A Monoacylglycerol Lipase from Mycobacterium smegmatis Involved in Bacterial Cell Interaction

Abstract

ABSTRACT MSMEG _ 0220 from Mycobacterium smegmatis , the ortholog of the Rv0183 gene from M. tuberculosis , recently identified and characterized as encoding a monoacylglycerol lipase, was cloned and expressed in Escherichia coli . The recombinant protein (rMSMEG_0220), which exhibits 68% amino acid sequence identity with Rv0183, showed the same substrate specificity and similar patterns of pH-dependent activity and stability as the M. tuberculosis enzyme. rMSMEG_0220 was found to hydrolyze long-chain monoacylglycerol with a specific activity of 143 ± 6 U mg −1 . Like Rv0183 in M. tuberculosis , MSMEG_0220 was found to be located in the cell wall. To assess the in vivo role of the homologous proteins, an MSMEG _ 0220 disrupted mutant of M. smegmatis (MsΔ0220) was produced. An intriguing change in the colony morphology and in the cell interaction, which were partly restored in the complemented mutant containing either an active (ComMsΔ0220) or an inactive (ComMsΔ0220S111A) enzyme, was observed. Growth studies performed in media supplemented with monoolein showed that the ability of both MsΔ0220 and ComMsΔ0220S111A to grow in the presence of this lipid was impaired. Moreover, studies of the antimicrobial susceptibility of the MsΔ0220 strain showed that this mutant is more sensitive to rifampin and more resistant to isoniazid than the wild-type strain, pointing to a critical structural role of this enzyme in mycobacterial physiology, in addition to its function in the hydrolysis of exogenous lipids.