Involved in lipopolysaccharide (LPS) biosynthesis. Translocates lipid A-core from the inner to the outer leaflet of the inner membrane. Transmembrane domains (TMD) form a pore in the inner membrane and the ATP-binding domain (NBD) is responsible for energy generation. ATP + H2O + lipid A-core oligosaccharideSide 1 = ADP + phosphate + lipid A-core oligosaccharideSide 2. Homodimer. In MsbA the ATP-binding domain (NBD) and the transmembrane domain (TMD) are fused. Belongs to the ABC transporter superfamily. Lipid exporter (TC 3.A.1.106) family.