Part of the ABC transporter complex NikABCDE (Opp2) involved in nickel import. Binds nickel and transfers it to the membrane-bound permease. Required for full urease activity and plays a significant role in the virulence of S.aureus during urinary tract infection (UTI) (PubMed:20662775). May bind nickel via a nickel-chelator (PubMed:25611161). The complex is composed of two ATP-binding proteins (NikD and NikE), two transmembrane proteins (NikB and NikC) and a solute-binding protein (NikA). Induced in response to decrease in pH and as a function of growth phase. Deletion of the gene strongly reduces nickel transport and urease activity. Mutant shows decreased virulence in a mouse model of ascending UTI. Nickel accumulation and urease activity are almost completely abolished in a nixA-nikA double mutant. Belongs to the bacterial solute-binding protein 5 family. Truncated N-terminus.