{"gene":"VTI1B","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":2003,"finding":"Vti1b is specifically required for the stability of its SNARE partner syntaxin 8; deletion of vti1b in mice leads to degradation of syntaxin 8 protein while syntaxin 7 and endobrevin/VAMP-8 levels remain unchanged. Vti1b-deficient mice show delayed lysosomal degradation of endocytosed proteins and accumulation of multivesicular bodies and autophagic vacuoles in hepatocytes.","method":"Vti1b knockout mouse model; western blotting for SNARE partners; endocytosis/lysosomal degradation assays; electron microscopy","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO mouse with multiple orthogonal readouts, replicated across tissues","pmids":["12861006"],"is_preprint":false},{"year":2004,"finding":"EpsinR functions as an adaptor for vti1b, selectively incorporating vti1b (but not vti1a) into clathrin-coated vesicles (CCVs); depletion of epsinR or AP-1 by siRNA causes vti1b redistribution from the perinuclear region to the cell periphery and reduces vti1b in CCV preparations by >70%.","method":"siRNA knockdown of epsinR and AP-1 in HeLa cells; CCV isolation and cargo content analysis; immunofluorescence microscopy","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (siRNA, CCV isolation, imaging) in single rigorous study","pmids":["15371541"],"is_preprint":false},{"year":2005,"finding":"Vti1b and syntaxin 6 form a novel intracellular Q-SNARE complex on Golgi membranes and on Golgi-derived TNFα vesicles; both proteins are up-regulated in LPS-activated macrophages and are rate-limiting for TNFα trafficking and secretion.","method":"Co-immunoprecipitation; Golgi membrane isolation; in vitro vesicle budding; overexpression of full-length and truncated proteins; confocal immunofluorescence","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — reciprocal Co-IP plus in vitro vesicle budding plus functional overexpression studies","pmids":["15640147"],"is_preprint":false},{"year":2010,"finding":"VAMP8 and Vti1b together mediate fusion of both antimicrobial autophagosomes (xenophagosomes) and canonical autophagosomes with lysosomes; siRNA knockdown of both SNAREs impairs LC3–LAMP1 colocalization and reduces bacterial killing, while knockdown of syntaxin 7 or syntaxin 8 has little effect.","method":"siRNA knockdown in human cells; confocal microscopy for LC3/LAMP1 colocalization; bactericidal efficiency assay with Group A Streptococcus; LC3-II degradation assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — genetic knockdown with specific phenotypic readouts and epistasis (Stx7/8 controls), replicated across two autophagy types","pmids":["20089838"],"is_preprint":false},{"year":2010,"finding":"Vti1b and VAMP8 are required for lytic granule exocytosis (degranulation) in CTL; Vti1b- and Vamp8-knockout CTL show significantly reduced CD107a surface expression and ~50% reduced cytolytic activity at early timepoints after antigen-specific stimulation.","method":"Vti1b and Vamp8 knockout mice (TCR-transgenic OT-I background); flow cytometry for CD107a degranulation marker; cytotoxicity assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with specific quantitative functional readouts","pmids":["20543108"],"is_preprint":false},{"year":2011,"finding":"Syntaxin 11 binds Vti1b and regulates its availability to form the Q-SNARE complexes Stx6/Stx7/Vti1b and Stx7/Stx8/Vti1b that mediate late endosome-to-lysosome fusion in macrophages; a disease-causing mutant Stx11 sequesters Vti1b from these complexes, and Stx11 depletion causes enlarged late endosomal compartments and inhibited late endosome-to-lysosome fusion.","method":"Co-immunoprecipitation; siRNA knockdown with rescue by siRNA-resistant construct; confocal microscopy; endosomal morphology analysis","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus knockdown/rescue with defined phenotypic readouts","pmids":["21388490"],"is_preprint":false},{"year":2011,"finding":"Vti1b is required for tethering lytic granules (LG) with CD3-containing endosomes (CD3-endo) in human CTL; Vti1b knockdown reduces LG–CD3-endo tethering, impairs accumulation and docking of LG at the immunological synapse, and reduces target cell killing.","method":"TIRF microscopy and fast deconvolution live imaging in primary human CD8+ T cells; siRNA knockdown of Vti1b; confocal microscopy in fixed cells; cytotoxicity assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — live imaging with quantitative tethering/docking readouts plus functional cytotoxicity assay in primary human cells","pmids":["21562157"],"is_preprint":false},{"year":2011,"finding":"Combined loss of vti1a and vti1b in mice causes perinatal lethality with massive peripheral neurodegeneration (>95% neuron loss in dorsal root and geniculate ganglia), missing/misrouted axon tracts, and absence of Golgi outposts in dendrites; fibroblasts lacking both SNAREs survive with only minor trafficking defects, indicating that specialized neuronal membrane trafficking demands are uniquely dependent on these SNAREs.","method":"Vti1a/Vti1b double-knockout mouse; histology and immunofluorescence of ganglia and axon tracts; organelle morphology in fibroblasts","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — genetic double-KO with cell-type-specific phenotypic readouts including neuron counting and organelle analysis","pmids":["21262811"],"is_preprint":false},{"year":2016,"finding":"During xenophagy of Group A Streptococcus, STX6 forms a SNARE complex with VTI1B and VAMP3 on GAS-containing autophagosome-like vacuoles (GcAVs) to mediate fusion between GcAVs and recycling endosomes; RABGEF1 mediates this RE-GcAV fusion through the STX6-VAMP3-VTI1B complex.","method":"Knockdown and knockout of STX6, VTI1B, VAMP3, and