Characterization of a DsbA family protein reveals its crucial role in oxidative stress tolerance of Listeria monocytogenes

ABSTRACT

Listeria monocytogenes is a facultative, intracellular foodborne pathogen widely distributed in nature and is responsible for severe invasive infection in humans and animals with a mortality rate as high as 30%. L. monocytogenes can adapt to various oxidative stresses since it has evolved oxidative modification and regulation mechanisms. The disulfide bond formation protein (Dsb) is required to catalyze the formation of disulfide bonds to promote oxidative folding or modification of proteins involved in bacterial virulence and survival. However, the functions of Lmo1059, a DsbA family protein of L. monocytogenes, remain unknown. In this study, we found that Lmo1059 could efficiently catalyze oxidized glutathione (GSSG) reduction, with the residues Cys36 and Cys39 as the key amino acids for its catalytic activity. Moreover, Lmo1059 plays a critical role in oxidative stress tolerance for L. monocytogenes, and Cys36 is the crucial amino acid to participate in this process. When Lmo1059 was deleted, the adhesion and invasion of L. monocytogenes were reduced while the cell-to-cell spread was increased, suggesting an intricate role of Lmo1059 during bacterial infection. Altogether, these data indicate that the DsbA family protein Lmo1059 is an important participant in the antioxidant stress system and works in concert with other proteins to help protect L. monocytogenes from oxidative stress and establish intracellular infection.

IMPORTANCE

The adaption and tolerance to various environmental stresses are the fundamental factors for the widespread existence of Listeria monocytogenes. Anti-oxidative stress is the critical mechanism for the survival and pathogenesis of L. monocytogenes. The thioredoxin (Trx) and glutaredoxin (Grx) systems are known to contribute to the anti-oxidative stress of L. monocytogenes, but whether the Dsb system has similar roles remains unknown. This study demonstrated that the DsbA family protein Lmo1059 of L. monocytogenes participates in bacterial oxidative stress tolerance, with Cys36 as the key amino acid of its catalytic activity and anti-oxidative stress ability. It is worth noting that Lmo1059 was involved in the invading and cell-to-cell spread of L. monocytogenes. This study lays a foundation for further understanding the specific mechanisms of oxidative cysteine repair and antioxidant stress regulation of L. monocytogenes, which contributes to an in-depth understanding of the environmental adaptation mechanisms for foodborne bacterial pathogens.