Abstact

Lipopolysaccharide (LPS) is an essential component of the outer membrane (OM) in most Gram-negative bacteria. LPS transport from the inner membrane (IM) to the OM is achieved by seven lipopolysaccharide transport proteins (LptA-G). LptB2FG, an type VI ATP-binding cassette (ABC) transporter, forms a stable complex with LptC, extracts LPS from the IM and powers LPS transport to the OM. Here we report the cryo-EM structures of LptB2FG and LptB2FGC from Klebsiella pneumoniae in complex with LPS. The KpLptB2FG-LPS structure provides detailed interactions between LPS and the transporter, while the KpLptB2FGC-LPS structure may represent an intermediate state that the transmembrane helix of LptC has not been fully inserted into the transmembrane domains of LptB2FG.