{"gene":"COA6","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2014,"finding":"COA6 (C1orf31) is required for respiratory complex IV (cytochrome c oxidase) biogenesis. Loss of COA6 in yeast, zebrafish, and human cells causes complex IV assembly defects. Conserved cysteine residues in the Cx9CxnCx10C motif are essential for COA6 function. Exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells, establishing a role in mitochondrial copper metabolism.","method":"Yeast genetic deletion (coa6Δ), site-directed mutagenesis of conserved motif residues, zebrafish morpholino knockdown, copper supplementation rescue assay, evolutionary and localization analysis","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal model systems (yeast, zebrafish, human cells), mutagenesis of conserved residues, chemical rescue with copper, replicated across organisms","pmids":["24549041"],"is_preprint":false},{"year":2015,"finding":"COA6 is specifically required for biogenesis of the copper-bound mtDNA-encoded subunit COX2. Loss of COA6 (by CRISPR gene editing in HEK293T cells) impairs COX2 maturation and causes accumulation of complex IV assembly intermediates. COA6 can bind copper and physically associates with newly translated COX2 and the mitochondrial copper chaperone SCO1. A pathogenic W59C mutation does not prevent mitochondrial import of COA6 but impairs its maturation and stability.","method":"CRISPR/Cas9 gene editing in HEK293T cells, growth assays, pulldown/co-immunoprecipitation with COX2 and SCO1, copper-binding assay, pulse-chase analysis, import assay","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, gene editing KO, copper-binding biochemistry, multiple orthogonal methods in one study","pmids":["26160915"],"is_preprint":false},{"year":2015,"finding":"COA6 interacts transiently with the copper-containing catalytic domain of newly synthesized COX2 and with the copper metallochaperone SCO2. COA6 and SCO2 interact physically, and pathogenic mutations in each protein disrupt this complex formation. COA6 deficiency causes rapid turnover of newly synthesized COX2, defining COA6 as a constituent of the mitochondrial copper relay system for COX2 metallation.","method":"Co-immunoprecipitation, pulse-chase analysis of COX2 synthesis/turnover, analysis of pathogenic mutation effects on COA6-SCO2 complex formation","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, pulse-chase, disease mutation validation, multiple orthogonal approaches","pmids":["25959673"],"is_preprint":false},{"year":2014,"finding":"In patient fibroblasts with undetectable COA6 protein, steady-state levels of complex IV and several of its subunits are reduced, monomeric COX1 assembly intermediate accumulates, and there is increased turnover of mitochondrially encoded complex IV subunits. CI/CIII2/CIVn supercomplexes remain unaffected. Copper supplementation partially rescues complex IV deficiency in patient fibroblasts.","method":"Patient fibroblast characterization, western blot for complex IV subunits and assembly intermediates, BN-PAGE for supercomplexes, pulse-chase for subunit turnover, copper supplementation rescue","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient-derived material with multiple biochemical readouts, single lab","pmids":["25339201"],"is_preprint":false},{"year":2015,"finding":"Genetic epistasis in yeast shows that simultaneous deletion of Coa6 and Sco2, or Coa6 and Cox12 (COX6B), completely abrogates Cox2 biogenesis. Copper supplementation fails to rescue Cox2 in these double mutants. Overexpression of Cox12 or Sco proteins partially rescues coa6Δ, indicating overlapping but non-redundant roles in copper delivery to Cox2. Patient mutations in Coa6 disrupt Coa6-Cox2 physical interaction, providing biochemical basis for disease pathogenesis. Physical interactions between Coa6, Cox2, Cox12, and Sco proteins were demonstrated biochemically.","method":"Yeast double-deletion genetic epistasis, copper supplementation rescue, overexpression suppression, co-immunoprecipitation/pulldown between Coa6, Cox2, Cox12, Sco proteins","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — comprehensive genetic epistasis with biochemical validation, multiple interaction partners tested, disease mutations functionally validated","pmids":["26669719"],"is_preprint":false},{"year":2019,"finding":"Solution NMR structure of COA6 reveals a coiled-coil-helix-coiled-coil-helix (CHCH) domain typical of redox-active IMS proteins. COA6 can reduce copper-coordinating disulfides of its client proteins SCO1 and COX2, enabling