{"gene":"TRAPPC2","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":2011,"finding":"TRAPPC2 (Sedlin) serves as an adaptor protein for the formation of mammalian TRAPPII and TRAPPIII complexes: TRAPPC2 binds to TRAPPII-specific subunit TRAPPC9 (which in turn binds TRAPPC10), and also binds TRAPPIII-specific subunit TRAPPC8. The disease-causing mutation D47Y abolishes these interactions, demonstrating that aspartate 47 is at or near the binding interface with TRAPPC9 and TRAPPC8.","method":"Co-immunoprecipitation in mammalian cells; disease-causing mutant D47Y used to map functional interface","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with multiple subunits, disease mutant validation, replicated in yeast orthologue studies","pmids":["21858081"],"is_preprint":false},{"year":2013,"finding":"Yeast Trs20 (ortholog of TRAPPC2/Sedlin) is required for TRAPPII assembly: Trs20 interacts with TRAPPII-specific subunit Trs120, and the SEDT-equivalent mutation D46Y prevents this interaction, thereby blocking TRAPPII assembly and its Ypt32 guanine-nucleotide exchange factor (GEF) activity.","method":"In vitro GEF assay, co-immunoprecipitation, SEDT-equivalent mutant (D46Y) analysis in yeast","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro GEF activity assay plus Co-IP with mutagenesis, ortholog confirmed functional equivalence","pmids":["23465091"],"is_preprint":false},{"year":2014,"finding":"Yeast Trs20 (ortholog of TRAPPC2/Sedlin) is required for TRAPPIII complex assembly at the pre-autophagosomal structure (PAS): recombinant Trs85 (TRAPPIII-specific subunit) associates with TRAPP only in the presence of Trs20 but not the D46Y mutant; live-cell colocalization shows Trs85 recruits core TRAPP to the PAS via Trs20; trs20ts mutants are defective in both selective and non-selective autophagy.","method":"Recombinant protein co-precipitation, in vitro GEF assay, live-cell colocalization imaging, autophagy assays in yeast trs20ts mutants","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including reconstitution, live imaging, and genetic loss-of-function with defined autophagy phenotype","pmids":["24329977"],"is_preprint":false},{"year":2013,"finding":"TRAPPC2 (C2/Sedlin) binds to the SNARE protein Syntaxin 5, and this interaction is weakened by the SEDT-causing missense mutation D47Y; the equivalent yeast mutation D46Y in Trs20 also interferes with interaction with Trs85 (TRAPPIII-specific), Trs120, and Trs130 (TRAPPII-specific subunits), and destabilizes the TRAPPIII complex involved in autophagy, blocking both the cytosol-to-vacuole (cvt) pathway and non-selective autophagy.","method":"Co-immunoprecipitation (TRAPPC2–Syntaxin 5 in mammalian cells), yeast mutant D46Y interaction studies, size exclusion chromatography, autophagy assays","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, size exclusion, genetic autophagy assays), disease mutant corroboration","pmids":["23898804"],"is_preprint":false},{"year":2023,"finding":"TRAPPC2 knockdown in SW1353 cells or primary human chondrocytes results in decreased COL2A1 (collagen II) expression and secretion; a nonsense variant (c.91A>T) that reduces TRAPPC2 protein levels also alters its membrane distribution, linking TRAPPC2 function to procollagen/collagen secretion in chondrocytes.","method":"siRNA knockdown of TRAPPC2 in chondrocyte cell lines and primary chondrocytes, Western blot for COL2A1, ELISA for secreted collagen II, cell fluorescence for subcellular localization","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — clean KD with defined secretion phenotype, single lab, corroborated by patient-derived mutant","pmids":["37693308"],"is_preprint":false},{"year":2024,"finding":"Human TRAPPC2 can functionally replace its yeast ortholog Trs20 in Saccharomyces cerevisiae (humanized yeast model), confirming conservation of its essential function in the TRAPP complex across species.","method":"CRISPR/Cas9-mediated humanization of yeast (replacement of yeast