{"gene":"COPS9","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2015,"finding":"CSNAP (COPS9) is a stoichiometric ninth subunit of the COP9 signalosome (CSN) complex. It binds CSN3, CSN5, and CSN6, and its incorporation into the CSN is mediated through its C-terminal region involving conserved aromatic residues. Depletion of CSNAP leads to reduced proliferation and flattened, enlarged cell morphology.","method":"Co-immunoprecipitation, mass spectrometry, mutagenesis, cell depletion assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, mutagenesis of conserved residues, multiple orthogonal methods in single rigorous study identifying stoichiometric subunit","pmids":["26456823"],"is_preprint":false},{"year":2019,"finding":"CSNAP (COPS9) reduces the affinity of the CSN complex toward CRL complexes through steric (non-enzymatic) inhibition. Removing CSNAP does not affect deneddylation activity itself, but causes global CRL dysregulation, resulting in altered reproductive capacity, suppressed DNA damage response, and delayed cell cycle progression.","method":"CSNAP knockout/depletion, in vitro deneddylation assays, cell cycle analysis, DNA damage response assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — enzymatic decoupling assay, KO with multiple defined phenotypic readouts, mechanistic separation of steric vs. catalytic CSN function","pmids":["31367012"],"is_preprint":false},{"year":2013,"finding":"Myeov2 (COPS9) associates with ribosomal protein L11 and withholds L11 in the nucleoplasm. Myeov2 expression reduces Nedd8 modification of L11 (and other proteins), though L11 deneddylation itself is mediated by Nedp1 independently of Myeov2. Myeov2 also interacts with the COP9 signalosome. Myeov2 expression upregulates p53 transcriptional activity.","method":"Co-immunoprecipitation, overexpression/knockdown, immunofluorescence localization, neddylation assays, p53 reporter assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP plus functional assays in single lab with multiple orthogonal methods; Nedd8 mechanism partially dissected","pmids":["23776465"],"is_preprint":false},{"year":2023,"finding":"The C-terminal 16 amino acid region of CSNAP is tightly packed within a groove formed by CSN3 and CSN8 in the CSN complex. A peptide derived from this region can displace endogenous CSNAP from the complex, leading to a CSNAP-null phenotype that attenuates CSN activity and CRL function.","method":"Peptide competition assay, functional CSN activity assay, structural mapping","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — peptide displacement with functional readout, single lab, identifies binding groove residues but no high-resolution structure in this paper alone","pmids":["37460146"],"is_preprint":false},{"year":2021,"finding":"NMR spectroscopy revealed that human CSNAP is an intrinsically disordered protein with distinct structural features from DSS1 (its proposed paralog in the 19S proteasome lid). CSNAP does not bind ubiquitin at relevant levels, indicating the two proteins have diverged in structure and function despite both being acidic IDPs associated with PCI complexes.","method":"NMR spectroscopy, ubiquitin-binding assay","journal":"Protein science","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR structural characterization in single study; negative ubiquitin-binding result is mechanistically informative","pmids":["34272906"],"is_preprint":false},{"year":2026,"finding":"Cryo-EM structures of CSN-CRL complexes located CSNAP within a groove formed by CSN3 and CSN8, confirming and extending the structural placement identified biochemically. The structures also capture distinct functional states of the deneddylation cycle.","method":"Cryo-electron microscopy (cryo-EM) of CSN-SCF complexes","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution cryo-EM structural determination with multiple functional states resolved in single rigorous study","pmids":["41577659"],"is_preprint":false},{"year":2005,"finding":"COPS9/JAB1 was found complexed with p27 (CDKN1B) together with D-type cyclins 1 and 3 in mouse B cell lymphomas with high proliferative activity.","method":"Co-immunoprecipitation from lymphoma cells","journal":"Leukemia research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP from a tumor model, no mechanistic follow-up of COPS9-specific function in this complex","pmids":["16122798"],"is_preprint":false}],"current_model":"CSNAP (COPS9) is the ninth, stoichiometric subunit of the COP9 signalosome (CSN), an intrinsically disordered acidic protein whose C-terminal tail anchors into a groove formed by CSN3 and CSN8; it does not affect CSN's deneddylase activity but reduces CSN affinity for cullin-RING ligase (CRL) complexes through steric inhibition, thereby modulating CRL-dependent ubiquitination, cell cycle progression, and DNA damage response, and it also interacts with ribosomal protein L11 to regulate its subnuclear localization and Nedd8 modification status, ultimately influencing p53 pathway activity."