RABGEF1 in human cells; co-immunoprecipitation; confocal microscopy for SNARE localization and GcAV-RE colocalization; GAS clearance assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 — Co-IP plus KO/KD with functional xenophagy readout and multiple pathway components tested","pmids":["27791468"],"is_preprint":false},{"year":2019,"finding":"Vti1b is in close proximity to and likely interacts (directly or indirectly) with TRPV1 in dorsal root ganglia neurons, as shown by proximity ligation assays and co-immunoprecipitation; virus-mediated knockdown of Vti1b in sensory neurons attenuates thermal hypersensitivity during inflammatory pain without affecting nociceptive pain, and Vti1b is less abundant in the TRPV1 protein complex during inflammatory conditions.","method":"Proximity ligation assay; co-immunoprecipitation; mass spectrometry-based quantitative interactomics; AAV-mediated knockdown in sensory neurons; behavioral pain assays in mice","journal":"Pain","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP/PLA plus in vivo KD with behavioral readout, but mechanism of interaction not fully resolved","pmids":["30335684"],"is_preprint":false},{"year":2020,"finding":"PTPN9 phosphatase dephosphorylates VTI1B as a substrate; the nonphosphorylatable VTI1B mutant (but not the phosphomimetic mutant) enhances SNARE complex assembly and autophagic flux. PTPN9-mediated dephosphorylation of VTI1B promotes homotypic ATG16L1+ vesicle fusion and early autophagosome biogenesis.","method":"PTPN9 knockout/knockdown; colocalization by confocal microscopy; phosphomimetic and nonphosphorylatable VTI1B mutants; autophagic flux assays; SNARE complex assembly assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1–2 — PTM writer identified with substrate validation using phospho-mutants and functional SNARE complex assembly readout","pmids":["33112705"],"is_preprint":false},{"year":2020,"finding":"The invariant chain (Ii/CD74) binds to Vti1b, recruits it to contact sites of fusing Ii-positive endosomes, and delays endosomal maturation; knockdown of Vti1b inhibits the Ii-induced maturation delay, and Ii lacking its cytoplasmic tail relocates Vti1b to the plasma membrane.","method":"Co-immunoprecipitation; confocal microscopy; siRNA knockdown of Vti1b; Ii-truncation mutant overexpression; endosomal maturation assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with domain mapping plus knockdown and functional endosomal maturation readout","pmids":["32907852"],"is_preprint":false},{"year":2021,"finding":"The SNARE complex VAMP4/Stx6/Stx7/Vti1b mediates fusion of Golgi-derived vesicles containing MT1-MMP with late endosomes in macrophages; depletion of any component of the Stx6/Stx7/Vti1b Q-SNARE complex reduces surface MT1-MMP and gelatin degradation, while overexpression increases surface MT1-MMP.","method":"Fixed and live imaging; siRNA depletion; overexpression; surface MT1-MMP quantification; gelatin degradation assay","journal":"Traffic","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple KD experiments with functional readout, but SNARE complex not directly reconstituted","pmids":["34476885"],"is_preprint":false},{"year":2024,"finding":"Trehalose dimycolate (TDM) from M. tuberculosis binds VTI1B and STX8 via a photoaffinity probe; in the presence of M. tuberculosis, VTI1B and STX8 complex with VAMP2 instead of their canonical partner VAMP8, reducing VAMP8 binding and inhibiting phagosome maturation to promote intracellular bacterial replication.","method":"Clickable photoaffinity TDM probe; Co-immunoprecipitation; macrophage infection assays; M. tuberculosis replication assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2–3 — chemical biology probe plus Co-IP with functional infectious readout, but preprint and novel mechanism not yet peer-reviewed","pmids":["bio_10.1101_2024.12.16.627577"],"is_preprint":true}],"current_model":"VTI1B is a Qb-SNARE protein that participates in multiple endosomal and autophagic membrane fusion events by assembling into distinct four-helix SNARE complexes (with partners including VAMP8, syntaxin 7, syntaxin 8, syntaxin 6, syntaxin 11, and VAMP3), mediating late endosome–lysosome fusion, autophagosome–lysosome fusion, Golgi-to-late-endosome trafficking, and recycling endosome–autophagosome fusion; its activity is regulated by PTPN9-mediated dephosphorylation that promotes SNARE complex assembly, and it is selectively incorporated into clathrin-coated vesicles by the adaptor epsinR, with specialized roles in lytic granule secretion in CTL, TNFα secretion in macrophages, and TRPV1-mediated inflammatory pain sensitization in sensory neurons."},"narrative":{"teleology":[{"year":2003,"claim":"Establishing that VTI1B stabilizes syntaxin 8 and is required for efficient late endosome–lysosome fusion resolved the question of which SNARE mediates this trafficking step and revealed in vivo functional redundancy allowing viability of single-knockout mice.","evidence":"Vti1b knockout mouse with western blot for SNARE partners, endocytic degradation assays, and electron microscopy","pmids":["12861006"],"confidence":"High","gaps":["Compensatory SNARE(s) permitting mouse survival not identified","Mechanism of syntaxin 8 destabilization not resolved"]},{"year":2004,"claim":"Identifying epsinR as the adaptor that selectively sorts VTI1B (but not VTI1A) into clathrin-coated vesicles explained how VTI1B reaches the correct membrane compartment for SNARE complex assembly.","evidence":"siRNA knockdown of epsinR and AP-1 in HeLa cells with CCV isolation and immunofluorescence","pmids":["15371541"],"confidence":"High","gaps":["Direct binding interface between epsinR and VTI1B not mapped","Whether other adaptors contribute to VTI1B sorting