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2.A.45 The Arsenite-Antimonite (ArsB) Efflux Family

Arsenite resistance (Ars) efflux pumps of bacteria consist either of two proteins (ArsB, the integral membrane constituent with twelve transmembrane spanners), and ArsA (the ATP-hydrolyzing, transport energizing subunit, as for the chromosomally-encoded E. coli system), or of one protein (the ArsB integral membrane protein of the plasmid-encoded Staphylococcus system) (Rensing et al., 1999; Rosen, 1996; Xu et al., 1998). ArsA proteins have two ATP binding domains and probably arose by a tandem gene duplication event. ArsB proteins all possess twelve transmembrane spanners and may also have arisen by a tandem gene duplication event. Structurally, the Ars pumps resemble ABC-type efflux pumps, but there is no significant sequence similarity between the Ars and ABC pumps. When only ArsB is present, the system operates by a pmf-dependent mechanism, and consequently belongs in TC subclass 2.A. When ArsA is also present, ATP hydrolysis drives efflux, and consequently the system belongs in TC subclass 3.A. ArsB therefore appears twice in the TC system but ArsA appears only once. These pumps actively expel both arsenite and antimonite.

Homologues of ArsB are found in Gram-negative and Gram-positive bacteria as well as cyanobacteria, and several paralogues are sometimes found in a single organism. Homologues are also found in archaea and eukarya. Among the distant homologues found in eukaryotes are members of the DASS family (TC #2.A.47) including the rat renal Na+:sulfate cotransporter (spQ07782) and the human renal Na+:dicarboxylate cotransporter (gbU26209). ArsB proteins are therefore members of a superfamily (called the IT (ion transporter) superfamily) (Prakash et al., 2003; Rabus et al., 1999). However, ArsB has uniquely gained the ability to function in conjunction with ArsA in order to couple ATP hydrolysis to anion efflux.

A unique member of the ArsB family is the rice silicon (silicate) efflux pump, Lsi2 (2.A.45.2.4). The silicon uptake systems, Lsi1 (1.A.8.12.2), and Lsi2 are expressed in roots, on the plasma membranes of cells in both the exodermis and the endodermis. In contrast to Lsi1, which is localized on the distal side, Lsi2 is localized on the proximal side of the same cells. Thus these cells have an influx transporter on one side and an efflux transporter on the other side of the cell to permit the effective transcellular transport of the nutrient.

ArsA homologues are found in bacteria, archaea and eukarya (both animals and plants), but there are far fewer of them in the databases than ArsB proteins, suggesting that many ArsB homologues function by a pmf-dependent mechanism, probably an arsenite:H+ antiport mechanism (Meng et al., 2004). ArsA proteins are homologous to nitrogenase iron (NifH) proteins 2 of bacteria and to protochlorophyllide reductase iron sulfur ATP-binding proteins of cyanobacteria, algae and plants.

The overall reaction catalyzed by ArsB (presumably by uniport) is:

Arsenite or Antimonite (in) Arsenite or Antimonite (out).


The overall reaction catalyzed by Lsi2 is:

silicate (in) → silicate (out)



This family belongs to the: IT Superfamily.

References associated with 2.A.45 family:

Bellono, N.W., I.E. Escobar, A.J. Lefkovith, M.S. Marks, and E. Oancea. (2014). An intracellular anion channel critical for pigmentation. Elife 3: e04543. 25513726
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Kuroda, M., S. Dey, O.I. Sanders and B.P. Rosen (1997). Alternate energy coupling of ArsB, the membrane subunit of the Ars anion-translocating ATPase. J. Biol. Chem. 272: 326-331. 8995265
Lee, S.-T., R.D. Nicholls, M.T.C. Jong, K. Fukai and R.A. Spritz (1995). Organization and sequence of the human P gene and identification of a new family of transport proteins. Genomics 26: 354-363. 7601462
Ma J.F., N. Yamaji, N. Mitani, K. Tamai, S. Konishi, T. Fujiwara, M. Katsuhara, M. Yano. (2007a). An efflux transporter of silicon in rice. Nature. 448: 209-212. 17625566
Ma, J.F., N. Yamaji, K. Tamai, and N. Mitani. (2007b). Genotypic difference in silicon uptake and expression of silicon transporter genes in rice. Plant Physiol. 145: 919-924. 17905867
Meng, Y.-L., Z. Liu, and B.P. Rosen. (2004). As(III) and Sb(III) uptake by GlpF and efflux by ArsB in Escherichia coli. J. Biol. Chem. 279: 18334-18341. 14970228
Murat, D., A. Quinlan, H. Vali, and A. Komeili. (2010). Comprehensive genetic dissection of the magnetosome gene island reveals the step-wise assembly of a prokaryotic organelle. Proc. Natl. Acad. Sci. USA 107: 5593-5598. 20212111
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Rabus, R., D.L. Jack, D.J. Kelly and M.H. Saier, Jr. (1999). TRAP transporters: an ancient family of extracytoplasmic solute-receptor-dependent secondary active transporters. Microbiology 145: 3431-3445. 10627041
Rensing, C., M. Ghosh and B.P. Rosen (1999). Families of soft-metal-ion transporting ATPase. J. Bacteriol. 181: 5891-5897. 10498699
Rosen, B.R. (1996). Bacterial resistance to heavy metals and metalloids. JBIC 1: 273-277. 10730185
Silver, S., G. Ji, S. Bröer, S. Dey, D. Dou and B.P. Rosen (1993). Orphan enzyme or patriarch of a new tribe: The arsenic resistance ATPase of bacterial plasmids. Mol. Microbiol. 8: 637-642. 8332056
Walmsley, A.R., T. Zhou, M.I. Borges-Walmsley and B.P. Rosen (2001). A kinetic model for the action of a resistance efflux pump. J. Biol. Chem. 276: 6378-6391. 11096086
Xu, C., T. Zhou, M. Kuroda and B.P. Rosen (1998). Metalloid resistance mechanisms in prokaryotes. J. Biochem. 123: 16-23. 9504403