Mutation of the Lipopolysaccharide Core Glycosyltransferase Encoded by waaG Destabilizes the Outer Membrane of Escherichia coli by Interfering with Core Phosphorylation

In Escherichia coli, phosphoryl substituents in the lipopolysaccharide core region are essential for outer membrane stability. Mutation of the core glucosyltransferase encoded by waaG (formerly rfaG) resulted in lipopolysaccharide truncated immediately after the inner core heptose residues, which serve as the sites for phosphorylation. Surprisingly, mutation of waaG also destabilized the outer membrane. Structural analyses of waaG mutant lipopolysaccharide showed that the cause for this phenotype was a decrease in core phosphorylation, an unexpected side effect of the waaG mutation.