{"gene":"FCHO2","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2007,"finding":"The FCHo2 F-BAR domain forms an intrinsically curved all-helical antiparallel dimer (Kd ~2.5 µM), binds liposomes via its concave face, and deforms them into tubules up to 130 nm in diameter; mutation of a phenylalanine on the N-terminal helix partially attenuated narrow tubule formation and conferred curvature sensitivity, establishing the structural basis for membrane curvature generation.","method":"Crystal structure, pulse EPR (DEER), liposome tubulation assay, site-directed mutagenesis","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and biophysical reconstitution in a single rigorous study","pmids":["17540576"],"is_preprint":false},{"year":2011,"finding":"FCHO2's EFC/F-BAR domain binds phosphatidylserine and phosphoinositides and deforms plasma membrane and liposomes into narrow tubes; FCHO2 localizes to clathrin-coated pits, binds the endocytic adaptor Eps15, and its knockdown reduces transferrin endocytosis, establishing its role in clathrin-mediated endocytosis.","method":"Lipid-binding assay, liposome tubulation, co-immunoprecipitation, siRNA knockdown with transferrin uptake assay, fluorescence microscopy","journal":"Genes to Cells","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (binding, morphology, Co-IP, KD + functional readout) in single study","pmids":["21762413"],"is_preprint":false},{"year":2011,"finding":"FCHO2 undergoes monoubiquitination and forms oligomers as determined by gel filtration, properties that may contribute to its role in clathrin-mediated endocytosis.","method":"Gel filtration chromatography, ubiquitination assay","journal":"Genes to Cells","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, biochemical assays without mechanistic follow-up on functional consequence","pmids":["21762413"],"is_preprint":false},{"year":2022,"finding":"FCHo2 self-assembles on PI(4,5)P2-enriched membrane domains into ring-like protein patches; its membrane binding promotes PI(4,5)P2 clustering at the boundary of cargo receptors, which in turn enhances clathrin assembly, providing a mechanistic framework for FCHo2-driven CME initiation.","method":"In vitro reconstitution on supported lipid bilayers, cellular imaging, minimal reconstituted and cellular systems combined","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 — minimal reconstitution plus cellular validation, multiple orthogonal approaches","pmids":["35044298"],"is_preprint":false},{"year":2022,"finding":"FCHo2 (and its yeast ortholog Syp1) bundles septin filaments into flat sheets via its intrinsically disordered region (IDR), independent of the F-BAR domain, revealing an IDR-dependent septin-organizing activity conserved between yeast and mammals.","method":"In vitro reconstitution, electron microscopy, advanced fluorescence microscopy","journal":"Cell Reports","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with domain mapping and EM structural validation","pmids":["36476870"],"is_preprint":false},{"year":2024,"finding":"FCHO2-generated membrane curvature recruits and activates the autoinhibited ubiquitin ligase Nedd4L at clathrin-coated pits: the Nedd4L C2 domain senses a specific degree of membrane curvature produced by the FCHO2 F-BAR domain, relieving the intramolecular C2–HECT autoinhibition, thereby enabling Nedd4L-mediated ubiquitination and endocytosis of ENaC cargo.","method":"In vitro reconstitution on FCHO2-tubulated membranes, co-localization, siRNA knockdown, ubiquitination assay, domain mutagenesis","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of recruitment and activation, corroborated by cellular loss-of-function","pmids":["39402328"],"is_preprint":false},{"year":2023,"finding":"FCHO2 interacts with Mon1a (identified by yeast two-hybrid and co-immunoprecipitation), and siRNA depletion of FCHO2 causes Golgi fragmentation, disrupted uniform distribution of Golgi enzymes, and loss of inter-ministack membrane protein exchange (by FRAP); the effect is partially cell-cycle dependent, requiring mitosis-dependent Golgi fragmentation, implicating FCHO2 in maintaining Golgi ribbon architecture.","method":"Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, FRAP, fluorescence microscopy","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple methods but preprint, single lab","pmids":["37461455"],"is_preprint":true},{"year":2026,"finding":"FCHo2 binds directly to the HDRRE motif