT1 (SLC16A1) of Homo sapiens


MCT8 (SLC16a2) homodimeric monocarboxylate thyroid hormone transporter 8 (Visser et al. 2009; Arjona et al., 2011).  The X-linked mental retardation Allan-Herndon-Dudley syndrome (AHDS) (a severe psychomotor retardation syndrome) protein (Schweizer and Köhrle 2012; Boccone et al. 2010; Johannes et al. 2016). Arg residues important for function have been identified (Groeneweg et al. 2013).  Thyroid hormone transporters in the brain and across the blood brain barrier have been reviewed (Wirth et al. 2014; Bernal et al. 2015).


SLC16A2 of Homo sapiens


Solute carrier family 16, member 5 (monocarboxylic acid transporter 6) of 505 aas and 12 TMSs. Found on the luminal side of small intestinal epithelial cells (Kohyama et al. 2013). MCT6 mediates uptake of nateglinide, an oral hypoglycemic agent. The K(t) for nateglinide is 46 μM. Thus, MCT6 may play a role in the intestinal absorption of nateglinide, although other transporters are also likely to be involved (Kohyama et al. 2013).


SLC16A5 of Homo sapiens


Solute carrier family 16, member 14 (monocarboxylic acid transporter 14), ATBo or MCT14.  Transports carnitine with low affinity (~ 1 mM) (Ingoglia et al. 2015). Its tissue localization in the mouse has been determined (Roshanbin et al. 2016).



SLC16A14 of Homo sapiens

2.A.1.13.13 solute carrier family 16, member 11 (monocarboxylic acid transporter 11)AnimalsSLC16A11 of Homo sapiens
2.A.1.13.14 solute carrier family 16, member 12 (monocarboxylic acid transporter 12)AnimalsSLC16A12 of Homo sapiens
2.A.1.13.15Monocarboxylate transporter 7 (MCT 7) (Monocarboxylate transporter 6) (MCT 6) (Solute carrier family 16 member 6)AnimalsSLC16A6 of Homo sapiens
2.A.1.13.16Monocarboxylate transporter 9 (MCT 9) (Solute carrier family 16 member 9)AnimalsSLC16A9 of Homo sapiens
2.A.1.13.17Monocarboxylate transporter 13 (MCT 13) (Solute carrier family 16 member 13)AnimalsSLC16A13 of Homo sapiens
2.A.1.13.18Probable transporter MCH2FungiMCH2 of Saccharomyces cerevisiae S288c
2.A.1.13.19Probable transporter MCH4FungiMCH4 of Saccharomyces cerevisiae

The low affinity aromatic amino acid (Tyr, Trp, Phe) transporter, TAT1 (T-type amino acid transporter), MCT10, Slc16a10.  Also transports N-methyl amino acids and thyroid hormones.  Essential for aromatic amino acid homeostasis in various tissues of mice (Mariotta et al. 2012). MCT10 is 58% identical to MCT8. Both transporters mediate T3 transport, but while MCT8 also transports rT3 and T4, these compounds are not efficiently transported by MCT10.  A few amino acyl residue substitutions in the human orthologue broadens the substrate specificity of this porter (Johannes et al. 2016).


Tat1 of Rattus norvegicus


Putative permease of 468 aas


Putative permease of Galdieria sulphuraria


MFS porter of 392 aas


MSF porter of Pseudomonas stutzeri


SLC16 Family protein of 771 aas and 12 TMSs, GEM-1.  GEM-1 acts in parallel to the GON-2 channel (TC# 1.A.4.5.10) to promote cation uptake within the developing gonad (Kemp et al. 2009).


Gem1 of Caenorhabditis elegans


Chicken MCT8 of 509 aas and 12 TMSs.  Transports pro-thyroid hormone, T4, with high affiinity, and T3 as well (Nele Bourgeois et al. 2016).

MCT8 of Gallus gallus (Chicken)


MCT10 (SLC16A10) of 400 aas and 11 TMSs.  Transports thyroid hormones, especially T3 (Nele Bourgeois et al. 2016).

MTC10 of Gallus gallus (chicken)


The thyroid hormone transporter, MCT8 (transports L- and D-isomers of thyroxine (T4), 3,3',5-triiodothyronine (T3), 3,3'5'-triiodothyronine (rT3) and 3,3'-diiodothyronine [Km values = 2-5 μM; Leu, Phe, Trp and Tyr were not transported]) (Friesema et al., 2003). Loss of function mutations in MCT8 leads to Allan-Herndon-Dudley syndrome, severe X-linked psychomotor retardation and elevated serum T3 levels (Jansen et al., 2008). Essential molecular determinants for thyroid hormone transport and their structural implications are presented by Kinne et al. (2010). Induced by retinoic acid (Kogai et al., 2010). Mediates energy-independent bidirectional transport. MCT8 is specific for L-iodothyronines and requires at least one iodine atom per aromatic ring. Thyronamines, decarboxylated metabolites of iodothyronines, triiodothyroacetic acid and tetraiodothyroacetic acid, TH derivatives lacking both chiral center and amino group, are not substrates (Kinne et al., 2010). A deficiency causes altered thyroid morphology and a persistent high triiodothyronine/thyroxine ratio after thyroidectomy (Wirth et al., 2011). Primary and secondary thyroid hormone transporters have been reviewed (Kinne et al., 2011).


MCT8 of Mus musculus (O70324)


The high affinity (17 μM) facilitated diffusion, riboflavin-regulated riboflavin uptake system, Mch5 (Reihl and Stolz, 2005)


Mch5 of Saccharomyces cerevisiae (NP_014951)


Monocarboxylate transporter-2 (MCT2). Transports γ-hydroxybutyrate (Wang and Morris, 2007). MCT2 requires the ancillary protein, embigin (Q6PCB8; 8.A.23.1.2) for plasma membrane localization (Ovens et al., 2010).  Partially localizes to the peroxysomal membrane (Visser et al. 2007).


MCT2 (SLC16A7) of Homo sapiens


Plasma membrane proton-linked monocarboxylate transporter, MCT4 (SLC16A3). Catalyzes the rapid plasma membrane transport of many monocarboxylates such as lactate, pyruvate, branched-chain oxo acids derived from leucine, valine and isoleucine, and the ketone bodies acetoacetate, beta-hydroxybutyrate and acetate.  Catalyzes lactate efflux from glycolyzing cells (Halestrap 2013).  Residues involved in high affinity inhibitors have been identified (Nancolas et al. 2015).  Forms a complex with binding partner, CD147/BSG, which regulates the transport activity (Fisel et al. 2015).


MCT4 (SLC16A3) of Homo sapiens


Monocarboxylate transporter-5 (MCT5 or SLC16A4; sometimes referred to as MCT4). Lactate transport via the MCT5 is non enzymatically stimulated by carbonic anhydrase II (Becker et al., 2010). MCTs require an ancillary 1TMS glycoprotein, either Embigin (Q6PCB8; TC# 8.A.23.1.2) or basigin (P35613; TC# 8.A.23.1.1) for plasma membrane localization (Ovens et al., 2010).  Upregulated in some cancers and maintains the metabolic phenotype of these cancer cells by mediating lactate efflux together with a proton, promoting pH homeostasis (Baltazar et al. 2014).  Also transports the chemotheraputic agent, 3-bromopyruvate (Baltazar et al. 2014).


SLC16A4 of Homo sapiens


Monocarboxylate transporter, MCTI0. Transports thyroid horomones (Visser et al., 2010). Primary and secondary thyroid hormone transporters have been reviewed (Kinne et al., 2011).

AnimalsSLC16A10 of Homo sapiens

Short chain monocarboxylate (lactate) transporter 3, MCT3. MCT1, 3 and 4 require the ancillary protein, basigin (P35613; 8.A.23.1.1) for plasma membrane localization (Ovens et al., 2010).

AnimalsSLC16A8 of Homo sapiens

2.A.1.14 The Anion:Cation Symporter (ACS) Family


TC#NameOrganismal TypeExample
2.A.1.14.1Glucarate porterBacteriaGudT of Bacillus subtilis

Lysosomal sialate transporter (Salla disease and infantile sialate storage disease protein (Morin et al., 2004)). Also transports glucuronic acid and aspartate. Structure-function studies have identify crucial residues and substrate-induced conformational changes (Courville et al., 2010). Also called SLC17A5. The substrate binding pocket has been identified based on modeling studies (Pietrancosta et al., 2012).  NAAG (N-acetylaspartylglutamate) an abundant neuropeptide in the vertebrate nervous system that is released from synaptic terminals in a calcium-dependent manner and acts as an agonist at the type II metabotropic glutamate receptor mGluR3, is transported into synaptic vesicles before it is secreted. Lodder-Gadaczek et al. 2013 demonstrate that vesicular uptake of NAAG and the related peptide NAAG2 (N-acetylaspartylglutamylglutamate) is mediated by sialin (SLC17A5). Sialin is probably the only vesicular transporter for NAAG and NAAG2, because transport of both peptides was not detectable in vesicles isolated from sialin-deficient mice.  Sialin also transports nitrate in the plasma membrane of salivary glands (Qin et al. 2012).


SLC17A5 of Homo sapiens

2.A.1.14.11Plasma membrane, high affinity nicotinate permease, Tna1YeastTna1 of Saccharomyces cerevisiae
2.A.1.14.12Plasma membrane, high affinity biotin:H+ symporter, Vht1YeastVht1 of Saccharomyces cerevisiae

Broad specificity brain synaptic vesicle anion:Na+ symporter (transports glutamate, phosphate, chloride, etc.)(BNPI, EAT-4, VGLUT1) Chloride and ketone bodies regulate VGLUT activities (Omote et al., 2011). 


BNPI of Rattus norvegicus


Probable D-galactarate (glucarate?):H+ symporter, GarP or YhaU.  May also function as a glucarate:glycerate antiporter (Moraes and Reithmeier 2012).


GarP (YhaU) of E. coli

2.A.1.14.15Apical membrane renal proximal tubule. Voltage-driven but Na+-independent organic anion transporter, OATv1 (transports p-aminohippurate; probably transports organic anions but not cations and not inorganic phosphate. It may catalyze excretion of various drugs, xenobiotics, and their metabolites) (Jutabha et al., 2003)AnimalsOATv1 of Sus scrofa (Q7YQJ7)

The broad specificity brain synaptic vesicle anion transporter (transports glutamate in a Δψ-dependent fashion requiring Cl- but phosphate by a Na+-dependent mechanism via a different pathway/mechanism (Juge et al., 2006). VGLUT1-3 concentrate glutamate into synaptic vesicles before its exocytotic release.


VGLUT2 of Rattus norvegicus (Q9JI12)

2.A.1.14.17Pantothenate:H+ symporter, Liz1 (mutants cause abnormal mitosis due to a defect in ribonucleotide reductase) (Stolz et al., 2004)YeastLiz1 of Schizosaccharomyces pombe (O43000)
2.A.1.14.18Pantothenate:H+ symporter, Fen2YeastFen2 of Saccharomyces cerevisiae (P25621)
2.A.1.14.19Plasma membrane, high affinity vitamin H transporter 1 (H+:biotin symporter), Vht1 (Stolz, 2003)YeastVht1 of Schizosaccharomyces pombe (O13880)

Hexuronate (glucuronate; galacturonate)
porter, ExuT (Nemoz et al. 1976).


ExuT of E. coli (P0AA78)


Endoplasmic reticular cysteine transporter, Yct1 (Kaur and Bachhawat, 2007)


Yct1 of Saccharomyces cerevisiae (Q12235)


The vesicular purine nucleotide (ADP, ATP, GTP) transporter. (Found in synaptic vesicles and chromafin granules, SLC17A9 (Sawada et al., 2008)).  Associated with disseminated superficial actinic porokeratosis (DSAP), a rare autosomal dominant genodermatosis (Cui et al. 2014).


SLC17A9 of Homo sapiens


The chloroplast thylakoid Na+:phosphate symporter, ANTR1 (512aas) (Pavón et al., 2008). Residues essential for function have been identified (Ruiz-Pavón et al., 2010). Functionally important amino acids have been identified (Ruiz-Pavón et al., 2010).


ANTR1 of Arabidopsis thaliana (O82390)


Vesicular glutamate transporter #3 (VGLUT3) [Its absence in mice causes sensorineural deafness and seizures]. 70% identical to VGLUT2 (TC# 2.A.1.14.16) (Gras et al., 2002). VGLUT1-3 concentrate glutamate into synaptic vesicles before its exocytotic release and contribute to the regulation of serotonergic transmission and anxiety (Amilhon et al., 2010). It may catalyze uptake of the neurotransmitter coupled with H+ export and K+ uptake (Farsi et al. 2016).


VGLUT3 of Mus musculus (Q8BFU8)


Intestinal mucosal sodium/phosphate symporter, SLC17A4. Maintains phosphate homeostasis; mediates intestinal absorption, bone deposition and resorption and renal excretion.

AnimalsSLC17A4 of Homo sapiens

The putative D-mannuronate porter, AlgT (Rodionov et al., 2010).


AlgT of Shewanella frigidimarina (Q07YH1)


The plasma membrane Lethal (2)01810 glutamate uptake porter (Km=0.07μM) (Inhibited by aspartate) (Shim et al., 2011)


L(2)01810 of Drosophila melanogaster (F2YPN7)


Voltage-driven Na+:phosphate cotransporter; solute carrier family 17, member 1.  Orthologous to 2.A.1.14.6.  Transports other anions including urate; functions in urate cell elimination at the renal apical membrane (Prestin et al. 2014).


SLC17A1 of Homo sapiens


Solute carrier family 17 (sodium phosphate), member 3.  Catalyzes voltage-driven Na+:phosphate cotransport, but also functions in cell elimination of urate at renal tubular cell apical membranes (Prestin et al. 2014).


SLC17A3 of Homo sapiens

2.A.1.14.29Sodium-dependent phosphate transport protein 3 (Na(+)/PI cotransporter 3) (Sodium/phosphate cotransporter 3) (Solute carrier family 17 member 2)AnimalsSLC17A2 of Homo sapiens
2.A.1.14.3Putative tartrate porterBacteriaTtuB of Agrobacterium vitis

Vesicular glutamate transporter 1, VGluT1. Brain-specific Na+-dependent inorganic phosphate cotransporter; Solute carrier family 17 member 7). Several proteins must be retrieved to the synatic vesicle before it can export neurotransmitters again, and cargo retrieval is a collective cargo-driven process, dependent on VGluT1 (Pan et al. 2015).


SLC17A7 of Homo sapiens

2.A.1.14.31Vesicular glutamate transporter 2 (VGluT2) (Differentiation-associated BNPI) (Differentiation-associated Na(+)-dependent inorganic phosphate cotransporter) (Solute carrier family 17 member 6)AnimalsSLC17A6 of Homo sapiens

Vesicular glutamate transporter 3 (VGluT3) (Solute carrier family 17 member 8). Loss in mice produces circadian-dependent hyperdopaminergia and amiliorates motor disfunction and dopa-mediated dyskinesias in a model of Parkinson's Disease (Divito et al. 2015). VGLUT3 is expressed selectively in the inner hair cells (IHCs) and transports the neurotransmitter glutamate into synaptic vesicles. Mutation of the SLC17A8 gene is associated with DFNA25 (deafness, autosomal dominant 25), a non-syndromic hearing loss (ADNSHL) in humans (Ryu et al. 2016; ).


SLC17A8 (VGluT3) of Homo sapiens


Putative L-galactonate transporter, YjjL


YjjL of Escherichia coli

2.A.1.14.34Putative inorganic phosphate cotransporterAnimalsPicot of Drosophila melanogaster
2.A.1.14.35Inner membrane transport protein RhmTBacteria

RhmT of Escherichia coli

2.A.1.14.36Thiamine pathway transporter THI73FungiTHI73 of Saccharomyces cerevisiae
2.A.1.14.37Probable transporter SEO1FungiSEO1 of Saccharomyces cerevisiae

Transporter YIL166c (Hellborg et al. 2008) of 542 aas and 12 TMSs. May transport inorganic sulfur-containing compounds such as sulfate, sulfite, thiosulfate and sulfonates.


YIL166c of Saccharomyces cerevisiae

2.A.1.14.39Uncharacterized transporter YybOBacilli

YybO of Bacillus subtilis

2.A.1.14.4Dipeptide (e.g., Gly-Leu), allantoate, ureidosuccinate, allantoin porter (Cai et al., 2007).YeastDal5 of Saccharomyces cerevisiae

Glucarate transporter, GudP.  Encoded in an operon with GudD, a glucarate dehydratase (Moraes and Reithmeier 2012).


GudP of E. coli


The Aldohexuronate (glucuronate, galacturonate) uptake porter (Valmeekam et al. 2001).


ExuT of Erwinia chrysanthemi  This sequence is incomplete.


Vesicular glutamate transporter, EAT-4/VGLUT of 576 aas (Serrano-Saiz et al. 2013).  EAT-4 is responsible for loading glutamate into synaptic vesicles, and thus in defining the glutamatergic phenotype of a neuron (Serrano-Saiz et al. 2013). 


EAT-4 of Caenorhabditis elegans


Uncharacterized but putative sulfonate (and other inorganic sulfur-containing compounds) uptake transporter of 537 aas and 12 TMSs.

UP of Ashbya gossypii (Yeast) (Eremothecium gossypii)


Vesicular Glutamate transporter, VGlut of 632 aas and 10 TMSs with the N- and C-termini in the cytoplasm (Fei et al. 2007).

VGlut of Drosophila melanogaster

2.A.1.14.5Phthalate porterBacteriaPht1 of Pseudomonas putida

Na:Pi symporter, NPT1 or SLC17A1. (Renal chloride-dependent polyspecific anion exporter; transports organic acids such as p-aminohippurate, ureate, and acetylsalicylate (asprin)). Catalyzes ureate excretion. A mutant form shows increased risk of gout in humans.


Npt1 of Mus musculus

2.A.1.14.7Galactonate transporterBacteriaDgoT (YidT) of E. coli (P0AA76)
2.A.1.14.8Phthalate porterBacteriaOphD of Burkholderia cepacia
2.A.1.14.9Putative p-hydroxyphenylacetate porterBacteriaHpaX of Salmonella dublin

2.A.1.15 The Aromatic Acid:H+ Symporter (AAHS) Family


TC#NameOrganismal TypeExample

4-Hydroxybenzoate/protocatachuate porter (Nichols and Harwood 1997).


PcaK of Pseudomonas putida


The gentisate (2,5-dihydroxybenzoate) uptake porter, GenK (does not take up either benzoate or 3-hydoxybenzoate).


GenK of Corynebacterium glutamicum (Q8NLB7)


The Vanillate porter, VanK 


VanK of Corynebacterium glutamicum (Q6M372)


Inner membrane transport protein YdiM.  Catalyzes export of medium chain alcohols such as isoprenol (Wang et al. 2015).


YdiM of Escherichia coli


Inner membrane transport protein, YdiN (similar to 2.A.1.15.12).  INduced under carbon limitation but not phosphate limitation (Johansson and Lidén 2006).


