{"gene":"F9","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1978,"finding":"Human Factor IX (FIX) is a single-chain plasma glycoprotein that is activated to a serine protease (Factor IXaβ) by Factor XIa through cleavage of two internal peptide bonds (Arg145-Ala146 and Arg180-Val181), releasing an activation peptide and generating a two-chain enzyme (light chain + heavy chain held by disulfide bond). The heavy chain contains the active-site serine. Factor IXaβ is inhibited by antithrombin III via tight binding to the heavy chain.","method":"Protein biochemistry: SDS-PAGE, amino acid sequencing, active-site labeling, antithrombin III inhibition assay","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — reconstituted activation reaction with sequence-level characterization of cleavage sites and active site, foundational study replicated across field","pmids":["659613"],"is_preprint":false},{"year":1982,"finding":"Human Factor IX cDNA encodes a 416-amino acid mature protein with a 46-amino acid leader sequence. The protein contains 12 N-terminal glutamic acid residues (substrate for gamma-carboxylation), an activation peptide (35 aa), a light chain (145 aa), and a heavy chain (236 aa) with catalytic triad His221, Asp270, Ser366 homologous to chymotrypsin His57, Asp102, Ser195. Two N-linked glycosylation sites are in the activation peptide.","method":"cDNA cloning and sequencing of human liver library; translation product analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — complete cDNA sequence with structural domain assignment; independently confirmed by multiple labs","pmids":["6959130"],"is_preprint":false},{"year":1982,"finding":"The F9 gene encoding human coagulation Factor IX was molecularly cloned from a human genomic library using bovine factor IX cDNA as probe, establishing it as a single large gene (≥20 kb) on the X chromosome.","method":"Molecular cloning, Southern blotting, hybridization with heterologous cDNA probe","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — direct gene isolation; foundational cloning paper","pmids":["6287289"],"is_preprint":false},{"year":1984,"finding":"The F9 gene spans approximately 33.5 kb on the X chromosome (Xq26-q27) and contains 8 exons and 7 introns; exons correspond roughly to functional protein domains (prepro leader, Gla domain, EGF-like domains, activation peptide, catalytic domain split across two exons). The gene was mapped to the Xq26-q27 region, and a TaqI restriction fragment length polymorphism was identified for carrier/prenatal diagnosis.","method":"Complete genomic DNA sequencing (~38 kb), exon-intron mapping, human-mouse somatic cell hybrid panel mapping, RFLP analysis","journal":"Biochemistry / Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 — complete gene sequence with structural characterization; independently confirmed","pmids":["2994716","6320191","6329734"],"is_preprint":false},{"year":1986,"finding":"A point mutation changing Arg-4 to Gln in the propeptide region of Factor IX causes hemophilia B by blocking proteolytic removal of the propeptide during post-translational maturation; signal peptidase cleaves between positions -18 and -19, but further processing to mature FIX requires the Arg at -4. The result is a stable longer protein with 18 extra N-terminal propeptide residues still attached.","method":"DNA sequencing of hemophilia B patient, in vitro expression, protein analysis by SDS-PAGE and N-terminal sequencing","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis linked to protein processing defect with direct biochemical characterization","pmids":["3009023"],"is_preprint":false},{"year":1989,"finding":"Molecular pathology of hemophilia B established by direct sequencing of amplified genomic DNA from patients: substitutions of Cys336 or Asn120 cause loss of circulating FIX antigen; deletion of Arg37 causes gross reduction of circulating protein and loss of activity; substitutions of Arg-4, Arg333, Asp64, and Pro55 cause loss of function without marked protein reduction; frameshift/nonsense mutations are associated with inhibitor (antibody) development; CpG dinucleotides show enhanced mutation rates accounting for ~25% of all point mutations.","method":"PCR amplification and direct sequencing of F9 genomic DNA from hemophilia B patients","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — systematic genotype-phenotype correlation across many patients with multiple mutation types; replicated across field","pmids":["2743975"],"is_preprint":false},{"year":1990,"finding":"Recombinant Factor VIIa activates both Factor IX and Factor X in the presence of calcium, phospholipids, and tissue factor. Under all cofactor conditions, the kcat/Km ratio for FIX activation by FVIIa was considerably greater than for FX activation, suggesting FIX is a preferred substrate. Tissue factor markedly increases both Vmax and kcat/Km for FIX activation.","method":"Steady-state enzyme kinetics with purified recombinant FVIIa and chromogenic substrates/clotting assays; varied calcium and phospholipid concentrations","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — rigorous in vitro kinetic characterization with recombinant proteins and multiple cofactor conditions","pmids":["2248955"],"is_preprint":false},{"year":1995,"finding":"The crystal structure of the Ca2+-binding EGF-like domain of human Factor IX was solved at 1.5 Å resolution in complex with Ca2+. Ca2+ adopts a pentagonal bipyramidal coordination with six ligands from one polypeptide and the seventh from a neighboring EGF domain. Ca2+ maintains the conformation of the N-terminal region of the domain and directly mediates protein-protein contacts, providing a structural basis for EGF-domain interactions in FIX and related proteins.","method":"X-ray crystallography at 1.5 Å resolution of recombinant Factor IX EGF-like domain","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional validation of Ca2+ coordination and protein-protein contact mediation","pmids":["7606779"],"is_preprint":false},{"year":1995,"finding":"Tissue factor pathway inhibitor (TFPI) directly inhibits activated Factor X and, in a FXa-dependent manner, produces feedback inhibition of the FVIIa/tissue factor complex, thereby limiting the extrinsic pathway initiation of coagulation and explaining the clinical requirement for the intrinsic pathway (including FIX) for sustained hemostasis.","method":"Biochemical reconstitution assays with purified proteins; kinetic inhibition studies","journal":"Annual review of medicine","confidence":"High","confidence_rationale":"Tier 1 — mechanistic reconstitution defining FIX's essential role in the revised coagulation model; widely replicated","pmids":["7598447"],"is_preprint":false},{"year":2005,"finding":"Self-complementary AAV (scAAV) vectors with a liver-specific mini-hFIX expression cassette achieve 20-fold higher FIX expression in mice compared to single-stranded AAV vectors, correcting the bleeding phenotype in FIX knock-out mice at only 1×10^10 particles (producing supraphysiologic FIX levels) and achieving therapeutic FIX levels (3–30% normal) in nonhuman primates at lower doses.","method":"In vivo gene delivery in FIX-KO mice and nonhuman primates; molecular analysis of vector genome forms; FIX clotting activity assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — in vivo reconstitution with functional correction in two animal models; multiple orthogonal assays","pmids":["16322469"],"is_preprint":false},{"year":2008,"finding":"The silent mutation G17736A/Val107Val in the F9 gene causes mild hemophilia B (FIX activity 15–20 U/dL) in five Swedish families, without exon skipping or intron retention detectable by RT-PCR. The probable mechanism involves subtle effects on splicing enhancer sites or altered codon usage reducing translation rate and thereby affecting FIX protein folding in vivo.","method":"RT-PCR and cDNA sequencing of patient lymphocyte mRNA; mutation scanning; FIX activity and antigen measurement","journal":"Haemophilia","confidence":"Medium","confidence_rationale":"Tier 2 — molecular characterization with RT-PCR ruling out gross splicing defects; mechanistic explanation remains inferential","pmids":["18459950"],"is_preprint":false},{"year":2013,"finding":"Analysis of 1113 unique F9 mutations in 3721 hemophilia B patients revealed that mutations occur in 336/461 (73%) FIX residues. Type II (qualitative, predominantly functional) mutations account for 64% of mild-severity cases with known protein phenotypes, and structural modeling indicates these predominantly disrupt regions involved in functional interactions (activation, Xase complex formation). Inhibitor development is rare (1.6%) and associated with 25 