An intermolecular disulfide bond serves as a thioredoxin-dependent redox-sensing switch for the regulation of the enzymatic activity of 3-mercaptopyruvate sulfurtransferase (MST, EC.126.96.36.199). A cysteine residue on the surface of each subunit was oxidized to form an intersubunit disulfide bond so as to decrease MST activity, and thioredoxin-specific conversion of a dimer to a monomer increased MST activity. Further, a low redox potential sulfenate was reversibly formed at a catalytic site cysteine so as to inhibit MST, and thioredoxin-dependent reduction of the sulfenate restored the MST activity. Concludingly, MST partly contributes to the maintenance of cellular redox homeostasis via exerting control over cysteine catabolism.
Keywords: Atmospheric oxygen, antioxidative stress, intermolecular disulfide bond, mercaptolactate-cysteine disulfiduria, mercaptopyruvate sulfurtransferase, molecular evolution, redox-sensing switch, thioredoxin