YdiN of Escherichia coli


Probable uptake transporter for 2,4-dichlorophenoxyacetic acid (2,4-D), CadK (Kitagawa et al. 2002).


CadK of Bradyrhizobium sp. HW13


MFS Homologue


MFS homologue of Streptomyces coelicolor (Q9RL01)


MFS uptake permease.  The gene is adjacent to a putative SAM-dependent methyl transferase, one homologue of which is a puromycin methyl transferase.  Perhaps the transport substrate is a drug that is modified by methylation for detoxification purposes. 


MFS uptake permease of Myxococcus xanthus


Fused protein with N-terminal transmembrane region of 7 putative TMSs and a C-terminal hydrophilic domain homologous to SAM-dependent spermidine synthase.  The N-terminus of this protein shows extensive sequence similarity with 2.A.1.15.16 but shows weak similarity with other MFS permeases.


Fused protein of Thiocapsa marina


Unncharacterized permease of 436 aas and 12 TMSs.


UP of Treponema brennaborense


MhpT. A specific 3-(3-hydroxyphenyl)propionate (3HPP) transporter; vital for E. coli K-12 W3110 to grow on this substrate.  Transports 3HPP but not benzoate, 3-hydroxybenzoate or gentisate (Xu et al. 2013).  May also export arabinose but not xylose (Koita and Rao 2012).


MhpT of E. coli


2,4-Dichlorophenoxyacetate porter (Hawkins and Harwood 2002).


TfdK of Ralstonia eutropha


cis,cis-muconate porter, MucK (Williams and Shaw 1997).


MucK of Acinetobacter sp. ADP1

2.A.1.15.5Benzoate porter, BenKBacteriaBenK of Acinetobacter sp. ADPP1

Vanillate porter, VanK


VanK of Acinetobacter sp. ADP1


Aromatic compound (benzoate) uptake transporter of 450 aas (Clark et al. 2002).


BenK of Acinetobacter baylyi

2.A.1.15.8Probable 1-hydroxy-2-naphthoate transporter, orf1 (Iwabuchi and Harayama, 1997). BacteriaOrf1 of Nocardioides sp. (O24723)
2.A.1.15.9Probable 4-methylmuconolactone transporter, MmlH (Erb et al., 1998)BacteriaMmlH of Ralstonia eutropha (O51798)

2.A.1.16 The Siderophore-Iron Transporter (SIT) Family


TC#NameOrganismal TypeExample
2.A.1.16.1Siderophore-iron (ferrioxamine):H+ sym-
porter, Sit1 (Arn3) (in vesicles)
YeastSit1 (YEL065w) of Saccharomyces cerevisiae
2.A.1.16.2The ferric enterobactin:H+ symporter, Enb1YeastEnb1 (YOL158c) of Saccharomyces cerevisiae
2.A.1.16.3The ferric triacetylfusarinine C:H+ symporter, Taf1YeastTaf1 (YHL047c) of Saccharomyces cerevisiae
2.A.1.16.4The ferrichrome:H+ symporter, Arn1p (Moore et al., 2003)YeastArn1 of Saccharomyces cerevisiae (NP_011823)
2.A.1.16.5Siderophore iron transporter 2Yeaststr2 of Schizosaccharomyces pombe

Siderophore iron transporter 1,


Str1 of Schizosaccharomyces pombe


Ferri-siderophore transporter, MirB. Transports hydroxamate siderophores such as triacetylfusarinine C (TAFC) (Raymond-Bouchard et al. 2012).


MirB of Emericella nidulans


2.A.1.17 The Cyanate Porter (CP) Family


TC#NameOrganismal TypeExample

Cyanate transport system, CynT.  Encoded with cyanate aminohydrolase, CynS, and carbonic anhydrase, CynX (Anderson et al. 1990; Moraes and Reithmeier 2012).


CynX of E. coli


Glucose transporter, OEOE_0819. Does not transport fructose (Kim et al., 2011)


OEOE_0819 of Oenococcus onei (Q04FN1)


Inner membrane transport protein YeaN


YeaN of Escherichia coli


2.A.1.18 The Polyol Porter (PP) Family


TC#NameOrganismal TypeExample
2.A.1.18.1D-Arabinitol:H+ symporterBacteriaDalT of Klebsiella pneumoniae
2.A.1.18.2Ribitol:H+ symporterBacteriaRbtT of Klebsiella pneumoniae
2.A.1.18.3Alpha-ketoglutarate permeaseBacilli

CsbX of Bacillus subtilis


2.A.1.19 The Organic Cation Transporter (OCT) Family (The SLC22A family including OCT1-3, OCTN1-3 and OAT1-5 of H. sapiens)

This family has been described by Koepsell 2013.  It contains 13 functionally characterized human plasma membrane proteins.The family includes organic cation transporters (OCTs), organic zwitterion/cation transporters (OCTNs), and organic anion transporters (OATs). The transporters operate as (1) uniporters which mediate facilitated diffusion (OCTs and some OCTNs), (2) anion exchangers (OATs), and (3) some Na+/zwitterion cotransporters (OCTNs). They participate in small intestinal absorption and hepatic and renal excretion of drugs, xenobiotics and endogenous compounds and perform homeostatic functions in the brain and heart. Important endogeneous substrates include monoamine neurotransmitters, l-carnitine, alpha-ketoglutarate, cAMP, cGMP, prostaglandins and urate. Mutations in the SLC22 genes cause specific diseases like primary systemic carnitine deficiency and idiopathic renal hypouricemia and are correlated with diseases such as Crohn's disease and gout. Drug-drug interactions at individual transporters may change pharmacokinetics and toxicities of drugs (Koepsell 2013).


TC#NameOrganismal TypeExample

The basolateral multivalent, potential-sensitive, organic cation (tetramethyl-ammonium; N'-methylnicotinamide; cationic drugs, xenobiotics, vitamins, neuro-transmitters, etc.) transporter (uni-porter)-1, Oct1.  Cysteyl residues essential for transport and substrate binding have been identified (Sturm et al. 2007).


Oct1 of Rattus norvegicus (Q63089)


The apical proximal tubular kidney/placenta organic anion transporter 4, Oat4 (Slc22a11) (transports estrone sulfate (Km = 1 µM), dehydroepiandrosterone sulfate (Km = 60µM), many anionic drugs, diuretics, bile salts, urate and ochratoxin A). Catalyzes Na+-independent efflux, possibly using glutamate as a counter anion in an exchange reaction, especially in the placenta (Lofthouse et al. 2015).  Functions in renal urate reabsorption (Prestin et al. 2014).


SLC22A11 (Oat4) of Homo sapiens


The apical proximal tubular renal urate:anion exchanger, URAT1 (Slc22a12) (catalyzes Na+-independent anion efflux (secretion) and reabsorption) (Eraly et al., 2003a,b; Anzai and Endou, 2011; Prestin et al. 2014)  Regulated by the PDZK1 protein; Anzai et al., 2004). Also transports orotate, a precursor of pyrimidine biosynthesis (Miura et al., 2011). Mutations in URAT1 cause hereditary renal hypouricemia/gaut.  Residues involved in urea and inhibitor binding have been identified (Tan et al. 2016).


SLC22A12 of Homo sapiens


The high affinity L-carnitine transporter, CT2 (present in the luminal membranes of epididymal epithelia and Sertoli cells of the testis) (Enomoto et al., 2002b)

AnimalsSLC22A16 of Homo sapiens
2.A.1.19.13The organic cation transporter, Oct1 (transports L-carnitine; expressed in vascular tissues of various organs and at sites of lateral root formation) (Lelandais-Briere et al, 2007)PlantsOct1 of Arabidopsis thaliana (Q9CAT6)

Brush boarder glycosylated urate (Km= 1.2 mM) tranporter, RST. Orthologous to the human URAT1. Inhibited by 50 μM benzbromarone, 1 mM probenecid and 10 mM lactate which may also be transported and trans-stimulate urate uptake. May be orthologous to 2.A.1.19.11 as well (Hosoyamada et al., 2004).  Involved in urate absorption across the apical membrane, but probably not the primary route (Eraly et al. 2008; Prestin et al. 2014).


URAT1 of Mus musculus

2.A.1.19.15The liver multispecific organic anion transporter, NLT or OAT2. Transports salicylate, KM=90µM, acetylsalicylate, prostaglandin E2, dicarboxylate, p-aminohippurate, etc. (Sekine et al., 1998)AnimalsNLT of Rattus norvegicus (Q63314)

The organic anion transporter, Oat6 (binding and transport rates for 40 anionic substrates were studied and compared with these for Oat1 (TC# 1.A.1.19.4) (Kaler et al., 2007); transports many antiviral agents (Truong et al., 2008).


Oat6 of Mus musculus (Q80UJ1)


Kidney organic cation transporter-like 3 ORCTL-3 (OAT10; SLC22A13; Like-3) (Bahn et al., 2008) (transports nicotinate, p-aminohippurate and urate; KM=20-40 mμM) via exchange for lactate).  Activated by tumorigeneic mutations in this antitumor gene to promote apoptosis (AbuAli and Grimm 2014).  Functions in urate reabsorption (Prestin et al. 2014).


SLC22A13 of Homo sapiens

2.A.1.19.18Oranic anion transporter, Oat7 (exchanges sulfate conjugates (steroids) and other anions for butyrate) (Shin et al., 2007)AnimalsSLC22A9 of Homo sapiens

The rat kidney basolateral potential-driven symport carrier, Oct2 (transports tetraethylammonium and many other organic cations) (Sweet and Pritchard 1999).  A cysteiyl residue critical for substrate binding and transport has been identified (Sturm et al. 2007).


Oct2 of Rattus norvegicus (Q9R0W2)


The ergothionine/organic cation porter, OctN1 (SLC22A4). Associated with rheumatoid arthritis (Barton et al., 2005).  Acetylcholine is a physiological substrate, and its transport could be involved in nonneuronal cholinergic functions (Pochini et al. 2013).  OCTN1 and OCTN2 are associated with several pathologies, such as inflammatory bowel disease, primary carnitine deficiency, diabetes, neurological disorders, and cancer. Transports TEA, and acetylcholine better than acetylcarnitine (Pochini et al. 2015).


OctN1 of Homo sapiens (O14546)


Prostaglandin (PGE2, PGE2α, and PGD(2)) -specific organic anion transporter. Exhibits Na+ -independent and saturable transport. Shows narrow substrate selectivity and high affinity (Shiraya et al., 2010).


OAT-PG of Homo sapiens (Q8R0S9)

2.A.1.19.21 solute carrier family 22, member 24AnimalsSLC22A24 of Homo sapiens

solute carrier family 22, member 14, Slc22a14, is crucial for sperm motility and male fertility in mice. It is expressed specifically in male germ cells, and mice lacking the Slc22a14 gene show severe male infertility as well as sperm morphological changes (Maruyama et al. 2016).


SLC22A14 of Homo sapiens

2.A.1.19.23 solute carrier family 22, member 31AnimalsSLC22A31 of Homo sapiens
2.A.1.19.24Solute carrier family 22 member 3 (Extraneuronal monoamine transporter) (EMT) (Organic cation transporter 3)AnimalsSLC22A3 of Homo sapiens

Solute carrier family 22 member 7 (liver transporter) (Organic anion transporter 2) (hOAT2), transports the anti-viral drug, acyclovir (Dahlin et al. 2013).


SLC22A7 of Homo sapiens


Multispecific anion transporter, OatA1, of 526 aas and 12 TMSs.


OatA1 of Caenorhabditis elegans

2.A.1.19.27Solute carrier family 22 member 10 (Organic anion transporter 5)AnimalsSLC22A10 of Homo sapiens

Solute carrier family 22 member 23.  The rat orthologue may be inactive (Bennett et al. 2011).


SLC22A23 of Homo sapiens


Solute carrier family 22 member 1 (Organic cation transporter 1) (hOCT1).  May be a primary polyamine uptake porter (Abdulhussein and Wallace 2013).


SLC22A1 of Homo sapiens


The polyspecific organic cation (L- and D-carnitine, butyryl-L-carnitine, acetyl carnitine, γ-butyro-betaine, glycinebetaine, β-lactam antibiotics with a quaternary nitrogen such as cephaloridine, and others):Na+ symporter, OctN2 (SLC22A5). Carnitine is transporter with high affinity (2 - 20 μM0 (Ingoglia et al. 2015). Associated with Crohn''s disease (Barton et al., 2005) as well as primary carnitine deficiency.  The protein is glycosylated on extracytoplasmic asparagines, and these residues are in a region important for function and turnover (Filippo et al. 2011).  OCTN2 maintains the carnitine homeostasis, resulting from intestinal absorption, distribution to tissues, and renal excretion/reabsorption (Pochini et al. 2013).  OCTN1 and OCTN2 are associated with several pathologies, such as inflammatory bowel disease, primary carnitine deficiency, diabetes, neurological disorders, and cancer.  OctN2 is activated in a process dependent on Caveolin1 (Q03135)which interacts directly with OctN2 and by protein kinase C which does not phosphorylate OctN2 directly (Czeredys et al. 2013).


SLC22A5 of Homo sapiens


Solute carrier family 22 member 2 (Organic cation transporter 2) (hOCT2).  Oct2 is a low affinity high efficiency choline transporter, enriched in synaptic vesicles of cholinergic neurons (Nakata et al. 2013).  May also transport peptides and peptide derivatives (Volková et al. 2015).


SLC22A2 or Oct2 of Homo sapiens


Solute carrier family 22 member 6 (Organic anion transporter 1) (hOAT1) (PAH transporter) (hPAHT) (Renal organic anion transporter 1) (hROAT1),  Probably orthologous to 2.A.1.19.4. Functions in urate uptake from the circulation across the basolateral membrane of tubular cells (Prestin et al. 2014).


SLC22A6 of Homo sapiens

2.A.1.19.32Solute carrier family 22 member 15 (Fly-like putative transporter 1) (Flipt 1)AnimalsSLC22A15 of Homo sapiens

Solute carrier family 22 member 25 (Organic anion transporter UST6).  Expressed exclusively in liver in both embryo and adult (Eraly et al. 2004).


SLC22A25 of Homo sapiens


Multispecific drug transporter, solute carrier family 22 member 8 (Organic anion transporter 3) (hOAT3).  Both OAT1 and OAT3 of humans are inhibited by caffeic acid (Ki ~ 17 μM) (Uwai et al. 2011; Wu et al. 2013).  It is the principal uptake system for steviol glucuronide (SVG), the major metabolite derived from steviol, the aglycone of stevioside and rebaudioside A (Wang et al. 2015).  Also functions in urate uptake from the circulation across the basolateral membrane of renal tubular cells (Prestin et al. 2014).

See also 2.A.1.19.9.


SLC22A8 of Homo sapiens

2.A.1.19.35Solute carrier family 22 member 20 (Organic anion transporter 6)AnimalsSLC22A20 of Homo sapiens

Organic cation transporter protein. OrcT


OrcT of Drosophila melanogaster

2.A.1.19.37Organic cation transporter 1 (CeOCT1)Worm

Oct-1 of Caenorhabditis elegans

2.A.1.19.38Uncharacterized MFS-type transporter PB1E7.08cYeastSPAPB1E7.08c of Schizosaccharomyces pombe
2.A.1.19.39Organic cation/carnitine transporter 6 (AtOCT6)PlantsOCT6 of Arabidopsis thaliana

The polyspecific organic anion, cation and neutral molecule transporter, Oat1 (Slc22a6) (transports neutral compounds such as cardiac glycosides [i.e., ouabain] and steroids [i.e., aldosterone; cortisol; dexamethasone]; cationic compounds such as N-propylajmalinium, and anionic compounds such as p-aminohippurate, dicarboxylates, cyclic nucleotides, prostaglandins, urate, β-lactam antibiotics, nonsteroidal anti-inflammatory drugs, diuretics, bile salts and steroid conjugates [i.e., estrone-3-sulfate and estradiol-17-glucuronide]) transporter (H+ symporter or uniporter) Probably catalyzes organic anion (uptake):dicarboxylate (efflux) antiport in the basolateral membrane of kidney proximal tubules) (Eraly et al., 2003a,b). A 3-dimensional model of OAT1 has led to the identification of residues involved in differential transport of substrates such as p-aminohippurate and cidofovir (Perry et al., 2006). Oat1 transports many antiviral agents (Truong et al., 2008).  The human orthologue (Q4U2R8; 563aas) has been shown to be a multispecific organic anion transporter on the basolateral membrane of the proximal tubule in human kidney (Hosoyamada et al. 1999). A substrate binding hinge domain is required for transport-related structural changes (Egenberger et al., 2012). Transports environmental toxins and clinically important drugs including anti-HIV therapeutics, anti-tumor drugs, antibiotics, anti-hypertensives, and anti-inflammatories (Duan et al., 2011). hOAT1 has two GXXXG motifs in TMSs 2 and 5 which play critical roles in stability (Duan et al., 2011).  Both OAT1 and OAT3 of humans are inhibited by caffeic acid (Ki ~ 17 μM) (Uwai et al. 2011).


Oat1 of Rattus norvegicus (O35956)


Organic anion transporter, Oat9.  A splice variant with 443 aas and 8 TMSs (Oa9S) was reported to transport L-carnitine (3 μM), cimetidine (16 μM) and salicylic acid (175 μM), but the full length protein of 551 aas and 12 TMSs (Oat9L) was reported to be inactive (Tsuchida et al. 2010).  


Oat9 of Mus musculus


Organocation transporter, OCTN3.  Identified only in mouse; mediates carnitine transport (Pochini et al. 2013).  81% identical to 2.A.1.19.3.  Also called SLC22a21 and SLC22a9.


OctN3 of Mus musculus


Slc22 homologue of 580 aas.

Plants (single celled marine green alga)

Slc19 homologue of Ostreococcus tauri


Organocation transporter, Oct4 of 526 aas


Oct4 of Arabidopsis thaliana (Mouse-ear cress)


Uncharacterized protein of 556 aas

Plants (Algae)

UP of Chlorella variabilis (Green alga)


MFS transporter of 569 aas


MFS transporter of Tetrahymena thermophila


MFS transporter of 593 aas

Alveolata (ciliates)

MFS porter of Oxytricha trifallax


MFS porter of 691 aas


MFS porter of Volvox carteri (Green alga)


Fungal MFS homologue of 520 aas


UP of Aspergillus terreus


Putative glucose transporter 1 (Gluct1) of 569 aas and 12 TMSs.  Constitutively synthesized in many tissues.  Serves as the receptor of white spot syndrom virus (WSSV) (Huang et al. 2012). 


Gluct1 of Litopenaeus vannamei (Whiteleg shrimp) (Penaeus vannamei)


The putative apical polyspecific organic cation transporter (cation:H+ or cation:cation antiporter), Oct2 (substrates include monoamine neurotransmitters such as dopamine, noradrenaline, adrenaline and 5-hydroxytryptamine) (Oct2 exhibits some properties of an ion channel with an inner diameter of ~4 Å. Selectivity: Cs+ > Rb+ > K+ > Na+ %u2248 Li+ (Schmitt and Koepsell, 2005)) Chloride dependent, but a single mutation (R466K) abolishes this dependency (Rizwan et al., 2007). Also transports ochratoxin (Rizwan et al., 2007) and cisplatin and oxaliplatin (Yonezama et al., 2006).

