Arsenite-antimonite transporter
Arsenite-antimonite transporters are membrane transporters that pump arsenite or antimonite out of a cell. Inorganic arsenic has two biological important oxidation states: As(V) (arsenate) and As(III) (arsenite). Arsenic uptake is adventitious because the arsenate and arsenite are chemically similar to required nutrients. Arsenate resembles phosphate and is a competitive inhibitor of many phosphate-utilizing enzymes. Arsenate is taken up by phosphate transport systems. In contrast, at physiological pH, the form of arsenite is As(OH)(3), which resembles organic molecules such as glycerol. Consequently, arsenite is taken into cells by aquaglyceroporin channels. Antimonite is the salt of antimony (Sb(III)) and has been found to significantly impact the toxicity of arsenite.[1] The similar structure of As(III) and Sb(III) makes it plausible that certain transporters function in the efflux of both substrates. Arsenic efflux systems are found in nearly every organism and evolved to rid cells of this toxic metalloid. These efflux systems include members of the multidrug resistance protein family and the bacterial exchangers Acr3 and ArsB. ArsB can also be a subunit of the ArsAB As(III)-translocating ATPase, an ATP-driven efflux pump. All three of these systems participate in efflux of either arsenite or antimonite.[2]
Subfamilies
As of early 2016, there are at least three known families of proteins known to participate in arsenite and antimonite efflux.
The membrane transporter ArsB can function as a secondary carrier or as a primary active transporter, in which case ArsA, an ATPase, must be superimposed onto ArsB. Arsenite and antimonite can also be pumped out of the cell by members of the ARC3 family, a member of the BART superfamily, which can participate in both secondary transport or primary active transport. Based on operon analyses, Arc3 homologues may similarly function either as secondary carriers or as primary active transporters. In the latter case ATP hydrolysis again energizes transport.[3]
See also
- Arsenic toxicity
- Arsenite-transporting ATPase
- Solute carrier family
- Active transport
- ATP-binding cassette transporter
References
- ^ Hasgekar, N.; Beck, J. P.; Dunkelberg, H.; Hirsch-Ernst, K. I.; Gebel, T. W. (2006-01-01). "Influence of antimonite, selenite, and mercury on the toxicity of arsenite in primary rat hepatocytes". Biological Trace Element Research. 111 (1–3): 167–183. doi:10.1385/BTER:111:1:167. ISSN 0163-4984. PMID 16943604.
- ^ Yang, Hung-Chi; Fu, Hsueh-Liang; Lin, Yung-Feng; Rosen, Barry P. (2012-01-01). "Pathways of arsenic uptake and efflux". Current Topics in Membranes. 69: 325–358. doi:10.1016/B978-0-12-394390-3.00012-4. ISSN 1063-5823. PMC 4578627. PMID 23046656.
- ^ "TCDB » SEARCH". www.tcdb.org. Retrieved 2016-03-13.
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