2.A.40 The Nucleobase:Cation Symporter-2 (NCS2) Family

The NCS2 family, also called the nucleobase/ascorbate transporter (NAT) family (Karatza et al., 2006), consists of over 100 currently sequenced proteins derived from Gram-negative and Gram-positive bacteria, archaea, fungi, plants and animals. Most functionally characterized members are specific for nucleobases including both purines and pyrimidines. However, two closely related rat members of the family, SVCT1 and SVCT2, localized to different tissues of the body, cotransport L-ascorbate and Na+ with a high degree of specificity and high affinity for the vitamin. Clustering of NCS2 family members on the phylogenetic tree is complex with bacterial proteins and eukaryotic proteins each falling into three distinct clusters. The plant and animal proteins cluster loosely together, but the fungal proteins branch from one of the three bacterial clusters. E. coli possesses four distantly related paralogous members of the NCS2 family. The NCS2 family appears to be distantly related to the NCS1 family (TC #2.A.39). An alternative designation for the NCS2 family is the Nucleobase-Ascorbate Transporter (NAT) family.

Proteins of the NCS2 family are 414-650 amino acyl residues in length and probably possess twelve transmembrane α-helical spanners (TMSs). The generalized transport reactions catalyzed by proteins of the NCS2 are:

Nucleobase (out) + H+(out) → Nucleobase (in) + H+(in).

Ascorbate (out) + Na+(out) → Ascorbate (in) + Na+(in).


 

References:

Loh, K.D., P. Gyaneshwar, E. Markenscoff Papadimitriou, R. Fong, K.S. Kim, R. Parales, Z. Zhou, W. Inwood, and S. Kustu. (2006). A previously undescribed pathway for pyrimidine catabolism. Proc. Natl. Acad. Sci. U.S.A. 103: 5114-5119.
Andersen, P.S., D. Frees, R. Fast and B. Mygind (1995). Uracil uptake in Escherichia coli K-12: Isolation of uraA mutants and cloning of the gene. J. Bacteriol. 177: 2008—2013.
Argyrou, E,. V. Sophianopoulou, N. Schultes, and G. Diallinas. (2001). Functional characterization of a maize purine transporter by expression in Aspergillus nidulans. Plant Cell. 13: 953-964.
Brynestad, S., L.A. Iwanejko, G.S. Stewart and P.E. Granum (1994). A complex array of Hpr consensus DNA recognition sequences proximal to the enterotoxin gene in Clostridium perfringens type A. Microbiol. 140: 97—104.
Daruwala, R., J. Song, W.S. Koh, S.C. Rumsey, M. Levine (1999). Cloning and functional characterization of the human sodium-dependent vitamin C transporters hSVCT1 and hSVCT2. FEBS Lett. 460: 480-484.
de Koning, H. and G. Diallinas (2000). Nucleobase transporters. Molec. Memb. Biol. 75:75-94.
Diallinas, G., J. Valdez, V. Sophianopoulou, A. Rosa and C. Scazzocchio (1998). Chimeric purine transporters of Aspergillus nidulans define a domain critical for function and specificity conserved in bacterial, plant and metazoan homologues. EMBO J. 17: 3827-3837.
Diallinas, G., L. Gorfinkiel, H.N. Arst, Jr., G. Cecchetto and C. Scazzocchio (1995). Genetic and molecular characterization of a gene encoding a wide specificity purine permease of Aspergillus nidulans reveals a novel family of transporters conserved in prokaryotes and eukaryotes. J. Biol. Chem. 270: 8610—8622.
Ghim, S.Y. and J. Neuhard (1994). The pyrimidine biosynthesis operon of the thermophile Bacillus caldolyticus includes genes for uracil phosphoribosyltransferase and uracil permease. J. Bacteriol. 176: 3698—3707.
Godoy, A., V. Ormazabal, G. Moraga-Cid, F.A. Zuniga, P. Sotomayor, V. Barra, O. Vasquez, V. Montecinos, L. Mardones, C. Guzman, M. Villagran, L.G. Aguayo, S.A. Onate, A.M. Reyes, J.G. Carcamo, C.I. Rivas, and J.C. Vera. (2007). Mechanistic insights and functional determinants of the transport cycle of the ascorbic acid transporter SVCT2. Activation by sodium and absolute dependence on bivalent cations. J. Biol. Chem. 282: 615-624.
Gorfinkiel, L., G. Diallinas and C. Scazzocchio (1993). Sequence and regulation of the uapA gene encoding a uric acid-xanthine permease in the fungus Aspergillus nidulans. J. Biol. Chem. 268: 23376—23381.
Karatza, P. and S. Frillingos. (2006). Cloning and functional characterization of two bacterial members of the NAT/NCS2 family in Escherichia coli. Mol. Membr. Biol. 22: 251-261.
Karatza, P., P. Panos, E. Georgopoulou, and S. Frillingos. (2006). Cysteine-scanning analysis of the nucleobase-ascorbate transporter signature motif in YgfO permease of Escherichia coli: Gln-324 and Asn-325 are essential, and Ile-329-Val-339 form an α-helix. J. Biol. Chem. 281: 39881-39890.
Mackenzie, B., A.C. Illing, and M.A. Hediger. (2008). Transport model of the human Na+-coupled L-ascorbic acid (vitamin C) transporter SVCT1. Am. J. Physiol. Cell Physiol. 294: C451-459.
Martinussen, J., J. Schallert, B. Andersen and K. Hammer (2001). The pyrimidine operon pyrRPB-carA from Lactococcus lactis. J. Bacteriol. 183: 2785-2794.
Papakostas, K., E. Georgopoulou, and S. Frillingos. (2008). Cysteine-scanning analysis of putative helix XII in the YgfO xanthine permease: ILE-432 and ASN-430 are important. J. Biol. Chem. 283: 13666-13678.
Quinn, C.L., B.T. Stephenson and R.L. Switzer (1991). Functional organization and nucleotide sequence of the Bacillus subtilis pyrimidine biosynthetic operon. J. Biol. Chem. 266: 9113—9127.
Saier, M.H., Jr., B.H. Eng, S. Fard, J. Garg, D.A. Haggerty, W.J. Hutchinson, D.L. Jack, E.C. Lai, H.J. Liu, D.P. Nusinew, A.M. Omar, S.S. Pao, I.T. Paulsen, J.A. Quan, M. Sliwinski, T.-T. Tseng, S. Wachi and G.B. Young (1999). Phylogenetic characterization of novel transport protein families revealed by genome analyses. Biochim. Biophys. Acta 1422: 1-56.
Schultz, A.C., P. Nygaard and H.H. Saxild (2001). Functional analysis of 14 genes that constitute the purine catabolic pathway in Bacillus subtilis and evidence for a novel regulon controlled by the PucR transcription activator. J. Bacteriol. 183: 3293-3302.
Tsukaguchi, H., T. Tokui, B. Mackenzie, U.V. Berger, X.Z. Chen, Y. Wang, R.F. Brubaker, and M.A. Hediger. (1999). A family of mammalian Na+-dependent L-ascorbic acid transporters. Nature 399: 70-75.
Turner, R.J., Y. Lu and R.L. Switzer (1994). Regulation of the Bacillus subtilis pyrimidine biosynthetic (pyr) gene cluster by an autogenous transcriptional attenuation mechanism. J. Bacteriol. 176: 3708—3722.
Examples:

