{"gene":"FCHO1","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2016,"finding":"Arrayed DPF (Asp-Pro-Phe) motifs within Eps15/R are differentially decoded by Fcho1/2 and AP-2; the crystal structure of an Eps15/R·Fcho1 μ-homology domain complex reveals a spacing-dependent DPF triad bound in a mechanistically distinct way from single DPF binding to AP-2. Fcho1/2, Eps15/R, and AP-2 form transient ternary nanoclusters, and the Fcho1/2 interdomain linker drives conformational activation of AP-2 to promote cargo engagement.","method":"X-ray crystallography of Eps15/R·Fcho1 μ-homology domain complex; cell-based assays with FCHO1/2 knockout cells and Eps15 sequestration from plasma membrane; structure-function mutagenesis","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with cell-based loss-of-function and mutagenesis, multiple orthogonal methods in one rigorous study","pmids":["27237791"],"is_preprint":false},{"year":2012,"finding":"The μ-homology domain of FCHO1/2 functions as an endocytic interaction hub; it directly interacts with the BMP receptor Alk8, and translational silencing of fcho1 in zebrafish embryos causes dorsoventral patterning defects consistent with impaired BMP signal transmission. The phenotype of fcho1 morphants is distinct from the more severe defects caused by AP-2 depletion, challenging the model that FCHO1/2 is a compulsory coat nucleator that invariably precedes AP-2.","method":"Morpholino-mediated translational silencing in zebrafish; co-immunoprecipitation / interaction assays of FCHO1/2 μ-homology domain with Alk8; comparison of fcho1 vs. AP-2 knockdown phenotypes","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction assays plus in vivo genetic epistasis in zebrafish, replicated across multiple functional readouts in one study","pmids":["22484487"],"is_preprint":false},{"year":2020,"finding":"Loss-of-function mutations in FCHO1 cause mislocalization of the protein or prevent its interaction with binding partners, resulting in impaired clathrin-coated pit (CCP) formation as shown by live-cell imaging. In FCHO1-deficient Jurkat T cells, TCR internalization is severely impaired but is rescued by re-expression of wild-type FCHO1, establishing a direct role for FCHO1 in TCR endocytosis and T-cell function.","method":"Live-cell imaging of mutant FCHO1 variants; shRNA/CRISPR knockout in Jurkat T cells; rescue by wild-type FCHO1 re-expression; patient-derived primary T cell analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with defined cellular phenotype, rescue experiment, and live-cell imaging across patient-derived and cell-line models","pmids":["32098969"],"is_preprint":false},{"year":2007,"finding":"GFP-FCHO1 localizes to a perinuclear region and its fluorescence intensity fluctuates periodically (~every 100 s) in live cells; this periodicity is temporally correlated with clathrin dynamics, linking FCHO1 behavior to clathrin-coated vesicle formation.","method":"Live-cell fluorescence imaging of GFP-FCHO1 in cultured cells; temporal correlation with clathrin dynamics","journal":"Bioscience, biotechnology, and biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single imaging method, correlation-based linkage without functional manipulation","pmids":["17617719"],"is_preprint":false},{"year":2020,"finding":"FCHO1 contains a PKB (AKT) substrate motif (560PPRRLRSRKVSC571), and a synthetic peptide derived from this motif inhibits cell proliferation via PKB/ERK/SMAD4 pathways, indicating that FCHO1 is phosphorylated by PKB to regulate cell division.","method":"In vitro cell proliferation assay with synthetic FCHO1 peptide; in vivo xenograft tumor model; pathway inhibition via PKB/ERK/SMAD4 readouts","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, indirect peptide-based approach without direct demonstration of PKB phosphorylation of endogenous FCHO1 or site-specific mutagenesis","pmids":["32507602"],"is_preprint":false},{"year":2024,"finding":"In budding yeast, Syp1 (yeast ortholog of FCHo1/2) cooperates with Yap1801/Yap1802 (CALM/AP180) to trigger Ede1 (Eps15)-centric CME initiation complex assembly at plasma membrane regions enriched in anionic phospholipids and cargo, establishing a cooperative molecular mechanism for CME site initiation.","method":"Quantitative live-cell imaging in S. cerevisiae mother vs. daughter cells; yeast genetics (double/triple mutant analysis); combined imaging and genetic epistasis","journal":"PLoS biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative