{"gene":"VPS16","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":1993,"finding":"Yeast Vps16p associates with a sedimentable, large protein complex (resistant to detergent and salt, extractable with urea/alkali), is essential for vacuolar protein sorting, and is required for normal vacuole morphology; it localizes to a particulate cell fraction.","method":"Subcellular fractionation, gene disruption, overexpression saturation assay, polyclonal antiserum detection","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (fractionation, KO phenotype, overexpression), foundational study with >100 citations","pmids":["8444873"],"is_preprint":false},{"year":1999,"finding":"Yeast Vps16p inhibits the mRNA decapping enzyme Dcp1p; mutations in VPS16 reduce decapping activity in vitro and stabilize mRNAs in vivo, and extracts from vps16 mutants inhibit purified Dcp1p activity; enhanced interaction of Dcp1p with Hsp70 (Ssa1p/2p) is observed in vps16 mutants.","method":"In vitro decapping assay, mRNA stability assay, co-purification of Dcp1p with Ssa1p/2p","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro assay plus in vivo mRNA stability, single lab","pmids":["10523645"],"is_preprint":false},{"year":2001,"finding":"Human VPS16, VPS11, VPS18, and VPS33 were molecularly cloned and identified as homologs of the yeast class C VPS genes required for lysosomal protein delivery.","method":"Molecular cloning, sequence analysis, expression profiling","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 — molecular identification without detailed functional reconstitution","pmids":["11250079"],"is_preprint":false},{"year":2003,"finding":"Mammalian Vps16 (mVps16) is a component of the class C Vps complex; mammalian class C Vps proteins interact with multiple syntaxins and Vps45, localizing to endosomal compartments, and their overexpression inhibits transferrin recycling without affecting internalization.","method":"Co-immunoprecipitation, transferrin trafficking assay, subcellular localization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — single Co-IP with functional trafficking readout, single lab","pmids":["14623309"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of human VPS33A alone and in complex with VPS16 (residues 642–736) was determined at 2.6 Å resolution; VPS16 residues 642–736 are necessary and sufficient to recruit VPS33A to the HOPS complex, and mutations at the binding interface disrupt the interaction both in vitro and in cells, preventing VPS33A incorporation into HOPS.","method":"X-ray crystallography, in vitro binding assay, interface mutagenesis, cell-based co-immunoprecipitation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis validated in vitro and in cells; replicated by a concurrent structural study","pmids":["23901104"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of yeast Vps33 alone and bound to a C-terminal portion of Vps16 determined at 2.6 Å; the Vps33–Vps16 interface is extensive but binding causes only subtle conformational change in Vps33; this confirms Vps33 as an SM-family protein that is stably integrated into HOPS via Vps16.","method":"X-ray crystallography","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — independent crystal structure corroborating the PNAS structure","pmids":["23840694"],"is_preprint":false},{"year":2015,"finding":"VPS16 recruits VPS33A to the HOPS complex, and this interaction is essential for lysosome fusion with late endosomes and autophagosomes; VPS16/VPS33A interface mutants (designed from the crystal structure) that cannot bind each other fail to rescue endosome–lysosome or autophagosome–lysosome fusion in cells depleted of endogenous proteins. Additionally, VIPAR and VPS33B form a separate complex distinct from HOPS and are not required for these fusion events.","method":"Crystal-structure-guided mutagenesis, fluorescent dextran delivery assay (endosome–lysosome fusion), autophagosome–lysosome fusion assay, siRNA depletion, co-immunoprecipitation","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1–2 — structure-guided mutagenesis combined with functional rescue assays in mammalian cells; >100 citations","pmids":["25783203"],"is_preprint":false},{"year":2021,"finding":"Bi-allelic reduction (~85%) of VPS16 protein similarly reduces levels of other HOPS/CORVET subunits including VPS33A; re-expression of VPS16 restores subunit levels and rescues defects in transferrin uptake/endosomal trafficking, autophagosome accumulation, and lysosomal compartment accumulation, demonstrating VPS16 as a scaffold required for HOPS/CORVET complex stability.","method":"Patient-derived fibroblast complementation, western blotting, transferrin trafficking assay, autophagosome/lysosome imaging, zebrafish vps16 knockdown model","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in patient cells plus in vivo zebrafish model with rescue","pmids":["33938619"],"is_preprint":false}],"current_model":"VPS16 functions as a scaffold subunit of the HOPS (and CORVET) tethering complexes: its C-terminal region (residues 642–736) directly binds the SM-family protein VPS33A (as revealed by crystal structure and mutagenesis), recruiting VPS33A into the complex and thereby enabling HOPS-mediated membrane tethering and fusion of late endosomes and autophagosomes with lysosomes; VPS16 is also required for the stability of other HOPS/CORVET subunits, and loss of VPS16 disrupts endolysosomal trafficking, causes lysosomal storage pathology, and in yeast additionally regulates mRNA decapping enzyme activity."