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. Can also mediate weak glycine betaine transport. The complex is composed of two ATP-binding proteins (OpuCA), two transmembrane proteins (OpuCB and OpuCD) and a solute-binding protein (OpuCC). The complex is induced by either hyperosmotic stress or by low temperature. Osmotic induction is sigma B-dependent. Mutants are impaired in both chill-activated and osmotically activated carnitine transport. Belongs to the binding-protein-dependent transport system permease family.