Myo-inositol-1-phosphate synthase (Ino-1) functions as a protection mechanism in Corynebacterium glutamicum under oxidative stress

Graphical The ino-1 deletion mutant showed obviously higher ROS levels than the WT(pXMJ19) and the complement Δino-1(pXMJ19-ino-1) strains under oxidative stress conditions. And clearer protein carbonyl groups were detected in the Δino-1(pXMJ19) strains after exposure to ROS-generating agents compared to that in the WT(pXMJ19) strains. Reactive oxygen species (ROS) generated in aerobic metabolism and oxidative stress lead to macromolecules damage, such as to proteins, lipids, and DNA, which can be eliminated by the redox buffer mycothiol (AcCys-GlcN-Ins, MSH). Myo -inositol-phosphate synthase (Ino-1) catalyzes the first committed step in the synthesis of MSH, thus playing a critical role in the growth of the organism. Although Ino-1s have been systematically studied in eukaryotes, their physiological and biochemical functions remain largely unknown in bacteria. In this study, we report that Ino-1 plays an important role in oxidative stress resistance in the gram-positive Actinobacteria Corynebacterium glutamicum . Deletion of the ino-1 gene resulted in a decrease in cell viability, an increase in ROS production, and the aggravation of protein carbonylation levels under various stress conditions. The physiological roles of Ino-1 in the resistance to oxidative stresses were corroborated by the absence of MSH in the Δ ino-1 mutant. In addition, we found that the homologous expression of Ino-1 in C. glutamicum yielded a functionally active protein, while when expressed in Escherichia coli BL21(DE3), it lacked measurable activity. An examination of the molecular mass (Mr) suggested that Ino-1 expressed in E. coli BL21(DE3) was not folded in a catalytically competent conformation. Together, the results unequivocally showed that Ino-1 was important for the mediation of oxidative resistance by C. glutamicum .