FIGURE 1.

Structure of LPS and the Lpt complex. (A) The lipopolysaccharide (LPS) molecule consists of three parts: (i) the lipid A moiety, comprising a phosphorylated glucosamine disaccharide linked to saturated acyl chains that insert into the outer membrane (OM); (ii) the core oligosaccharide formed by non-repeating sugar units; and (iii) the O antigen (not depicted), a long oligosaccharide chain that varies highly between species and strains. (B) LPS is extracted from the inner membrane (IM) by the IM complex LptB₂FG and translocated through the hydrophobic cavity of the protein bridge formed by LptC, LptA, and the N-terminal region of LptD. The C-terminal domain of LptD forms the β-barrel that, together with LptE, inserts LPS into the OM.