Gene Ontology annotation through association of InterPro records with GO terms
Annotation inferences using phylogenetic trees
Combined Automated Annotation using Multiple IEA Methods
Systematic analysis of the twin cx(9)c protein family.
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Systematic survey of the 14 yeast twin Cx9C proteins, which identified Cmc2-Cmc4 (Cmc3 is the protein later renamed Coa4) and showed that their import depends on the Mia40-Erv1 disulfide relay. Most family members are critical for assembly or stability of respiratory chain complexes.
"which we demonstrated to be dependent for import"
Analysis of Leigh syndrome mutations in the yeast SURF1 homolog reveals a new member of the cytochrome oxidase assembly factor family.
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First characterization of yeast Coa4 (renamed from Cmc3). It is a twin CX9C intermembrane space protein associated with the inner membrane. Cells lacking Coa4 have depressed cytochrome c oxidase activity but normal Cox1 maturation and a normal Shy1-stabilized Cox1 assembly intermediate, placing Coa4 downstream of Cox1 synthesis and hemylation.
"Cells lacking Coa4 are depressed in CcO activity but show no impairment in Cox1 maturation or formation of the Shy1-stabilized Cox1 assembly intermediate"
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coa4-null cells have reduced mitochondrial copper content, prompting the suggestion that Coa4 participates in copper routing.
"Cells lacking Coa4 resemble shy1 Δ cells in exhibiting a reduced mitochondrial copper content"
Inaccurately assembled cytochrome c oxidase can lead to oxidative stress-induced growth arrest.
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Respiratory growth of yeast coa4-null cells is rescued by dithiothreitol, glutathione or ascorbate without restoring cytochrome c oxidase assembly, showing that the growth defect is driven by hydrogen peroxide from partially assembled complex IV intermediates. Important caveat when reading respiratory-growth rescue as evidence of restored assembly.
"the presence of the reductants does not suppress these assembly defects and the levels of cytochrome c oxidase remain reduced"
Protein import and oxidative folding in the mitochondrial intermembrane space of intact mammalian cells.
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Study of MIA40/CHCHD4- and ALR-dependent import and oxidative folding in living mammalian cells. Cited by UniProt as the source of both the COA4 mitochondrial localization and the two intramolecular disulfide assignments.
"Oxidation of cysteine residues to disulfides drives import of many proteins into the intermembrane space of mitochondria"
Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context.
A yeast suppressor screen links Coa4 to the mitochondrial copper delivery pathway for cytochrome c oxidase.
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Overexpression of the copper metallochaperone Cox11 restores Cox1 abundance, cytochrome c oxidase assembly and respiration in yeast coa4-null cells, and the rescue requires the copper-coordinating cysteines of Cox11 - establishing that the rescue is restored copper delivery, not suppression of reactive oxygen species.
"cysteine mutants of Cox11 that are incapable of binding copper, failed to rescue the respiratory defect"
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The rescue is unidirectional, placing Coa4 upstream of Cox11 in the copper delivery pathway to the CuB site of Cox1.
"suggests that Coa4 acts upstream of Cox11 in the copper delivery pathway"
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Coa4 is not a copper metallochaperone - it lacks the copper-binding cysteine motif of Cox17, and its deletion phenotype is far milder than that of the bona fide chaperones.
"Importantly, Coa4 lacks the copper-binding cysteine motif that is found in Cox17, further negating its metallochaperone role"
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Human COA4 complements the yeast coa4-null mutant, establishing that the function is evolutionarily conserved and licensing transfer of the yeast mechanism to the human protein.
"we demonstrate that human COA4 can replace the function of yeast Coa4 indicating its evolutionarily conserved role"
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The authors explicitly could not detect a physical Coa4-Cox11 interaction by co-immunoprecipitation/mass spectrometry, leaving the genetic interaction unexplained at the biochemical level. This is the gap closed by the 2026 MitoMatch study using chemical crosslinking.
"Our initial attempts to detect protein:protein interaction between Cox11 and Coa4 via coimmunoprecipitation/mass spectrometry experiments were not successful"
The predicted interactome of the human mitochondrial proteome.
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AlphaFold-Multimer predicted an evolutionarily conserved COA4-COX11 interaction, with intermembrane-space-localized COA4 contacting the IMS-facing domain of COX11. Reciprocal co-immunoprecipitation confirmed it in crosslinked yeast mitochondria (Coa4-V5 recovering Cox11) and in human 293T cells. Critically, COA4-V5 recovered COX11 but not COX1 or COX2, matching the prediction of no direct contact between COA4 and the catalytic subunits.
"we did not recover COX1 and COX2 proteins in our COA4-V5-IP, which"
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CRISPR knockout of COA4 in human MCH58 fibroblasts strikingly reduces COX11 abundance, consistent with a direct COA4-COX11 interaction.
"reduction in COX11 abundance (Fig. 4i). Loss of COA4 also results in"
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COA4 knockout lowers mitochondrial copper content specifically, without affecting other transition metals - an important control, since it distinguishes a copper-pathway defect from general mitochondrial dysfunction.
"reduced mitochondrial copper content without impacting the levels of"
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COA4 knockout drastically and specifically depletes complex IV-containing supercomplexes and reduces respiration. This is the first human loss-of-function characterization of COA4 and the basis for treating mitochondrial respiratory chain complex IV assembly as an experimentally grounded human annotation rather than a purely phylogenetic inference.
"reduction in the levels of complex IV-containing supercomplexes in"