imaging plus genetic epistasis in yeast ortholog system, single lab but two orthogonal methods","pmids":["39316607"],"is_preprint":false},{"year":2026,"finding":"FCHO1 is required for synaptic vesicle endocytosis at central synapses; shRNA knockdown slows endocytic kinetics across all stimulation intensities (25–300 action potentials at 10 Hz) and is rescued by an shRNA-resistant construct. Domain-specific analyses show the F-BAR domain is sufficient under low stimulation, whereas the μ-homology domain becomes essential at higher stimulation strengths, indicating stimulation-strength-dependent functional partitioning of FCHO1 domains.","method":"shRNA-mediated knockdown in neurons; pHluorin-based live imaging of SV endocytosis; domain-deletion rescue experiments with shRNA-resistant constructs","journal":"Molecular brain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with quantitative functional readout, domain-specific rescue, single lab but multiple orthogonal manipulations","pmids":["41943152"],"is_preprint":false}],"current_model":"FCHO1 is an early-arriving endocytic pioneer that uses its F-BAR domain for membrane curvature sensing and its μ-homology domain as an interaction hub (binding Eps15/R DPF motifs, the BMP receptor Alk8, and other partners); together with Eps15/R it forms transient ternary nanoclusters that recruit and conformationally activate AP-2 for cargo engagement, thereby nucleating clathrin-coated pit formation, with the F-BAR domain sufficient for low-demand endocytosis and the μ-homology domain additionally required under high endocytic load, and FCHO1 phosphorylation by PKB implicated in cell-cycle regulation."},"narrative":{"mechanistic_narrative":"FCHO1 is an early-acting organizer of clathrin-mediated endocytosis that nucleates clathrin-coated pit formation by integrating membrane recognition with assembly of the endocytic initiation machinery [PMID:27237791, PMID:32098969]. Through its μ-homology domain it serves as an interaction hub, decoding spacing-dependent DPF triads in Eps15/R, and together with Eps15/R and AP-2 it forms transient ternary nanoclusters in which the FCHO1 interdomain linker drives conformational activation of AP-2 to promote cargo engagement [PMID:27237791]. The μ-homology domain also engages additional partners such as the BMP receptor Alk8, linking FCHO1 to receptor handling beyond a strictly compulsory coat-nucleation role [PMID:22484487]. Loss-of-function mutations mislocalize FCHO1 or abolish partner binding and impair coated-pit formation; in T cells this manifests as severely defective TCR internalization that is restored by wild-type FCHO1, establishing FCHO1 as causative for a human immunodeficiency [PMID:32098969]. The two functional modules are deployed in a demand-dependent manner: the F-BAR domain alone suffices for low endocytic load, whereas the μ-homology domain becomes essential under high endocytic demand, as shown for synaptic vesicle endocytosis [PMID:41943152]. This cooperative initiation logic is conserved, with the yeast ortholog Syp1 acting with Yap1801/Yap1802 to assemble an Ede1 (Eps15)-centric initiation complex at anionic-lipid- and cargo-enriched membrane sites [PMID:39316607].","teleology":[{"year":2007,"claim":"Whether FCHO1 dynamics are coupled to clathrin-coated vesicle formation was unknown; correlating its temporal behavior with clathrin established a candidate role in coated-pit cycling.","evidence":"Live-cell fluorescence imaging of GFP-FCHO1 with temporal correlation to clathrin dynamics in cultured cells","pmids":["17617719"],"confidence":"Low","gaps":["Correlation-based without functional manipulation","Does not define molecular partners or curvature role","Perinuclear localization not mechanistically explained"]},{"year":2012,"claim":"It was unclear whether FCHO1 is an obligatory coat nucleator preceding AP-2; identifying the μ-homology domain as an interaction hub binding Alk8 and showing a milder phenotype than AP-2 loss reframed it as a non-compulsory organizer.","evidence":"Morpholino silencing in zebrafish with dorsoventral patterning readouts plus co-IP of the μ-homology domain with Alk8 and comparison to AP-2 knockdown","pmids":["22484487"],"confidence":"High","gaps":["Alk8 interaction not extended to mammalian receptors","Does not resolve molecular ordering relative to AP-2 at single pits","In vivo phenotype is indirect readout of endocytic activity"]},{"year":2016,"claim":"How FCHO1 