4.A.1 The PTS Glucose-Glucoside (Glc) Family

The Glc family includes porters specific for glucose, glucosamine, N-acetylglucosamine and a large variety of α- and β-glucosides. However, not all β-glucoside PTS porters are in this class, as the PTS porter first described as the cellobiose (Cel) β-glucoside porter is the diacetylchitobiose porter in the Lac family (TC #4.A.3). The IIA, IIB and IIC domains of all of the group translocators listed below are demonstrably homologous. These porters (the IIC domains) show limited sequence similarity with and are homologous to members of the Fru family (TC #4.A.2) and with (but less so) with members of the Lac family (TC #4.A.3). The IIC domains of the glucose (4.A.1.1) and glucoside (4.A.1.2) subfamilies are nearly as distant from each other as they are from the Fru, Mtl and Lac families. As is true of other members of the PTS-GFL superfamily, the IIC domains of these permeases probably have a uniform 10 TMS topology (McCoy et al. 2016; Vastermark and Saier 2016).  Butanol toxicity in Clostridium acetobutylicum results in destruction of the PTS, thereby preventing glucose transport and phosphorylation (Gao et al. 2021).

Several of the PTS porters in the Glc family lack their own IIA domains and instead use the glucose IIA protein (IIAglc or Crr). Most of these porters have the B and C domains linked together in a single polypeptide chain. A cysteyl residue in the IIB domain is phosphorylated by direct phosphoryl transfer from IIAglc(his~P) or one of its homologues. Those porters which lack a IIA domain include the maltose (Mal), arbutin-salicin-cellobiose (ASC), trehalose (Tre), putative glucoside (Glv) and sucrose (Scr) porters of E. coli. Most, but not all Scr porters of other bacteria also lack a IIA domain.

BglF consists of a transmembrane domain, which in addition to TMSs, contains a large cytoplasmic loop. According to Yagur-Kroll et al., 2009, this loop, connecting TMSI to TMSII, contains regions that alternate between facing-in and facing-out states and creates the sugar translocation channel. Yagur-Kroll et al., 2009 demonstrated spatial proximity between positions at the center of the big loop and the phosphorylation site, suggesting that the two regions come together to execute sugar phosphotransfer.

The three-dimensional structures of the IIA and IIB domains of the E. coli glucose porter have been elucidated. IIAglc has a complex β-sandwich structure while IIBglc is a split αβ-sandwich with a topology unrelated to the split αβ-sandwich structure of HPr.  Some bacteria have many PTS transport systems belonging to different families.  For example, the solventogenic Clostridium acetobutylicum ATCC 824 has 13 altogether with 6 in the Glc family, 2 in the Fru family, 2 in the Lac family, 1 in the Gat family and 2 in the Man family.  However, Clostridium beijerinckii has 43 phosphotransferases (Mitchell 2015).

This family belongs to the PTS-GFL Superfamily.



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Pickering, B.S., J.E. Lopilato, D.R. Smith, and P.I. Watnick. (2014). The transcription factor Mlc promotes Vibrio cholerae biofilm formation through repression of phosphotransferase system components. J. Bacteriol. 196: 2423-2430.

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TC#NameOrganismal TypeExample

