Characterization and function of Mycobacterium tuberculosis H37Rv Lipase Rv1076 (LipU)

Lipids and lipases/esterases are essential for Mycobacterium tuberculosis (Mtb) survival and persistence, even virulence. Mycobacterium tuberculosis H37Rv Rv1076 (LipU), a member of lipase family, is homologous to the human Hormone Sensitive Lipase (HSL) based on the presence of conserved motif 'GXSXG'. To define the enzymatic characteristics of rv1076, the gene was cloned, and expressed in Escherichia coli. The protein was purified for enzymatic characterization. LipU showed high specific activity for the hydrolysis of short carbon chain substrates with optimal activity at 40 °C/pH 8.0 and stability at low temperature and near-neutral pH. The specific activity, Km and Vmax of LipU was calculated to 176.7 U/mg, 1.73 μM and 62.24 μM/min respectively. Ionic detergents can inhibit its activity. The active-site residues of LipU were determined to be Ser140, Asp244 and His269 by site-directed mutagenesis. The upregulation of Mycobacterium tuberculosis rv1076 under nutritive stress implicates a role in starvation.