Figure 1. Architecture of the Gram-negative cell envelope.

(A) Diagram showing the four elements of the Gram-negative cell envelope. LPS lipopolysaccharide, PL phospholipid. Note the outer membrane protein depicted in pale pink (B) Chemical structure of membrane glycerophospholipids of Escherichia coli and a molecule of lysophospholipid. (C) Diagram showing the simplified chemical structure of E. coli lipopolysaccharide. Kdo: 3-deoxy-D -manno-octulosonic acid, GlcN: D-glucosamine, sugars are represented as blue or green hexagons, phosphate group depicted as P in red. The acyl chain in cyan represents the palmitate transferred from a PL to the lipid A of a molecule of LPS by PagP, generating a hepta-acylated lipid A.