Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency

Abstract

Mitochondrial respiratory chain biogenesis is orchestrated by hundreds of assembly factors, many of which are yet to be discovered. Using an integrative approach based on clues from evolutionary history, protein localization and human genetics, we have identified a conserved mitochondrial protein, C1orf31/COA6, and shown its requirement for respiratory complex IV biogenesis in yeast, zebrafish and human cells. A recent next-generation sequencing study reported potential pathogenic mutations within the evolutionarily conserved Cx₉CxnCx₁₀C motif of COA6, implicating it in mitochondrial disease biology. Using yeast coa6Δ cells, we show that conserved residues in the motif, including the residue mutated in a patient with mitochondrial disease, are essential for COA6 function, thus confirming the pathogenicity of the patient mutation. Furthermore, we show that zebrafish embryos with zfcoa6 knockdown display reduced heart rate and cardiac developmental defects, recapitulating the observed pathology in the human mitochondrial disease patient who died of neonatal hypertrophic cardiomyopathy. The specific requirement of Coa6 for respiratory complex IV biogenesis, its intramitochondrial localization and the presence of the Cx₉CxnCx₁₀C motif suggested a role in mitochondrial copper metabolism. In support of this, we show that exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells. Taken together, our results establish an evolutionarily conserved role of Coa6 in complex IV assembly and support a causal role of the COA6 mutation in the human mitochondrial disease patient.

Loop recognition and copper-mediated disulfide reduction underpin metal site assembly of Cu A in human cytochrome oxidase

“…The fact that this reaction occurs in the mitochondria strongly suggests that there are other cofactors mediating this process. One possible candidate for this role is protein COA6, recently identified as an essential cofactor for oxidase assembly containing a Cys-rich motif, which was proposed to interact with COX II and Sco2 (43,44).…”

Mitochondrial Proteins Containing Coiled-Coil-Helix-Coiled-Coil-Helix (CHCH) Domains in Health and Disease

“…Mutations in the CIV assembly factor COA5 (the human ortholog of yeast Pet191) 152 [47,52]), which carries a typical (CX 9 C) 2 motif, can give rise to a mitochondrial 153 cardiomyopathy [53]. Mutations in yet another CIV assembly factor, COA6, which contains 154 an unusual cysteine motif [20,54], destabilize the newly synthesized mitochondrial DNA-155 encoded subunit COX2 and lead to neonatal hypertrophic cardiomyopathy [54][55][56][57][58] (Tables 1 156 and 2). 157…”

Human mitochondrial cytochrome c oxidase assembly factor COX18 acts transiently as a membrane insertase within the subunit 2 maturation module

“…The N-tail of newly synthesized COX2 is translocated across the membrane and then stabilized by interaction with COX20 (5), a transmembrane protein found to be mutated in several cases of dystonia-ataxia syndrome (6). Formation of the Cu A center has received major attention because mutations in the SCO1 and SCO2 metallochaperones specific for this function result in severe cardiomyopathies (7)(8)(9). Recently, the twin CX 9 C IMS protein COA6 has been shown to participate in COX2 maturation by interacting with SCO1, SCO2, or both (7,8,10).…”

“…Formation of the Cu A center has received major attention because mutations in the SCO1 and SCO2 metallochaperones specific for this function result in severe cardiomyopathies (7)(8)(9). Recently, the twin CX 9 C IMS protein COA6 has been shown to participate in COX2 maturation by interacting with SCO1, SCO2, or both (7,8,10). Co-immunoprecipitation (co-IP) assays have detected several COX2 stability and maturation modules containing newly synthesized COX2 and COX20-SCO1-SCO2 (5), COA6-SCO2 (11), or COA6-SCO1 (10).…”