{"gene":"STXBP1","run_date":"2026-04-28T21:42:57","timeline":{"discoveries":[{"year":1994,"finding":"STXBP1 (n-Sec1/Munc18-1) was identified as a neural-specific syntaxin-binding protein; it binds syntaxin 1a, 2, and 3 but not syntaxin 4, and becomes membrane-associated in the presence of syntaxin 1a, implicating it in synaptic vesicle docking and fusion.","method":"Pulldown with syntaxin fusion proteins coupled to agarose beads; subcellular fractionation; RNA blot analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — original identification replicated independently in two labs the same year (PMID:8108429 and PMID:8134339) using reciprocal biochemical approaches","pmids":["8108429","8134339"],"is_preprint":false},{"year":1994,"finding":"rbSec1 (rat brain STXBP1 homolog) specifically interacts with syntaxin but not with SNAP-25 or synaptobrevin/VAMP in brain detergent extracts, establishing that Sec1-family function in membrane fusion involves direct interaction with a t-SNARE.","method":"GST pulldown from Triton X-100 brain extract; Northern blot; immunoblot","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean biochemical specificity data, replicated same year by Pevsner et al.","pmids":["8134339"],"is_preprint":false},{"year":1996,"finding":"Munc18-1 is phosphorylated by conventional PKC (Ca2+- and phospholipid-dependent) at Ser306 and Ser313 in a cell-free system; PKC-catalyzed phosphorylation inhibits Munc18-1 interaction with syntaxin, and the Munc18-1/syntaxin complex is not a PKC substrate, revealing a regulatory switch for synaptic vesicle docking/fusion.","method":"In vitro kinase assay with recombinant Munc18-1 and purified PKC; phosphorylation-site mapping; pulldown binding assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis/site mapping, rigorous controls","pmids":["8631738"],"is_preprint":false},{"year":2000,"finding":"Endogenous presynaptic PKC isoforms phosphorylate Munc18-1 in nerve terminals in a Ca2+-dependent manner following depolarization; PKC activation inhibits synaptic Munc18-1 interaction with syntaxin-1A by ~50%, and constitutive phosphatase activity (PP1/PP2B) keeps basal phosphorylation low, defining a dynamic regulatory mechanism for neurotransmitter release.","method":"Phosphorylation assays in isolated rat brain nerve terminals with phorbol esters, PKC inhibitors, phosphatase inhibitors, and K+-evoked depolarization; immunoprecipitation of Munc18-1/syntaxin complexes","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in native synaptosomal preparations, Strong evidence","pmids":["10651895"],"is_preprint":false},{"year":2003,"finding":"Munc18-1 Ser313 is phosphorylated in intact chromaffin cells (by histamine/Ca2+) and in synaptosomes (by depolarization/mGluR activation) in a PKC-dependent manner, with PP1 and PP2B as the dephosphorylating phosphatases, linking this phosphorylation to regulation of transmitter release kinetics.","method":"Phospho-Ser313-specific antisera; permeabilized chromaffin cells; intact synaptosomes with pharmacological stimulation; kinase/phosphatase inhibitor profiling","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 — site-specific phospho-antibody combined with multiple stimulation paradigms and inhibitor profiling","pmids":["12950453"],"is_preprint":false},{"year":2004,"finding":"Munc18-1 co-purifies and co-localizes with neuronal cytoskeletal proteins (neurofilaments, microtubules) and with Cdk5; reciprocal immunoaffinity chromatography confirmed strong protein–protein interaction between Munc18-1, cytoskeletal elements, and Cdk5, suggesting a role in cytoskeletal dynamics.","method":"Munc18-1 immunoaffinity chromatography; immunofluorescence in PC12 cells; immunohistochemistry and immuno-electron microscopy in rat olfactory bulb","journal":"Neurochemistry international","confidence":"Medium","confidence_rationale":"Tier 3 — co-purification and localization, single lab, no functional rescue","pmids":["12963086"],"is_preprint":false},{"year":2004,"finding":"Munc18-1 and syntaxin-1A interact in living cells, as demonstrated by FRET; the interaction occurs first at the Golgi and then at the plasma membrane, syntaxin-1A trafficking to the plasma membrane depends on Munc18-1, and phosphomimetic mutations at Ser313 (PKC site) and Thr574 (Cdk5 site) reduce Munc18-1/syntaxin-1A interaction.","method":"FRET between CFP-Munc18-1 and citrine-YFP-syntaxin-1A in HEK293 and chromaffin cells; fluorescence lifetime imaging; syntaxin open/closed conformation mutants; phosphomimetic Munc18-1 mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — FRET in living cells with multiple mutants, two cell types, orthogonal measurement approaches","pmids":["15489225"],"is_preprint":false},{"year":1999,"finding":"rbSec1 (STXBP1) prevents syntaxin-1A-induced blockade of Golgi-to-plasma-membrane traffic and Golgi disassembly in neurosecretion-incompetent cells, demonstrating that Munc18-1 interaction with syntaxin-1A is required not only for plasma membrane exocytosis but also for proper intracellular trafficking of syntaxin-1A.","method":"Transfection of syntaxin-1A ± rbSec1 in non-neurosecretory cells; immunofluorescence for Golgi markers; protein transport assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — defined cellular phenotype with rescue by rbSec1 expression, single lab","pmids":["10341206"],"is_preprint":false},{"year":2006,"finding":"The linker domain of Slp4-a/granuphilin interacts directly with Munc18-1 and promotes docking of dense-core vesicles to the plasma membrane; despite increased docking, exocytosis is inhibited, identifying a Slp4-a/Munc18-1/syntaxin-1a ternary docking complex.","method":"Deletion/chimeric analysis; co-immunoprecipitation; TIRF-based exocytosis assays in PC12 cells","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — domain mapping plus functional exocytosis readout, single lab","pmids":["16481396"],"is_preprint":false},{"year":2007,"finding":"Munc18-1 interacts with neuronal SNAREs in two distinct modes: binding to isolated syntaxin-1 in a closed conformation, and binding to assembled SNARE complexes. Both modes involve the same low-affinity interaction with the extreme syntaxin-1 N-terminus, which links the two modes; disrupting the N-terminal syntaxin/Munc18 interaction with a competing peptide blocks neurotransmitter release at the calyx of Held synapse.","method":"Transfected cell in vitro assay; electrophysiology at calyx of Held (N-terminal peptide injection); co-immunoprecipitation; truncated syntaxin constructs","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including reconstitution, electrophysiology, and mutagenesis, strong evidence","pmids":["17989281"],"is_preprint":false},{"year":2007,"finding":"Binding