{"gene":"FEM1C","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2021,"finding":"Crystal structures of FEM1C in complex with Arg/C-degron peptides revealed that FEM1C uses a semi-open binding pocket to capture the C-terminal arginine residue, with the extreme C-terminal arginine being the major structural determinant for recognition. Biochemical and mutagenesis studies confirmed this mechanism of substrate recognition.","method":"X-ray crystallography, biochemical binding assays, mutagenesis","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with functional mutagenesis and biochemical validation in single rigorous study","pmids":["33398170"],"is_preprint":false},{"year":2021,"finding":"FEM1A/C and FEM1B selectively target distinct classes of Arg/C-degrons: FEM1A and FEM1C recognize one subset of arginine-terminated C-degrons while FEM1B targets a distinct subset, as demonstrated by structural studies and global protein stability (GPS) analyses.","method":"X-ray crystallography, binding assays, global protein stability (GPS) profiling","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 — multiple structures combined with functional GPS assays","pmids":["33398168"],"is_preprint":false},{"year":2018,"finding":"FEM1C was identified as one of eight CRL2 substrate adaptors that recognize C-terminal degrons (C-degrons), specifically those ending in arginine, using CRISPR screening and global protein stability profiling of a synthetic human peptidome.","method":"CRISPR screening, global protein stability (GPS) profiling, synthetic peptidome","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — genome-wide functional screen with orthogonal validation, highly cited","pmids":["29779948"],"is_preprint":false},{"year":2018,"finding":"CRL2 ubiquitin ligase complexes using interchangeable substrate receptors (including FEM1C) recognize unusual C termini of abnormal proteins (C-end degrons) via the DesCEND mechanism; C-terminal end position is essential for degron function, and substrates include truncated selenoproteins and the USP1 N-terminal fragment.","method":"Genetic and biochemical assays, protein degradation assays, mutagenesis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 — mechanistic reconstitution with defined substrates and mutagenesis","pmids":["29775578"],"is_preprint":false},{"year":2017,"finding":"FEM1C (along with FEM1A and FEM1B) interacts with and mediates the ubiquitin-dependent degradation of Stem-Loop Binding Protein (SLBP), a conserved regulator of histone mRNA processing. FEM1 proteins interact with an N-terminal region of SLBP using a distinct degron from that used by cyclin F, and this regulation is evolutionarily conserved from C. elegans and Drosophila to mammals.","method":"Co-immunoprecipitation, protein degradation assays, epistasis in C. elegans and Drosophila","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2–3 — reciprocal co-IP and genetic evidence across species, single lab","pmids":["28118078"],"is_preprint":false},{"year":2003,"finding":"Human, mouse, and zebrafish FEM1C proteins are encoded by a conserved gene family member that uniquely terminates with a C-terminal arginine residue (distinguishing them from FEM1A and FEM1B), with >99% amino acid identity between human and mouse and conserved intron-exon structure and expression pattern.","method":"cDNA cloning, sequence analysis, genomic mapping, RT-PCR expression profiling","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 — molecular characterization of gene structure and expression, foundational identification paper","pmids":["14527725"],"is_preprint":false},{"year":2004,"finding":"Insertion of the beta-Geo gene trap into the first intron of mouse Fem1c disrupts normal Fem1c transcript processing in homozygous ROSA3 mice; Fem1c(R3/R3) mice show no adverse effects in sexual development, fertility, or neuronal cell death, suggesting Fem1c is not individually required for these processes in mice.","method":"Gene trap mouse model, RT-PCR, histological and phenotypic analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function genetic model with defined phenotypic readouts","pmids":["15082774"],"is_preprint":false},{"year":2023,"finding":"A de novo missense variant p.(Asp126His) in FEM1C causes a neurodevelopmental disorder with absent speech, pyramidal signs, and limb ataxia. The equivalent variant FEM1C(Asp126Ala) is functionally compromised in vitro for substrate binding. In C. elegans, the homologous FEM-1(Asp133His) variant causes impaired mobility due to synaptic abnormalities (sensitivity to aldicarb but not levamisole), placing FEM1C function at the synapse.","method":"Exome sequencing, in vitro binding assay, C. elegans locomotion assay, aldicarb/levamisole pharmacological assays","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro functional validation plus animal model with mechanistic pharmacological dissection","pmids":["36336956"],"is_preprint":false},{"year":2023,"finding":"A fluorescent probe (ES148, Ki = 1.6 µM) targeting the C-degron binding pocket of FEM1C was developed and validated by fluorescence polarization and isothermal titration calorimetry, establishing that FEM1C recognizes proteins with an R/K-X-R or R/K-X-X-R motif at the C-terminus and enabling small-molecule ligand discovery for PROTAC applications.","method":"Fluorescence polarization assay, isothermal titration calorimetry, competitive binding assay","journal":"Bioorganic & medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical assay with validated binding constants and orthogonal confirmation","pmids":["37339537"],"is_preprint":false},{"year":2021,"finding":"FEM1C knockdown in colorectal cancer cells significantly promotes migration, invasion, and proliferation in vitro and enhances liver and lung metastasis in vivo; knockdown cells shift from epithelial to fibroblast-like morphology, and GSEA analysis indicates enrichment of epithelial-to-mesenchymal transition (EMT) signatures, implicating FEM1C as a suppressor of EMT.","method":"siRNA knockdown, CCK-8 proliferation assay, colony formation assay, transwell invasion assay, in vivo metastasis models, GSEA","journal":"Annals of translational medicine","confidence":"Low","confidence_rationale":"Tier 3 — loss-of-function with cellular phenotype but no direct molecular substrate identified","pmids":["34733943"],"is_preprint":false}],"current_model":"FEM1C is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase that uses a semi-open binding pocket to selectively recognize proteins bearing C-terminal arginine (Arg/C-degron) motifs—including the SLBP histone mRNA regulator and truncated selenoproteins—and targets them for proteasomal degradation; structural and mutagenesis studies show FEM1C and FEM1A share a distinct substrate specificity from FEM1B within this family, and loss-of-function variants at the conserved Asp126 residue compromise substrate binding and cause neurodevelopmental disease."