Glucose porter (PtsG; GlcA; Umg) (transports D-glucose and α-methyl-D-glucopyranoside).  The IIC domain has been crystallized, and x-ray data to 4.5 Å resolution have been described (Zurbriggen et al. 2010).  The system has been manipulated to engineer increased production of aromatic metabolites (Carmona et al. 2015, Vargas-Tah et al. 2015). The presence or absence of D-glucose reflects the transporter before and after release of the transported glucose into the cytoplasm. The transition associated with substrate release appears to require a subtle structural rearrangement in the region that includes hairpin 1 (Kalbermatter et al. 2017).  Mlc (for makes large colonies) represses transcription of the genes encoding enzyme I, HPr, EIIBCGlc and EIIABCDMan in defined media that lack PTS substrates. When glucose is present, the unphosphorylated form of EIIBCGlc sequesters Mlc to the cell membrane, preventing its interaction with DNA (Plumbridge 2002, Joyet et al. 2013). The Vibrio Mlc functions similarly (Pickering et al. 2014). A small (43 aa) protein, SgrT, acts in tandem with a well-characterized small RNA during metabolic stress, due to the accumulation of cytoplasmic sugar-Ps to help bacterial cells maintain balanced metabolism and continue growing. SgrT acts on the glucose transport system, inhibiting its activity under stress conditions in order to allow cells to utilize alternative carbon sources (Lloyd et al. 2017). ptsG mRNA localization to the inner membrane, coupled with the membrane insertion of nascent peptide, mediates Hfq/SgrS-dependent ptsG mRNA destabilization, presumably by reducing second rounds of translation (Kawamoto et al. 2005). SgrT is a small protein of 43 aas that allosterically inhibits IICBGlc. while SgrS is a small RNA coompementary to ptsG mRNA that influences its expression.  The sgrST operon is regulated by SgrR, a glucose-6-P-dependent transcriptional activator (Jeckelmann and Erni 2020).


Bacteria, proteobacteria

PtsG/Crr; Glucose IICB/IIA complex of E. coli

4.A.1.1.10The α-glucoside-specific IICB, AglB (transports glucose, methyl-α-glucoside, maltitol, isomaltose, trehalulose α(1→1), turanose α(1→3), maltulose α(1→4), leucrose α(1→5), and palatinose α(1→6), but not sucrose (most resembles 4.A.1.1.4 and 4.A.1.1.8) (Pikis et al., 2006)BacteriaGlucose/α-glucoside IICB complex of Klebsiella pneumoniae (Q9AGA7)

The glucose/maltose/maltotriose porter, MalT or PtsG (31% identical to 4.A.1.1.9) (Webb et al., 2007).  Lactoperoxidase (LPO) shows promise in the prevention of dental caries. It has antimicrobial properties and is part of the non-specific antimicrobial immune system. A thiocyanate-iodide mixture strongly inhibited glucose and sucrose consumption as well as transmembrane PTS glucose transport. Thus, the LPO-iodide system had a strong inhibitory effect on biofilm growth and lactate synthesis (complete inhibition) (Magacz et al. 2023).


MalT/PtsG IICBA of Streptococcus mutans (Q8DS05)

4.A.1.1.12Maltose/Maltotriose PTS transporter, MalT (Shelburne et al., 2008) 631aas (68% identical to 4.A.1.1.11 from S. mutansBacteriaMalT IICBA of Streptococcus pyogenes (Q48WG5)

Glucose porter, GlcA (IICBA). Glucose uptake is inhibited by 2-deoxyglucose and methyl-β-D-glucoside (Christiansen and Hengstenberg, 1999).


GlcA of Staphylococcus carnosus (Q57071)


Glucose porter GlcB (IICBA). Glucose uptake is inhibited by methyl-α-D-glucoside, methyl-β-D-glucoside, p-nitrophenyl-α-D-glucoside, o-nitrophenyl-β-D-glucoside and salicin, but not by 2-deoxyglucose. Mannose and N-acetylglucosamine are not transported (Christiansen and Hengstenberg, 1999).


GlcB of Staphylococcus carnosus (Q53922)


N-acetyl glucosamine-specific PTS permease, GlcNAc IIBC/GlcNAc I-HPr-IIA (Johnson et al. 2008)


GlcNAc IIBC/GlcNAc I-HPr-IIA of Pseudomonas aeruginosa


PTS uptake porter for sucrose isomers, IICB (Thompson and Pikis 2012).


IICB for sucose isomers of Leptotrichia buccalis


The Maltose group translocator, MalT of 470 aas and 10 TMSs. Takes up extracellular maltose, releasing maltose-phosphate into the cytoplasm.  The 3-d structure at 2.55 Å resolution has been solved (McCoy et al. 2016; Vastermark and Saier 2016).