of Munc18-1 to closed syntaxin-1 stimulates vesicle docking, while a distinct Munc18-1 interaction mode regulates the subsequent vesicle priming step in chromaffin cells; Munc18-1 null chromaffin cells show abolished vesicle docking and reduced syntaxin levels that are restored by Munc18-1 variants.","method":"Expression of Munc18 variants in Munc18-1 null chromaffin cells; electron microscopy for vesicle docking; capacitance recordings for exocytosis; syntaxin-1 immunoblot","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — null background rescue with structure-function variants, multiple readouts, replicated concept","pmids":["17687045"],"is_preprint":false},{"year":2007,"finding":"Rab3a promotes secretory vesicle docking in chromaffin cells in a manner that requires Munc18-1; GTP- or GDP-locked Rab3a mutants fail to support docking, and wild-type Rab3a cannot promote docking in Munc18-1 null cells, placing Rab3a upstream of Munc18-1 in the docking cascade.","method":"Expression of Rab3a conformation-locked mutants in wild-type and munc18-1 null chromaffin cells; electron microscopy vesicle distribution analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with null background, morphological readout, single lab","pmids":["17637832"],"is_preprint":false},{"year":2008,"finding":"S-nitrosylation of syntaxin 1a at Cys145 disrupts binding of Munc18-1 to the closed conformation of syntaxin 1a in vitro without affecting SNARE complex formation or Munc18-1/SNARE complex binding; nitrosomimetic Cys145 mutants alter Munc18-1 localization and exocytosis kinetics in cells.","method":"In vitro NO treatment; site-directed mutagenesis (C145S, nitrosomimetic mutants); Munc18-1 binding assays; live-cell imaging; carbon fiber amperometry","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro mechanism with mutagenesis plus functional cell assays, multiple methods","pmids":["18452404"],"is_preprint":false},{"year":2008,"finding":"C. elegans UNC-18 (STXBP1 ortholog) acts as a molecular chaperone for syntaxin-1 (UNC-64) in neurons, promoting its anterograde ER-to-plasma-membrane transport; this chaperone function requires both closed-syntaxin binding and N-terminal syntaxin binding modes, while N-terminal binding is especially important for locomotion behavior.","method":"unc-18 mutant analysis; colocalization with ER markers; carbohydrate modification assays for ER retention; double mutants disrupting syntaxin binding modes; behavioral assays","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — epistasis in C. elegans with multiple orthogonal methods, strong mechanistic dissection","pmids":["18596236"],"is_preprint":false},{"year":2009,"finding":"Presynaptic metabotropic glutamate receptor 4 (mGluR4) binds Munc18-1 at resting Ca2+ levels and releases it upon Ca2+-calmodulin activation; sequestration of Munc18-1 by mGluR4 suppresses basal synaptic vesicle release, and release of Munc18-1 from mGluR4 mediates paired-pulse facilitation.","method":"Co-immunoprecipitation; Ca2+-binding assay (EC50 determination); permeabilized PC12 cell secretion assay; electrophysiology (paired-pulse facilitation); mGluR4 domain peptide experiments","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including electrophysiology, biochemistry, and secretion assays","pmids":["19822743"],"is_preprint":false},{"year":2010,"finding":"Munc18-1 binds directly to synaptobrevin (VAMP2) and to the SNARE four-helix bundle with low-micromolar affinity through the same cavity that binds syntaxin-1; the Munc18-1 binding site on synaptobrevin is at the C-terminus of its SNARE motif, placing Munc18-1 at the site of membrane fusion.","method":"NMR; isothermal titration calorimetry; fluorescence anisotropy; analytical ultracentrifugation — multiple biophysical approaches","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — multiple independent biophysical methods demonstrating direct binding, rigorous quantitative analysis","pmids":["20102228"],"is_preprint":false},{"year":2010,"finding":"The SNARE four-helix bundle and the syntaxin N-peptide constitute a minimal complement for Munc18-1 activation of membrane fusion; the syntaxin Habc domain is dispensable for Munc18-1 stimulation of fusion, and the central cavity of Munc18-1 is required for fusion stimulation.","method":"Reconstituted membrane fusion assay; Munc18-1 and syntaxin domain deletion mutants; liposome fusion","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro fusion assay with systematic domain deletions","pmids":["20603329"],"is_preprint":false},{"year":2010,"finding":"Munc18-1 stimulates neuronal SNARE-mediated membrane fusion via its interaction with the SNARE core even when both the Habc domain and N-peptide of syntaxin are absent, as shown by single-vesicle FRET fusion assay and EPR analysis of SNARE core/Munc18 interaction.","method":"Single-molecule FRET vesicle fusion assay; electron paramagnetic resonance (EPR)","journal":"ACS chemical neuroscience","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with EPR structural validation","pmids":["20300453"],"is_preprint":false},{"year":2011,"finding":"Munc18-1 modulates fusion pore properties via distinct interactions: the R39C mutation (disrupting syntaxin-1 binding) and P242S (disrupting Mint interaction) stabilize narrow fusion pores and increase fusion event amplitude; wild-type Munc18-1 abrogates synaptobrevin2/syntaxin-1 binary trans-complex formation, providing a proofreading function that favors vesicle tethering to preformed syntaxin-SNAP-25 binary cis-complexes.","method":"Patch-clamp capacitance recordings; STED microscopy; single-molecule atomic force microscopy; transfection of Munc18-1 mutants in lactotrophs","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — multiple high-resolution methods with defined mutants and functional readouts","pmids":["21677188"],"is_preprint":false},{"year":2011,"finding":"Munc18-1 inhibition of membrane fusion requires syntaxin-1 in a closed conformation; concurrent incubation with VAMP2 liposomes and SNAP-25 releases the inhibition and stimulates fusion specifically for VAMP2 (not VAMP8), requiring N-terminal syntaxin binding for robust stimulation, demonstrating Munc18-1 as a stage-specific off/on switch.","method":"Reconstituted sequential t-SNARE/v-SNARE assembly assay; liposome lipid mixing assay; temperature-controlled incubations; SNARE and Munc18-1 mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — fully reconstituted fusion assay with molecular specificity controls","pmids":["21730064"],"is_preprint":false},{"year":2011,"finding":"Munc18-1 dual roles (chaperone of syntaxin-1A vs. SNARE complex activation) rely on distinct binding modes of its central cavity; a novel cavity mutant