specific mutations.","method":"Mutation database analysis combined with homology modeling of FIXa structure based on closely related crystal structures","journal":"Journal of thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 3 — large-scale genotype-phenotype correlation with structural modeling; no direct in vitro functional reconstitution for individual variants","pmids":["23617593"],"is_preprint":false},{"year":2014,"finding":"Fusion of FIX to the Fc fragment of IgG (rFIXFc) prolongs FIX half-life 3–4 fold in Phase I/IIa studies by exploiting physiological binding of the Fc domain to the neonatal Fc receptor (FcRn), demonstrating that the FcRn recycling pathway can extend FIX circulatory half-life without altering FIX functional activity.","method":"Recombinant protein engineering; pharmacokinetic studies in preclinical models and Phase I/IIa/III clinical trials","journal":"Drug design, development and therapy","confidence":"High","confidence_rationale":"Tier 2 — mechanism validated in multiple preclinical models and confirmed in clinical trials; FcRn-mediated half-life extension directly demonstrated","pmids":["24729686"],"is_preprint":false},{"year":2019,"finding":"Factor IX binds to collagen IV (Col4) in the subendothelial basement membrane, creating a vascular cache of FIX (estimated ~405 nM available Col4 binding capacity) that reduces plasma recovery of infused FIX and contributes to hemostasis. In CRM+ hemophilia B mice expressing dysfunctional FIXR333Q, endogenous dysfunctional FIX competes with infused therapeutic FIX for Col4 binding sites, impairing prophylactic hemostatic therapy.","method":"Mouse hemophilia B models (CRM- and CRM+), saphenous vein bleeding assay, pharmacokinetic analysis of FIX plasma recovery, comparison of FIXWT, FIXFC (Alprolix), and FIXAlb (Idelvion)","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — direct in vivo demonstration of FIX-Col4 competition with quantitative pharmacokinetic analysis in two mouse models","pmids":["30992271"],"is_preprint":false},{"year":2022,"finding":"FIX deficiency in hemophilia B results from diverse mechanisms depending on mutation type: deletions/insertions/indels in exons cause frameshift or inframe mutations; intronic mutations cause aberrant splicing; F9 promoter point mutations cause hemophilia B Leyden (developmentally regulated loss of expression); nonsense mutations produce truncated non-functional FIX; missense mutations impair translation, protein folding, stability, post-translational modifications (including gamma-carboxylation, beta-hydroxylation, glycosylation, phosphorylation), FIX activation to FIXa, or formation of the functional Xase complex.","method":"Systematic review of >1000 F9 mutations correlated with structural/functional data from published biochemical studies","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 2 — comprehensive synthesis of experimentally validated mechanistic data across >1000 mutations with structural framework","pmids":["35269902"],"is_preprint":false},{"year":2022,"finding":"Codon optimization (recoding) of F9 alters cotranslational folding kinetics as revealed by ribosome profiling showing differences in local translation kinetics. Recoded FIX variants show altered protein conformations and suboptimal post-translational modifications due to overexpression. Furthermore, MHC class II-associated peptide proteomics revealed distinct presentation of FIX-derived peptides from recoded versus wild-type F9, indicating that synonymous codon substitutions can alter FIX immunogenicity despite identical amino acid sequence.","method":"Ribosome profiling, protein conformation analysis, MHC-associated peptide proteomics, post-translational modification analysis of multiple recoded F9 constructs","journal":"Blood advances","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (ribosome profiling, structural assays, immunopeptidomics) in single study","pmids":["35413099"],"is_preprint":false},{"year":2022,"finding":"A genome-wide CRISPR/Cas9 screen identified F9 (coagulation Factor IX) as a regulator of cellular senescence. Downregulation of F9 using sgRNA or shRNA prevents cell cycle arrest and the senescent-like phenotype induced by CDK4/6 inhibitor (Palbociclib) in MCF7 breast cancer cells. Conversely, treatment with recombinant FIX protein is sufficient to induce cell cycle arrest and senescence-like state in MCF7 cells. Endogenous F9 is upregulated in primary human cells undergoing senescence.","method":"Genome-wide CRISPR/Cas9 loss-of-function screen; shRNA knockdown; recombinant FIX protein treatment; cell cycle analysis; validation in T47D cells and with Abemaciclib; panel of 22 cancer cell lines","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — functional screen with orthogonal validation (sgRNA, shRNA, recombinant protein) in multiple cell lines; mechanism linking FIX to senescence pathway not yet elucidated","pmids":["35184131"],"is_preprint":false}],"current_model":"Coagulation Factor IX (FIX), encoded by the X-linked F9 gene, is a vitamin K-dependent serine protease zymogen that undergoes multi-step post-translational maturation (signal peptide cleavage, propeptide removal requiring Arg-4, gamma-carboxylation of 12 Glu residues, glycosylation, and beta-hydroxylation) before circulating in plasma; it is proteolytically activated to FIXa by FXIa (intrinsic pathway) or FVIIa/tissue factor (extrinsic pathway) through cleavage of two peptide bonds, releasing an activation peptide and generating a two-chain serine protease whose active-site triad (His221, Asp270, Ser366) resides in the heavy chain; FIXa assembles with FVIIIa, phospholipid, and Ca2+ into the intrinsic Xase complex to activate FX, with the Ca2+-binding EGF-like domain (structurally defined at 1.5 Å) mediating critical protein-protein contacts; FIX also binds collagen IV in the subendothelial basement membrane creating a vascular reservoir; over 1000 F9 mutations cause hemophilia B through diverse mechanisms including impaired propeptide processing, aberrant splicing, defective post-translational modification, instability, or failure to form the Xase complex; and beyond coagulation, FIX participates in CDK4/6-inhibitor-induced cellular senescence, as shown by CRISPR screening."},"narrative":{"teleology":[{"year":1978,"claim":"Establishing how Factor IX is converted from a zymogen to an active serine protease answered the fundamental question of FIX's enzymatic mechanism: Factor XIa cleaves two internal peptide bonds to release an activation peptide and generate a disulfide-linked two-chain enzyme whose heavy chain carries the active-site serine and is regulated by antithrombin III.","evidence":"SDS-PAGE, amino acid sequencing, active-site labeling, and antithrombin III inhibition assays with purified human plasma FIX","pmids":["659613"],"confidence":"High","gaps":["Precise cleavage site sequences inferred from protein chemistry, not yet confirmed by cDNA sequencing","Structural basis of FXIa recognition of FIX not defined"]},{"year":1982,"claim":"Cloning the F9 cDNA and gene resolved the complete primary structure, revealing domain organization (Gla domain with 12 γ-carboxylation sites, EGF-like domains, activation peptide, and catalytic domain with His221/Asp270/Ser366 triad) and establishing F9 as a single X-linked gene spanning ~33.5 kb with 8 exons whose boundaries correspond to functional domains.","evidence":"cDNA cloning from human liver library, complete genomic DNA sequencing, exon-intron mapping, and somatic cell hybrid panel mapping","pmids":["6959130","6287289","2994716","6320191"],"confidence":"High","gaps":["Three-dimensional structure not yet determined","Regulatory elements controlling liver-specific expression not characterized"]},{"year":1986,"claim":"Identification of the Arg-4→Gln mutation established that propeptide processing is a discrete essential step in FIX maturation, distinct from signal peptide cleavage, and that disruption of this single residue causes hemophilia B by producing an abnormally elongated, non-functional FIX molecule.","evidence":"DNA sequencing of hemophilia B patient, in vitro expression, SDS-PAGE, and N-terminal sequencing of the aberrant protein","pmids":["3009023"],"confidence":"High","gaps":["Whether propeptide retention also impairs γ-carboxylation was not tested","Identity of the propeptidase was not established"]},{"year":1989,"claim":"Systematic genotype-phenotype correlation across hemophilia B patients revealed that different mutation types produce distinct pathophysiological mechanisms—some abolishing circulating antigen, others selectively destroying function—and identified CpG dinucleotides as mutation hotspots, providing a framework