Part of the ABC transporter complex LptBFG involved in the translocation of lipopolysaccharide (LPS) from the inner membrane to the outer membrane. 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 LptF/LptG family.