Function of alkyl hydroperoxidase AhpD in resistance to oxidative stress in Corynebacterium glutamicum

Alkyl hydroperoxidase reductase AhpD, which is functionally equivalent to the bacterial flavin-containing disulfide reductase AhpF, acts as a proton donor for the organic peroxide-scavenging alkyl hydroperoxidase AhpC. Although AhpD has long been demonstrated in Mycobacterium tuberculosis, its physiological and biochemical functions remain largely unknown in other actinobacteria, including Corynebacterium glutamicum, Streptomyces, and Mycobacterium smegmatis. Here, we report that C. glutamicum AhpD contributed to regenerate a variety of thiol-dependent peroxidase in the decomposition of peroxide by linking a dihydrolipoamide dehydrogenase (Lpd)/dihydrolipoamide succinyltransferase (SucB)/NADH system through the cyclization of their own active site dithiol to the oxidized disulphide. The CXXC motif of AhpD was essential to maintain the peroxides reduction activity of thiol-dependent peroxidase. ΔahpD1ΔahpD2 mutants exhibited significantly decreased resistance to adverse stress conditions and obviously increased the accumulation of reactive oxygen species (ROS). The physiological roles of AhpD in resistance to adverse stresses, were corroborated by their induced expression under various stresses and their direct regulation under the stress-responsive ECF-sigma factor SigH. C. glutamicum AhpDs were disulfide oxidoreductases behaving like thioredoxin (Trx) in regenerating thiol-dependent peroxidase for stress response, which provides the theoretical basis for an in-depth study of the reduction system in ahpC-lacking bacteria.