for understanding structure-function relationships across the entire FIX protein.","evidence":"PCR amplification and direct sequencing of F9 genomic DNA from a large cohort of hemophilia B patients","pmids":["2743975"],"confidence":"High","gaps":["Individual variants not reconstituted biochemically","Structural basis for each functional defect not defined"]},{"year":1990,"claim":"Quantitative kinetic characterization of FIX activation by Factor VIIa/tissue factor demonstrated that FIX is a preferred substrate over Factor X for the extrinsic pathway initiator complex, establishing the dual-pathway activation of FIX and defining the role of tissue factor and phospholipids as cofactors.","evidence":"Steady-state enzyme kinetics with purified recombinant FVIIa under varied cofactor conditions","pmids":["2248955"],"confidence":"High","gaps":["Structural basis for substrate preference not determined","Relative contributions of the two activation pathways in vivo not quantified"]},{"year":1995,"claim":"The 1.5 Å crystal structure of the Ca²⁺-binding EGF-like domain explained how Ca²⁺ maintains domain conformation and directly mediates protein-protein contacts, while the elucidation of TFPI-mediated shutdown of the extrinsic pathway explained why the intrinsic pathway (and thus FIX) is essential for sustained hemostasis despite extrinsic pathway initiation.","evidence":"X-ray crystallography of recombinant FIX EGF domain; biochemical reconstitution of TFPI inhibition kinetics","pmids":["7606779","7598447"],"confidence":"High","gaps":["Full-length FIX or FIXa structure not solved","Atomic details of FIXa–FVIIIa interface unknown"]},{"year":2013,"claim":"Analysis of over 1100 unique F9 mutations across >3700 patients established that functional (Type II) mutations predominantly map to regions mediating activation and Xase complex assembly, and that inhibitor development is rare and mutation-specific, providing a comprehensive genotype-phenotype map.","evidence":"Mutation database analysis with homology-based structural modeling of FIXa","pmids":["23617593"],"confidence":"Medium","gaps":["Structural modeling based on homology rather than experimental FIXa structure","No direct functional reconstitution for individual variants in this study"]},{"year":2019,"claim":"Discovery that FIX binds collagen IV in the subendothelial basement membrane revealed an extravascular reservoir of FIX that affects pharmacokinetics and therapeutic efficacy—CRM+ hemophilia B patients' dysfunctional FIX competes for binding sites with infused therapeutic FIX, explaining reduced recovery.","evidence":"Mouse hemophilia B models (CRM− and CRM+), saphenous vein bleeding assay, FIX pharmacokinetic analysis","pmids":["30992271"],"confidence":"High","gaps":["Col4 binding site on FIX not mapped","Quantitative contribution of the vascular reservoir to normal hemostasis in humans not established"]},{"year":2022,"claim":"Three complementary studies expanded understanding of FIX biology: codon optimization of F9 alters cotranslational folding kinetics and MHC class II peptide presentation (affecting immunogenicity despite identical amino acid sequence), comprehensive mutation review catalogued mechanistic classes of hemophilia B, and a CRISPR screen unexpectedly identified FIX as a regulator of CDK4/6-inhibitor-induced cellular senescence.","evidence":"Ribosome profiling and immunopeptidomics of recoded F9 constructs; systematic review of >1000 mutations; genome-wide CRISPR/Cas9 screen with shRNA and recombinant protein validation in MCF7 cells","pmids":["35413099","35269902","35184131"],"confidence":"High","gaps":["Mechanism by which FIX protein promotes senescence is unknown","Whether codon-usage effects on immunogenicity are clinically significant is untested","Whether FIX's senescence role is relevant to hemophilia B pathophysiology is unexplored"]},{"year":null,"claim":"Key unresolved questions include the molecular mechanism by which extracellular/intracellular FIX promotes cellular senescence, the structural basis of the complete FIXa–FVIIIa–phospholipid Xase complex, and the precise mapping of the FIX–collagen IV interaction interface.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length FIXa crystal structure or cryo-EM structure of Xase complex available","Senescence mechanism entirely undefined at the signaling level","FIX–Col4 binding interface not mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,13]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[0,1,6,7,8]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[4,5,11,14]}],"complexes":["intrinsic tenase (Xase) complex"],"partners":["F11","F8","F10","F7","COL4A1","SERPINC1"],"other_free_text":[]},"mechanistic_narrative":"Coagulation factor IX (FIX) is a vitamin K-dependent serine protease zymogen that circulates in plasma and, upon proteolytic activation by Factor XIa or the Factor VIIa/tissue factor complex, assembles with Factor VIIIa, Ca²⁺, and phospholipid into the intrinsic tenase (Xase) complex to activate Factor X, thereby propagating the coagulation cascade [PMID:659613, PMID:2248955, PMID:7598447]. The mature 416-residue protein undergoes extensive post-translational processing—signal peptide and propeptide cleavage (requiring Arg-4), γ-carboxylation of 12 glutamic acid residues, β-hydroxylation, and glycosylation—and its Ca²⁺-binding EGF-like domain (solved at 1.5 Å) mediates critical protein–protein contacts within the Xase complex [PMID:6959130, PMID:7606779, PMID:3009023]. FIX also binds collagen IV in the subendothelial basement membrane, forming a vascular reservoir that modulates plasma recovery and hemostatic efficacy of infused FIX [PMID:30992271]. Loss-of-function mutations in the X-linked F9 gene cause hemophilia B through diverse mechanisms including impaired propeptide processing, defective post-translational modification, protein instability, and failure of Xase complex assembly [PMID:2743975, PMID:35269902]."},"prefetch_data":{"uniprot":{"accession":"P00740","full_name":"Coagulation factor IX","aliases":["Christmas factor","Plasma thromboplastin component","PTC"],"length_aa":461,"mass_kda":51.8,"function":"Factor IX is a vitamin K-dependent plasma protein that participates in the intrinsic pathway of blood coagulation by converting factor X to its active form in the presence of Ca(2+) ions, phospholipids, and factor VIIIa (PubMed:8295821, PubMed:2592373, PubMed:20121197, PubMed:20121198, PubMed:1730085, PubMed:19846852, PubMed:39880037)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P00740/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/F9","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/F9","total_profiled":1310},"omim":[{"mim_id":"621143","title":"HOLOPROSENCEPHALY 10; HPE10","url":"https://www.omim.org/entry/621143"},{"mim_id":"620152","title":"HYPOMAGNESEMIA 7, RENAL, WITH OR WITHOUT DILATED CARDIOMYOPATHY; HOMG7","url":"https://www.omim.org/entry/620152"},{"mim_id":"620025","title":"DIAPHRAGMATIC HERNIA 4, WITH CARDIOVASCULAR DEFECTS; DIH4","url":"https://www.omim.org/entry/620025"},{"mim_id":"619525","title":"CONGENITAL DISORDER OF GLYCOSYLATION, TYPE IIw; CDG2W","url":"https://www.omim.org/entry/619525"},{"mim_id":"619114","title":"SET AND MYND DOMAIN-CONTAINING PROTEIN 5; SMYD5","url":"https://www.omim.org/entry/619114"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"liver","ntpm":659.1}],"url":"https://www.proteinatlas.org/search/F9"},"hgnc":{"alias_symbol":["FIX"],"prev_symbol":[]},"alphafold":{"accession":"P00740","domains":[{"cath_id":"-","chopping":"60-94","consensus_level":"medium","plddt":83.1823,"start":60,"end":94},{"cath_id":"2.10.25.10","chopping":"133-173","consensus_level":"high","plddt":89.7498,"start":133,"end":173},{"cath_id":"2.40.10.10","chopping":"177-183_228-461","consensus_level":"medium","plddt":89.3991,"start":177,"end":461}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P00740","model_url":"https://alphafold.ebi.ac.uk/files/AF-P00740-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P00740-F1-predicted_aligned_error_v6.png","plddt_mean":80.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=F9","jax_strain_url":"https://www.jax.org/strain/search?query=F9"},"sequence":{"accession":"P00740","fasta_url":"https://rest.uniprot.org/uniprotkb/P00740.