},"narrative":{"teleology":[{"year":2003,"claim":"Identification and molecular cloning of FEM1C established it as a conserved vertebrate member of the FEM1 family, notable for its unique C-terminal arginine residue, setting the stage for later functional studies.","evidence":"cDNA cloning, genomic mapping, and expression profiling in human, mouse, and zebrafish","pmids":["14527725"],"confidence":"Medium","gaps":["No biochemical function assigned at this stage","Expression data limited to RT-PCR without protein-level confirmation"]},{"year":2004,"claim":"A gene-trap knockout mouse revealed that Fem1c is dispensable for sexual development, fertility, and neuronal cell death in isolation, suggesting functional redundancy among FEM1 family members.","evidence":"Fem1c gene-trap homozygous mice with histological and phenotypic analysis","pmids":["15082774"],"confidence":"Medium","gaps":["Potential compensation by FEM1A or FEM1B not tested","No proteomic or ubiquitin-substrate analysis performed"]},{"year":2017,"claim":"Identification of SLBP as a conserved substrate of FEM1C linked the E3 ligase to histone mRNA metabolism, revealing a degron distinct from cyclin F–mediated degradation.","evidence":"Co-immunoprecipitation, degradation assays, and epistasis analysis in C. elegans and Drosophila","pmids":["28118078"],"confidence":"Medium","gaps":["Single-lab study; independent replication not reported","The precise degron motif in SLBP recognized by FEM1C was not structurally defined"]},{"year":2018,"claim":"Genome-wide CRISPR screens and synthetic peptidome profiling established that FEM1C functions as a CRL2 substrate adaptor within the C-end degron (DesCEND) pathway, recognizing C-terminal arginine-ending sequences on aberrant proteins including truncated selenoproteins.","evidence":"CRISPR screening, global protein stability profiling, and biochemical reconstitution with defined substrates","pmids":["29779948","29775578"],"confidence":"High","gaps":["Full repertoire of endogenous substrates remains undefined","Relative contributions of FEM1A versus FEM1C to shared Arg/C-degron substrates not resolved"]},{"year":2021,"claim":"Crystal structures of FEM1C bound to Arg/C-degron peptides defined the semi-open binding pocket architecture and showed that FEM1A/C recognize a distinct Arg/C-degron subset from FEM1B, providing a structural basis for substrate selectivity within the family.","evidence":"X-ray crystallography, mutagenesis, and global protein stability profiling","pmids":["33398170","33398168"],"confidence":"High","gaps":["No full-length substrate-bound structure available","Structural basis for FEM1C versus FEM1A discrimination among overlapping substrates not determined"]},{"year":2023,"claim":"A human de novo variant (Asp126His) at the substrate-binding pocket was shown to cause neurodevelopmental disease, and the equivalent C. elegans mutation produced synaptic dysfunction, establishing a direct genotype–phenotype link for FEM1C in the nervous system.","evidence":"Exome sequencing, in vitro binding assay (Asp126Ala), C. elegans locomotion and pharmacological (aldicarb/levamisole) assays","pmids":["36336956"],"confidence":"Medium","gaps":["Single affected individual; additional cases needed to confirm genotype–phenotype spectrum","The synaptic substrate(s) of FEM1C relevant to neurodevelopment are unidentified"]},{"year":2023,"claim":"Development of a fluorescent chemical probe for the FEM1C C-degron pocket validated the R/K-X-R and R/K-X-X-R recognition motifs biochemically and enabled small-molecule ligand discovery for potential PROTAC applications.","evidence":"Fluorescence polarization and isothermal titration calorimetry with competitive binding assays","pmids":["37339537"],"confidence":"Medium","gaps":["No cellular target degradation via PROTAC demonstrated","Selectivity over FEM1A pocket not characterized"]},{"year":null,"claim":"The full endogenous substrate repertoire of FEM1C, the structural basis for its discrimination from FEM1A, and the identity of neuronal substrates underlying neurodevelopmental disease remain to be determined.","evidence":"","pmids":[],"confidence":"High","gaps":["Comprehensive endogenous substrate identification by proteomics not yet performed","No high-resolution structure of FEM1C in complex with a full-length physiological substrate","Mechanism linking FEM1C loss-of-function to synaptic defects is molecularly undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3]}],"localization":[],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,3,4]}],"complexes":["CRL2 (Cullin 2-RING E3 ubiquitin ligase)"],"partners":["CUL2","SLBP","ELOB","ELOC"],"other_free_text":[]},"mechanistic_narrative":"FEM1C is a substrate-recognition subunit of the CRL2 (Cullin 2–RING) E3 ubiquitin ligase complex that selectively targets proteins bearing C-terminal arginine degrons (Arg/C-degrons) for proteasomal degradation. Crystal structures show FEM1C uses a semi-open binding pocket to capture the extreme C-terminal arginine residue, and global protein stability profiling demonstrates that FEM1C and FEM1A share a substrate specificity distinct from FEM1B within the Arg/C-degron pathway [PMID:33398170, PMID:33398168, PMID:29779948]. Endogenous substrates include the histone mRNA regulator SLBP and truncated selenoproteins, linking FEM1C to protein quality control and histone mRNA metabolism [PMID:28118078, PMID:29775578]. A de novo missense variant (p.Asp126His) that disrupts substrate binding causes a neurodevelopmental disorder with absent speech, pyramidal signs, and limb ataxia, and the equivalent mutation in C. elegans FEM-1 produces synaptic dysfunction [PMID:36336956]."