Dephosphorylated NPr of the nitrogen PTS regulates lipid A biosynthesis by direct interaction with LpxD

Bacterial phosphoenolpyruvate-dependent phosphotransferase systems (PTS) play multiple roles in addition to sugar transport. Recent studies revealed that enzyme IIA^Ntr of the nitrogen PTS regulates the intracellular concentration of K⁺ by direct interaction with TrkA and KdpD. In this study, we show that dephosphorylated NPr of the nitrogen PTS interacts with Escherichia coli LpxD which catalyzes biosynthesis of lipid A of the lipopolysaccharide (LPS) layer. Mutations in lipid A biosynthetic genes such as lpxD are known to confer hypersensitivity to hydrophobic antibiotics such as rifampin; a ptsO (encoding NPr) deletion mutant showed increased resistance to rifampin and increased LPS biosynthesis. Taken together, our data suggest that unphosphorylated NPr decreases lipid A biosynthesis by inhibiting LpxD activity.