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P00740/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P00740"}},"corpus_meta":[{"pmid":"20051983","id":"PMC_20051983","title":"DNA 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-4.","date":"1986","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/3009023","citation_count":183,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"2248955","id":"PMC_2248955","title":"Proteolytic activation of human factors IX and X by recombinant human factor VIIa: effects of calcium, phospholipids, and tissue factor.","date":"1990","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2248955","citation_count":176,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"6320191","id":"PMC_6320191","title":"Regional localization on the human X chromosome and polymorphism of the coagulation factor IX gene (hemophilia B locus).","date":"1984","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/6320191","citation_count":174,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"19913121","id":"PMC_19913121","title":"Gene-centric association signals for lipids and apolipoproteins identified via the HumanCVD BeadChip.","date":"2009","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19913121","citation_count":164,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"6687940","id":"PMC_6687940","title":"Isolation of a human anti-haemophilic factor IX cDNA clone using a unique 52-base synthetic oligonucleotide probe deduced from the amino acid sequence of bovine factor IX.","date":"1983","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/6687940","citation_count":155,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23533145","id":"PMC_23533145","title":"In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.","date":"2013","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/23533145","citation_count":138,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23617593","id":"PMC_23617593","title":"An interactive mutation database for human coagulation factor IX provides novel insights into the phenotypes and genetics of hemophilia B.","date":"2013","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/23617593","citation_count":134,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":45155,"output_tokens":1961,"usd":0.08244},"stage2":{"model":"claude-opus-4-6","input_tokens":5230,"output_tokens":2073,"usd":0.116962},"total_usd":0.493356,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":57039,"output_tokens":6028,"usd":0.130769},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":8323,"output_tokens":2687,"usd":0.163185}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2022,\n      \"finding\": \"Coagulation factor IX (FIX) deficiency in hemophilia B arises through diverse molecular mechanisms depending on mutation type: large deletions/frameshifts cause loss of function; promoter mutations cause hemophilia B Leyden; nonsense mutations produce truncated non-functional FIX; missense mutations can impair translation, protein folding, stability, post-translational modifications, activation to FIXa, or formation of the functional Xase complex.\",\n      \"method\": \"Systematic review of structural and functional data, mutational analysis, and biochemical assays from literature\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods across many independent studies, strong preponderance of evidence\",\n      \"pmids\": [\"35269902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FIX binds to collagen IV (Col4) in the subendothelial basement membrane, and this interaction reduces plasma recovery of infused FIX. Dysfunctional endogenous FIX (FIXR333Q) competes with infused wild-type FIX for Col4 binding, thereby impairing hemostatic efficacy of prophylactic therapy in CRM+ hemophilia B mice.\",\n      \"method\": \"Mouse hemophilia B model (CRM- and CRM+ mice), saphenous vein bleeding assay, pharmacokinetic analysis of FIX plasma recovery\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo mouse model with defined mechanistic readout (Col4 binding competition), replicated across multiple FIX products\",\n      \"pmids\": [\"30992271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Synonymous codon substitutions (recoding) of F9 alter cotranslational folding kinetics (as measured by ribosome profiling), change protein conformation, cause suboptimal post-translational processing, and result in distinct MHC class II peptide presentation, suggesting altered immunogenicity despite identical amino acid sequence.\",\n      \"method\": \"Ribosome profiling, MHC-associated peptide proteomics, conformational assessment, post-translational modification analysis\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods in a single study with rigorous controls\",\n      \"pmids\": [\"35413099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"FIX is a vitamin K-dependent coagulation factor; the gain-of-function missense mutation Arg338Leu (FIX Padua) in exon 8 of F9 results in approximately 10-fold increased FIX activity while antigen is only slightly elevated, causing a thrombophilic state with venous thrombosis.\",\n      \"method\": \"Molecular biology analysis, coagulation activity assays, clinical correlation\",\n      \"journal\": \"Clinical and applied thrombosis/hemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional activity assay with clinical validation, single study summarizing prior molecular biology work\",\n      \"pmids\": [\"30428703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The silent mutation G17736A/Val107Val in the F9 gene causes mild hemophilia B (FIX activity 15-20%) without exon skipping or intron retention, suggesting the synonymous change may affect splicing enhancer function or alter codon usage in a way that impairs FIX protein folding in vivo.\",\n      \"method\": \"RT-PCR of lymphocyte mRNA, cDNA sequencing, coagulation activity assays\",\n      \"journal\": \"Haemophilia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional assay with molecular analysis, single lab with mechanistic follow-up\",\n      \"pmids\": [\"18459950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Downregulation of F9 (coagulation factor IX) using sgRNA or shRNA prevents the cell cycle arrest and senescent-like phenotype induced in MCF7 breast cancer cells by CDK4/6 inhibitor Palbociclib; conversely, treatment with recombinant FIX protein is sufficient to induce cell cycle arrest and senescence-like state in MCF7 cells, establishing F9 as a regulator of CDK4/6 inhibitor-induced senescence.\",\n      \"method\": \"Genome-wide CRISPR/Cas9 screen, sgRNA/shRNA knockdown, recombinant FIX protein treatment, cell cycle analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide screen followed by orthogonal KD and gain-of-function with defined phenotypic readout, single lab\",\n      \"pmids\": [\"35184131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Large deletions in F9 (11.1 to 884 kb) cause severe hemophilia B; breakpoint analysis revealed microhomologies of 2-6 bp at junctions, implicating non-homologous end joining (NHEJ) and microhomology-mediated break-induced replication (MMBIR) as the main causative mechanisms for most deletions, while one deletion occurred via non-allelic homologous recombination (NAHR) between tandem LINE/L1 elements.\",\n      \"method\": \"AccuCopy technique, genome walking, primer walking, breakpoint sequencing\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct breakpoint characterization with sequence-level evidence, single study\",\n      \"pmids\": [\"24816826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Induction of immune tolerance to FIX following intramuscular AAV1-hFIX gene transfer is dependent on the dose of AAV and the level of FIX antigen expressed; unlike hepatic AAV gene transfer, FIX tolerance induced by intramuscular injection is not driven by regulatory T cells.\",\n      \"method\": \"Intramuscular AAV injection in normal and hemophilia B mice, dose-response analysis, antibody/T cell assays\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo mouse model with defined immunological mechanism, single lab with dose-response\",\n      \"pmids\": [\"19240690\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Coagulation factor IX (FIX), encoded by F9, is a vitamin K-dependent serine protease that participates in the intrinsic coagulation cascade by forming the Xase complex; its activity is governed by post-translational modifications, activation cleavage, and binding to collagen IV in the subendothelial basement membrane, with loss-of-function mutations causing hemophilia B through diverse mechanisms (misfolding, impaired activation, aberrant splicing, or truncation) and rare gain-of-function missense mutations (e.g., Arg338Leu/FIX Padua) producing thrombophilia; additionally, F9 has been identified as a regulator of CDK4/6 inhibitor-induced cellular senescence in breast cancer cells.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper, then extract discoveries only from KEEP papers.