in the cytoplasmic tail of integrin β5 (but not β3) and inside-out activates integrin αvβ5 specifically in curved adhesions; a conserved Trp→Tyr substitution at position 766 in β5 (absent in other β isoforms) is required for curved-adhesion formation, and the phosphorylation state of Y766 governs whether αvβ5 engages curved adhesions versus focal adhesions.","method":"Binding assays, mutagenesis (Y766W and domain truncations), loss-of-function/replacement experiments, integrin activation assays, curved-adhesion imaging","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1–2 — binding identified by mutagenesis with clear functional readout, peer-reviewed, multiple orthogonal methods","pmids":["41651837"],"is_preprint":false},{"year":2025,"finding":"FCHo2 participates in phase-separated protein condensates at nascent endocytic sites that provide a platform for clathrin triskelion recruitment and assembly; clathrin assembly in turn restricts condensate growth through surfactant-like behavior, establishing reciprocal regulation between condensates and the clathrin coat.","method":"In vitro reconstitution, NMR spectroscopy, fluorescence microscopy","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 method (reconstitution + NMR) but preprint, single lab","pmids":[],"is_preprint":true}],"current_model":"FCHO2 is an F-BAR/EFC domain protein that senses and generates membrane curvature at clathrin-coated pits by forming curved dimers that tubulate PI(4,5)P2-enriched membranes, nucleating clathrin assembly through phase-separated condensates with Eps15, activating the ubiquitin ligase Nedd4L via curvature-dependent relief of autoinhibition to ubiquitinate cargo, inside-out activating integrin αvβ5 at curved adhesions by binding the β5 HDRRE tail motif, bundling septin filaments via its intrinsically disordered region, and maintaining Golgi ribbon architecture through interaction with Mon1a."},"narrative":{"teleology":[{"year":2007,"claim":"Determining how F-BAR proteins generate membrane curvature: the FCHO2 F-BAR domain crystal structure revealed a curved antiparallel dimer whose concave face binds and tubulates liposomes, establishing the first structural basis for curvature sensing and generation by this protein family.","evidence":"Crystal structure, pulse EPR (DEER), liposome tubulation, site-directed mutagenesis","pmids":["17540576"],"confidence":"High","gaps":["Lipid specificity of membrane binding not resolved","Cellular context of curvature generation not addressed","Relationship to clathrin coat assembly unknown"]},{"year":2011,"claim":"Connecting FCHO2's membrane-deforming activity to a specific cellular process: FCHO2 localizes to clathrin-coated pits, binds Eps15, and its knockdown reduces transferrin endocytosis, establishing it as a functional component of clathrin-mediated endocytosis.","evidence":"Lipid-binding assays, liposome tubulation, co-immunoprecipitation with Eps15, siRNA knockdown with transferrin uptake assay, fluorescence microscopy","pmids":["21762413"],"confidence":"High","gaps":["Mechanism by which FCHO2 initiates coat assembly not defined","Functional consequence of FCHO2 monoubiquitination and oligomerization unclear","Whether FCHO2 acts upstream or in parallel with other nucleation factors not resolved"]},{"year":2022,"claim":"Revealing how FCHO2 nucleates clathrin assembly: reconstitution showed FCHO2 self-assembles into ring-like patches on PI(4,5)P2 domains, clustering lipids at cargo-receptor boundaries to enhance clathrin recruitment, providing a mechanistic framework for endocytic site initiation.","evidence":"In vitro reconstitution on supported lipid bilayers combined with cellular imaging","pmids":["35044298"],"confidence":"High","gaps":["Role of Eps15 and other adaptors in patch formation not dissected","How ring-like patches transition to invaginated pits not shown","Contribution of phase separation to patch assembly not addressed"]},{"year":2022,"claim":"Uncovering a non-endocytic function: FCHO2 bundles septin filaments into flat sheets via its intrinsically disordered region, independent of the F-BAR domain, revealing a conserved cytoskeletal organizing activity distinct from membrane remodeling.","evidence":"In vitro reconstitution, electron microscopy, advanced fluorescence microscopy; conservation shown with yeast ortholog Syp1","pmids":["36476870"],"confidence":"High","gaps":["Physiological consequence of septin bundling in mammalian