Part of the ABC transporter complex GbuABC involved in glycine betaine uptake. Responsible for the translocation of the substrate across the membrane. Involved, with BetL and OpuC, in osmoprotection and cryoprotection of Listeria. Can also uptake carnitine when carnitine is abundant in the growth medium. The complex is activated by an osmotic gradient or by low temperature. The complex is composed of two ATP-binding proteins (GbuA), two transmembrane proteins (GbuB) and a solute-binding protein (GbuC). Belongs to the binding-protein-dependent transport system permease family.