in non-HeLa cell types unknown"]},{"year":2005,"claim":"Demonstrating that VTI1B and syntaxin 6 form a Q-SNARE complex on Golgi membranes that is rate-limiting for TNFα vesicle trafficking established VTI1B's role in regulated secretion beyond constitutive endosomal fusion.","evidence":"Co-immunoprecipitation, Golgi membrane isolation, in vitro vesicle budding, and overexpression studies in macrophages","pmids":["15640147"],"confidence":"High","gaps":["R-SNARE partner for this TNFα trafficking complex not fully defined","How LPS upregulates VTI1B/STX6 expression not determined"]},{"year":2010,"claim":"Showing that VTI1B and VAMP8 jointly mediate autophagosome–lysosome fusion (for both canonical autophagy and xenophagy) while syntaxin 7/8 are dispensable redefined the SNARE requirements for autophagic flux and bacterial killing.","evidence":"siRNA knockdown with LC3–LAMP1 colocalization, LC3-II degradation assay, and Group A Streptococcus killing assay in human cells","pmids":["20089838"],"confidence":"High","gaps":["Identity of the complete four-helix SNARE complex for autophagosome–lysosome fusion not established","Whether other R-SNAREs substitute for VAMP8 in specific tissues unknown"]},{"year":2010,"claim":"Establishing that VTI1B and VAMP8 are required for lytic granule exocytosis in CTL extended VTI1B's function to regulated secretory events critical for adaptive immunity.","evidence":"Vti1b and Vamp8 knockout CTL on OT-I TCR-transgenic background with CD107a degranulation and cytotoxicity assays","pmids":["20543108"],"confidence":"High","gaps":["Whether VTI1B acts at granule–plasma membrane fusion or an upstream maturation step not resolved","Q-SNARE complex partners for lytic granule exocytosis not defined"]},{"year":2011,"claim":"Three contemporaneous studies revealed that VTI1B acts in specialized neuronal and immune contexts: syntaxin 11 regulates VTI1B availability for late endosome fusion in macrophages; VTI1B mediates lytic granule tethering at the immunological synapse in CTL; and combined loss of VTI1A/VTI1B causes lethal neurodegeneration, demonstrating essential neuronal requirements for these SNAREs.","evidence":"Co-IP and siRNA rescue for STX11–VTI1B interaction; TIRF/live imaging with VTI1B knockdown in primary human CTL; Vti1a/Vti1b double-KO mouse with histological and organelle analysis","pmids":["21388490","21562157","21262811"],"confidence":"High","gaps":["How disease-causing STX11 mutants mechanistically sequester VTI1B not determined at atomic level","Whether neurodegeneration is due to loss of Golgi outposts, endosomal defects, or both is unresolved","Whether VTI1B tethering function at the synapse requires a specific tethering factor is unknown"]},{"year":2016,"claim":"Identifying the STX6–VTI1B–VAMP3 SNARE complex as the machinery for recycling endosome–autophagosome fusion during xenophagy, recruited by RABGEF1, revealed a new fusion route that feeds membrane from recycling endosomes into the autophagic pathway.","evidence":"Knockdown/knockout of STX6, VTI1B, VAMP3, RABGEF1 with Co-IP and GAS clearance assays in human cells","pmids":["27791468"],"confidence":"High","gaps":["Fourth Q-SNARE in this complex not identified","Whether this pathway operates in autophagy beyond xenophagy not tested"]},{"year":2019,"claim":"Discovering that VTI1B associates with TRPV1 in sensory neurons and that its knockdown attenuates inflammatory thermal hypersensitivity without affecting basal nociception extended VTI1B's functional repertoire to pain signaling modulation.","evidence":"Proximity ligation assay, Co-IP, quantitative interactomics, AAV-mediated knockdown in sensory neurons, and behavioral pain assays in mice","pmids":["30335684"],"confidence":"Medium","gaps":["Whether VTI1B–TRPV1 interaction is direct or bridged by an intermediate unknown","Mechanism by which VTI1B modulates TRPV1 surface delivery or channel function not defined","Not replicated in an independent study"]},{"year":2020,"claim":"Two studies in 2020 defined upstream regulation of VTI1B: PTPN9 dephosphorylates VTI1B to promote SNARE complex assembly and early autophagosome biogenesis, while the invariant chain (CD74/Ii) binds VTI1B to recruit it to endosomal contact sites and delay endosomal maturation.","evidence":"PTPN9 KO/KD with phosphomimetic/nonphosphorylatable VTI1B mutants and SNARE assembly assays; Co-IP and Ii-truncation mutants with endosomal maturation readouts","pmids":["33112705","32907852"],"confidence":"High","gaps":["Phosphorylation site(s) on VTI1B and the upstream kinase not identified","How Ii-mediated VTI1B recruitment delays maturation at molecular level unclear","Whether PTPN9 regulation of VTI1B occurs in all cell types not tested"]},{"year":2021,"claim":"Demonstrating that the VAMP4/STX6/STX7/VTI1B SNARE complex mediates Golgi-to-late-endosome delivery of MT1-MMP in macrophages showed that VTI1B participates in trafficking that controls extracellular matrix degradation.","evidence":"siRNA depletion and overexpression with surface MT1-MMP quantification and gelatin degradation assay","pmids":["34476885"],"confidence":"Medium","gaps":["SNARE complex not directly reconstituted in vitro","Whether this pathway operates in invasive cancer cells not established"]},{"year":null,"claim":"Key unresolved questions include: the identity of the kinase that phosphorylates VTI1B to counterbalance PTPN9-mediated activation; the structural basis for VTI1B's selective incorporation into multiple distinct SNARE complexes; and whether the neurodegeneration phenotype of VTI1A/VTI1B double knockouts reflects a specific trafficking defect (e.g., Golgi outpost loss) or general membrane fusion failure.","evidence":"","pmids":[],"confidence":"Low","gaps":["VTI1B phosphorylation