shows reduced syntaxin-1A binding and impaired chaperone function while retaining SNARE complex binding and ability to stimulate liposome fusion and secretion in neuroendocrine cells.","method":"Site-directed mutagenesis; co-immunoprecipitation; liposome fusion assay; secretion assay in neuroendocrine cells","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution plus cell-based rescue with structure-function mutants","pmids":["21900493"],"is_preprint":false},{"year":2012,"finding":"Vesicle docking by synaptotagmin-1 is a prerequisite for Munc18-1 to accelerate trans-SNARE (SNAREpin) assembly and membrane fusion in a reconstituted giant unilamellar vesicle system; Munc18-1 was positioned as central to a sequential cascade: docking → priming → fusion.","method":"Reconstituted giant unilamellar vesicle docking/fusion assay with synaptotagmin-1, Munc18-1, complexin II, and Ca2+","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — fully reconstituted system with sequential epistasis","pmids":["22810233"],"is_preprint":false},{"year":2013,"finding":"Domain 3a of Munc18-1 plays a crucial role in vesicle priming (downstream of docking) independently of its syntaxin-1 chaperoning activity; insertion mutations in domain 3a abolish secretion rescue while fully restoring syntaxin-1 plasma membrane expression and vesicle docking, and these mutants show impaired binding to the assembled SNARE complex.","method":"Munc18-1 null/knockdown PC12 cell rescue with domain 3a insertion mutants; exocytosis assay; electron microscopy for vesicle docking; SNARE complex binding assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — null-background rescue with domain-specific mutants, multiple functional readouts","pmids":["23525015"],"is_preprint":false},{"year":2013,"finding":"The Munc18-1 domain 3a loop (residues 317-333) is essential for neuroexocytosis but dispensable for syntaxin-1A chaperoning and plasma membrane delivery; deletion of this loop fully rescues syntaxin-1A transport but not secretory granule fusion, and reduces SNARE complex binding at the cell surface.","method":"Munc18-1 deletion mutant (Δ317-333) expressed in DKD-PC12 cells; exocytosis assay; immunofluorescence; in vitro binding","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — clean domain separation of two functions, null-like background, replicated by same group and others","pmids":["23761923"],"is_preprint":false},{"year":2013,"finding":"Munc18-1 allosterically controls syntaxin-1a conformational exchange between closed and open states; EPR shows that Munc18-1 binding shifts syntaxin H3 toward the ordered, folded state, suppresses the minor open population, and narrows H3-Habc distance distributions.","method":"Electron paramagnetic resonance (EPR) spectroscopy on spin-labeled syntaxin; membrane-reconstituted full-length syntaxin ± Munc18-1","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 — EPR structural analysis with and without Munc18-1, membrane-reconstituted system","pmids":["23561535"],"is_preprint":false},{"year":2014,"finding":"Disease-linked Munc18-1 C180Y mutation renders the protein unstable at 37°C (but functional at permissive temperature), and undergoes K48-linked polyubiquitination leading to proteasomal (not lysosomal) degradation; mutant protein retains t-SNARE chaperone function but cannot support neuroexocytosis, which is rescued at lower temperature.","method":"Temperature-sensitive exocytosis assay in Munc18-null PC12 cells; ubiquitination assay; proteasome/lysosome inhibitor experiments; in vitro stability assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including proteasome inhibition, temperature rescue, and ubiquitination assays","pmids":["25284778"],"is_preprint":false},{"year":2014,"finding":"Munc18-1 rapidly redistributes from synapses during stimulation and reclusters within minutes; reclustering is independent of syntaxin-1 but requires Ca2+ influx and PKC activity; a PKC-insensitive Munc18-1 mutant fails to recluster; synaptic Munc18-1 levels correlate with synaptic strength and releasable vesicle pool size.","method":"FRAP on fluorescently tagged endogenous Munc18-1 knock-in mouse neurons; PKC inhibitors; Ca2+ chelation; PKC phosphorylation site mutant","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — endogenous knock-in FRAP, pharmacological dissection, mutant analysis, functional correlation","pmids":["24590174"],"is_preprint":false},{"year":2014,"finding":"Pro335 in Munc18-1 domain 3a plays a pivotal role balancing syntaxin-1 chaperoning vs. exocytic priming functions; P335A mutation reduces syntaxin-1 binding but enhances exocytosis rescue, while combination with flanking mutations abolishes both functions; the hinged/extended helix conformation controls the balance.","method":"Site-directed mutagenesis of domain 3a residues; rescue of exocytosis and syntaxin-1 expression in Munc18-1/2 double-knockdown PC12 cells; pulldown binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic mutagenesis with dual functional readouts in null-like background","pmids":["25326390"],"is_preprint":false},{"year":2015,"finding":"Heterozygous STXBP1 loss-of-function mutations reduce Munc18-1 protein levels by ~30% and also reduce its binding partner Syntaxin-1 by ~30%, decreasing spontaneous and evoked neurotransmitter release by ~50% in isogenic human ES cell-derived neurons.","method":"Conditional heterozygous/homozygous STXBP1 knockin human ES cells; human neuron differentiation; immunoblot; electrophysiology (spontaneous and evoked release)","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — isogenic human neuron model with electrophysiology and biochemistry, rigorous genetic controls","pmids":["26280581"],"is_preprint":false},{"year":2015,"finding":"The trans-SNARE-regulating function of Munc18-1 (promoting SNARE complex zippering) is essential for both spontaneous and evoked neurotransmitter release in neurons; v-SNARE mutations that selectively impair Munc18-1's ability to promote trans-SNARE zippering strongly inhibit release; and an Ohtahara Syndrome-associated Munc18-1 mutation compromises this trans-SNARE-regulating function.","method":"Reconstituted SNARE zippering assay; cultured neuron electrophysiology with v-SNARE mutants; disease variant analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution plus neuronal electrophysiology linking molecular mechanism to disease","pmids":["26572858"],"is_preprint":false},{"year":2016,"finding":"Extension of helix 12 in Munc18-1 domain 3a is required for vesicle priming but not docking or syntaxin-1 chaperoning; gain-of-function P335A mutation (extended helix) markedly increases priming and secretory amplitude, while disruptive mutations (L348R, Δ324-339) reduce