},"narrative":{"mechanistic_narrative":"COPS9 (CSNAP) is the ninth, stoichiometric subunit of the COP9 signalosome (CSN), an intrinsically disordered acidic protein that binds CSN3, CSN5, and CSN6 and integrates into the complex through conserved aromatic residues in its C-terminal region [PMID:26456823, PMID:34272906]. This C-terminal segment anchors into a groove formed by CSN3 and CSN8, a placement established biochemically and confirmed by cryo-EM of CSN-CRL complexes; a peptide derived from this region displaces endogenous CSNAP and recapitulates the CSNAP-null state [PMID:37460146, PMID:41577659]. Functionally, CSNAP does not alter the deneddylase activity of CSN but instead reduces CSN affinity for cullin-RING ligase (CRL) complexes through steric inhibition, and its loss causes global CRL dysregulation manifesting as delayed cell cycle progression, suppressed DNA damage response, altered reproductive capacity, and reduced proliferation with enlarged, flattened cell morphology [PMID:26456823, PMID:31367012]. Independently of its CSN role, COPS9 (Myeov2) associates with ribosomal protein L11, withholding it in the nucleoplasm and reducing Nedd8 modification of L11, thereby upregulating p53 transcriptional activity [PMID:23776465]. Although structurally an acidic IDP analogous to DSS1, CSNAP has diverged functionally and does not bind ubiquitin at relevant levels [PMID:34272906].","teleology":[{"year":2013,"claim":"Before its CSN role was defined, the question of how this small acidic protein influences neddylation and tumor-suppressor signaling was addressed by linking it to L11 sequestration and p53 activity.","evidence":"Co-IP, overexpression/knockdown, immunofluorescence, neddylation and p53 reporter assays for Myeov2","pmids":["23776465"],"confidence":"Medium","gaps":["Does not establish whether L11 regulation depends on CSN integration","Mechanism of how Myeov2 reduces Nedd8 modification is not resolved","p53 effect not connected to CRL substrate dynamics"]},{"year":2015,"claim":"The central question of what this protein is was answered by identifying CSNAP as a bona fide stoichiometric ninth subunit of the CSN, defining its interaction partners and the determinants of its incorporation.","evidence":"Reciprocal Co-IP, mass spectrometry, mutagenesis of conserved aromatic residues, and depletion assays","pmids":["26456823"],"confidence":"High","gaps":["Did not determine the functional consequence of CSNAP within CSN","Precise binding surface on CSN not mapped at this stage"]},{"year":2019,"claim":"Whether CSNAP acts through CSN catalysis or by another route was resolved by decoupling its function from deneddylation, showing it sterically reduces CSN-CRL affinity to control CRL output.","evidence":"Knockout/depletion, in vitro deneddylation assays, cell cycle and DNA damage response readouts","pmids":["31367012"],"confidence":"High","gaps":["Direct structural basis of the steric inhibition not shown here","Range of affected CRL substrates not enumerated"]},{"year":2021,"claim":"The structural nature of CSNAP and its relationship to the proposed proteasome-lid paralog DSS1 was clarified, establishing CSNAP as an intrinsically disordered protein that has diverged in structure and function.","evidence":"NMR spectroscopy and ubiquitin-binding assays on human CSNAP","pmids":["34272906"],"confidence":"Medium","gaps":["Disordered ensemble in the bound state within CSN not defined","Negative ubiquitin-binding result does not exclude other ligand interactions"]},{"year":2023,"claim":"The binding site of CSNAP on CSN was localized to a CSN3-CSN8 groove, and a competing peptide was shown to displace CSNAP and phenocopy its loss, providing a means to perturb the interaction.","evidence":"Peptide competition assay with functional CSN activity readout and structural mapping","pmids":["37460146"],"confidence":"Medium","gaps":["No high-resolution structure within this study","Specificity of the displacement peptide in cells not fully characterized"]},{"year":2026,"claim":"High-resolution structural placement of CSNAP was achieved, confirming its location in the CSN3-CSN8 groove and capturing distinct states of the deneddylation cycle.","evidence":"Cryo-EM of CSN-SCF complexes","pmids":["41577659"],"confidence":"High","gaps":["Conformational dynamics of the disordered regions of CSNAP not fully resolved","Structural basis linking CSNAP to its L11/p53 role not addressed"]},{"year":null,"claim":"How CSNAP's CSN-integral function mechanistically intersects with its L11-sequestering, p53-modulating activity remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unified