site and kinase unidentified","No structural model of VTI1B in any SNARE complex","Cell-type-specific roles of VTI1B versus VTI1A not systematically resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,3,5,8,10]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,5,11]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2,12]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,8]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,2,5,8,11,12]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3,8,10]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5,6]}],"complexes":["STX7/STX8/VTI1B/VAMP8 SNARE complex","STX6/STX7/VTI1B/VAMP4 SNARE complex","STX6/VTI1B/VAMP3 SNARE complex"],"partners":["STX8","STX7","STX6","STX11","VAMP8","VAMP3","VAMP4","PTPN9"],"other_free_text":[]},"mechanistic_narrative":"VTI1B is a Qb-SNARE protein that functions as a versatile fusogenic component in endosomal, lysosomal, and autophagic membrane trafficking by assembling into distinct four-helix SNARE complexes with partners including syntaxin 6, syntaxin 7, syntaxin 8, syntaxin 11, VAMP8, VAMP3, and VAMP4. VTI1B is required for late endosome–lysosome fusion, autophagosome–lysosome fusion, recycling endosome–autophagosome fusion during xenophagy, and Golgi-to-late-endosome transport of cargo such as TNFα and MT1-MMP; its loss leads to accumulation of multivesicular bodies and autophagic vacuoles, degradation of its stabilizing partner syntaxin 8, and impaired lysosomal degradation [PMID:12861006, PMID:20089838, PMID:27791468, PMID:34476885]. PTPN9-mediated dephosphorylation of VTI1B promotes SNARE complex assembly and autophagic flux, while selective incorporation of VTI1B into clathrin-coated vesicles requires the adaptor epsinR [PMID:33112705, PMID:15371541]. VTI1B has specialized roles in lytic granule exocytosis in cytotoxic T lymphocytes, TNFα secretion in macrophages, and modulation of TRPV1-dependent inflammatory pain sensitization in sensory neurons, and combined loss of Vti1a and Vti1b causes perinatal lethality with massive peripheral neurodegeneration [PMID:20543108, PMID:15640147, PMID:30335684, PMID:21262811]."},"prefetch_data":{"uniprot":{"accession":"Q9UEU0","full_name":"Vesicle transport through interaction with t-SNAREs homolog 1B","aliases":["Vesicle transport v-SNARE protein Vti1-like 1","Vti1-rp1"],"length_aa":232,"mass_kda":26.7,"function":"V-SNARE that mediates vesicle transport pathways through interactions with t-SNAREs on the target membrane. These interactions are proposed to mediate aspects of the specificity of vesicle trafficking and to promote fusion of the lipid bilayers. May be concerned with increased secretion of cytokines associated with cellular senescence","subcellular_location":"Early endosome membrane; Late endosome membrane; Lysosome membrane; Cytoplasmic granule; Recycling endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9UEU0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/VTI1B","classification":"Common Essential","n_dependent_lines":311,"n_total_lines":1208,"dependency_fraction":0.2574503311258278},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000100568","cell_line_id":"CID000757","localizations":[{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"STX8","stoichiometry":10.0},{"gene":"VTI1A","stoichiometry":10.0},{"gene":"VAMP3;VAMP2","stoichiometry":10.0},{"gene":"NSF","stoichiometry":10.0},{"gene":"STX12","stoichiometry":4.0},{"gene":"SCFD1","stoichiometry":4.0},{"gene":"LAMP1","stoichiometry":0.2},{"gene":"NAPA","stoichiometry":0.2},{"gene":"STX7","stoichiometry":0.2},{"gene":"VAMP3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000757","total_profiled":1310},"omim":[{"mim_id":"607265","title":"CLATHRIN INTERACTOR 1; CLINT1","url":"https://www.omim.org/entry/607265"},{"mim_id":"603207","title":"VESICLE TRANSPORT THROUGH INTERACTION WITH T-SNARES 1B; VTI1B","url":"https://www.omim.org/entry/603207"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Golgi apparatus","reliability":"Enhanced"},{"location":"Vesicles","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/VTI1B"},"hgnc":{"alias_symbol":["VTI2"],"prev_symbol":[]},"alphafold":{"accession":"Q9UEU0","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UEU0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UEU0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UEU0-F1-predicted_aligned_error_v6.png","plddt_mean":83.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=VTI1B","jax_strain_url":"https://www.jax.org/strain/search?query=VTI1B"},"sequence":{"accession":"Q9UEU0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UEU0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UEU0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UEU0"}},"corpus_meta":[{"pmid":"20089838","id":"PMC_20089838","title":"Combinational soluble N-ethylmaleimide-sensitive factor attachment protein receptor proteins VAMP8 and Vti1b mediate fusion of antimicrobial and canonical autophagosomes with lysosomes.","date":"2010","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/20089838","citation_count":177,"is_preprint":false},{"pmid":"15640147","id":"PMC_15640147","title":"Syntaxin 6 and Vti1b form a novel SNARE complex, which is up-regulated in activated macrophages to facilitate exocytosis of tumor necrosis Factor-alpha.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15640147","citation_count":129,"is_preprint":false},{"pmid":"12861006","id":"PMC_12861006","title":"Deletion of the SNARE vti1b in mice results in the loss of a single SNARE partner, syntaxin 8.