TRS20 with human TRAPPC2), functional complementation assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — direct genetic complementation, preprint with no peer review yet","pmids":["bio_10.1101_2024.08.04.605925"],"is_preprint":true}],"current_model":"TRAPPC2 (Sedlin) functions as an adaptor subunit within the TRAPP complex, mediating assembly of both TRAPPII (by bridging core TRAPP to TRAPPC9/Trs120) and TRAPPIII (by bridging core TRAPP to TRAPPC8/Trs85) complexes; it also interacts with the SNARE Syntaxin 5, and its loss disrupts Ypt/Rab GEF activity, autophagy, and procollagen/collagen II secretion from chondrocytes — with SEDT-causing mutations (e.g., D47Y) specifically abolishing these adaptor interactions."},"narrative":{"teleology":[{"year":2011,"claim":"Establishing how higher-order TRAPP complexes are assembled, this study showed TRAPPC2 acts as a bridging adaptor that independently recruits TRAPPII-specific (TRAPPC9) and TRAPPIII-specific (TRAPPC8) subunits to the core complex, with the SEDT mutation D47Y abolishing both interactions.","evidence":"Co-immunoprecipitation in mammalian cells with wild-type and D47Y mutant TRAPPC2","pmids":["21858081"],"confidence":"High","gaps":["Structural basis of the D47-mediated interface not resolved at atomic level","Whether TRAPPC2 bridges both complexes simultaneously or in separate pools is unclear","Functional consequences for vesicular trafficking not directly measured in this study"]},{"year":2013,"claim":"The adaptor role of TRAPPC2 was validated in yeast and extended to GEF function and SNARE binding: Trs20/TRAPPC2 is required for TRAPPII assembly and its Ypt32 GEF activity, and mammalian TRAPPC2 binds Syntaxin 5 — both interactions being disrupted by the D46Y/D47Y SEDT mutation.","evidence":"In vitro GEF assays and Co-IP with yeast D46Y mutant; mammalian Co-IP for TRAPPC2–Syntaxin 5; autophagy assays in yeast trs20 mutants","pmids":["23465091","23898804"],"confidence":"High","gaps":["Whether the Syntaxin 5 interaction is direct or mediated through TRAPP complex context","Relative contribution of TRAPPII vs TRAPPIII disruption to the SEDT disease phenotype unclear"]},{"year":2014,"claim":"TRAPPC2/Trs20 was shown to be essential for TRAPPIII complex assembly at the pre-autophagosomal structure, establishing it as a critical node linking vesicular trafficking to both selective and non-selective autophagy.","evidence":"Recombinant protein co-precipitation, in vitro GEF assay, live-cell colocalization, and autophagy assays in yeast trs20ts mutants","pmids":["24329977"],"confidence":"High","gaps":["Whether mammalian TRAPPC2 loss similarly impairs autophagy in relevant tissues not yet shown","Mechanism by which TRAPPC2-dependent TRAPPIII is recruited specifically to PAS membranes is unresolved"]},{"year":2023,"claim":"Connecting TRAPPC2 function to the tissue-specific SEDT phenotype, TRAPPC2 knockdown in chondrocytes was shown to reduce collagen II expression and secretion, demonstrating a direct role in procollagen trafficking.","evidence":"siRNA knockdown in SW1353 cells and primary human chondrocytes; Western blot and ELISA for collagen II; patient nonsense variant analysis","pmids":["37693308"],"confidence":"Medium","gaps":["Whether collagen II reduction is due to ER retention, degradation, or transcriptional effects not fully resolved","Other cargo affected by TRAPPC2 loss in chondrocytes not catalogued","No in vivo animal model validation of the chondrocyte secretion defect"]},{"year":null,"claim":"Key open questions include the atomic-resolution structure of TRAPPC2 at the TRAPPII/III assembly interface, the mechanism by which TRAPPC2 loss causes tissue-restricted skeletal pathology despite its ubiquitous expression, and whether TRAPPC2-dependent autophagy defects contribute to SEDT pathogenesis.