cells not demonstrated","Whether septin bundling occurs at endocytic sites or other cellular locations unknown","Structural basis of IDR–septin interaction not determined"]},{"year":2024,"claim":"Explaining how membrane curvature is transduced into cargo-selective ubiquitination: FCHO2-generated tubule curvature recruits Nedd4L by engaging its C2 domain, relieving C2–HECT autoinhibition to ubiquitinate ENaC, linking geometric membrane information to E3 ligase activation.","evidence":"In vitro reconstitution on FCHO2-tubulated membranes, domain mutagenesis, siRNA knockdown, ubiquitination assay","pmids":["39402328"],"confidence":"High","gaps":["Whether other E3 ligases are similarly curvature-activated at FCHO2 sites unknown","Range of cargo substrates beyond ENaC not defined","Quantitative curvature threshold for Nedd4L activation not precisely measured"]},{"year":2026,"claim":"Establishing FCHO2 as a curvature-dependent integrin activator: FCHO2 directly binds the HDRRE motif of the integrin β5 cytoplasmic tail and inside-out activates αvβ5 specifically at curved adhesions, with Y766 phosphorylation governing adhesion-type selectivity.","evidence":"Binding assays, Trp→Tyr mutagenesis, domain truncations, integrin activation assays, curved-adhesion imaging in cells","pmids":["41651837"],"confidence":"High","gaps":["Whether FCHO2-mediated integrin activation is linked to its endocytic function not resolved","Structural basis of FCHO2–β5 tail interaction not determined","Upstream regulation of Y766 phosphorylation unknown"]},{"year":null,"claim":"How FCHO2's multiple activities — endocytic nucleation, Nedd4L activation, septin bundling, integrin activation, and Golgi maintenance — are spatiotemporally coordinated within a single cell remains undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No integrated model linking FCHO2's distinct functions through shared or competing domain usage","In vivo phenotype of FCHO2 knockout in mammals not reported in the timeline","Role of phase separation in coordinating FCHO2 functions awaits peer-reviewed validation"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,3,7]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,3,5]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,3,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,7]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[7]}],"complexes":[],"partners":["EPS15","NEDD4L","ITGB5","MON1A"],"other_free_text":[]},"mechanistic_narrative":"FCHO2 is a membrane-sculpting F-BAR domain protein that initiates clathrin-mediated endocytosis by generating membrane curvature, clustering PI(4,5)P2, and scaffolding early endocytic machinery. Its F-BAR domain forms an intrinsically curved antiparallel dimer that tubulates phosphoinositide-enriched membranes and recruits the autoinhibited ubiquitin ligase Nedd4L, whose C2 domain senses FCHO2-generated curvature to relieve C2–HECT autoinhibition and ubiquitinate cargo such as ENaC [PMID:17540576, PMID:39402328]. FCHO2 self-assembles into ring-like patches on PI(4,5)P2 domains to promote clathrin nucleation, binds the endocytic adaptor Eps15, and its depletion impairs transferrin uptake [PMID:35044298, PMID:21762413]. Beyond endocytosis, FCHO2 bundles septin filaments through its intrinsically disordered region independently of the F-BAR domain and directly binds the integrin β5 cytoplasmic tail HDRRE motif to inside-out activate αvβ5 at curved adhesions [PMID:36476870, PMID:41651837]."},"prefetch_data":{"uniprot":{"accession":"Q0JRZ9","full_name":"F-BAR domain only protein 2","aliases":[],"length_aa":810,"mass_kda":88.9,"function":"Functions in an early step of clathrin-mediated endocytosis. Has both a membrane binding/bending activity and the ability to recruit proteins essential to the formation of functional clathrin-coated pits. Has a lipid-binding activity with a preference for membranes enriched in phosphatidylserine and phosphoinositides (Pi(4,5) biphosphate) like the plasma membrane. Its membrane-bending activity might be important for the subsequent action of clathrin and adaptors in the formation of clathrin-coated vesicles. Involved in adaptor protein complex AP-2-dependent endocytosis of the transferrin receptor, it also functions in the AP-2-independent endocytosis of the LDL receptor","subcellular_location":"Membrane, clathrin-coated pit","url":"https://www.uniprot.org/uniprotkb/Q0JRZ9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FCHO2","classification":"Not