{"gene":"CLTB","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1987,"finding":"Clathrin light chains LCA and LCB are encoded by two closely related genes and share a central set of ten heptad elements forming alpha-helical coiled coils. In the intact triskelion, one light chain (either LCA or LCB) binds the proximal segment of a heavy chain leg. The alpha-helical segment was proposed (based on structural sequence analysis) to mediate heavy chain binding, while amino- and carboxyl-terminal segments mediate interactions with other proteins. Tissue-dependent size variation is explained by differential splicing producing deletions at the same position.","method":"cDNA cloning and sequence analysis of rat brain and liver LCA and LCB; structural modeling of heptad repeat motifs","journal":"Science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cDNA sequence analysis with structural inference; single study but multiple sequence-based orthogonal observations; binding model inferred, not directly reconstituted","pmids":["3563513"],"is_preprint":false},{"year":1988,"finding":"LCB is preferentially phosphorylated at serine residues 11 and 13 (relative to LCA, which is not preferentially phosphorylated), and this phosphorylation is mediated by a coated vesicle-associated casein kinase II. Four monoclonal antibodies against distinct epitopes of clathrin light chains can each inhibit this phosphorylation in vitro.","method":"In vitro phosphorylation of LCB within coated vesicles using [32P]ATP, followed by chymotryptic peptide sequencing to map phosphorylation sites; inhibition by monoclonal antibodies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro kinase assay with radiolabeled ATP, site-specific mapping by peptide sequencing, and antibody inhibition providing multiple orthogonal validations in a single study","pmids":["3128543"],"is_preprint":false},{"year":1990,"finding":"LCB is expressed at higher levels relative to LCA in cells and tissues that maintain a regulated secretory pathway (LCa/LCb ratios from 5:1 to 0.33:1), suggesting a specialized role for LCB in regulated secretion. Light chains are incorporated into triskelions and coated vesicles in proportion to their total cellular expression, with no preferential incorporation of either isoform. LCB has a longer half-life (~45 h) than LCA (~24 h), while LCB and clathrin heavy chain half-lives are similar (~45–50 h), indicating LCA is turned over independently of the other subunits.","method":"Quantitative comparison of LCa/LCb expression ratios across cell types; pulse-chase metabolic labeling to determine half-lives; analysis of light chain composition in assembled clathrin/coated vesicle fractions","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — pulse-chase labeling, fractionation of coated vesicles, and comparative expression analysis across multiple tissues; multiple orthogonal methods in one study","pmids":["2211818"],"is_preprint":false},{"year":1994,"finding":"The CLTB gene encoding LCb maps to chromosome 4q2-q3 in humans. The neuron-specific insertion sequence of LCb is encoded by a single discrete exon, establishing that tissue-specific LCb isoforms are generated by alternative mRNA splicing. An intronic sequence of CLTB shows similarity to the second neuron-specific exon of the CLTA gene.","method":"Chromosomal mapping and isolation/characterization of partial human CLTB genomic clones; exon identification by sequence comparison","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct genomic cloning and sequencing establishing gene structure; single study, single lab","pmids":["7713494"],"is_preprint":false}],"current_model":"CLTB (clathrin light chain B/LCb) binds the proximal segment of the clathrin heavy chain leg via a central alpha-helical coiled-coil domain, is specifically phosphorylated at serines 11 and 13 by coated vesicle-associated casein kinase II, is incorporated into triskelions and coated vesicles in proportion to its cellular expression level, has a longer half-life than LCA (~45 h), and is expressed at relatively higher levels in cells with a regulated secretory pathway; its tissue-specific isoforms are generated by alternative splicing of a discrete exon encoding the neuron-specific insert."