copper binding. Interaction surfaces and reduction potentials of COA6 and its client proteins were determined, supporting a mechanism where COA6 acts as a disulfide reductase to facilitate copper delivery to cytochrome c oxidase.","method":"Solution NMR structure determination, thiol-disulfide oxidoreductase activity assay, reduction potential measurements, interaction surface mapping","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure with functional validation (enzyme activity assay, reduction potentials, interaction mapping) in one rigorous study","pmids":["31851937"],"is_preprint":false},{"year":2019,"finding":"Crystal structures of human COA6 and the pathogenic W59C mutant protein were solved. COA6 adopts a 3-helical bundle structure with the first two helices tethered by disulfide bonds; one disulfide likely provides the copper-binding site. The W59C pathogenic mutant undergoes disulfide-mediated oligomerization, providing a structural explanation for its loss-of-function.","method":"X-ray crystallography of wild-type and W59C COA6","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of wild-type and disease mutant, structural basis for loss-of-function established, single lab","pmids":["31515291"],"is_preprint":false},{"year":2020,"finding":"COA6 acts as a thiol-reductase to reduce disulfide bridges on critical cysteine residues in SCO1 and SCO2, which is required for CuA center formation in COX2. Cysteines within the CX3CXNH domain of SCO2 mediate its interaction with COA6 but are dispensable for SCO2-SCO1 interaction. Loss of COA6 causes combined complex I and complex IV deficiency and impairs membrane potential-driven protein transport across the inner mitochondrial membrane.","method":"Biochemical thiol-reductase activity assays, domain mutagenesis (SCO2 CX3CXNH cysteines), co-immunoprecipitation, assessment of mitochondrial membrane potential and protein import","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical enzyme activity assays, domain mutagenesis, multiple readouts, orthogonal methods in one study","pmids":["32061935"],"is_preprint":false},{"year":2025,"finding":"COA6 physically interacts with NDUFA4L2 in hepatocellular carcinoma cells (by Co-IP). COA6 deficiency promotes ROS accumulation and activates cuproptosis in HCC cells and blocks the JAK-STAT signaling pathway.","method":"Co-immunoprecipitation (COA6 with NDUFA4L2), siRNA knockdown, ROS assay, western blot for JAK-STAT pathway components, in vivo xenograft","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP for NDUFA4L2 interaction, JAK-STAT pathway link is downstream inference with limited mechanistic depth, single lab","pmids":["41015250"],"is_preprint":false},{"year":2026,"finding":"CoQ10 directly binds to COA6 (Coa6) as identified by drug-target engagement approaches. Viral vector-mediated overexpression of Coa6 in Purkinje cells partially recapitulates CoQ10-associated improvements in respiratory chain complex levels and working memory in PC-Drp1-/- mice; Coa6 knockdown attenuates these CoQ10 benefits, placing Coa6 as a direct molecular target through which CoQ10 enhances mitochondrial respiratory chain function.","method":"Drug-target engagement assay (CoQ10-COA6 binding), viral vector-mediated Coa6 overexpression and knockdown in Purkinje cells, respiratory chain complex activity assays, behavioral testing (eight-arm radial maze)","journal":"Translational neurodegeneration","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding assay plus in vivo genetic rescue/knockdown, but single lab with limited mechanistic detail in abstract","pmids":["42036720"],"is_preprint":false}],"current_model":"COA6 is a mitochondrial intermembrane space protein with a CHCH/twin CX9C domain that functions as a thiol-disulfide oxidoreductase, reducing disulfide bonds on SCO1, SCO2, and COX2 to facilitate copper loading into the CuA site of cytochrome c oxidase (complex IV); it physically interacts with COX2, SCO1, SCO2, and COX6B (Cox12) within the mitochondrial copper relay pathway, and loss of COA6 impairs COX2 maturation and complex IV assembly, causing cardiomyopathy in humans."