Expression and biochemical characterization of a patatin-like medium-chain esterase Rv1063c from Mycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis is extremely dependent upon lipid-hydrolyzing enzymes to utilize the resources of host lipids and survive within the cell. Rv1063c is a conserved hypothetical protein predicted to share sequence homology with the patatin-like family. In the present study, the rv1063c gene was cloned and heterologously expressed in Escherichia coli BL21 (DE3). Functional enzyme was obtained by solubilizing inclusion bodies in 8 mol·L −1 urea, refolding via gradient dialysis, and purifying through Ni-affinity chromatography. Bioinformatic homology analysis indicates Rv1063c is homologous to members of the patatin-like family containing a putative Ser52-Asp166 catalytic dyad, though this residue pair has not been experimentally validated in the present study. The recombinant Rv1063c was mainly expressed as inclusion bodies without significant soluble cytoplasmic expression. Biochemical assays demonstrated the recombinant protein exclusively hydrolyzes medium-chain pnitrophenyl esters (C8–12), with maximum hydrolytic activity toward p-NP-C8 (caprylate), followed by C10 and C12, and exhibited the highest activity at 40 °C and pH 7.0. The enzyme exhibited moderate catalytic efficiency but poor thermal stability. All catalytic data in this paper were obtained from artificial p-nitrophenyl ester substrates, which cannot fully reflect natural lipid substrate preference of mycobacteria in vivo. This work biochemically characterizes Rv1063c as a medium-chain-specific esterase encoded by a protein homologous to the patatin superfamily. Its physiological and pathogenic roles remain undetermined, and further multi-level experiments are required to clarify its biological functions.