},"narrative":{"mechanistic_narrative":"CLTB encodes clathrin light chain B (LCb), a regulatory subunit of the clathrin triskelion that, together with its close relative LCA, binds the proximal segment of a clathrin heavy chain leg through a central set of ten heptad-repeat alpha-helical coiled-coil elements, with the amino- and carboxyl-terminal segments positioned to mediate interactions with other proteins [PMID:3563513]. LCb is incorporated into triskelions and coated vesicles in proportion to its cellular expression level rather than by preferential selection, and is distinguished from LCA by site-specific regulation: it is preferentially phosphorylated at serines 11 and 13 by a coated vesicle-associated casein kinase II [PMID:3128543, PMID:2211818]. LCb is expressed at relatively higher levels than LCA in cells maintaining a regulated secretory pathway and has a longer metabolic half-life (~45 h, comparable to clathrin heavy chain), indicating it is turned over coordinately with the assembled coat [PMID:2211818]. Tissue-specific LCb isoforms, including a neuron-specific insert, are generated by alternative splicing of a discrete exon, and the human CLTB gene maps to chromosome 4q2-q3 [PMID:7713494]. Beyond these properties, the functional consequence of LCb phosphorylation and its specialized role in regulated secretion have not been mechanistically resolved in the available corpus.","teleology":[{"year":1987,"claim":"Establishing how clathrin light chains are organized at the sequence level answered how LCb associates with the triskelion and predicted which regions mediate heavy chain versus accessory interactions.","evidence":"cDNA cloning and structural sequence analysis of rat LCA and LCB heptad-repeat coiled-coil motifs","pmids":["3563513"],"confidence":"Medium","gaps":["Heavy chain binding was inferred from sequence/structural modeling, not directly reconstituted","Identity of the proteins binding the terminal segments was not established","Functional distinction between LCA and LCB not addressed"]},{"year":1988,"claim":"Identifying serines 11 and 13 as preferential phosphorylation sites distinguished LCb biochemically from LCA and tied it to a coat-associated kinase activity.","evidence":"In vitro [32P]ATP phosphorylation within coated vesicles, chymotryptic peptide mapping, and monoclonal antibody inhibition","pmids":["3128543"],"confidence":"High","gaps":["Functional consequence of serine 11/13 phosphorylation on coat assembly or disassembly not determined","Physiological trigger and regulation of the casein kinase II activity unknown"]},{"year":1990,"claim":"Quantifying LCb expression, incorporation, and turnover tested whether LCb has a specialized role and showed it correlates with the regulated secretory pathway while being assembled stoichiometrically with the coat.","evidence":"Comparative LCa/LCb expression ratios across tissues, pulse-chase half-life measurement, and coated vesicle fractionation","pmids":["2211818"],"confidence":"High","gaps":["Correlation with regulated secretion does not establish a causal mechanistic role","Why LCb turnover matches heavy chain while LCA turns over independently is unexplained"]},{"year":1994,"claim":"Defining the human CLTB gene structure explained how tissue-specific LCb variants arise and placed the locus in the genome.","evidence":"Chromosomal mapping and genomic clone characterization identifying a discrete neuron-specific exon","pmids":["7713494"],"confidence":"Medium","gaps":["Functional difference between neuronal and non-neuronal LCb isoforms not characterized","Regulation of the alternative splicing event not addressed"]},{"year":null,"claim":"The downstream function of LCb phosphorylation and its mechanistic contribution to regulated secretion versus constitutive endocytosis remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No reconstituted assay linking serine 11/13 phosphorylation to coat dynamics","No defined accessory protein partners for the LCb terminal segments","No structural model of LCb within the assembled coat in the corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[2]}],"complexes":["clathrin triskelion","clathrin coated vesicle"],"partners":["CLTC","CLTA"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P09497","full_name":"Clathrin light chain B","aliases":[],"length_aa":229,"mass_kda":25.2,"function":"Clathrin is the major protein of the polyhedral coat of coated pits and vesicles","subcellular_location":"Cytoplasmic vesicle membrane; Membrane, coated pit","url":"https://www.uniprot.org/uniprotkb/P09497/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CLTB","classification":"Not