{"gene":"WFIKKN1","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2001,"finding":"WFIKKN1 (WFIKKN) is a secreted multidomain protein containing WAP, follistatin/Kazal, immunoglobulin, two Kunitz-type, and NTR domain modules, predicted to function as a multivalent protease inhibitor. cDNA cloning from a lung library confirmed the gene structure and protein sequence.","method":"Homology-search, gene prediction, cDNA cloning from lung library, domain analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cDNA cloning with functional domain annotation; structural prediction validated by sequencing but no biochemical activity assay in this paper","pmids":["11274388"],"is_preprint":false},{"year":2003,"finding":"The second Kunitz-type protease inhibitor domain of WFIKKN1, expressed in E. coli and purified by affinity chromatography, inhibits trypsin with Ki = 9.6 nM but does not inhibit chymotrypsin, elastase, plasmin, pancreatic kallikrein, lung tryptase, plasma kallikrein, thrombin, urokinase, or tissue plasminogen activator at 1 µM concentration.","method":"Recombinant protein expression in E. coli, affinity chromatography, CD spectroscopy, in vitro protease inhibition assays","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with purified recombinant domain, quantitative Ki measurement, multiple negative controls tested","pmids":["12709070"],"is_preprint":false},{"year":2008,"finding":"WFIKKN1 binds mature GDF8/myostatin, myostatin propeptide, and GDF11 with high affinity. Structure-function studies revealed that the follistatin domain is primarily responsible for binding mature GDF8/GDF11, whereas the NTR domain contributes most significantly to interaction with myostatin propeptide.","method":"Binding assays (surface plasmon resonance/pulldown), domain deletion/truncation structure-function analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — domain-level structure-function mapping with multiple deletion constructs, SPR binding measurements, replicated in same study for both GDF8 and GDF11","pmids":["18596030"],"is_preprint":false},{"year":2010,"finding":"WFIKKN1 binds TGFβ1, BMP2, and BMP4 with relatively high affinity (Kd ~10⁻⁶ M) as measured by SPR, but does not inhibit the biological activity of TGFβ1, BMP2, or BMP4 even at micromolar concentrations in reporter assays, while it inhibits GDF8 and GDF11 activity in the nanomolar range.","method":"Surface plasmon resonance (SPR) binding assays, luciferase reporter assays","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — quantitative SPR measurements plus functional reporter assay, two orthogonal methods, clear mechanistic distinction between binding and inhibition","pmids":["21054789"],"is_preprint":false},{"year":2013,"finding":"WFIKKN1 efficiently blocks myostatin receptor binding to semilatent myostatin (a complex in which the dimeric growth factor domain interacts with only one myostatin propeptide molecule). WFIKKN1 is more potent than WFIKKN2 at inhibiting semilatent myostatin because WFIKKN1 (but not WFIKKN2) has affinity for the propeptide domain, which increases its ability to suppress receptor-binding activity. Latent myostatin preparations exhibit significant myostatin activity due to noncovalent complex dissociation.","method":"Reporter assays, receptor-binding competition assays, comparative analysis of WFIKKN1 vs WFIKKN2 domain binding","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional reporter assays combined with domain-binding comparison, mechanistic explanation supported by two orthogonal approaches","pmids":["23829672"],"is_preprint":false},{"year":2015,"finding":"GASP-2 (WFIKKN1) binds myostatin in a symmetrical 2:1 (two GASP-2 per one myostatin dimer) complex as determined by low-resolution solution structure, in contrast to GASP-1 (WFIKKN2) which binds asymmetrically 1:1. C-terminal truncations of GASP-1 shift it to a 2:1 complex, suggesting C-terminal domains mediate asymmetric binding.","method":"Small-angle X-ray scattering (SAXS) / low-resolution solution structure determination of myostatin-free and myostatin-bound states","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — low-resolution structural determination plus truncation mutant analysis, single lab study","pmids":["25657005"],"is_preprint":false},{"year":2016,"finding":"WFIKKN1 does not inhibit processing of promyostatin by furin, but significantly enhances the rate of cleavage of latent myostatin by BMP1/tolloid protease. This enhancer activity is superstimulated by heparin. BMP1 cleaves WFIKKN1 itself, generating a KKN1 fragment that is the primary mediator of the BMP1-enhancer activity, likely by shifting latent myostatin from a closed homodimeric structure to a more open form accessible to BMP1.","method":"In vitro cleavage assays with furin and BMP1, reporter assays, homology modeling of latent myostatin, heparin supplementation experiments","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro biochemical assays with defined proteases, functional reporter readout, structural