Multicopper oxidase involved in copper homeostasis and copper tolerance under both aerobic and anaerobic conditions (PubMed:12442888, PubMed:17768242). Is responsible for the oxidation of Cu(+) to the less harmful Cu(2+) in the periplasm, thereby preventing Cu(+) from entering the cytoplasm (By similarity). 4 Cu(+) + 4 H(+) + O2 = 4 Cu(2+) + 2 H2O Binds 4 Cu cations per monomer. Monomer. By CueR, at increased levels of cytoplasmic cuprous ions. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has not been experimentally proven. Mutant is very sensitive to copper after copper shock (PubMed:12442888). Causes a moderate defect in aerobic growth on CuSO(4), strongly impairs survival during anaerobic growth on CuSO(4) (PubMed:17768242). Belongs to the multicopper oxidase family.