},"narrative":{"mechanistic_narrative":"COA6 is a mitochondrial intermembrane space protein that functions in the copper relay pathway required for biogenesis of cytochrome c oxidase (complex IV) [PMID:24549041]. Its conserved twin Cx9C cysteine motif folds into a CHCH/3-helical bundle domain typical of redox-active IMS proteins, with intramolecular disulfides that create a copper-binding site [PMID:31851937, PMID:31515291]. COA6 acts as a thiol-disulfide oxidoreductase, reducing copper-coordinating disulfides on its client proteins SCO1, SCO2, and the mtDNA-encoded subunit COX2 to enable formation of the CuA center [PMID:31851937, PMID:32061935]. Mechanistically, it associates physically with newly synthesized COX2, the copper metallochaperones SCO1 and SCO2, and COX6B/Cox12, and yeast epistasis defines these as overlapping but non-redundant partners in delivering copper to COX2 [PMID:26160915, PMID:25959673, PMID:26669719]. Loss of COA6 destabilizes nascent COX2, blocks complex IV assembly, and the requirement for copper is shown by copper supplementation rescuing the assembly defect [PMID:24549041, PMID:25339201]. Pathogenic COA6 mutations, including W59C, retain mitochondrial import but disrupt protein maturation, client interactions, and complex IV assembly, providing the biochemical basis for COA6-associated human disease [PMID:26160915, PMID:26669719, PMID:31515291].","teleology":[{"year":2014,"claim":"Established COA6 as a conserved factor required for complex IV biogenesis and linked it specifically to mitochondrial copper metabolism, answering what cellular process COA6 serves.","evidence":"Yeast deletion, conserved-motif mutagenesis, zebrafish knockdown, and copper-supplementation rescue across model systems","pmids":["24549041"],"confidence":"High","gaps":["Did not define the direct molecular client or enzymatic activity","Mechanism of copper handling left unresolved"]},{"year":2014,"claim":"Showed in patient material that COA6 loss reduces complex IV, accumulates assembly intermediates, and accelerates turnover of mtDNA-encoded subunits, establishing the disease-relevant assembly defect.","evidence":"Patient fibroblast characterization, BN-PAGE, pulse-chase, and copper-supplementation rescue","pmids":["25339201"],"confidence":"Medium","gaps":["Single lab, patient-derived material only","Did not identify direct binding partners"]},{"year":2015,"claim":"Identified COX2, SCO1, and SCO2 as physical partners and showed COA6 binds copper, defining it as a constituent of the copper relay for COX2 metallation.","evidence":"CRISPR KO in HEK293T, reciprocal Co-IP, copper-binding and pulse-chase assays across two studies","pmids":["26160915","25959673"],"confidence":"High","gaps":["The catalytic mechanism (reductase vs. carrier) was not yet established","Stoichiometry and order of copper transfer unresolved"]},{"year":2015,"claim":"Genetic epistasis defined COA6, SCO2, and Cox12/COX6B as overlapping but non-redundant in copper delivery to Cox2 and tied patient mutations to disrupted COA6-Cox2 binding.","evidence":"Yeast double-deletion epistasis, overexpression suppression, and biochemical interaction mapping among Coa6, Cox2, Cox12, Sco proteins","pmids":["26669719"],"confidence":"High","gaps":["Did not resolve the biochemical activity underlying copper delivery","Functional hierarchy of the partners not fully ordered"]},{"year":2019,"claim":"Structural determination revealed the CHCH/3-helix-bundle fold with disulfides forming a copper-binding site and explained W59C loss-of-function via aberrant disulfide oligomerization.","evidence":"Solution NMR and X-ray crystallography of wild-type and W59C COA6, with reduction-potential and interaction-surface measurements","pmids":["31851937","31515291"],"confidence":"High","gaps":["Structures of COA6-client complexes not solved","In vivo redox cycling/regeneration of COA6 not defined"]},{"year":2020,"claim":"Demonstrated COA6 acts as a thiol-reductase reducing SCO1/SCO2 disulfides required for CuA formation, and linked its loss to combined complex I/IV deficiency and impaired inner-membrane protein transport.","evidence":"Biochemical thiol-reductase assays, SCO2 CX3CXNH domain mutagenesis, Co-IP, and membrane-potential/import assessment","pmids":["32061935"],"confidence":"High","gaps":["Source of reducing equivalents that regenerate COA6 not identified","Mechanism linking COA6 loss to complex I deficiency not fully explained"]},{"year":2025,"claim":"Extended COA6 beyond copper relay to a cancer context, reporting an NDUFA4L2 interaction and effects on ROS, cuproptosis, and JAK-STAT signaling in HCC.","evidence":"Single Co-IP, siRNA knockdown, ROS assay, and xenograft in hepatocellular carcinoma cells","pmids":["41015250"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation for NDUFA4L2","JAK-STAT link is downstream inference with limited mechanistic depth"]},{"year":2026,"claim":"Identified COA6 as a direct CoQ10-binding target through which CoQ10 improves respiratory