coordinates Eps15/R and AP-2 was undefined; structural and cellular work showed it decodes spacing-dependent DPF triads, forms transient ternary nanoclusters, and conformationally activates AP-2 for cargo engagement.","evidence":"X-ray crystallography of the Eps15/R·Fcho1 μ-homology domain complex with FCHO1/2 knockout cell assays and structure-function mutagenesis","pmids":["27237791"],"confidence":"High","gaps":["Stoichiometry and lifetime of nanoclusters in vivo not fully quantified","Linker-driven AP-2 activation mechanism not resolved at atomic level"]},{"year":2020,"claim":"Whether FCHO1 is essential for cargo-specific endocytosis in human cells and disease was unknown; patient mutations impairing coated-pit formation and TCR internalization, rescued by wild-type, established a causative physiological role.","evidence":"Live-cell imaging of mutant variants, knockout and rescue in Jurkat T cells, and patient-derived primary T cell analysis","pmids":["32098969"],"confidence":"High","gaps":["Scope of affected cargoes beyond TCR not delineated","Mechanistic link from individual mutations to specific partner-binding defects not fully mapped"]},{"year":2020,"claim":"Whether FCHO1 is post-translationally regulated to influence proliferation was untested; a PKB substrate motif and a peptide that inhibits proliferation implicated FCHO1 phosphorylation in cell-cycle control.","evidence":"Synthetic FCHO1 peptide proliferation assays, xenograft tumor model, and PKB/ERK/SMAD4 pathway readouts","pmids":["32507602"],"confidence":"Low","gaps":["No direct demonstration of PKB phosphorylation of endogenous FCHO1","No site-specific mutagenesis","Link between endocytic function and proliferation not established"]},{"year":2024,"claim":"The molecular logic of CME site initiation was incompletely defined; the yeast ortholog Syp1 was shown to cooperate with CALM/AP180 orthologs to assemble an Eps15-centric initiation complex at lipid- and cargo-enriched membrane.","evidence":"Quantitative live-cell imaging in S. cerevisiae with double/triple mutant genetic epistasis","pmids":["39316607"],"confidence":"Medium","gaps":["Conservation of the cooperative mechanism in human FCHO1 not directly demonstrated","Single ortholog system"]},{"year":2026,"claim":"Whether FCHO1's two domains have distinct functional contributions was unknown; domain-specific rescue of synaptic vesicle endocytosis revealed demand-dependent partitioning, with the F-BAR domain sufficient at low load and the μ-homology domain essential at high load.","evidence":"shRNA knockdown in neurons with pHluorin imaging of SV endocytosis and domain-deletion rescue using shRNA-resistant constructs","pmids":["41943152"],"confidence":"Medium","gaps":["Molecular basis of high-load dependence on μ-homology domain not defined","Generalizability beyond synapses untested"]},{"year":null,"claim":"How FCHO1 curvature sensing, partner decoding, and AP-2 activation are integrated quantitatively at single coated pits across cell types and endocytic demand remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified spatiotemporal model linking F-BAR membrane sensing to μ-homology partner switching","Phosphoregulation of endogenous FCHO1 unverified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,5]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,2,6]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2]}],"complexes":["FCHO1·Eps15/R·AP-2 ternary nanocluster"],"partners":["EPS15","EPS15R","AP2","ALK8"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14526","full_name":"F-BAR domain only protein 1","aliases":[],"length_aa":889,"mass_kda":96.9,"function":"Functions in an early step of clathrin-mediated endocytosis (PubMed:30822429). Has both a membrane binding/bending activity and the ability to recruit proteins essential to the formation of functional clathrin-coated pits. May regulate Bmp signaling by regulating clathrin-mediated endocytosis of Bmp receptors. Involved in the regulation of T-cell poliferation and activation (PubMed:30822429, PubMed:32098969). Affects TCR clustering upon receptor triggering and modulates its internalisation, playing a role in TCR-dependent T-cell activation (PubMed:32098969)","subcellular_location":"Membrane, clathrin-coated pit","url":"https://www.uniprot.org/uniprotkb/O14526/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FCHO1","classification":"Not