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of TRAPPC2 in complex with TRAPPC9 or TRAPPC8","Tissue-specific vulnerability mechanism for SEDT not explained","Whether autophagy defects contribute to chondrocyte dysfunction in SEDT is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,2]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,3]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[2,4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,3,4]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[2,3]}],"complexes":["TRAPPII","TRAPPIII"],"partners":["TRAPPC9","TRAPPC8","TRAPPC10","STX5"],"other_free_text":[]},"mechanistic_narrative":"TRAPPC2 (Sedlin) is a core adaptor subunit of the TRAPP trafficking complex that bridges the shared TRAPP core to complex-specific subunits, thereby enabling assembly of both TRAPPII (via interaction with TRAPPC9/Trs120 and TRAPPC10/Trs130) and TRAPPIII (via interaction with TRAPPC8/Trs85), and consequently supporting their Rab/Ypt GEF activities, ER-to-Golgi transport, and autophagy [PMID:21858081, PMID:23465091, PMID:24329977]. TRAPPC2 also binds the SNARE protein Syntaxin 5, and the spondyloepiphyseal dysplasia tarda (SEDT)-causing D47Y missense mutation abolishes interactions with both complex-specific TRAPP subunits and Syntaxin 5, establishing this residue as a critical binding interface [PMID:21858081, PMID:23898804]. Loss of TRAPPC2 in chondrocytes impairs collagen II expression and secretion, providing a direct mechanistic link between TRAPPC2-dependent vesicular trafficking and the cartilage defect in X-linked SEDT [PMID:37693308]."},"prefetch_data":{"uniprot":{"accession":"P0DI81","full_name":"Trafficking protein particle complex subunit 2","aliases":["Sedlin"],"length_aa":140,"mass_kda":16.4,"function":"Prevents transcriptional repression and induction of cell death by ENO1 (By similarity). May play a role in vesicular transport from endoplasmic reticulum to Golgi","subcellular_location":"Cytoplasm, perinuclear region; Endoplasmic reticulum-Golgi intermediate compartment; Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P0DI81/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TRAPPC2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":70,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000196459","cell_line_id":"CID000473","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"golgi","grade":2},{"compartment":"nucleoplasm","grade":1}],"interactors":[{"gene":"TRAPPC5","stoichiometry":10.0},{"gene":"TRAPPC11","stoichiometry":10.0},{"gene":"TRAPPC6B","stoichiometry":10.0},{"gene":"TRAPPC4","stoichiometry":10.0},{"gene":"TRAPPC8","stoichiometry":10.0},{"gene":"TRAPPC12;CGI-87","stoichiometry":10.0},{"gene":"TRAPPC1","stoichiometry":10.0},{"gene":"TRAPPC2L","stoichiometry":10.0},{"gene":"TRAPPC3","stoichiometry":10.0},{"gene":"TRAPPC13","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000473","total_profiled":1310},"omim":[{"mim_id":"614139","title":"TRAFFICKING PROTEIN PARTICLE COMPLEX, SUBUNIT 12; TRAPPC12","url":"https://www.omim.org/entry/614139"},{"mim_id":"614138","title":"TRAFFICKING PROTEIN PARTICLE COMPLEX, SUBUNIT 11; TRAPPC11","url":"https://www.omim.org/entry/614138"},{"mim_id":"614137","title":"TRAFFICKING PROTEIN PARTICLE COMPLEX, SUBUNIT 3-LIKE; TRAPPC3L","url":"https://www.omim.org/entry/614137"},{"mim_id":"614136","title":"TRAFFICKING PROTEIN PARTICLE COMPLEX, SUBUNIT 8; TRAPPC8","url":"https://www.omim.org/entry/614136"},{"mim_id":"610970","title":"TRAFFICKING PROTEIN PARTICLE COMPLEX, SUBUNIT 2L; TRAPPC2L","url":"https://www.omim.org/entry/610970"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Endoplasmic reticulum","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TRAPPC2"},"hgnc":{"alias_symbol":["TRS20","SEDT","MIP-2A","ZNF547L","hYP38334"],"prev_symbol":["SEDL"]},"alphafold":{"accession":"P0DI81","domains":[{"cath_id":"3.30.450.70","chopping":"4-137","consensus_level":"high","plddt":93.062,"start":4,"end":137}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P0DI81","model_url":"https://alphafold.ebi.ac.uk/files/AF-P0DI81-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P0DI81-F1-predicted_aligned_error_v6.png","plddt_mean":92.