},"narrative":{"teleology":[{"year":1993,"claim":"Establishing that Vps16p is a component of a large protein complex required for vacuolar protein sorting answered the foundational question of whether VPS16 acts alone or as part of a multi-subunit machine in the endolysosomal pathway.","evidence":"Subcellular fractionation, gene disruption, and overexpression in S. cerevisiae","pmids":["8444873"],"confidence":"High","gaps":["Identity of other complex components unknown","Mechanism by which complex promotes vacuolar sorting undefined","No mammalian homolog characterized"]},{"year":1999,"claim":"Discovery that Vps16p inhibits the mRNA decapping enzyme Dcp1p revealed an unexpected non-trafficking function, raising the question of whether VPS16 moonlights in mRNA metabolism.","evidence":"In vitro decapping assay and mRNA stability measurements in vps16 mutant yeast","pmids":["10523645"],"confidence":"Medium","gaps":["Direct physical interaction between Vps16p and Dcp1p not demonstrated","Not replicated in mammalian systems","Relationship between decapping and vacuolar sorting functions unclear"]},{"year":2003,"claim":"Identification of mammalian VPS16 as a class C Vps complex member that localizes to endosomes and interacts with syntaxins extended the yeast paradigm to mammalian endolysosomal trafficking.","evidence":"Co-immunoprecipitation, transferrin trafficking assay, and subcellular localization in mammalian cells","pmids":["14623309"],"confidence":"Medium","gaps":["Architecture of the mammalian complex not defined","Specific binding partners within the complex not mapped","Single-lab Co-IP without reciprocal validation"]},{"year":2013,"claim":"Crystal structures of the VPS33A–VPS16 interface in both human and yeast systems answered how VPS33 is recruited into the HOPS complex, revealing that VPS16 residues 642–736 are necessary and sufficient for this interaction.","evidence":"X-ray crystallography at 2.6 Å resolution with interface mutagenesis validated in vitro and in cells (two independent labs, human and yeast)","pmids":["23901104","23840694"],"confidence":"High","gaps":["Full HOPS complex architecture not resolved","How VPS16 contacts other HOPS subunits beyond VPS33 not structurally defined","Functional consequence of interface disruption on membrane fusion not yet tested"]},{"year":2015,"claim":"Structure-guided mutagenesis demonstrated that the VPS16–VPS33A interaction is essential for both late endosome–lysosome and autophagosome–lysosome fusion, establishing VPS16 as functionally required for HOPS-dependent membrane fusion events.","evidence":"Crystal-structure-guided interface mutants tested in siRNA-rescue experiments with dextran delivery and autophagosome–lysosome fusion assays in mammalian cells","pmids":["25783203"],"confidence":"High","gaps":["SNARE-pairing mechanism downstream of VPS33A recruitment not resolved","Whether VPS16 has fusogenic roles independent of VPS33A not addressed","Contribution of CORVET versus HOPS not dissected"]},{"year":2021,"claim":"Patient-derived cells with bi-allelic VPS16 reduction showed that VPS16 stabilizes all HOPS/CORVET subunits and is required for normal endosomal trafficking, autophagy flux, and lysosome homeostasis, establishing VPS16 as a master scaffold of the complex.","evidence":"Patient fibroblast complementation, western blotting of subunit levels, transferrin uptake, autophagosome/lysosome imaging, and zebrafish vps16 knockdown with rescue","pmids":["33938619"],"confidence":"High","gaps":["Structural basis for VPS16-dependent stabilization of non-VPS33 subunits unknown","Whether partial VPS16 loss differentially affects HOPS versus CORVET not resolved","Tissue-specific consequences of VPS16 deficiency not fully explored"]},{"year":null,"claim":"A complete structural model of HOPS/CORVET with all VPS16 contact surfaces, the mechanism by which VPS16 stabilizes non-VPS33 subunits, and whether the yeast mRNA decapping role is conserved in mammals remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Full HOPS/CORVET holocomplex structure with VPS16 contacts not available","Mechanism of coordinate subunit stabilization by VPS16 undefined","Conservation of VPS16 decapping function beyond yeast untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,5,6,7]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3,7]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[6,7]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,3,6,7]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[6,7]}],"complexes":["HOPS","CORVET"],"partners":["VPS33A","VPS11","VPS18"],"other_free_text":[]},"mechanistic_narrative":"VPS16 is a scaffold subunit of the HOPS and CORVET tethering complexes that is essential for endolysosomal trafficking, autophagosome–lysosome fusion, and vacuolar/lysosomal biogenesis. Its C-terminal region (residues 642–736) directly binds the SM-family protein VPS33A through an extensive interface resolved by X-ray crystallography in both yeast and human systems, and this interaction is necessary and sufficient to recruit VPS33A into the HOPS complex and to enable late endosome–lysosome and autophagosome–lysosome fusion [PMID:23901104, PMID:23840694, PMID:25783203]. VPS16 also stabilizes other HOPS/CORVET subunits; bi-allelic loss of VPS16 causes coordinate depletion of complex members, accumulation of autophagosomes and lysosomes, and impaired endosomal trafficking, all rescued by VPS16 re-expression [PMID:33938619]. In yeast, Vps16p additionally modulates mRNA decapping by inhibiting Dcp1p activity [PMID:10523645]."},"prefetch_data":{"uniprot":{"accession":"Q9H269","full_name":"Vacuolar protein sorting-associated protein 16 homolog","aliases":[],"length_aa":839,"mass_kda":94.7,"function":"Plays a role in vesicle-mediated protein trafficking to lysosomal compartments including the endocytic membrane transport and autophagic pathways. Believed to act as a core component of the putative HOPS and CORVET endosomal tethering complexes which are proposed to be involved in the Rab5-to-Rab7 endosome conversion probably implicating MON1A/B, and via binding SNAREs and SNARE complexes to mediate tethering and docking events during SNARE-mediated membrane fusion. The HOPS complex is proposed to be recruited to Rab7 on the late endosomal membrane and to regulate late endocytic, phagocytic and autophagic traffic towards lysosomes. The CORVET complex is proposed to function as a Rab5 effector to mediate early endosome fusion probably in specific endosome subpopulations (PubMed:11382755, PubMed:23351085, PubMed:24554770, PubMed:25266290, PubMed:25783203). Required for recruitment of VPS33A to the HOPS complex (PubMed:23901104). Required for fusion of endosomes and autophagosomes with lysosomes; the function is dependent on its association with VPS33A but not VPS33B (PubMed:25783203). The function in autophagosome-lysosome fusion implicates STX17 but not UVRAG (PubMed:24554770)","subcellular_location":"Late endosome membrane; Lysosome membrane; Early endosome; Cytoplasmic vesicle, clathrin-coated vesicle; Cytoplasmic vesicle, autophagosome","url":"https://www.uniprot.org/uniprotkb/Q9H269/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/VPS16","classification":"Not Classified","n_dependent_lines":407,"n_total_lines":1208,"dependency_fraction":0.33692052980132453},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000215305","cell_line_id":"CID001857","localizations":[{"compartment":"vesicles","grade":3},{"compartment":"cytoplasmic","grade":2}],"interactors":[{"gene":"VPS41","stoichiometry":10.0},{"gene":"VPS33A","stoichiometry":10.0},{"gene":"VPS18","stoichiometry":10.0},{"gene":"TGFBRAP1","stoichiometry":0.2},{"gene":"VPS11","stoichiometry":0.2},{"gene":"VPS8","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001857","total_profiled":1310},"omim":[{"mim_id":"619389","title":"SPINOCEREBELLAR ATAXIA, AUTOSOMAL RECESSIVE 29; SCAR29","url":"https://www.omim.org/entry/619389"},{"mim_id":"619291","title":"DYSTONIA 30; DYT30","url":"https://www.omim.org/entry/619291"},{"mim_id":"618366","title":"VPS8 CORVET COMPLEX SUBUNIT; VPS8","url":"https://www.omim.org/entry/618366"},{"mim_id":"610034","title":"VPS33A CORE SUBUNIT OF CORVET AND HOPS COMPLEXES; VPS33A","url":"https://www.omim.org/entry/610034"},{"mim_id":"608552","title":"VPS33B LATE ENDOSOME AND LYSOSOME ASSOCIATED; VPS33B","url":"https://www.omim.org/entry/608552"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/VPS16"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9H269","domains":[{"cath_id":"2.40.128","chopping":"1-18_211-330","consensus_level":"medium","plddt":91.9364,"start":1,"end":330},{"cath_id":"1.25.40","chopping":"518-601","consensus_level":"medium","plddt":92.1106,"start":518,"end":601}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H269","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H269-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H269-F1-predicted_aligned_error_v6.png","plddt_mean":91.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=VPS16","jax_strain_url":"https://www.jax.org/strain/search?query=VPS16"},"sequence":{"accession":"Q9H269","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H269.