Biochemical pathway for the biosynthesis of the Cu center in bacterial cytochrome c oxidase.

The di-copper center Cu is an essential metal cofactor in cytochrome oxidase (Cox) of mitochondria and many prokaryotes, mediating one-electron transfer from cytochrome c to the site for oxygen reduction. Cu is located in subunit II (CoxB) of Cox and protrudes into the periplasm of Gram-negative bacteria or the mitochondrial intermembrane space. How the two copper ions are brought together to build CoxB·Cu is the subject of this review. It had been known that the reductase TlpA and the metallochaperones ScoI and PcuC are required for Cu formation in bacteria, but the mechanism of copper transfer has emerged only recently for the Bradyrhizobium diazoefficiens system. It consists of the following steps: (a) TlpA keeps the active site cysteine pair of CoxB in its dithiol state as a prerequisite for metal insertion; (b) ScoI·Cu rapidly forms a transient complex with apo-CoxB; (c) PcuC, loaded with Cu and Cu , dissociates this complex to CoxB·Cu , and a second PcuC·Cu ·Cu transfers Cu to CoxB·Cu , yielding mature CoxB·Cu . Variants of this pathway might exist in other bacteria or mitochondria.