Part of the ABC transporter complex TcyABC involved in L-cystine import. Responsible for energy coupling to the transport system (Probable). The complex is composed of two ATP-binding proteins (TcyC), two transmembrane proteins (TcyB) and a solute-binding protein (TcyA). Belongs to the ABC transporter superfamily. L-cystine importer (TC 3.A.1.3.14) family.