chain function and behavior in a neurodegeneration model.","evidence":"Drug-target engagement binding assay, viral Coa6 overexpression/knockdown in Purkinje cells, respiratory assays, and behavioral testing in PC-Drp1-/- mice","pmids":["42036720"],"confidence":"Medium","gaps":["Single lab with limited mechanistic detail","Structural basis and functional consequence of CoQ10 binding to COA6 undefined"]},{"year":null,"claim":"The physiological electron donor that regenerates reduced COA6 and the structural basis of COA6-client copper handoff remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No defined upstream reductant for COA6 redox cycling","No solved COA6-SCO/COX2 complex structure","Mechanism connecting COA6 to complex I and to membrane-potential-driven import not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[5,7]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5,7]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[1,5]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,4]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1]}],"complexes":[],"partners":["COX2","SCO1","SCO2","COX6B","NDUFA4L2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5JTJ3","full_name":"Cytochrome c oxidase assembly factor 6 homolog","aliases":[],"length_aa":125,"mass_kda":14.1,"function":"Involved in the maturation of the mitochondrial respiratory chain complex IV subunit MT-CO2/COX2. Thereby, may regulate early steps of complex IV assembly. Mitochondrial respiratory chain complex IV or cytochrome c oxidase is the component of the respiratory chain that catalyzes the transfer of electrons from intermembrane space cytochrome c to molecular oxygen in the matrix and as a consequence contributes to the proton gradient involved in mitochondrial ATP synthesis. May also be required for efficient formation of respiratory supercomplexes comprised of complexes III and IV","subcellular_location":"Mitochondrion intermembrane space","url":"https://www.uniprot.org/uniprotkb/Q5JTJ3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/COA6","classification":"Not Classified","n_dependent_lines":382,"n_total_lines":1208,"dependency_fraction":0.3162251655629139},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/COA6","total_profiled":1310},"omim":[{"mim_id":"618064","title":"CYTOCHROME c OXIDASE ASSEMBLY FACTOR 16; COX16","url":"https://www.omim.org/entry/618064"},{"mim_id":"616501","title":"MITOCHONDRIAL COMPLEX IV DEFICIENCY, NUCLEAR TYPE 13; MC4DN13","url":"https://www.omim.org/entry/616501"},{"mim_id":"614772","title":"CYTOCHROME c OXIDASE ASSEMBLY FACTOR 6; COA6","url":"https://www.omim.org/entry/614772"},{"mim_id":"220110","title":"MITOCHONDRIAL COMPLEX IV DEFICIENCY, NUCLEAR TYPE 1; MC4DN1","url":"https://www.omim.org/entry/220110"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/COA6"},"hgnc":{"alias_symbol":[],"prev_symbol":["C1orf31"]},"alphafold":{"accession":"Q5JTJ3","domains":[{"cath_id":"-","chopping":"51-112","consensus_level":"high","plddt":94.3153,"start":51,"end":112}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5JTJ3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5JTJ3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5JTJ3-F1-predicted_aligned_error_v6.png","plddt_mean":77.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=COA6","jax_strain_url":"https://www.jax.org/strain/search?query=COA6"},"sequence":{"accession":"Q5JTJ3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5JTJ3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5JTJ3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5JTJ3"}},"corpus_meta":[{"pmid":"24549041","id":"PMC_24549041","title":"Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency.","date":"2014","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24549041","citation_count":99,"is_preprint":false},{"pmid":"26160915","id":"PMC_26160915","title":"COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2.","date":"2015","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/26160915","citation_count":89,"is_preprint":false},{"pmid":"25959673","id":"PMC_25959673","title":"Cooperation between COA6 and SCO2 in COX2 maturation during cytochrome c oxidase assembly links two mitochondrial