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H269/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H269"}},"corpus_meta":[{"pmid":"25783203","id":"PMC_25783203","title":"Recruitment of VPS33A to HOPS by VPS16 Is Required for Lysosome Fusion with Endosomes and Autophagosomes.","date":"2015","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/25783203","citation_count":125,"is_preprint":false},{"pmid":"8444873","id":"PMC_8444873","title":"The VPS16 gene product associates with a sedimentable protein complex and is essential for vacuolar protein sorting in yeast.","date":"1993","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8444873","citation_count":103,"is_preprint":false},{"pmid":"32808683","id":"PMC_32808683","title":"Loss-of-Function Variants in HOPS Complex Genes VPS16 and VPS41 Cause Early Onset Dystonia Associated with Lysosomal Abnormalities.","date":"2020","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/32808683","citation_count":94,"is_preprint":false},{"pmid":"23901104","id":"PMC_23901104","title":"Structural basis of Vps33A recruitment to the human HOPS complex by Vps16.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/23901104","citation_count":81,"is_preprint":false},{"pmid":"11250079","id":"PMC_11250079","title":"Molecular cloning and characterization of human VPS18, VPS 11, VPS16, and VPS33.","date":"2001","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/11250079","citation_count":59,"is_preprint":false},{"pmid":"23840694","id":"PMC_23840694","title":"Crystal Structures of the Sec1/Munc18 (SM) Protein Vps33, Alone and Bound to the Homotypic Fusion and Vacuolar Protein Sorting (HOPS) Subunit Vps16*.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23840694","citation_count":51,"is_preprint":false},{"pmid":"27174565","id":"PMC_27174565","title":"Homozygous mutation of VPS16 gene is responsible for an autosomal recessive adolescent-onset primary dystonia.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27174565","citation_count":48,"is_preprint":false},{"pmid":"10523645","id":"PMC_10523645","title":"Mutations in VPS16 and MRT1 stabilize mRNAs by activating an inhibitor of the decapping enzyme.","date":"1999","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10523645","citation_count":29,"is_preprint":false},{"pmid":"33938619","id":"PMC_33938619","title":"Bi-allelic VPS16 variants limit HOPS/CORVET levels and cause a mucopolysaccharidosis-like disease.","date":"2021","source":"EMBO molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33938619","citation_count":27,"is_preprint":false},{"pmid":"34013567","id":"PMC_34013567","title":"Homozygous missense VPS16 variant is associated with a novel disease, resembling mucopolysaccharidosis-plus syndrome in two siblings.","date":"2021","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34013567","citation_count":21,"is_preprint":false},{"pmid":"34901436","id":"PMC_34901436","title":"Transcript-Specific Loss-of-Function Variants in VPS16 Are Enriched in Patients With Dystonia.","date":"2021","source":"Neurology. 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it localizes to a particulate cell fraction.\",\n      \"method\": \"Subcellular fractionation, gene disruption, overexpression saturation assay, polyclonal antiserum detection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (fractionation, KO phenotype, overexpression), foundational study with >100 citations\",\n      \"pmids\": [\"8444873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Yeast Vps16p inhibits the mRNA decapping enzyme Dcp1p; mutations in VPS16 reduce decapping activity in vitro and stabilize mRNAs in vivo, and extracts from vps16 mutants inhibit purified Dcp1p activity; enhanced interaction of Dcp1p with Hsp70 (Ssa1p/2p) is observed in vps16 mutants.\",\n      \"method\": \"In vitro decapping assay, mRNA stability assay, co-purification of Dcp1p with Ssa1p/2p\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro assay plus in vivo mRNA stability, single lab\",\n      \"pmids\": [\"10523645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Human VPS16, VPS11, VPS18, and VPS33 were molecularly cloned and identified as homologs of the yeast class C VPS genes required for lysosomal protein delivery.\",\n      \"method\": \"Molecular cloning, sequence analysis, expression profiling\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — molecular identification without detailed functional reconstitution\",\n      \"pmids\": [\"11250079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mammalian Vps16 (mVps16) is a component of the class C Vps complex; mammalian class C Vps proteins interact with multiple syntaxins and Vps45, localizing to endosomal compartments, and their overexpression inhibits transferrin recycling without affecting internalization.