Multiple thioredoxin-mediated routes to detoxify hydroperoxides in Mycobacterium tuberculosis

Drug resistance and virulence of Mycobacterium tuberculosis are in part related to the pathogen's antioxidant defense systems. KatG(-) strains are resistant to the first line tuberculostatic isoniazid but need to compensate their catalase deficiency by alternative peroxidase systems to stay virulent. So far, only NADH-driven and AhpD-mediated hydroperoxide reduction by AhpC has been implicated as such virulence-determining mechanism. We here report on two novel pathways which underscore the importance of the thioredoxin system for antioxidant defense in M. tuberculosis: (i) NADPH-driven hydroperoxide reduction by AhpC that is mediated by thioredoxin reductase and thioredoxin C and (ii) hydroperoxide reduction by the atypical peroxiredoxin TPx that equally depends on thioredoxin reductase but can use both, thioredoxin B and C. Kinetic analyses with different hydroperoxides including peroxynitrite qualify the redox cascade comprising thioredoxin reductase, thioredoxin C, and TPx as the most efficient system to protect M. tuberculosis against oxidative and nitrosative stress in situ.