cardiomyopathies.","date":"2015","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/25959673","citation_count":74,"is_preprint":false},{"pmid":"25339201","id":"PMC_25339201","title":"Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.","date":"2014","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/25339201","citation_count":67,"is_preprint":false},{"pmid":"31851937","id":"PMC_31851937","title":"COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.","date":"2019","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/31851937","citation_count":45,"is_preprint":false},{"pmid":"26669719","id":"PMC_26669719","title":"Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis.","date":"2015","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/26669719","citation_count":44,"is_preprint":false},{"pmid":"32061935","id":"PMC_32061935","title":"COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.","date":"2020","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/32061935","citation_count":42,"is_preprint":false},{"pmid":"35053273","id":"PMC_35053273","title":"The Role of COA6 in the Mitochondrial Copper Delivery Pathway to Cytochrome c Oxidase.","date":"2022","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/35053273","citation_count":38,"is_preprint":false},{"pmid":"31515291","id":"PMC_31515291","title":"Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6.","date":"2019","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/31515291","citation_count":19,"is_preprint":false},{"pmid":"32977416","id":"PMC_32977416","title":"What Role Does COA6 Play in Cytochrome C Oxidase Biogenesis: A Metallochaperone or Thiol Oxidoreductase, or Both?","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32977416","citation_count":18,"is_preprint":false},{"pmid":"40596639","id":"PMC_40596639","title":"The Key Role of COA6 in Pancreatic Ductal Adenocarcinoma: Metabolic Reprogramming and Regulation of the Immune Microenvironment.","date":"2025","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40596639","citation_count":9,"is_preprint":false},{"pmid":"39132153","id":"PMC_39132153","title":"COA6 promotes the oncogenesis and progression of breast cancer by oxidative phosphorylation pathway.","date":"2024","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/39132153","citation_count":4,"is_preprint":false},{"pmid":"41015250","id":"PMC_41015250","title":"COA6 deficiency inhibits hepatocellular carcinoma progression by regulating cuproptosis through the JAK/STAT signaling pathway.","date":"2025","source":"Biochimica et biophysica acta. Molecular cell research","url":"https://pubmed.ncbi.nlm.nih.gov/41015250","citation_count":0,"is_preprint":false},{"pmid":"42036720","id":"PMC_42036720","title":"The Drp1-CoQ10-Coa6-ETC axis represents a therapeutic potential for working memory impairment caused by neuronal mitochondrial dysfunction.","date":"2026","source":"Translational neurodegeneration","url":"https://pubmed.ncbi.nlm.nih.gov/42036720","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8377,"output_tokens":2858,"usd":0.034001,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10239,"output_tokens":2818,"usd":0.060823,"stage2_stop_reason":"end_turn"},"total_usd":0.094824,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"COA6 (C1orf31) is required for respiratory complex IV (cytochrome c oxidase) biogenesis. Loss of COA6 in yeast, zebrafish, and human cells causes complex IV assembly defects. Conserved cysteine residues in the Cx9CxnCx10C motif are essential for COA6 function. Exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells, establishing a role in mitochondrial copper metabolism.\",\n      \"method\": \"Yeast genetic deletion (coa6Δ), site-directed mutagenesis of conserved motif residues, zebrafish morpholino knockdown, copper supplementation rescue assay, evolutionary and localization analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal model systems (yeast, zebrafish, human cells), mutagenesis of conserved residues, chemical rescue with copper, replicated across organisms\",\n      \"pmids\": [\"24549041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"COA6 is specifically required for biogenesis of the copper-bound mtDNA-encoded subunit COX2. Loss of COA6 (by CRISPR gene editing in HEK293T cells) impairs COX2 maturation and causes accumulation of complex IV assembly intermediates. COA6 can bind copper and physically associates with newly translated COX2 and the mitochondrial copper chaperone SCO1. A pathogenic W59C mutation does not prevent mitochondrial import of COA6 but impairs its maturation and stability.