STATIONARY PHASE-ASSOCIATED PROTEIN EXPRESSION IN MYCOBACTERIUM-TUBERCULOSIS - FUNCTION OF THE MYCOBACTERIAL ALPHA-CRYSTALLIN HOMOLOG

The majority of active tuberculosis cases arise as a result of reactiv ation of latent organisms which are quiescent within the host, The abi lity of mycobacteria to survive extended periods without active replic ation is a complex process whose details await elucidation. We used tw o-dimensional gel electrophoresis to examine both steady-state protein composition and time-dependent protein synthetic profiles in aging cu ltures of virulent Mycobacterium tuberculosis. At least seven proteins were maximally synthesized 1 to 2 weeks following the end of log-phas e growth, One of these proteins accumulated to become a predominant st ationary-phase protein, N-terminal amino acid sequencing and immunorea ctivity identified this protein as the 16-kDa alpha-crystallin-like sm all heat shock protein, The gene for this protein was shown to be limi ted to the slowly growing M. tuberculosis complex of organisms as asse ssed by Southern blotting, Overexpression of this protein in wild-type M. tuberculosis resulted in a slower decline in viability following t he end of log-phase growth. Accumulation of this protein was observed in log-phase cultures following a shift to oxygen-limiting conditions but not by other external stimuli, The protein was purified to homogen eity from overexpressing M. smegmatis in two steps and shown to have a significant ability to suppress the thermal denaturation of alcohol d ehydrogenase. Collectively, these results suggest that the mycobacteri al alpha-crystallin protein may play a role in enhancing long term pro tein stability and therefore long-term survival of M. tuberculosis.