Abstract
Arsenic contamination of drinking water affects more than 140 million people worldwide. While toxic to humans, inorganic forms of arsenic (arsenite and arsenate), can be used as energy sources for microbial respiration. AioX and its orthologues (ArxX and ArrX) represent the first members of a new sub-family of periplasmic-binding proteins that serve as the first component of a signal transduction system, that’s role is to positively regulate expression of arsenic metabolism enzymes. As determined by X-ray crystallography for AioX, arsenite binding only requires subtle conformational changes in protein structure, providing insights into protein-ligand interactions. The binding pocket of all orthologues is conserved but this alone is not sufficient for oxyanion selectivity, with proteins selectively binding either arsenite or arsenate. Phylogenetic evidence, clearly demonstrates that the regulatory proteins evolved together early in prokaryotic evolution and had a separate origin from the metabolic enzymes whose expression they regulate.
Highlights
Arsenic, toxic to most living organisms, can be used for respiration by some prokaryotes
The aioXSR regulatory gene cluster is found in some arsenite oxidisers of the Alpha- and Betaproteobacteria
AioR and ArxR are the response regulators controlling expression of the arsenite oxidase genes and are members of the AtoC family of response-regulators, which contain a AAA+ ATPase domain
Summary
Toxic to most living organisms, can be used for respiration by some prokaryotes. The respiratory arsenate reductase (Arr) has been purified and characterised from three organisms[6,8,11] and like the Aio consists of two heterologous subunits, a molybdenum-containing subunit (ArrA), which based on sequence analysis contains one 4Fe-4S cluster and a small subunit (ArrB) with four 4Fe-4S clusters[8]. The regulatory cluster consists of three genes, aioX, aioS and aioR, which encode a periplasmic-binding protein (PBP), a sensor histidine kinase and a response regulator, respectively. We report the identification and characterisation of a new subfamily of arsenic oxyanion-binding proteins from phylogenetically distant bacteria that have evolved to regulate bioenergetic arsenic metabolism. These proteins, which demonstrate substrate selectivity, could be used as novel sensors for both toxic arsenic oxyanions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