model linking CSN-bound CSNAP to nucleoplasmic L11 regulation","COPS9/JAB1 association with p27 and D-type cyclins lacks mechanistic follow-up"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,3]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1]}],"complexes":["COP9 signalosome (CSN)"],"partners":["CSN3","CSN5","CSN6","CSN8","RPL11","CDKN1B"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8WXC6","full_name":"COP9 signalosome complex subunit 9","aliases":["CSN acidic protein","CSNAP","Myeloma-overexpressed gene 2 protein"],"length_aa":57,"mass_kda":6.2,"function":"Component of the COP9 signalosome complex (CSN), a complex involved in various cellular and developmental processes. The CSN complex is an essential regulator of the ubiquitin (Ubl) conjugation pathway by mediating the deneddylation of the cullin subunits of SCF-type E3 ligase complexes, leading to decrease the Ubl ligase activity of SCF-type complexes such as SCF, CSA or DDB2. The complex is also involved in phosphorylation of p53/TP53, c-jun/JUN, IkappaBalpha/NFKBIA, ITPK1 and IRF8/ICSBP, possibly via its association with CK2 and PKD kinases. CSN-dependent phosphorylation of TP53 and JUN promotes and protects degradation by the Ubl system, respectively. Plays a role in cell proliferation Negatively regulates neddylation of proteins, including ribosoaml protein RPL11","subcellular_location":"Nucleus, nucleoplasm","url":"https://www.uniprot.org/uniprotkb/Q8WXC6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/COPS9","classification":"Not Classified","n_dependent_lines":57,"n_total_lines":1208,"dependency_fraction":0.04718543046357616},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"DDB1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/COPS9","total_profiled":1310},"omim":[{"mim_id":"619349","title":"COP9 SIGNALOSOME, SUBUNIT 9; COPS9","url":"https://www.omim.org/entry/619349"},{"mim_id":"604175","title":"RIBOSOMAL PROTEIN L11; RPL11","url":"https://www.omim.org/entry/604175"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/COPS9"},"hgnc":{"alias_symbol":["CSNAP"],"prev_symbol":["MYEOV2"]},"alphafold":{"accession":"Q8WXC6","domains":[{"cath_id":"-","chopping":"4-54","consensus_level":"medium","plddt":62.4247,"start":4,"end":54}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WXC6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WXC6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WXC6-F1-predicted_aligned_error_v6.png","plddt_mean":62.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=COPS9","jax_strain_url":"https://www.jax.org/strain/search?query=COPS9"},"sequence":{"accession":"Q8WXC6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WXC6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WXC6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WXC6"}},"corpus_meta":[{"pmid":"16328705","id":"PMC_16328705","title":"Child food insecurity and iron deficiency anemia in low-income infants and toddlers in the United States.","date":"2006","source":"Maternal and child health journal","url":"https://pubmed.ncbi.nlm.nih.gov/16328705","citation_count":191,"is_preprint":false},{"pmid":"22306320","id":"PMC_22306320","title":"Spread of onabotulinumtoxinA after bladder injection. Experimental study using the distribution of cleaved SNAP-25 as the marker of the toxin action.","date":"2012","source":"European urology","url":"https://pubmed.ncbi.nlm.nih.gov/22306320","citation_count":62,"is_preprint":false},{"pmid":"21541338","id":"PMC_21541338","title":"Proteomic analyses of nucleoid-associated proteins in Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21541338","citation_count":59,"is_preprint":false},{"pmid":"26456823","id":"PMC_26456823","title":"CSNAP Is a Stoichiometric Subunit of the COP9 Signalosome.","date":"2015","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/26456823","citation_count":47,"is_preprint":false},{"pmid":"25826798","id":"PMC_25826798","title":"Large-scale chemical similarity networks for target profiling of compounds identified in cell-based chemical screens.","date":"2015","source":"PLoS computational 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England)","url":"https://pubmed.ncbi.nlm.nih.gov/24756904","citation_count":37,"is_preprint":false},{"pmid":"28247455","id":"PMC_28247455","title":"On the relationships in rhesus macaques between chronic ethanol consumption and the brain transcriptome.","date":"2017","source":"Addiction biology","url":"https://pubmed.ncbi.nlm.nih.gov/28247455","citation_count":28,"is_preprint":false},{"pmid":"16122798","id":"PMC_16122798","title":"Expression of the cyclin-dependent kinase inhibitor p27 and its deregulation in mouse B cell lymphomas.","date":"2005","source":"Leukemia research","url":"https://pubmed.ncbi.nlm.nih.gov/16122798","citation_count":25,"is_preprint":false},{"pmid":"31367012","id":"PMC_31367012","title":"CSNAP, the smallest CSN subunit, modulates proteostasis through cullin-RING ubiquitin ligases.","date":"2019","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/31367012","citation_count":19,"is_preprint":false},{"pmid":"26103053","id":"PMC_26103053","title":"Molecular Features of Triple Negative Breast Cancer: Microarray Evidence and Further Integrated Analysis.