AnimalsOct2 of Sus scrofa (O02713)

The polyspecific potential-sensitive organic cation uptake transporter, Oct3 (transport substrates include the neurotoxin 1-methyl-4-phenylpyridinium and monoamine neurotransmitters such as dopamine). Mediates paraquat (herbicide) neurotoxicity (Rappold et al., 2011).


Oct3 of Rattus norvegicus (O88446)

2.A.1.19.7The polyspecific organic anion (and cation) (anions: p-aminohippurate, ochratoxin A, estrone sulfate, anionic drugs, anionic neurotransmitter metabolites; cation: cimetidine) transporter, Oat3 (slc22a8) (catalyzes organic anion (uptake): dicarboxylate (efflux) antiport in the basolateral membrane of the renal proximal tubule) (Eraly et al., 2003a,b); transports many antiviral agents (Truong et al., 2008).AnimalsOat3 of Rattus norvegicus (Q9R1U7)

The human organic cation transporter, SLC22A17.  The rat orthologue may be inactive (Bennett et al. 2011).

It is also the cell surface receptor for Lipocalin-2 (LCN2; 24p3) that plays a key role in iron homeostasis and transport. Able to bind iron-bound LCN2, followed by internalization and release of iron, thereby increasing intracellular iron concentration and leading to inhibition of apoptosis. Also binds iron-free LCN2, followed by internalization and its association with an intracellular siderophore, leading to iron chelation and iron transfer to the extracellular medium, thereby reducing intracellular iron concentration and resulting in apoptosis.


SLC22A17 of Homo sapiens


The osteosclerosis protein, Roct (organic anion transporter 3, Oat3) (Slc22a8) (catalyzes organic anion (uptake):di-carboxylate (efflux) antiport in the basolateral membrane of the renal proximal tubule) (Eraly et al., 2003a,b); transports glutathione and many antiviral agents (Truong et al., 2008).  It is a multispecific drug transporter, critical for the renal handling of common drugs (e.g, antibiotics, antivirals, diuretics) and toxins.  Probably handles hydroxylated and glucouronidated metabolites, consistent with the "remote sensing and signaling hypothesis" (Wu et al. 2013).  It may also handle dietary flavonoids and antioxidants.


Roct (Oat3) of Mus musculus (O88909)


2.A.1.2 The Drug:H+ Antiporter-1 (12 Spanner) (DHA1) Family


TC#NameOrganismal TypeExample

Pyridoxine, pyridoxal, pyridoxamine, amiloride:H+ cotransporter (Km (pyridoxine) = 22 μM) (Stolz et al., 2005). Also takes up thiamine (Vogl et al., 2008).


Bsu1 (Car1) of Schizosaccharomyces pombe (P33532)


Quinolone (and other drug):H+ antiporter, NorA.  Many synthetic inhibitors have been identified (Bhaskar et al. 2016).


NorA of Staphylococcus aureus (P0A0J7)


Bcr/CflA family drug resistance efflux transporter of 389 aas and 12 TMSs.

MDR exporter of Staphylococcus aureus


Bmr-like protein SblA of 395 aas and 12 TMSs.

SblA of Staphylococcus aureus

2.A.1.2.11Monoamine transporter; drug (doxorubicin, ethidium bromide-6-G):H+ antiporterAnimalsVMAT1 of Rattus norvegicus
2.A.1.2.12Chromaffin granule monoamine (and drug) transporter, VAT1AnimalsSLC18A1 of Homo sapiens

Vesicular acetylcholine:H+ antiporter, UNC-17/VAChT.  Mutants grow slowly and are uncoordinated, but the defect can be corrected by mutation of an interacting monotopic protein, SUP-1 (Mathews et al. 2012). 


Unc17 of Caenorhabditis elegans


Putative arabinose efflux porter, AraJ.


AraJ of E. coli


Arabinose (but not xylose) and isopropyl β-D-thio-galactopyranoside:H+ antiporter, YdeA (Koita and Rao 2012).


YdeA of E. coli

2.A.1.2.16Polyamines (spermine, spermidine, putrescene); paraquat; methylgloxal bis(guanylhydrazone):H+ antiporter (in the plasma membrane) (activated by phosphorylation) (Uemura et al., 2005)YeastTPO1 (YLL028w) of Saccharomyces cerevisiae
2.A.1.2.17Fluconazole:H+ antiporterYeastFlr1 of Saccharomyces cerevisiae
2.A.1.2.18Lactose and melibiose (>>IPTG) efflux pump, SotBBacteriaSotB of Erwinia chrysanthemi

The multidrug (chloramphenicol, tetra-
cycline, norfloxacin, doxorubicin, trimethoprim, acriflavin, ethidium bromide, tetraphenylphosphonium, TPP, benzalkonium, ciprofloxacin, thiamphenicol, IPTG) resistance exporter, MdfA (catalyzes both electrogenic and electroneutral transport) (Adler and Bibi, 2004). Can function as a Na (K )/H antiporter (Lewinson and Bibi 2001; Higgins, 2007). For review of MdfA see Lewinson et al., 2006. The conformational switch accompanying transport is induced by promiscuous binding of substrates and/or inhibitors to the binding pocket (Fluman et al., 2009). Normally extrudes monovalent cationic drugs in exchange for a single proton, but it transports divalent cationic drugs poorly. It can be mutated to antiport a divalent cationic drug for 2 protons (Tirosh et al., 2012).


MdfA of E. coli (P0AEY8)

2.A.1.2.2Cycloheximide:H+ antiporterYeastCyhR of Candida maltosa

Broad specificity MDR efflux pump, MdtG (YceE) (under SoxSR control) (Fàbrega et al., 2010).  Confer resistance to fosfomycin, fluoroquinolone and many other drugs (Nishino and Yamaguchi 2001).


MdtG of E. coli


The norfloxacin/enoxacin resistance protein, MdtH or YceL (Nishino and Yamaguchi 2001).


MdtH or YceL of E. coli (P69367)


The multidrug resistance protein, YidY (Nishino and Yamaguchi 2001).


YidY of E. coli

2.A.1.2.23The fructose-specific facilitator (uniporter), Ffz1 (Pina et al., 2004)YeastFfz1 of Zygosaccharomyces bailii (CAD56485)
2.A.1.2.24The multidrug resistance efflux pump, CgMDR (exports fluoroquinolones and chloramphenicol) (Vardy et al., 2005)BacteriaCgMDR of Corynebacterium glutamicum (NP_600365)

The purine base/nucleoside (nucleosides: inosine, adenosine and guanosine; bases: hypoxanthine adenine, guanine 2-fluoroadenine) efflux pump, YdhL (PbuE) (Johansen et al., 2003; Nygaard and Saxild, 2005; Zakataeva et al., 2007; Sheremet et al. 2011).


PbuE of Bacillus subtilis (O05504)


The purine ribonucleoside (inosine, adenosine, guanosine, 6-mercaptopurine ribonucleoside) efflux pump (H+ antiporter), NepI (YicM) (Gronskiy et al., 2005; Sheremet et al. 2011)


NepI of E. coli (P0ADL1)

2.A.1.2.27The alcaligin siderophore exporter, AlcS (Brickman and Armstrong, 2005)BacteriaAlcS of Bordetella pertussis (CAE42734)

The vesicular acetylcholine transporter, VAChT (pumps acetylcholine into synaptic vesicles).  The acetyl choline and vesamicol binding sites are near the luminal end of the transport pathway (Khare et al. 2010).


SLC18A3 of Homo sapiens


The vesicular monoamine transporter, VMAT2 (pumps dopamine, norepinephrine, serotonin and histamine into synaptic vesicles) (Cliburn et al. 2016). VMAT2 physically and functionally interacts with the enzymes responsible for dopamine synthesis (Cartier et al., 2010).  Molecular hinge points mediating alternating access have been identified (Yaffe et al. 2013).


VMAT2 (SLC18A2) of Homo sapiens


Chloramphenicol:H+ antiporter, CmlA; Cmr; MdfA.  Multidrug exporter that also catalyzes efflux of arabinose (but not xylose) and  isopropyl β-thiogalactoside (Koita and Rao 2012).


CmlA of Pseudomonas aeruginosa

2.A.1.2.30The hippocampus abundant transcript-like 1 protein, HIATL1 (putative drux exporter)AnimalsHIATL1 of Homo sapiens (NP_115947)
2.A.1.2.31The multidrug transporter, QDR2, required for resistance to quinidine, barban, cisplatin, and bleomycin; may have a role in potassium uptakeBacteriaQDR2 of Saccharomyces cerevisiae (P40474)
2.A.1.2.32The chloramphenicol resistance protein, ChlRBacteriaChlR of Streptomyces lividans (P31141)
2.A.1.2.33The Hol1 MFS transporter (Mutation allows the uptake of histidinol and other cations (Wright et al., 1996). The N-terminal 200 residues show 22% identity with 2.A.1.2.1 and 2.A.1.2.16).YeastHol1 of Saccharomyces cerevisiae (P53389)

The MDR efflux pump, PmrA (exports fluoroquinolone and other compounds) and other components including the antimicrobial peptide, colistin (Martinez-Garriga et al. 2007; Pamp et al., 2008).


PmrA of Streptococcus pneumoniae (P0A4K4)


The caffeine resistance protein 5 (Caf5) (Benko et al., 2004)


Caf5 of Schizosaccharomyces pombe (O94528)

2.A.1.2.36The multidrug resistance protein Aqr1 (YNL065w) (exports short chain monocarboxylates but not more hydrophobic acids such as octonate and quinidine. Also exports ketoconazole and crystal violet (Tenreiro et al., 2002)).YeastAqr1 of Saccharomyces cerevisiae (P53943)
2.A.1.2.37The legiobactin (siderophore) exporter (most similar to 2.A.1.2.9; 23% identity) (Allard et al., 2006)Gram-negative bacteriumIbtB of Legionella pneumophila
LbtA (Q45RG2)
LbtB (Q5WX21)
2.A.1.2.38Tetracycline-specific exporter, TetA39 (most like 2.A.1.2.4) (Thompson et al., 2007).BacteriaTetA39 of Acinetobacter spp. (Q56RY7)
2.A.1.2.39Tetracycline-specific exporter, TetA41 (most like 2.A.1.2.4) (Thompson et al., 2007).BacteriaTetA41 of Serratia marcescens (Q5JAK9)
2.A.1.2.4Tetracycline:H+ antiporterBacteriaTetA of E. coli
2.A.1.2.40The dityrosine exporter, Dtr1 (required for formation of the outer layer of the cell wall (Morishita and Engebrecht, 2008)).


Dtr1 of Saccharomyces cerevisiae (P38125)

2.A.1.2.41The tetracycline resistance determinant, TetA42 from a deep terrestrial subsurface bacterium (Brown et al., 2008).


TetA42 of Micrococcus sp. SMCC G8878 (B2YGG2)


The multidrug efflux pump, EmrD-3 (exports ethidium, linezolid, tetraphenylphosphonium chloride, rifampin, erythromycin, minocycline, trimethoprim, chloramphenicol, and rhodamine) (Smith et al., 2009).


EmrD-3 of Vibrio cholerae (Q9KMQ3)


The multidrug efflux pump, Qdr3 (exports polyamines, quinidine, barban, cisplatin and bleomycin). The two halves of the protein each have an N-terminal. 150 residue hydrophilic region found in many fungi followed by a 200 residue, 6 TMS, transmembrane region. This suggests that an intragenic duplication event gave rise to 12 TMS proteins independently of most other MFS carriers, but this has not been demonstrated, possibly because of extensive sequence divergence of the second half.


Qdr3 of Saccharomyces cerevisiae (P38227)


Diglucosyl-diacylglycerol exporter or flippase, LtaA (lipoteichoic acid protein A) (Gründling and Schneewind, 2007).


LtaA of Staphylococcus aureus (Q2FZP8)


The fructose-specific uniporter, Ffz1 (69% identical to Ffz2 
(2.A.1.2.46) and 66% identical to (2.A.1.2.23) (Leandro et al., 2011). 


Ffz1 of Zygosaccharomyces rouxii (C5E4Z7)


The fructose/glucose uniporter, Ffz2 (64% identical to 2.A.1.2.23). Both sugars are transported with similar affinities and efficiencies (Leandro et al., 2011). 


Ffz2 of Zygosaccharomyces rouxii (C5DX43)


The multidrug resistance efflux pump, HsMDR (YfmO2).  Exports drugs such as fluoroquinolones and chloramphenicol (Vardy et al., 2005).


HsMDR of Halobacterium salinarum


tetracycline exporter


tetR exporter of Aspergillus niger (A2QTF4)


Putative tetracycline resistance protein


Putative tet resistance pump of Pyrobaculum aerophilum (Q8ZUX8)


Multidrug (14- and 15-membered macrolides, lincosamides, streptogramins, tetracyclines, daunomycin, ethidium bromide, etc.):H+ antiporter, LmrP. Two proton translocation pathways have been proposed (Bapna et al., 2007), but Schaedler and van Veen, 2010 have provided evidence that a flexible cation binding site in LmrP is associated with variable proton coupling. Basic residues R260 and K357 affect the conformational dynamics of LmrP (Wang and van Veen, 2012).  Basic residues, R260 and K357 control the conformational dynamics of the protein (Wang and van Veen 2012).  Also specifically catalyzes Ca2+:3H+ antiport with an affinity of 7 μM (Zhang et al. 2012). Two carboxylates (Asp-235 and Glu-327) are critical for Ca2+ binding.  Protonation drives major conformational switches (Masureel et al. 2013). The system exhibits plasticity in proton interactions, which is a consequence of the flexibility in the location of key residues that are responsible for proton/multidrug antiport (Nair et al. 2016).


Gram-positive bacteria

LmrP of Lactococcus lactis


MFS porter

Slime molds

MFS porter of Dictyostelium purpureum (F0ZU09)


Chloramphenicol (specific) resistance pump, CraA (43% identical to MdfA of E. coli) (Roca et al., 2009).


CraA of Acinetobacter baumannii (A3M9E9)


Puromycin resistance MDR protein, MdtM (Soo et al., 2011).  Also catalyzes bile salt:H+ antiport, and binds cholate and deoxycholate to the protein with micromolar affinity. Functions as an MDR pump (Nishino and Yamaguchi 2001). Acts synergistically with AcrAB-TolC (Paul et al. 2014).


MdtM of E. coli (P39386)


MDR pump, SLC22A18 in lung cancer cells (Lei et al., 2012).

AnimalsSLC22A18 of Homo sapiens

LigA-like protein


LigA-like protein of Streptomyces coelicolor (Q9KYE9)


Peptide exporter (Ala-Gln and Ala-branched chain amino and dipeptides) (Hayashi et al., 2010).  May also export arabinose (but not xylose) and function as an MDRpump (Koita and Rao 2012).


YdeE of E. coli (P31126)


NCL7 or MFSD8. Neuronal ceroid lipofuscinosis, NCL, a neuro-degenerative genetic disease, is caused by mutations in at least 8 different human genes, one of which, CLN7 (MFSD8), is associated with late infantile NCL. CLN7 is localized to lysosomes (Sharifi et al., 2010).  Loss of this putative lysosomal transporter in the brain leads to lysosomal dysfunction, impaired constitutive autophagy and neurodegeneration late in the disease (Brandenstein et al. 2015).


NCL7 of Homo sapiens (Q8NHS3)

2.A.1.2.57MFS-type transporter SLC18B1 (Solute carrier family 18 member B1)AnimalsC6orf192 of Homo sapiens
2.A.1.2.58Protein ZINC INDUCED FACILITATOR 1PlantsZIF1 of Arabidopsis thaliana

Ucharacterized MFS-type transporter C330.07c; YJ87


YJ87 of Schizosaccharomyces pombe


(Benomyl, cycloheximide, methotrexate, fluconazole, etc.):H+ antiporter, CaMDR1 (Basso et al., 2010; Cannon et al., 1998). MDR1 catalyzes efflux of commonly used azoles. The central cytoplasmic loop is critical for MDR function, but does not impart substrate specificity (Mandal et al., 2012).


CaMDR1 of Candida albicans


YajR of 454 aas and 12 TMSs.  The 3-D structure in the outward-facing conformation is available at 3.15Å resolution, and the cytoplasmic C-terminal YAM domain has been solved to 1.07Å resolution.  This 65 aa YAM domain is thought to control the conformational states of the protein (Jiang et al. 2013; Jiang et al. 2014).


YajR of E. coli


SPX domain-containing membrane protein At1g63010


At1g63010 of Arabidopsis thaliana


Putative MDR pump, YdhC.  Probably exports arabinose but not xylose (Koita and Rao 2012).


YdhC of Escherichia coli

2.A.1.2.63Probable drug/proton antiporter YHK8FungiYHK8 of Saccharomyces cerevisiae

Polyamine exporter 4 (Igarashi and Kashiwagi 2010).


TPO4 of Saccharomyces cerevisiae


Inner membrane transport protein YdhP


YdhP of Escherichia coli


Polyamine exporter 3 (Igarashi and Kashiwagi 2010).


TPO3 of Saccharomyces cerevisiae


Polyamine exporter 2 (Igarashi and Kashiwagi 2010).


TPO2 of Saccharomyces cerevisiae


Tetracycline resistance protein, class B (TetA(B)) (Metal-tetracycline/H+ antiporter).  Mutants defective in either transport or tetracycline binding have been isolated (Wright and Tate 2015).


TetA of Escherichia coli


Uncharacterized MFS-type transporter YttB


YttB of Bacillus subtilis


Bicyclomycin, sulfathiazole, tetracycline, fosfomycin, acriflavin, etc.):H+ antiporter (Nishino and Yamaguchi 2001).  Also exports L-cysteine (Yamada et al., 2006).

Gram-negative bacteria

Bcr of E. coli

2.A.1.2.70Multidrug resistance protein 1 (Multidrug-efflux transporter 1)Bacilli

Bmr of Bacillus subtilis

2.A.1.2.71Uncharacterized MFS-type transporter Rv2456c/MT2531BacteriaRv2456c of Mycobacterium tuberculosis
2.A.1.2.72Major facilitator superfamily domain-containing protein 9AnimalsMfsd9 of Mus musculus
2.A.1.2.73Major facilitator superfamily domain-containing protein 10 (Tetracycline transporter-like protein)AnimalsMfsd10 of Mus musculus
2.A.1.2.74Multidrug resistance protein MdtL


MdtL of Shewanella sp.

2.A.1.2.75Tetracycline resistance protein, class E (TetA(E))


TetA of Escherichia coli


Major facilitator copper transporter 1, Mfc1.  Takes up copper in meiotic sporulating cells; present in the forespore membrane.  Induced under copper limitation.  Required for normal forespore development and spore copper-dependent amine oxidase activity (Beaudoin et al. 2011).


Mfc1 of Schizosaccharomyces pombe


CefT confers phenyacetate resistance (Fernández-Aguado et al. 2012).  It has been reported to be a hydrophilic beta-lactam transporter that is involved in the secretion of hydrophilic beta-lactams containing an α-aminoadipic acid side chain (isopenicillin N, penicillin N and deacetylcephalosporin C) (Cesareo et al. 2007; Ullán et al. 2002).