Classified","n_dependent_lines":27,"n_total_lines":1208,"dependency_fraction":0.022350993377483443},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FCHO1","total_profiled":1310},"omim":[{"mim_id":"619164","title":"IMMUNODEFICIENCY 76; IMD76","url":"https://www.omim.org/entry/619164"},{"mim_id":"613438","title":"FCH DOMAIN ONLY PROTEIN 2; FCHO2","url":"https://www.omim.org/entry/613438"},{"mim_id":"613437","title":"FCH DOMAIN ONLY PROTEIN 1; FCHO1","url":"https://www.omim.org/entry/613437"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":23.8},{"tissue":"lymphoid tissue","ntpm":14.9},{"tissue":"skin 1","ntpm":20.2}],"url":"https://www.proteinatlas.org/search/FCHO1"},"hgnc":{"alias_symbol":["KIAA0290"],"prev_symbol":[]},"alphafold":{"accession":"O14526","domains":[{"cath_id":"1.20.1270.60","chopping":"15-249","consensus_level":"medium","plddt":94.8126,"start":15,"end":249},{"cath_id":"-","chopping":"627-745","consensus_level":"medium","plddt":89.8929,"start":627,"end":745},{"cath_id":"2.60.40.1170","chopping":"754-852","consensus_level":"medium","plddt":87.6633,"start":754,"end":852}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O14526","model_url":"https://alphafold.ebi.ac.uk/files/AF-O14526-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O14526-F1-predicted_aligned_error_v6.png","plddt_mean":71.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FCHO1","jax_strain_url":"https://www.jax.org/strain/search?query=FCHO1"},"sequence":{"accession":"O14526","fasta_url":"https://rest.uniprot.org/uniprotkb/O14526.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O14526/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O14526"}},"corpus_meta":[{"pmid":"27237791","id":"PMC_27237791","title":"Transient Fcho1/2⋅Eps15/R⋅AP-2 Nanoclusters Prime the AP-2 Clathrin Adaptor for Cargo Binding.","date":"2016","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/27237791","citation_count":84,"is_preprint":false},{"pmid":"22484487","id":"PMC_22484487","title":"Distinct and separable activities of the endocytic clathrin-coat components Fcho1/2 and AP-2 in developmental patterning.","date":"2012","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22484487","citation_count":76,"is_preprint":false},{"pmid":"32098969","id":"PMC_32098969","title":"Human FCHO1 deficiency reveals role for clathrin-mediated endocytosis in development and function of T cells.","date":"2020","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/32098969","citation_count":24,"is_preprint":false},{"pmid":"30822429","id":"PMC_30822429","title":"F-BAR domain only protein 1 (FCHO1) deficiency is a novel cause of combined immune deficiency in human subjects.","date":"2019","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30822429","citation_count":22,"is_preprint":false},{"pmid":"17617719","id":"PMC_17617719","title":"Dynamic behavior of FCHO1 revealed by live-cell imaging microscopy: its possible involvement in clathrin-coated vesicle formation.","date":"2007","source":"Bioscience, biotechnology, and biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17617719","citation_count":11,"is_preprint":false},{"pmid":"32507602","id":"PMC_32507602","title":"FCHO1560-571 peptide, a PKB kinase motif, inhibits tumor progression.","date":"2020","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/32507602","citation_count":5,"is_preprint":false},{"pmid":"34413495","id":"PMC_34413495","title":"FCH domain only 1 (FCHo1), a potential new biomarker for lung cancer.","date":"2021","source":"Cancer gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/34413495","citation_count":3,"is_preprint":false},{"pmid":"39316607","id":"PMC_39316607","title":"The conserved protein adaptors CALM/AP180 and FCHo1/2 cooperatively recruit Eps15 to promote the initiation of clathrin-mediated endocytosis in yeast.","date":"2024","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/39316607","citation_count":3,"is_preprint":false},{"pmid":"39166479","id":"PMC_39166479","title":"Comprehensive exploration of FCHO1 mutations: Clinical manifestations and implications across disorders.","date":"2024","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/39166479","citation_count":1,"is_preprint":false},{"pmid":"39498505","id":"PMC_39498505","title":"Human FCHO1 deficiency: review of the literature and additional two cases.","date":"2025","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/39498505","citation_count":1,"is_preprint":false},{"pmid":"41943152","id":"PMC_41943152","title":"FCHO1 fine-tunes synaptic vesicle endocytosis in an activity-dependent