Structural and Functional Investigation of the Periplasmic Arsenate-Binding Protein ArrX from <i>Chrysiogenes arsenatis</i>

The anaerobic bacterium Chrysiogenes arsenatis respires using the oxyanion arsenate (AsO43–) as terminal electron acceptor, where it is reduced to arsenite (AsO33–) while concomitantly oxidizing various organic (e.g., acetate) donors. This respiratory activity catalyzed in periplasm of by enzyme reductase (Arr), with expression controlled a sensor histidine kinase (ArrS) and periplasmic-binding protein (PBP), ArrX. Here, we report for first time, molecular structure ArrX absence presence bound ligand arsenate. Comparison ligand-bound other PBPs shows high level conservation critical residues binding these proteins; however, this suite different structural alterations upon binding. For its homologue AioX (from Rhizobium sp. str. NT-26), which specifically binds arsenite, structures substrate-binding sites vicinity conserved cysteine residue contribute discrimination chemically similar ligands.