Part of the ABC transporter complex OpuCABCD involved in carnitine uptake. Probably responsible for energy coupling to the transport system. Involved, with BetL and GbuABC, in osmoprotection and cryoprotection of Listeria. ATP + H2O + quaternary ammonium(out) = ADP + H(+) + phosphate + quaternary ammonium(in) The complex is composed of two ATP-binding proteins (OpuCA), two transmembrane proteins (OpuCB and OpuCD) and a solute-binding protein (OpuCC). Mutants are impaired for growth at high osmolarity in brain heart infusion broth, fail to grow in a defined medium and show no detectable carnitine uptake. Belongs to the ABC transporter superfamily.