Classified","n_dependent_lines":152,"n_total_lines":1208,"dependency_fraction":0.12582781456953643},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"EPS15","stoichiometry":10.0},{"gene":"AP2S1","stoichiometry":4.0},{"gene":"AP2B1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/FCHO2","total_profiled":1310},"omim":[{"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":"Approved","locations":[{"location":"Centrosome","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FCHO2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q0JRZ9","domains":[{"cath_id":"1.20.1270.60","chopping":"23-243","consensus_level":"medium","plddt":96.7815,"start":23,"end":243},{"cath_id":"2.60.40","chopping":"543-663","consensus_level":"medium","plddt":91.4877,"start":543,"end":663},{"cath_id":"2.60.40.1170","chopping":"665-786_796-807","consensus_level":"medium","plddt":94.0352,"start":665,"end":807}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q0JRZ9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q0JRZ9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q0JRZ9-F1-predicted_aligned_error_v6.png","plddt_mean":76.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FCHO2","jax_strain_url":"https://www.jax.org/strain/search?query=FCHO2"},"sequence":{"accession":"Q0JRZ9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q0JRZ9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q0JRZ9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q0JRZ9"}},"corpus_meta":[{"pmid":"17540576","id":"PMC_17540576","title":"Structure and analysis of FCHo2 F-BAR domain: a dimerizing and membrane recruitment module that effects membrane curvature.","date":"2007","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/17540576","citation_count":242,"is_preprint":false},{"pmid":"21762413","id":"PMC_21762413","title":"Characterization of the EFC/F-BAR domain protein, FCHO2.","date":"2011","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/21762413","citation_count":29,"is_preprint":false},{"pmid":"15254787","id":"PMC_15254787","title":"Identification and characterization of human FCHO2 and mouse Fcho2 genes in silico.","date":"2004","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/15254787","citation_count":15,"is_preprint":false},{"pmid":"35044298","id":"PMC_35044298","title":"Structural organization and dynamics of FCHo2 docking on membranes.","date":"2022","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/35044298","citation_count":14,"is_preprint":false},{"pmid":"36476870","id":"PMC_36476870","title":"The Syp1/FCHo2 protein induces septin filament bundling through its intrinsically disordered domain.","date":"2022","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/36476870","citation_count":8,"is_preprint":false},{"pmid":"39402328","id":"PMC_39402328","title":"The Nedd4L ubiquitin ligase is activated by FCHO2-generated membrane curvature.","date":"2024","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/39402328","citation_count":3,"is_preprint":false},{"pmid":"37461455","id":"PMC_37461455","title":"Mon1a and FCHO2 are required for maintenance of Golgi architecture.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37461455","citation_count":0,"is_preprint":false},{"pmid":"41184265","id":"PMC_41184265","title":"Circular RNA FCHO2 promotes airway remodeling in COPD via regulating nuclear translocation of PTBP1 to repress the splicing of GRN pre-mRNA.","date":"2025","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41184265","citation_count":0,"is_preprint":false},{"pmid":"41383757","id":"PMC_41383757","title":"FCHo2, instead of talin, enables inside-out activation of integrin ɑvβ5 in curved adhesions.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41383757","citation_count":0,"is_preprint":false},{"pmid":"41651837","id":"PMC_41651837","title":"FCHo2, not talin, enables inside-out activation of integrin ɑvβ5 in curved adhesions.