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12861006","citation_count":90,"is_preprint":false},{"pmid":"15371541","id":"PMC_15371541","title":"EpsinR is an adaptor for the SNARE protein Vti1b.","date":"2004","source":"Molecular biology of the 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1950)","url":"https://pubmed.ncbi.nlm.nih.gov/21562157","citation_count":51,"is_preprint":false},{"pmid":"20543108","id":"PMC_20543108","title":"The exocytosis of lytic granules is impaired in Vti1b- or Vamp8-deficient CTL leading to a reduced cytotoxic activity following antigen-specific activation.","date":"2010","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/20543108","citation_count":45,"is_preprint":false},{"pmid":"27791468","id":"PMC_27791468","title":"The STX6-VTI1B-VAMP3 complex facilitates xenophagy by regulating the fusion between recycling endosomes and autophagosomes.","date":"2016","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/27791468","citation_count":39,"is_preprint":false},{"pmid":"30335684","id":"PMC_30335684","title":"Vti1b promotes TRPV1 sensitization during inflammatory pain.","date":"2019","source":"Pain","url":"https://pubmed.ncbi.nlm.nih.gov/30335684","citation_count":20,"is_preprint":false},{"pmid":"33112705","id":"PMC_33112705","title":"PTPN9-mediated dephosphorylation of VTI1B promotes ATG16L1 precursor fusion and autophagosome formation.","date":"2020","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/33112705","citation_count":12,"is_preprint":false},{"pmid":"34476885","id":"PMC_34476885","title":"The trans-SNARE complex VAMP4/Stx6/Stx7/Vti1b is a key regulator of Golgi to late endosome MT1-MMP transport in macrophages.","date":"2021","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/34476885","citation_count":12,"is_preprint":false},{"pmid":"36419086","id":"PMC_36419086","title":"Primary neurons lacking the SNAREs vti1a and vti1b show altered neuronal development.","date":"2022","source":"Neural 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Vti1b.","date":"2026","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/41859820","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.16.627577","title":"Trehalose dimycolate inhibits phagosome maturation and promotes intracellular <i>M. tuberculosis</i> growth via noncanonical SNARE interaction","date":"2024-12-16","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.16.627577","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12585,"output_tokens":3739,"usd":0.04692},"stage2":{"model":"claude-opus-4-6","input_tokens":7159,"output_tokens":3242,"usd":0.175267},"total_usd":0.222187,"stage1_batch_id":"msgbatch_01BparvgRZ9S2LMidvaoo86K","stage2_batch_id":"msgbatch_01NkBfv9SVZWthhS7j6mU6G3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Vti1b is specifically required for the stability of its SNARE partner syntaxin 8; deletion of vti1b in mice leads to degradation of syntaxin 8 protein while syntaxin 7 and endobrevin/VAMP-8 levels remain unchanged. Vti1b-deficient mice show delayed lysosomal degradation of endocytosed proteins and accumulation of multivesicular bodies and autophagic vacuoles in hepatocytes.\",\n      \"method\": \"Vti1b knockout mouse model; western blotting for SNARE partners; endocytosis/lysosomal degradation assays; electron microscopy\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO mouse with multiple orthogonal readouts, replicated across tissues\",\n      \"pmids\": [\"12861006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"EpsinR functions as an adaptor for vti1b, selectively incorporating vti1b (but not vti1a) into clathrin-coated vesicles (CCVs); depletion of epsinR or AP-1 by siRNA causes vti1b redistribution from the perinuclear region to the cell periphery and reduces vti1b in CCV preparations by >70%.\",\n      \"method\": \"siRNA knockdown of epsinR and AP-1 in HeLa cells; CCV isolation and cargo content analysis; immunofluorescence microscopy\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (siRNA, CCV isolation, imaging) in single rigorous study\",\n      \"pmids\": [\"15371541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Vti1b and syntaxin 6 form a novel intracellular Q-SNARE complex on Golgi membranes and on Golgi-derived TNFα vesicles; both proteins are up-regulated in LPS-activated macrophages and are rate-limiting for TNFα trafficking and secretion.\",\n      \"method\": \"Co-immunoprecipitation; Golgi membrane isolation; in vitro vesicle budding; overexpression of full-length and truncated proteins; confocal immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reciprocal Co-IP plus in vitro vesicle budding plus functional overexpression studies\",\n      \"pmids\": [\"15640147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"VAMP8 and Vti1b together mediate fusion of both antimicrobial autophagosomes (xenophagosomes) and canonical autophagosomes with lysosomes; siRNA knockdown of both SNAREs impairs LC3–LAMP1 colocalization and reduces bacterial killing, while knockdown of syntaxin 7 or syntaxin 8 has little effect.\",\n      \"method\": \"siRNA knockdown in human cells; confocal microscopy for LC3/LAMP1 colocalization; bactericidal efficiency assay with Group A Streptococcus; LC3-II degradation assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockdown with specific phenotypic readouts and epistasis (Stx7/8 controls), replicated across two autophagy types\",\n      \"pmids\": [\"20089838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Vti1b and VAMP8 are required for lytic granule exocytosis (degranulation) in CTL; Vti1b- and Vamp8-knockout CTL show significantly reduced CD107a surface expression and ~50% reduced cytolytic activity at early timepoints after antigen-specific stimulation.