modeling, identification of the proteolytic fragment mediating activity","pmids":["27782377"],"is_preprint":false},{"year":2019,"finding":"The follistatin domain (FSD) of WFIKKN2 (closely homologous to WFIKKN1 FSD) interacts with GDF8 and GDF11 and blocks their interaction with the type II receptor ActRIIB. Crystal structure of the WFIKKN2 FSD solved to 1.39 Å; alanine-substitution of surface-exposed FSD residues reduces GDF8 antagonism in full-length WFIKKN2. The FSD of WFIKKN uses different binding interactions than follistatin FSDs to block type II receptor.","method":"Crystal structure determination (1.39 Å resolution), native gel shift, surface plasmon resonance, alanine-scanning mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution crystal structure combined with mutagenesis and SPR, multiple orthogonal methods; note this is WFIKKN2 FSD but directly informs WFIKKN1 FSD function by structural comparison","pmids":["30814254"],"is_preprint":false},{"year":2004,"finding":"OC29, the rat homologue of human WFIKKN1, is expressed in the developing inner ear (otocyst), first broadly in the dorsolateral region giving rise to the vestibular organ (E11.5), then restricted to the BMP4-positive presumptive cristae region (E12.5), suggesting a role in early sensory organ development, particularly formation of the semicircular canal cristae.","method":"In situ hybridization on rat embryos, signal sequence trap cDNA cloning from otocyst library","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization by in situ hybridization in multiple developmental stages; no loss-of-function experiment to confirm functional consequence","pmids":["15497143"],"is_preprint":false},{"year":2022,"finding":"In zebrafish, wfikkn1 expression is dependent on Ahr2 (zebrafish ortholog of human AHR) upon TCDD exposure. CRISPR-Cas9 knockout of wfikkn1 (16-bp deletion) alters the 48-hpf transcriptome (>700 differentially expressed genes) and proteome (325 differentially expressed proteins), with functional enrichment in skeletal muscle development and neurological pathways. wfikkn1 mutant zebrafish show significant behavioral deficiencies at all life stages despite normal morphology.","method":"CRISPR-Cas9 knockout, RNA-seq transcriptomics, mass spectrometry proteomics, behavioral assays, morphological analysis","journal":"Toxicological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with multiple phenotypic readouts (transcriptome, proteome, behavior), zebrafish ortholog study; behavioral phenotype lacks direct mechanistic placement","pmids":["35377459"],"is_preprint":false},{"year":2024,"finding":"Activin E (ActE) is resistant to antagonism by WFIKKN (tested as extracellular antagonist), in contrast to GDF8 and GDF11 which are inhibited by WFIKKN proteins. This establishes a negative result defining the ligand specificity boundary of WFIKKN antagonism within the TGFβ superfamily.","method":"Reporter assays testing resistance to extracellular antagonists including WFIKKN","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional reporter assay establishing negative result (resistance to WFIKKN antagonism), single lab, single method","pmids":["38533769"],"is_preprint":false}],"current_model":"WFIKKN1 is a secreted multidomain extracellular antagonist whose follistatin domain binds mature GDF8/myostatin and GDF11 to block type II receptor (ActRIIB) interactions, while its NTR domain binds the myostatin propeptide; the second Kunitz domain inhibits trypsin (Ki ~9.6 nM); WFIKKN1 also binds TGFβ1, BMP2, and BMP4 without inhibiting their activity; it enhances BMP1-mediated activation of latent myostatin by promoting an open conformation, and is itself cleaved by BMP1 to generate an active KKN1 fragment; WFIKKN1 does not antagonize Activin E, defining the boundaries of its ligand specificity within the TGFβ superfamily."},"narrative":{"mechanistic_narrative":"WFIKKN1 is a secreted multidomain extracellular antagonist of TGFβ-superfamily growth factors, built from WAP, follistatin/Kazal, immunoglobulin, two Kunitz-type, and NTR domain modules and predicted to act as a multivalent protease inhibitor [PMID:11274388]. Its principal characterized activity is high-affinity capture and inhibition of mature GDF8/myostatin and GDF11: the follistatin domain binds the mature growth factor and blocks engagement of the type II receptor ActRIIB, while the NTR domain mediates interaction with the myostatin propeptide [PMID:18596030, PMID:30814254]. This dual binding makes WFIKKN1 a potent blocker of semilatent myostatin receptor engagement, more potent than its homolog WFIKKN2 owing to its propeptide affinity [PMID:23829672], and structural analysis shows WFIKKN1 assembles a symmetrical 2:1 complex around the myostatin dimer [PMID:25657005]. WFIKKN1 also binds TGFβ1, BMP2, and BMP4 with appreciable affinity but does not inhibit their activity, and it fails to antagonize Activin E, defining the boundaries of its ligand specificity within the superfamily [PMID:21054789, PMID:38533769]. Beyond