Part of the ABC transporter complex NikABCDE (Opp2) involved in nickel import. Probably responsible for the translocation of the substrate across the membrane. The complex is composed of two ATP-binding proteins (NikD and NikE), two transmembrane proteins (NikB and NikC) and a solute-binding protein (NikA). Belongs to the binding-protein-dependent transport system permease family. OppBC subfamily.