\",\n      \"method\": \"Vti1b and Vamp8 knockout mice (TCR-transgenic OT-I background); flow cytometry for CD107a degranulation marker; cytotoxicity assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific quantitative functional readouts\",\n      \"pmids\": [\"20543108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Syntaxin 11 binds Vti1b and regulates its availability to form the Q-SNARE complexes Stx6/Stx7/Vti1b and Stx7/Stx8/Vti1b that mediate late endosome-to-lysosome fusion in macrophages; a disease-causing mutant Stx11 sequesters Vti1b from these complexes, and Stx11 depletion causes enlarged late endosomal compartments and inhibited late endosome-to-lysosome fusion.\",\n      \"method\": \"Co-immunoprecipitation; siRNA knockdown with rescue by siRNA-resistant construct; confocal microscopy; endosomal morphology analysis\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus knockdown/rescue with defined phenotypic readouts\",\n      \"pmids\": [\"21388490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Vti1b is required for tethering lytic granules (LG) with CD3-containing endosomes (CD3-endo) in human CTL; Vti1b knockdown reduces LG–CD3-endo tethering, impairs accumulation and docking of LG at the immunological synapse, and reduces target cell killing.\",\n      \"method\": \"TIRF microscopy and fast deconvolution live imaging in primary human CD8+ T cells; siRNA knockdown of Vti1b; confocal microscopy in fixed cells; cytotoxicity assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — live imaging with quantitative tethering/docking readouts plus functional cytotoxicity assay in primary human cells\",\n      \"pmids\": [\"21562157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Combined loss of vti1a and vti1b in mice causes perinatal lethality with massive peripheral neurodegeneration (>95% neuron loss in dorsal root and geniculate ganglia), missing/misrouted axon tracts, and absence of Golgi outposts in dendrites; fibroblasts lacking both SNAREs survive with only minor trafficking defects, indicating that specialized neuronal membrane trafficking demands are uniquely dependent on these SNAREs.\",\n      \"method\": \"Vti1a/Vti1b double-knockout mouse; histology and immunofluorescence of ganglia and axon tracts; organelle morphology in fibroblasts\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic double-KO with cell-type-specific phenotypic readouts including neuron counting and organelle analysis\",\n      \"pmids\": [\"21262811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"During xenophagy of Group A Streptococcus, STX6 forms a SNARE complex with VTI1B and VAMP3 on GAS-containing autophagosome-like vacuoles (GcAVs) to mediate fusion between GcAVs and recycling endosomes; RABGEF1 mediates this RE-GcAV fusion through the STX6-VAMP3-VTI1B complex.\",\n      \"method\": \"Knockdown and knockout of STX6, VTI1B, VAMP3, and RABGEF1 in human cells; co-immunoprecipitation; confocal microscopy for SNARE localization and GcAV-RE colocalization; GAS clearance assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus KO/KD with functional xenophagy readout and multiple pathway components tested\",\n      \"pmids\": [\"27791468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Vti1b is in close proximity to and likely interacts (directly or indirectly) with TRPV1 in dorsal root ganglia neurons, as shown by proximity ligation assays and co-immunoprecipitation; virus-mediated knockdown of Vti1b in sensory neurons attenuates thermal hypersensitivity during inflammatory pain without affecting nociceptive pain, and Vti1b is less abundant in the TRPV1 protein complex during inflammatory conditions.\",\n      \"method\": \"Proximity ligation assay; co-immunoprecipitation; mass spectrometry-based quantitative interactomics; AAV-mediated knockdown in sensory neurons; behavioral pain assays in mice\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP/PLA plus in vivo KD with behavioral readout, but mechanism of interaction not fully resolved\",\n      \"pmids\": [\"30335684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PTPN9 phosphatase dephosphorylates VTI1B as a substrate; the nonphosphorylatable VTI1B mutant (but not the phosphomimetic mutant) enhances SNARE complex assembly and autophagic flux. PTPN9-mediated dephosphorylation of VTI1B promotes homotypic ATG16L1+ vesicle fusion and early autophagosome biogenesis.\",\n      \"method\": \"PTPN9 knockout/knockdown; colocalization by confocal microscopy; phosphomimetic and nonphosphorylatable VTI1B mutants; autophagic flux assays; SNARE complex assembly assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — PTM writer identified with substrate validation using phospho-mutants and functional SNARE complex assembly readout\",\n      \"pmids\": [\"33112705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The invariant chain (Ii/CD74) binds to Vti1b, recruits it to contact sites of fusing Ii-positive endosomes, and delays endosomal maturation; knockdown of Vti1b inhibits the Ii-induced maturation delay, and Ii lacking its cytoplasmic tail relocates Vti1b to the plasma membrane.\",\n      \"method\": \"Co-immunoprecipitation; confocal microscopy; siRNA knockdown of Vti1b; Ii-truncation mutant overexpression; endosomal maturation assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with domain mapping plus knockdown and functional endosomal maturation readout\",\n      \"pmids\": [\"32907852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The SNARE complex VAMP4/Stx6/Stx7/Vti1b mediates fusion of Golgi-derived vesicles containing MT1-MMP with late endosomes in macrophages; depletion of any component of the Stx6/Stx7/Vti1b Q-SNARE complex reduces surface MT1-MMP and gelatin degradation, while overexpression increases surface MT1-MMP.