Mycobacterium tuberculosisRv0991c is a redox-regulated molecular chaperone

ABSTRACTThe bacterial pathogenMycobacterium (M.) tuberculosisis the leading cause of death by an infectious disease among humans. Here, we describe a previously uncharacterizedM. tuberculosisprotein, 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-characterizedEscherichia coliredox-regulated chaperone Hsp33, despite a dissimilar protein sequence. Rv0991c is transcriptionally co-regulated withhsp60andhsp70chaperone genes inM. 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 proteinin vitro, and promotes its refolding by theM. tuberculosisHsp70 chaperone system. Furthermore, Rv0991c interacts with DnaK and associates with many otherM. tuberculosisproteins. Importantly, we found Rv0991c is required for the full virulence ofM. tuberculosisin mice. We therefore propose that Rv0991c, which we named “Ruc” (redox-regulated protein withunstructuredC-terminus), represents a founding member of a new chaperone family that protectsM. tuberculosisand other species from proteotoxicity during oxidative stress.IMPORTANCEM. tuberculosisinfections are responsible for more than one million human deaths per year. Developing effective strategies to combat this disease requires a greater understanding ofM. tuberculosisbiology. As in all cells, protein quality control is essential for the viability ofM. tuberculosis, which likely faces proteome stress within a host. Here, we identify anM. tuberculosisprotein, 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 fullM. tuberculosisvirulence 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 inM. tuberculosispathogenesis.