TC#NameOrganismal TypeExample
2.A.40.1.1Uracil permease Bacteria UraA of E. coli (P0AGM7)
 
2.A.40.1.2High affinity uracil permeaseBacteriaPyrP of Lactococcus lactis (gbCAB89870)
 
2.A.40.1.3Putative pyrimidine permease, RutG (Loh et al., 2006) BacteriaRutG of E. coli (P75892)
 
Examples:

TC#NameOrganismal TypeExample
2.A.40.2.1Purine permease Bacteria YcpX of Clostridium perfringens
 
Examples:

TC#NameOrganismal TypeExample
2.A.40.3.1Xanthine permease Bacteria PbuX (XanP) of Bacillus subtilis
 
2.A.40.3.2Uric acid permease Bacteria PucJ of Bacillus subtilis
 
2.A.40.3.3Xanthine permease, YgfO (Karatza et al., 2006). Ile432 and Asn430 in helix 7 are important for xanthine binding (Papakostas et al., 2008).

Bacteria

YgfO of E. coli (P67444)

 
Examples:

TC#NameOrganismal TypeExample
2.A.40.4.1High affinity uric acid-xanthine permease, UapA Fungi UapA of Emericella nidulans
 
2.A.40.4.2The putative xanthine permease, YicE (Karatza and Frillingos, 2005)BacteriaYicE of E. coli (POAGM9)
 
Examples:

TC#NameOrganismal TypeExample
2.A.40.5.1General purine permease, UapC Fungi UapC of Emericella nidulans
 
Examples:

TC#NameOrganismal TypeExample
2.A.40.6.1L-ascorbate:Na+ symporter, SVCT1. (L-ascorbate:Na+= 1:2; Mackenzie et al., 2008)Animals SVCT1 of Rattus norvegicus
 
2.A.40.6.2Ca2+/Mg2+-dependent L-ascorbate:Na+ symporter, SVCT2; Na+:ascorbate = 2:1; binding order: Na+, ascorbate, Na+ (Na+ increases the affinity for ascorbate; Ca2+/Mg2+ are required for function) (Godoy et al., 2007). AnimalsSVCT2 of Homo sapiens (Q9WTW8)
 
2.A.40.6.3High affinity (Km = 30 µM) uric acid-xanthine transporter; leaf permease protein 1, LPE1 (necessary for proper chloroplast development in maize) (Argyrou et al., 2001) PlantsLPE1 of Zea mays (Q41760)