Feedback Inhibition of DszC, a Crucial Enzyme for Crude Oil Biodessulfurization

The Rhodococcus erythropolis (strain IGTS8) bacterium has a tremendous industrial interest as it can remove sulfur from crude oil through its four-enzyme (DszA-D) 4S metabolic pathway. DszC is one of the rate-limiting enzymes of the pathway and the one that most suffers from feedback inhibition. We have combined molecular docking and molecular dynamics simulations to identify binding sites through which two products of the 4S pathway, 2-hydroxybiphenyl and 2 ' -hydroxybiphenyl-2sulfinate, induce DszC feedback inhibition. We have identified four potential binding sites: two adjacent binding sites close to the 280-295 lid loop proposed to contribute to DszC oligomerization and proper binding of the flavin mononucleotide cofactor, and two other close to the active site of DszC and the substrate binding site. By considering (i) the occupancy of the binding sites and (ii) the similar inhibitor poses, we propose that the mechanism of feedback inhibition of DszC occurs through disturbance of the DszC oligomerization and consequent binding of the flavin mononucleotide due to the weakening of the interactions between the 280-295 lid loop, and both the 131-142 loop and the C-terminal tail. Nevertheless, inhibitor binding close to the active site or the substrate binding sites also compromises critical interactions within the active site of DszC. The disclosed molecular details provide valuable insight for future rational enzyme engineering protocols to develop DszC mutants more resistant against the observed feedback inhibition mechanism.