1. Lipopolysaccharide Transport to the Cell Surface: New Insights in Assembly into the Outer Membrane 
Paola Sperandeo, Alessandra Polissi 
Structure 
Volume 24, Issue 6, Pages (June 2016)
DOI: /j.str
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2. Figure 1 LPS Transport to the Cell Surface in Gram-Negative Bacteria
(A) After its synthesis in the cytoplasm and at the inner membrane (IM), LPS is translocated across the IM by the ABC transporter MsbA. The Lpt molecular machinery (LptA-G) then transports LPS across the periplasm and inserts it into the outer membrane (OM) at the expense of ATP hydrolysis. During transport, the lipid portion of lipid A is shielded in the hydrophobic cavity formed by the β-jellyroll structures of LptC and LptA, while the saccharide portion of LPS is exposed into the periplasm. The number of LptA molecules present in the system is not known. Once LPS reaches the LptDE complex in the OM, its saccharide moiety is inserted into the hydrophilic lumen of LptD, while lipid A is retained into the cavity of the β-jellyroll of the N-terminal domain of LptD.
(B) LPS sugar chain is supposed to pass vertically through the β-barrel lumen of LptD. Residues Pro231 and 246 are responsible for weakening the barrel structure between β1 and β26 strands and allow the lateral opening of the gate. Lipid A is inserted directly into the outer leaflet of the OM through an intramembrane hydrophobic hole.
Structure  , DOI: ( /j.str )
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