\",\n      \"method\": \"Fixed and live imaging; siRNA depletion; overexpression; surface MT1-MMP quantification; gelatin degradation assay\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple KD experiments with functional readout, but SNARE complex not directly reconstituted\",\n      \"pmids\": [\"34476885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Trehalose dimycolate (TDM) from M. tuberculosis binds VTI1B and STX8 via a photoaffinity probe; in the presence of M. tuberculosis, VTI1B and STX8 complex with VAMP2 instead of their canonical partner VAMP8, reducing VAMP8 binding and inhibiting phagosome maturation to promote intracellular bacterial replication.\",\n      \"method\": \"Clickable photoaffinity TDM probe; Co-immunoprecipitation; macrophage infection assays; M. tuberculosis replication assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — chemical biology probe plus Co-IP with functional infectious readout, but preprint and novel mechanism not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.12.16.627577\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"VTI1B is a Qb-SNARE protein that participates in multiple endosomal and autophagic membrane fusion events by assembling into distinct four-helix SNARE complexes (with partners including VAMP8, syntaxin 7, syntaxin 8, syntaxin 6, syntaxin 11, and VAMP3), mediating late endosome–lysosome fusion, autophagosome–lysosome fusion, Golgi-to-late-endosome trafficking, and recycling endosome–autophagosome fusion; its activity is regulated by PTPN9-mediated dephosphorylation that promotes SNARE complex assembly, and it is selectively incorporated into clathrin-coated vesicles by the adaptor epsinR, with specialized roles in lytic granule secretion in CTL, TNFα secretion in macrophages, and TRPV1-mediated inflammatory pain sensitization in sensory neurons.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"VTI1B is a Qb-SNARE protein that functions as a versatile fusogenic component in endosomal, lysosomal, and autophagic membrane trafficking by assembling into distinct four-helix SNARE complexes with partners including syntaxin 6, syntaxin 7, syntaxin 8, syntaxin 11, VAMP8, VAMP3, and VAMP4. VTI1B is required for late endosome–lysosome fusion, autophagosome–lysosome fusion, recycling endosome–autophagosome fusion during xenophagy, and Golgi-to-late-endosome transport of cargo such as TNFα and MT1-MMP; its loss leads to accumulation of multivesicular bodies and autophagic vacuoles, degradation of its stabilizing partner syntaxin 8, and impaired lysosomal degradation [PMID:12861006, PMID:20089838, PMID:27791468, PMID:34476885]. PTPN9-mediated dephosphorylation of VTI1B promotes SNARE complex assembly and autophagic flux, while selective incorporation of VTI1B into clathrin-coated vesicles requires the adaptor epsinR [PMID:33112705, PMID:15371541]. VTI1B has specialized roles in lytic granule exocytosis in cytotoxic T lymphocytes, TNFα secretion in macrophages, and modulation of TRPV1-dependent inflammatory pain sensitization in sensory neurons, and combined loss of Vti1a and Vti1b causes perinatal lethality with massive peripheral neurodegeneration [PMID:20543108, PMID:15640147, PMID:30335684, PMID:21262811].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing that VTI1B stabilizes syntaxin 8 and is required for efficient late endosome–lysosome fusion resolved the question of which SNARE mediates this trafficking step and revealed in vivo functional redundancy allowing viability of single-knockout mice.\",\n      \"evidence\": \"Vti1b knockout mouse with western blot for SNARE partners, endocytic degradation assays, and electron microscopy\",\n      \"pmids\": [\"12861006\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensatory SNARE(s) permitting mouse survival not identified\", \"Mechanism of syntaxin 8 destabilization not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identifying epsinR as the adaptor that selectively sorts VTI1B (but not VTI1A) into clathrin-coated vesicles explained how VTI1B reaches the correct membrane compartment for SNARE complex assembly.\",\n      \"evidence\": \"siRNA knockdown of epsinR and AP-1 in HeLa cells with CCV isolation and immunofluorescence\",\n      \"pmids\": [\"15371541\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding interface between epsinR and VTI1B not mapped\", \"Whether other adaptors contribute to VTI1B sorting in non-HeLa cell types unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating that VTI1B and syntaxin 6 form a Q-SNARE complex on Golgi membranes that is rate-limiting for TNFα vesicle trafficking established VTI1B's role in regulated secretion beyond constitutive endosomal fusion.\",\n      \"evidence\": \"Co-immunoprecipitation, Golgi membrane isolation, in vitro vesicle budding, and overexpression studies in macrophages\",\n      \"pmids\": [\"15640147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"R-SNARE partner for this TNFα trafficking complex not fully defined\", \"How LPS upregulates VTI1B/STX6 expression not determined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showing that VTI1B and VAMP8 jointly mediate autophagosome–lysosome fusion (for both canonical autophagy and xenophagy) while syntaxin 7/8 are dispensable redefined the SNARE requirements for autophagic flux and bacterial killing.\",\n      \"evidence\": \"siRNA knockdown with LC3–LAMP1 colocalization, LC3-II degradation assay, and Group A Streptococcus killing assay in human cells\",\n      \"pmids\": [\"20089838\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the complete four-helix SNARE complex for autophagosome–lysosome fusion not established\", \"Whether other R-SNAREs substitute for VAMP8 in specific tissues unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Establishing that VTI1B and VAMP8 are required for lytic granule exocytosis in CTL extended VTI1B's function to regulated secretory events critical for adaptive immunity.