LipG a bifunctional phospholipase/thioesterase involved in mycobacterial envelope remodeling

Tuberculosis caused by Mycobacterium tuberculosis is currently one of the leading causes of death from an infectious agent. The main difficulties encountered in eradicating this bacteria are mainly related to i) a very complex lipid composition of the bacillus cell wall, ii) its ability to hide from the immune system inside the granulomas, and iii) the increasing number of resistant strains. In this context, we were interested in the Rv0646c ( lipG MTB ) gene located upstream to the mmaA cluster which is described as being crucial for the production of cell-wall components and required for the bacilli adaptation and survival in mouse macrophages . Using biochemical experiments combined with the construction of deletion and overexpression mutant strains in M. smegmatis , we found that LipG MTB is a cytoplasmic membrane-associated enzyme that displays both phospholipase and thioesterase activities. Overproduction of LipG MTB decreases the glycopeptidolipids (GPL) level concomitantly to an increase of phosphatidylinositol (PI) which is the precursor of the phosphatidylinositol mannoside (PIM), an essential lipid component of the bacterial cell wall. Conversely, deletion of the lipG MS gene in M. smegmatis leads to an overproduction of GPL, and subsequently decreases the strain susceptibility to various antibiotics. All these findings demonstrate that LipG is involved in cell-envelope biosynthesis/remodeling, and consequently this enzyme may thus play an important role in mycobacterial physiology.