ligand sequestration, WFIKKN1 enhances BMP1/tolloid-mediated cleavage of latent myostatin—an activity superstimulated by heparin and mediated by a KKN1 fragment liberated when BMP1 cleaves WFIKKN1 itself, shifting latent myostatin to an open, processable conformation [PMID:27782377]. Its second Kunitz domain is a selective trypsin inhibitor (Ki ~9.6 nM) [PMID:12709070]. Expression and genetic studies place WFIKKN1 in sensory organ and skeletal-muscle/neurological developmental programs: it marks the BMP4-positive presumptive cristae of the developing inner ear [PMID:15497143], and zebrafish knockouts show transcriptomic and proteomic enrichment for muscle and neurological pathways with behavioral deficits [PMID:35377459].","teleology":[{"year":2001,"claim":"Established WFIKKN1 as a secreted multidomain protein, framing the hypothesis that it acts as a multivalent protease inhibitor through its WAP, follistatin/Kazal, Ig, dual Kunitz, and NTR modules.","evidence":"Homology search, gene prediction, and cDNA cloning from a lung library with domain analysis","pmids":["11274388"],"confidence":"Medium","gaps":["No biochemical activity demonstrated in this study","Individual domain functions not assigned"]},{"year":2003,"claim":"Resolved the functional identity of the second Kunitz domain by showing it is a selective protease inhibitor, addressing whether the predicted inhibitor modules carry real enzymatic-inhibitory activity.","evidence":"Recombinant domain expression in E. coli, affinity purification, CD spectroscopy, and in vitro protease inhibition assays with multiple controls","pmids":["12709070"],"confidence":"High","gaps":["Physiological trypsin-family target unknown","Activity of the other Kunitz and WAP domains not assessed"]},{"year":2004,"claim":"Linked WFIKKN1 to sensory organ development by localizing its rat homolog to the BMP4-positive presumptive cristae of the developing inner ear, hinting at a role in TGFβ/BMP-related morphogenesis.","evidence":"In situ hybridization across rat embryonic stages and signal-sequence-trap cloning from an otocyst library","pmids":["15497143"],"confidence":"Medium","gaps":["No loss-of-function to confirm developmental requirement","Mechanistic connection to BMP4 not tested"]},{"year":2008,"claim":"Identified WFIKKN1 as a myostatin/GDF11 binding protein and mapped domain-level division of labor, answering which modules engage the mature growth factor versus the propeptide.","evidence":"Binding assays (SPR/pulldown) with domain deletion and truncation constructs","pmids":["18596030"],"confidence":"High","gaps":["Receptor-blocking consequence not yet demonstrated","Structural basis of binding unresolved"]},{"year":2010,"claim":"Distinguished binding from inhibition by showing WFIKKN1 binds TGFβ1/BMP2/BMP4 but only neutralizes GDF8/GDF11, establishing functional ligand specificity.","evidence":"Surface plasmon resonance binding measurements paired with luciferase reporter activity assays","pmids":["21054789"],"confidence":"High","gaps":["Reason binding does not translate to inhibition for BMPs unexplained","In vivo relevance of low-affinity BMP binding unknown"]},{"year":2013,"claim":"Explained why WFIKKN1 outperforms WFIKKN2 against semilatent myostatin, attributing potency to its propeptide affinity that suppresses receptor binding.","evidence":"Receptor-binding competition and reporter assays comparing WFIKKN1 and WFIKKN2 domain binding","pmids":["23829672"],"confidence":"High","gaps":["In vivo significance of semilatent-myostatin blockade untested","Quantitative affinity hierarchy across complexes not fully mapped"]},{"year":2015,"claim":"Defined the stoichiometry of antagonism, showing WFIKKN1 forms a symmetrical 2:1 complex with the myostatin dimer, contrasting with the asymmetric 1:1 binding of WFIKKN2.","evidence":"Small-angle X-ray scattering low-resolution solution structures of free and myostatin-bound states with truncation analysis","pmids":["25657005"],"confidence":"Medium","gaps":["Low resolution limits atomic interpretation","Single-lab structural model"]},{"year":2016,"claim":"Uncovered an unexpected pro-activation role: WFIKKN1 enhances BMP1-mediated cleavage of latent myostatin and is itself cleaved into an active KKN1 fragment, reframing it as both antagonist and conditional activator.","evidence":"In vitro furin and BMP1 cleavage assays, reporter readouts, heparin supplementation, and homology modeling of latent myostatin","pmids":["27782377"],"confidence":"High","gaps":["Physiological balance between antagonism and BMP1-enhancer activity unknown","In vivo requirement for the KKN1 fragment untested"]},{"year":2019,"claim":"Provided atomic-resolution mechanism for receptor blockade via the closely homologous WFIKKN2 follistatin domain, showing it binds GDF8/GDF11 and blocks ActRIIB using interactions distinct from canonical follistatin.","evidence":"1.39 Å crystal structure of WFIKKN2 FSD, native gel shift, SPR, and alanine-scanning mutagenesis","pmids":["30814254"],"confidence":"High","gaps":["Direct