\",\n      \"method\": \"CRISPR/Cas9 gene editing in HEK293T cells, growth assays, pulldown/co-immunoprecipitation with COX2 and SCO1, copper-binding assay, pulse-chase analysis, import assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, gene editing KO, copper-binding biochemistry, multiple orthogonal methods in one study\",\n      \"pmids\": [\"26160915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"COA6 interacts transiently with the copper-containing catalytic domain of newly synthesized COX2 and with the copper metallochaperone SCO2. COA6 and SCO2 interact physically, and pathogenic mutations in each protein disrupt this complex formation. COA6 deficiency causes rapid turnover of newly synthesized COX2, defining COA6 as a constituent of the mitochondrial copper relay system for COX2 metallation.\",\n      \"method\": \"Co-immunoprecipitation, pulse-chase analysis of COX2 synthesis/turnover, analysis of pathogenic mutation effects on COA6-SCO2 complex formation\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, pulse-chase, disease mutation validation, multiple orthogonal approaches\",\n      \"pmids\": [\"25959673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In patient fibroblasts with undetectable COA6 protein, steady-state levels of complex IV and several of its subunits are reduced, monomeric COX1 assembly intermediate accumulates, and there is increased turnover of mitochondrially encoded complex IV subunits. CI/CIII2/CIVn supercomplexes remain unaffected. Copper supplementation partially rescues complex IV deficiency in patient fibroblasts.\",\n      \"method\": \"Patient fibroblast characterization, western blot for complex IV subunits and assembly intermediates, BN-PAGE for supercomplexes, pulse-chase for subunit turnover, copper supplementation rescue\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient-derived material with multiple biochemical readouts, single lab\",\n      \"pmids\": [\"25339201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Genetic epistasis in yeast shows that simultaneous deletion of Coa6 and Sco2, or Coa6 and Cox12 (COX6B), completely abrogates Cox2 biogenesis. Copper supplementation fails to rescue Cox2 in these double mutants. Overexpression of Cox12 or Sco proteins partially rescues coa6Δ, indicating overlapping but non-redundant roles in copper delivery to Cox2. Patient mutations in Coa6 disrupt Coa6-Cox2 physical interaction, providing biochemical basis for disease pathogenesis. Physical interactions between Coa6, Cox2, Cox12, and Sco proteins were demonstrated biochemically.\",\n      \"method\": \"Yeast double-deletion genetic epistasis, copper supplementation rescue, overexpression suppression, co-immunoprecipitation/pulldown between Coa6, Cox2, Cox12, Sco proteins\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — comprehensive genetic epistasis with biochemical validation, multiple interaction partners tested, disease mutations functionally validated\",\n      \"pmids\": [\"26669719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Solution NMR structure of COA6 reveals a coiled-coil-helix-coiled-coil-helix (CHCH) domain typical of redox-active IMS proteins. COA6 can reduce copper-coordinating disulfides of its client proteins SCO1 and COX2, enabling copper binding. Interaction surfaces and reduction potentials of COA6 and its client proteins were determined, supporting a mechanism where COA6 acts as a disulfide reductase to facilitate copper delivery to cytochrome c oxidase.\",\n      \"method\": \"Solution NMR structure determination, thiol-disulfide oxidoreductase activity assay, reduction potential measurements, interaction surface mapping\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure with functional validation (enzyme activity assay, reduction potentials, interaction mapping) in one rigorous study\",\n      \"pmids\": [\"31851937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structures of human COA6 and the pathogenic W59C mutant protein were solved. COA6 adopts a 3-helical bundle structure with the first two helices tethered by disulfide bonds; one disulfide likely provides the copper-binding site. The W59C pathogenic mutant undergoes disulfide-mediated oligomerization, providing a structural explanation for its loss-of-function.\",\n      \"method\": \"X-ray crystallography of wild-type and W59C COA6\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of wild-type and disease mutant, structural basis for loss-of-function established, single lab\",\n      \"pmids\": [\"31515291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"COA6 acts as a thiol-reductase to reduce disulfide bridges on critical cysteine residues in SCO1 and SCO2, which is required for CuA center formation in COX2. Cysteines within the CX3CXNH domain of SCO2 mediate its interaction with COA6 but are dispensable for SCO2-SCO1 interaction. Loss of COA6 causes combined complex I and complex IV deficiency and impairs membrane potential-driven protein transport across the inner mitochondrial membrane.