},"prefetch_data":{"uniprot":{"accession":"Q96JP0","full_name":"Protein fem-1 homolog C","aliases":["FEM1-gamma"],"length_aa":617,"mass_kda":68.7,"function":"Substrate-recognition component of a Cul2-RING (CRL2) E3 ubiquitin-protein ligase complex of the DesCEND (destruction via C-end degrons) pathway, which recognizes a C-degron located at the extreme C terminus of target proteins, leading to their ubiquitination and degradation (PubMed:29775578, PubMed:29779948, PubMed:33398168, PubMed:33398170, PubMed:38326650). The C-degron recognized by the DesCEND pathway is usually a motif of less than ten residues and can be present in full-length proteins, truncated proteins or proteolytically cleaved forms (PubMed:29775578, PubMed:29779948, PubMed:33398168, PubMed:33398170). The CRL2(FEM1C) complex specifically recognizes proteins with an arginine at the C-terminus: recognizes and binds proteins ending with -Lys/Arg-Xaa-Arg and -Lys/Arg-Xaa-Xaa-Arg C-degrons, such as SIL1 or OR51B2, leading to their ubiquitination and degradation (PubMed:33398168, PubMed:33398170, PubMed:38326650). The CRL2(FEM1C) complex mediates ubiquitination and degradation of truncated MSRB1/SEPX1 selenoproteins produced by failed UGA/Sec decoding (PubMed:26138980). Promotes ubiquitination and degradation of SLBP (PubMed:28118078)","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q96JP0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FEM1C","classification":"Not Classified","n_dependent_lines":28,"n_total_lines":1208,"dependency_fraction":0.023178807947019868},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FEM1C","total_profiled":1310},"omim":[{"mim_id":"608767","title":"FEM1 HOMOLOG C; FEM1C","url":"https://www.omim.org/entry/608767"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"bone marrow","ntpm":59.6}],"url":"https://www.proteinatlas.org/search/FEM1C"},"hgnc":{"alias_symbol":["KIAA1785","EUROIMAGE686608","EUROIMAGE783647","FEM1A"],"prev_symbol":[]},"alphafold":{"accession":"Q96JP0","domains":[{"cath_id":"1.10.750","chopping":"585-617","consensus_level":"medium","plddt":87.7236,"start":585,"end":617}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96JP0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96JP0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96JP0-F1-predicted_aligned_error_v6.png","plddt_mean":94.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FEM1C","jax_strain_url":"https://www.jax.org/strain/search?query=FEM1C"},"sequence":{"accession":"Q96JP0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96JP0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96JP0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96JP0"}},"corpus_meta":[{"pmid":"33398170","id":"PMC_33398170","title":"Molecular 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CRL2 aids elimination of truncated selenoproteins produced by failed UGA/Sec decoding.","date":"2015","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/26138980","citation_count":62,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"31253590","id":"PMC_31253590","title":"ARIH2 Is a Vif-Dependent Regulator of CUL5-Mediated APOBEC3G Degradation in HIV Infection.","date":"2019","source":"Cell host & microbe","url":"https://pubmed.ncbi.nlm.nih.gov/31253590","citation_count":57,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28786561","id":"PMC_28786561","title":"Mapping the interactome of HPV E6 and E7 oncoproteins with the ubiquitin-proteasome system.","date":"2017","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/28786561","citation_count":56,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"33398168","id":"PMC_33398168","title":"Molecular basis for arginine C-terminal degron recognition by Cul2FEM1 E3 ligase.","date":"2021","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/33398168","citation_count":50,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"36138187","id":"PMC_36138187","title":"NUDT21 limits CD19 levels through alternative mRNA polyadenylation in B cell acute lymphoblastic leukemia.","date":"2022","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/36138187","citation_count":46,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28118078","id":"PMC_28118078","title":"FEM1 proteins are ancient regulators of SLBP degradation.","date":"2017","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/28118078","citation_count":31,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"30720688","id":"PMC_30720688","title":"Tolerance Biomarkers in Liver Transplantation: Independent External Validation of the Predictive Strength of SENP6 and FEM1C Gene Expression.","date":"2019","source":"Transplantation","url":"https://pubmed.ncbi.nlm.nih.gov/30720688","citation_count":15,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"40593736","id":"PMC_40593736","title":"Human protein interaction networks of ancestral and variant SARS-CoV-2 in organ-specific cells and bodily fluids.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/40593736","citation_count":2,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7809,"output_tokens":1676,"usd":0.024283},"stage2":{"model":"claude-opus-4-6","input_tokens":4933,"output_tokens":3640,"usd":0.173497},"total_usd":0.356683,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":17485,"output_tokens":2259,"usd":0.04317},"round2_rules_fired":"R2","round2_stage2":{"model":"claude-opus-4-6","input_tokens":5821,"output_tokens":1922,"usd":0.115733}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"FEM1C functions as a substrate receptor within the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex, recognizing C-terminal arginine residues (Arg/C-degron) through a semi-open binding pocket. Crystal structures revealed that the extreme C-terminal arginine is the major structural determinant for recognition, and biochemical and mutagenesis studies confirmed the molecular mechanism of substrate capture.