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TRAPPC2","jax_strain_url":"https://www.jax.org/strain/search?query=TRAPPC2"},"sequence":{"accession":"P0DI81","fasta_url":"https://rest.uniprot.org/uniprotkb/P0DI81.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P0DI81/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P0DI81"}},"corpus_meta":[{"pmid":"21858081","id":"PMC_21858081","title":"The adaptor function of TRAPPC2 in mammalian TRAPPs explains TRAPPC2-associated SEDT and TRAPPC9-associated congenital intellectual disability.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21858081","citation_count":54,"is_preprint":false},{"pmid":"24329977","id":"PMC_24329977","title":"Trs20 is required for TRAPP III complex assembly at the PAS and its function in autophagy.","date":"2014","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/24329977","citation_count":29,"is_preprint":false},{"pmid":"23898804","id":"PMC_23898804","title":"A trs20 mutation that mimics an SEDT-causing mutation blocks selective and non-selective autophagy: a model for TRAPP III organization.","date":"2013","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/23898804","citation_count":23,"is_preprint":false},{"pmid":"23465091","id":"PMC_23465091","title":"Trs20 is required for TRAPP II assembly.","date":"2013","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/23465091","citation_count":20,"is_preprint":false},{"pmid":"12700240","id":"PMC_12700240","title":"Modulation of human luteinizing hormone beta gene transcription by MIP-2A.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12700240","citation_count":11,"is_preprint":false},{"pmid":"22563562","id":"PMC_22563562","title":"X-linked spondyloepiphyseal dysplasia tarda: Identification of a TRAPPC2 mutation in a Korean pedigree.","date":"2012","source":"Annals of laboratory medicine","url":"https://pubmed.ncbi.nlm.nih.gov/22563562","citation_count":9,"is_preprint":false},{"pmid":"23656395","id":"PMC_23656395","title":"Whole exome sequencing and functional studies identify an intronic mutation in TRAPPC2 that causes SEDT.","date":"2013","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23656395","citation_count":9,"is_preprint":false},{"pmid":"17363178","id":"PMC_17363178","title":"Mutant WISP3 triggers the phenotype shift of articular chondrocytes by promoting sensitivity to IGF-1 hypothesis of spondyloepiphyseal dysplasia tarda with progressive arthropathy (SEDT-PA).","date":"2007","source":"Medical hypotheses","url":"https://pubmed.ncbi.nlm.nih.gov/17363178","citation_count":8,"is_preprint":false},{"pmid":"32471379","id":"PMC_32471379","title":"A novel deletion variant in TRAPPC2 causes spondyloepiphyseal dysplasia tarda in a five-generation Chinese family.","date":"2020","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32471379","citation_count":7,"is_preprint":false},{"pmid":"31053099","id":"PMC_31053099","title":"Novel loss-of-function variants of TRAPPC2 manifesting X-linked spondyloepiphyseal dysplasia tarda: report of two cases.","date":"2019","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31053099","citation_count":6,"is_preprint":false},{"pmid":"24098805","id":"PMC_24098805","title":"MIP-2A is a novel target of an anilinoquinazoline derivative for inhibition of tumour cell proliferation.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24098805","citation_count":5,"is_preprint":false},{"pmid":"25521980","id":"PMC_25521980","title":"Novel TRAPPC2 mutation in a boy with X-linked spondylo-epiphyseal dysplasia tarda.","date":"2014","source":"Pediatrics international : official journal of the Japan Pediatric Society","url":"https://pubmed.ncbi.nlm.nih.gov/25521980","citation_count":4,"is_preprint":false},{"pmid":"26252088","id":"PMC_26252088","title":"[Mutation analysis of the TRAPPC2 gene in a Chinese family with X-linked spondyloepiphyseal dysplasia tarda].","date":"2015","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/26252088","citation_count":2,"is_preprint":false},{"pmid":"33726005","id":"PMC_33726005","title":"A novel missense variant in TRAPPC2 causes X-linked spondyloepiphyseal dysplasia tarda: A case report.","date":"2021","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33726005","citation_count":2,"is_preprint":false},{"pmid":"37693308","id":"PMC_37693308","title":"Functional analysis of a novel nonsense variant c.91A>T of the TRAPPC2 gene in a Chinese family with X-linked recessive autosomal spondyloepiphyseal dysplasia tarda.