Figure 1: Major lipid components of the E. coli outer membrane.
A) Structure of the three types of phospholipids found in E. coli. The whole-cell phospholipid content of E. coli is 75% phosphatidylethanolamine, 20% phosphatidylglycerol, and 5% cardiolipin.9 Although fatty acid composition can change in response to signals, the major fatty acids in phospholipids under normal growth are 16:0, 16:1, and 18:1.5 B) Structure and main components of E. coli K-12 LPS. Potential modifications of Lipid A and the corresponding modifying enzymes are color coded. PagP cleaves an acyl chain from a phospholipid and ligates it (shown in red) onto Lipid A. PagL deacylates LPS by removing the R-3-hydroxymyristate shown in green. The C1 and C4′ phosphates can be modified with L-4-aminoarabinose (pink) by ArnT and phosphoethanolamine (blue) by EptA, respectively. The core oligosaccharide is composed of glucose (Glu), heptose (Hep), galactose (Gal), and 3-deoxy-d-manno-octulosonic acid (Kdo). Heptose residues are phosphorylated (P) and modified with phosphoethanolamine (PEtN). The numbers represent glycosidic linkage positions. The structure of the highly variable O antigen is not shown.