Classified","n_dependent_lines":23,"n_total_lines":1208,"dependency_fraction":0.01903973509933775},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000175416","cell_line_id":"CID000402","localizations":[{"compartment":"vesicles","grade":3},{"compartment":"cytoplasmic","grade":2},{"compartment":"golgi","grade":2},{"compartment":"membrane","grade":2}],"interactors":[{"gene":"CLTA","stoichiometry":10.0},{"gene":"ARHGAP18","stoichiometry":0.2},{"gene":"EDC4","stoichiometry":0.2},{"gene":"AP1AR","stoichiometry":0.2},{"gene":"MIA3","stoichiometry":0.2},{"gene":"DCP1B","stoichiometry":0.2},{"gene":"DCP2","stoichiometry":0.2},{"gene":"AFTPH","stoichiometry":0.2},{"gene":"AP2B1","stoichiometry":0.2},{"gene":"LSM6","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000402","total_profiled":1310},"omim":[{"mim_id":"607327","title":"MUSCLEBLIND-LIKE SPLICING REGULATOR 2; MBNL2","url":"https://www.omim.org/entry/607327"},{"mim_id":"606516","title":"MUSCLEBLIND-LIKE SPLICING REGULATOR 1; MBNL1","url":"https://www.omim.org/entry/606516"},{"mim_id":"300413","title":"MUSCLEBLIND-LIKE SPLICING REGULATOR 3; MBNL3","url":"https://www.omim.org/entry/300413"},{"mim_id":"118970","title":"CLATHRIN, LIGHT POLYPEPTIDE B; CLTB","url":"https://www.omim.org/entry/118970"},{"mim_id":"118960","title":"CLATHRIN, LIGHT POLYPEPTIDE A; CLTA","url":"https://www.omim.org/entry/118960"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CLTB"},"hgnc":{"alias_symbol":["Lcb"],"prev_symbol":[]},"alphafold":{"accession":"P09497","domains":[{"cath_id":"-","chopping":"91-186","consensus_level":"medium","plddt":88.6798,"start":91,"end":186},{"cath_id":"-","chopping":"188-203_210-229","consensus_level":"medium","plddt":80.2142,"start":188,"end":229}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P09497","model_url":"https://alphafold.ebi.ac.uk/files/AF-P09497-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P09497-F1-predicted_aligned_error_v6.png","plddt_mean":72.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CLTB","jax_strain_url":"https://www.jax.org/strain/search?query=CLTB"},"sequence":{"accession":"P09497","fasta_url":"https://rest.uniprot.org/uniprotkb/P09497.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P09497/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P09497"}},"corpus_meta":[{"pmid":"3563513","id":"PMC_3563513","title":"Clathrin light chains LCA and LCB are similar, polymorphic, and share repeated heptad motifs.","date":"1987","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/3563513","citation_count":88,"is_preprint":false},{"pmid":"2211818","id":"PMC_2211818","title":"Predominance of clathrin light chain LCb correlates with the presence of a regulated secretory pathway.","date":"1990","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/2211818","citation_count":67,"is_preprint":false},{"pmid":"3128543","id":"PMC_3128543","title":"Identification of the phosphorylation sites of clathrin light chain LCb.","date":"1988","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/3128543","citation_count":42,"is_preprint":false},{"pmid":"27479571","id":"PMC_27479571","title":"Functional characterization of the Aspergillus nidulans glucosylceramide pathway reveals that LCB Δ8-desaturation and C9-methylation are relevant to filamentous growth, lipid raft localization and Psd1 defensin activity.","date":"2016","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/27479571","citation_count":35,"is_preprint":false},{"pmid":"22128347","id":"PMC_22128347","title":"LCB 03-0110, a novel pan-discoidin domain receptor/c-Src family tyrosine kinase inhibitor, suppresses scar formation by inhibiting fibroblast and macrophage activation.","date":"2011","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/22128347","citation_count":31,"is_preprint":false},{"pmid":"16455749","id":"PMC_16455749","title":"The LCB Data Warehouse.","date":"2006","source":"Bioinformatics (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/16455749","citation_count":31,"is_preprint":false},{"pmid":"23020072","id":"PMC_23020072","title":"Topical administration of the pan-Src kinase inhibitors, dasatinib and LCB 03-0110, prevents allergic contact dermatitis in mice.","date":"2013","source":"The British journal of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/23020072","citation_count":14,"is_preprint":false},{"pmid":"7713494","id":"PMC_7713494","title":"Chromosomal