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37693308","citation_count":1,"is_preprint":false},{"pmid":"18245897","id":"PMC_18245897","title":"[Construction of WISP3 gene's mutants in SEDT-PA and their expression in COS-7 cells].","date":"2008","source":"Zhong nan da xue xue bao. Yi xue ban = Journal of Central South University. Medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/18245897","citation_count":1,"is_preprint":false},{"pmid":"41732158","id":"PMC_41732158","title":"Identification and functional analysis of a novel TRAPPC2 intronic variant in a four-generation Chinese pedigree with SEDT.","date":"2026","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/41732158","citation_count":0,"is_preprint":false},{"pmid":"41059451","id":"PMC_41059451","title":"A Novel Premature Termination Codon Mutation in TRAPPC2 Is Associated with X-Linked Spondyloepiphyseal Dysplasia Tarda.","date":"2024","source":"Molecular syndromology","url":"https://pubmed.ncbi.nlm.nih.gov/41059451","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.08.04.605925","title":"A humanized yeast model for studying TRAPP complex mutations; proof-of-concept using variants from an individual with a<i>TRAPPC1</i>-associated neurodevelopmental syndrome","date":"2024-08-06","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.04.605925","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11078,"output_tokens":1725,"usd":0.029555},"stage2":{"model":"claude-opus-4-6","input_tokens":4967,"output_tokens":1701,"usd":0.10104},"total_usd":0.130595,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2011,\n      \"finding\": \"TRAPPC2 (Sedlin) serves as an adaptor protein for the formation of mammalian TRAPPII and TRAPPIII complexes: TRAPPC2 binds to TRAPPII-specific subunit TRAPPC9 (which in turn binds TRAPPC10), and also binds TRAPPIII-specific subunit TRAPPC8. The disease-causing mutation D47Y abolishes these interactions, demonstrating that aspartate 47 is at or near the binding interface with TRAPPC9 and TRAPPC8.\",\n      \"method\": \"Co-immunoprecipitation in mammalian cells; disease-causing mutant D47Y used to map functional interface\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with multiple subunits, disease mutant validation, replicated in yeast orthologue studies\",\n      \"pmids\": [\"21858081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Yeast Trs20 (ortholog of TRAPPC2/Sedlin) is required for TRAPPII assembly: Trs20 interacts with TRAPPII-specific subunit Trs120, and the SEDT-equivalent mutation D46Y prevents this interaction, thereby blocking TRAPPII assembly and its Ypt32 guanine-nucleotide exchange factor (GEF) activity.\",\n      \"method\": \"In vitro GEF assay, co-immunoprecipitation, SEDT-equivalent mutant (D46Y) analysis in yeast\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro GEF activity assay plus Co-IP with mutagenesis, ortholog confirmed functional equivalence\",\n      \"pmids\": [\"23465091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Yeast Trs20 (ortholog of TRAPPC2/Sedlin) is required for TRAPPIII complex assembly at the pre-autophagosomal structure (PAS): recombinant Trs85 (TRAPPIII-specific subunit) associates with TRAPP only in the presence of Trs20 but not the D46Y mutant; live-cell colocalization shows Trs85 recruits core TRAPP to the PAS via Trs20; trs20ts mutants are defective in both selective and non-selective autophagy.