CefT of Acremonium chrysogenum


The PaaT (PenT) exporter.  PaaT is involved in penicillin production, possibly through the translocation of side-chain precursors (phenylacetate and phenoxyacetate) from the cytosol to the peroxisomal lumen across the peroxisomal membrane of P. chrysogenum.  It has a Pex19 (peroxisome biogenesis factor 19) binding sequence (residues 258 - 269) accounting for its peroxysomal location (Fernández-Aguado et al. 2012; Yang et al. 2012).


PaaT of Penicillum chysogenum (notatum)


The perylenequinone toxin, cercosporin, exporter, Ctb4


Ctb4 of Cercospora nicotianae

2.A.1.2.8(Spermidine; fluoroquinolones, acriflavin, chloramphenicol, ethidium bromide, etc.):H+ antiporterGram-positive bacteriaBlt of Bacillus subtilis

Putative permease of 458 aas


Putative permease of Galdieria sulphuraria


Uncharacterized MFS permease; encoded by a gene adjacent to one encoding a peroxiredoxin (an electron donor and antioxidant; Hanschmann et al. 2013).


UP of Deinococcus peraridilitoris


Uncharacterized MFS permease of 402 aas and 12 TMSs


UP of Leptospira interrogans


MmrA MFS protein. Homologous to drug exporter. RppA and MmrA are involved in amino acid uptake and efflux of antimicrobial agents including streptomycin, ethidium bromide and norfloxacin (Kimura et al. 2004).


MXAN_5906 of Myxococcus xanthus.  


Probable siderophore-specific exporter of 407 aas and 12 TMSs, MxcK.


MxcK of Stigmatella aurantiaca


Peeroxysomal phenylacetate/penoxyacetate transporter, PaaT (CefT) of 564 aas (Fernández-Aguado et al. 2013).


PaaT of Penicillium chrysogenum (Penicillium notatum)


Peroxisomal isopenicillin N importer, PenM (Evers et al. 2004; Fernández-Aguado et al. 2014).


PenM of Penicillium chrysogenum (Penicillium notatum)


Purine efflux porter of 392 aas, CepA.  Exports purine analogues, 6-mercaptopurine and 6-mercaptoguanine, but not to 2-aminopurine and purine nucleoside analogues. May show increased resistance to the antibiotics nalidixic acid and ampicillin (Sim et al. 2014).


CepA of Corynebacterium glutamicum


MFS porter of 442 aas


MFS porter of Pyrococcus furiosus


MFS porter of 454 aas


MFS porter of Streptomyces coelicolor


(Hydrophobic uncoupler e.g., CCCP, benzalkonium, SDSand other drugs):H+ antiporter, EmrD (Nishino and Yamaguchi 2001). The 3-d structure (3.5 Å resolution) has been determined (Yin et al., 2006).  conformational dynamics studies have revealed details of the transport pathway and some motions of EmrD at an atomic level (Baker et al. 2012).  Probably exports arabinose but not xylose (Koita and Rao 2012).

Gram-negative bacteria

EmrD of E. coli


UMF4F of 405 aas and 12 TMSs


UMF4F of Aectobacterium woodii


MFS permease of 554 aas and 12 TMSs


Putative MFS carrier of Metarhizium robertsii (Metarhizium anisopliae)


The CefM protein of 482 aas and 12 TMSs. Probably involved in the translocation of penicillin N from the lumen of peroxisomes (or peroxisome-like microbodies) to the cytosol, where it is converted into cephalosporin C (Teijeira et al. 2009).  A null mutant accumulates  penicillin N, is unable to synthesize deacetoxy- and deacetyl-cephalosporin C as well as cephalosporin C, and shows impaired differentiation into arthrospores (Teijeira et al. 2009).

CefM of Acremonium chrysogenum (Cephalosporium acremonium)


Uncharacterized MFS permease of 433 aas and 12 TMSs

UP of Lactobacillus buchneri


Uncharacterized MFS permease of 445 aas and 12 TMSs

UP of Microbacterium maritypicum


Blt of 422 aas and 12 TMSs.  Exports antibiotics such as fluoroquinolones and chloramphenicol (Vardy et al. 2005)

Blt of Mycobacterium smegmatis


ZIF2 (Zinc-Induced Facilitator 2) of 484 aas and 12 TMSs localises primarily at the tonoplast of root cortical cells and is a functional transporter able to mediate Zn efflux from the cytoplasm (Remy et al. 2014).  Activity is controlled by alternative RNA splicing. 

ZIF2 of Arabidopsis thaliana


Bcr/CflA family drug exporter, MSMEG_2991 of 428 aas and 12 TMSs. A pmf-dependent multidrug efflux pump that expels diverse groups of antibiotics including ciprofloxacin. May also be involved in biofilm enhancement (Bansal et al. 2016).

Bcr-like exporter of Mycobacterium smegmatis


Uncharacterized MFS transporter of 427 aas and 12 TMSs.

UP of Aeropyrum camini


Putative siderophore exporter, SbnD of 418 aas and 12 TMSs (Marklevitz and Harris 2016).

SbnD of Staphylococcus aureus


2.A.1.20 The Sugar Efflux Transporter (SET) Family


TC#NameOrganismal TypeExample

Sugar efflux transporter A, SetA.  Exports lactose, glucose, aromatic glucosides and galactosides, cellobiose, maltose, α-methylglucoside and isopropyl β-thiogalactosides (IPTG); amino-glycosides, streptomycin and kanamycin are weakly expelled (Liu et al. 1999).  Regulated by SgrR (a transcriptional regulator of sgrS) and SgrS (a small RNA that represses trascription of setA).  These two regulatory genes are upstream of the setA gene.  Uses a pmf-dependent mechanism of energization.  Induced in response to glucose-phosphate stress which occurs when a sugar phosphates accumulate in the cytoplam (Sun and Vanderpool 2011).


SetA (YabM) of E. coli


Efflux system, SetB, for lactose and glucose, but not IPTG or galactose (Liu et al. 1999).


SetB (YeiO) of E. coli


Arabinose (but not xylose) exporter, SetC (Koita and Rao 2012).


SetC (YicK) of E. coli

2.A.1.20.4Efflux system for arabinose and IPTG (>>lactose), SotA BacteriaSotA of Erwinia chrysanthemi

2.A.1.21 The Drug:H+ Antiporter-3 (12 Spanner) (DHA3) Family


TC#NameOrganismal TypeExample
2.A.1.21.1The macrolide (erythromycin; oleando-mycin; azithromycin) efflux, MefA BacteriaMefA of Streptococcus pyogenes

MFS porter


MFS porter of Sulfolobus islandicus (D2PCQ8)


MFS porter


MFS porter of Stackebrandtia nassauensis (D3Q871)

2.A.1.21.12Probable multidrug-efflux transporter Rv1258c/MT1297BacteriaRv1258c of Mycobacterium tuberculosis
2.A.1.21.13Uncharacterized MFS-type transporter yjbBBacilli

YjbB of Bacillus subtilis

2.A.1.21.14Uncharacterized MFS-type transporter Mb0038cActinobacteriaMb0038c of Mycobacterium bovis

MFS Homologue


MFS homologue of Streptomyces coelicolor (Q9X9Y0)


MFS Homologue


MFS homologue of Streptomyces coelicolor (Q9X8T4)


Uncharacterized MFS-type transporter YxaM


YxaM of Bacillus subtilis


Uncharacterized protein


Uncharacterized protein of Streptomyces coelicolor


Uncharacterized Major Facilitator


UMF of Streptomyces coelicolor

2.A.1.21.2The multidrug (erythromycin, tetracycline, puromycin, bleomycin) resistance protein,
BacteriaCmr of Corynebacterium glutamicum

Unidentified Major Facilitator


UMF of Pseudomonas syringae


Unidentified major facilitator


UMF of Saccharomonospora marina


Macrolide efflux pump, MefE (Mef; MefA) of 405 aas.  Induced by erythromycin and the antimicrobial peptide, LL-37 (Zähner et al. 2010).  May act in conjunction with Mel (Q93QE4), an ABC-type ATPase that is encoded in the same operon with the mefA gene (Ambrose et al. 2005).


MefE of Streptococcus pneumoniae


Uncharacterized MFS permease of 433 aas and 12 TMSs

UP of Deinococcus geothermalis


MFS_1 protein of 476 aas and 12 TMSs.

MFS_1 of Bifidobacterium longum

2.A.1.21.3The tetracycline resistance determinant, TetV BacteriaTetV of Mycobacterium smegmatis
2.A.1.21.4Multidrug resistance efflux pump, Tap BacteriaTap of Mycobacterium fortuitum
2.A.1.21.5The putative bacilysin exporter, BacEBacteriaBacE of Bacillus subtilis (P39642)
2.A.1.21.6The tetracycline resistance efflux pump, TetA(P) (Bannam et al., 2004) (21% identity (e-07) with 2.A.1.21.5 and 22% identity (2xe-7) with 2.A.1.2.10). It may be the link between DHA1 and DHA3.


TetA (P) of Clostridium perfringens (Q46305)


The Staphyloferrin A (siderophore) exporter, NWMN-2081 (Beasley et al. 2009). Independently suggested to be a macrolide exporter (Marklevitz and Harris 2016; ).


NWMN-2081 of Staphylococcus aureus (A6QJ21)


The putative macrolide exporter, TIGR00900 (most similar to 2.A.1.21.1).


TIGR00900 of Bacillus clausii (Q5WAS7)


MFS carrier of unknown function


MFS carrier of Thermoplasma acidophilum (Q9HLP1)


2.A.1.22 The Vesicular Neurotransmitter Transporter (VNT) Family (Related to the SP Family (TC #2.1.1))


TC#NameOrganismal TypeExample

Synaptic vesicle neurotransmitter (e.g., dopamine) transporter, SV2.  This protein localizes to neurotransmitter-containing vesicles and has a nucleotide binding site (Yao and Bajjalieh 2009).


SV2 of Rattus norvegicus


Synaptic vesicle glycoprotein 2B of 556 aas


Glycoprotein 2B of Tribolium castaneum


AgaP of 537 aas

Animals (Insects)

AgaP of Anopheles gambiae


Uncharacterized protein of 537 aas


UP of Acyrthosiphon pisum


Uncharacterized protein of 561 aas


UP of Trichoplax adhaerens (Trichoplax reptans)


2.A.1.23 The Conjugated Bile Salt Transporter (BST) Family


TC#NameOrganismal TypeExample
2.A.1.23.1Conjugated bile salt:H+ symporter, CbsT1 BacteriaCbsT1 of Lactobacillus johnsonii 100-100
2.A.1.23.2Taurocholate:cholate antiporter, CbsT2BacteriaCbsT2 of Lactobacillus johnsonii 100-100 (AAC34380)

2.A.1.24 The Unknown Major Facilitator-1 (UMF1) Family


TC#NameOrganismal TypeExample
2.A. KDa protein, YCL038c YeastYCL038c of Saccharomyces cerevisiae

Vacuolar amino acid (Arg, Lys, His) transporter, Atg22 (Autophagy-related protein-22) (Sugimoto et al. 2011).


Atg22 of Schizosaccharomyces pombe (Q09812)


MFS permease


MFS permease of Chloroflexus aurantiacus (A9WGR7)


MFS permease


MFS permease of Myxococcus xanthus (Q1CWQ3)


MFS permease


MFS permease of Micrococcus luteus (Micrococcus lysodeikticus)


MFS porter of 474 aas


MFS porter of Hyphomonas neptunium


2.A.1.25 The Peptide-Acetyl-Coenzyme A Transporter (PAT) Family


TC#NameOrganismal TypeExample

The endoplasmic reticular/golgi acetyl-CoA:CoA antiporter 1, ACATN/ACATN1 (SLC33A1).  Allows acetylation of sialic acid residues in gangliosides and lysine residues in membrane proteins.  It is associated with neurodegenerative disorders such as sporadic amyotrophic laterial sclerosis (ALS) and Spastic Paraplegia 42, and it is essential for motor neuron viability (Hirabayashi et al. 2013).


SLC33A1 of Homo sapiens


Cell wall degradation product (peptides and glycopeptides including N-acetylglucosaminyl β-1,4-anhydro-N-acetyl-muramyl-tripeptide) as well as penicillin derivative uptake porter, AmpG (Cheng and Park 2002).


AmpG of E. coli (P0AE16)

2.A.1.25.3The AmpG peptidoglycan uptake porter; part of the peptidoglycan recycling pathway (Garcia and Dillard, 2008)BacteriaAmpG of Neisseria gonorrhoeae (Q5F6G0)

Putative peptide/acety-CoA transporter of 560 aas and 12 TMSs.

Uncharacterized protein of Saccharomyces cerevisiae (Baker's yeast)


Transporter of N-acetylglucosamine anhydrous N-acetylmuramyl peptides, AmpG (Kong et al. 2010).  Necessary for induction of β-lactam resistance (Zhang et al. 2010).


AmpG of Pseudomonas aeruginosa


2.A.1.26 The Drug:H+ Antiporter-4 (DHA4) Family; formerly the Unknown Major Facilitator-2 (UMF2) Family


TC#NameOrganismal TypeExample
2.A. KDa Protein, YcaD BacteriaYcaD of E. coli

MFS porter, YfkF; possible drug exporter


YfkF of Bacillus subtilis (O34929)


Multidrug resistance efflux porter, BC3310 of 396 aas and 12 TMSs.  Exports ethidium bromide, sodium dodecyl sulfate and silver nitrate.  D105 in TMS4 is essential for activity (Kroeger et al. 2015).

BC3310 of Bacillus cereus


2.A.1.27 The Phenyl Propionate Permease (PPP) Family


TC#NameOrganismal TypeExample

The phenylpropionate porter, HcaT (YfhS) (Díaz et al. 1998).


HcaT (YfhS) of E. coli


2.A.1.28 The Feline Leukemia Virus Subgroup C Receptor (FLVCR) Family


TC#NameOrganismal TypeExample

Cell surface receptor (c-receptor) for anemia-inducing feline leukemia virus subgroup C (FLCVR); functions in haem export in haemopoietic cells (Latunde-Dada et al., 2006Khan and Quigley, 2011). May cause Diamond-Blackfan anemia when defective (Keel et al., 2008). Mutations of FLVCR1 in posterior column ataxia and retinitis pigmentosa result in the loss of heme export activity (Yanatori et al., 2012). Heme accumulation causes toxicity.  FLVCR1 is co-induced upon iron insufficiency in the placenta with the LDL recpetor-related protein 1 (LRP1) heme receptor, and these two proteins may be important for neonatal iron status (Cao et al. 2014).  It is required for erythroid and αβ-, CD4 and CD8 T- cell development (Philip et al. 2015).


C-receptor of Homo sapiens

2.A.1.28.2The MFS-Domain7 protein (516aa)
(the MFS-D7 mRNA is expressed in many human tissues, especially in lungs and testis).
AnimalsMFSD7 of Mus musculus

Unknown major facilitator


UMF of Coriobacterium glomerans (F2NBU7)


The Fowler syndrome-associated protein, feline leukemia virus subgroup C receptor-related protein 2, is a heme importer (Duffy et al., 2010).


FLVC2 of Homo sapiens (Q9UPI3)


MFS porter


MFS porter of Leptospira biflexa (B0SL69)


Electrogenic DIRC2 (Disrupted in renal carcinoma 2) (glycosylated and proteolytically processed (Savalas et al., 2011)). Targeted to lysosomes via an N-terminal dileueine motif. 


DIRC2 of Homo sapiens (Q96SL1)

2.A.1.28.7Feline leukemia virus subgroup C receptor-related protein 1


FLVCR1 of Felis catus

2.A.1.29 The Unknown Major Facilitator-3 (UMF3) Family


TC#NameOrganismal TypeExample
2.A.1.29.1Archaeal open reading frame ArchaeaOrf of Archaeoglobus fulgidus
2.A.1.29.2Archaeal open reading frame ArchaeaOrf of Aeropyrum pernix

Bacterial unknown major facilitator


UMF3 member of Frankia sp. Eul1c (E3J3E7)


2.A.1.3 The Drug:H+ Antiporter-2 (14 Spanner) (DHA2) Family


TC#NameOrganismal TypeExample

The main boron exporter in yeast, Atr1 (Kaya et al. 2009) (Aminotriazole, 4-nitroquinoline-N-oxide, etc.):H+ antiporter. Also exports L-cysteine (Yamada et al., 2006).


Atr1 of Saccharomyces cerevisiae

2.A.1.3.10Methylenomycin:H+ antiporterGram-positive bacteriaMmrB of Bacillus subtilis
2.A.1.3.11Puromycin:H+ antiporterGram-positive bacteriaPur8 of Streptomyces lipmanii
2.A.1.3.12Tetracenomycin:H+ antiporterGram-positive bacteriaTcmA of Streptomyces glaucescens
2.A.1.3.13Unconjugated bile acid uptake transporterBacteriaBaiG of Eubacterium sp. strain VPI 12708
2.A.1.3.14Methylviologen (paraquat):H+ antiporter
(also exports ethidium bromide, acriflavin, malachite green, pyonine B and benzyl viologen)
BacteriaSmvA of Salmonella typhimurium
2.A.1.3.15Rifamycin:H+ antiporterBacteriaRifP of Amycolatopsis mediterranei

The Me2+·tetracycline:2H+ antiporter
(Me2+ = Co2+, Mg2+, Mn2+) (also probably
a Na+ or K+:2H+ antiporter) (Wang et al. 2000).


TetA(L) of Bacillus subtilis

2.A.1.3.17The trimethoprim-sensitivity protein, YebQ (increases sensitivity to trimethoprim)BacteriaYebQ of E. coli
2.A.1.3.18Efflux pump for plant-bacterial signaling molecules, phytoalexins, flavenoids and salicylate as well as drugs, RmrBBacteriaRmrB of Rhizobium etli
2.A.1.3.19Paraquot efflux pump, PqrB (Cho et al., 2003)BacteriaPqrB of Streptomyces coelicolor (AAG45950)

Exporter of CCCP, nalidixic acid, rhodamine 6G, methylviologen, deoxycholate, growth inhibitory steroid hormones (estradiol and progesterone) (Elkins and Mullis, 2006) SDS, organomercurials, etc. (Nishino and Yamaguchi 2001).