priming; effects are consistent in chromaffin cells and in an in vitro fusion assay.","method":"Expression of Munc18-1 helix-12 mutants in null chromaffin cells; capacitance recordings; electron microscopy; in vitro fusion assay","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — null-background rescue, multiple loss-of-function and gain-of-function mutants, in vitro corroboration","pmids":["27358447"],"is_preprint":false},{"year":2016,"finding":"The Munc18-1 domain 3a hinge-loop controls syntaxin-1A nanodomain assembly and single-molecule dynamics; upon stimulation, wild-type Munc18-1 mobility increases while syntaxin-1A becomes less mobile (confinement); hinge-loop deletion (Δ317-333) blocks both diffusional switches and prolongs vesicle docking, establishing the loop as a conformational switch coupling Munc18-1 to syntaxin-1A SNARE complex assembly during priming.","method":"Single-molecule tracking of Munc18-1 and syntaxin-1A; TIRF microscopy; electron microscopy for docking; BoNT/E control","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — single-molecule live imaging plus electron microscopy, loss-of-function mutant, mechanistic specificity controls","pmids":["27646276"],"is_preprint":false},{"year":2017,"finding":"Munc18-1 is autoinhibited in its synaptobrevin-binding activity via a 'furled conformation' of a loop; D326K mutation disrupting this conformation enhances specific synaptobrevin binding and stimulates Munc18-1 activity in Munc18-1/Munc13-1-dependent reconstitution assays, enables Munc13-1-independent fusion, and produces gain-of-function in C. elegans unc-18 nulls; conversely, L348R inhibits binding and activity.","method":"NMR (specific vs. non-specific synaptobrevin binding); reconstituted membrane fusion assay (with/without Munc13-1); C. elegans rescue experiments with gain/loss-of-function mutants","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — NMR structural data combined with reconstitution and in vivo epistasis in two systems","pmids":["28477408"],"is_preprint":false},{"year":2017,"finding":"Tyrosine phosphorylation of Munc18-1 at Y473 by neuronal Src family kinases abolishes its SNARE-templating activity and prevents vesicle priming (but not docking) in hippocampal null neurons; the mechanism involves occlusion of the synaptobrevin/VAMP2 binding groove and hindrance of domain 3a conformational changes.","method":"Phosphomimetic Y473D mutant; in vitro SNARE complex formation assay; hippocampal munc18-1 null neuron rescue; electrophysiology; high-frequency stimulation rescue","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro assay plus null-background neuronal rescue with electrophysiology, mechanistic interpretation supported by structural reasoning","pmids":["29150433"],"is_preprint":false},{"year":2017,"finding":"Munc18-1/UNC-18 primes vesicle fusion downstream of Munc13-1/UNC-13 by templating SNARE complex assembly; UNC-18 P334A (gain-of-function) partially bypasses UNC-13 requirement, and this bypass is synergistically augmented by tom-1 (tomosyn) null mutation; P335A Munc18-1 shows enhanced SNARE complex formation and SNARE complex binding in vitro.","method":"C. elegans behavioral and electrophysiology assays; mammalian neuron electrophysiology; liposome fusion assay; biochemical SNARE assembly assays","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — epistasis genetics combined with reconstitution and electrophysiology in two systems","pmids":["28821673"],"is_preprint":false},{"year":2018,"finding":"At least five disease-linked Munc18-1 missense mutations cause protein destabilization and aggregation; mutant Munc18-1 aggregates sequester wild-type Munc18-1, depleting functional protein beyond hemizygous levels; chemical chaperones (4-phenylbutyrate, sorbitol, trehalose) reverse these deficits in vitro and in vivo in yeast, C. elegans, and mouse neurons.","method":"S. cerevisiae, C. elegans, and conditional Munc18-1 KO mouse neurons; aggregation assays; western blot; behavioral rescue; chemical chaperone treatment","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple organisms and multiple orthogonal methods, Strong evidence across systems","pmids":["30266908"],"is_preprint":false},{"year":2018,"finding":"STXBP1 disease variants have severely decreased protein stability; heterozygous STXBP1 mutations do not reduce exocytosis when overexpressed on a heterozygous background, indicating haploinsufficiency (not dominant-negative) as the primary cellular mechanism; GABAergic neuron-specific Stxbp1 haploinsufficiency causes cortical hyperexcitability.","method":"Allelic series of seven STXBP1 mutants in null and heterozygous mouse neurons; EEG recordings in four mouse models; c-Fos staining; conditional GABAergic neuron-specific knockout","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants, null and heterozygous backgrounds, in vivo EEG, conditional genetics","pmids":["29538625"],"is_preprint":false},{"year":2019,"finding":"The MUN domain of Munc13-1 stabilizes the Munc18-1/syntaxin-1/VAMP2 template complex by ~2.1 kBT, as measured by single-molecule force spectroscopy; this MUN-bound template complex enhances SNAP-25 binding and full SNARE assembly; mutational disruption of the complex impairs SNARE assembly and neurotransmitter release.","method":"Single-molecule force spectroscopy; mutagenesis of MUN-template interface; SNARE assembly assay; neurotransmitter release assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — single-molecule force spectroscopy with mutagenesis and functional validation","pmids":["31888993"],"is_preprint":false},{"year":2020,"finding":"Stxbp1 haploinsufficiency specifically reduces cortical inhibitory neurotransmission from both parvalbumin-expressing and somatostatin-expressing interneurons via distinct mechanisms, contributing to cortical hyperexcitability and seizures in mice.","method":"Stxbp1+/- mouse; in vivo EEG; whole-cell patch clamp of inhibitory synaptic transmission; conditional interneuron-specific knockouts; behavioral assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — conditional genetics, in vivo electrophysiology, multiple inhibitory neuron subtypes characterized","pmids":["32073399"],"is_preprint":false},{"year":2020,"finding":"A homozygous Munc18-1 L446F mutation causes a gain-of-function in synaptic transmission (2-fold increased evoked release probability) with minor impact on protein stability compared to heterozygous disease mutants, demonstrating that STXBP1 mutations can produce divergent cellular effects (loss vs. gain of function) leading to different clinical features.","method":"Patch clamp recordings in Munc18-1 null mouse neurons expressing L446F; protein stability assays; morphological