WFIKKN1 FSD structure not solved","Full-length WFIKKN1 receptor-blocking interface inferred by homology"]},{"year":2022,"claim":"Connected WFIKKN1 to developmental programs in vivo, with zebrafish knockout altering muscle and neurological gene/protein networks and producing behavioral deficits, and placing it downstream of Ahr2/TCDD signaling.","evidence":"CRISPR-Cas9 knockout with RNA-seq, mass-spectrometry proteomics, behavioral and morphological assays","pmids":["35377459"],"confidence":"Medium","gaps":["Behavioral phenotype not mechanistically tied to myostatin/GDF11 axis","Direct AHR regulation of human WFIKKN1 not shown"]},{"year":2024,"claim":"Sharpened the ligand-specificity boundary by showing Activin E resists WFIKKN antagonism, distinguishing it from the inhibited GDF8/GDF11.","evidence":"Reporter assays testing ligand resistance to extracellular antagonists including WFIKKN","pmids":["38533769"],"confidence":"Medium","gaps":["Single method/lab negative result","Structural basis for Activin E resistance not determined"]},{"year":null,"claim":"The physiological role of WFIKKN1 in mammalian muscle and inner-ear development, and the in vivo balance between its myostatin antagonist and BMP1-enhancer functions, remain to be established.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mammalian loss-of-function phenotype reported in the corpus","Tissue-level relevance of the KKN1 fragment unknown","Function of WAP and Ig domains uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3,4,7]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[2,4,5]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,7]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[8,9]}],"complexes":[],"partners":["MSTN","GDF11","BMP1","TGFB1","BMP2","BMP4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96NZ8","full_name":"WAP, Kazal, immunoglobulin, Kunitz and NTR domain-containing protein 1","aliases":["Growth and differentiation factor-associated serum protein 2","GASP-2","hGASP-2","WAP, follistatin, immunoglobulin, Kunitz and NTR domain-containing protein"],"length_aa":548,"mass_kda":58.8,"function":"Protease-inhibitor that contains multiple distinct protease inhibitor domains. Probably has serine protease- and metalloprotease-inhibitor activity (By similarity)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q96NZ8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/WFIKKN1","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/WFIKKN1","total_profiled":1310},"omim":[{"mim_id":"610895","title":"WAP, FOLLISTATIN, IMMUNOGLOBULIN, KUNITZ, AND NTR DOMAINS-CONTAINING PROTEIN 2; WFIKKN2","url":"https://www.omim.org/entry/610895"},{"mim_id":"608021","title":"WAP, FOLLISTATIN, IMMUNOGLOBULIN, KUNITZ, AND NTR DOMAINS-CONTAINING PROTEIN 1; WFIKKN1","url":"https://www.omim.org/entry/608021"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":5.0}],"url":"https://www.proteinatlas.org/search/WFIKKN1"},"hgnc":{"alias_symbol":["RJD2","WFIKKN","WFDC20A"],"prev_symbol":["C16orf12"]},"alphafold":{"accession":"Q96NZ8","domains":[{"cath_id":"-","chopping":"35-78","consensus_level":"high","plddt":73.7439,"start":35,"end":78},{"cath_id":"3.30.60,3.30.60","chopping":"117-158","consensus_level":"medium","plddt":84.074,"start":117,"end":158},{"cath_id":"4.10.410.10","chopping":"358-409","consensus_level":"medium","plddt":88.5323,"start":358,"end":409},{"cath_id":"2.40.50.120","chopping":"419-547","consensus_level":"high","plddt":85.2259,"start":419,"end":547}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96NZ8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96NZ8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96NZ8-F1-predicted_aligned_error_v6.png","plddt_mean":78.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=WFIKKN1","jax_strain_url":"https://www.jax.org/strain/search?query=WFIKKN1"},"sequence":{"accession":"Q96NZ8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96NZ8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96NZ8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96NZ8"}},"corpus_meta":[{"pmid":"18596030","id":"PMC_18596030","title":"Both WFIKKN1 and WFIKKN2 have high affinity for growth and differentiation factors 8 and 11.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18596030","citation_count":67,"is_preprint":false},{"pmid":"11274388","id":"PMC_11274388","title":"A human protein containing multiple types of protease-inhibitory modules.","date":"2001","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/11274388","citation_count":50,"is_preprint":false},{"pmid":"21054789","id":"PMC_21054789","title":"WFIKKN1 and WFIKKN2 bind growth factors TGFβ1, BMP2 and BMP4 but do not inhibit their signalling activity.","date":"2010","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/21054789","citation_count":41,"is_preprint":false},{"pmid":"11928817","id":"PMC_11928817","title":"Distinct expression pattern of two related human proteins containing multiple types of protease-inhibitory