Inositol acylation of phosphatidylinositol mannosides: a rapid mass response to membrane fluidization in mycobacteria

Abstract

Mycobacteria share an unusually complex, multilayered cell envelope, which contributes to adaptation to changing environments. The plasma membrane is the deepest layer of the cell envelope and acts as the final permeability barrier against outside molecules. There is an obvious need to maintain the plasma membrane integrity, but the adaptive responses of plasma membrane to stress exposure remain poorly understood. Using chemical treatment and heat stress to fluidize the membrane, we show here that phosphatidylinositol (PI)-anchored plasma membrane glycolipids known as PI mannosides (PIMs) rapidly remodel their structures upon membrane fluidization in Mycobacterium smegmatis. Without membrane stress, PIMs are predominantly in a tri-acylated form: two acyl chains of PI moiety plus one acyl chain modified at one of the mannose residues. Upon membrane fluidization, the fourth fatty acid is added to the inositol moiety of PIMs, making them tetra-acylated variants. PIM inositol acylation is a rapid response independent of de novo protein synthesis, representing one of the fastest mass conversions of lipid molecules found in nature. Strikingly, we found that M. smegmatis is more resistant to the bactericidal effect of a cationic detergent after benzyl alcohol preexposure. We further demonstrate that fluidization-induced PIM inositol acylation is conserved in pathogens such as Mycobacterium tuberculosis and Mycobacterium abscessus. Our results demonstrate that mycobacteria possess a mechanism to sense plasma membrane fluidity change. We suggest that inositol acylation of PIMs is a novel membrane stress response that enables mycobacterial cells to resist membrane fluidization.

Genetic and lipidomic identification of tuberculostearic acid as a controller of mycobacterial membrane compartmentalization

“…S4F). This outcome of altered PIM pools after gene deletion matches the separately observed response of PIMs to membrane fluidizers (6,14). Combined, these results, as well as the emergence of cfa from a membrane fluidizer-based screen (Fig.…”

“…We recently reported inositol acylation of PIMs as a response to membrane fluidization conserved in M. tuberculosis (6). Our current study indicates the role of TBSA-containing lipids, which are widely conserved in mycobacteria including M. tuberculosis , in homeoviscous adaptation.…”

“…However, the inner plasma membrane may also contribute to the regulation of the permeability of mycobacterial cellular response (5). Indeed, our recent study suggests that mycobacteria have a rapid stress response mechanism to remodel the plasma membrane after exposure to membrane fluidizing chemicals (6). The main building blocks of the plasma membrane are phospholipids; where cardiolipin, phosphatidylethanolamine (PE), phosphatidylinositol (PI), and PI mannosides (PIMs) are the major phospholipid species.…”