Part of the ABC transporter complex OpuCABCD involved in carnitine uptake. Probably responsible for the translocation of the substrate across the membrane. Involved, with BetL and GbuABC, in osmoprotection and cryoprotection of Listeria. The complex is composed of two ATP-binding proteins (OpuCA), two transmembrane proteins (OpuCB and OpuCD) and a solute-binding protein (OpuCC). Belongs to the binding-protein-dependent transport system permease family.