modules.","date":"2002","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11928817","citation_count":33,"is_preprint":false},{"pmid":"21189161","id":"PMC_21189161","title":"Epigenetic modification of retinoic acid-treated human embryonic stem cells.","date":"2010","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/21189161","citation_count":23,"is_preprint":false},{"pmid":"27325460","id":"PMC_27325460","title":"WFIKKN1 and WFIKKN2: \"Companion\" proteins regulating TGFB activity.","date":"2016","source":"Cytokine & growth factor reviews","url":"https://pubmed.ncbi.nlm.nih.gov/27325460","citation_count":22,"is_preprint":false},{"pmid":"25657005","id":"PMC_25657005","title":"Alternative binding modes identified for growth and differentiation factor-associated serum protein (GASP) family antagonism of myostatin.","date":"2015","source":"The Journal of biological 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Adults.","date":"2019","source":"The journals of gerontology. Series A, Biological sciences and medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/30380014","citation_count":18,"is_preprint":false},{"pmid":"23829672","id":"PMC_23829672","title":"Latent myostatin has significant activity and this activity is controlled more efficiently by WFIKKN1 than by WFIKKN2.","date":"2013","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/23829672","citation_count":17,"is_preprint":false},{"pmid":"30814254","id":"PMC_30814254","title":"Crystal structure of the WFIKKN2 follistatin domain reveals insight into how it inhibits growth differentiation factor 8 (GDF8) and GDF11.","date":"2019","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30814254","citation_count":16,"is_preprint":false},{"pmid":"34925462","id":"PMC_34925462","title":"Identification of Immune-Related Biomarkers for Sciatica in Peripheral Blood.","date":"2021","source":"Frontiers in 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science","url":"https://pubmed.ncbi.nlm.nih.gov/40544678","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14392,"output_tokens":3031,"usd":0.04432,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10397,"output_tokens":3665,"usd":0.071805,"stage2_stop_reason":"end_turn"},"total_usd":0.116125,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"WFIKKN1 (WFIKKN) is a secreted multidomain protein containing WAP, follistatin/Kazal, immunoglobulin, two Kunitz-type, and NTR domain modules, predicted to function as a multivalent protease inhibitor. cDNA cloning from a lung library confirmed the gene structure and protein sequence.\",\n      \"method\": \"Homology-search, gene prediction, cDNA cloning from lung library, domain analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cDNA cloning with functional domain annotation; structural prediction validated by sequencing but no biochemical activity assay in this paper\",\n      \"pmids\": [\"11274388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The second Kunitz-type protease inhibitor domain of WFIKKN1, expressed in E. coli and purified by affinity chromatography, inhibits trypsin with Ki = 9.6 nM but does not inhibit chymotrypsin, elastase, plasmin, pancreatic kallikrein, lung tryptase, plasma kallikrein, thrombin, urokinase, or tissue plasminogen activator at 1 µM concentration.\",\n      \"method\": \"Recombinant protein expression in E. coli, affinity chromatography, CD spectroscopy, in vitro protease inhibition assays\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with purified recombinant domain, quantitative Ki measurement, multiple negative controls tested\",\n      \"pmids\": [\"12709070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"WFIKKN1 binds mature GDF8/myostatin, myostatin propeptide, and GDF11 with high affinity. Structure-function studies revealed that the follistatin domain is primarily responsible for binding mature GDF8/GDF11, whereas the NTR domain contributes most significantly to interaction with myostatin propeptide.\",\n      \"method\": \"Binding assays (surface plasmon resonance/pulldown), domain deletion/truncation structure-function analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — domain-level structure-function mapping with multiple deletion constructs, SPR binding measurements, replicated in same study for both GDF8 and GDF11\",\n      \"pmids\": [\"18596030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"WFIKKN1 binds TGFβ1, BMP2, and BMP4 with relatively high affinity (Kd ~10⁻⁶ M) as measured by SPR, but does not inhibit the biological activity of TGFβ1, BMP2, or BMP4 even at micromolar concentrations in reporter assays, while it inhibits GDF8 and GDF11 activity in the nanomolar range.