\",\n      \"method\": \"Crystal structure determination of FEM1C in complex with Arg/C-degron peptide, combined with biochemical assays and site-directed mutagenesis\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation by mutagenesis and biochemical assays in a single rigorous study\",\n      \"pmids\": [\"33398170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human FEM1C protein ends with a C-terminal arginine residue, distinguishing it from other FEM-1 family members, a feature subsequently shown to be relevant to its substrate recognition mechanism.\",\n      \"method\": \"Cloning, sequence analysis, and comparative genomics of human, mouse, and zebrafish Fem1c genes\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — sequence characterization identifying a key structural feature later validated functionally; single study\",\n      \"pmids\": [\"14527725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Disruption of the Fem1c gene in homozygous ROSA3 (Fem1c R3/R3) mice did not result in adverse effects on sexual development, fertility, or neuronal cell death attenuation, indicating Fem1c is dispensable for these processes in mice, at least when partial transcript expression remains possible.\",\n      \"method\": \"Retroviral gene trap insertion into first intron of Fem1c; phenotypic analysis of homozygous mice\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic disruption with defined phenotypic readout (sexual development and neuronal survival), single study\",\n      \"pmids\": [\"15082774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"FEM1C-Z protein is expressed in a cytoplasmic localization in zebra finch fibroblast cells, consistent with its cytoplasmic localization reported in C. elegans.\",\n      \"method\": \"Immunofluorescence imaging of FEM1C-Z in zebra finch fibroblast cells\",\n      \"journal\": \"Chromosoma\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single localization experiment, no functional consequence linked\",\n      \"pmids\": [\"19139913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A de novo missense variant at FEM1C Asp126 (p.Asp126His) disrupts protein substrate binding as shown by computational analysis, and the equivalent variant (Asp126Ala) was functionally compromised in vitro. In C. elegans, the homologous FEM-1 Asp133His variant caused impaired mobility due to synaptic abnormalities (sensitivity to aldicarb but not levamisole), placing Asp126 as a critical residue for FEM1C substrate interaction.\",\n      \"method\": \"In vitro functional assay of FEM1C Asp126Ala variant, computational modeling, C. elegans locomotion assay with aldicarb/levamisole pharmacology\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro functional compromise of variant combined with orthogonal in vivo C. elegans pharmacological epistasis, single study\",\n      \"pmids\": [\"36336956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FEM1C selectively binds C-degron substrates containing arginine-terminated motifs (R/K-X-R or R/K-X-X-R at the C-terminus), and a fluorescent probe (ES148, Ki = 1.6 µM) was developed to characterize FEM1C ligand binding by fluorescence polarization and validated by isothermal titration calorimetry.\",\n      \"method\": \"Fluorescence polarization competition assay and isothermal titration calorimetry with synthetic fluorescent probe\",\n      \"journal\": \"Bioorganic & medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal binding assays confirming substrate motif specificity, single study\",\n      \"pmids\": [\"37339537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Knockdown of FEM1C in colorectal cancer cells promoted migration, invasion, and proliferation in vitro, and enhanced liver and lung metastasis in vivo, with cells exhibiting epithelial-to-mesenchymal transition (EMT) morphology; GSEA confirmed enrichment of EMT signatures upon FEM1C knockdown, indicating FEM1C acts as a tumor suppressor by suppressing EMT.\",\n      \"method\": \"siRNA knockdown, CCK-8/colony formation/transwell assays, in vivo metastasis mouse models, GSEA\",\n      \"journal\": \"Annals of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined cellular and in vivo phenotype plus pathway analysis (EMT), single study\",\n      \"pmids\": [\"34733943\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FEM1C is a substrate-recognition receptor of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that binds C-terminal arginine-containing degrons (Arg/C-degrons) through a semi-open binding pocket, targeting substrates with R/K-X-R or R/K-X-X-R C-terminal motifs for proteasomal degradation, with the Asp126 residue being critical for substrate binding; loss of FEM1C promotes epithelial-to-mesenchymal transition and tumor metastasis, and specific point mutations at Asp126 cause neurodevelopmental dysfunction via synaptic abnormalities.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"Crystal structures of FEM1C in complex with Arg/C-degron peptides revealed that FEM1C uses a semi-open binding pocket to capture the C-terminal arginine residue, with the extreme C-terminal arginine being the major structural determinant for recognition. Biochemical and mutagenesis studies confirmed this mechanism of substrate recognition.\",\n      \"method\": \"X-ray crystallography, biochemical binding assays, mutagenesis\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with functional mutagenesis and biochemical validation in single rigorous study\",\n      \"pmids\": [\"33398170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FEM1A/C and FEM1B selectively target distinct classes of Arg/C-degrons: FEM1A and FEM1C recognize one subset of arginine-terminated C-degrons while FEM1B targets a distinct subset, as demonstrated by structural studies and global protein stability (GPS) analyses.