Affinage

COX16

Cytochrome c oxidase assembly protein COX16 homolog, mitochondrial · UniProt Q9P0S2

Length
106 aa
Mass
12.3 kDa
Annotated
2026-06-09
16 papers in source corpus 7 papers cited in narrative 7 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

COX16 is a small mitochondrial inner-membrane protein that functions as an assembly factor for cytochrome c oxidase (Complex IV), where it is essential for COX biogenesis in both yeast and human cells (PMID:12446688, PMID:29355485, PMID:33169484). Its C-terminus faces the intermembrane space, and it is physically present in COX1-containing assembly intermediates, mature COX, and COX–bc1 supercomplexes (PMID:12446688, PMID:28821616). Mechanistically, COX16 associates specifically with newly synthesized COX2 and with the copper metallochaperones SCO1, SCO2, and COA6, and is required for recruitment of SCO1 to the COX2 assembly module; patient-mimicking SCO1 mutations disrupt this interaction, and COX16 further participates in merging the COX1 and COX2 assembly lines (PMID:29381136). Consistent with a role in copper delivery to COX2, copper supplementation partially rescues COX activity and restores COX subunit levels in COX16-null cells despite COX16 lacking a canonical copper-binding motif (PMID:29355485). A homozygous nonsense variant abolishing COX16 causes complete loss of holo-Complex IV, with rescue by wild-type cDNA confirming its requirement for human COX biogenesis (PMID:33169484).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2002 Medium

    Establishing whether Cox16p is a COX assembly factor and where it sits answered the basic question of its membrane topology and functional category.

    Evidence Myc-epitope tagging, subcellular fractionation, and complementation of yeast cox16 mutant

    PMID:12446688

    Open questions at the time
    • Specific assembly step and molecular partners not defined
    • Excluded roles (subunit 2 maturation, copper recruitment, heme A) defined only negatively in yeast
  2. 2017 Medium

    Placing Cox16p physically within Cox1p assembly intermediates, mature COX, and supercomplexes showed when and where it acts during assembly.

    Evidence Co-immunopurification of dual-tagged Cox16p with Western blot in yeast

    PMID:28821616

    Open questions at the time
    • Substoichiometric association leaves stoichiometry and residence time unresolved
    • Does not establish direct binding partners versus co-purifying complex members
  3. 2018 High

    Demonstrating that human COX16 ablation impairs COX assembly and co-IPs with COX2, with copper supplementation rescue, identified its module of action and a role in copper delivery.

    Evidence HEK293 knockout, BN-PAGE assembly intermediate analysis, reciprocal co-IP with COX2, copper rescue, and C. elegans knockdown

    PMID:29355485

    Open questions at the time
    • No canonical copper-binding motif identified, so the mechanism of copper handling is indirect
    • Direct metal-transfer chemistry not demonstrated
  4. 2018 High

    Mapping COX16 interactions to newly synthesized COX2 and the SCO1/SCO2/COA6 metallochaperones, and showing it is required for SCO1 recruitment, defined its precise role in CuA-site formation and in merging the COX1 and COX2 lines.

    Evidence Co-IP of pulse-labeled nascent subunits, SCO1 patient-mimicking mutant interaction studies, and BN-PAGE

    PMID:29381136

    Open questions at the time
    • Structural basis of the COX16–COX2 and COX16–SCO1 interactions not resolved
    • Mechanism by which COX16 coordinates merging of the two assembly lines not defined
  5. 2020 Medium

    A homozygous nonsense COX16 variant causing complete loss of holo-Complex IV, rescued by wild-type cDNA, confirmed COX16 as required for human COX biogenesis in a disease context.

    Evidence Western blot of patient fibroblasts and lentiviral complementation rescue

    PMID:33169484

    Open questions at the time
    • Genotype–phenotype relationship across patients not established from a single case
    • Does not refine the molecular step beyond loss of holo-complex
  6. 2022 Medium

    Characterizing a SYNJ2BP-COX16 fusion protein in breast cancer addressed a non-canonical, splicing-derived activity distinct from native COX16 assembly function.

    Evidence SUMO-site mutagenesis (K107R), co-IP of DRP1 and UBC9, mitochondrial imaging, xenografts, and Mdivi-1 rescue

    PMID:35998797

    Open questions at the time
    • Concerns a fusion protein, not canonical COX16 alone
    • Relevance to native COX16 mitochondrial fission control unestablished
  7. 2024 Medium

    Linking DAZAP1-driven alternative splicing to COX16 expression positioned COX16 as an effector of mitochondrial respiration in cancer, though the regulation is upstream of COX16's own mechanism.

    Evidence RNA-seq splicing analysis, DAZAP1 knockdown/knockout in OSCC cells and mouse models, and respiration assays

    PMID:39120588

    Open questions at the time
    • Mechanism is upstream (DAZAP1 regulating COX16 splicing), not a direct COX16 activity
    • Which COX16 splice isoforms drive the respiratory phenotype not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How COX16 chemically handles copper without a canonical binding motif and the structural basis of its coordination of COX2 with the SCO chaperones remain unresolved.
  • No structural model of COX16 within assembly intermediates
  • Direct copper-transfer chemistry not demonstrated
  • Mechanism of COX1/COX2 assembly-line merging not resolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 2 GO:0140104 molecular carrier activity 1
Localization
GO:0005739 mitochondrion 2
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 4
Partners
COA6COX1COX2SCO1SCO2
Complex memberships
COX–bc1 supercomplexcytochrome c oxidase (Complex IV)