analysis","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 — null-background electrophysiology with biochemical validation, clear gain-of-function result","pmids":["31855252"],"is_preprint":false},{"year":2020,"finding":"STXBP1 protein variants associated with epilepsy in humanized C. elegans unc-18 null strains show reduced protein levels (20-30% of wild-type) despite normal mRNA levels, indicating that the mutations cause protein instability rather than transcriptional defects.","method":"CRISPR/Cas9 unc-18 null rescue with human STXBP1 variants; behavioral assays; electrophysiology; western blot; RT-PCR","journal":"Epilepsia","confidence":"High","confidence_rationale":"Tier 2 — humanized in vivo model with biochemical, electrophysiological, and behavioral readouts","pmids":["32112430"],"is_preprint":false},{"year":2021,"finding":"Munc18-1 is essential specifically for neuropeptide/dense-core vesicle (DCV) secretion in CNS neurons; MUNC18-2 and MUNC18-3 cannot substitute; heterozygous Munc18-1 reduction impairs DCV exocytosis especially during initial high-frequency stimulation.","method":"Conditional Munc18-1 null neurons; pHluorin/mCherry-tagged NPY and BDNF single-vesicle imaging; action potential train stimulation; rescue with MUNC18-1/2/3","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — conditional null, single-vesicle resolution, isoform-specificity rescue, strong mechanistic conclusion","pmids":["34103363"],"is_preprint":false},{"year":2024,"finding":"STXBP1 physically interacts with the phospholipase A1 enzyme DDHD2 (via pulldown-mass spectrometry); STXBP1 controls DDHD2 targeting to the plasma membrane and the generation of saturated free fatty acids (especially myristic acid C14:0) in the brain during neuronal stimulation and memory acquisition.","method":"Pulldown-mass spectrometry; DDHD2 knockout mice; STXBP1+/- haploinsufficient mice; lipidomics; behavioral memory assays; STXBP1/2 knockout neurosecretory cells","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal pulldown-MS, multiple genetic models, lipidomics, behavioral readouts","pmids":["38316990"],"is_preprint":false}],"current_model":"STXBP1/Munc18-1 is a neural-specific SM (Sec1/Munc18) protein that orchestrates every step of SNARE-dependent exocytosis: it binds the closed conformation of syntaxin-1 to act as a molecular chaperone for syntaxin-1 trafficking from ER to plasma membrane, then undergoes conformational changes in its domain 3a helix 12 to template SNARE complex assembly (syntaxin-1/VAMP2/SNAP-25) cooperatively with Munc13-1, promotes sequential trans-SNARE zippering to drive vesicle priming and membrane fusion, and modulates fusion pore properties; its activity is regulated by PKC-mediated phosphorylation (at Ser306/313) that disrupts syntaxin binding, by Src kinase phosphorylation at Y473 that blocks SNARE templating, by S-nitrosylation of syntaxin-1 Cys145, and by Ca2+-calmodulin–dependent release from presynaptic mGluRs, while disease-causing mutations primarily destabilize the protein leading to haploinsufficiency, impaired inhibitory synaptic transmission, and epileptic encephalopathy."},"narrative":{"teleology":[{"year":1994,"claim":"Identification of STXBP1 as a neural syntaxin-binding protein established that a Sec1-family member directly and specifically engages the t-SNARE syntaxin (but not SNAP-25 or VAMP) at synapses, providing the first molecular handle on SM-protein function in neurotransmitter release.","evidence":"Pulldown assays with syntaxin fusion proteins and brain extracts in two independent laboratories","pmids":["8108429","8134339"],"confidence":"High","gaps":["No information on whether the interaction was direct or via a complex","Binding mode (closed vs. open syntaxin) unknown","Functional consequence for exocytosis not yet tested"]},{"year":1996,"claim":"Demonstration that PKC phosphorylates Munc18-1 at Ser306/Ser313 and that phosphorylation disrupts syntaxin binding revealed the first regulatory switch controlling the Munc18-1/syntaxin interaction, later confirmed in native nerve terminals and chromaffin cells.","evidence":"In vitro kinase assay with site mapping; subsequently validated in synaptosomes and chromaffin cells with phospho-specific antibodies and depolarization paradigms","pmids":["8631738","10651895","12950453"],"confidence":"High","gaps":["In vivo phosphorylation stoichiometry at individual sites not quantified","Downstream effect on vesicle pool sizes not directly measured"]},{"year":1999,"claim":"Showing that Munc18-1 prevents syntaxin-1A–induced Golgi disruption and is required for syntaxin trafficking to the plasma membrane established a chaperone function distinct from a direct role in fusion, later confirmed in C. elegans neurons.","evidence":"Syntaxin-1A overexpression ± rbSec1 in non-neurosecretory cells; C. elegans unc-18 mutant ER-retention assays","pmids":["10341206","18596236"],"confidence":"High","gaps":["Whether chaperoning requires a specific closed-conformation lock or simply stoichiometric binding was initially unclear","Chaperone function not reconstituted with purified components"]},{"year":2004,"claim":"FRET imaging in living cells demonstrated that Munc18-1 and syntaxin-1A first interact at the Golgi and then at the plasma membrane, and that PKC (Ser313) and Cdk5 (Thr574) phosphomimetic mutations reduce the interaction, linking phospho-regulation to the trafficking and exocytic pathways in real time.","evidence":"FRET/FLIM between CFP-Munc18-1 and YFP-syntaxin-1A in HEK293 and chromaffin cells with phosphomimetic mutants","pmids":["15489225"],"confidence":"High","gaps":["Cdk5-mediated phosphorylation at Thr574 not validated with phospho-specific antibodies in neurons","Whether Golgi interaction is required for subsequent plasma membrane function not resolved"]},{"year":2007,"claim":"Discovery that Munc18-1 binds syntaxin in two modes—closed-conformation binding (promoting docking) and SNARE-complex binding via the syntaxin N-terminus (promoting priming/fusion)—and that disrupting the N-terminal interaction blocks neurotransmitter release at the calyx of Held, established a dual-mode framework for SM-protein function.","evidence":"Co-IP with truncated syntaxins; electrophysiology with competing N-terminal peptide at calyx of Held; Munc18-1 variant rescue in null chromaffin cells with EM and capacitance","pmids":["17989281","17687045"],"confidence":"High","gaps":["Structural basis for how the two binding modes interconvert was not resolved","Whether additional interaction surfaces beyond the N-peptide contribute was unknown"]},{"year":2010,"claim":"Biophysical and reconstitution studies showed Munc18-1 directly binds synaptobrevin/VAMP2 and stimulates SNARE-mediated