Figure 1.

The LPS export pathway in Gram-negative bacteria. Following flipping across the IM by the ABC transporter MsbA, LPS is extracted from the IM and transported across the periplasm to the OM at the expense of ATP hydrolysis by the transenvelope Lpt protein machine composed, in E. coli, by seven essential proteins (LptA–G). See text for details. Only the lipid A–core moiety is represented, whereas the O-antigen repeat moiety is omitted. PG, peptidoglycan. Inset. the structure of E. coli LPS with a K-12 core region is shown. The lipid A moiety and the core oligosaccharide are indicated in black and orange, respectively. The chemical composition of the O-antigen is not shown. Gal, d-galactose; Glu, d-glucose; Hep, l-glycero-d-manno-heptose; Kdo, 3-deoxy-d-manno-octulosonic acid. n, number of LptA monomers.