\n\n**Classification:**\n\nThe gene F9 = human coagulation Factor IX (hemophilia B gene). I need to keep papers about this canonical coagulation protein.\n\n- Papers about F9 mouse embryonal carcinoma cell line: EXCLUDE (alias collision - \"F9\" refers to a cell line, not the F9 gene)\n- Papers about F9 fimbriae in E. coli: EXCLUDE (symbol collision - bacterial fimbriae)\n- Papers about Arabidopsis GSTF9: EXCLUDE (symbol collision - plant gene)\n- Papers about Lin_F9 scoring function: EXCLUDE (algorithm, not gene)\n- Papers about CX-F9 RSK2 inhibitor: EXCLUDE (compound name collision)\n- Papers about allotetraploid crucian carp F9-F11: EXCLUDE (fish generation notation)\n- Papers about polyomavirus F9 mutant: EXCLUDE (viral mutant notation)\n- Papers about nitrogen fixation Fix genes: EXCLUDE (microbial fix genes)\n- Papers clearly about human/mammalian coagulation Factor IX: KEEP\n\n**KEEP papers:**\n- PMID:35269902 (Shen et al. 2022 - FIX deficiency molecular basis)\n- PMID:22103590 (Miller et al. 2011 - F8/F9 mutations, hemophilia)\n- PMID:30428703 (Girolami et al. 2018 - FIX Padua mutation)\n- PMID:35184131 (Carpintero-Fernández et al. 2022 - CRISPR screen F9 senescence)\n- PMID:30992271 (Cooley et al. 2019 - FIX-Col4 binding)\n- PMID:35413099 (Katneni et al. 2022 - F9 recoding)\n- PMID:18459950 (Knobe et al. 2008 - silent mutation hemophilia B)\n- PMID:19240690 (Kelly et al. 2009 - FIX tolerance AAV)\n- PMID:29480214 - dysferlin: EXCLUDE\n- PMID:24729686 (Mancuso et al. 2014 - Fc-fusion FIX): KEEP (describes FIX half-life extension via FcRn)\n- PMID:24679056 (Quade-Lyssy et al. 2014 - oral FIX gene therapy): KEEP\n- PMID:30301136 (Wang et al. 2018 - CRISPR F9 integration): KEEP\n- PMID:26988465 (Morfini et al. 2016 - FIX genotype/PK): KEEP\n- PMID:24816826 (Wu et al. 2014 - large F9 deletions): KEEP\n- PMID:22544209 (Yu et al. 2012 - F9 mutations Chinese): KEEP\n\n**Gene2pubmed KEEP papers:**\n- PMID:2994716 (Yoshitake et al. 1985 - F9 gene structure)\n- PMID:6959130 (Kurachi & Davie 1982 - F9 cDNA)\n- PMID:12524220 (Mann et al. 2003 - thrombin dynamics)\n- PMID:7606779 (Rao et al. 1995 - Ca2+-binding EGF domain structure)\n- PMID:659613 (Di Scipio et al. 1978 - FIX activation)\n- PMID:7598447 (Broze 1995 - TFPI)\n- PMID:237463 (Davie & Fujikawa 1975 - blood coagulation)\n- PMID:3009023 (Bentley et al. 1986 - propeptide processing)\n- PMID:2743975 (Green et al. 1989 - hemophilia B molecular pathology)\n- PMID:6329734 (Anson et al. 1984 - F9 gene structure)\n- PMID:6287289 (Choo et al. 1982 - F9 gene cloning)\n- PMID:2248955 (Komiyama et al. 1990 - FVIIa activation of FIX)\n- PMID:6320191 (Camerino et al. 1984 - X chromosome localization)\n- PMID:6687940 (Jaye et al. 1983 - F9 cDNA)\n- PMID:23617593 (Rallapalli et al. 2013 - mutation database)\n- PMID:16322469 (Nathwani et al. 2005 - scAAV FIX gene therapy)\n- PMID:9834200 (Lenting et al. 1998 - FVIII life cycle, mentions FIX interactions) - KEEP\n- PMID:17048007 (Wadelius et al. 2006 - warfarin/F9 haplotypes) - mostly GWAS, EXCLUDE for mechanism\n- PMID:3340835 (Stoflet et al. 1988 - GAWTS method on F9) - method paper, limited mechanism, KEEP for F9 sequence context\n- PMID:12477932, 10391209, 28514442, 33961781, 14718574, 21873635, 15489334, 25037231 - proteomics/genomics databases: EXCLUDE (no F9-specific mechanism)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1978,\n      \"finding\": \"Human Factor IX (FIX) is a single-chain plasma glycoprotein that is activated to a serine protease (Factor IXaβ) by Factor XIa through cleavage of two internal peptide bonds (Arg145-Ala146 and Arg180-Val181), releasing an activation peptide and generating a two-chain enzyme (light chain + heavy chain held by disulfide bond). The heavy chain contains the active-site serine. Factor IXaβ is inhibited by antithrombin III via tight binding to the heavy chain.\",\n      \"method\": \"Protein biochemistry: SDS-PAGE, amino acid sequencing, active-site labeling, antithrombin III inhibition assay\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted activation reaction with sequence-level characterization of cleavage sites and active site, foundational study replicated across field\",\n      \"pmids\": [\"659613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1982,\n      \"finding\": \"Human Factor IX cDNA encodes a 416-amino acid mature protein with a 46-amino acid leader sequence. The protein contains 12 N-terminal glutamic acid residues (substrate for gamma-carboxylation), an activation peptide (35 aa), a light chain (145 aa), and a heavy chain (236 aa) with catalytic triad His221, Asp270, Ser366 homologous to chymotrypsin His57, Asp102, Ser195. Two N-linked glycosylation sites are in the activation peptide.\",\n      \"method\": \"cDNA cloning and sequencing of human liver library; translation product analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete cDNA sequence with structural domain assignment; independently confirmed by multiple labs\",\n      \"pmids\": [\"6959130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1982,\n      \"finding\": \"The F9 gene encoding human coagulation Factor IX was molecularly cloned from a human genomic library using bovine factor IX cDNA as probe, establishing it as a single large gene (≥20 kb) on the X chromosome.\",\n      \"method\": \"Molecular cloning, Southern blotting, hybridization with heterologous cDNA probe\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct gene isolation; foundational cloning paper\",\n      \"pmids\": [\"6287289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"The F9 gene spans approximately 33.5 kb on the X chromosome (Xq26-q27) and contains 8 exons and 7 introns; exons correspond roughly to functional protein domains (prepro leader, Gla domain, EGF-like domains, activation peptide, catalytic domain split across two exons). The gene was mapped to the Xq26-q27 region, and a TaqI restriction fragment length polymorphism was identified for carrier/prenatal diagnosis.\",\n      \"method\": \"Complete genomic DNA sequencing (~38 kb), exon-intron mapping, human-mouse somatic cell hybrid panel mapping, RFLP analysis\",\n      \"journal\": \"Biochemistry / Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete gene sequence with structural characterization; independently confirmed\",\n      \"pmids\": [\"2994716\", \"6320191\", \"6329734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"A point mutation changing Arg-4 to Gln in the propeptide region of Factor IX causes hemophilia B by blocking proteolytic removal of the propeptide during post-translational maturation; signal peptidase cleaves between positions -18 and -19, but further processing to mature FIX requires the Arg at -4. The result is a stable longer protein with 18 extra N-terminal propeptide residues still attached.\",\n      \"method\": \"DNA sequencing of hemophilia B patient, in vitro expression, protein analysis by SDS-PAGE and N-terminal sequencing\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis linked to protein processing defect with direct biochemical characterization\",\n      \"pmids\": [\"3009023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"Molecular pathology of hemophilia B established by direct sequencing of amplified genomic DNA from patients: substitutions of Cys336 or Asn120 cause loss of circulating FIX antigen; deletion of Arg37 causes gross reduction of circulating protein and loss of activity; substitutions of Arg-4, Arg333, Asp64, and Pro55 cause loss of function without marked protein reduction; frameshift/nonsense mutations are associated with inhibitor (antibody) development; CpG dinucleotides show enhanced mutation rates accounting for ~25% of all point mutations.\",\n      \"method\": \"PCR amplification and direct sequencing of F9 genomic DNA from hemophilia B patients\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — systematic genotype-phenotype correlation across many patients with multiple mutation types; replicated across field\",\n      \"pmids\": [\"2743975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Recombinant Factor VIIa activates both Factor IX and Factor X in the presence of calcium, phospholipids, and tissue factor. Under all cofactor conditions, the kcat/Km ratio for FIX activation by FVIIa was considerably greater than for FX activation, suggesting FIX is a preferred substrate. Tissue factor markedly increases both Vmax and kcat/Km for FIX activation.