\",\n      \"method\": \"Recombinant protein co-precipitation, in vitro GEF assay, live-cell colocalization imaging, autophagy assays in yeast trs20ts mutants\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including reconstitution, live imaging, and genetic loss-of-function with defined autophagy phenotype\",\n      \"pmids\": [\"24329977\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TRAPPC2 (C2/Sedlin) binds to the SNARE protein Syntaxin 5, and this interaction is weakened by the SEDT-causing missense mutation D47Y; the equivalent yeast mutation D46Y in Trs20 also interferes with interaction with Trs85 (TRAPPIII-specific), Trs120, and Trs130 (TRAPPII-specific subunits), and destabilizes the TRAPPIII complex involved in autophagy, blocking both the cytosol-to-vacuole (cvt) pathway and non-selective autophagy.\",\n      \"method\": \"Co-immunoprecipitation (TRAPPC2–Syntaxin 5 in mammalian cells), yeast mutant D46Y interaction studies, size exclusion chromatography, autophagy assays\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, size exclusion, genetic autophagy assays), disease mutant corroboration\",\n      \"pmids\": [\"23898804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TRAPPC2 knockdown in SW1353 cells or primary human chondrocytes results in decreased COL2A1 (collagen II) expression and secretion; a nonsense variant (c.91A>T) that reduces TRAPPC2 protein levels also alters its membrane distribution, linking TRAPPC2 function to procollagen/collagen secretion in chondrocytes.\",\n      \"method\": \"siRNA knockdown of TRAPPC2 in chondrocyte cell lines and primary chondrocytes, Western blot for COL2A1, ELISA for secreted collagen II, cell fluorescence for subcellular localization\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — clean KD with defined secretion phenotype, single lab, corroborated by patient-derived mutant\",\n      \"pmids\": [\"37693308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Human TRAPPC2 can functionally replace its yeast ortholog Trs20 in Saccharomyces cerevisiae (humanized yeast model), confirming conservation of its essential function in the TRAPP complex across species.\",\n      \"method\": \"CRISPR/Cas9-mediated humanization of yeast (replacement of yeast TRS20 with human TRAPPC2), functional complementation assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct genetic complementation, preprint with no peer review yet\",\n      \"pmids\": [\"bio_10.1101_2024.08.04.605925\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TRAPPC2 (Sedlin) functions as an adaptor subunit within the TRAPP complex, mediating assembly of both TRAPPII (by bridging core TRAPP to TRAPPC9/Trs120) and TRAPPIII (by bridging core TRAPP to TRAPPC8/Trs85) complexes; it also interacts with the SNARE Syntaxin 5, and its loss disrupts Ypt/Rab GEF activity, autophagy, and procollagen/collagen II secretion from chondrocytes — with SEDT-causing mutations (e.g., D47Y) specifically abolishing these adaptor interactions.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TRAPPC2 (Sedlin) is a core adaptor subunit of the TRAPP trafficking complex that bridges the shared TRAPP core to complex-specific subunits, thereby enabling assembly of both TRAPPII (via interaction with TRAPPC9/Trs120 and TRAPPC10/Trs130) and TRAPPIII (via interaction with TRAPPC8/Trs85), and consequently supporting their Rab/Ypt GEF activities, ER-to-Golgi transport, and autophagy [PMID:21858081, PMID:23465091, PMID:24329977]. TRAPPC2 also binds the SNARE protein Syntaxin 5, and the spondyloepiphyseal dysplasia tarda (SEDT)-causing D47Y missense mutation abolishes interactions with both complex-specific TRAPP subunits and Syntaxin 5, establishing this residue as a critical binding interface [PMID:21858081, PMID:23898804]. Loss of TRAPPC2 in chondrocytes impairs collagen II expression and secretion, providing a direct mechanistic link between TRAPPC2-dependent vesicular trafficking and the cartilage defect in X-linked SEDT [PMID:37693308].