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41651837","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.11.28.691229","title":"FCHo2, instead of talin, enables inside-out activation of integrin αvβ5 in curved adhesions","date":"2025-12-01","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.28.691229","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.05.13.653742","title":"Of condensates and coats - reciprocal regulation of clathrin assembly and the growth of protein networks","date":"2025-05-14","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.13.653742","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6985,"output_tokens":2152,"usd":0.026617},"stage2":{"model":"claude-opus-4-6","input_tokens":5482,"output_tokens":2165,"usd":0.122302},"total_usd":0.148919,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"The FCHo2 F-BAR domain forms an intrinsically curved all-helical antiparallel dimer (Kd ~2.5 µM), binds liposomes via its concave face, and deforms them into tubules up to 130 nm in diameter; mutation of a phenylalanine on the N-terminal helix partially attenuated narrow tubule formation and conferred curvature sensitivity, establishing the structural basis for membrane curvature generation.\",\n      \"method\": \"Crystal structure, pulse EPR (DEER), liposome tubulation assay, site-directed mutagenesis\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and biophysical reconstitution in a single rigorous study\",\n      \"pmids\": [\"17540576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FCHO2's EFC/F-BAR domain binds phosphatidylserine and phosphoinositides and deforms plasma membrane and liposomes into narrow tubes; FCHO2 localizes to clathrin-coated pits, binds the endocytic adaptor Eps15, and its knockdown reduces transferrin endocytosis, establishing its role in clathrin-mediated endocytosis.\",\n      \"method\": \"Lipid-binding assay, liposome tubulation, co-immunoprecipitation, siRNA knockdown with transferrin uptake assay, fluorescence microscopy\",\n      \"journal\": \"Genes to Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (binding, morphology, Co-IP, KD + functional readout) in single study\",\n      \"pmids\": [\"21762413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FCHO2 undergoes monoubiquitination and forms oligomers as determined by gel filtration, properties that may contribute to its role in clathrin-mediated endocytosis.\",\n      \"method\": \"Gel filtration chromatography, ubiquitination assay\",\n      \"journal\": \"Genes to Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, biochemical assays without mechanistic follow-up on functional consequence\",\n      \"pmids\": [\"21762413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FCHo2 self-assembles on PI(4,5)P2-enriched membrane domains into ring-like protein patches; its membrane binding promotes PI(4,5)P2 clustering at the boundary of cargo receptors, which in turn enhances clathrin assembly, providing a mechanistic framework for FCHo2-driven CME initiation.\",\n      \"method\": \"In vitro reconstitution on supported lipid bilayers, cellular imaging, minimal reconstituted and cellular systems combined\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — minimal reconstitution plus cellular validation, multiple orthogonal approaches\",\n      \"pmids\": [\"35044298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FCHo2 (and its yeast ortholog Syp1) bundles septin filaments into flat sheets via its intrinsically disordered region (IDR), independent of the F-BAR domain, revealing an IDR-dependent septin-organizing activity conserved between yeast and mammals.\",\n      \"method\": \"In vitro reconstitution, electron microscopy, advanced fluorescence microscopy\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with domain mapping and EM structural validation\",\n      \"pmids\": [\"36476870\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FCHO2-generated membrane curvature recruits and activates the autoinhibited ubiquitin ligase Nedd4L at clathrin-coated pits: the Nedd4L C2 domain senses a specific degree of membrane curvature produced by the FCHO2 F-BAR domain, relieving the intramolecular C2–HECT autoinhibition, thereby enabling Nedd4L-mediated ubiquitination and endocytosis of ENaC cargo.\",\n      \"method\": \"In vitro reconstitution on FCHO2-tubulated membranes, co-localization, siRNA knockdown, ubiquitination assay, domain mutagenesis\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of recruitment and activation, corroborated by cellular loss-of-function\",\n      \"pmids\": [\"39402328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FCHO2 interacts with Mon1a (identified by yeast two-hybrid and co-immunoprecipitation), and siRNA depletion of FCHO2 causes Golgi fragmentation, disrupted uniform distribution of Golgi enzymes, and loss of inter-ministack membrane protein exchange (by FRAP); the effect is partially cell-cycle dependent, requiring mitosis-dependent Golgi fragmentation, implicating FCHO2 in maintaining Golgi ribbon architecture.