MalT of Bacillus cereus


Glucose-specific Enzyme IIBC of the PTS, PtsG.  Essential for infectivity and virulence in mice although no other PTS Enzyme II is required (Khajanchi et al. 2016).

IIBCGlc (PtsG) of Borrelia burgdorferi


PTS α-glucoside transporter, subunit IICB (Francl et al. 2010).

IICB of Lactobacillus gasseri


N-Acetyl glucosamine (NAG) porter (NagE) (Plumbridge 2015).


NagE, the IICBANag complex of E. coli


The N-acetylglucosamine PTS transporter/kinase, NagE2 (416 aas; IIC)/NagF (77 aas; IIB).  The IIA specific for glucose (Crr) is the IIA for this system, and activity depends on Enzyme I and HPr (Nothaft et al. 2010). The genes encoding these enzymes are regulated by two transcription factors, DasR and AtrA, and the system serves as a sensor as well as a transporter/kinase (Nothaft et al. 2010).

NagE2F of Streptomyces coelicolor


Enzyme IIA of 168 aas.  It is of the glucose type and can phosphorylate maltose via MalP (TC# 4.A..1.1.8), N-acetyl glucosamine via NagP (TC#4.A.1.1.7), sucrose via SacX (TC#4.A.1.2.10) and SacP (TC# 4.A.1.2.9), and trehalose via TreP (TC# 4.A.1.2.8), none of which have their own IIA protein (Morabbi Heravi and Altenbuchner 2018). Other Enzymes IIA could also phosphorlyate these sugars via their respective IIBC proteins.

PtsA (YpqE) IIA protein of Bacillus subtilis


Maltose/glucose porter (MalX) of 510 aas and 10 TMSs.  This system functions with the glucose IIA protein (Reidl and Boos 1991; Jeckelmann and Erni 2020).


Maltose IICB complex (MalX) of E. coli

4.A.1.1.4The α-glucoside-specific IICB (MalB) (substrates probably include glucosyl-α-fructose disaccharides: trehalurose (α-1,1), turanose (α-1,3), malturose (α-1,4), leucrose (α-1,5) and palatinose (α-1,6)).BacteriaThe α-glucoside IICB, MalB of Fusobacterium mortiferum

N-Acetylglucosamine (NAG) porter (PtsBC1C2)(also may facilitate xylose transport) (Saito and Schrempf 2004).


The NAG IICC'B complex of Streptomyces olivaceoviridis (IIA not identified)
IICNag (PtsC1)
IIC'Nag (PtsC2)
IIBNag (PtsB)


The glucosamine IICBA porter (GamP) (40% identical to 4.A.1.1.2) (Plumbridge 2015). The IIA domain in this protein can transfer the phosphoryl moiety to the maltose, N-acetylglucosamine, sucrose and trehalose PTS systems (MalP, NagP, SacP and TreP, respectively) (Morabbi Heravi and Altenbuchner 2018).

Bacteria; firmicute

GamP of Bacillus subtilis (gi2632521)


The N-acetylglucosamine IICB porter (NagP; YflF) (45% identical to 4.A.1.1.2) (Plumbridge 2015).

Bacteria; firmicute

NagP of Bacillus subtilis (gi2443228)


The maltose IICB porter (MalP; GlvC) (56% identical to 4.A.1.1.4) (Yamamoto et al., 2001).


MalP of Bacillus subtilis (IICBA) (P54715)

4.A.1.1.9The glucose IICBA porter (PtsG) 44% identical to 4.A.1.1.1)BacteriaPtsG of Bacillus subtilis (P20166)

TC#NameOrganismal TypeExample
4.A.1.2.1Sucrose porter (ScrA) BacteriaSucrose IIBC complex (ScrA) of plasmid pUR400 from Salmonella typhimurium

Sucrose porter and regulatory sensor, IIBC (SacX) (43% identical to 4.A.1.2.1) (Tortosa and Le Coq 1995). The IIA domains of PtsA, GamP, PtsG and GmuA can all phosphorylate the IIB domain in the SacX sensor (Morabbi Heravi and Altenbuchner 2018).