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing how higher-order TRAPP complexes are assembled, this study showed TRAPPC2 acts as a bridging adaptor that independently recruits TRAPPII-specific (TRAPPC9) and TRAPPIII-specific (TRAPPC8) subunits to the core complex, with the SEDT mutation D47Y abolishing both interactions.\",\n      \"evidence\": \"Co-immunoprecipitation in mammalian cells with wild-type and D47Y mutant TRAPPC2\",\n      \"pmids\": [\"21858081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the D47-mediated interface not resolved at atomic level\",\n        \"Whether TRAPPC2 bridges both complexes simultaneously or in separate pools is unclear\",\n        \"Functional consequences for vesicular trafficking not directly measured in this study\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The adaptor role of TRAPPC2 was validated in yeast and extended to GEF function and SNARE binding: Trs20/TRAPPC2 is required for TRAPPII assembly and its Ypt32 GEF activity, and mammalian TRAPPC2 binds Syntaxin 5 — both interactions being disrupted by the D46Y/D47Y SEDT mutation.\",\n      \"evidence\": \"In vitro GEF assays and Co-IP with yeast D46Y mutant; mammalian Co-IP for TRAPPC2–Syntaxin 5; autophagy assays in yeast trs20 mutants\",\n      \"pmids\": [\"23465091\", \"23898804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the Syntaxin 5 interaction is direct or mediated through TRAPP complex context\",\n        \"Relative contribution of TRAPPII vs TRAPPIII disruption to the SEDT disease phenotype unclear\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"TRAPPC2/Trs20 was shown to be essential for TRAPPIII complex assembly at the pre-autophagosomal structure, establishing it as a critical node linking vesicular trafficking to both selective and non-selective autophagy.\",\n      \"evidence\": \"Recombinant protein co-precipitation, in vitro GEF assay, live-cell colocalization, and autophagy assays in yeast trs20ts mutants\",\n      \"pmids\": [\"24329977\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether mammalian TRAPPC2 loss similarly impairs autophagy in relevant tissues not yet shown\",\n        \"Mechanism by which TRAPPC2-dependent TRAPPIII is recruited specifically to PAS membranes is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connecting TRAPPC2 function to the tissue-specific SEDT phenotype, TRAPPC2 knockdown in chondrocytes was shown to reduce collagen II expression and secretion, demonstrating a direct role in procollagen trafficking.\",\n      \"evidence\": \"siRNA knockdown in SW1353 cells and primary human chondrocytes; Western blot and ELISA for collagen II; patient nonsense variant analysis\",\n      \"pmids\": [\"37693308\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether collagen II reduction is due to ER retention, degradation, or transcriptional effects not fully resolved\",\n        \"Other cargo affected by TRAPPC2 loss in chondrocytes not catalogued\",\n        \"No in vivo animal model validation of the chondrocyte secretion defect\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the atomic-resolution structure of TRAPPC2 at the TRAPPII/III assembly interface, the mechanism by which TRAPPC2 loss causes tissue-restricted skeletal pathology despite its ubiquitous expression, and whether TRAPPC2-dependent autophagy defects contribute to SEDT pathogenesis.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of TRAPPC2 in complex with TRAPPC9 or TRAPPC8\",\n        \"Tissue-specific vulnerability mechanism for SEDT not explained\",\n        \"Whether autophagy defects contribute to chondrocyte dysfunction in SEDT is untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 3, 4]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"complexes\": [\n      \"TRAPPII\",\n      \"TRAPPIII\"\n    ],\n    \"partners\": [\n      \"TRAPPC9\",\n      \"TRAPPC8\",\n      \"TRAPPC10\",\n      \"STX5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}