Gram-negative bacteria

EmrB of E. coli (P0AEJ0)

2.A.1.3.20Long chain fatty acid efflux pump, FarB (Lee et al., 2003) (exports antimicrobial long chain fatty acids; functions with MFP auxillary protein, FarA (TC# 8.A.1.1.2)) (Lee et al., 2006)BacteriaFarB of Neisseria gonorrhoeae (AAD54074)
2.A.1.3.21Siderophore, achromobactin efflux pump, YhcA (Franza et al., 2005)BacteriaYhcA of Erwinia (Pectobacterium) chrysanthemi (AAL14569)
2.A.1.3.22The Tet38 tetracycline-resistance protein of Staphylococcus aureus (Truong-Bolduc et al., 2005)BacteriaTet38 of Staphylococcus aureus (AAV80464)
2.A.1.3.23The NorB multidrug resistance pump (exports hydrophilic quinolones, ethidium bromide, cetrimide, sparfloxacin, moxifloxacin and tetracycline) (Truong-Bolduc et al., 2005)BacteriaNorB of Staphylococcus aureus (BAB42529)

The VceAB multidrug (hydrophobic compounds including deoxycholate (DOC), antibiotics, such as chloramphenicol and nalidixic acid, and the proton motive force uncoupler, cyanide carbonyl m-chlorophenylhydrazone (CCCP)) resistance pump (functions with outer membrane VceC (TC#1.B.17.3.6) or OprM (2.A.6.2.21), an OMF family member; The C-terminal domain of the Pseudomonas aeruginosa OprM and the alpha-helical hairpin domain of Vibrio cholerae VceA play important roles in recognition/specificity/recruitment in the assembly of a functional, VceAB-OprM chimeric efflux pump (Bai et al., 2010).


VceAB of Vibrio cholerae
VceB (MFS), NP_231054
VceA (MFP), NP_231053


Actinorhodin (blue pigmented antibiiotic) transporter, ActII-2


ActII-2, Actinorhodin transporter of Streptomyces coelicolor (P46105).


Novobiocin/deoxycholate exporting MDR efflux pump, MdtD or YegB (Baranova and Nikaido, 2002).  Also exports arabinose but not xylose (Koita and Rao 2012). Regulated by the transcription factor, BaeR (Nagakubo et al. 2002).


YegB of E. coli (P36554)


The vacuolar basic amino acid (Arg, Lys, His) transporter, Vba3 (Shimazu et al., 2005)


Vba3 of Saccharomyces cerevisiae (P25594)

2.A.1.3.28MDR multidrug efflux pump, EbrE (involved in colony growth, dependent on Ca2+, Mg2+, Na+ and K+) (Lee et al., 2007)BacteriaEbrE of Streptomyces lividans (Q939A4)
2.A.1.3.29The metal:tetracycline/oxytetracycline resistance efflux pump, TctB (563 aas)BacteriaTctB of Streptomyces rimosus (O69070)

(Acriflavin, ethidium bromide, fluoroquinolones, etc.):H+ antiporter (Li et al. 2004; Rodrigues et al. 2011).

Gram-positive bacteria

LfrA of Mycobacterium smegmatis

2.A.1.3.30Lincomycin resistance protein; Lincomycin:H+ antiporter, LmrBBacteriaLmrB of Bacillus subtilis (O35018)

The hydrophilic fluroquinolones efflux pump, QepA (Perichon et al., 2008). Exports hydrophilic quinolones, norfloxacin, and ciprofloxacin.

BacteriaQepA of E. coli (A5H8A5)
2.A.1.3.32Landomycin A efflux pump, LanJ (Otash et al., 2008)BacteriaLanJ of Streptomyces cyanogenus (Q9ZGB6)
2.A.1.3.33Multidrug (including novobiocin, streptomycin, and actinomycin D) resistance porter, MdtP (YusP)


MdtP of Bacillus subtilis (O32182)


The P55 drug efflux pump (Rv141Oc) (extrudes drugs including rifampicin and clifazimine, first- and second-line anti-tuberculosis drugs. CCCP and valinomycin inhibited drug resistance) (Ramón-García et al., 2009).  P55 also exports malachite green, ethidium bromide, isoniazid and ethambutol (Bianco et al. 2011).  Functions together with the outer membrane lipoprotein porin, LprG, also called P27 and Lpp-27 (Bianco et al. 2011; Farrow and Rubin 2008).  Required together with LprG for normal colony morphology and sliding motility, possibly due to alterred cell wall composition (Farrow and Rubin 2008).


P55 drug efflux pump of Mycobacterium tuberculosis (P71678)


The 14 TMS FmtC (MprF: Multiple peptide resistance factor) protein of 840 aas, involved in methecillin and daptomycin resistance. Residues 1-550 comprise a 14TMS MFS permease domain while residues 551-840 comprise a "phosphatidylglycerol lysyl transferase" (or synthetase) domain (DUF2156), also called "lysyl cardiolipid synthase" (Oku et al. 2004; Staubitz et al. 2004; Ernst et al. 2009). FmtC may be distantly related to lysyl-tRNA synthetases (TC# 9.B.111). Similar to 2.A.1.3.44 in all these respects.  Ernst et al. 2015 and Slavetinsky et al. 2012 have reported that TMSs 1-6 of FmtC of S. aureus is a flippase for lysylinated phosphatidyl glycerol, and that the entire system is a dimer.


FmtC of Staphylococcus aureus (D1QCY9)


EmrKY-TolC MDR efflux pump (Nishino and Yamaguchi 2001). (also exports cysteine (Yamada et al., 2006)) (similar to 2.A.1.3.2)


EmrKY-TolC of E. coli
EmrK (MFP) (C5W790)
EmrY (MFS) (C5W789)


The uridine/deoxyuridine/5-fluorouridine uptake transporter, UriP (llmg_0856) (480aas; 14TMSs) (Martinussen et al., 2010)


UriP of Lactococcus lactis (A2RJJ9)


MFS porter of unknown function


MFS porter of Streptomyces viridochromogenes (D9X7X8)


The antimicrobial efflux pump, LmrS. Exports linezolid and tetraphenylphosphonium chloride (TPCL) > sodium dodecyl sulfate (SDS), trimethoprim, and chloramphenicol. (most similar to LmrB (2.A.1.3.30)) (Floyd et al., 2010).


LmrS of Staphylococcus aureus (Q5HE38)


(Mono- and divalent organocation):H+ antiporter. Transmembrane helix 12 of QacA lines the bivalent cationic drug binding pocket (Hassan et al., 2007).

Gram-positive bacteria

QacA of Staphylococcus aureus (P0A0J9)


The phenazine resistance pump. Also exports D-alanyl-griseoluteic acid; possibly in conjunction with a chaperone protein, EhpR. The crystal structure of EhpR is known (Yu et al., 2011). Note: Phenazines are toxic redox active secondary metabolites that many bacteria secrete.


EhpJ of Panloea (Enterobacter) agglomerans (O32600)


Rv0585c; 795aas: 1 - 220aas, TMSs 1-6; 221-490aas, kinase domain; 491-795, TMS: 7-14. The C-terminal 8 TMS hydrophobic domain is homologous to an N-terminal domain in fused Mg2+-ATPases (3.A.3.4.3 and 3.A.3.4.4) and members of family 9.B.3.


Rv0585c of Mycobacterium tuberculosis (O53781)


Putative oxacillin resistance-associated protein, FmtC (872 aas; 14 N-terminal TMSs (residues 1-530) plus a largely hydrophilic DUF2156 domain (residues 531-872). Similar throughout its length to FmtC of Staphylococcus aureus (2.A.1.3.35). Residues 67-326 (TMSs 2-8) are homologous to residues 527-786 (TMSs 8-14) in Rv0585c of Mycobacterium tuberculosis (2.A.1.3.43). Residues 6-314 are also homologous  to an extra hydrophobic domain in Mg2+ P-type ATPases  (3.A.3.4.3 and 3.A.3.4.4). The C-terminal domain belongs to the DUF2156 superfamily. Homologues of the hydrophilic domain retrieved with NCBI BLAST searches are annotated as "putative" lysylphosphatidyl-glycerol synthetase. Some include full length MFS fusion proteins.


FmtC of Brucella melitensis (D1F3T8)


MFS efflux pump, AmvA (AedF). Mediates drug, dye, detergent, antibiotic and disinfectant resistance (Rajamohan et al., 2010; Hassan et al. 2011). 98.6% identical to AdeF (2.A.1.3.46).


AmvA of Acinetobacter baumannii (C4PAW9)


MDR pump, AdeF (AmvA) exports ethidium, DAPI, and chlorhexidine (Hassan et al. 2011). 98.6% identical to AmvA (2.A.1.3.45).


AdeF of Acinetobacter baumannii (A3M6E0)


Putative MFS permease TMSs 10-13 (shows limited sequence similarity with TMSs 2-5 in 9.B.111.1.1 and 9.B.111.1.2).


MFS permease of Bilophila wadsworthia (E5Y3Y1)


The phenicol (florfenicol/chloramphenicol) exporter, FexB (Liu et al., 2012)


FexB of Enterococcus faecium (G9FS16)


The trichothecene efflux pump, TRI12 (Alexander et al., 1999; Wuchiyama et al., 2000). Trichothecenes are plant growth promoters and bio-control agents (See also Fang et al. (2012)). TRI12 secretes toxic trichothecene compounds like T-2 toxin, nivalenol and deoxynivalenol.


TRI12 of Fusarium sporotrichioides (Q9C1B3)


Probable multidrug-efflux transporter Rv1634/MT1670


Rv1634 of Mycobacterium tuberculosis


Multidrug resistance protein Stp (Spectinomycin tetracycline efflux pump)


Stp of Myconbacterium tuberculosis

2.A.1.3.5(Pristinamycin I and II, rifamycin, etc.):H+ antiporterGram-positive bacteriaPtr of Streptomyces pristinaespiralis
2.A.1.3.50Multidrug resistance protein 3 (Multidrug-efflux transporter 3)Bacilli

Bmr3 of Bacillus subtilis

2.A.1.3.51Probable transport protein HsrA (High-copy suppressor of RspA)Bacteria

HsrA of Escherichia coli


Drug resistance protein YOR378W.  Does not export boron (Bozdag et al. 2011).


YOR378W of Saccharomyces cerevisiae

2.A.1.3.53Azole resistance protein 1FungiAZR1 of Saccharomyces cerevisiae
2.A.1.3.54Protein SGE1 (10-N-nonyl acridine orange resistance protein) (Crystal violet resistance protein)FungiSGE1 of Saccharomyces cerevisiae

Uncharacterized MFS-type transporter YubD


YubD of Bacillus subtilis


Uncharacterized MFS-type transporter YvmA

BacilliyvmA of Bacillus subtilis

Uncharacterized MFS-type transporter YwoD


YwoD of Bacillus subtilis


Uncharacterized MFS-type transporter YfiU


YfiU of Bacillus subtilis


MDR efflux pump, NorC (Truong-Bolduc et al. 2006). Proposed to be a quinolone resistance exporter, NorB (Marklevitz and Harris 2016).


NorC (NorB) of Staphylococcus aureus

2.A.1.3.6Me2+·tetracycline:2H+ or 2K+ antiporter
(the optimal Me2+ = Co2+) (Also transports Na+ or K+out in exchange for 2H+.)
BacteriaTetK of Staphylococcus aureus (P02983)

MDR efflux pump, SdrM.  Exports norfloxacin, acriflavin and ethidium bromide (Yamada et al. 2006).


SdrM of Staphylococcus aureus


MDR efflux pump, MdeA.  Exports hoechst 33342, doxorubicin, daunorubicin, tetraphenyl phosphonium, ethidium bromide and rhodamine 6G (Yamada et al. 2006).


MdeA of Staphylococcus aureus


MDR efflux pump, AedC (Hassan et al. 2011).  Shown to export chloramphenicol and tetracycline.


AedC of Acinetobacter baumannii


Iron homeostasis protein, AedD; may function in siderophore export (Hassan et al. 2011).


AedD of Acinetobacter baumannii


Uptake permease for cholate (steroid) metabolites, CamM of 513 aas and 14 TMSs.  Uptake of 3,7(R),12(S)-trihydroxy-9-oxo-9,10-seco-23,24-bisnorchola-1,3,5(10)-trien-22-oate was observed (Swain et al. 2012).


CamM of Rhodococcus jostii


ThMFS1 of 563 aas and 14 TMSs.  Catalyzes export of fungicides causing tolerance.  It exports trichodermin, but it is not the only exporter of this secondary metabolite (Liu et al. 2012). Trichothecenes are the sesquiterpenes secreted by Trichoderma spp. residing in the rhizosphere. These compounds have been reported to act as plant growth promoters and bio-control agents (Chaudhary et al. 2016).


MFS1 of Trichoderma harzianum (Hypocrea lixii)


MFS permease of 413 aas and 12 TMSs. Encoded within the SoxR regulon; possibly a drug exporter (Naseer et al. 2014).


MFS permease of Pseudomonas aeruginosa


MFS porter of 462 aas and 14 TMSs


MFS porter of Deinococcus radiodurans

The PfMFS transporter (551 aas; 14 putative TMSs) is involved in the acid resistance and 
intracellular pH homeostasis of Penicillium funiculosum (Xu et al. 2014). This protein was
not in UniProt, and its closest orthologue, PmMFS of Penicillium marneffei, is therefore
presented here.


PfMFS of Talaromyces (Penicillium) funiculosum


Drug resistance pump, YMR279c of 540 aas.  When overexpressed, confers boron resistance, but is not induced by boron (Bozdag et al. 2011). 

YMR279c of Saccharomyces cerevisiae (Baker's yeast)

2.A.1.3.7Actinorhodin:H+ antiporter, ActVa or ActA (Tahlan et al., 2007)Gram-positive bacteriaActVa of Streptomyces coelicolor

Probable exporter of aromatic compounds of 559 aas and 16 putative TMSs in an apparent 4 + 4 + 4 + 4 arrangement. May function in aromatic compoound detoxification.  Regulated by a MarR-like transcriptional regulator that is encoded in the same operon. Ten-fold induction occurs in response to aromatic aldehydes such as benzaldehyde (Fiorentino et al. 2007). The same MarR protein controls transcription of a gene encoding an NADH-dependent alcohol dehydrogenase (Sso2536).

Sso1351 of Sulfolobus solfataricus


Putative multidrug-resistance exporter of 553 aas and 14 putative TMSs, KNQ1. It is a drug efflux permease for several toxic compounds that in multiple copies confer increased dithiothreitol resistance. KNQ1 does not export dithiothreitol or function in recombinant protein secretion. KNQ1 gene amplification or deletion resulted in enhanced transcription of iron transport genes, suggesting,  a role in iron homeostasis on which dithiothreitol tolerance may depend (Marchi et al. 2007).

KNQ1 of Kluyveromyces lactis (Yeast) (Candida sphaerica)


Riboflavin transporter of 456 aas and 14 TMSs, RibZ (Gutiérrez-Preciado et al. 2015).

RibZ of Peptoclostridium difficile (Clostridium difficile)

2.A.1.3.8Cephamycin:H+ antiporterGram-positive bacteriaCmcT of Nocardia lactamdurans
2.A.1.3.9Lincomycin:H+ antiporterGram-positive bacteriaLmrA of Streptomyces lincolnensis

2.A.1.30 The Putative Abietane Diterpenoid Transporter (ADT) Family


TC#NameOrganismal TypeExample
2.A.1.30.1Putative abietane uptake permease (in gene cluster for degradation of abietane diterpenoids), DitE BacteriaDitE of Pseudomonas abietaniphila BKME-9

2.A.1.31 The Nickel Resistance (Nre) Family


TC#NameOrganismal TypeExample
2.A.1.31.1The Ni2+ efflux pump, NreB (Ni2+ inductible) BacteriaNreB of Achromobacter xylosoxidans plasmid pTOM
2.A.1.31.2The Ni2+ resistance protein, NrsD BacteriaNrsD of Synechocystis PCC6803

The unknown porter, YfiS


YfiS of Bacillus subtilis (O31561)

Kurstakin/surfactin exporter of 417 aas (in B. subtilis) (Li et al. 2015).  This protein is an ortholog of the B subtilis protein (Li et al. 2015).


KrsE of Bacillus cereus


Uncharacterized MFS porter of 455 aas

Green Algae

UP of Chlamydomonas reinhardtii (Chlamydomonas smithii)


Uncharacterized MFS porter (residiues 1 - 450) with hydrophilic C-terminal protein kinase domain.  The protein is of 858 aas.

Green algae

UP of Chlamydomonas reinhardtii (Chlamydomonas smithii)


2.A.1.32 The Putative Aromatic Compound/Drug Exporter (ACDE) Family


TC#NameOrganismal TypeExample

Putative aromatic compound/drug exporter. Enhances expression of the sigma X gene that functions to modify the cell envelope (Turner and Helmann, 2000). yitG is reported to be a mutator gene that inhibits transition base substitutions (Sasaki and Kurusu, 2004).


YitG of Bacillus subtilis

2.A.1.32.2Bacillibactin exporter, YmfE (199aas; 6TMSs) (Miethke et al., 2008) (resembles the 2nd half of YitG of B. subtilis (2.A.1.32.1). The sequence provided under acc# O31763 is only a fragment of the full length gene.BacteriaYmfE of Bacillus subtilis (O31763)

Putative copper/multidrug efflux protein, YfmO.  The yfmPO operon is autoregulated by the MerR homologue, YfmP (a repressor). The copZA operon encodes CopA, a copper ATPase (TC# 3.A.3.5.18) which is induced by a copper dependent mechanism. Since a yfmP null mutant had poor copZA induction but elevated levels of the YfmO efflux pump, YfmO could catalyze copper efflux and be responsible for reduced copZA induction. Consistent with this model, a yfmP yfmO double mutant showed normal induction by copper (Gaballa et al. 2003).


YfmO of Bacillus subtilis


2.A.1.33 The Putative YqgE Transporter (YqgE; UMF4) Family


TC#NameOrganismal TypeExample

MFS homologue, YqgE. Co-transcribed with ftsI, encoding the peptidoglycan transpeptidase that crosslinks peptidoglycan strands, releasing free D-alanine. Possibly YqgE is a D-alanine uptake porter.

Bacteria; Archaea

YqgE of Bacillus subtilis (P54487)


UMF4 family member


UMF4 family member form Bacteroides ovatus (A7LYG9)


UMF4 family member (encoded near an α-glucuronidase; GH31 family; divergently transcribed). 


UMF4 family member of Sulfolobus tokodaii (Q96XI6)


2.A.1.34 The Sensor Kinase-MFS Fusion (SK-MFS) Family


TC#NameOrganismal TypeExample

Sensor kinase (N-terminal 400 residues)/MFS fusion protein. The N-terminal domain resembles the sensor kinase of 414 aas of Anaeromyxobacter sp. KJ (ACG71775).


Fusion protein of Bordetella pertussis (Q7VWI9)


2.A.1.35 The Fosmidomycin Resistance (Fsr) Family


TC#NameOrganismal TypeExample
2.A.1.35.1The fosmidomycin resistance (Fsr) protein (confers fosmidomycin, trimethoprim and carbonylcyanide m-chlorophenylhydrazone (CCCP) resistance)BacteriaFsr of E. coli
2.A.1.35.2The cationic microbial peptide resistance (RosA) proteinBacteriaRosA of Yersinia enterocolitica

MFS transporter of 388 aas and 12 TMSs


MFS porter of Sulfobacillus acidophilus


2.A.1.36 The Acriflavin-sensitivity (YnfM) Family


TC#NameOrganismal TypeExample

The acriflavin-sensitivity protein, YnfM (increases sensitivity to acriflavin specifically).  Also exports arabinose but not xylose (Koita and Rao 2012).