\",\n      \"method\": \"X-ray crystallography, binding assays, global protein stability (GPS) profiling\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple structures combined with functional GPS assays\",\n      \"pmids\": [\"33398168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"FEM1C was identified as one of eight CRL2 substrate adaptors that recognize C-terminal degrons (C-degrons), specifically those ending in arginine, using CRISPR screening and global protein stability profiling of a synthetic human peptidome.\",\n      \"method\": \"CRISPR screening, global protein stability (GPS) profiling, synthetic peptidome\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide functional screen with orthogonal validation, highly cited\",\n      \"pmids\": [\"29779948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CRL2 ubiquitin ligase complexes using interchangeable substrate receptors (including FEM1C) recognize unusual C termini of abnormal proteins (C-end degrons) via the DesCEND mechanism; C-terminal end position is essential for degron function, and substrates include truncated selenoproteins and the USP1 N-terminal fragment.\",\n      \"method\": \"Genetic and biochemical assays, protein degradation assays, mutagenesis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic reconstitution with defined substrates and mutagenesis\",\n      \"pmids\": [\"29775578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FEM1C (along with FEM1A and FEM1B) interacts with and mediates the ubiquitin-dependent degradation of Stem-Loop Binding Protein (SLBP), a conserved regulator of histone mRNA processing. FEM1 proteins interact with an N-terminal region of SLBP using a distinct degron from that used by cyclin F, and this regulation is evolutionarily conserved from C. elegans and Drosophila to mammals.\",\n      \"method\": \"Co-immunoprecipitation, protein degradation assays, epistasis in C. elegans and Drosophila\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — reciprocal co-IP and genetic evidence across species, single lab\",\n      \"pmids\": [\"28118078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human, mouse, and zebrafish FEM1C proteins are encoded by a conserved gene family member that uniquely terminates with a C-terminal arginine residue (distinguishing them from FEM1A and FEM1B), with >99% amino acid identity between human and mouse and conserved intron-exon structure and expression pattern.\",\n      \"method\": \"cDNA cloning, sequence analysis, genomic mapping, RT-PCR expression profiling\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — molecular characterization of gene structure and expression, foundational identification paper\",\n      \"pmids\": [\"14527725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Insertion of the beta-Geo gene trap into the first intron of mouse Fem1c disrupts normal Fem1c transcript processing in homozygous ROSA3 mice; Fem1c(R3/R3) mice show no adverse effects in sexual development, fertility, or neuronal cell death, suggesting Fem1c is not individually required for these processes in mice.\",\n      \"method\": \"Gene trap mouse model, RT-PCR, histological and phenotypic analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function genetic model with defined phenotypic readouts\",\n      \"pmids\": [\"15082774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A de novo missense variant p.(Asp126His) in FEM1C causes a neurodevelopmental disorder with absent speech, pyramidal signs, and limb ataxia. The equivalent variant FEM1C(Asp126Ala) is functionally compromised in vitro for substrate binding. In C. elegans, the homologous FEM-1(Asp133His) variant causes impaired mobility due to synaptic abnormalities (sensitivity to aldicarb but not levamisole), placing FEM1C function at the synapse.\",\n      \"method\": \"Exome sequencing, in vitro binding assay, C. elegans locomotion assay, aldicarb/levamisole pharmacological assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro functional validation plus animal model with mechanistic pharmacological dissection\",\n      \"pmids\": [\"36336956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A fluorescent probe (ES148, Ki = 1.6 µM) targeting the C-degron binding pocket of FEM1C was developed and validated by fluorescence polarization and isothermal titration calorimetry, establishing that FEM1C recognizes proteins with an R/K-X-R or R/K-X-X-R motif at the C-terminus and enabling small-molecule ligand discovery for PROTAC applications.\",\n      \"method\": \"Fluorescence polarization assay, isothermal titration calorimetry, competitive binding assay\",\n      \"journal\": \"Bioorganic & medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical assay with validated binding constants and orthogonal confirmation\",\n      \"pmids\": [\"37339537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FEM1C knockdown in colorectal cancer cells significantly promotes migration, invasion, and proliferation in vitro and enhances liver and lung metastasis in vivo; knockdown cells shift from epithelial to fibroblast-like morphology, and GSEA analysis indicates enrichment of epithelial-to-mesenchymal transition (EMT) signatures, implicating FEM1C as a suppressor of EMT.\",\n      \"method\": \"siRNA knockdown, CCK-8 proliferation assay, colony formation assay, transwell invasion assay, in vivo metastasis models, GSEA\",\n      \"journal\": \"Annals of translational medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — loss-of-function with cellular phenotype but no direct molecular substrate identified\",\n      \"pmids\": [\"34733943\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FEM1C is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase that uses a semi-open binding pocket to selectively recognize proteins bearing C-terminal arginine (Arg/C-degron) motifs—including the SLBP histone mRNA regulator and truncated selenoproteins—and targets them for proteasomal degradation; structural and mutagenesis studies show FEM1C and FEM1A share a distinct substrate specificity from FEM1B within this family, and loss-of-function variants at the conserved Asp126 residue compromise substrate binding and cause neurodevelopmental disease.