3.A.1.152.9
Lipopolysaccharide transporter that exports LPS from the external surface of the cytoplasmic membrane to the outer membrane, LptB₂FG. The 134-kDa protein complex is unique among ABC transporters because it extracts lipopolysaccharide from the external leaflet of the inner membrane and propels it along a filament that extends across the periplasm to directly deliver lipopolysaccharide into the external leaflet of the outer membrane. Dong et al. 2017 reported the crystal structure of this transporter in which both LptF and LptG are composed of a beta-jellyroll-like periplasmic domain and six TMSs. LptF and LptG together form a central cavity containing highly conserved hydrophobic residues. Structural and functional studies suggest that LptB₂FG uses an alternating lateral access mechanism to extract lipopolysaccharide and traffic it along the hydrophobic cavity toward the transporter's periplasmic domains. The structure has been presented by Dong et al. 2017. LPS transport involves long-ranging bi- directional coupling across cellular compartments between cytoplasmic LptB and periplasmic regions of the Lpt transporter (Lundstedt et al. 2020).