manner.","date":"2026","source":"Molecular brain","url":"https://pubmed.ncbi.nlm.nih.gov/41943152","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6496,"output_tokens":2056,"usd":0.025164,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9067,"output_tokens":2881,"usd":0.05868,"stage2_stop_reason":"end_turn"},"total_usd":0.083844,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2016,\n      \"finding\": \"Arrayed DPF (Asp-Pro-Phe) motifs within Eps15/R are differentially decoded by Fcho1/2 and AP-2; the crystal structure of an Eps15/R·Fcho1 μ-homology domain complex reveals a spacing-dependent DPF triad bound in a mechanistically distinct way from single DPF binding to AP-2. Fcho1/2, Eps15/R, and AP-2 form transient ternary nanoclusters, and the Fcho1/2 interdomain linker drives conformational activation of AP-2 to promote cargo engagement.\",\n      \"method\": \"X-ray crystallography of Eps15/R·Fcho1 μ-homology domain complex; cell-based assays with FCHO1/2 knockout cells and Eps15 sequestration from plasma membrane; structure-function mutagenesis\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with cell-based loss-of-function and mutagenesis, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"27237791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The μ-homology domain of FCHO1/2 functions as an endocytic interaction hub; it directly interacts with the BMP receptor Alk8, and translational silencing of fcho1 in zebrafish embryos causes dorsoventral patterning defects consistent with impaired BMP signal transmission. The phenotype of fcho1 morphants is distinct from the more severe defects caused by AP-2 depletion, challenging the model that FCHO1/2 is a compulsory coat nucleator that invariably precedes AP-2.\",\n      \"method\": \"Morpholino-mediated translational silencing in zebrafish; co-immunoprecipitation / interaction assays of FCHO1/2 μ-homology domain with Alk8; comparison of fcho1 vs. AP-2 knockdown phenotypes\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction assays plus in vivo genetic epistasis in zebrafish, replicated across multiple functional readouts in one study\",\n      \"pmids\": [\"22484487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Loss-of-function mutations in FCHO1 cause mislocalization of the protein or prevent its interaction with binding partners, resulting in impaired clathrin-coated pit (CCP) formation as shown by live-cell imaging. In FCHO1-deficient Jurkat T cells, TCR internalization is severely impaired but is rescued by re-expression of wild-type FCHO1, establishing a direct role for FCHO1 in TCR endocytosis and T-cell function.\",\n      \"method\": \"Live-cell imaging of mutant FCHO1 variants; shRNA/CRISPR knockout in Jurkat T cells; rescue by wild-type FCHO1 re-expression; patient-derived primary T cell analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with defined cellular phenotype, rescue experiment, and live-cell imaging across patient-derived and cell-line models\",\n      \"pmids\": [\"32098969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GFP-FCHO1 localizes to a perinuclear region and its fluorescence intensity fluctuates periodically (~every 100 s) in live cells; this periodicity is temporally correlated with clathrin dynamics, linking FCHO1 behavior to clathrin-coated vesicle formation.\",\n      \"method\": \"Live-cell fluorescence imaging of GFP-FCHO1 in cultured cells; temporal correlation with clathrin dynamics\",\n      \"journal\": \"Bioscience, biotechnology, and biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single imaging method, correlation-based linkage without functional manipulation\",\n      \"pmids\": [\"17617719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FCHO1 contains a PKB (AKT) substrate motif (560PPRRLRSRKVSC571), and a synthetic peptide derived from this motif inhibits cell proliferation via PKB/ERK/SMAD4 pathways, indicating that FCHO1 is phosphorylated by PKB to regulate cell division.\",\n      \"method\": \"In vitro cell proliferation assay with synthetic FCHO1 peptide; in vivo xenograft tumor model; pathway inhibition via PKB/ERK/SMAD4 readouts\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, indirect peptide-based approach without direct demonstration of PKB phosphorylation of endogenous FCHO1 or site-specific mutagenesis\",\n      \"pmids\": [\"32507602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In budding yeast, Syp1 (yeast ortholog of FCHo1/2) cooperates with Yap1801/Yap1802 (CALM/AP180) to trigger Ede1 (Eps15)-centric CME initiation complex assembly at plasma membrane regions enriched in anionic phospholipids and cargo, establishing a cooperative molecular mechanism for CME site initiation.