Figure 1. The Raetz pathway of lipid A biosynthesis.
(A) Lipid A biosynthesis in E. coli consists of nine enzymes. The first six enzymes—LpxA, LpxC, LpxD, LpxH, LpxB, and LpxK—colored in pink, are essential. The substitution of the fourth enzyme LpxH in β- and γ-proteobacteria by LpxI in α-proteobacteria and LpxG in Chlamydiae is denoted in green and orange, respectively. The remaining three enzymes—KdtA, LpxL, and LpxM—colored in blue, are not essential, but are important virulence factors. (B) Timeline for the discovery and structural characterization of essential lipid A enzymes.