\",\n      \"method\": \"Biochemical thiol-reductase activity assays, domain mutagenesis (SCO2 CX3CXNH cysteines), co-immunoprecipitation, assessment of mitochondrial membrane potential and protein import\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical enzyme activity assays, domain mutagenesis, multiple readouts, orthogonal methods in one study\",\n      \"pmids\": [\"32061935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"COA6 physically interacts with NDUFA4L2 in hepatocellular carcinoma cells (by Co-IP). COA6 deficiency promotes ROS accumulation and activates cuproptosis in HCC cells and blocks the JAK-STAT signaling pathway.\",\n      \"method\": \"Co-immunoprecipitation (COA6 with NDUFA4L2), siRNA knockdown, ROS assay, western blot for JAK-STAT pathway components, in vivo xenograft\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP for NDUFA4L2 interaction, JAK-STAT pathway link is downstream inference with limited mechanistic depth, single lab\",\n      \"pmids\": [\"41015250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CoQ10 directly binds to COA6 (Coa6) as identified by drug-target engagement approaches. Viral vector-mediated overexpression of Coa6 in Purkinje cells partially recapitulates CoQ10-associated improvements in respiratory chain complex levels and working memory in PC-Drp1-/- mice; Coa6 knockdown attenuates these CoQ10 benefits, placing Coa6 as a direct molecular target through which CoQ10 enhances mitochondrial respiratory chain function.\",\n      \"method\": \"Drug-target engagement assay (CoQ10-COA6 binding), viral vector-mediated Coa6 overexpression and knockdown in Purkinje cells, respiratory chain complex activity assays, behavioral testing (eight-arm radial maze)\",\n      \"journal\": \"Translational neurodegeneration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding assay plus in vivo genetic rescue/knockdown, but single lab with limited mechanistic detail in abstract\",\n      \"pmids\": [\"42036720\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"COA6 is a mitochondrial intermembrane space protein with a CHCH/twin CX9C domain that functions as a thiol-disulfide oxidoreductase, reducing disulfide bonds on SCO1, SCO2, and COX2 to facilitate copper loading into the CuA site of cytochrome c oxidase (complex IV); it physically interacts with COX2, SCO1, SCO2, and COX6B (Cox12) within the mitochondrial copper relay pathway, and loss of COA6 impairs COX2 maturation and complex IV assembly, causing cardiomyopathy in humans.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"COA6 is a mitochondrial intermembrane space protein that functions in the copper relay pathway required for biogenesis of cytochrome c oxidase (complex IV) [#0]. Its conserved twin Cx9C cysteine motif folds into a CHCH/3-helical bundle domain typical of redox-active IMS proteins, with intramolecular disulfides that create a copper-binding site [#5, #6]. COA6 acts as a thiol-disulfide oxidoreductase, reducing copper-coordinating disulfides on its client proteins SCO1, SCO2, and the mtDNA-encoded subunit COX2 to enable formation of the CuA center [#5, #7]. Mechanistically, it associates physically with newly synthesized COX2, the copper metallochaperones SCO1 and SCO2, and COX6B/Cox12, and yeast epistasis defines these as overlapping but non-redundant partners in delivering copper to COX2 [#1, #2, #4]. Loss of COA6 destabilizes nascent COX2, blocks complex IV assembly, and the requirement for copper is shown by copper supplementation rescuing the assembly defect [#0, #3]. Pathogenic COA6 mutations, including W59C, retain mitochondrial import but disrupt protein maturation, client interactions, and complex IV assembly, providing the biochemical basis for COA6-associated human disease [#1, #4, #6].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established COA6 as a conserved factor required for complex IV biogenesis and linked it specifically to mitochondrial copper metabolism, answering what cellular process COA6 serves.\",\n      \"evidence\": \"Yeast deletion, conserved-motif mutagenesis, zebrafish knockdown, and copper-supplementation rescue across model systems\",\n      \"pmids\": [\"24549041\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the direct molecular client or enzymatic activity\", \"Mechanism of copper handling left unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed in patient material that COA6 loss reduces complex IV, accumulates assembly intermediates, and accelerates turnover of mtDNA-encoded subunits, establishing the disease-relevant assembly defect.