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26103053","citation_count":17,"is_preprint":false},{"pmid":"27044515","id":"PMC_27044515","title":"The Evolution of COP9 Signalosome in Unicellular and Multicellular Organisms.","date":"2016","source":"Genome biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/27044515","citation_count":17,"is_preprint":false},{"pmid":"23776465","id":"PMC_23776465","title":"Myeloma overexpressed 2 (Myeov2) regulates L11 subnuclear localization through Nedd8 modification.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23776465","citation_count":15,"is_preprint":false},{"pmid":"35324657","id":"PMC_35324657","title":"Antinociceptive Actions of Botulinum Toxin A1 on Immunogenic Hypersensitivity in Temporomandibular Joint of Rats.","date":"2022","source":"Toxins","url":"https://pubmed.ncbi.nlm.nih.gov/35324657","citation_count":14,"is_preprint":false},{"pmid":"25157668","id":"PMC_25157668","title":"Antigen detection via the rate of ion current rectification change of the antibody-modified glass nanopore membrane.","date":"2014","source":"Langmuir : the ACS journal of surfaces and colloids","url":"https://pubmed.ncbi.nlm.nih.gov/25157668","citation_count":10,"is_preprint":false},{"pmid":"34272906","id":"PMC_34272906","title":"The disordered PCI-binding human proteins CSNAP and DSS1 have diverged in structure and function.","date":"2021","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/34272906","citation_count":9,"is_preprint":false},{"pmid":"36939389","id":"PMC_36939389","title":"Intratympanic Botulinum Toxin Injection as a New Therapeutic Modality for Middle Ear 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of senescence gene CsNAP and B-class floral development gene CsAP3 during different stages of flower development in Saffron (Crocus sativus L.).","date":"2015","source":"Physiology and molecular biology of plants : an international journal of functional plant biology","url":"https://pubmed.ncbi.nlm.nih.gov/26261412","citation_count":4,"is_preprint":false},{"pmid":"37460146","id":"PMC_37460146","title":"The C-terminal tail of CSNAP attenuates the CSN complex.","date":"2023","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/37460146","citation_count":4,"is_preprint":false},{"pmid":"36116794","id":"PMC_36116794","title":"Botulinum Toxin A, a Better Choice for Skeletal Muscle Block in a Comparative Study With Lidocaine in Rats.","date":"2022","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/36116794","citation_count":1,"is_preprint":false},{"pmid":"41754547","id":"PMC_41754547","title":"Single-Cell Transcriptomic Profile Associated with Sub-Subtype A6 and CRF63-02A6 HIV-1 Strain Infection.","date":"2026","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/41754547","citation_count":0,"is_preprint":false},{"pmid":"41577659","id":"PMC_41577659","title":"Structural basis of CSN-mediated SCF deneddylation.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41577659","citation_count":0,"is_preprint":false},{"pmid":"39763868","id":"PMC_39763868","title":"Crosslinking-mediated Interactome Analysis Identified PHD2-HIF1α Interaction Hotspots and the Role of PHD2 in Regulating Protein Neddylation.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/39763868","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15192,"output_tokens":1705,"usd":0.035576,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8488,"output_tokens":2297,"usd":0.049932,"stage2_stop_reason":"end_turn"},"total_usd":0.085508,"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\": 2015,\n      \"finding\": \"CSNAP (COPS9) is a stoichiometric ninth subunit of the COP9 signalosome (CSN) complex. It binds CSN3, CSN5, and CSN6, and its incorporation into the CSN is mediated through its C-terminal region involving conserved aromatic residues. Depletion of CSNAP leads to reduced proliferation and flattened, enlarged cell morphology.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry, mutagenesis, cell depletion assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, mutagenesis of conserved residues, multiple orthogonal methods in single rigorous study identifying stoichiometric subunit\",\n      \"pmids\": [\"26456823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CSNAP (COPS9) reduces the affinity of the CSN complex toward CRL complexes through steric (non-enzymatic) inhibition. Removing CSNAP does not affect deneddylation activity itself, but causes global CRL dysregulation, resulting in altered reproductive capacity, suppressed DNA damage response, and delayed cell cycle progression.