M. leprae HSP18 suppresses copper (II) mediated ROS generation: Effect of redox stress on its structure and function.

Mycobacterium leprae, causative organism of leprosy, is known to counter redox stress generated by reactive oxygen species (ROS) during its survival inside host macrophages. But, the involvement of any antigenic protein(s) for countering such redox stress is still unknown. Interestingly, M. leprae HSP18, an important antigenic protein that helps in the growth and survival of M. leprae pathogen inside host macrophages, is induced under redox stress. Moreover, HSP18 also interacts with Cu. Copper (II) can induce redox stress via Fenton reaction. But, whether HSP18 suppresses Cu mediated ROS generation, is still far from clear. Also, the effect of redox stress on its structure and function is not known. In this study, we show that HSP18 efficiently suppresses Cu mediated generation of ROS and also prevents the redox mediated aggregation of a client protein (γD-crystallin). Upon exposure to substantial redox stress, irreversible perturbation in the secondary and tertiary structure of HSP18 and the tryptophan and tyrosine oxidation are evidenced. Interestingly, HSP18 retains a considerable amount of functionality even after being exposed to substantial redox stress. Perhaps, the redox scavenging ability as well as the chaperone function of HSP18 may possibly help M. leprae pathogen to counter redox stress inside host macrophages.