SacX of Bacillus subtilis (P15400)

4.A.1.2.11Aryl β-glucoside porter, IIBCA (BglP; SytA) (35% identical to 4.A.1.2.2)BacteriaBglP of Bacillus subtilis (P40739)
4.A.1.2.12The sucrose porter, PtsS (regulated by SugR which also regulates other enzymes II) (Engels and Wendisch, 2007)BacteriaPtsS (IIBCA) complex of Corynebacterium glutamicum (Q8NMD6)

Trehalose PTS permease IIBC of 494 aas (Ells and Truelstrup Hansen 2011).


Trehalose IIBC of Listeria monocytogenese


PTS beta-glucoside transporter, EIIBCA of 672 aas and 12 predicted TMSs (Francl et al. 2010).

EIIBCA of Lactobacillus gasseri


PTS beta-glucoside transporter, EIIBCA of 624 aas and 10 predicted TMSs (Francl et al. 2010).

EIIBCA of Lactobacillus gasseri


PTS beta-glucoside transporter, EIIBCA of 647 aas and 10 predicted TMSs (Francl et al. 2010).

EIIBCA of Lactobacillus gasseri


N-acetylmuramic acid (MurNAc)-selective PTS transport system, MurP, IIBC, of 455 aas and 10 - 12 TMSs.

MurP of Bacillus velezensis


Glucose/fructose/glucosamine/mannose PTS IIABC system, FruA.  FruA phosphorylates the sugar subrates on the 6-hydroxyl group (Mazé et al. 2007).

FruA of Bifidobacterium breve


Fructooligosaccharide uptake porter of 651 aas and 10 TMSs, Pts1BCA (Chen et al. 2015).

Pts1CA of Lactobacillus plantarum


β-Glucoside (salicin, arbutin, cellobiose, etc) group translocator, BglF.  The bgl operon, encoding BglF, is regulated by antitermination when the RNA antiterminator protein, BglG, binds to one of two RAT sites in the mRNA (Gordon et al. 2015).

Bacteria; proteobacteria

BglF (IIBCAbgl) complex of E. coli


β-Glucoside [arbutin-salicin-cellobiose] (ASC) group translocator, AscF (Desai et al. 2010).

Bacteria; proteobacteria

AscF (IICBAsc complex) of E. coli


Trehalose porter, TreB (IIBC) which can take up maltose by facilitated diffusion (Decker et al. 1999).  Can also transport sucrose at a low rate (Steen et al. 2014).


Trehalose IIBC complex of E. coli

4.A.1.2.5β-glucoside (methyl-β-glucoside, salicin, arbutin) porter, BglF [a V317A or V317M mutation allows it to transport cellobiose as well] (Kotrba et al., 2003)Bacteriaβ-glucoside IIBCA (BglF) of Corynebacterium glutamicum
4.A.1.2.6β-glucoside (Aesculin/arbutin) porter, BglP (Cote et al., 2000; Cote and Honeyman, 2003)Bacteriaβ-glucoside IIBCA (BglP) of Streptococcus mutans (AAF89975)
4.A.1.2.7N-Acetylmuramic acid porter, MurP (YfeV) (Dahl et al., 2004)BacteriaN-Acetylmuramate IIBC (MurP or YfeV) of E. coli (P77272)

Trehalose porter, IIBC (TreP) (38% identical to 4.A.1.2.4) (Schöck and Dahl 1996; Ujiie et al. 2009).


TreP of Bacillus subtilis (P39794)

4.A.1.2.9Sucrose porter, IIBC (SacP) (55% identical to 4.A.1.2.1)BacteriaSacP of Bacillus subtilis (P05306)