\",\n      \"evidence\": \"Patient fibroblast characterization, BN-PAGE, pulse-chase, and copper-supplementation rescue\",\n      \"pmids\": [\"25339201\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, patient-derived material only\", \"Did not identify direct binding partners\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified COX2, SCO1, and SCO2 as physical partners and showed COA6 binds copper, defining it as a constituent of the copper relay for COX2 metallation.\",\n      \"evidence\": \"CRISPR KO in HEK293T, reciprocal Co-IP, copper-binding and pulse-chase assays across two studies\",\n      \"pmids\": [\"26160915\", \"25959673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The catalytic mechanism (reductase vs. carrier) was not yet established\", \"Stoichiometry and order of copper transfer unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Genetic epistasis defined COA6, SCO2, and Cox12/COX6B as overlapping but non-redundant in copper delivery to Cox2 and tied patient mutations to disrupted COA6-Cox2 binding.\",\n      \"evidence\": \"Yeast double-deletion epistasis, overexpression suppression, and biochemical interaction mapping among Coa6, Cox2, Cox12, Sco proteins\",\n      \"pmids\": [\"26669719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the biochemical activity underlying copper delivery\", \"Functional hierarchy of the partners not fully ordered\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Structural determination revealed the CHCH/3-helix-bundle fold with disulfides forming a copper-binding site and explained W59C loss-of-function via aberrant disulfide oligomerization.\",\n      \"evidence\": \"Solution NMR and X-ray crystallography of wild-type and W59C COA6, with reduction-potential and interaction-surface measurements\",\n      \"pmids\": [\"31851937\", \"31515291\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of COA6-client complexes not solved\", \"In vivo redox cycling/regeneration of COA6 not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated COA6 acts as a thiol-reductase reducing SCO1/SCO2 disulfides required for CuA formation, and linked its loss to combined complex I/IV deficiency and impaired inner-membrane protein transport.\",\n      \"evidence\": \"Biochemical thiol-reductase assays, SCO2 CX3CXNH domain mutagenesis, Co-IP, and membrane-potential/import assessment\",\n      \"pmids\": [\"32061935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source of reducing equivalents that regenerate COA6 not identified\", \"Mechanism linking COA6 loss to complex I deficiency not fully explained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended COA6 beyond copper relay to a cancer context, reporting an NDUFA4L2 interaction and effects on ROS, cuproptosis, and JAK-STAT signaling in HCC.\",\n      \"evidence\": \"Single Co-IP, siRNA knockdown, ROS assay, and xenograft in hepatocellular carcinoma cells\",\n      \"pmids\": [\"41015250\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation for NDUFA4L2\", \"JAK-STAT link is downstream inference with limited mechanistic depth\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified COA6 as a direct CoQ10-binding target through which CoQ10 improves respiratory chain function and behavior in a neurodegeneration model.\",\n      \"evidence\": \"Drug-target engagement binding assay, viral Coa6 overexpression/knockdown in Purkinje cells, respiratory assays, and behavioral testing in PC-Drp1-/- mice\",\n      \"pmids\": [\"42036720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab with limited mechanistic detail\", \"Structural basis and functional consequence of CoQ10 binding to COA6 undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The physiological electron donor that regenerates reduced COA6 and the structural basis of COA6-client copper handoff remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No defined upstream reductant for COA6 redox cycling\", \"No solved COA6-SCO/COX2 complex structure\", \"Mechanism connecting COA6 to complex I and to membrane-potential-driven import not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [5, 7]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5, 7]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"COX2\", \"SCO1\", \"SCO2\", \"COX6B\", \"NDUFA4L2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}