\",\n      \"method\": \"Surface plasmon resonance (SPR) binding assays, luciferase reporter assays\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — quantitative SPR measurements plus functional reporter assay, two orthogonal methods, clear mechanistic distinction between binding and inhibition\",\n      \"pmids\": [\"21054789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"WFIKKN1 efficiently blocks myostatin receptor binding to semilatent myostatin (a complex in which the dimeric growth factor domain interacts with only one myostatin propeptide molecule). WFIKKN1 is more potent than WFIKKN2 at inhibiting semilatent myostatin because WFIKKN1 (but not WFIKKN2) has affinity for the propeptide domain, which increases its ability to suppress receptor-binding activity. Latent myostatin preparations exhibit significant myostatin activity due to noncovalent complex dissociation.\",\n      \"method\": \"Reporter assays, receptor-binding competition assays, comparative analysis of WFIKKN1 vs WFIKKN2 domain binding\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reporter assays combined with domain-binding comparison, mechanistic explanation supported by two orthogonal approaches\",\n      \"pmids\": [\"23829672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GASP-2 (WFIKKN1) binds myostatin in a symmetrical 2:1 (two GASP-2 per one myostatin dimer) complex as determined by low-resolution solution structure, in contrast to GASP-1 (WFIKKN2) which binds asymmetrically 1:1. C-terminal truncations of GASP-1 shift it to a 2:1 complex, suggesting C-terminal domains mediate asymmetric binding.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS) / low-resolution solution structure determination of myostatin-free and myostatin-bound states\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — low-resolution structural determination plus truncation mutant analysis, single lab study\",\n      \"pmids\": [\"25657005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"WFIKKN1 does not inhibit processing of promyostatin by furin, but significantly enhances the rate of cleavage of latent myostatin by BMP1/tolloid protease. This enhancer activity is superstimulated by heparin. BMP1 cleaves WFIKKN1 itself, generating a KKN1 fragment that is the primary mediator of the BMP1-enhancer activity, likely by shifting latent myostatin from a closed homodimeric structure to a more open form accessible to BMP1.\",\n      \"method\": \"In vitro cleavage assays with furin and BMP1, reporter assays, homology modeling of latent myostatin, heparin supplementation experiments\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro biochemical assays with defined proteases, functional reporter readout, structural modeling, identification of the proteolytic fragment mediating activity\",\n      \"pmids\": [\"27782377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The follistatin domain (FSD) of WFIKKN2 (closely homologous to WFIKKN1 FSD) interacts with GDF8 and GDF11 and blocks their interaction with the type II receptor ActRIIB. Crystal structure of the WFIKKN2 FSD solved to 1.39 Å; alanine-substitution of surface-exposed FSD residues reduces GDF8 antagonism in full-length WFIKKN2. The FSD of WFIKKN uses different binding interactions than follistatin FSDs to block type II receptor.\",\n      \"method\": \"Crystal structure determination (1.39 Å resolution), native gel shift, surface plasmon resonance, alanine-scanning mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution crystal structure combined with mutagenesis and SPR, multiple orthogonal methods; note this is WFIKKN2 FSD but directly informs WFIKKN1 FSD function by structural comparison\",\n      \"pmids\": [\"30814254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"OC29, the rat homologue of human WFIKKN1, is expressed in the developing inner ear (otocyst), first broadly in the dorsolateral region giving rise to the vestibular organ (E11.5), then restricted to the BMP4-positive presumptive cristae region (E12.5), suggesting a role in early sensory organ development, particularly formation of the semicircular canal cristae.\",\n      \"method\": \"In situ hybridization on rat embryos, signal sequence trap cDNA cloning from otocyst library\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization by in situ hybridization in multiple developmental stages; no loss-of-function experiment to confirm functional consequence\",\n      \"pmids\": [\"15497143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In zebrafish, wfikkn1 expression is dependent on Ahr2 (zebrafish ortholog of human AHR) upon TCDD exposure. CRISPR-Cas9 knockout of wfikkn1 (16-bp deletion) alters the 48-hpf transcriptome (>700 differentially expressed genes) and proteome (325 differentially expressed proteins), with functional enrichment in skeletal muscle development and neurological pathways. wfikkn1 mutant zebrafish show significant behavioral deficiencies at all life stages despite normal morphology.\",\n      \"method\": \"CRISPR-Cas9 knockout, RNA-seq transcriptomics, mass spectrometry proteomics, behavioral assays, morphological analysis\",\n      \"journal\": \"Toxicological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with multiple phenotypic readouts (transcriptome, proteome, behavior), zebrafish ortholog study; behavioral phenotype lacks direct mechanistic placement\",\n      \"pmids\": [\"35377459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Activin E (ActE) is resistant to antagonism by WFIKKN (tested as extracellular antagonist), in contrast to GDF8 and GDF11 which are inhibited by WFIKKN proteins. This establishes a negative result defining the ligand specificity boundary of WFIKKN antagonism within the TGFβ superfamily.