\",\n      \"method\": \"Steady-state enzyme kinetics with purified recombinant FVIIa and chromogenic substrates/clotting assays; varied calcium and phospholipid concentrations\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous in vitro kinetic characterization with recombinant proteins and multiple cofactor conditions\",\n      \"pmids\": [\"2248955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The crystal structure of the Ca2+-binding EGF-like domain of human Factor IX was solved at 1.5 Å resolution in complex with Ca2+. Ca2+ adopts a pentagonal bipyramidal coordination with six ligands from one polypeptide and the seventh from a neighboring EGF domain. Ca2+ maintains the conformation of the N-terminal region of the domain and directly mediates protein-protein contacts, providing a structural basis for EGF-domain interactions in FIX and related proteins.\",\n      \"method\": \"X-ray crystallography at 1.5 Å resolution of recombinant Factor IX EGF-like domain\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional validation of Ca2+ coordination and protein-protein contact mediation\",\n      \"pmids\": [\"7606779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Tissue factor pathway inhibitor (TFPI) directly inhibits activated Factor X and, in a FXa-dependent manner, produces feedback inhibition of the FVIIa/tissue factor complex, thereby limiting the extrinsic pathway initiation of coagulation and explaining the clinical requirement for the intrinsic pathway (including FIX) for sustained hemostasis.\",\n      \"method\": \"Biochemical reconstitution assays with purified proteins; kinetic inhibition studies\",\n      \"journal\": \"Annual review of medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic reconstitution defining FIX's essential role in the revised coagulation model; widely replicated\",\n      \"pmids\": [\"7598447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Self-complementary AAV (scAAV) vectors with a liver-specific mini-hFIX expression cassette achieve 20-fold higher FIX expression in mice compared to single-stranded AAV vectors, correcting the bleeding phenotype in FIX knock-out mice at only 1×10^10 particles (producing supraphysiologic FIX levels) and achieving therapeutic FIX levels (3–30% normal) in nonhuman primates at lower doses.\",\n      \"method\": \"In vivo gene delivery in FIX-KO mice and nonhuman primates; molecular analysis of vector genome forms; FIX clotting activity assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo reconstitution with functional correction in two animal models; multiple orthogonal assays\",\n      \"pmids\": [\"16322469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The silent mutation G17736A/Val107Val in the F9 gene causes mild hemophilia B (FIX activity 15–20 U/dL) in five Swedish families, without exon skipping or intron retention detectable by RT-PCR. The probable mechanism involves subtle effects on splicing enhancer sites or altered codon usage reducing translation rate and thereby affecting FIX protein folding in vivo.\",\n      \"method\": \"RT-PCR and cDNA sequencing of patient lymphocyte mRNA; mutation scanning; FIX activity and antigen measurement\",\n      \"journal\": \"Haemophilia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — molecular characterization with RT-PCR ruling out gross splicing defects; mechanistic explanation remains inferential\",\n      \"pmids\": [\"18459950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Analysis of 1113 unique F9 mutations in 3721 hemophilia B patients revealed that mutations occur in 336/461 (73%) FIX residues. Type II (qualitative, predominantly functional) mutations account for 64% of mild-severity cases with known protein phenotypes, and structural modeling indicates these predominantly disrupt regions involved in functional interactions (activation, Xase complex formation). Inhibitor development is rare (1.6%) and associated with 25 specific mutations.\",\n      \"method\": \"Mutation database analysis combined with homology modeling of FIXa structure based on closely related crystal structures\",\n      \"journal\": \"Journal of thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — large-scale genotype-phenotype correlation with structural modeling; no direct in vitro functional reconstitution for individual variants\",\n      \"pmids\": [\"23617593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Fusion of FIX to the Fc fragment of IgG (rFIXFc) prolongs FIX half-life 3–4 fold in Phase I/IIa studies by exploiting physiological binding of the Fc domain to the neonatal Fc receptor (FcRn), demonstrating that the FcRn recycling pathway can extend FIX circulatory half-life without altering FIX functional activity.\",\n      \"method\": \"Recombinant protein engineering; pharmacokinetic studies in preclinical models and Phase I/IIa/III clinical trials\",\n      \"journal\": \"Drug design, development and therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanism validated in multiple preclinical models and confirmed in clinical trials; FcRn-mediated half-life extension directly demonstrated\",\n      \"pmids\": [\"24729686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Factor IX binds to collagen IV (Col4) in the subendothelial basement membrane, creating a vascular cache of FIX (estimated ~405 nM available Col4 binding capacity) that reduces plasma recovery of infused FIX and contributes to hemostasis. In CRM+ hemophilia B mice expressing dysfunctional FIXR333Q, endogenous dysfunctional FIX competes with infused therapeutic FIX for Col4 binding sites, impairing prophylactic hemostatic therapy.\",\n      \"method\": \"Mouse hemophilia B models (CRM- and CRM+), saphenous vein bleeding assay, pharmacokinetic analysis of FIX plasma recovery, comparison of FIXWT, FIXFC (Alprolix), and FIXAlb (Idelvion)\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo demonstration of FIX-Col4 competition with quantitative pharmacokinetic analysis in two mouse models\",\n      \"pmids\": [\"30992271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FIX deficiency in hemophilia B results from diverse mechanisms depending on mutation type: deletions/insertions/indels in exons cause frameshift or inframe mutations; intronic mutations cause aberrant splicing; F9 promoter point mutations cause hemophilia B Leyden (developmentally regulated loss of expression); nonsense mutations produce truncated non-functional FIX; missense mutations impair translation, protein folding, stability, post-translational modifications (including gamma-carboxylation, beta-hydroxylation, glycosylation, phosphorylation), FIX activation to FIXa, or formation of the functional Xase complex.\",\n      \"method\": \"Systematic review of >1000 F9 mutations correlated with structural/functional data from published biochemical studies\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive synthesis of experimentally validated mechanistic data across >1000 mutations with structural framework\",\n      \"pmids\": [\"35269902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Codon optimization (recoding) of F9 alters cotranslational folding kinetics as revealed by ribosome profiling showing differences in local translation kinetics. Recoded FIX variants show altered protein conformations and suboptimal post-translational modifications due to overexpression. Furthermore, MHC class II-associated peptide proteomics revealed distinct presentation of FIX-derived peptides from recoded versus wild-type F9, indicating that synonymous codon substitutions can alter FIX immunogenicity despite identical amino acid sequence.\",\n      \"method\": \"Ribosome profiling, protein conformation analysis, MHC-associated peptide proteomics, post-translational modification analysis of multiple recoded F9 constructs\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (ribosome profiling, structural assays, immunopeptidomics) in single study\",\n      \"pmids\": [\"35413099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A genome-wide CRISPR/Cas9 screen identified F9 (coagulation Factor IX) as a regulator of cellular senescence. Downregulation of F9 using sgRNA or shRNA prevents cell cycle arrest and the senescent-like phenotype induced by CDK4/6 inhibitor (Palbociclib) in MCF7 breast cancer cells. Conversely, treatment with recombinant FIX protein is sufficient to induce cell cycle arrest and senescence-like state in MCF7 cells. Endogenous F9 is upregulated in primary human cells undergoing senescence.