location and some structural features of human clathrin light-chain genes (CLTA and CLTB).","date":"1994","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/7713494","citation_count":12,"is_preprint":false},{"pmid":"24510621","id":"PMC_24510621","title":"Fpk1/2 kinases regulate cellular sphingoid long-chain base abundance and alter cellular resistance to LCB elevation or depletion.","date":"2014","source":"MicrobiologyOpen","url":"https://pubmed.ncbi.nlm.nih.gov/24510621","citation_count":12,"is_preprint":false},{"pmid":"36119591","id":"PMC_36119591","title":"Overexpression of a ceramide synthase gene,GhCS1, inhibits fiber cell initiation and elongation by promoting the synthesis of ceramides containing dihydroxy LCB and VLCFA.","date":"2022","source":"Frontiers in plant science","url":"https://pubmed.ncbi.nlm.nih.gov/36119591","citation_count":8,"is_preprint":false},{"pmid":"39490931","id":"PMC_39490931","title":"Orm proteins control ceramide synthesis and endocytosis via LCB-mediated Ypk1 regulation.","date":"2024","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/39490931","citation_count":4,"is_preprint":false},{"pmid":"7989136","id":"PMC_7989136","title":"LCB 2183 inhibits the inflammation associated with oxazolone-induced contact sensitivity.","date":"1994","source":"International journal of immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/7989136","citation_count":3,"is_preprint":false},{"pmid":"28273820","id":"PMC_28273820","title":"In Vitro Activities of LCB 01-0648, a Novel Oxazolidinone, against Gram-Positive Bacteria.","date":"2017","source":"Molecules (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/28273820","citation_count":3,"is_preprint":false},{"pmid":"38698590","id":"PMC_38698590","title":"Statistical Experimental Designs for cLTB-Syn Vaccine Production Using Daucus carota Cell Suspension Cultures.","date":"2024","source":"Planta medica","url":"https://pubmed.ncbi.nlm.nih.gov/38698590","citation_count":1,"is_preprint":false},{"pmid":"39539175","id":"PMC_39539175","title":"Anti-inflammatory effects of LCB 03-0110 on human corneal epithelial and murine T helper 17 cells.","date":"2024","source":"The Korean journal of physiology & pharmacology : official journal of the Korean Physiological Society and the Korean Society of Pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39539175","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.25.672208","title":"Dyslipidemic SPTLC3 Integrates Bile Acid-FXR Signaling with Sphingolipid Remodeling in MASLD","date":"2025-08-29","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.25.672208","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.06.22.600045","title":"Comparison of microbial and sono-assisted alkaline pre-treatment of sugarcane bagasse, followed by one-pot synthesis of microbial extracellular polymeric substance through simultaneous delignification, saccharification, and fermentation","date":"2024-06-27","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.22.600045","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.01.05.631360","title":"NF-κB mediates transactivation of HNRNPD, resulting in PTEN destabilization and constitutive activation of the PI3K-AKT pathway in oral cancer cells","date":"2025-01-05","source":"bioRxiv","url":"https://doi.org/10.1101/2025.01.05.631360","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10891,"output_tokens":1488,"usd":0.027497,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7893,"output_tokens":1839,"usd":0.04272,"stage2_stop_reason":"end_turn"},"total_usd":0.070217,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"Looking at the corpus, I need to identify papers about CLTB (clathrin light chain B, also known as LCb). Let me classify each paper:\n\n- Papers 1, 2, 3, 8: Directly about clathrin light chain LCB/CLTB — INCLUDE\n- Papers 4, 9, 10, 11, 16, 17: \"LCB\" refers to \"long-chain base\" (sphingolipid) — EXCLUDE (symbol collision)\n- Papers 5, 7, 12, 13, 15: \"LCB\" refers to company/drug names — EXCLUDE\n- Paper 6: \"LCB\" = Linnaeus Centre for Bioinformatics — EXCLUDE\n- Paper 14: \"cLTB\" = cholera toxin B subunit fusion — EXCLUDE\n- Paper 18: \"LC3b\" = autophagy protein, not CLTB — EXCLUDE\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1987,\n      \"finding\": \"Clathrin light chains LCA and LCB are encoded by two closely related genes and share a central set of ten heptad elements forming alpha-helical coiled coils. In the intact triskelion, one light chain (either LCA or LCB) binds the proximal segment of a heavy chain leg. The alpha-helical segment was proposed (based on structural sequence analysis) to mediate heavy chain binding, while amino- and carboxyl-terminal segments mediate interactions with other proteins. Tissue-dependent size variation is explained by differential splicing producing deletions at the same position.