Corynebacterium glutamicum is an important industrial strain for
amino acids and a key model organism for human pathogens. The study of C. glutamicum
oxidoreductases, such as mycoredoxin 1 (Mrx1),
dithiol-
disulfide isomerase DsbA, and DsbA-like Mrx1, is helpful for understanding the survival, pathogenic
infection, and stress resistance of its homologous species. However, the action mode and enzymatic function of C. glutamicum NCgl0018 preserving the
Cys-Pro-Phe-Cys motif, annotated as a putative DsbA, have remained enigmatic. Here, we report that the NCgl0018-deleted strain increased sensitivity to various oxidative stresses. The ncgl0018 expression was induced in the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH- and organic
peroxide- and
antibiotic-sensing regulator (OasR)-dependent manner by stress. NCgl0018 reduced S-mycothiolated mixed
disulfides and intramolecular
disulfides via a monothiol-
disulfide mechanism preferentially linking the
mycothiol/
mycothione reductase/
NADPH electron pathway. Site-directed mutagenesis confirmed Cys107 was the resolving Cys residue, while Cys104 was the nucleophilic
cysteine that was oxidized to a
sulfenic acid and then could form an intramolecular
disulfide bond with Cys107 or a mixed
disulfide with
mycothiol under stress. Biochemical analyses indicated that NCgl0018 lacked
oxidase properties like the classical DsbA. Further, enzymatic rates and substrate preferences of NCgl0018 were highly similar to those of DsbA-like Mrx1. Collectively, our study presented the first evidence that NCgl0018 protected against stresses by functioning as a novel DsbA-like Mrx1 but not DsbA and Mrx1.