\",\n      \"evidence\": \"Vti1b and Vamp8 knockout CTL on OT-I TCR-transgenic background with CD107a degranulation and cytotoxicity assays\",\n      \"pmids\": [\"20543108\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether VTI1B acts at granule–plasma membrane fusion or an upstream maturation step not resolved\", \"Q-SNARE complex partners for lytic granule exocytosis not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Three contemporaneous studies revealed that VTI1B acts in specialized neuronal and immune contexts: syntaxin 11 regulates VTI1B availability for late endosome fusion in macrophages; VTI1B mediates lytic granule tethering at the immunological synapse in CTL; and combined loss of VTI1A/VTI1B causes lethal neurodegeneration, demonstrating essential neuronal requirements for these SNAREs.\",\n      \"evidence\": \"Co-IP and siRNA rescue for STX11–VTI1B interaction; TIRF/live imaging with VTI1B knockdown in primary human CTL; Vti1a/Vti1b double-KO mouse with histological and organelle analysis\",\n      \"pmids\": [\"21388490\", \"21562157\", \"21262811\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How disease-causing STX11 mutants mechanistically sequester VTI1B not determined at atomic level\", \"Whether neurodegeneration is due to loss of Golgi outposts, endosomal defects, or both is unresolved\", \"Whether VTI1B tethering function at the synapse requires a specific tethering factor is unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identifying the STX6–VTI1B–VAMP3 SNARE complex as the machinery for recycling endosome–autophagosome fusion during xenophagy, recruited by RABGEF1, revealed a new fusion route that feeds membrane from recycling endosomes into the autophagic pathway.\",\n      \"evidence\": \"Knockdown/knockout of STX6, VTI1B, VAMP3, RABGEF1 with Co-IP and GAS clearance assays in human cells\",\n      \"pmids\": [\"27791468\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fourth Q-SNARE in this complex not identified\", \"Whether this pathway operates in autophagy beyond xenophagy not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Discovering that VTI1B associates with TRPV1 in sensory neurons and that its knockdown attenuates inflammatory thermal hypersensitivity without affecting basal nociception extended VTI1B's functional repertoire to pain signaling modulation.\",\n      \"evidence\": \"Proximity ligation assay, Co-IP, quantitative interactomics, AAV-mediated knockdown in sensory neurons, and behavioral pain assays in mice\",\n      \"pmids\": [\"30335684\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether VTI1B–TRPV1 interaction is direct or bridged by an intermediate unknown\", \"Mechanism by which VTI1B modulates TRPV1 surface delivery or channel function not defined\", \"Not replicated in an independent study\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two studies in 2020 defined upstream regulation of VTI1B: PTPN9 dephosphorylates VTI1B to promote SNARE complex assembly and early autophagosome biogenesis, while the invariant chain (CD74/Ii) binds VTI1B to recruit it to endosomal contact sites and delay endosomal maturation.\",\n      \"evidence\": \"PTPN9 KO/KD with phosphomimetic/nonphosphorylatable VTI1B mutants and SNARE assembly assays; Co-IP and Ii-truncation mutants with endosomal maturation readouts\",\n      \"pmids\": [\"33112705\", \"32907852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation site(s) on VTI1B and the upstream kinase not identified\", \"How Ii-mediated VTI1B recruitment delays maturation at molecular level unclear\", \"Whether PTPN9 regulation of VTI1B occurs in all cell types not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that the VAMP4/STX6/STX7/VTI1B SNARE complex mediates Golgi-to-late-endosome delivery of MT1-MMP in macrophages showed that VTI1B participates in trafficking that controls extracellular matrix degradation.\",\n      \"evidence\": \"siRNA depletion and overexpression with surface MT1-MMP quantification and gelatin degradation assay\",\n      \"pmids\": [\"34476885\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SNARE complex not directly reconstituted in vitro\", \"Whether this pathway operates in invasive cancer cells not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the identity of the kinase that phosphorylates VTI1B to counterbalance PTPN9-mediated activation; the structural basis for VTI1B's selective incorporation into multiple distinct SNARE complexes; and whether the neurodegeneration phenotype of VTI1A/VTI1B double knockouts reflects a specific trafficking defect (e.g., Golgi outpost loss) or general membrane fusion failure.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"VTI1B phosphorylation site and kinase unidentified\", \"No structural model of VTI1B in any SNARE complex\", \"Cell-type-specific roles of VTI1B versus VTI1A not systematically resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 3, 5, 8, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 5, 11]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2, 12]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 2, 5, 8, 11, 12]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3, 8, 10]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5, 6]}\n    ],\n    \"complexes\": [\n      \"STX7/STX8/VTI1B/VAMP8 SNARE complex\",\n      \"STX6/STX7/VTI1B/VAMP4 SNARE complex\",\n      \"STX6/VTI1B/VAMP3 SNARE complex\"\n    ],\n    \"partners\": [\n      \"STX8\",\n      \"STX7\",\n      \"STX6\",\n      \"STX11\",\n      \"VAMP8\",\n      \"VAMP3\",\n      \"VAMP4\",\n      \"PTPN9\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}