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, FRAP, fluorescence microscopy\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple methods but preprint, single lab\",\n      \"pmids\": [\"37461455\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FCHo2 binds directly to the HDRRE motif in the cytoplasmic tail of integrin β5 (but not β3) and inside-out activates integrin αvβ5 specifically in curved adhesions; a conserved Trp→Tyr substitution at position 766 in β5 (absent in other β isoforms) is required for curved-adhesion formation, and the phosphorylation state of Y766 governs whether αvβ5 engages curved adhesions versus focal adhesions.\",\n      \"method\": \"Binding assays, mutagenesis (Y766W and domain truncations), loss-of-function/replacement experiments, integrin activation assays, curved-adhesion imaging\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — binding identified by mutagenesis with clear functional readout, peer-reviewed, multiple orthogonal methods\",\n      \"pmids\": [\"41651837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FCHo2 participates in phase-separated protein condensates at nascent endocytic sites that provide a platform for clathrin triskelion recruitment and assembly; clathrin assembly in turn restricts condensate growth through surfactant-like behavior, establishing reciprocal regulation between condensates and the clathrin coat.\",\n      \"method\": \"In vitro reconstitution, NMR spectroscopy, fluorescence microscopy\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 method (reconstitution + NMR) but preprint, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"FCHO2 is an F-BAR/EFC domain protein that senses and generates membrane curvature at clathrin-coated pits by forming curved dimers that tubulate PI(4,5)P2-enriched membranes, nucleating clathrin assembly through phase-separated condensates with Eps15, activating the ubiquitin ligase Nedd4L via curvature-dependent relief of autoinhibition to ubiquitinate cargo, inside-out activating integrin αvβ5 at curved adhesions by binding the β5 HDRRE tail motif, bundling septin filaments via its intrinsically disordered region, and maintaining Golgi ribbon architecture through interaction with Mon1a.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FCHO2 is a membrane-sculpting F-BAR domain protein that initiates clathrin-mediated endocytosis by generating membrane curvature, clustering PI(4,5)P2, and scaffolding early endocytic machinery. Its F-BAR domain forms an intrinsically curved antiparallel dimer that tubulates phosphoinositide-enriched membranes and recruits the autoinhibited ubiquitin ligase Nedd4L, whose C2 domain senses FCHO2-generated curvature to relieve C2–HECT autoinhibition and ubiquitinate cargo such as ENaC [PMID:17540576, PMID:39402328]. FCHO2 self-assembles into ring-like patches on PI(4,5)P2 domains to promote clathrin nucleation, binds the endocytic adaptor Eps15, and its depletion impairs transferrin uptake [PMID:35044298, PMID:21762413]. Beyond endocytosis, FCHO2 bundles septin filaments through its intrinsically disordered region independently of the F-BAR domain and directly binds the integrin β5 cytoplasmic tail HDRRE motif to inside-out activate αvβ5 at curved adhesions [PMID:36476870, PMID:41651837].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Determining how F-BAR proteins generate membrane curvature: the FCHO2 F-BAR domain crystal structure revealed a curved antiparallel dimer whose concave face binds and tubulates liposomes, establishing the first structural basis for curvature sensing and generation by this protein family.\",\n      \"evidence\": \"Crystal structure, pulse EPR (DEER), liposome tubulation, site-directed mutagenesis\",\n      \"pmids\": [\"17540576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Lipid specificity of membrane binding not resolved\",\n        \"Cellular context of curvature generation not addressed\",\n        \"Relationship to clathrin coat assembly unknown\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connecting FCHO2's membrane-deforming activity to a specific cellular process: FCHO2 localizes to clathrin-coated pits, binds Eps15, and its knockdown reduces transferrin endocytosis, establishing it as a functional component of clathrin-mediated endocytosis.