New insight into the role of glutathione reductase in glutathione peroxidase-like activity determination by coupled reductase assay: Molecular Docking Study

Previously we have shown that among 15 substituted salicyloyl (2-hydroxybenzoyl) 5-seleninic acids (SSAs) 4 compounds with longer side chains or a cyclohexyl group exhibit no glutathione peroxidase (GPx)-like activity in the coupled reductase assay. Experimental inhibition of glutathione reductase (GR) by the selenenylsulfide (a main intermediate in the catalytic cycle for GPx-like activity determination) of one of the inactive compounds led us to assess the interactions between 15 selenenylsulfide compounds and the active site of GR by molecular docking. Docking results showed that S and Se atoms in selenenylsulfides of the compounds with no GPx-like activity were beyond 5 Å from S atom of Cys-58 or N atom of imidazole ring of His-467 (Root Mean Square Distances for general assessment of 3 major distances were over 4.8 Å) in the active site, so that they could not be catalyzed to be reduced by GR. Furthermore, their docking scores over 89 Kcal/mol meant that the selenenylsulfides were bound too strongly to the active site to leave it, leading eventually to inhibition of GR. We also applied the molecular docking to other GPx mimics such as ebselen, cyclic seleninate esters and di(propylaminomethylphenyl) diselenides to explain the differences in their GPx-like activity depending to the assays used. Our results suggest that the reduction of a selenenylsulfide by GR plays a positive role in GPx-like activity of GPx mimics in the coupled assay and recommended the prediction of possibility and strength of GPx-like activity by molecular docking before entering experimental research. Molecular docking studies have been performed to show possible interactions between the active site of glutathione reductase and selenenylsulfides, intermediates of glutathione peroxidase-like mimics in the catalytic cycle. The results suggested semi-quantitative criteria for the mimics and recommended the docking study prior to synthesis or activity determination of mimic candidates. [Display omitted] •Synthesis and glutathione reductase inhibition of a new selenenylsulfide.•Docking of some selenylsulfides into the active site of glutathione reductase (GR).•Elucidation of discrepancies in 2 assays for glutathione peroxidase (GPx)-like activity.•Importance of GR-based reduction of a selenylsulfide intermediate in the coupled assay.•Preference of molecular docking to experiments in designing new GPx mimics.