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FEM1C is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that targets proteins bearing C-terminal arginine-containing degrons (Arg/C-degrons) with R/K-X-R or R/K-X-X-R motifs for proteasomal degradation, with a semi-open binding pocket in which the extreme C-terminal arginine is the major structural determinant for substrate capture [PMID:33398170, PMID:37339537]. Asp126 is a critical residue for substrate binding; a de novo Asp126His missense variant abolishes substrate interaction in vitro and produces synaptic abnormalities (presynaptic defects) in the orthologous C. elegans FEM-1, linking FEM1C dysfunction to neurodevelopmental impairment [PMID:36336956]. Loss of FEM1C in colorectal cancer cells promotes epithelial-to-mesenchymal transition, enhanced migration and invasion in vitro, and liver and lung metastasis in vivo, indicating a tumor-suppressive role [PMID:34733943].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Cloning and sequence analysis of FEM1C revealed that the human protein terminates with a C-terminal arginine, distinguishing it from other FEM-1 family members—a structural feature whose functional significance was unknown at the time.\",\n      \"evidence\": \"Comparative genomics and cloning of human, mouse, and zebrafish Fem1c\",\n      \"pmids\": [\"14527725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional significance of the C-terminal arginine was not tested\",\n        \"No biochemical activity or binding partners identified\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Gene-trap disruption of Fem1c in mice showed it is dispensable for sexual development and neuronal cell death, leaving its physiological function unresolved despite a clear loss-of-function model.\",\n      \"evidence\": \"Retroviral gene-trap insertion into the first intron of Fem1c; phenotypic analysis of homozygous mice\",\n      \"pmids\": [\"15082774\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Partial transcript expression from the trapped allele may mask phenotype\",\n        \"Redundancy with FEM1A/FEM1B not assessed\",\n        \"No molecular substrates or binding partners identified\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Crystal structures of FEM1C bound to Arg/C-degron peptides established that FEM1C functions as a CRL2 substrate receptor recognizing C-terminal arginine through a semi-open binding pocket, defining the molecular basis of substrate capture.\",\n      \"evidence\": \"X-ray crystallography of FEM1C–degron peptide complex, mutagenesis, and biochemical binding assays\",\n      \"pmids\": [\"33398170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Endogenous physiological substrates not identified\",\n        \"Structural basis for selectivity between FEM1A/B/C family members not fully resolved\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"FEM1C knockdown in colorectal cancer cells revealed a tumor-suppressive function: loss of FEM1C promoted EMT, migration, invasion, and metastasis in vivo, connecting its E3 ligase activity to epithelial homeostasis.\",\n      \"evidence\": \"siRNA knockdown in CRC cell lines, transwell/colony formation assays, in vivo liver/lung metastasis models, GSEA\",\n      \"pmids\": [\"34733943\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The EMT-relevant substrate(s) ubiquitinated by FEM1C-CRL2 are unknown\",\n        \"No rescue experiment with catalytic-dead or substrate-binding mutants performed\",\n        \"Mechanism by which FEM1C loss activates EMT signaling not established\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A fluorescent probe (ES148) and orthogonal binding assays refined the substrate-binding motif to R/K-X-R and R/K-X-X-R C-terminal sequences, enabling quantitative characterization of FEM1C ligand affinity.\",\n      \"evidence\": \"Fluorescence polarization competition assay and isothermal titration calorimetry with synthetic probe\",\n      \"pmids\": [\"37339537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Probe developed only for in vitro use; cellular target-engagement assay not reported\",\n        \"Whether motif preference differs between FEM1 family members not fully resolved\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A de novo FEM1C Asp126His variant was linked to neurodevelopmental dysfunction: the mutation disrupts substrate binding in vitro, and the homologous C. elegans variant causes presynaptic (but not postsynaptic) defects, establishing Asp126 as essential for FEM1C function in neural circuits.\",\n      \"evidence\": \"In vitro binding assay of Asp126Ala variant, computational modeling, C. elegans aldicarb/levamisole pharmacological epistasis\",\n      \"pmids\": [\"36336956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Human patient phenotype based on single de novo variant; additional families not reported\",\n        \"The neural substrate(s) of FEM1C whose degradation is impaired by Asp126 mutation are unknown\",\n        \"Mammalian neuronal validation of synaptic phenotype not performed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The identities of endogenous physiological substrates targeted by FEM1C-CRL2 in both neural and epithelial contexts remain unknown, leaving a gap between the well-characterized structural mechanism of degron recognition and its downstream biological consequences.