YnfM of E. coli


Hypothetical MFS carrier


MFS carrier of Serratia proteamaculans (A8GHT9)


Putative uncharacterized transporter YgaY


YgaY of Escherichia coli


MdrA.  Putative MDR transporter that may export cationic and hydrophobic compounds, Sco4007.  Regulated by a TetR-like repressor that binds drugs (Hayashi et al. 2013).


MdrA (Sco4007) of Streptomyces coelicolor


MFS carrier of 389 aas


MFS carrier of Rhizobium loti


2.A.1.37 The Unknown Major Facilitator-4 (UMF4) Family


TC#NameOrganismal TypeExample

Unknown Major Facilitator-4 family member, UMF4A, of 396 aas and 12 TMSs.


UMF4A of Brachyspira pilosicoli


UMF4 family member of 399 aas and 12 TMSs, UMF4B.


UMF4B of Brachyspira murdochii


UMF4C of 407 aas and 12 TMSs.


UMF4C of Ferroplasma sp. 


UMF4D of 399 aas and 12 TMSs


UMF4D of Sphaerochaeta pleomorpha


UMF4E of 373 aas and 12 TMSs


UMF4E of Caldisphaera lagunensis


2.A.1.38 The Enterobactin (Siderophore) Exporter (EntS) Family


TC#NameOrganismal TypeExample

The enterobactin (siderophore) exporter, EntS or YbdA (Bleuel et al., 2005).  May also export arabinose but not xylose (Koita and Rao 2012).


EntS (YbdA) of E. coli

2.A.1.38.2The putative siderophore exporter (DUF 894; Pfam 05977), VabSBacteriaVabS of Listonella anguillarum (Q0E7C5)
2.A.1.38.3Enterobactin exporter, EntS (Crouch et al., 2008) (probably orthologous to 2.A.1.38.1). BacteriaEntS of Salmonella typhimurium

Uncharacterized MFS protein of 429 aas and 12 TMSs.

UP of Lactobacillus rhamnosus


2.A.1.39 The Vibrioferrin (Siderophore) Exporter (PrsC) Family


TC#NameOrganismal TypeExample
2.A.1.39.1The vibrioferrin (siderophore) exporter, PrsC (Tanabe et al., 2003)BacteriaPrsC of Vibrio parahaemolyticus (BAC16546)

2.A.1.4 The Organophosphate:Pi Antiporter (OPA) Family


TC#NameOrganismal TypeExample
2.A.1.4.1Sugar-P:Pi antiporter (transports many sugar-phosphates - both 1- and 6-P esters)BacteriaUhpT of E. coli (P0AGC0)

2-phosphonoacetate/2-phosponoproprionate uptake porter of 428 aas, PhnB.  The PhnA protein is a hydrolase, and PhnC is a positive transcriptional regulator.  Induction occurs with either of the two substrates (Kulakova et al. 2001).


PhnB of Pseudomonas fluorescens


Glycerol-3-phosphate:inorganic phosphate antiporter, GlpT (Frohlich and Audia 2013).


GlpT of Rickettsia prowazekii


P-glycerate:Pi antiporter, Pgt.  Takes up phosphoenolpyruvate, 2-phosphoglycerate, and 3-phosphoglycerate as sole sources of carbon and energy for rapid growth (Saier et al. 1975).  Not present in E. coli K12, but is present in many intracellular pathogenic strains of E. coli (Tang and Saier, unpublished observations).


PgtP of Salmonella typhimurium


Glycerol-P:Pi antiporter (may function by a 'rocker switch' mechanism; Law et al., 2007). The 3-d structure is known (3.3Å resolution) (Huang et al., 2003; Lemieux et al., 2005; Lemieux, 2007).


GlpT of E. coli

2.A.1.4.4Hexose-P:Pi antiporter regulatory protein; senses external glucose-6-P and transports it with high affinity and low efficiencyBacteriaUhpC of E. coli

Microsomal (ER/Golgi) glucose-6-P:Pi antiporter (glycogen storage disease (GSD1b and 1c); Gierke''s disease protein) (SLC37A2 in mice, associated with white adipose tissue obesity and expressed at high levels in macrophage) (4 isoforms present in humans (Chen et al., 2008)).  SLC37A1 and A2 can not substitute for A4.  91 mutations have been observed in human patients (Chou and Mansfield 2014).  Inhibited by cholorogenic acid although SLC37A1 and A2 are not.  SLC37A3 had not been characterized by 2014 (Chou and Mansfield 2014).


SLC37A4 of Homo sapiens

2.A.1.4.6Glucose-6-P:Pi antiporter, Hpt (may also transport other organophosphates including C3 organophosphates).BacteriaHpt of Chlamydia pneumoniae (spQ9Z7N9 & gi9979188) & pirA72050

Putative glycerol-3-phosphate (G-3-P) transporter, G3PP (most similar to TC# 2.A.1.4.6, 22% identity).  Has been shown to catalyze glucose 6-P:Pi antiport across the endoplasmic reticular membrane(Pan et al. 2011).


SLC37A1 of Homo sapiens


solute carrier family 37 (putative glycerol-3-phosphate transporter), member 2.  Has been shown to catalyze glucose 6-P:Pi antiport across the endoplasmic reticular membrane (Pan et al. 2011).


SLC37A2 of Homo sapiens

2.A.1.4.9 solute carrier family 37 (glycerol-3-phosphate transporter), member 3AnimalsSLC37A3 of Homo sapiens

2.A.1.40 Major Facilitator Superfamily Domain-containing Protein Family


TC#NameOrganismal TypeExample
2.A.1.40.1Major facilitator superfamily domain-containing protein 5Animals

Mfsd5 of Danio rerio

2.A.1.40.2Major facilitator superfamily domain-containing protein 5


MFSD5 of Pongo abelii
2.A.1.40.3Major facilitator superfamily domain-containing protein 5Animalsmfsd5 of Xenopus tropicalis

2.A.1.41 The Putative Bacteriochlorophyll Delivery (BCD) Family


TC#NameOrganismal TypeExample
2.A.1.41.1Putative pigment transporter (Young and Beatty, 1998)Photosynthetic bacteriaLhaA of Rhodobacter capsulatus
2.A.1.41.2Putative pigment transporter (Young and Beatty, 1998)Photosynthetic bacteriaPucC of Rhodobacter capsulatus
2.A.1.41.3Putative bacteriochlorophyll synthasePhotosynthetic bacteriaBch2 of Rhodobacter capsulatus

2.A.1.42 The Lysophospholipid Transporter (LplT) Family


TC#NameOrganismal TypeExample

The lysophospholipid transporter, LplT (Harvat et al., 2005).  Substrates include lyso-PE, lyso-cardiolipin, diacylcardiolipin, fully-deacylated cardiolipin and lyso-phosphatidylglycerol, but not lysophosphatidylcholine, lysophosphatidic acid or phosphatidic acid (Lin et al. 2016). Reacylation by acyltransferase/acyl-acyl carrier protein synthetase then occurs on the inner leaflet of the membrane.Thus, a fatty acid chain is not required for LplT transport. A "sideways sliding" mechanism was proposed to explain how a conserved membrane-embedded α-helical interface excludes diacylphospholipids from the LplT binding site to facilitate efficient flipping of lysophospho-lipids across the cell membrane (Lin et al. 2016). Thus, a fatty acid chain is not required for LplT transport. Fruther, LplT cannot transport lysophosphatidic acid, and its substrate binding was not inhibited by either orthophosphate or glycerol 3-phosphate, indicating that either a glycerol or ethanolamine headgroup is the chemical determinant for substrate recognition. Diacyl forms of PE, phosphatidylglycerol, or the tetra-acylated form of cardiolipin could not serve as competitive inhibitors .A "sideways sliding" mechanism was proposed to explain how a conserved membrane-embedded α-helical interface can exclude diacylphospholipids from the LplT binding site.


LplT of E. coli (NP_417312)


The lysophospholipid transporter-2-acyl glycerophosphoethanolamine acyl transferase/acyl ACP synthetase (LplT-Pls-ACS) fusion protein (Harvat et al., 2005). 


The fused LplT-PlsC-ACS of Bradyrhizobium japonicum (BAC47589)


2.A.1.43 The Putative Magnetosome Permease (PMP) Family


TC#NameOrganismal TypeExample
2.A.1.43.1The putative magnetosomal permease, MamH (Schubbe et al., 2003)BacteriaMamH of Magnetospirillum gryphiswaldense (Q6NE63)

The putative magnetosome (Fe?) permease fused to a C-terminal YedZ-like domain (von Rozycki et al., 2004). This protein has 649 aas and 18 TMSs with a C-terminal YedZ domain and is therefore in the YedZ superfamily.


PMP of Magnetospirillum magneticum (Q2W8K5)


2.A.1.44 The L-Amino Acid Transporter-3 (LAT3) Family (also called the SLC43 family)


TC#NameOrganismal TypeExample
2.A.1.44.1The L-amino acid transporter-3, LAT3 (transports neutral amino acids such as L-leucine, L-isoleucine, L-valine, and L-phenylalanine by a Na+-independent, electroneutral, facilitated diffusion process; also transports amino acid alcohols) (Prostate cancer up-regulated gene product)AnimalsSLC43A1 of Homo sapiens
2.A.1.44.2L-amino acid transporter-4 (LAT4) has the same specificity and is 57% identity to LAT3. Na+, Cl- and pH independent; not trans-stimulated; two kinetic components, a low affinity component sensitive to NEM, and a high affinity component insensitive to NEM. Found in the basolateral membrane of epithelial cells in the distal tubule and collecting duct of the kidney and the crypt cells in the intestine (Bodoy et al., 2005). AnimalsSLC43A2 of Homo sapiens
2.A.1.44.3 solute carrier family 43, member 3AnimalsSLC43A3 of Homo sapiens

2.A.1.45 The 2,4-diacetylphloroglucinol (PHL) Exporter (PHL-E) Family


TC#NameOrganismal TypeExample
2.A.1.45.1The 2,4-diacetylphloroglucinol resistance/general stress porter, PhlE (Abbas et al., 2004)BacteriaPhlE of Pseudomonas fluorescens (CAD65845)

2.A.1.46 The Unknown Major Facilitator-5 (UMF5) Family


TC#NameOrganismal TypeExample

Probable transporter


Probable transporter of Bordetella pertussis (Q7W0Q7)


Probable staphylopine exporter, CntE.  Staphylopine is a broad spectrum metalophore similar to plant nicotianamine that binds several divalent ions (nickel, cobalt, zinc, copper and iron) (Ghssein et al. 2016).  The uptake system for metal bound staphylpine is TC# 3.A.1.5.43).  CntE is downstream of the genes coding for the uptake system, CntABCDF (Ghssein et al. 2016).

CntE of Staphylococcus aureus

2.A.1.46.2Putative transporter


Putative transporter of Tropheryma whipplei (Q83N16)


Putative drug resistance UMF5 family member


Putative MDR pump of Leishmania infantum


UMF15 family member


UMF5 homologue of Methanosphaerula palustris (B8GFY3)


Putative quinolone resistance protein


MFS porter of Bacillus cereus (C2UR80)


UPF0226 protein YfcJ.  Catalyzes export of arabinose but not xylose (Koita and Rao 2012).


YfcJ of E. coli


UPF0226 protein, YhhS.  Exports arabinose but not xylose (Koita and Rao 2012).  Also may export the herbicide, glyphosate (Staub et al. 2012).


YhhS of E. coli


MFS carrier of 366 aa


MFS carrier of Sulfolobus solfataricus


Uncharacterized MFS porter of 430 aas


MFS porter of Halosimplex carlsbadense


2.A.1.47 The Unknown Major Facilitator-6 (UMF6) Family


TC#NameOrganismal TypeExample
2.A.1.47.1Putative transporterBacteriaPutative transporter of Lactobacillus plantarum (NP_784357)

UMF6 family member


MFS carrier of Streptococcus suis (A4VY05)


Possible antibiotic peptide exporter (encoded in an operon together with lantibiotic biosynthesis enzymes)


UMF6 family member of Streptococcus pneumoniae (B2IRN2)


MFS permease of 408 aas


MFS permease of Streptococcus pneumoniae


2.A.1.48 The Vacuolar Basic Amino Acid Transporter (V-BAAT) Family


TC#NameOrganismal TypeExample
2.A.1.48.1The vacuolar basic amino acid (histidine, lysine and arginine) transporter, Vba1 (catalyzes uptake into the vacuoles (equivalent to efflux from the cytoplasm)) (most similar to family 2.A.1.3; DHA2; 13-14 putative TMSs) (Shimazu et al., 2005)YeastVba1 of Saccharomyces cerevisiae (NP_013806)
2.A.1.48.2The vacuolar basic amino acid (Arg, Lys, His) transporter, Vba2 (Shimazu et al., 2005)YeastVba2 of Saccharomyces cerevisiae (P38358)
2.A.1.48.3Vacuolar G0 arrest protein, Fnx1; involved in amino acid (e.g., his, lys, ile, asn, etc) uptake into the vacuole (Chardwiriyapreecha et al., 2008).YeastFnx1 of Schizosaccharomyces pombe (Q09752)
2.A.1.48.4Vacuolar amino acid uptake system, Fnx2 (Chardiwiriyapreecha et al., 2008)YeastFnx2 of Schizosaccharomyces pombe (O59726)

Vacuolar basic amino acid transporter 4.  Probably does not act on amino acids, but exports drugs such as azoles.  May also play a role in vacuolar morphology (Kawano-Kawada et al. 2015).


VBA4 of Saccharomyces cerevisiae S288c


2.A.1.49 The Endosomal Spinster (Spinster) Family


TC#NameOrganismal TypeExample

The spinster protein, spin1 or spns1 gene product (involved in synaptic growth regulation; interacts with Bcl-2/Bcl-xL, affecting programmed cell death) (Nakano et al., 2001; Sanyal and Ramaswami, 2002; Yanagisawa et al., 2003).  Probably transports sphingosine-1-phosphate (Fukuhara et al. 2012).


Spinster of Drosophila melanogaster (AAG43825)


MFS multidrug exporter of 429 aas and 12 TMSs.  Exports capreomycin and ethidium bromide, and deletion mutants grow faster than wild type cells (Zhang et al. 2015).


MDR pump of Mycobacterium smegmatis


Uncharacterized protein of 656 aas and 12 TMSs

UP of Chlamydomonas reinhardtii (Chlamydomonas smithii)


The spinster homologue, Spin1 or Spns1 gene (interacts with Bc1-2/Bc1-XL to induce a caspase-independent autophagic cell death; may be required for embryogenesis) (Yanagisawa et al., 2003). Probable spingosine-1-phosphate (or sphingolipid) transporter (Nijnik et al. 2012).


Spin1 of Homo sapiens (Q9H2V7)


Probable sphingosine-1-phosphate (or sphingolipid) transporter, spinster homologue 3 (by similarity).


Spinster homologue 3 of Arabidopsis thaliana (F4IKF6)


Protein Spinster homolog 2 (Spns2 or protein two of hearts).  Transports sphingosine-1-P (S1P) and the immunomodulating agent, FTY720 (Hisano et al. 2011; Nijnik et al. 2012).  S1P is a secreted lipid mediator that functions in vascular development. In the yolk syncytial layer, Spns2 functions in S1P secretion, thereby regulating myocardial precursor migration (Kawahara et al. 2009).


Spns2 of Danio rerio


Probable sphingosine-1-phosphate or sphingolipid transporter, Spinster homolog 1 (by similarity).

PlantsAt5g65687 of Arabidopsis thaliana

Sphingosine-1-phosphate/dehydroshpingosine-1-P transport protein, Spinster 2. Involved in immune development and lymphocyte trafficing (Nijnik et al. 2012; Fukuhara et al. 2012). 


SPNS2 of Homo sapiens


Bacterial Spinster homologue; possible sphingosine-1-phosphate transporter (by similarity only).


Spinster homologue of Myxococcus xanthus


Bacterial spinster homologue.  Possible sphingosine-1-phosphate transporter (by similarity only).


Spinster homologue of Terriglobus saanensis


The cis, cis muconate transporter of 508 aas.

Animals (Insects)


MucK of Bombyx mori (Silk moth)


2.A.1.5 The Oligosaccharide:H+ Symporter (OHS) Family


TC#NameOrganismal TypeExample

Lactose:H+ symporter, LacY. Transports lactose, melibiose and TMG. Crystal structures and modeling reveal the cytoplasmic open state and the periplasmic open state (PDB ID: 1PV7; Abramson et al., 2003Pendse et al., 2010). The membrane lipid composition determines the topology of LacY (Dowhan and Bogdanov, 2011). Smirnova et al. (2011) have provided evidence that the opening of the periplasmic cavity in LacY is the limiting step for sugar binding. Evidence for an alternating sites mechanism of transport has been summarized (Smirnova et al., 2011). Eames and Kortemme (2012) have shown that when considering expression of the lac operon, LacY function (H+ transport) and not protein production is the primary origin of cost fitness. Homology threading of several MFS porters based on the LacY 3-d structure has been reported (Kasho et al., 2006). The alternating-access mechanism has been suggested to arise from inverted topological repeats (Radestock and Forrest, 2011; Madej et al. 2012), but this proposal has been contested (Västermark and Saier 2014; Västermark et al. 2014). Mechanistic features of LacY have been summarized (Kaback 2015). 


LacY of E. coli


Raffinose:H+ symporter, RafB, can be mutated to transport maltose (Van Camp et al., 2007).


RafB of E. coli

2.A.1.5.3Sucrose:H+ symporter, CscB, also transports maltose (Peng et al. 2009).


CscB of E. coli

2.A.1.5.4Melibiose:H+ symporter, MelY (Shinnick et al., 2003). Transports melibiose and lactose, but not TMG (Tavoulari and Frillingos, 2007)BacteriaMelY of Enterobacter cloacae

2.A.1.50 The Proton Coupled Folate Transporter/Heme Carrier Protein (PCFT/HCP) Family


TC#NameOrganismal TypeExample

The apical intestinal and choroid plexus proton-coupled, high affinity folate transporter, the hereditary folate malabsorption protein, PCFT/HCP1 (Shin et al. 2010).  Also reported to mediate heme-iron uptake from the gut lumen with duodenal epithelial cells (Shayeghi et al., 2005; Latunde-Dada et al., 2006; Subramanian et al., 2008, Shin et al., 2012b), but it shows a higher affinity for folate than heme) (Qiu et al., 2006). Responsible for folate uptake by choroid plexus epithelial cells (Wollack et al., 2007) and placenta (Yasuda et al., 2008). The rat orthologue (Q5EBA8) catalyzes H+-dependent folate uptake in the intestine (Inoue et al., 2008). Responsible for the rare autosomal recessive disorder, hereditary folate malabsorption (Zhao and Goldman, 2007). PCFT/ICP1, when mutated, is the cause of Hereditary Folate Malabsorption in humans (Qiu et al., 2006; Shin et al., 2012). Evidence for a 12 TMS topology with a renetrant look between TMSs 2 and 3 has been presented (Zhao et al., 2010; Qiu et al., 2006; Zhao et al., 2011; Wilson et al. 2014).  Downregulated in Chronic Kidney Disease (CKD) in heart, liver, and brain causing malabsorption (Bukhari et al., 2011). An IGXXG motif in TMS5 is important for folate binding and a GXXXG motif is involved in dimerization (Zhao et al., 2012). Inhibited by bicarbonate, bisulfite, nitrite and other anions (Zhao et al. 2013).  Its role in antifolate cancer chemotherapy has been reviewed (Matherly et al. 2014). TMSs 3 and 6 may provide critical interfaces for formation of hPCFT oligomers, facilitated by the GXXXG motifs in TMS2 and TMS4 (Wilson et al. 2015).  The extracellular gate has been identified (Zhao et al. 2016), and mechanistic aspects have been considered (Date et al. 2016).


