Part of the ABC transporter complex LptBFG involved in the translocation of lipopolysaccharide (LPS) from the inner membrane to the outer membrane. Probably responsible for energy coupling to the transport system (By similarity). Component of the lipopolysaccharide transport and assembly complex. The LptBFG transporter is composed of two ATP-binding proteins (LptB) and two transmembrane proteins (LptF and LptG) (By similarity). Belongs to the ABC transporter superfamily. Outer membrane lipopolysaccharide export (TC 1.B.42) family.