\",\n      \"method\": \"Quantitative live-cell imaging in S. cerevisiae mother vs. daughter cells; yeast genetics (double/triple mutant analysis); combined imaging and genetic epistasis\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative imaging plus genetic epistasis in yeast ortholog system, single lab but two orthogonal methods\",\n      \"pmids\": [\"39316607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FCHO1 is required for synaptic vesicle endocytosis at central synapses; shRNA knockdown slows endocytic kinetics across all stimulation intensities (25–300 action potentials at 10 Hz) and is rescued by an shRNA-resistant construct. Domain-specific analyses show the F-BAR domain is sufficient under low stimulation, whereas the μ-homology domain becomes essential at higher stimulation strengths, indicating stimulation-strength-dependent functional partitioning of FCHO1 domains.\",\n      \"method\": \"shRNA-mediated knockdown in neurons; pHluorin-based live imaging of SV endocytosis; domain-deletion rescue experiments with shRNA-resistant constructs\",\n      \"journal\": \"Molecular brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with quantitative functional readout, domain-specific rescue, single lab but multiple orthogonal manipulations\",\n      \"pmids\": [\"41943152\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FCHO1 is an early-arriving endocytic pioneer that uses its F-BAR domain for membrane curvature sensing and its μ-homology domain as an interaction hub (binding Eps15/R DPF motifs, the BMP receptor Alk8, and other partners); together with Eps15/R it forms transient ternary nanoclusters that recruit and conformationally activate AP-2 for cargo engagement, thereby nucleating clathrin-coated pit formation, with the F-BAR domain sufficient for low-demand endocytosis and the μ-homology domain additionally required under high endocytic load, and FCHO1 phosphorylation by PKB implicated in cell-cycle regulation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FCHO1 is an early-acting organizer of clathrin-mediated endocytosis that nucleates clathrin-coated pit formation by integrating membrane recognition with assembly of the endocytic initiation machinery [#0, #2]. Through its μ-homology domain it serves as an interaction hub, decoding spacing-dependent DPF triads in Eps15/R, and together with Eps15/R and AP-2 it forms transient ternary nanoclusters in which the FCHO1 interdomain linker drives conformational activation of AP-2 to promote cargo engagement [#0]. The μ-homology domain also engages additional partners such as the BMP receptor Alk8, linking FCHO1 to receptor handling beyond a strictly compulsory coat-nucleation role [#1]. Loss-of-function mutations mislocalize FCHO1 or abolish partner binding and impair coated-pit formation; in T cells this manifests as severely defective TCR internalization that is restored by wild-type FCHO1, establishing FCHO1 as causative for a human immunodeficiency [#2]. The two functional modules are deployed in a demand-dependent manner: the F-BAR domain alone suffices for low endocytic load, whereas the μ-homology domain becomes essential under high endocytic demand, as shown for synaptic vesicle endocytosis [#6]. This cooperative initiation logic is conserved, with the yeast ortholog Syp1 acting with Yap1801/Yap1802 to assemble an Ede1 (Eps15)-centric initiation complex at anionic-lipid- and cargo-enriched membrane sites [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Whether FCHO1 dynamics are coupled to clathrin-coated vesicle formation was unknown; correlating its temporal behavior with clathrin established a candidate role in coated-pit cycling.\",\n      \"evidence\": \"Live-cell fluorescence imaging of GFP-FCHO1 with temporal correlation to clathrin dynamics in cultured cells\",\n      \"pmids\": [\"17617719\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Correlation-based without functional manipulation\", \"Does not define molecular partners or curvature role\", \"Perinuclear localization not mechanistically explained\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"It was unclear whether FCHO1 is an obligatory coat nucleator preceding AP-2; identifying the μ-homology domain as an interaction hub binding Alk8 and showing a milder phenotype than AP-2 loss reframed it as a non-compulsory organizer.