SLC46A1 or PCFT of Homo sapiens

2.A.1.50.2Thymic stromal cotransporter, TSCOT (Kim et al. 2000)AnimalsSLC46A2 of Homo sapiens
2.A.1.50.3 solute carrier family 46, member 3AnimalsSLC46A3 of Homo sapiens

Multidrug efflux transporter, MET, of 507 aas and 12 TMSs (Chahine et al. 2012).  Exposure to dietary methotrexate was associated with increased fluid secretion rate and increased flux of methotrexate, but not salicylate. Exposure to methotrexate in the diet resulted in increases in the expression of a multidrug efflux transporter gene (MET; CG30344) in the Malpighian tubules. There were also increases in expression of genes for either a Drosophila multidrug resistance-associated protein (dMRP; CG6214; TC# 3.A.1.208.39) or an organic anion transporting polypeptide (OATP; CG3380; TC# 2.A.60.1.27), depending on the concentration of methotrexate in the diet.  MET probably does not export methotrexate (Chahine et al. 2012).

MET of Drosophila melanogaster (Fruit fly)


2.A.1.51 The Unknown Major Facilitator 7 (UMF7) Family


TC#NameOrganismal TypeExample
2.A.1.51.1Putative permeaseBacteriaPutative transporter of Azoarcus sp. EbN1 (CAI06874)

YjiJ MFS porter, a member of the DUF2118 family in Pfam.


YjiJ of E. coli (D6IHN4)


MFS permease


MFS permease of Thermus thermophilus (F6DF77)


Uncharacterized MFS permease


UP of Pseudomonas aeruginosa


2.A.1.52 The Glycerophhosphodiester Uptake (GlpU) Family


TC#NameOrganismal TypeExample
2.A.1.52.1The putative permease, YihN (most like NarK and UhpC, 21% identity)BacteriaYihN of E. coli (P32135)

YqcE putative transporter


YqcE pf E. coli (F4TJX1)


MFS permease


MFS permease of Propionibacterium acnes


The glycerophosphodiester, glycerophosphocholine uptake porter, GlpU.  The cytoplasmic compound is hydrolyzed to α-glycerolphosphate and choline (Großhennig et al. 2013).


GlpU of Mycoplasma pneumoniae


2.A.1.53 The Proteobacterial Intraphagosomal Amino Acid Transporter (Pht) Family


TC#NameOrganismal TypeExample
2.A.1.53.1The threonine uptake permease, PhtA (Sauer et al., 2005) (required for maximal growth in macrophages and Acanthamoeba castellanii)Gamma proteobacteriaPhtA of Legionella pneumophila (YP_094583)

PhtF of 425 aas

PhtF of Legionella pneumophila


PhtG of 432 aas

PhtG of Legionella pneumophila


PhtH of 430 aas

PhtH of Legionella pneumophila


PhtI of 390 aas

PhtI of Legionella pneumophila


PhtK of 410 aas

PhtK of Legionella pneumophila


The valine uptake permease, PhtJ (required for maximal growth in macrophages and Acanthamoeba castellanii) (Chen et al., 2008)

Gamma proteobacteria

PhtJ of Legionella pneumophila (YP_095910)


The putative MFSD1 (SMAP4) transporter (463aas; 12 TMSs).  Expression is increased in mice by amino acid starvation and decreased by a high fat diet (Perland et al. 2016).


MFSDI of Homo sapiens (A6NID9)


Uncharacterized protein of 575 aas and 14 TMSs.


UP of Cyanidioschyzon merolae


Putative amino acid transporter of 478 aas and 12 TMSs, CG8602, isoform A.  May play a role in macrophage migration in the Drosophila embryo (Dr. Daria Siekhaus, personal communication).

SG8602A of Drosophila melanogaster (Fruit fly)


MFS uptake permease specific for pyrimidines, PhtC of 422 aas and 12 TMSs.  Together with PhtD (TC# 2.A.1.53.6), it contributes to protection of L. pneumophila from dTMP starvation, protects the cell from 5-fluorodeoxyuridine (FUdR) toxicity and is required for growth of L. pneumophila in macrophage (Fonseca et al. 2014).

PhtC of Legionella pneumophila


MFS uptake permease, probably specific for pyrimidines, PhtD of 427 aas and 12 TMSs.  Together with PhtC (TC# 2.A.1.53.6), it contributes to protection of L. pneumophila from dTMP starvatioin, protects the cell from 5-fluorodeoxyuridine (FUdR) toxicity and is required for growth of L. pneumophila in macrophage (Fonseca et al. 2014).

PhtD of Legionella pneumophila


PhtB of 431 aas

PhtB of Legionella pneumophila


PhtE of 430 aas

PhtE of Legionella pneumophila


2.A.1.54 The Unknown (Archaeal/Bacterial) Major Facilitator-9 (UMF9) Family


TC#NameOrganismal TypeExample

The archaeal uptake permease, MMP0835 (function unknown) (31% I, 49% S with PhtA)


MMP0835 of Methanococcus maripaludis (CAF30391)


UMF-9 homologue of 414 aa


UMF9 homologue of Geobacter sulfurreducens (Q747F2)


Functionally uncharacterized MFS porter of 414 aas

UP of Syntrophothermus lipocalidus


TC#NameOrganismal TypeExample

Uncharacterized MFS porter of 397 aas and 12 TMSs

UP of Halorubrum distributum


Uncharacterized protein of 390 aas

UP of Natrinema versiforme


Uncharacterized protein of 406 aas

UP of Haloterrigena salina


Putative phthalate porter of 377 aas

UP of Haloferax gibbonsii


2.A.1.56 The 1,3-Dihydroxybenzene Transporter (DHB-T) Family


TC#NameOrganismal TypeExample
2.A.1.56.1The 1,3-dihydroxybenzene (resorcinol) uptake permease, MFS_1 (Darley et al., 2007)BacteriaMFS_1 of Azoarcus anaerobius (YP_285101)

Uncharacterized protein of 405 aas and 12 TMSs.


UP of Bradyrhizobium japonicum


2.A.1.57 The Ferripyochelin Transporter (FptX) Family


TC#NameOrganismal TypeExample

The Ferripyochelin uptake permease, FptX (Michel et al., 2007).  Also transports N-acetylglucosamine anhydrous N-acetylmuramyl peptides and is called AmpP or AmpGh1 (Kong et al. 2010).  However, it does not play a role in the induction of β-lactam resistance (Zhang et al. 2010).


FptX or AmpP of Pseudomonas aeruginosa (Q9HWG8)


The ferric rhizbactin 1021 uptake porter, RhtX (Cuív et al. 2004).


RhtX of Sinorhizobium meliloti


Putative iron chelate transporter of 467 aas


Uncharacterized protein of E. coli


Siderophore transporter, RhtX/FptX family


Siderophore transporter of Myxococcus xanthus


The iron (Fe3+)·pyridine-2,6-bis(thiocarboxylic acid (PDTC)) uptake transporter, PdtE. Functions with the OMR, PdtK, 1.B.14.8.2 (most similar to 2.A.1.57.4) (Leach and Lewis 2006).


PdtE of Pseudomonas putida (ABC8353)

2.A.1.57.6Major facilitator superfamily domain-containing protein 3AnimalsMfsd3 of Rattus norvegicus

2.A.1.58 The N-Acetylglucosamine Transporter (NAG-T) Family


TC#NameOrganismal TypeExample

The N-acetylglucosamine:H+ symporter, Ngt1 (Alvarez and Konopka, 2007)


Ngt1 of Candida albicans (Q5A7S4)


May contribute to coordination of muscle contraction as regulatory subunit of a nonessential potassium channel complex.  Subunit structure:  May form a complex with sup-9 and sup-10 where unc-93 and sup-10 act as regulatory subunits of the two pore potassium channel sup-9.



Unc-93 of Caenorhabditis elegans (Q93380)


UNC93-like protein MFSD11 (Major facilitator superfamily domain-containing protein 11) (Protein ET)


MFSD11 of Mus musculus


MFS permease of 467 aas


MFS permease of Oryza sativa


Duf895 protein of 450 aas


Duf895 protein of Verticillium albo-atrum


MFS permease of 425 aas

Slime molds

MFS permease of Dictyostellium discoideum


Unc-93b1 or Unc93b1 of 597 aas and 12 TMSs.  Plays a role in innate and adaptive immunity by regulating nucleotide-sensing Toll-like receptor (TLR) signaling. Required for the transport of a subset of TLRs (including TLR3, TLR7 and TLR9) from the endoplasmic reticulum to endolysosomes where they can engage pathogen nucleotides and activate signaling cascades. May play a role in autoreactive B-cells removal (Isnardi et al. 2008).  Induces apoptotic cell death and is cleaved by host and viral proteases (Harris and Coyne 2015).

Unc93b1 of Homo sapiens


2.A.1.59 Unidentified Major Facilitator-10 (UMF10) Family (mostly from Archaea but some from bacteria)


TC#NameOrganismal TypeExample

UMF10a of unknown function, (COG2270).


UMF10a of Methanococcus aeolicus (A6UVW2)


UMF10b (in an operon with a sensor kinase/response regulator pair and an 8 TMS rhomboid protease)



UMF10b of Nostoc punctiforme (B2JBG5)


MFS permease, AF1541


AF1541 of Archaeoglobus fulgidus (O28731)


MFS permease, LepA


LepA of Hydrogenivirga sp.128-5-R1-1 (A8UT57)


2.A.1.6 The Metabolite:H+ Symporter (MHS) Family


TC#NameOrganismal TypeExample
2.A.1.6.1Citrate:H+ symporterBacteriaCitA of Klebsiella pneumoniae

Inner membrane metabolite transport protein YhjE


YhjE of Escherichia coli


Acetate/haloacid transporter, Dehp2, with a possible atypical topology (Tse et al. 2009).  Transports acetate, chloroacetate, bromoacetate, 2-chloropropionate, and possibly, with low affinity, glycolate, lactate and pyruvate (based on weak inhibition results).  Inducible by chloroacetate (Su and Tsang 2012).  This protein is 79% identical to its paralogue, Deh4p (TC# 2.A.1.6.8) which differs in that it shows lower apparent affinity for 2-chloropropionate.


Dehp2 of Burkholderia caribensis (formerly sp. MBA4)


The putative thiazole transporter, ThiU. Regulatyed by TPP riboswitch (Rodionov et al. 2002)


ThiU of Haemophilus influenzae (P44699)


Acetate/monochloroacetate permease, Deh4p, of 468 aas and 12 TMSs.  Transports various carboxylates.  Dehalococcoides mccartyi degrades haloacids (Su et al. 2016).

Deh4p of Dehalococcoides mccartyi


α-Ketoglutarate (oxoglutarate):H+ symporter (Seol and Shatkin 1992; Seol and Shatkin 1992).  May also export arabinose but not xylose (Koita and Rao 2012).


KgtP of E. coli (P0AEX3)


Dicarboxylate:H+ symporter.  Transports and serves as a chemoreceptor for β-ketoadipate (Karimian and Ornston 1981).


PcaT of Pseudomonas putida


(Proline/glycine-betaine):(H+/Na+) symporter, ProP (also transports taurine, ectoine, pipecolate, proline-betaine, N,N-dimethylglycine, carnitine, and 1-carboxymethyl-pyridinium) (subject to osmotic activation). Transmembrane helix I and periplasmic loop 1 are involved in osmosensing and osmoprotectant transport (Keates et al., 2010).


ProP of E. coli (P0C0L7)

2.A.1.6.54-Methyl-o-phthalate:H+ symporterBacteriaMopB of Burkholderia cepacia
2.A.1.6.6Shikimate:H+ symporterBacteriaShiA of E. coli
2.A.1.6.7The citrate/tricarballylate:H+ symporter (CitA or TcuC); probably orthologous to 2.A.1.6.1 (Lewis et al., 2004)BacteriaTcuC of Salmonella enterica serovar Typhimurium LT2 (P0A2G3)

The acetate/monochloroacetate (haloacid) permease, Deh4p (Km = 5.5 mμM for acetate; 9 mμM for monochloroacetate) (Yu et al., 2007; Su and Tsang 2012).


Deh4 of Burkholderia cepacia or sp. MBA4 (Q7X4L6)


YdfJ. Can function as an inward rectifying K+ channel when expressed in animal cells as measured by whole cell patch clamping. Blocked by barium and protopine (Tang et al., 2011).


YdfJ of E. coli (P77228)


2.A.1.60 The Rhizopine-related MocC (MocC) Family


TC#NameOrganismal TypeExample
2.A.1.60.1The rhizopine related transporter, MocC (could either transport a precursor for rhizopine biosynthesis into bacteroids or the finished product from the bacteroids) (Murphy et al., 1993)BacteriaMocC of Sinorhizobium meliloti (Q07609)

Inner membrane protein YbjJ


YbjJ of Escherichia coli


The multidrug (quinolone; tetarcycline) resistance pump, TcrA (Chang et al. 2011).


TcrA of Stenotrophomonas maltophilia (F2WVP9)


2.A.1.61 The Microcin C51 Immunity Protein (MccC) Family


TC#NameOrganismal TypeExample
2.A.1.61.1The MccC microcin C51 immunity protein (exports the peptide-nucleotide 'Trojan horse' antibiotic) (Fomenko et al., 2003; Kazakov et al., 2007)BacteriaMccC of E. coli (Q83Y57)

2.A.1.62 The Unidentified Major Facilitator-11 (UMF11) Family

Possibly involved in transport of amino acids and their derivatives.


TC#NameOrganismal TypeExample

The UMF11 homologue


UMF11 of Staphylococcus aureus (A8YZ14)


Putative Macrolide efflux pump (P-MEP), possibly involved in transport of amino acids and their derivatives.



P-MEP of Fusobacterium sp. 7_1 (C3WVU9)


UMF11 (links UMF11 with UMF13)


UMF11 of Bacillus clausii (Q5WGH2)


2.A.1.63 The Unidentified Major Facilitator-12 (UMF12) Family


TC#NameOrganismal TypeExample

The UMF12 protein 


UMF12 of Methanosarcina barkeri (Q467Y6)


UMF12 Possible amino acid exporter


UMF12 of Methanosarcina mazei (Q8PRW9)


Possible nucleotide or oligonucleotide uptake porter, UMF12


UMF12 of Deinococcus radiodurans (Q9RXM0)




MFS carrier


MFS carrier of Saccharomyces cerevisiae K7 (P47159)


2.A.1.64 The Unidentified Major Facilitator-13 (UMF13) Family


TC#NameOrganismal TypeExample

The UMF13 protein


UMF13 of Streptococcus thermophilus (Q5M4L1)

2.A.1.64.2Uncharacterized protein RP255BacteriaRP255 of Rickettsia prowazekii

Uncharacterized protein of 611 aas

UP of Spiroplasma diminutum


2.A.1.65 The Unidentified Major Facilitator-14 (UMF14) Family


TC#NameOrganismal TypeExample
2.A.1.65.1The putative MFS carrier, Sugar Baby (Sug, isoform D); has a hydrophilic domain between TMSs 3 and 4. Overexpression causes an increased lifespan by 17%.


Sugar Baby of Drosophila melanogaster (Q7KUF9)

2.A.1.65.10Major facilitator superfamily domain-containing protein 6-likeAnimalsMFSD6L of Homo sapiens

Duplicated MFS permease (901 amino acyl residues; ~24 TMSs)


Duplicated MFS permease of Chlamydomonas reinhardtii

2.A.1.65.2Unknown MFS homologue; e-6 with 2.A.1.5 family members; has a hydrophilic domain between TMSs 3 and 4.


UMF14 of Culex quinquefasciatus (B0W435)


Unknown MFS homologue UMF14 ( 833 aas, 12 TMSs in a 3+9 arrangement )


UMF14 of Anopheles gambiae (Q7Q0Z9)


Uncharacterized protein of 474 aas


UP of Nematostella vectensis (Starlet sea anemone)


MFS porter


MFS porter of Daphnia pulex (E9I268)


Macrophage MHC Class I receptor 2, Mmr2 or MFSD6


Mmr2 of Mus musculus (Q8CBH5)


MFS porter


MFS porter of Chlorella variablis (E1ZG13)


MFS permease


MFS permease of Thermoanaerobacter tengcongensis (Q8R7B7)

2.A.1.65.9Maltose permease


MalA of Geobacillus stearothermophilus


2.A.1.66 The Unidentified Major Facilitator-15 (UMF15) Family


TC#NameOrganismal TypeExample

MFS permease of unknown function (First half resembles 2.A.1.3.7 (e-11) and 2.A.1.15.3 (e-8)). Very likely to be a galactoside/galactose transporter; encoded within a gene cluster with β-galactosidase and galactose metabolic genes.


MFS permease of Thermofilum pendens (A1RW34)


Putative 4-hydroxybenzoate uptake transporter, MFS_1 (in an operon with 2,3-diketo-5-methylthiopentyl-1-phosphate enolase-phosphatase of the methionine salvage pathway), using S-adenyl methionine (SAM) as substrate. May transport SAM.


MFS1 of Leptospira interrogans (Q8F7L4)


UMF15 Homologue

Eukaryotes (Stramenophiles)

UMF15 homologue of Thalassiosira pseudonana (B8BU21)



MFS transporter of 531 aas.  Present in the membrane of the organelle called the rhoptries which is involved in host invasion and hijacking host cell functions (Peter Bradley, personal communication).


MFS porter of Toxoplasma gondii


MFS transporter of 428 aas.  Present in the membrane of the organelle called the rhoptries which is involved in host invasion and hijacking host cell functions (Peter Bradley, personal communication).


Porter of Toxoplasma gondii


Uncharacterized protein of 646 aas and 12 TMSs

UP of Chlorella variabilis (Green alga)


2.A.1.67 The Unidentified Major Facilitator-16 (UMF16) Family


TC#NameOrganismal TypeExample

MFS permease of unknown function (second half distantly resembles the first half of 2.A.1.41.3/e value of 0.001)


UMF16 of Kribbella flavida (D2PP09)


MFS porter


MFS porter of Arthrobacter aurescens (A1R564)


MFS porter


MFS porter of Erwinia pyrifoliae (D0FNI7)


MFS porter of 402 aas and 12 TMSs.


MFS porter of Propionibacterium acnes (D1YEI1)


2.A.1.68 The Glucose Transporter (GT) Family


TC#NameOrganismal TypeExample

The glucose transporter, OEOE_1574 does not transport fructose (Kim et al., 2011).