membrane fusion through its central cavity, even without the syntaxin Habc domain, positioning Munc18-1 as a direct fusion catalyst rather than merely a syntaxin clamp.","evidence":"NMR, ITC, and analytical ultracentrifugation for VAMP2 binding; reconstituted liposome fusion with domain-deletion mutants; single-vesicle FRET and EPR","pmids":["20102228","20603329","20300453"],"confidence":"High","gaps":["Affinity for VAMP2 was low-micromolar—relevance at synaptic concentrations debated","How Munc18-1 coordinates simultaneous binding to syntaxin and synaptobrevin structurally unresolved"]},{"year":2011,"claim":"Reconstitution showed Munc18-1 acts as a stage-specific off/on switch: it inhibits fusion when bound to closed syntaxin, then stimulates fusion specifically upon VAMP2 and SNAP-25 addition, while also modulating fusion pore geometry through distinct interaction surfaces.","evidence":"Sequential t-SNARE/v-SNARE liposome fusion assay; patch-clamp capacitance and STED microscopy with Munc18-1 mutants in lactotrophs","pmids":["21730064","21677188","21900493"],"confidence":"High","gaps":["How the inhibitory-to-stimulatory transition is triggered at native synapses was not clear","Whether fusion pore effects are direct or secondary to SNARE zippering kinetics not resolved"]},{"year":2013,"claim":"Domain 3a of Munc18-1—specifically its hinge-loop (residues 317–333) and helix 12—was identified as essential for vesicle priming and SNARE complex binding but dispensable for syntaxin chaperoning, cleanly separating the two major functions of the protein.","evidence":"Domain 3a insertion and deletion mutants rescuing Munc18-1 null/knockdown PC12 cells; exocytosis, EM docking, and SNARE binding assays; EPR of syntaxin conformational exchange","pmids":["23525015","23761923","23561535"],"confidence":"High","gaps":["Atomic-resolution structure of the extended helix 12 conformation not yet available","Whether domain 3a conformational change is triggered by a specific signal (e.g., Munc13) was unknown"]},{"year":2015,"claim":"Heterozygous STXBP1 mutations reduce Munc18-1 and syntaxin-1 protein levels by ~30% each and decrease neurotransmitter release by ~50% in isogenic human neurons, establishing haploinsufficiency as the primary cellular disease mechanism for STXBP1 encephalopathy.","evidence":"Isogenic heterozygous/homozygous human ES cell-derived neurons; electrophysiology and immunoblot","pmids":["26280581"],"confidence":"High","gaps":["Which neuron subtypes are most vulnerable to haploinsufficiency was not determined in the human model","Whether protein aggregation contributes to haploinsufficiency in patient neurons was not tested"]},{"year":2017,"claim":"Structural and functional work revealed that Munc18-1 templates SNARE complex assembly via an autoinhibited domain 3a loop that, when unfurled (e.g., D326K), specifically binds synaptobrevin and can bypass the Munc13 requirement; Src kinase phosphorylation at Y473 blocks this templating without affecting docking, establishing two orthogonal regulatory inputs on the same priming step.","evidence":"NMR of specific vs. non-specific VAMP2 binding; reconstituted fusion ± Munc13; C. elegans rescue; phosphomimetic Y473D in null hippocampal neurons with electrophysiology","pmids":["28477408","29150433","28821673"],"confidence":"High","gaps":["How Munc13 physically unfurls the domain 3a loop was not structurally resolved","Whether Y473 phosphorylation occurs under physiological stimulation patterns in vivo not shown"]},{"year":2018,"claim":"Multiple disease-associated Munc18-1 mutations were shown to cause protein aggregation that co-aggregates wild-type protein (dominant-negative at the protein level though functionally haploinsufficient), and GABAergic neuron-specific Stxbp1 haploinsufficiency was demonstrated to cause cortical hyperexcitability, pinpointing inhibitory neurons as the vulnerable population.","evidence":"Aggregation assays in yeast, C. elegans, and mouse neurons with chemical chaperone rescue; conditional GABAergic Stxbp1 knockout with EEG and c-Fos","pmids":["30266908","29538625"],"confidence":"High","gaps":["Whether chemical chaperones are effective in patient-derived neurons not tested","Relative contributions of parvalbumin vs. somatostatin interneurons not dissected in these studies"]},{"year":2019,"claim":"Single-molecule force spectroscopy quantified Munc13-1 MUN domain stabilization of the Munc18-1/syntaxin-1/VAMP2 template complex by ~2.1 kBT, showing how Munc13 cooperatively promotes full SNARE assembly through this intermediate.","evidence":"Single-molecule force spectroscopy; mutagenesis of MUN-template interface; SNARE assembly and neurotransmitter release assays","pmids":["31888993"],"confidence":"High","gaps":["Whether additional factors (e.g., synaptotagmin, complexin) modulate template stability not measured","In vivo relevance of the ~2.1 kBT stabilization energy not confirmed"]},{"year":2020,"claim":"A homozygous L446F mutation demonstrated gain-of-function (2-fold increased release probability), showing that not all STXBP1 mutations cause loss of function and that the clinical spectrum includes divergent cellular mechanisms; independently, humanized C. elegans confirmed that most epilepsy-associated variants cause protein instability rather than transcriptional defects.","evidence":"Null-background electrophysiology with L446F; humanized C. elegans STXBP1 variant panel with western blot and RT-PCR","pmids":["31855252","32073399","32112430"],"confidence":"High","gaps":["Structural basis for L446F gain-of-function not determined","Whether gain-of-function and loss-of-function variants require different therapeutic strategies not addressed"]},{"year":2021,"claim":"Munc18-1 was shown to be uniquely required for dense-core vesicle (neuropeptide) exocytosis in CNS neurons, with no substitution by Munc18-2 or Munc18-3, extending the protein's essential role beyond synaptic vesicle fusion.","evidence":"Conditional Munc18-1 null neurons; single-vesicle pHluorin imaging of NPY and BDNF release; isoform rescue","pmids":["34103363"],"confidence":"High","gaps":["Whether DCV secretion deficits contribute to STXBP1 encephalopathy phenotypes not tested","Mechanism for isoform specificity not resolved"]},{"year":2024,"claim":"Discovery of a physical interaction between STXBP1 and the phospholipase DDHD2 revealed an unexpected role in controlling plasma membrane lipid remodeling—specifically saturated free fatty acid generation during neuronal stimulation and memory acquisition—expanding STXBP1 function beyond SNARE-mediated fusion.","evidence":"Pulldown-mass spectrometry; DDHD2 KO and STXBP1+/- mice; lipidomics; behavioral memory assays","pmids":["38316990"],"confidence":"High","gaps":["Whether DDHD2 interaction is direct or within a larger complex not confirmed by recombinant reconstitution","How lipid remodeling feeds back on SNARE-dependent exocytosis unknown","Relevance to STXBP1 encephalopathy not established"]},{"year":null,"claim":"Key unresolved questions include the atomic-resolution structure of the fully assembled Munc18-1/Munc13-1/SNARE template complex, the precise mechanism by which Munc13 unfurls the domain 3a autoinhibitory loop, how STXBP1 gain-of-function mutations produce distinct clinical phenotypes from haploinsufficiency variants, and whether the DDHD2-dependent lipid remodeling pathway contributes to disease.