Characterization of a Novel Esterase Rv0045c from Mycobacterium tuberculosis

BACKGROUND: It was proposed that there are at least 250 enzymes in M. tuberculosis involved in lipid metabolism. Rv0045c was predicted to be a hydrolase by amino acid sequence similarity, although its precise biochemical characterization and function remained to be defined. METHODOLOGY/PRINCIPAL FINDINGS: We expressed the Rv0045c protein to high levels in E. coli and purified the protein to high purity. We confirmed that the prepared protein was the Rv0045c protein by mass spectrometry analysis. Circular dichroism spectroscopy analysis showed that the protein possessed abundant β-sheet secondary structure, and confirmed that its conformation was stable in the range pH 6.0–10.0 and at temperatures ≤40°C. Enzyme activity analysis indicated that the Rv0045c protein could efficiently hydrolyze short chain p-nitrophenyl esters (C(2)–C(8)), and its suitable substrate was p-nitrophenyl caproate (C(6)) with optimal catalytic conditions of 39°C and pH 8.0. CONCLUSIONS/SIGNIFICANCE: Our results demonstrated that the Rv0045c protein is a novel esterase. These experiments will be helpful in understanding ester/lipid metabolism related to M. tuberculosis.