Membrane remodeling capacity of a vesicle‐inducing glycosyltransferase

Abstract

Intracellular vesicles are abundant in eukaryotic cells but absent in the Gram‐negative bacterium E scherichia coli . However, strong overexpression of a monotopic glycolipid‐synthesizing enzyme, monoglucosyldiacylglycerol synthase from A choleplasma laidlawii (al MGS ), leads to massive formation of vesicles in the cytoplasm of E. coli . More importantly, al MGS provides a model system for the regulation of membrane properties by membrane‐bound enzymes, which is critical for maintaining cellular integrity. Both phenomena depend on how al MGS binds to cell membranes, which is not well understood. Here, we carry out a comprehensive investigation of the membrane binding of al MGS by combining bioinformatics methods with extensive biochemical studies, structural modeling and molecular dynamics simulations. We find that al MGS binds to the membrane in a fairly upright manner, mainly by residues in the N‐terminal domain, and in a way that induces local enrichment of anionic lipids and a local curvature deformation. Furthermore, several al MGS variants resulting from substitution of residues in the membrane anchoring segment are still able to generate vesicles, regardless of enzymatic activity. These results clarify earlier theories about the driving forces for vesicle formation, and shed new light on the membrane binding properties and enzymatic mechanism of al MGS and related monotopic GT ‐B fold glycosyltransferases.