\",\n      \"method\": \"Genome-wide CRISPR/Cas9 loss-of-function screen; shRNA knockdown; recombinant FIX protein treatment; cell cycle analysis; validation in T47D cells and with Abemaciclib; panel of 22 cancer cell lines\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional screen with orthogonal validation (sgRNA, shRNA, recombinant protein) in multiple cell lines; mechanism linking FIX to senescence pathway not yet elucidated\",\n      \"pmids\": [\"35184131\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Coagulation Factor IX (FIX), encoded by the X-linked F9 gene, is a vitamin K-dependent serine protease zymogen that undergoes multi-step post-translational maturation (signal peptide cleavage, propeptide removal requiring Arg-4, gamma-carboxylation of 12 Glu residues, glycosylation, and beta-hydroxylation) before circulating in plasma; it is proteolytically activated to FIXa by FXIa (intrinsic pathway) or FVIIa/tissue factor (extrinsic pathway) through cleavage of two peptide bonds, releasing an activation peptide and generating a two-chain serine protease whose active-site triad (His221, Asp270, Ser366) resides in the heavy chain; FIXa assembles with FVIIIa, phospholipid, and Ca2+ into the intrinsic Xase complex to activate FX, with the Ca2+-binding EGF-like domain (structurally defined at 1.5 Å) mediating critical protein-protein contacts; FIX also binds collagen IV in the subendothelial basement membrane creating a vascular reservoir; over 1000 F9 mutations cause hemophilia B through diverse mechanisms including impaired propeptide processing, aberrant splicing, defective post-translational modification, instability, or failure to form the Xase complex; and beyond coagulation, FIX participates in CDK4/6-inhibitor-induced cellular senescence, as shown by CRISPR screening.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"Coagulation factor IX (FIX) is a vitamin K-dependent serine protease essential for the intrinsic coagulation cascade, where it forms the Xase complex to propagate thrombin generation. Loss-of-function mutations in F9—including large deletions, frameshifts, nonsense mutations, promoter mutations (hemophilia B Leyden), and missense variants that impair folding, activation, or Xase assembly—cause hemophilia B, while the gain-of-function Arg338Leu (FIX Padua) variant confers ~10-fold elevated activity and thrombophilia [PMID:35269902, PMID:30428703]. FIX binds collagen IV in the subendothelial basement membrane, a property that governs plasma recovery of infused FIX and can be competitively occupied by dysfunctional endogenous FIX in CRM-positive hemophilia B, reducing prophylactic efficacy [PMID:30992271]. Synonymous codon changes in F9 alter cotranslational folding kinetics, protein conformation, post-translational processing, and MHC class II peptide presentation, linking translation dynamics to immunogenicity [PMID:35413099].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrating that even synonymous mutations in F9 can cause mild hemophilia B established that codon identity—not just amino acid sequence—contributes to functional FIX production, raising the question of whether splicing regulation or cotranslational folding is affected.\",\n      \"evidence\": \"RT-PCR and cDNA sequencing of lymphocyte mRNA from a hemophilia B patient carrying G17736A/Val107Val\",\n      \"pmids\": [\"18459950\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Exact molecular mechanism (splicing enhancer disruption vs. altered cotranslational folding) was not resolved\",\n        \"Single kindred without in vitro protein expression validation\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showing that immune tolerance to FIX after intramuscular AAV gene transfer is dose-dependent and regulatory T cell-independent clarified how route-specific immune mechanisms govern therapeutic FIX expression.\",\n      \"evidence\": \"Intramuscular AAV1-hFIX injection in hemophilia B mice with dose-response analysis and T cell profiling\",\n      \"pmids\": [\"19240690\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism of tolerance induction without Tregs was not identified\",\n        \"Translation to human immune responses not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Characterizing breakpoints of large F9 deletions revealed that NHEJ and microhomology-mediated mechanisms, rather than classical homologous recombination, are the predominant mutational processes causing severe hemophilia B.\",\n      \"evidence\": \"AccuCopy quantitation and genome/primer walking with breakpoint sequencing in hemophilia B patients\",\n      \"pmids\": [\"24816826\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Limited cohort size; generalizability to all large-deletion hemophilia B unknown\",\n        \"No functional reconstitution of deletions in cell models\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of Arg338Leu (FIX Padua) as a gain-of-function variant producing ~10-fold elevated specific activity established that F9 missense mutations can cause thrombophilia, not just hemophilia.\",\n      \"evidence\": \"Coagulation activity and antigen assays with clinical thrombosis correlation\",\n      \"pmids\": [\"30428703\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural basis for enhanced catalytic activity not fully resolved\",\n        \"Single-study clinical summary rather than large cohort\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Discovery that FIX binds collagen IV in the subendothelial basement membrane, and that dysfunctional endogenous FIX competes for this site, explained the reduced plasma recovery and impaired hemostatic efficacy of replacement therapy in CRM-positive hemophilia B.\",\n      \"evidence\": \"Saphenous vein bleeding assays and pharmacokinetic studies in CRM-positive vs. CRM-negative hemophilia B mice\",\n      \"pmids\": [\"30992271\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural determinants of the FIX–collagen IV interaction not mapped\",\n        \"Relevance of Col4 binding competition in human patients not directly tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Systematic classification of F9 mutations into mechanistic categories—loss of expression, misfolding, impaired activation, defective Xase assembly—provided an integrated framework linking genotype to hemophilia B severity.\",\n      \"evidence\": \"Systematic review integrating structural modeling, mutational databases, and biochemical assays from the literature\",\n      \"pmids\": [\"35269902\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Many individual missense variants lack direct biochemical characterization\",\n        \"Genotype–phenotype correlations for moderate hemophilia B remain incomplete\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showing that synonymous recoding of F9 alters ribosome dynamics, protein conformation, post-translational processing, and MHC class II peptide presentation established that codon usage directly modulates FIX immunogenicity—critical for gene therapy design.\",\n      \"evidence\": \"Ribosome profiling, MHC-associated peptide proteomics, and conformational analysis of recoded F9 constructs\",\n      \"pmids\": [\"35413099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"In vivo immune consequences of altered peptide presentation not tested\",\n        \"Applicability across different codon-optimization strategies unclear\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A genome-wide CRISPR screen identified F9 as a regulator of CDK4/6 inhibitor-induced senescence in breast cancer cells, revealing an unexpected non-hemostatic function where exogenous FIX protein suffices to induce cell cycle arrest.\",\n      \"evidence\": \"CRISPR/Cas9 screen, shRNA knockdown, and recombinant FIX treatment in MCF7 cells with cell cycle analysis\",\n      \"pmids\": [\"35184131\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which FIX triggers senescence signaling is unknown\",\n        \"Findings limited to a single breast cancer cell line\",\n        \"Relevance to in vivo tumor biology not established\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis by which FIX binds collagen IV, the mechanism of FIX-mediated senescence induction, and the in vivo immunogenic consequences of codon-optimized F9 constructs remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of the FIX–collagen IV complex\",\n        \"Signaling pathway linking FIX to CDK4/6 inhibitor-induced senescence not identified\",\n        \"In vivo validation of codon-usage-driven immunogenicity differences lacking\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"complexes\": [\n      \"Xase complex\"\n    ],\n    \"partners\": [\n      \"COL4A1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"Coagulation factor IX (FIX) is a vitamin K-dependent serine protease zymogen that circulates in plasma and, upon proteolytic activation by Factor XIa or the Factor VIIa/tissue factor complex, assembles with Factor VIIIa, Ca²⁺, and phospholipid into the intrinsic tenase (Xase) complex to activate Factor X, thereby propagating the coagulation cascade [PMID:659613, PMID:2248955, PMID:7598447]. The mature 416-residue protein undergoes extensive post-translational processing—signal peptide and propeptide cleavage (requiring Arg-4), γ-carboxylation of 12 glutamic acid residues, β-hydroxylation, and glycosylation—and its Ca²⁺-binding EGF-like domain (solved at 1.5 Å) mediates critical protein–protein contacts within the Xase complex [PMID:6959130, PMID:7606779, PMID:3009023]. FIX also binds collagen IV in the subendothelial basement membrane, forming a vascular reservoir that modulates plasma recovery and hemostatic efficacy of infused FIX [PMID:30992271]. Loss-of-function mutations in the X-linked F9 gene cause hemophilia B through diverse mechanisms including impaired propeptide processing, defective post-translational modification, protein instability, and failure of Xase complex assembly [PMID:2743975, PMID:35269902].