Oxidant-dependent switching between reversible and sacrificial oxidation pathways for Bacillus subtilis OhrR.

The Bacillus subtilis OhrR protein functions as a transcriptional repressor of the inducible peroxidase, OhrA. Derepression is mediated by the organic-peroxide selective oxidation of an active site cysteine (C15). In the presence of cumene hydroperoxide (CHP), oxidation of OhrR leads to a sulphenic acid intermediate which reacts to form either a mixed-disulphide or a protein sulphenamide. These inactive forms of OhrR can be reactivated by thiol-disulphide exchange reactions allowing restoration of repression. Here, we demonstrate that linoleic acid hydroperoxide (LHP) is a potent oxidant for OhrR and even low levels lead to overoxidation of OhrR to cysteine sulphinic (and sulphonic) acid derivatives. Kinetic competition experiments indicate that further oxidation of the initial OhrR sulphenate product occurs at least 100-fold more rapidly with LHP than with CHP. Thus, depending on the oxidant, OhrR can be either reversibly oxidized or can instead function as a sacrificial regulator.