\",\n      \"method\": \"Co-immunoprecipitation, transferrin trafficking assay, subcellular localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP with functional trafficking readout, single lab\",\n      \"pmids\": [\"14623309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of human VPS33A alone and in complex with VPS16 (residues 642–736) was determined at 2.6 Å resolution; VPS16 residues 642–736 are necessary and sufficient to recruit VPS33A to the HOPS complex, and mutations at the binding interface disrupt the interaction both in vitro and in cells, preventing VPS33A incorporation into HOPS.\",\n      \"method\": \"X-ray crystallography, in vitro binding assay, interface mutagenesis, cell-based co-immunoprecipitation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis validated in vitro and in cells; replicated by a concurrent structural study\",\n      \"pmids\": [\"23901104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of yeast Vps33 alone and bound to a C-terminal portion of Vps16 determined at 2.6 Å; the Vps33–Vps16 interface is extensive but binding causes only subtle conformational change in Vps33; this confirms Vps33 as an SM-family protein that is stably integrated into HOPS via Vps16.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — independent crystal structure corroborating the PNAS structure\",\n      \"pmids\": [\"23840694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"VPS16 recruits VPS33A to the HOPS complex, and this interaction is essential for lysosome fusion with late endosomes and autophagosomes; VPS16/VPS33A interface mutants (designed from the crystal structure) that cannot bind each other fail to rescue endosome–lysosome or autophagosome–lysosome fusion in cells depleted of endogenous proteins. Additionally, VIPAR and VPS33B form a separate complex distinct from HOPS and are not required for these fusion events.\",\n      \"method\": \"Crystal-structure-guided mutagenesis, fluorescent dextran delivery assay (endosome–lysosome fusion), autophagosome–lysosome fusion assay, siRNA depletion, co-immunoprecipitation\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-guided mutagenesis combined with functional rescue assays in mammalian cells; >100 citations\",\n      \"pmids\": [\"25783203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Bi-allelic reduction (~85%) of VPS16 protein similarly reduces levels of other HOPS/CORVET subunits including VPS33A; re-expression of VPS16 restores subunit levels and rescues defects in transferrin uptake/endosomal trafficking, autophagosome accumulation, and lysosomal compartment accumulation, demonstrating VPS16 as a scaffold required for HOPS/CORVET complex stability.\",\n      \"method\": \"Patient-derived fibroblast complementation, western blotting, transferrin trafficking assay, autophagosome/lysosome imaging, zebrafish vps16 knockdown model\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in patient cells plus in vivo zebrafish model with rescue\",\n      \"pmids\": [\"33938619\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"VPS16 functions as a scaffold subunit of the HOPS (and CORVET) tethering complexes: its C-terminal region (residues 642–736) directly binds the SM-family protein VPS33A (as revealed by crystal structure and mutagenesis), recruiting VPS33A into the complex and thereby enabling HOPS-mediated membrane tethering and fusion of late endosomes and autophagosomes with lysosomes; VPS16 is also required for the stability of other HOPS/CORVET subunits, and loss of VPS16 disrupts endolysosomal trafficking, causes lysosomal storage pathology, and in yeast additionally regulates mRNA decapping enzyme activity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"VPS16 is a scaffold subunit of the HOPS and CORVET tethering complexes that is essential for endolysosomal trafficking, autophagosome–lysosome fusion, and vacuolar/lysosomal biogenesis. Its C-terminal region (residues 642–736) directly binds the SM-family protein VPS33A through an extensive interface resolved by X-ray crystallography in both yeast and human systems, and this interaction is necessary and sufficient to recruit VPS33A into the HOPS complex and to enable late endosome–lysosome and autophagosome–lysosome fusion [PMID:23901104, PMID:23840694, PMID:25783203]. VPS16 also stabilizes other HOPS/CORVET subunits; bi-allelic loss of VPS16 causes coordinate depletion of complex members, accumulation of autophagosomes and lysosomes, and impaired endosomal trafficking, all rescued by VPS16 re-expression [PMID:33938619]. In yeast, Vps16p additionally modulates mRNA decapping by inhibiting Dcp1p activity [PMID:10523645].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing that Vps16p is a component of a large protein complex required for vacuolar protein sorting answered the foundational question of whether VPS16 acts alone or as part of a multi-subunit machine in the endolysosomal pathway.