Involved in a high affinity multicomponent binding-protein-dependent transport system for glycine betaine, carnitine and choline; probably responsible for energy coupling to the transport system. The complex is composed of two ATP-binding proteins (OpuCA), two transmembrane proteins (OpuCB and OpuCD) and a solute-binding protein (OpuCC). Repressed by OpcR. Belongs to the ABC transporter superfamily.