Figure 1

(A) Current model for the LPS transport pathway of E. coli. LPS is translocated to the periplasmic side of the IM by the ABC transporter MsbA, extracted from the IM in an ATP-dependent manner by the IM complex LptB₂FG, and pushed through the hydrophobic cavity of the protein bridge formed by the β-jellyroll domains of LptC, LptA, and the N-terminal region of LptD. The number of LptA monomers in the bridge is unclear. The C-terminal domain of LptD forms the β-barrel that, assisted by the OM lipoprotein LptE, inserts LPS into the OM. (B) Model of the head-to-tail LptH dimer obtained by molecular dynamic simulation. The monomers are reported as cyan and green cartoons for the head and tail protomers, respectively. (C) Close view of strands contacts β1–β16, β2–β15 and β13–β16. H-bonds are reported as yellow-dot lines. Arrows highlight the amino acid residues that have been either deleted or replaced in LptH mutant variants: wild-type residues are in black, mutant residues present in LptH variants β1mut, β13mut, β15mut and β16mut are in red (Table 1). The β2mut variant was not obtained and, thus, not tested in this work (see text for details).