Mycobacterium tuberculosis Rv0991c is a redox-regulated molecular chaperone

Abstract

The bacterial pathogen Mycobacterium (M.) tuberculosis is the leading cause of death by an infectious disease among humans. Here, we describe a previously uncharacterized M. tuberculosis protein, Rv0991c, as a molecular chaperone that is activated by oxidation. Rv0991c has homologues in most bacterial lineages and appears to function analogously to the well-characterized Escherichia coli redox-regulated chaperone Hsp33, despite a dissimilar protein sequence. Rv0991c is transcriptionally co-regulated with hsp60 and hsp70 chaperone genes in M. tuberculosis, suggesting that Rv0991c functions with these chaperones in maintaining protein quality control. Supporting this hypothesis, we found that, like oxidized Hsp33, oxidized Rv0991c prevents the aggregation of a model unfolded protein in vitro, and promotes its refolding by the M. tuberculosis Hsp70 chaperone system. Furthermore, Rv0991c interacts with DnaK and associates with many other M. tuberculosis proteins. Importantly, we found Rv0991c is required for the full virulence of M. tuberculosis in mice. We therefore propose that Rv0991c, which we named "Ruc" (redox-regulated protein with unstructured C-terminus), represents a founding member of a new chaperone family that protects M. tuberculosis and other species from proteotoxicity during oxidative stress. IMPORTANCEM. tuberculosis infections are responsible for more than one million human deaths per year. Developing effective strategies to combat this disease requires a greater understanding of M. tuberculosis biology. As in all cells, protein quality control is essential for the viability of M. tuberculosis, which likely faces proteome stress within a host. Here, we identify an M. tuberculosis protein, Ruc, that gains chaperone activity upon oxidation. Ruc represents a previously unrecognized family of redox-regulated chaperones found throughout the bacterial super-kingdom. In addition to elucidating the activity of this chaperone, we found that Ruc was required for full M. tuberculosis virulence in mice. This work contributes to a growing appreciation that oxidative stress may provide a particular strain on protein stability in cells, and may likewise play a role in M. tuberculosis pathogenesis.