Step 1 , ArsD binds As(III) by exchange of the three hydroxyls of As(OH)3 for the thiols of MBS1 residues Cys12, Cys13, and Cys18. For simplicity, the cysteine residues of MBS1 are shown on only one subunit of the ArsD dimer. Step 2 , exchange of one thiol ligand in MBS1 of ArsD for one thiol ligand in MBS1 of ArsA. Step 3 , As(III) exchanges a second thiol ligand in ArsD for a second in ArsA. Step 4 , As(III) is transferred to MBS1 in ArsA by a final ligand exchange, inducing a conformational change in ArsA that increases the rate of ATP hydrolysis. The model should not be taken to specify an order of ligand exchange in the transfer reaction.
Conceptual representation of the complex arsenite oxidation process in H. arsenicoxydans . Several major control mechanisms are involved: A. a transcriptional regulation: AoxS acts as a sensor of As(III) environmental signal and then phosphorylates AoxR. The phosphorylated AoxR binds to RpoN, which interacts with RNA polymerase. The RpoN-RNA polymerase complex with its AoxR co-activator initiates the aox operon transcription. DnaJ may regulate aox mRNA stability or act on the folding of AoxR or σ54; B. Then, arsenite oxidase is synthesized and exported by the TAT secretion system; C. consequently, arsenite oxidase exerts a key role in arsenic detoxification, by the transformation of the more toxic form As(III) into a less toxic form As(V). This process is known to affect motility, which may involve a MCP chemotaxis protein and requires the DnaJ co-chaperone. IM= Inner Membrane, OM= Outer membrane. Koechler et al. BMC Microbiology 2010 10 :53 doi:10.1186/1471-2180-10-53 http://www.biomedcentral.com/1471-2180/10/53
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