\",\n      \"evidence\": \"Lipid-binding assays, liposome tubulation, co-immunoprecipitation with Eps15, siRNA knockdown with transferrin uptake assay, fluorescence microscopy\",\n      \"pmids\": [\"21762413\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which FCHO2 initiates coat assembly not defined\",\n        \"Functional consequence of FCHO2 monoubiquitination and oligomerization unclear\",\n        \"Whether FCHO2 acts upstream or in parallel with other nucleation factors not resolved\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealing how FCHO2 nucleates clathrin assembly: reconstitution showed FCHO2 self-assembles into ring-like patches on PI(4,5)P2 domains, clustering lipids at cargo-receptor boundaries to enhance clathrin recruitment, providing a mechanistic framework for endocytic site initiation.\",\n      \"evidence\": \"In vitro reconstitution on supported lipid bilayers combined with cellular imaging\",\n      \"pmids\": [\"35044298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Role of Eps15 and other adaptors in patch formation not dissected\",\n        \"How ring-like patches transition to invaginated pits not shown\",\n        \"Contribution of phase separation to patch assembly not addressed\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Uncovering a non-endocytic function: FCHO2 bundles septin filaments into flat sheets via its intrinsically disordered region, independent of the F-BAR domain, revealing a conserved cytoskeletal organizing activity distinct from membrane remodeling.\",\n      \"evidence\": \"In vitro reconstitution, electron microscopy, advanced fluorescence microscopy; conservation shown with yeast ortholog Syp1\",\n      \"pmids\": [\"36476870\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Physiological consequence of septin bundling in mammalian cells not demonstrated\",\n        \"Whether septin bundling occurs at endocytic sites or other cellular locations unknown\",\n        \"Structural basis of IDR–septin interaction not determined\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Explaining how membrane curvature is transduced into cargo-selective ubiquitination: FCHO2-generated tubule curvature recruits Nedd4L by engaging its C2 domain, relieving C2–HECT autoinhibition to ubiquitinate ENaC, linking geometric membrane information to E3 ligase activation.\",\n      \"evidence\": \"In vitro reconstitution on FCHO2-tubulated membranes, domain mutagenesis, siRNA knockdown, ubiquitination assay\",\n      \"pmids\": [\"39402328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether other E3 ligases are similarly curvature-activated at FCHO2 sites unknown\",\n        \"Range of cargo substrates beyond ENaC not defined\",\n        \"Quantitative curvature threshold for Nedd4L activation not precisely measured\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Establishing FCHO2 as a curvature-dependent integrin activator: FCHO2 directly binds the HDRRE motif of the integrin β5 cytoplasmic tail and inside-out activates αvβ5 specifically at curved adhesions, with Y766 phosphorylation governing adhesion-type selectivity.\",\n      \"evidence\": \"Binding assays, Trp→Tyr mutagenesis, domain truncations, integrin activation assays, curved-adhesion imaging in cells\",\n      \"pmids\": [\"41651837\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether FCHO2-mediated integrin activation is linked to its endocytic function not resolved\",\n        \"Structural basis of FCHO2–β5 tail interaction not determined\",\n        \"Upstream regulation of Y766 phosphorylation unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FCHO2's multiple activities — endocytic nucleation, Nedd4L activation, septin bundling, integrin activation, and Golgi maintenance — are spatiotemporally coordinated within a single cell remains undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No integrated model linking FCHO2's distinct functions through shared or competing domain usage\",\n        \"In vivo phenotype of FCHO2 knockout in mammals not reported in the timeline\",\n        \"Role of phase separation in coordinating FCHO2 functions awaits peer-reviewed validation\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 3, 7]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 7]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"EPS15\",\n      \"NEDD4L\",\n      \"ITGB5\",\n      \"MON1A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}