Coordination of metal center biogenesis in human cytochrome c oxidase

Mitochondrial cytochrome c oxidase (CcO) or respiratory chain complex IV is a heme aa₃-copper oxygen reductase containing metal centers essential for holo-complex biogenesis and enzymatic function that are assembled by subunit-specific metallochaperones. The enzyme has two copper sites located in the catalytic core subunits. The COX1 subunit harbors the Cu_B site that tightly associates with heme a₃ while the COX2 subunit contains the binuclear Cu_A site. Here, we report that in human cells the CcO copper chaperones form macromolecular assemblies and cooperate with several twin CX₉C proteins to control heme a biosynthesis and coordinate copper transfer sequentially to the Cu_A and Cu_B sites. These data on CcO illustrate a mechanism that regulates the biogenesis of macromolecular enzymatic assemblies with several catalytic metal redox centers and prevents the accumulation of cytotoxic reactive assembly intermediates.