\",\n      \"method\": \"Reporter assays testing resistance to extracellular antagonists including WFIKKN\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional reporter assay establishing negative result (resistance to WFIKKN antagonism), single lab, single method\",\n      \"pmids\": [\"38533769\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"WFIKKN1 is a secreted multidomain extracellular antagonist whose follistatin domain binds mature GDF8/myostatin and GDF11 to block type II receptor (ActRIIB) interactions, while its NTR domain binds the myostatin propeptide; the second Kunitz domain inhibits trypsin (Ki ~9.6 nM); WFIKKN1 also binds TGFβ1, BMP2, and BMP4 without inhibiting their activity; it enhances BMP1-mediated activation of latent myostatin by promoting an open conformation, and is itself cleaved by BMP1 to generate an active KKN1 fragment; WFIKKN1 does not antagonize Activin E, defining the boundaries of its ligand specificity within the TGFβ superfamily.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"WFIKKN1 is a secreted multidomain extracellular antagonist of TGFβ-superfamily growth factors, built from WAP, follistatin/Kazal, immunoglobulin, two Kunitz-type, and NTR domain modules and predicted to act as a multivalent protease inhibitor [#0]. Its principal characterized activity is high-affinity capture and inhibition of mature GDF8/myostatin and GDF11: the follistatin domain binds the mature growth factor and blocks engagement of the type II receptor ActRIIB, while the NTR domain mediates interaction with the myostatin propeptide [#2, #7]. This dual binding makes WFIKKN1 a potent blocker of semilatent myostatin receptor engagement, more potent than its homolog WFIKKN2 owing to its propeptide affinity [#4], and structural analysis shows WFIKKN1 assembles a symmetrical 2:1 complex around the myostatin dimer [#5]. WFIKKN1 also binds TGFβ1, BMP2, and BMP4 with appreciable affinity but does not inhibit their activity, and it fails to antagonize Activin E, defining the boundaries of its ligand specificity within the superfamily [#3, #10]. Beyond ligand sequestration, WFIKKN1 enhances BMP1/tolloid-mediated cleavage of latent myostatin—an activity superstimulated by heparin and mediated by a KKN1 fragment liberated when BMP1 cleaves WFIKKN1 itself, shifting latent myostatin to an open, processable conformation [#6]. Its second Kunitz domain is a selective trypsin inhibitor (Ki ~9.6 nM) [#1]. Expression and genetic studies place WFIKKN1 in sensory organ and skeletal-muscle/neurological developmental programs: it marks the BMP4-positive presumptive cristae of the developing inner ear [#8], and zebrafish knockouts show transcriptomic and proteomic enrichment for muscle and neurological pathways with behavioral deficits [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established WFIKKN1 as a secreted multidomain protein, framing the hypothesis that it acts as a multivalent protease inhibitor through its WAP, follistatin/Kazal, Ig, dual Kunitz, and NTR modules.\",\n      \"evidence\": \"Homology search, gene prediction, and cDNA cloning from a lung library with domain analysis\",\n      \"pmids\": [\"11274388\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No biochemical activity demonstrated in this study\", \"Individual domain functions not assigned\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Resolved the functional identity of the second Kunitz domain by showing it is a selective protease inhibitor, addressing whether the predicted inhibitor modules carry real enzymatic-inhibitory activity.\",\n      \"evidence\": \"Recombinant domain expression in E. coli, affinity purification, CD spectroscopy, and in vitro protease inhibition assays with multiple controls\",\n      \"pmids\": [\"12709070\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological trypsin-family target unknown\", \"Activity of the other Kunitz and WAP domains not assessed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Linked WFIKKN1 to sensory organ development by localizing its rat homolog to the BMP4-positive presumptive cristae of the developing inner ear, hinting at a role in TGFβ/BMP-related morphogenesis.\",\n      \"evidence\": \"In situ hybridization across rat embryonic stages and signal-sequence-trap cloning from an otocyst library\",\n      \"pmids\": [\"15497143\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No loss-of-function to confirm developmental requirement\", \"Mechanistic connection to BMP4 not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified WFIKKN1 as a myostatin/GDF11 binding protein and mapped domain-level division of labor, answering which modules engage the mature growth factor versus the propeptide.