Structure, interaction and post-translational modification study of arsenic reduction system in Bifidobacterium longum

Microbial metabolism contributes to degradation of organoarsenicals, where arsenic reductases (glutaredoxins) play pivotal role in bacterial resistance to arsenic. Ars operon studies have revealed reduction of arsenate As(V) to arsenite As(III) by respiratory-chainlinked reductase enzyme complexes. Although structure of some bacterial arsenate reductases has been solved but not attempted for Bifidobacterium longum DJO10A colonizing the human gastrointestinal tract. Here it has been endeavoured to analyze and understand the structure, properties, interaction, evolution and action mechanism of this enzyme (arsC1) and its accessory interactors (arsB1, arsB2 and arsR). A systematic bioinformatic based analysis was carried out using a battery of tools and web servers for this purpose. Arsenic resistance gene cluster of gram-positive Bifidobacterium obtained from STRING database illustrated contiguous arsC and arsB genes and absence of arsA gene. ArsC1 was determined to be a cytoplasmic small-molecular-mass protein (~15 kDa) related to a class of tyrosine phosphatases mediating the reduction of As(V) to As(III). ArsC1 was found to be involved in dephosphorylation of arsR, arsB1 and arsB2, indicating its role in post translational modification (PTM) of interacting proteins. 3D structure analysis revealed that it was composed of 1 sheet,1 beta alpha beta unit, 4 strands, 5 helices, 3 helix-helix interacs, 13 beta turns and 1 gamma turn. All proteins in the cluster exhibited hydrophobic interactions. Explicit protein-protein hydrogen, ionic, aromatic and cation-pi interactions in arsenate reducing operon of Bifidobacterium longum DJO10A further aided structural understanding of arsenate reduction process.