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of the Munc18-1/Munc13-MUN/SNARE template intermediate","Therapeutic potential of chemical chaperones not validated in patient-derived neurons or clinical trials","Gain-of-function vs. loss-of-function variant-specific therapeutic strategies undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,9,15,32]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[7,13,20]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[18,19,24,30,37]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[16,17]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,6,10,31,42]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[6,7]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,26]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[10,21,41]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,9,28,29,38]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[10,16,19,21,41]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,14,33]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[7,13,22]}],"complexes":["Munc18-1/syntaxin-1 binary complex","Munc18-1/SNARE core complex","Munc18-1/Munc13-1/SNARE template complex"],"partners":["STX1A","VAMP2","SNAP25","UNC13A","GRM4","SYTL4","DDHD2","CDK5"],"other_free_text":[]},"mechanistic_narrative":"STXBP1 (Munc18-1) is a neuron-enriched Sec1/Munc18-family protein that orchestrates every major step of SNARE-dependent synaptic vesicle exocytosis—from syntaxin-1 chaperoning and trafficking, through vesicle docking and priming, to membrane fusion and fusion-pore regulation. It binds the closed conformation of syntaxin-1 via its central cavity to chaperone syntaxin-1 from the ER to the plasma membrane, then undergoes a conformational transition in its domain 3a hinge-loop/helix 12 that templates SNARE complex assembly cooperatively with Munc13-1, directly engaging synaptobrevin/VAMP2 at the C-terminus of its SNARE motif and promoting sequential trans-SNARE zippering to drive fusion [PMID:8108429, PMID:18596236, PMID:28477408, PMID:31888993, PMID:27358447]. Its activity is dynamically regulated by PKC phosphorylation at Ser306/Ser313 (disrupting syntaxin binding and controlling synaptic reclustering), Src-family kinase phosphorylation at Y473 (blocking SNARE templating), S-nitrosylation of syntaxin-1 Cys145, and Ca²⁺-calmodulin–dependent release from presynaptic mGluR4 [PMID:8631738, PMID:24590174, PMID:29150433, PMID:18452404, PMID:19822743]. Heterozygous loss-of-function mutations in STXBP1 cause protein destabilization and haploinsufficiency that preferentially impairs inhibitory synaptic transmission, leading to epileptic encephalopathy (including Ohtahara syndrome), while rare mutations such as L446F produce gain-of-function effects on release probability [PMID:29538625, PMID:32073399, PMID:31855252, PMID:26572858]."},"prefetch_data":{"uniprot":{"accession":"P61764","full_name":"Syntaxin-binding protein 1","aliases":["MUNC18-1","N-Sec1","Protein unc-18 homolog 1","Unc18-1","Protein unc-18 homolog A","Unc-18A","p67"],"length_aa":594,"mass_kda":67.6,"function":"Participates in the regulation of synaptic vesicle docking and fusion through interaction with GTP-binding proteins (By similarity). Essential for neurotransmission and binds syntaxin, a component of the synaptic vesicle fusion machinery probably in a 1:1 ratio. Can interact with syntaxins 1, 2, and 3 but not syntaxin 4. Involved in the release of neurotransmitters from neurons through interacting with SNARE complex component STX1A and mediating the assembly of the SNARE complex at synaptic membranes (By similarity). May play a role in determining the specificity of intracellular fusion reactions","subcellular_location":"Cytoplasm, cytosol; Membrane","url":"https://www.uniprot.org/uniprotkb/P61764/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/STXBP1","classification":"Not Classified","n_dependent_lines":31,"n_total_lines":1208,"dependency_fraction":0.02566225165562914},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"STX2","stoichiometry":10.0},{"gene":"HSPH1","stoichiometry":0.2},{"gene":"STX3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/STXBP1","total_profiled":1310},"omim":[{"mim_id":"620465","title":"EPILEPSY, EARLY-ONSET, 3, WITH OR WITHOUT DEVELOPMENTAL DELAY; EPEO3","url":"https://www.omim.org/entry/620465"},{"mim_id":"615744","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 19; DEE19","url":"https://www.omim.org/entry/615744"},{"mim_id":"613477","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 5; DEE5","url":"https://www.omim.org/entry/613477"},{"mim_id":"612164","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 4; DEE4","url":"https://www.omim.org/entry/612164"},{"mim_id":"605836","title":"UNC13 HOMOLOG B; UNC13B","url":"https://www.omim.org/entry/605836"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Nucleoplasm","reliability":"Uncertain"},{"location":"Nucleoli","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":252.0},{"tissue":"retina","ntpm":188.2}],"url":"https://www.proteinatlas.org/search/STXBP1"},"hgnc":{"alias_symbol":["hUNC18","MUNC18-1","UNC18","rbSec1","nSec1"],"prev_symbol":[]},"alphafold":{"accession":"P61764","domains":[{"cath_id":"3.40.50.2060","chopping":"4-136","consensus_level":"high","plddt":93.9156,"start":4,"end":136},{"cath_id":"3.40.50.1910","chopping":"138-238_480-503_528-588","consensus_level":"high","plddt":93.0753,"start":138,"end":588},{"cath_id":"3.90.830.10","chopping":"248-358","consensus_level":"medium","plddt":87.6744,"start":248,"end":358}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P61764","model_url":"https://alphafold.ebi.ac.uk/files/AF-P61764-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P61764-F1-predicted_aligned_error_v6.png","plddt_mean":90.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=STXBP1","jax_strain_url":"https://www.jax.org/strain/search?query=STXBP1"},"sequence":{"accession":"P61764","fasta_url":"https://rest.uniprot.org/uniprotkb/P61764.