Functional characterization of a mycothiol peroxidase in Corynebacterium glutamicum that uses both mycoredoxin and thioredoxin reducing systems in the response to oxidative stress

Previous studies have identified a putative mycothiol peroxidase (MPx) in Corynebacterium glutamicum that shared high sequence similarity to sulfur-containing Gpx (glutathione peroxidase; CysGPx). In the present study, we investigated the MPx function by examining its potential peroxidase activity using different proton donors. The MPx degrades hydrogen peroxide and alkyl hydroperoxides in the presence of either the thioredoxin/Trx reductase (Trx/TrxR) or the mycoredoxin 1/mycothione reductase/mycothiol (Mrx1/Mtr/MSH) regeneration system. Mrx1 and Trx employ different mechanisms in reducing MPx. For the Mrx1 system, the catalytic cycle of MPx involves mycothiolation/demycothiolation on the Cys36 sulfenic acid via the monothiol reaction mechanism. For the Trx system, the catalytic cycle of MPx involves formation of an intramolecular disulfide bond between Cys36 and Cys79 that is pivotal to the interaction with Trx. Both the Mrx1 pathway and the Trx pathway are operative in reducing MPx under stress conditions. Expression of mpx markedly enhanced the resistance to various peroxides and decreased protein carbonylation and intracellular reactive oxygen species (ROS) accumulation. The expression of mpx was directly activated by the stress-responsive extracytoplasmic function-σ (ECF-σ) factor [SigH]. Based on these findings, we propose that the C. glutamicum MPx represents a new type of GPx that uses both mycoredoxin and Trx systems for oxidative stress response. * AMS, : 4-acetamido-4′-maleimidyldystilbene-2,2′-disulfonic acid; Cumene-OOH, : cumene hydroperoxide; CysGPx, : sulfur-containing peroxidase; DCFH-DA, : 2′,7′-dichlorofluorescein diacetate; DTNB, : 5,5′-dithio bis-(2-nitrobenzoic acid); ECF-σ, : extracytoplasmic function-σ; FOX, : ferrous Xylenol Orange; GPx, : glutathione peroxidase; Grx, : glutaredoxin; IAM, : iodoacetamide; LA-OOH, : linoleic acid hydroperoxide; LMWT, : low-molecular-mass thiol; MPx, : mycothiol peroxidase; Mrx1, : mycoredoxin 1; MSH, : mycothiol; Mtr, : mycothione reductase; NBD-Cl, : 4-chloro-7-nitrobenzofurazan; PCdili-OOH, : L-α-phosphatidylcholine dilinoleoyl hydroperoxide; ROS, : reactive oxygen species; SecGPx, : selenoperoxidase; SigH, : stress-responsive ECF-σ factor; t-butyl-OOH, : t-butyl hydroperoxide; TCA, : trichloroacetic acid; Trx, : thioredoxin; TrxR, : thioredoxin reductase; WT, : wild-type