\",\n      \"method\": \"CSNAP knockout/depletion, in vitro deneddylation assays, cell cycle analysis, DNA damage response assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — enzymatic decoupling assay, KO with multiple defined phenotypic readouts, mechanistic separation of steric vs. catalytic CSN function\",\n      \"pmids\": [\"31367012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Myeov2 (COPS9) associates with ribosomal protein L11 and withholds L11 in the nucleoplasm. Myeov2 expression reduces Nedd8 modification of L11 (and other proteins), though L11 deneddylation itself is mediated by Nedp1 independently of Myeov2. Myeov2 also interacts with the COP9 signalosome. Myeov2 expression upregulates p53 transcriptional activity.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/knockdown, immunofluorescence localization, neddylation assays, p53 reporter assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP plus functional assays in single lab with multiple orthogonal methods; Nedd8 mechanism partially dissected\",\n      \"pmids\": [\"23776465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The C-terminal 16 amino acid region of CSNAP is tightly packed within a groove formed by CSN3 and CSN8 in the CSN complex. A peptide derived from this region can displace endogenous CSNAP from the complex, leading to a CSNAP-null phenotype that attenuates CSN activity and CRL function.\",\n      \"method\": \"Peptide competition assay, functional CSN activity assay, structural mapping\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — peptide displacement with functional readout, single lab, identifies binding groove residues but no high-resolution structure in this paper alone\",\n      \"pmids\": [\"37460146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NMR spectroscopy revealed that human CSNAP is an intrinsically disordered protein with distinct structural features from DSS1 (its proposed paralog in the 19S proteasome lid). CSNAP does not bind ubiquitin at relevant levels, indicating the two proteins have diverged in structure and function despite both being acidic IDPs associated with PCI complexes.\",\n      \"method\": \"NMR spectroscopy, ubiquitin-binding assay\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR structural characterization in single study; negative ubiquitin-binding result is mechanistically informative\",\n      \"pmids\": [\"34272906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Cryo-EM structures of CSN-CRL complexes located CSNAP within a groove formed by CSN3 and CSN8, confirming and extending the structural placement identified biochemically. The structures also capture distinct functional states of the deneddylation cycle.\",\n      \"method\": \"Cryo-electron microscopy (cryo-EM) of CSN-SCF complexes\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution cryo-EM structural determination with multiple functional states resolved in single rigorous study\",\n      \"pmids\": [\"41577659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"COPS9/JAB1 was found complexed with p27 (CDKN1B) together with D-type cyclins 1 and 3 in mouse B cell lymphomas with high proliferative activity.\",\n      \"method\": \"Co-immunoprecipitation from lymphoma cells\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP from a tumor model, no mechanistic follow-up of COPS9-specific function in this complex\",\n      \"pmids\": [\"16122798\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CSNAP (COPS9) is the ninth, stoichiometric subunit of the COP9 signalosome (CSN), an intrinsically disordered acidic protein whose C-terminal tail anchors into a groove formed by CSN3 and CSN8; it does not affect CSN's deneddylase activity but reduces CSN affinity for cullin-RING ligase (CRL) complexes through steric inhibition, thereby modulating CRL-dependent ubiquitination, cell cycle progression, and DNA damage response, and it also interacts with ribosomal protein L11 to regulate its subnuclear localization and Nedd8 modification status, ultimately influencing p53 pathway activity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"COPS9 (CSNAP) is the ninth, stoichiometric subunit of the COP9 signalosome (CSN), an intrinsically disordered acidic protein that binds CSN3, CSN5, and CSN6 and integrates into the complex through conserved aromatic residues in its C-terminal region [#0, #4]. This C-terminal segment anchors into a groove formed by CSN3 and CSN8, a placement established biochemically and confirmed by cryo-EM of CSN-CRL complexes; a peptide derived from this region