\",\n      \"method\": \"cDNA cloning and sequence analysis of rat brain and liver LCA and LCB; structural modeling of heptad repeat motifs\",\n      \"journal\": \"Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cDNA sequence analysis with structural inference; single study but multiple sequence-based orthogonal observations; binding model inferred, not directly reconstituted\",\n      \"pmids\": [\"3563513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"LCB is preferentially phosphorylated at serine residues 11 and 13 (relative to LCA, which is not preferentially phosphorylated), and this phosphorylation is mediated by a coated vesicle-associated casein kinase II. Four monoclonal antibodies against distinct epitopes of clathrin light chains can each inhibit this phosphorylation in vitro.\",\n      \"method\": \"In vitro phosphorylation of LCB within coated vesicles using [32P]ATP, followed by chymotryptic peptide sequencing to map phosphorylation sites; inhibition by monoclonal antibodies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro kinase assay with radiolabeled ATP, site-specific mapping by peptide sequencing, and antibody inhibition providing multiple orthogonal validations in a single study\",\n      \"pmids\": [\"3128543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"LCB is expressed at higher levels relative to LCA in cells and tissues that maintain a regulated secretory pathway (LCa/LCb ratios from 5:1 to 0.33:1), suggesting a specialized role for LCB in regulated secretion. Light chains are incorporated into triskelions and coated vesicles in proportion to their total cellular expression, with no preferential incorporation of either isoform. LCB has a longer half-life (~45 h) than LCA (~24 h), while LCB and clathrin heavy chain half-lives are similar (~45–50 h), indicating LCA is turned over independently of the other subunits.\",\n      \"method\": \"Quantitative comparison of LCa/LCb expression ratios across cell types; pulse-chase metabolic labeling to determine half-lives; analysis of light chain composition in assembled clathrin/coated vesicle fractions\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pulse-chase labeling, fractionation of coated vesicles, and comparative expression analysis across multiple tissues; multiple orthogonal methods in one study\",\n      \"pmids\": [\"2211818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The CLTB gene encoding LCb maps to chromosome 4q2-q3 in humans. The neuron-specific insertion sequence of LCb is encoded by a single discrete exon, establishing that tissue-specific LCb isoforms are generated by alternative mRNA splicing. An intronic sequence of CLTB shows similarity to the second neuron-specific exon of the CLTA gene.\",\n      \"method\": \"Chromosomal mapping and isolation/characterization of partial human CLTB genomic clones; exon identification by sequence comparison\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct genomic cloning and sequencing establishing gene structure; single study, single lab\",\n      \"pmids\": [\"7713494\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CLTB (clathrin light chain B/LCb) binds the proximal segment of the clathrin heavy chain leg via a central alpha-helical coiled-coil domain, is specifically phosphorylated at serines 11 and 13 by coated vesicle-associated casein kinase II, is incorporated into triskelions and coated vesicles in proportion to its cellular expression level, has a longer half-life than LCA (~45 h), and is expressed at relatively higher levels in cells with a regulated secretory pathway; its tissue-specific isoforms are generated by alternative splicing of a discrete exon encoding the neuron-specific insert.