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 Yeast Cox16p is an integral component of the mitochondrial inner membrane with its C terminus exposed to the intermembrane space, and is essential for cytochrome c oxidase (COX) assembly. Cox16p is not involved in maturation of subunit 2, copper recruitment, or heme A biosynthesis. Myc-epitope tagging, subcellular fractionation, complementation of yeast cox16 mutant The Journal of biological chemistry Medium 12446688
2017 Yeast Cox16p is physically present in Cox1p assembly intermediates, in mature cytochrome c oxidase, and in COX–bc1 supercomplexes, and appears substoichiometric with Cox1p and Cox4p. Co-immunopurification using dual His/protein-C tag on Cox16p, Western blot The Journal of biological chemistry Medium 28821616
2018 Human COX16 encodes a small mitochondrial transmembrane protein that faces the intermembrane space; its ablation in HEK293 cells impairs COX assembly and it co-immunoprecipitates with COX2, indicating a role in the COX2 subassembly module. Copper supplementation rescues COX activity and restores steady-state COX subunit levels in COX16 knockout cells, implicating COX16 in copper delivery to COX2 despite lacking a canonical copper-binding motif. Gene knockout in HEK293 cells, Blue-Native PAGE of assembly intermediates, co-immunoprecipitation with COX2, copper supplementation rescue experiment, C. elegans knockdown Biochimica et biophysica acta. Bioenergetics High 29355485
2018 Human COX16 interacts specifically with newly synthesized COX2 and with its copper-center-forming metallochaperones SCO1, SCO2, and COA6. COX16 is required for recruitment of SCO1 to the COX2 assembly module. Patient-mimicking mutations in SCO1 disrupt interaction with COX16. COX16 is also found in COX1-containing assembly intermediates and participates in merging the COX1 and COX2 assembly lines. Co-immunoprecipitation of newly synthesized subunits (radiolabeling/pulse-chase), interaction studies with SCO1 patient-mimicking mutants, Blue-Native PAGE assembly intermediate analysis eLife High 29381136
2020 Complete loss of COX16 protein (homozygous nonsense variant p.Arg82*) leads to total absence of holo-complex IV, and lentiviral transduction with wild-type COX16 cDNA rescues complex IV biosynthesis in patient fibroblasts, confirming COX16 is required for cytochrome c oxidase biogenesis in human cells. Western blot of patient fibroblasts, lentiviral complementation rescue assay Human mutation Medium 33169484
2022 The SYNJ2BP-COX16 fusion protein (resulting from abnormal gene splicing) promotes mitochondrial fission in breast cancer; SUMOylation at K107 is required for its mitochondrial subcellular localization. SUMOylated SYNJ2BP-COX16 recruits DRP1 to mitochondria, promotes UBC9 binding to DRP1, enhances DRP1 SUMOylation and phosphorylation at S616, and induces mitochondrial fission. The non-SUMOylatable K107R mutant fails to promote these effects. SUMO site mutagenesis (K107R), co-immunoprecipitation of DRP1 and UBC9, mitochondrial localization imaging, ATP production and COX activity assays, in vivo xenograft models, DRP1 inhibitor (Mdivi-1) rescue Cancer letters Medium 35998797
2024 The RNA-binding protein DAZAP1 undergoes liquid-liquid phase separation in the nucleus and enhances COX16 expression by regulating pre-mRNA alternative splicing of COX16, thereby promoting mitochondrial respiration and OSCC invasion. Loss of DAZAP1 in mouse OSCC models suppressed COX16 expression and reduced tumor growth and metastasis. RNA sequencing, alternative splicing analysis, DAZAP1 knockdown/knockout in OSCC cells and mouse models, mitochondrial respiration assays, Western blot Cancer research Medium 39120588

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2017 A genome-wide siRNA screen for regulators of tumor suppressor p53 activity in human non-small cell lung cancer cells identifies components of the RNA splicing machinery as targets for anticancer treatment. Molecular oncology 55 28296343
2018 COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis. eLife 49 29381136
2020 Survival-Associated Metabolic Genes in Human Papillomavirus-Positive Head and Neck Cancers. Cancers 48 31968678
2019 Identification of hub genes and key pathways associated with the progression of gynecological cancer. Oncology letters 35 31788113
2002 COX16 encodes a novel protein required for the assembly of cytochrome oxidase in Saccharomyces cerevisiae. The Journal of biological chemistry 33 12446688
2024 DAZAP1 Phase Separation Regulates Mitochondrial Metabolism to Facilitate Invasion and Metastasis of Oral Squamous Cell Carcinoma. Cancer research 24 39120588
2022 SUMOylation of SYNJ2BP-COX16 promotes breast cancer progression through DRP1-mediated mitochondrial fission. Cancer letters 22 35998797
2018 COX16 is required for assembly of cytochrome c oxidase in human cells and is involved in copper delivery to COX2. Biochimica et biophysica acta. Bioenergetics 22 29355485
2013 Deletions in 14q24.1q24.3 are associated with congenital heart defects, brachydactyly, and mild intellectual disability. American journal of medical genetics. Part A 20 24357125
2017 Cox16 protein is physically associated with Cox1p assembly intermediates and with cytochrome oxidase. The Journal of biological chemistry 15 28821616
2004 Studies of COX16, COX19, and PET191 in human cytochrome-c oxidase deficiency. Archives of neurology 8 15596615
2020 A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction. Human mutation 5 33169484
2024 Molecular Mechanisms Associated with the Development of the Metritis Complex in Dairy Cattle. Genes 3 38674374
2008 Characterization of Paracoccidioides brasiliensis COX9, COX12, and COX16 respiratory genes. Mycological research 2 18672058
2026 Proteomic Analysis Comparing Effect of Feeding Practices on the Milk Fat Globule Membrane Proteins from Camelus dromedarius. Foods (Basel, Switzerland) 0 41683090
2026 Integrated molecular and metabolomic assessment of copper hydroxide nanopesticide toxicity in zebrafish. Fish physiology and biochemistry 0 42171887

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