\",\n      \"evidence\": \"Morpholino silencing in zebrafish with dorsoventral patterning readouts plus co-IP of the μ-homology domain with Alk8 and comparison to AP-2 knockdown\",\n      \"pmids\": [\"22484487\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Alk8 interaction not extended to mammalian receptors\", \"Does not resolve molecular ordering relative to AP-2 at single pits\", \"In vivo phenotype is indirect readout of endocytic activity\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"How FCHO1 coordinates Eps15/R and AP-2 was undefined; structural and cellular work showed it decodes spacing-dependent DPF triads, forms transient ternary nanoclusters, and conformationally activates AP-2 for cargo engagement.\",\n      \"evidence\": \"X-ray crystallography of the Eps15/R·Fcho1 μ-homology domain complex with FCHO1/2 knockout cell assays and structure-function mutagenesis\",\n      \"pmids\": [\"27237791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and lifetime of nanoclusters in vivo not fully quantified\", \"Linker-driven AP-2 activation mechanism not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Whether FCHO1 is essential for cargo-specific endocytosis in human cells and disease was unknown; patient mutations impairing coated-pit formation and TCR internalization, rescued by wild-type, established a causative physiological role.\",\n      \"evidence\": \"Live-cell imaging of mutant variants, knockout and rescue in Jurkat T cells, and patient-derived primary T cell analysis\",\n      \"pmids\": [\"32098969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Scope of affected cargoes beyond TCR not delineated\", \"Mechanistic link from individual mutations to specific partner-binding defects not fully mapped\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Whether FCHO1 is post-translationally regulated to influence proliferation was untested; a PKB substrate motif and a peptide that inhibits proliferation implicated FCHO1 phosphorylation in cell-cycle control.\",\n      \"evidence\": \"Synthetic FCHO1 peptide proliferation assays, xenograft tumor model, and PKB/ERK/SMAD4 pathway readouts\",\n      \"pmids\": [\"32507602\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct demonstration of PKB phosphorylation of endogenous FCHO1\", \"No site-specific mutagenesis\", \"Link between endocytic function and proliferation not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The molecular logic of CME site initiation was incompletely defined; the yeast ortholog Syp1 was shown to cooperate with CALM/AP180 orthologs to assemble an Eps15-centric initiation complex at lipid- and cargo-enriched membrane.\",\n      \"evidence\": \"Quantitative live-cell imaging in S. cerevisiae with double/triple mutant genetic epistasis\",\n      \"pmids\": [\"39316607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conservation of the cooperative mechanism in human FCHO1 not directly demonstrated\", \"Single ortholog system\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Whether FCHO1's two domains have distinct functional contributions was unknown; domain-specific rescue of synaptic vesicle endocytosis revealed demand-dependent partitioning, with the F-BAR domain sufficient at low load and the μ-homology domain essential at high load.\",\n      \"evidence\": \"shRNA knockdown in neurons with pHluorin imaging of SV endocytosis and domain-deletion rescue using shRNA-resistant constructs\",\n      \"pmids\": [\"41943152\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of high-load dependence on μ-homology domain not defined\", \"Generalizability beyond synapses untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FCHO1 curvature sensing, partner decoding, and AP-2 activation are integrated quantitatively at single coated pits across cell types and endocytic demand remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified spatiotemporal model linking F-BAR membrane sensing to μ-homology partner switching\", \"Phosphoregulation of endogenous FCHO1 unverified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 2, 6]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\n      \"FCHO1·Eps15/R·AP-2 ternary nanocluster\"\n    ],\n    \"partners\": [\n      \"EPS15\",\n      \"EPS15R\",\n      \"AP2\",\n      \"ALK8\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}