Molecular mechanisms of Mycoredoxin-1 in resistance to oxidative stress in Corynebacterium glutamicum.

Glutaredoxins (Grxs) with Cys-Pro-Phe (Tyr)-Cys motif and a thioredoxin fold structure play an important role in the anti-oxidant system of bacteria by catalyzing a variety of thiol-disulfide exchange reactions with a 2-Cys mechanism or a 1-Cys mechanism. However, the catalytic and physiological mechanism of Corynebacterium glutamicum Mycoredoxin 1 (Mrx1) that shares a high amino acid sequence similarity to Grxs has not been fully elucidated. Here, we report that Mrx1 has a protective function against various adverse conditions, and the decrease of cell viability to various stress conditions by deletion of the Mrx1 in C. glutamicum was confirmed in the mrx1 mutant. The physiological roles of Mrx1 in defence to oxidative stress were corroborated by its induced expression under various stresses, regulated directly by the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH. As well as reducing mycothiol (MSH) mixed disulfide bonds via a 1-Cys mechanism, C. glutamicum Mrx1 catalytically reduced the disulfides in the Ib RNR, insulin and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) by exclusively linking the MSH/Mtr (mycothiol disulfide reductase)/NADPH electron pathway via a 2-Cys mechanism. Thus, we present the first evidence that the Mrx1 is able to protect against the damaging effects of various exogenous stresses by acting as a disulfide oxidoreductase, thereby giving a new insight in how C. glutamicum survives oxidative stressful conditions.