OEOE_1574 of Oenococcus onei (Q04DP6)


2.A.1.69 Unidentified Major Facilitator-17 (UMF17) Family


TC#NameOrganismal TypeExample

The UMF17A porter


UMF17A porter of Streptomyces coelicolor (Q9KZY0)


2.A.1.7 The Fucose: H+ Symporter (FHS) Family


TC#NameOrganismal TypeExample

L-Fucose:H+ symporter. The x-ray structure (3.1Å resolution) with an outward open, amphipathic cavity has been solved. Asp46 and Glu135 can undergo cycles of protonation (Dang et al., 2010). 


FucP of E. coli


The putative glucose porter, GlcP (Rodionov et al., 2010).


GlcP of Shewanella amazonensis (A1S5F4)


The putative mannose porter, ManPl (Rodionov et al., 2010).


ManPl of Shewanella amazonensis (A1S297)


The putative trehalose porter, TreT (Rodionov et al., 2010)


TreT of Shewanella frigidimarina (Q07XD1)

2.A.1.7.13Bypass of stop codon protein 6FungiBSC6 of Saccharomyces cerevisiae S288c

Protein TsgA


TgsA of E. coli

2.A.1.7.15Major facilitator superfamily domain-containing protein 4-AAnimals

Mfsd4a of Danio rerio


The putative mannose porter, ManP (Rodionov D.A., personal communication).
Regulated by mannose regulon ManR.


ManP (Q8A5Y0) of Bacteroides thetaiotaomicron


The putative fructose porter, FruP (Rodionov D.A., personal communication).
Regulated by fructose oligosaccharide utilization regulon.


FruP (Q8A6W8) of Bacteroides thetaiotaomicron


The putative N-acetylglucosamine porter, NagP (Rodionov D.A., personal communication).
Regulated by heparin utilization regulon.


NagP (Q89YS8) of Bacteroides thetaiotaomicron


Probable glucose transporter encoded by a gene sandwiched in between two genes encoding a glucose 1-dehydrogenase and a gluconolactonase.


Glucose permease of Parachlamydia acanthamoebae

2.A.1.7.2Glucose/galactose porterBacteriaGgp of Brucella abortus (P0C105)

Uncharacterized MFS protein of 392 aas and 12 TMSs.

UMFS of Bdellovibrio exovorus


Uncharacterized protein of the MFS of 505 aas and 12 TMSs

UP of Chlamydomonas reinhardtii (Chlamydomonas smithii)


Uncharacterized protein of 494 aas and 12 TMSs.

UP of Chlamydomonas reinhardtii (Chlamydomonas smithii)


Na+-dependent glucose transporter 1, Mfsd4b, of 491 aas and 12  TMSs.  May also serve as a channels for urea in the inner medulla of the kidney.

Mfsd4b of Xenopus laevis (African clawed frog)


Glucose/Mannose/Xylose: H+ symporter (Paulsen et al., 1998; G.Gosset, personal communication).


GlcP of Bacillus subtilis

2.A.1.7.4Rat kidney Na+-dependent glucose (methyl α-glucoside) transporter, NaGLT1 (glucose:Na+:Na+=1:1) (Horiba et al., 2003)AnimalsNaGLT1 of Rattus norvegicus (BAC57446)

2-Deoxy-D-ribose porter, DeoP (Christensen et al., 2003).  Plays a role in colonization of the mouse intestine (Martinez-Jéhanne et al. 2009).


DeoP of Salmonella typhimurium LT-2 (gi 16767076)


Sucrose permease, ScrT (Rodionov et al., 2010)


ScrT of Shewanella frigidimarina (ABI73814)

2.A.1.7.7The Na+-dependent sugar transporter, HP1174 (transports glucose, galactose, mannose and 2-deoxyglucose (Psakis et al. 2009)). (most similar to 2.A.1.7.2; 49% identity)


HP1174 of Helicobacter pylori (O25788)


N-acetylglucosamine porter, NagP (Rodionov et al. 2010).


NagP of Shewanella oneidensis (Q8EBL0)


The putative N-acetylgalactosamine porter, AgaP (Leyn et al. 2012).


AgaP of Shewanella amazonensis (A1S4V0)


2.A.1.70 Unidentified Major Facilitaor-18 (UMF18) Family


TC#NameOrganismal TypeExample



UMF18A of Streptomyces coelicolor (Q9L223)




UMF18B of Saccharomonospora azurea (G4JJZ0)




UMF18C of Salinispora tropica (A4X2L1)


2.A.1.71 The Valanimycin-resistance (Val-R) Family


TC#NameOrganismal TypeExample

The Valanimycin-resistance determinant, VlmF (probably a valanimycin:H  antiporter (Ma et al., 2000))


VlmF of Streptomyces viridifaciens (Q9LA76)


The UMF19a porter


UMF19a porter of Streptomyces coelicolor (Q93J85)


Uncharacterized protein of 375 aas and 11 TMSs

UP of Patulibacter americanus


2.A.1.72 The Unidentified Major Facilitator-20 (UMF20) Family


TC#NameOrganismal TypeExample

The UMF20A porter


UMF20A of Streptomyces coelicolor (Q9RL01)


2.A.1.73 The Unidentified Major Facilitator-21 (UMF21) Family


TC#NameOrganismal TypeExample

The UMF21A porter


UMF21A porter of Streptomyces coelicolor (Q9L102)


2.A.1.74 The Unidentified Major Facilitator-22 (UMF22) Family


TC#NameOrganismal TypeExample

UMF22a porter 


UMF22 porter of Streptomyces coelicolor (Q9S243)


2.A.1.75 The Unidentified Major Faciilitator-23 (UMF23) Family


TC#NameOrganismal TypeExample
2.A.1.75.1Probable transporter MCH1 (Monocarboxylate transporter homolog 1)FungiMCH1 of Saccharomyces cerevisiae


Mct of Coccidioides posadasii (E9CYW5)


Uncharacterized major facilitator, UMF23C


UMF23C of Candida albicans


Uncharacterized major facilitator UMF23D


UMF23D of Naegleria gruberi


UMF23 permease of 572 aa


UMF23 of Arabidopsis thaliana


Uncharacterized protein of 591 aas and 12 TMSs

UP of Chlamydomonas reinhardtii (Chlamydomonas smithii)


2.A.1.76 The Uncharacterized Major Facilitator 24 Family


TC#NameOrganismal TypeExample

Uncharacterized protein Mhp246


Mhp246 of Mycoplasma hyopneumoniae


Uncharacterized Mycoplama MFS carrier, UMF24B


UMF24B of Mycoplasma capricolum


Uncharacterized MFS carrier, UMF24C


UMF24C of Lactobacillus salivarius


MFS carrier of 525 aas and 12 TMSs.

MFS porter of Mycoplasma galisepticum


2.A.1.77 Uncharacterized Major Facilitator-25 (UMF25) Family


TC#NameOrganismal TypeExample

Unknown Major Facilitator UMF25a


UMF25a of Rhodopirellula baltica


Unknown Major Facilitator, UMF25b


UMF25b of Planctomyces limnophilus


2.A.1.78 The Uncharacterized Major Facilitator-26 (UMF26) Family


TC#NameOrganismal TypeExample

UMF26a of 416 aas and 12 TMSs.  Encoded by a gene that is adjacent to two ATP hydrolyzing subunits homologous to ABC proteins of the peptide transporters of TC family 3.A.1.5.


UMF26a of Parachlamydia acanthaemoebae (F8KXQ8)


UMF26b of 419 aas and 12 TMSs


UMF26b of Simkania negevensis (F8L9E4)


UMF26c of 457 aas and 12 TMSs


UMF26c of Phycisphaera mikurensis (I0II84)


UMF26d of 413 aas and 12 TMSs


UMF26d of Verrucomicrobiae bacterium (B5JEI3)


2.A.1.79 The Uncharacterized Major Facilitator-27 (UMF27) Family


TC#NameOrganismal TypeExample

MFS permease of 485 aas


MFS permease of Cyanidioschyzon merolae


Uncharacterized MFS proter of 724 aas and 12 TMSs with a C-terminal hydrophilic extension.

UP of Chondrus crispus (Carrageen Irish moss) (Polymorpha crispa)


2.A.1.8 The Nitrate/Nitrite Porter (NNP) family


TC#NameOrganismal TypeExample

Nitrate/H+ symporter (K1);Nitrate/nitrite antiporter (K2).  The 3-d structure is available revealing a positively charged pathway for nitrate/nitrite lined with arginine residues with no apparent proton pathway suggesting exchange transport is the primary or sole mechanism.  The pathway is between the two halves of the protein and a rocker switch mechanism was proposed (Zheng et al. 2013).  In an in vitro reconstituted system, NarK appeared to be a nitrate/nitrite antiporter.  High-resolution crystal structures in the nitrate-bound occluded, nitrate-bound inward-open and apo inward-open states have been solved (Fukuda et al. 2015).


NarK (NarK1-K2) of E. coli


NO3-/NO2- transporter (NO3- uptake permease; NO2- exporter) (probable NO3-/NO2- antiporter) (stress-induced; Clegg et al., 2006; Jia et al. 2009)


NarU of E. coli

2.A.1.8.11The 24 TMS, 2 domain, NarK1-NarK2 porter (NarK1 = a NO3-/H+ symporter; NarK2 = a NO3-/NO2- antiporter).  NarK1 is a nitrate/proton symporter with high affinity for nitrate while NarK2 is a nitrate/nitrite antiporter with lower affinity for nitrate (Goddard et al., 2008).  Each transporter requires two conserved arginine residues for activity.  A transporter consisting of inactivated NarK1 fused to active NarK2 has a dramatically increased affinity for nitrate compared with NarK2 alone, implying a functional interaction between the two domains (Goddard et al., 2008).


NarK1/NarK2 of Roseobacter denitrificans (Q166T6)


The root cortical and epidermal cell, high affinity, plasma membrane, NO3- uptake transporter, NRT2.1 (Wirth et al., 2007). Also functions in nitrate sensing and signaling (Miller et al., 2007; Girin et al., 2010). Activity only occurs when NRT2.1 is complexed with NAR2.1 (WR3; 8.A.20.1.1) in a 2:2 tetrameric complex (Yong et al., 2010). NAR2.1 has an N-terminal and a C-terminal TMS and has been annotated as a calcineurin-like phosphoesterase family member (Yong et al., 2010).  Ntr transporters may also play a role in gaseous NO2 uptake by leaves (Hu et al. 2014).  The Medicago truncatula ortholog has been characterized (Pellizzaro et al. 2014).


NRT2.1 of Arabidopsis thaliana (O82811)


High affinity nitrate/nitrite antiporter and uptake porter, NrtB (Unkles et al., 1991; 2011; Wang et al. 2008).


NrtB of Emericella (Aspergillus) nidulans (Q8X193)


Nitrate/nitrite uptake porter, NapA (Wang et al., 2000)


NapA of Trichodesmium sp. WH 9601 (Q9RA38)


Probable nitrate transporter NarT


NarT of Staphylococcus carnosus


MFS porter of 430 aas


MFS porter of Rhizobium loti

2.A.1.8.2Nitrate uptake porterBacteriaNasA of Bacillus subtilis
2.A.1.8.3Nitrate/nitrite uptake porterBacteriaNrtP of Synechococcus PCC7002
2.A.1.8.4Nitrate transporterDiatomsNitrate porter of Cylindrotheca fusiformis

Nitrate/nitrite transporter/antiporter, CrnA/NrtA (Unkles et al., 1991; Beckham et al. 2010). The nitrate signature sequences (NS1 and NS2) in TMSs 5 and 11 and arg residues in TMSs 2 and 8 may influence substrate binding (Unkles et al., 2012).


CrnA of Emericella nidulans

2.A.1.8.6Nitrate transporterAlgaeNitrate porter of Chlamydomonas reinhardtii

High affinity Nitrate/nitrite uptake transporter, Nar4.


Nar4 of Chlamydomonas reinhardtii (A8J4P3) 

2.A.1.8.8NO2- extrusion, NO3-/NO2- exchange permease, NarK1BacteriaNarK1 of Thermus thermophilus HB8
2.A.1.8.9NO2- extrusion, NO3-/NO2- exchange permease, NarK2BacteriaNarK2 of Thermus thermophilus HB8

2.A.1.80 The Uncharacterized Major Facilitator-28 (UMF28) Family


TC#NameOrganismal TypeExample

Uncharacterized MFS permease of 515 aas


Putative peremease of Galdieria sulphuraria


2.A.1.81 The Copper Uptake Porter (Cu-UP)


TC#NameOrganismal TypeExample

The copper (Cu2+) uptake porter, CcoA of 405 aas and 12 TMSs. CcoA-mediated Cu2+ import relies on conserved Met and His residues that could act as metal ligands at the membrane-embedded Cu2+-binding domain (Khalfaoui-Hassani et al. 2016).


CcoA of Rhodobacter capsulatus


Putative copper uptake porter, MFS_1 of 420 aas


MFS_1 of Chloroflexus aggregans


MFS permease of 403 aas.


MFSA permease of Corynebacterium glutamicum


MFS porter of 350 aas

Thaumarchaeota (Archaea)

MFS porter of Candidatus Caldiarchaeum subterraneum


Riboflavin uptake transporter of 398 aas and 12 TMSs, RfnT (Gutiérrez-Preciado et al. 2015).

RfnT of Ochrobactrum anthropi


2.A.1.82 The Plant Copper Uptake Porter (Pl-Cu-UP)


TC#NameOrganismal TypeExample

The barley copper uptake porter, CT-1 of 749 aas; nearly identical to the wheat orthologue (Li et al. 2013).


CT-1 of Hordeum vulgare (F2CRE4)


The putative copper uptake porter, CT1, of 825 aas. The C-terminal domain of 300 aas is a DUF572 (COG5134) domain.


CT1 of Ostreococcus tauri (Q010B9)


Synaptic vesicle 2-related protein (SV2-related protein), SVOP.  This protein localizes to neurotransmitter-containing vesicles and has a nucleotide binding site (Yao and Bajjalieh 2009). ATP, GTP and NAD show binding affinities with the highest affinity for NAD, in contrast to SV2 (TC# 2.A.1.22.1), which binds both NAD and ATP with equal affinity.


Sv2p of Mus musculus


Niacin uptake porter NiaP (Jeanguenin et al. 2012)


YceI of Bacillus subtilis (O34691)


Uncharacterized MFS protein of 460 aas


UP of Volvox carteri (Green alga)


TC#NameOrganismal TypeExample

MFS porter; possibly a 1-arseno-3-phosphoglycerate exporter.  Present in an operon concerned with arsenic resistance, possibly encoding the enzymes and transporters of a new pathway of arsenic biotransformation.  The adjacent gene encodes a 3-phosphoglycerate dehydrogenase homologue that could form the presumed substrate of the MFS porter which could be expelled from the cell (Barry Rosen personal communication.


MFS porter of Aliivibrio (Vibrio) salmonicida


Putative 1-arseno-3-phosphoglycerate exporter, MFS-83.


MFS-83 of Ferrimonas balearica


Putative 1-arseno-3-phosphoglycerate exporter of 460 aas (see 2.A.1.83.1).


MFS-83 of Ectocarpus siliculosus (Brown alga


TC#NameOrganismal TypeExample

Putative MFS permease of 467 aas and 12 TMSs


MFS permease of Treponema denticola


Uncharacterized protein of 435 aas and 12 TMSs.


UP of Slackia heliotrinireducens (Peptococcus heliotrinreducens)


Uncharacterized protein


UP of Streptosporangium roseum


TC#NameOrganismal TypeExample

Uncharacterized protein of 541 aas and 12 TMSs

UP of Isoptericola variabilis


Putative 12 TMS permease of 534 aas, HalU (Besse et al. 2015).

HalU of Halalkalicoccus jeotgali


Putative MFS permease

MFS permease of Actinoplanes friuliensis


Putative permease of 510 aas

PP of Halobacterium salinarum (Halobacterium halobium)


TC#NameOrganismal TypeExample

2.A.1.9 The Phosphate: H+ Symporter (PHS) Family


TC#NameOrganismal TypeExample

High affinity Pi uptake porter (also functions in Mn2+ homeostasis); may transport a phosphate · Mn2+ complex (Jensen et al., 2003). Also takes up selenite (Lazard et al., 2010).



Pho84 of Saccharomyces cerevisiae (P25297)


High affinity (25 mμM) phosphate uptake porter, PiPT (Yadav et al. 2010).  The high resolution structure has been determined by x-ray crystallography (Pedersen et al. 2013).


PiPT of Piriformospora indica


Phosphate transporter, PT, of 543 aas and 12 TMSs. It has a micormolar Km for phosphate uptake, is found in the plasma membrane and is induced by low medium phosphate concentrations (Wang et al. 2014).


PT in the ectomycorrhizal fungus, Boletus edulis


Phosphate transporter and receptor (transceptor) of 543 aas and 12 TMSs.  Important for signalling and uptake of phosphate.  The majority of terrestrial vascular plants can form mutualistic associations with obligate biotrophic arbuscular mycorrhizal (AM) fungi from the phylum Glomeromycota. This mutualistic symbiosis provides carbohydrates to the fungus, and reciprocally improves plant phosphate uptake. AM fungal transporters can acquire phosphate from the soil through the hyphal networks. Xie et al. 2016 reported a high-affinity phosphate transporter GigmPT that is required for AM symbiosis. GigmPT functions as a phosphate transceptor for the activation of the phosphate signaling pathway as well as the protein kinase A signaling cascade.

PT of Gigaspora margarita


Pi uptake porter, Pho84


Pho-84 of Neurospora crassa (Q7RVX9)


Pi uptake porter. Four close paralogues in Medicago truncatula (PT1-4), all localized to roots, show differing affinities for phosphate (Liu et al. 2008).


PT1 of Solanum tuberosum


Pht1;2(1;4) (PT2), a low affinity Pi uptake transporter, functioning throughout the plant (Ai et al., 2009) (76% identical to 2.A.1.9.3).


Pht1;2(1;4) of Oryza sativa (Q01MW8)


Pht1;6 (PT6), a high affinity Pi uptake transporter, functioning thoughout the plant (Ai et al., 2009) (75% identical to 2.A.1.9.3)


Pht1;6 (PT6) of Oryza sativa (Q8H6H0)


Phosphate transporter-5, PT5. Catalyzes phosphate:H+ symport (Liu et al., 2008).


PT5 of Medicago truncatula (A5H2U6)


Organic phosphate (glycerophosphoinositol and glycerophosphocholine, the products of phospholipase-B mediated deacylation of phosphatidylinositol and phosphatidylcholine, respectively) transport protein GIT1 (Almaguer et al. 2006).


GIT1 of Saccharomyces cerevisiae

2.A.1.9.8Putative inorganic phosphate transporter C23D3.12YeastSPAC23D3.12 of Schizosaccharomyces pombe

Inorganic phosphate transporter 1-1 (AtPht1;1) (H(+)/Pi cotransporter).  A Brassica napus homologue, Pht1;4, catalyzes phosphate uptake and affects root architecture (Ren et al. 2014).


PHT1-1 of Arabidopsis thaliana