Dependency of sugar transport and phosphorylation by the phosphoenolpyruvate-dependent phosphotransferase system on membranous phosphatidyl glycerol in Escherichia coli: studies with a pgsA mutant lacking phosphatidyl glycerophosphate synthase

Abstract

It has been reported that phosphatidyl glycerol (PG) is specifically required for the in vitro activities of the hexose-phosphorylating Enzymes II of the Escherichia coli phosphoenolpyruvate-dependent sugar transporting phosphotransferase system (PTS). We have examined this possibility by measuring the properties of a null pgsA mutant that lacks detectable PG. The mutant showed lower in vitro phosphorylation activities towards several sugars when both PEP-dependent and sugar-phosphate-dependent [14C]sugar phosphorylation reactions were measured. The order of dependency on PG for the different enzymes II was: IIMannose > IIGlucose > IIFructose > IIMannitol. Nonsedimentable (40000 rpm for 2 h) Enzymes II exhibited a greater dependency on PG than pelletable Enzymes II. Western blot analyses showed that the glucose Enzyme II is present in normal amounts. Transport and fermentation measurements revealed diminished activities for all Enzymes II. Thermal stability of all of these enzymes except the mannitol-specific Enzyme II was significantly decreased by the pgsA mutation, and sensitivity to detergent treatments was enhanced. Sugar transport proved to be the most sensitive indicator of proper Enzyme II-phospholipid association. Our results show that PG stimulates but is not required for Enzyme II function in E. coli.