Characterization of an extracellular protein, Rv1076 from M. tuberculosis with a potential role in humoral response

Many mycobacterial proteins involved in lipid metabolism are reported to be essential for survival and pathogenesis of M. tuberculosis. Rv1076 of M. tuberculosis has been annotated as a putative esterase/lipase based on the consensus sequence 'GXSXG'. It is conserved in all the mycobacterial species. Therefore, in the present study we have characterized Rv1076 gene product in detail. The gene rv1076 was expressed in E. coli and purified from inclusion bodies with approx. 40% yield. The protein showed high specific activity with pNP- butyrate as preferred substrate. The enzyme was stable upto 50 °C and in pH range of 6-8 i.e. under acidic conditions. Ser-140, Glu-239 and His-269 were confirmed as active site residues using site directed mutagenesis. The specific activity, Km and Vmax of enzyme was determined to be 177 U mg−1 protein, 334 μM and 262 μmol ml−1 min−1, respectively. Western blot analysis established Rv1076 to be an extracellular protein. Several putative immunodominant epitopes were predicted in Rv1076. Rv1076 elicited strong humoral response in both extrapulmonary and relapsed cases of TB patients. Therefore, we conclude that Rv1076 is a novel secretory esterase of M. tuberculosis which could be a potential immunodominant antigen of M. tuberculosis.