The arsenical resistance-3 (ACR3) family
TC# 2.A.59 is a member of the
BART superfamily. Based on operon analyses, ARC3 homologues may function either as secondary carriers or as primary active transporters, similarly to the
ArsB and ArsAB families. In the latter case ATP hydrolysis again energizes transport. ARC3 homologues transport the same anions as ArsA/AB homologues, though ArsB homologues are members of the
IT Superfamily and homologues of the ARC3 family are within the
BART Superfamily suggesting they may not be evolutionarily related.
Structure and Homology
''Bacillus'' ARC3 (ArsB
TC# 2.A.59.1.2 probably has a 10 TMS topology. ACR3 of ''S. cerevisiae'' is 404 amino acyl residues long and exhibits 10 putative transmembrane α-helical spanners (TMSs). Homologues are found in ''
Mycobacterium tuberculosis
''Mycobacterium tuberculosis'' (M. tb) is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' has an unusual, waxy coating on its c ...
'' (498 aas; gbZ80225), ''
Archaeoglobus fulgidus
''Archaeoglobus'' is a genus of the phylum Euryarchaeota. ''Archaeoglobus'' can be found in high-temperature oil fields where they may contribute to oil field souring.
Metabolism
''Archaeoglobus'' grow anaerobically at extremely high temperat ...
'' (370 aas; gbAE001071), ''
Methanobacterium thermoautotrophicum'' (365 aas; gbAE000865) and ''
Synechocystis
''Synechocystis'' is a genus of unicellular, freshwater cyanobacteria in the family Merismopediaceae. It includes a strain, ''Synechocystis'' sp. PCC 6803, which is a well studied model organism.
Like all cyanobacteria, ''Synechocystis'' b ...
'' (383 aas; spP74311). Thus, members of the ACR3 family are found in bacteria, archaea and eukarya. Sequence similarity of several members of the ACR3 family with members of the bile acid:Na
+ symporter (BASS) family
TC# 2.A.28 is sufficient to establish homology.
Bioinformatic analyses have revealed that some ACR3 porters are involved in operons together with ArsA-like ATPases, implying that some of these porters may be driven by ATP hydrolysis as primary active transporters.
This may occur in addition to or instead of the secondary active transport mechanism established for ACR3 members noted above. Homologous ATPases are found in familie
TC# 3.A.4TC# 3.A.19
an
TC# 3.A.21
as well a
TC# 2.A.59
A region of the ABC ATPase
TC# 3.A.1.26.8
the ribose transporter) shows significant sequence similarity to the ArsA unde
TC# 3.A.19.1.1
(28% identical; 49% similarity, 0 gaps, e−5) as revealed by TC Blast.
Function
Two proteins of the ACR3 family have been functionally characterized. These proteins are the ACR3 protein of ''Saccharomyces cerevisiae
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...
,'' also called the ARR3 protein, and the 'ArsB' protein of '' Bacillus subtilis.'' While the nomenclature of the ARC3 ArsB protein overlaps with ArsB of ''E. coli'' (ArsB family), it is important to note they are not related''.'' The former yeast protein is present in the plasma membrane and pumps arsenite and antimonite, but not arsenate, tellurite, cadmium or phenylarsine oxide out of the cell in response to the proton motive force (pmf). It uses a proton antiport mechanism to extrude the anions with low affinity.antimonite
In chemistry, antimonite refers to a salt of antimony(III), such as NaSb(OH)4 and NaSbO2 (meta-antimonite), which can be prepared by reacting alkali with antimony trioxide, Sb2O3.Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemist ...
. The exact transport mechanism has not established.
The generalized reaction catalyzed by members of the ACR3 family is:arsenite or antimonite (in) → arsenite or antimonite (out).
See also
* Arsenite-Antimonite efflux Arsenite-antimonite transporters are membrane transporters that pump arsenite or antimonite out of a cell. Antimonite is the salt of antimony (Sb(III)) and has been found to significantly impact the toxicity of arsenite. The similar structure of As ...
* ArsB and ArsAB transporters
Arsenite resistance (Ars) efflux pumps of bacteria may consist of two proteins, ArsBTC# 2.A.45.1.1 the integral membrane constituent with twelve transmembrane spanners) and ArsATC# 3.A.4.1.1 the ATP-hydrolyzing, transport energizing subunit, as f ...
* Bart Superfamily
Further reading
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References
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Protein families
Solute carrier family