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No endogenous substrates validated by ubiquitination assays or global proteomics upon FEM1C loss\",\n        \"Functional redundancy among FEM1A/B/C not systematically addressed in mammalian systems\",\n        \"No structural model of the full CRL2-FEM1C holo-complex available\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\"CRL2 (Cullin 2-RING E3 ubiquitin ligase)\"],\n    \"partners\": [\"CUL2\"],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway field — it should use Reactome term_ids, not GO terms. Let me correct:\n\n```json\n{\n  \"mechanistic_narrative\": \"FEM1C is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that targets proteins bearing C-terminal arginine-containing degrons (Arg/C-degrons) with R/K-X-R or R/K-X-X-R motifs for proteasomal degradation, with a semi-open binding pocket in which the extreme C-terminal arginine is the major structural determinant for substrate capture [PMID:33398170, PMID:37339537]. Asp126 is a critical residue for substrate binding; a de novo Asp126His missense variant abolishes substrate interaction in vitro and produces synaptic abnormalities (presynaptic defects) in the orthologous C. elegans FEM-1, linking FEM1C dysfunction to neurodevelopmental impairment [PMID:36336956]. Loss of FEM1C in colorectal cancer cells promotes epithelial-to-mesenchymal transition, enhanced migration and invasion in vitro, and liver and lung metastasis in vivo, indicating a tumor-suppressive role [PMID:34733943].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Cloning and sequence analysis of FEM1C revealed that the human protein terminates with a C-terminal arginine, distinguishing it from other FEM-1 family members—a structural feature whose functional significance was unknown at the time.\",\n      \"evidence\": \"Comparative genomics and cloning of human, mouse, and zebrafish Fem1c\",\n      \"pmids\": [\"14527725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional significance of the C-terminal arginine was not tested\",\n        \"No biochemical activity or binding partners identified\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Gene-trap disruption of Fem1c in mice showed it is dispensable for sexual development and neuronal cell death, leaving its physiological function unresolved despite a clear loss-of-function model.\",\n      \"evidence\": \"Retroviral gene-trap insertion into the first intron of Fem1c; phenotypic analysis of homozygous mice\",\n      \"pmids\": [\"15082774\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Partial transcript expression from the trapped allele may mask phenotype\",\n        \"Redundancy with FEM1A/FEM1B not assessed\",\n        \"No molecular substrates or binding partners identified\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Crystal structures of FEM1C bound to Arg/C-degron peptides established that FEM1C functions as a CRL2 substrate receptor recognizing C-terminal arginine through a semi-open binding pocket, defining the molecular basis of substrate capture.\",\n      \"evidence\": \"X-ray crystallography of FEM1C–degron peptide complex, mutagenesis, and biochemical binding assays\",\n      \"pmids\": [\"33398170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Endogenous physiological substrates not identified\",\n        \"Structural basis for selectivity between FEM1A/B/C family members not fully resolved\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"FEM1C knockdown in colorectal cancer cells revealed a tumor-suppressive function: loss of FEM1C promoted EMT, migration, invasion, and metastasis in vivo, connecting its E3 ligase activity to epithelial homeostasis.\",\n      \"evidence\": \"siRNA knockdown in CRC cell lines, transwell/colony formation assays, in vivo liver/lung metastasis models, GSEA\",\n      \"pmids\": [\"34733943\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The EMT-relevant substrate(s) ubiquitinated by FEM1C-CRL2 are unknown\",\n        \"No rescue experiment with catalytic-dead or substrate-binding mutants performed\",\n        \"Mechanism by which FEM1C loss activates EMT signaling not established\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A fluorescent probe and orthogonal binding assays refined the substrate-binding motif to R/K-X-R and R/K-X-X-R C-terminal sequences, enabling quantitative characterization of FEM1C ligand affinity.\",\n      \"evidence\": \"Fluorescence polarization competition assay and isothermal titration calorimetry with synthetic probe\",\n      \"pmids\": [\"37339537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Probe developed only for in vitro use; cellular target-engagement assay not reported\",\n        \"Whether motif preference differs between FEM1 family members not fully resolved\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A de novo FEM1C Asp126His variant was linked to neurodevelopmental dysfunction: the mutation disrupts substrate binding in vitro, and the homologous C. elegans variant causes presynaptic defects, establishing Asp126 as essential for FEM1C function in neural circuits.\",\n      \"evidence\": \"In vitro binding assay of Asp126Ala variant, computational modeling, C. elegans aldicarb/levamisole pharmacological epistasis\",\n      \"pmids\": [\"36336956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Human patient phenotype based on single de novo variant; additional families not reported\",\n        \"The neural substrate(s) of FEM1C whose degradation is impaired by Asp126 mutation are unknown\",\n        \"Mammalian neuronal validation of synaptic phenotype not performed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The identities of endogenous physiological substrates targeted by FEM1C-CRL2 in both neural and epithelial contexts remain unknown, leaving a gap between the well-characterized structural mechanism of degron recognition and its downstream biological consequences.