\",\n      \"evidence\": \"Binding assays (SPR/pulldown) with domain deletion and truncation constructs\",\n      \"pmids\": [\"18596030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor-blocking consequence not yet demonstrated\", \"Structural basis of binding unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Distinguished binding from inhibition by showing WFIKKN1 binds TGFβ1/BMP2/BMP4 but only neutralizes GDF8/GDF11, establishing functional ligand specificity.\",\n      \"evidence\": \"Surface plasmon resonance binding measurements paired with luciferase reporter activity assays\",\n      \"pmids\": [\"21054789\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reason binding does not translate to inhibition for BMPs unexplained\", \"In vivo relevance of low-affinity BMP binding unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Explained why WFIKKN1 outperforms WFIKKN2 against semilatent myostatin, attributing potency to its propeptide affinity that suppresses receptor binding.\",\n      \"evidence\": \"Receptor-binding competition and reporter assays comparing WFIKKN1 and WFIKKN2 domain binding\",\n      \"pmids\": [\"23829672\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of semilatent-myostatin blockade untested\", \"Quantitative affinity hierarchy across complexes not fully mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the stoichiometry of antagonism, showing WFIKKN1 forms a symmetrical 2:1 complex with the myostatin dimer, contrasting with the asymmetric 1:1 binding of WFIKKN2.\",\n      \"evidence\": \"Small-angle X-ray scattering low-resolution solution structures of free and myostatin-bound states with truncation analysis\",\n      \"pmids\": [\"25657005\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Low resolution limits atomic interpretation\", \"Single-lab structural model\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Uncovered an unexpected pro-activation role: WFIKKN1 enhances BMP1-mediated cleavage of latent myostatin and is itself cleaved into an active KKN1 fragment, reframing it as both antagonist and conditional activator.\",\n      \"evidence\": \"In vitro furin and BMP1 cleavage assays, reporter readouts, heparin supplementation, and homology modeling of latent myostatin\",\n      \"pmids\": [\"27782377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological balance between antagonism and BMP1-enhancer activity unknown\", \"In vivo requirement for the KKN1 fragment untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided atomic-resolution mechanism for receptor blockade via the closely homologous WFIKKN2 follistatin domain, showing it binds GDF8/GDF11 and blocks ActRIIB using interactions distinct from canonical follistatin.\",\n      \"evidence\": \"1.39 Å crystal structure of WFIKKN2 FSD, native gel shift, SPR, and alanine-scanning mutagenesis\",\n      \"pmids\": [\"30814254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct WFIKKN1 FSD structure not solved\", \"Full-length WFIKKN1 receptor-blocking interface inferred by homology\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected WFIKKN1 to developmental programs in vivo, with zebrafish knockout altering muscle and neurological gene/protein networks and producing behavioral deficits, and placing it downstream of Ahr2/TCDD signaling.\",\n      \"evidence\": \"CRISPR-Cas9 knockout with RNA-seq, mass-spectrometry proteomics, behavioral and morphological assays\",\n      \"pmids\": [\"35377459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Behavioral phenotype not mechanistically tied to myostatin/GDF11 axis\", \"Direct AHR regulation of human WFIKKN1 not shown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Sharpened the ligand-specificity boundary by showing Activin E resists WFIKKN antagonism, distinguishing it from the inhibited GDF8/GDF11.\",\n      \"evidence\": \"Reporter assays testing ligand resistance to extracellular antagonists including WFIKKN\",\n      \"pmids\": [\"38533769\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method/lab negative result\", \"Structural basis for Activin E resistance not determined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The physiological role of WFIKKN1 in mammalian muscle and inner-ear development, and the in vivo balance between its myostatin antagonist and BMP1-enhancer functions, remain to be established.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mammalian loss-of-function phenotype reported in the corpus\", \"Tissue-level relevance of the KKN1 fragment unknown\", \"Function of WAP and Ig domains uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 4, 7]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [2, 4, 5]},\n      {\"term_id\": \"GO:0004867\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 7]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MSTN\", \"GDF11\", \"BMP1\", \"TGFB1\", \"BMP2\", \"BMP4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}