\",\n  \"teleology\": [\n    {\n      \"year\": 1978,\n      \"claim\": \"Establishing how Factor IX is converted from a zymogen to an active serine protease answered the fundamental question of FIX's enzymatic mechanism: Factor XIa cleaves two internal peptide bonds to release an activation peptide and generate a disulfide-linked two-chain enzyme whose heavy chain carries the active-site serine and is regulated by antithrombin III.\",\n      \"evidence\": \"SDS-PAGE, amino acid sequencing, active-site labeling, and antithrombin III inhibition assays with purified human plasma FIX\",\n      \"pmids\": [\"659613\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise cleavage site sequences inferred from protein chemistry, not yet confirmed by cDNA sequencing\", \"Structural basis of FXIa recognition of FIX not defined\"]\n    },\n    {\n      \"year\": 1982,\n      \"claim\": \"Cloning the F9 cDNA and gene resolved the complete primary structure, revealing domain organization (Gla domain with 12 γ-carboxylation sites, EGF-like domains, activation peptide, and catalytic domain with His221/Asp270/Ser366 triad) and establishing F9 as a single X-linked gene spanning ~33.5 kb with 8 exons whose boundaries correspond to functional domains.\",\n      \"evidence\": \"cDNA cloning from human liver library, complete genomic DNA sequencing, exon-intron mapping, and somatic cell hybrid panel mapping\",\n      \"pmids\": [\"6959130\", \"6287289\", \"2994716\", \"6320191\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional structure not yet determined\", \"Regulatory elements controlling liver-specific expression not characterized\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Identification of the Arg-4→Gln mutation established that propeptide processing is a discrete essential step in FIX maturation, distinct from signal peptide cleavage, and that disruption of this single residue causes hemophilia B by producing an abnormally elongated, non-functional FIX molecule.\",\n      \"evidence\": \"DNA sequencing of hemophilia B patient, in vitro expression, SDS-PAGE, and N-terminal sequencing of the aberrant protein\",\n      \"pmids\": [\"3009023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether propeptide retention also impairs γ-carboxylation was not tested\", \"Identity of the propeptidase was not established\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"Systematic genotype-phenotype correlation across hemophilia B patients revealed that different mutation types produce distinct pathophysiological mechanisms—some abolishing circulating antigen, others selectively destroying function—and identified CpG dinucleotides as mutation hotspots, providing a framework for understanding structure-function relationships across the entire FIX protein.\",\n      \"evidence\": \"PCR amplification and direct sequencing of F9 genomic DNA from a large cohort of hemophilia B patients\",\n      \"pmids\": [\"2743975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual variants not reconstituted biochemically\", \"Structural basis for each functional defect not defined\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Quantitative kinetic characterization of FIX activation by Factor VIIa/tissue factor demonstrated that FIX is a preferred substrate over Factor X for the extrinsic pathway initiator complex, establishing the dual-pathway activation of FIX and defining the role of tissue factor and phospholipids as cofactors.\",\n      \"evidence\": \"Steady-state enzyme kinetics with purified recombinant FVIIa under varied cofactor conditions\",\n      \"pmids\": [\"2248955\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for substrate preference not determined\", \"Relative contributions of the two activation pathways in vivo not quantified\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The 1.5 Å crystal structure of the Ca²⁺-binding EGF-like domain explained how Ca²⁺ maintains domain conformation and directly mediates protein-protein contacts, while the elucidation of TFPI-mediated shutdown of the extrinsic pathway explained why the intrinsic pathway (and thus FIX) is essential for sustained hemostasis despite extrinsic pathway initiation.\",\n      \"evidence\": \"X-ray crystallography of recombinant FIX EGF domain; biochemical reconstitution of TFPI inhibition kinetics\",\n      \"pmids\": [\"7606779\", \"7598447\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length FIX or FIXa structure not solved\", \"Atomic details of FIXa–FVIIIa interface unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Analysis of over 1100 unique F9 mutations across >3700 patients established that functional (Type II) mutations predominantly map to regions mediating activation and Xase complex assembly, and that inhibitor development is rare and mutation-specific, providing a comprehensive genotype-phenotype map.\",\n      \"evidence\": \"Mutation database analysis with homology-based structural modeling of FIXa\",\n      \"pmids\": [\"23617593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural modeling based on homology rather than experimental FIXa structure\", \"No direct functional reconstitution for individual variants in this study\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Discovery that FIX binds collagen IV in the subendothelial basement membrane revealed an extravascular reservoir of FIX that affects pharmacokinetics and therapeutic efficacy—CRM+ hemophilia B patients' dysfunctional FIX competes for binding sites with infused therapeutic FIX, explaining reduced recovery.\",\n      \"evidence\": \"Mouse hemophilia B models (CRM− and CRM+), saphenous vein bleeding assay, FIX pharmacokinetic analysis\",\n      \"pmids\": [\"30992271\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Col4 binding site on FIX not mapped\", \"Quantitative contribution of the vascular reservoir to normal hemostasis in humans not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Three complementary studies expanded understanding of FIX biology: codon optimization of F9 alters cotranslational folding kinetics and MHC class II peptide presentation (affecting immunogenicity despite identical amino acid sequence), comprehensive mutation review catalogued mechanistic classes of hemophilia B, and a CRISPR screen unexpectedly identified FIX as a regulator of CDK4/6-inhibitor-induced cellular senescence.\",\n      \"evidence\": \"Ribosome profiling and immunopeptidomics of recoded F9 constructs; systematic review of >1000 mutations; genome-wide CRISPR/Cas9 screen with shRNA and recombinant protein validation in MCF7 cells\",\n      \"pmids\": [\"35413099\", \"35269902\", \"35184131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which FIX protein promotes senescence is unknown\", \"Whether codon-usage effects on immunogenicity are clinically significant is untested\", \"Whether FIX's senescence role is relevant to hemophilia B pathophysiology is unexplored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the molecular mechanism by which extracellular/intracellular FIX promotes cellular senescence, the structural basis of the complete FIXa–FVIIIa–phospholipid Xase complex, and the precise mapping of the FIX–collagen IV interaction interface.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length FIXa crystal structure or cryo-EM structure of Xase complex available\", \"Senescence mechanism entirely undefined at the signaling level\", \"FIX–Col4 binding interface not mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 13]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 1, 6, 7, 8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 5, 11, 14]}\n    ],\n    \"complexes\": [\n      \"intrinsic tenase (Xase) complex\"\n    ],\n    \"partners\": [\n      \"F11\",\n      \"F8\",\n      \"F10\",\n      \"F7\",\n      \"COL4A1\",\n      \"SERPINC1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}