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CLTB encodes clathrin light chain B (LCb), a regulatory subunit of the clathrin triskelion that, together with its close relative LCA, binds the proximal segment of a clathrin heavy chain leg through a central set of ten heptad-repeat alpha-helical coiled-coil elements, with the amino- and carboxyl-terminal segments positioned to mediate interactions with other proteins [#0]. LCb is incorporated into triskelions and coated vesicles in proportion to its cellular expression level rather than by preferential selection, and is distinguished from LCA by site-specific regulation: it is preferentially phosphorylated at serines 11 and 13 by a coated vesicle-associated casein kinase II [#1, #2]. LCb is expressed at relatively higher levels than LCA in cells maintaining a regulated secretory pathway and has a longer metabolic half-life (~45 h, comparable to clathrin heavy chain), indicating it is turned over coordinately with the assembled coat [#2]. Tissue-specific LCb isoforms, including a neuron-specific insert, are generated by alternative splicing of a discrete exon, and the human CLTB gene maps to chromosome 4q2-q3 [#3]. Beyond these properties, the functional consequence of LCb phosphorylation and its specialized role in regulated secretion have not been mechanistically resolved in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 1987,\n      \"claim\": \"Establishing how clathrin light chains are organized at the sequence level answered how LCb associates with the triskelion and predicted which regions mediate heavy chain versus accessory interactions.\",\n      \"evidence\": \"cDNA cloning and structural sequence analysis of rat LCA and LCB heptad-repeat coiled-coil motifs\",\n      \"pmids\": [\"3563513\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Heavy chain binding was inferred from sequence/structural modeling, not directly reconstituted\",\n        \"Identity of the proteins binding the terminal segments was not established\",\n        \"Functional distinction between LCA and LCB not addressed\"\n      ]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Identifying serines 11 and 13 as preferential phosphorylation sites distinguished LCb biochemically from LCA and tied it to a coat-associated kinase activity.\",\n      \"evidence\": \"In vitro [32P]ATP phosphorylation within coated vesicles, chymotryptic peptide mapping, and monoclonal antibody inhibition\",\n      \"pmids\": [\"3128543\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of serine 11/13 phosphorylation on coat assembly or disassembly not determined\",\n        \"Physiological trigger and regulation of the casein kinase II activity unknown\"\n      ]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Quantifying LCb expression, incorporation, and turnover tested whether LCb has a specialized role and showed it correlates with the regulated secretory pathway while being assembled stoichiometrically with the coat.\",\n      \"evidence\": \"Comparative LCa/LCb expression ratios across tissues, pulse-chase half-life measurement, and coated vesicle fractionation\",\n      \"pmids\": [\"2211818\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Correlation with regulated secretion does not establish a causal mechanistic role\",\n        \"Why LCb turnover matches heavy chain while LCA turns over independently is unexplained\"\n      ]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Defining the human CLTB gene structure explained how tissue-specific LCb variants arise and placed the locus in the genome.\",\n      \"evidence\": \"Chromosomal mapping and genomic clone characterization identifying a discrete neuron-specific exon\",\n      \"pmids\": [\"7713494\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional difference between neuronal and non-neuronal LCb isoforms not characterized\",\n        \"Regulation of the alternative splicing event not addressed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The downstream function of LCb phosphorylation and its mechanistic contribution to regulated secretion versus constitutive endocytosis remain open.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No reconstituted assay linking serine 11/13 phosphorylation to coat dynamics\",\n        \"No defined accessory protein partners for the LCb terminal segments\",\n        \"No structural model of LCb within the assembled coat in the corpus\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\"clathrin triskelion\", \"clathrin coated vesicle\"],\n    \"partners\": [\"CLTC\", \"CLTA\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}