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No endogenous substrates validated by ubiquitination assays or global proteomics upon FEM1C loss\",\n        \"Functional redundancy among FEM1A/B/C not systematically addressed in mammalian systems\",\n        \"No structural model of the full CRL2-FEM1C holo-complex available\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"complexes\": [\"CRL2 (Cullin 2-RING E3 ubiquitin ligase)\"],\n    \"partners\": [\"CUL2\"],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"FEM1C is a substrate-recognition subunit of the CRL2 (Cullin 2–RING) E3 ubiquitin ligase complex that selectively targets proteins bearing C-terminal arginine degrons (Arg/C-degrons) for proteasomal degradation. Crystal structures show FEM1C uses a semi-open binding pocket to capture the extreme C-terminal arginine residue, and global protein stability profiling demonstrates that FEM1C and FEM1A share a substrate specificity distinct from FEM1B within the Arg/C-degron pathway [PMID:33398170, PMID:33398168, PMID:29779948]. Endogenous substrates include the histone mRNA regulator SLBP and truncated selenoproteins, linking FEM1C to protein quality control and histone mRNA metabolism [PMID:28118078, PMID:29775578]. A de novo missense variant (p.Asp126His) that disrupts substrate binding causes a neurodevelopmental disorder with absent speech, pyramidal signs, and limb ataxia, and the equivalent mutation in C. elegans FEM-1 produces synaptic dysfunction [PMID:36336956].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification and molecular cloning of FEM1C established it as a conserved vertebrate member of the FEM1 family, notable for its unique C-terminal arginine residue, setting the stage for later functional studies.\",\n      \"evidence\": \"cDNA cloning, genomic mapping, and expression profiling in human, mouse, and zebrafish\",\n      \"pmids\": [\"14527725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No biochemical function assigned at this stage\",\n        \"Expression data limited to RT-PCR without protein-level confirmation\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"A gene-trap knockout mouse revealed that Fem1c is dispensable for sexual development, fertility, and neuronal cell death in isolation, suggesting functional redundancy among FEM1 family members.\",\n      \"evidence\": \"Fem1c gene-trap homozygous mice with histological and phenotypic analysis\",\n      \"pmids\": [\"15082774\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Potential compensation by FEM1A or FEM1B not tested\",\n        \"No proteomic or ubiquitin-substrate analysis performed\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of SLBP as a conserved substrate of FEM1C linked the E3 ligase to histone mRNA metabolism, revealing a degron distinct from cyclin F–mediated degradation.\",\n      \"evidence\": \"Co-immunoprecipitation, degradation assays, and epistasis analysis in C. elegans and Drosophila\",\n      \"pmids\": [\"28118078\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study; independent replication not reported\",\n        \"The precise degron motif in SLBP recognized by FEM1C was not structurally defined\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Genome-wide CRISPR screens and synthetic peptidome profiling established that FEM1C functions as a CRL2 substrate adaptor within the C-end degron (DesCEND) pathway, recognizing C-terminal arginine-ending sequences on aberrant proteins including truncated selenoproteins.\",\n      \"evidence\": \"CRISPR screening, global protein stability profiling, and biochemical reconstitution with defined substrates\",\n      \"pmids\": [\"29779948\", \"29775578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Full repertoire of endogenous substrates remains undefined\",\n        \"Relative contributions of FEM1A versus FEM1C to shared Arg/C-degron substrates not resolved\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Crystal structures of FEM1C bound to Arg/C-degron peptides defined the semi-open binding pocket architecture and showed that FEM1A/C recognize a distinct Arg/C-degron subset from FEM1B, providing a structural basis for substrate selectivity within the family.\",\n      \"evidence\": \"X-ray crystallography, mutagenesis, and global protein stability profiling\",\n      \"pmids\": [\"33398170\", \"33398168\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No full-length substrate-bound structure available\",\n        \"Structural basis for FEM1C versus FEM1A discrimination among overlapping substrates not determined\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A human de novo variant (Asp126His) at the substrate-binding pocket was shown to cause neurodevelopmental disease, and the equivalent C. elegans mutation produced synaptic dysfunction, establishing a direct genotype–phenotype link for FEM1C in the nervous system.\",\n      \"evidence\": \"Exome sequencing, in vitro binding assay (Asp126Ala), C. elegans locomotion and pharmacological (aldicarb/levamisole) assays\",\n      \"pmids\": [\"36336956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single affected individual; additional cases needed to confirm genotype–phenotype spectrum\",\n        \"The synaptic substrate(s) of FEM1C relevant to neurodevelopment are unidentified\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Development of a fluorescent chemical probe for the FEM1C C-degron pocket validated the R/K-X-R and R/K-X-X-R recognition motifs biochemically and enabled small-molecule ligand discovery for potential PROTAC applications.\",\n      \"evidence\": \"Fluorescence polarization and isothermal titration calorimetry with competitive binding assays\",\n      \"pmids\": [\"37339537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No cellular target degradation via PROTAC demonstrated\",\n        \"Selectivity over FEM1A pocket not characterized\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The full endogenous substrate repertoire of FEM1C, the structural basis for its discrimination from FEM1A, and the identity of neuronal substrates underlying neurodevelopmental disease remain to be determined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Comprehensive endogenous substrate identification by proteomics not yet performed\",\n        \"No high-resolution structure of FEM1C in complex with a full-length physiological substrate\",\n        \"Mechanism linking FEM1C loss-of-function to synaptic defects is molecularly undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4]}\n    ],\n    \"complexes\": [\n      \"CRL2 (Cullin 2-RING E3 ubiquitin ligase)\"\n    ],\n    \"partners\": [\n      \"CUL2\",\n      \"SLBP\",\n      \"ELOB\",\n      \"ELOC\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}