Delivers copper to copper zinc superoxide dismutase (SOD1). Binds 2 copper ions per subunit. Binds 1 zinc ion per subunit. Homodimer, and heterodimer with SOD1. Interacts with COMMD1 (By similarity). Interacts with XIAP/BIRC4 (By similarity). Ubiquitinion by XIAP/BIRC4 leads to enhancement of its chaperone activity toward its physiologic target, SOD1, rather than proteasomal degradation. XIAP/BIRC4 preferentially ubiquitinates at Lys-241. In the C-terminal section; belongs to the Cu-Zn superoxide dismutase family.