The Atypical Hsp60s of Mycobacterium tuberculosis

Heat shock proteins (Hsps) are a diverse set of proteins that mediate the correct folding, assembly, transport and degradation of other proteins. The Hsps have thus appropriately been termed as molecular chaperones. The 60kDa heat shock proteins (Hsp60s) form a sub-group of Hsps and are found to exist in all domains of life. In bacteria Hsp60s are encoded by the essential hsp60 genes arranged on the bicistronic groESL operon. Interestingly, in addition to their role as molecular chaperones, Hsp60s have also been shown to play a variety of important roles in immunity and represent prominent antigens in the humoral and cellular immune response. Mycobacterium tuberculosis contains two copies of the hsp60 genes. The cognate partner of Hsp60 is the 10kDa protein, Hsp10 and exists in a single copy in M. tuberculosis. The existence of a duplicate set of hsp60 genes in M. tuberculosis has been perplexing. Interestingly, both the Hsp60s of M. tuberculosis have been shown to be highly antigenic in nature, eliciting strong B and T cell immune responses. Recent work has shown interesting structural, biochemical and signaling properties of the M. tuberculosis Hsp60s. This review details the recent developments in the study of the M. tuberculosis Hsp60s.