displaces endogenous CSNAP and recapitulates the CSNAP-null state [#3, #5]. Functionally, CSNAP does not alter the deneddylase activity of CSN but instead reduces CSN affinity for cullin-RING ligase (CRL) complexes through steric inhibition, and its loss causes global CRL dysregulation manifesting as delayed cell cycle progression, suppressed DNA damage response, altered reproductive capacity, and reduced proliferation with enlarged, flattened cell morphology [#0, #1]. Independently of its CSN role, COPS9 (Myeov2) associates with ribosomal protein L11, withholding it in the nucleoplasm and reducing Nedd8 modification of L11, thereby upregulating p53 transcriptional activity [#2]. Although structurally an acidic IDP analogous to DSS1, CSNAP has diverged functionally and does not bind ubiquitin at relevant levels [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Before its CSN role was defined, the question of how this small acidic protein influences neddylation and tumor-suppressor signaling was addressed by linking it to L11 sequestration and p53 activity.\",\n      \"evidence\": \"Co-IP, overexpression/knockdown, immunofluorescence, neddylation and p53 reporter assays for Myeov2\",\n      \"pmids\": [\"23776465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish whether L11 regulation depends on CSN integration\", \"Mechanism of how Myeov2 reduces Nedd8 modification is not resolved\", \"p53 effect not connected to CRL substrate dynamics\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The central question of what this protein is was answered by identifying CSNAP as a bona fide stoichiometric ninth subunit of the CSN, defining its interaction partners and the determinants of its incorporation.\",\n      \"evidence\": \"Reciprocal Co-IP, mass spectrometry, mutagenesis of conserved aromatic residues, and depletion assays\",\n      \"pmids\": [\"26456823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not determine the functional consequence of CSNAP within CSN\", \"Precise binding surface on CSN not mapped at this stage\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Whether CSNAP acts through CSN catalysis or by another route was resolved by decoupling its function from deneddylation, showing it sterically reduces CSN-CRL affinity to control CRL output.\",\n      \"evidence\": \"Knockout/depletion, in vitro deneddylation assays, cell cycle and DNA damage response readouts\",\n      \"pmids\": [\"31367012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural basis of the steric inhibition not shown here\", \"Range of affected CRL substrates not enumerated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The structural nature of CSNAP and its relationship to the proposed proteasome-lid paralog DSS1 was clarified, establishing CSNAP as an intrinsically disordered protein that has diverged in structure and function.\",\n      \"evidence\": \"NMR spectroscopy and ubiquitin-binding assays on human CSNAP\",\n      \"pmids\": [\"34272906\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Disordered ensemble in the bound state within CSN not defined\", \"Negative ubiquitin-binding result does not exclude other ligand interactions\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The binding site of CSNAP on CSN was localized to a CSN3-CSN8 groove, and a competing peptide was shown to displace CSNAP and phenocopy its loss, providing a means to perturb the interaction.\",\n      \"evidence\": \"Peptide competition assay with functional CSN activity readout and structural mapping\",\n      \"pmids\": [\"37460146\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure within this study\", \"Specificity of the displacement peptide in cells not fully characterized\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"High-resolution structural placement of CSNAP was achieved, confirming its location in the CSN3-CSN8 groove and capturing distinct states of the deneddylation cycle.\",\n      \"evidence\": \"Cryo-EM of CSN-SCF complexes\",\n      \"pmids\": [\"41577659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational dynamics of the disordered regions of CSNAP not fully resolved\", \"Structural basis linking CSNAP to its L11/p53 role not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CSNAP's CSN-integral function mechanistically intersects with its L11-sequestering, p53-modulating activity remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unified model linking CSN-bound CSNAP to nucleoplasmic L11 regulation\", \"COPS9/JAB1 association with p27 and D-type cyclins lacks mechanistic follow-up\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"COP9 signalosome (CSN)\"],\n    \"partners\": [\"CSN3\", \"CSN5\", \"CSN6\", \"CSN8\", \"RPL11\", \"CDKN1B\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}