Biological redox reactions of inorganic sulfur compounds are important for the proper maintenance of environmental sulfur balance. These reactions are mediated by phylogeneticaly diverse set of microorganisms. The protein complex that is involved in such redox reactions of sulfur compounds is the complex encoded by dsr operon. The ecological and industrial importance of these microorganisms led us to investigate the structural details of the mechanism of the process of electron transport during such redox reactions performed by the dsr operon. Among the gene products of the operon, the proteins DsrE, DsrF, and DsrH are small soluble cytoplasmic proteins acting as α₂β₂γ₂ heterohexamer and are involved in the process of electron transport in these ecologically as well as industrially important microorganisms.

Since no structural details of the proteins were available we employed homology modeling to construct the three-dimensional structures of the DsrE, DsrF, and DsrH from Chlorobium tepidum. The putative three dimensional structures of the proteins were predicted from the models. Since DsrE, DsrF, and DsrH proteins act as a hetero-hexameric complex, the modeled proteins were subjected to molecular docking analyses to generate the model of the biochemically active complex. This allowed us to predict the probable binding modes of the proteins as well as the biochemical and the structural basis of the mechanism of the electron transport process by this complex. The hexamerization of the proteins would help to bring the Cys residues in close proximity, which enables the complex to actively take part electron transport process.

Key words: Sulfur oxidation; dsr operon; Homology modeling; Molecular docking; and Heterohexamer.