Structural and functional characterization of soxW-a thioredoxin involved in the transport of reductants during sulfur oxidation by the global sulfur oxidation reaction cycle

Abstract

Microbial oxidation-reduction reactions involving inorganic sulfur compounds, mainly the sulfur anions, are one of the vital reactions responsible for the environmental sulfur balance. These reactions are carried out by phylogenetically diverse prokaryotes. These sulfur-oxidizing microbes oxidize inorganic sulfur compounds like sulfide, thiosulfate etc. to produce reductants, which are, involved in the fixation of carbon dioxide or in respiratory electron transport chains. The sulfur oxidizing gene cluster (sax) of ct-Proteobacteria comprises of at least 15 genes, forming two transcriptional units, viz., soxSR and soxVWXYZABCDEFGH. SoxW is a periplasmic thioredoxin and an essential component of sax operon. It is required for optimal expression of the sox gene cluster. All thioredoxins are involvedin interaction with DNA polymerase. With the help of docking and molecular dynamics studies we have identified the amino acid residues of the protein involved in the interaction with DNA polymerase to structurally classify SoxW as a thioredoxin. The probable biochemical mechanism of the involvement of the protein in sulfur oxidation has also been investigated. Present study provides a rational basis to interpret the structural classification of SoxW as a thioredoxin and thereby to predict the possible molecular mechanism of the regulation of sulfur anion oxidation reactions by these ecologically important organisms.