\",\n      \"evidence\": \"Subcellular fractionation, gene disruption, and overexpression in S. cerevisiae\",\n      \"pmids\": [\"8444873\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of other complex components unknown\",\n        \"Mechanism by which complex promotes vacuolar sorting undefined\",\n        \"No mammalian homolog characterized\"\n      ]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that Vps16p inhibits the mRNA decapping enzyme Dcp1p revealed an unexpected non-trafficking function, raising the question of whether VPS16 moonlights in mRNA metabolism.\",\n      \"evidence\": \"In vitro decapping assay and mRNA stability measurements in vps16 mutant yeast\",\n      \"pmids\": [\"10523645\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct physical interaction between Vps16p and Dcp1p not demonstrated\",\n        \"Not replicated in mammalian systems\",\n        \"Relationship between decapping and vacuolar sorting functions unclear\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of mammalian VPS16 as a class C Vps complex member that localizes to endosomes and interacts with syntaxins extended the yeast paradigm to mammalian endolysosomal trafficking.\",\n      \"evidence\": \"Co-immunoprecipitation, transferrin trafficking assay, and subcellular localization in mammalian cells\",\n      \"pmids\": [\"14623309\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Architecture of the mammalian complex not defined\",\n        \"Specific binding partners within the complex not mapped\",\n        \"Single-lab Co-IP without reciprocal validation\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Crystal structures of the VPS33A–VPS16 interface in both human and yeast systems answered how VPS33 is recruited into the HOPS complex, revealing that VPS16 residues 642–736 are necessary and sufficient for this interaction.\",\n      \"evidence\": \"X-ray crystallography at 2.6 Å resolution with interface mutagenesis validated in vitro and in cells (two independent labs, human and yeast)\",\n      \"pmids\": [\"23901104\", \"23840694\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Full HOPS complex architecture not resolved\",\n        \"How VPS16 contacts other HOPS subunits beyond VPS33 not structurally defined\",\n        \"Functional consequence of interface disruption on membrane fusion not yet tested\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Structure-guided mutagenesis demonstrated that the VPS16–VPS33A interaction is essential for both late endosome–lysosome and autophagosome–lysosome fusion, establishing VPS16 as functionally required for HOPS-dependent membrane fusion events.\",\n      \"evidence\": \"Crystal-structure-guided interface mutants tested in siRNA-rescue experiments with dextran delivery and autophagosome–lysosome fusion assays in mammalian cells\",\n      \"pmids\": [\"25783203\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"SNARE-pairing mechanism downstream of VPS33A recruitment not resolved\",\n        \"Whether VPS16 has fusogenic roles independent of VPS33A not addressed\",\n        \"Contribution of CORVET versus HOPS not dissected\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Patient-derived cells with bi-allelic VPS16 reduction showed that VPS16 stabilizes all HOPS/CORVET subunits and is required for normal endosomal trafficking, autophagy flux, and lysosome homeostasis, establishing VPS16 as a master scaffold of the complex.\",\n      \"evidence\": \"Patient fibroblast complementation, western blotting of subunit levels, transferrin uptake, autophagosome/lysosome imaging, and zebrafish vps16 knockdown with rescue\",\n      \"pmids\": [\"33938619\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for VPS16-dependent stabilization of non-VPS33 subunits unknown\",\n        \"Whether partial VPS16 loss differentially affects HOPS versus CORVET not resolved\",\n        \"Tissue-specific consequences of VPS16 deficiency not fully explored\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A complete structural model of HOPS/CORVET with all VPS16 contact surfaces, the mechanism by which VPS16 stabilizes non-VPS33 subunits, and whether the yeast mRNA decapping role is conserved in mammals remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Full HOPS/CORVET holocomplex structure with VPS16 contacts not available\",\n        \"Mechanism of coordinate subunit stabilization by VPS16 undefined\",\n        \"Conservation of VPS16 decapping function beyond yeast untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 5, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3, 7]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 3, 6, 7]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"complexes\": [\n      \"HOPS\",\n      \"CORVET\"\n    ],\n    \"partners\": [\n      \"VPS33A\",\n      \"VPS11\",\n      \"VPS18\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}