Part of the ABC transporter complex DdpABCDF, which is probably involved in D,D-dipeptide transport (PubMed:9097039). Probably responsible for energy coupling to the transport system. The complex is composed of two ATP-binding proteins (DdpD and DdpF), two transmembrane proteins (DdpB and DdpC) and a solute-binding protein (DdpA). Induced by RpoS in stationary phase. Belongs to the ABC transporter superfamily.