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P61764/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P61764"}},"corpus_meta":[{"pmid":"8108429","id":"PMC_8108429","title":"n-Sec1: 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the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — original identification replicated independently in two labs the same year (PMID:8108429 and PMID:8134339) using reciprocal biochemical approaches\",\n      \"pmids\": [\"8108429\", \"8134339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"rbSec1 (rat brain STXBP1 homolog) specifically interacts with syntaxin but not with SNAP-25 or synaptobrevin/VAMP in brain detergent extracts, establishing that Sec1-family function in membrane fusion involves direct interaction with a t-SNARE.\",\n      \"method\": \"GST pulldown from Triton X-100 brain extract; Northern blot; immunoblot\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean biochemical specificity data, replicated same year by Pevsner et al.\",\n      \"pmids\": [\"8134339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Munc18-1 is phosphorylated by conventional PKC (Ca2+- and phospholipid-dependent) at Ser306 and Ser313 in a cell-free system; PKC-catalyzed phosphorylation inhibits Munc18-1 interaction with syntaxin, and the Munc18-1/syntaxin complex is not a PKC substrate, revealing a regulatory switch for synaptic vesicle docking/fusion.\",\n      \"method\": \"In vitro kinase assay with recombinant Munc18-1 and purified PKC; phosphorylation-site mapping; pulldown binding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis/site mapping, rigorous controls\",\n      \"pmids\": [\"8631738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Endogenous presynaptic PKC isoforms phosphorylate Munc18-1 in nerve terminals in a Ca2+-dependent manner following depolarization; PKC activation inhibits synaptic Munc18-1 interaction with syntaxin-1A by ~50%, and constitutive phosphatase activity (PP1/PP2B) keeps basal phosphorylation low, defining a dynamic regulatory mechanism for neurotransmitter release.\",\n      \"method\": \"Phosphorylation assays in isolated rat brain nerve terminals with phorbol esters, PKC inhibitors, phosphatase inhibitors, and K+-evoked depolarization; immunoprecipitation of Munc18-1/syntaxin complexes\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in native synaptosomal preparations, Strong evidence\",\n      \"pmids\": [\"10651895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Munc18-1 Ser313 is phosphorylated in intact chromaffin cells (by histamine/Ca2+) and in synaptosomes (by depolarization/mGluR activation) in a PKC-dependent manner, with PP1 and PP2B as the dephosphorylating phosphatases, linking this phosphorylation to regulation of transmitter release kinetics.\",\n      \"method\": \"Phospho-Ser313-specific antisera; permeabilized chromaffin cells; intact synaptosomes with pharmacological stimulation; kinase/phosphatase inhibitor profiling\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — site-specific phospho-antibody combined with multiple stimulation paradigms and inhibitor profiling\",\n      \"pmids\": [\"12950453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Munc18-1 co-purifies and co-localizes with neuronal cytoskeletal proteins (neurofilaments, microtubules) and with Cdk5; reciprocal immunoaffinity chromatography confirmed strong protein–protein interaction between Munc18-1, cytoskeletal elements, and Cdk5, suggesting a role in cytoskeletal dynamics.\",\n      \"method\": \"Munc18-1 immunoaffinity chromatography; immunofluorescence in PC12 cells; immunohistochemistry and immuno-electron microscopy in rat olfactory bulb\",\n      \"journal\": \"Neurochemistry international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-purification and localization, single lab, no functional rescue\",\n      \"pmids\": [\"12963086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Munc18-1 and syntaxin-1A interact in living cells, as demonstrated by FRET; the interaction occurs first at the Golgi and then at the plasma membrane, syntaxin-1A trafficking to the plasma membrane depends on Munc18-1, and phosphomimetic mutations at Ser313 (PKC site) and Thr574 (Cdk5 site) reduce Munc18-1/syntaxin-1A interaction.\",\n      \"method\": \"FRET between CFP-Munc18-1 and citrine-YFP-syntaxin-1A in HEK293 and chromaffin cells; fluorescence lifetime imaging; syntaxin open/closed conformation mutants; phosphomimetic Munc18-1 mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — FRET in living cells with multiple mutants, two cell types, orthogonal measurement approaches\",\n      \"pmids\": [\"15489225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"rbSec1 (STXBP1) prevents syntaxin-1A-induced blockade of Golgi-to-plasma-membrane traffic and Golgi disassembly in neurosecretion-incompetent cells, demonstrating that Munc18-1 interaction with syntaxin-1A is required not only for plasma membrane exocytosis but also for proper intracellular trafficking of syntaxin-1A.\",\n      \"method\": \"Transfection of syntaxin-1A ± rbSec1 in non-neurosecretory cells; immunofluorescence for Golgi markers; protein transport assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined cellular phenotype with rescue by rbSec1 expression, single lab\",\n      \"pmids\": [\"10341206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The linker domain of Slp4-a/granuphilin interacts directly with Munc18-1 and promotes docking of dense-core vesicles to the plasma membrane; despite increased docking, exocytosis is inhibited, identifying a Slp4-a/Munc18-1/syntaxin-1a ternary docking complex.\",\n      \"method\": \"Deletion/chimeric analysis; co-immunoprecipitation; TIRF-based exocytosis assays in PC12 cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping plus functional exocytosis readout, single lab\",\n      \"pmids\": [\"16481396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Munc18-1 interacts with neuronal SNAREs in two distinct modes: binding to isolated syntaxin-1 in a closed conformation, and binding to assembled SNARE complexes. Both modes involve the same low-affinity interaction with the extreme syntaxin-1 N-terminus, which links the two modes; disrupting the N-terminal syntaxin/Munc18 interaction with a competing peptide blocks neurotransmitter release at the calyx of Held synapse.\",\n      \"method\": \"Transfected cell in vitro assay; electrophysiology at calyx of Held (N-terminal peptide injection); co-immunoprecipitation; truncated syntaxin constructs\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including reconstitution, electrophysiology, and mutagenesis, strong evidence\",\n      \"pmids\": [\"17989281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Binding of Munc18-1 to closed syntaxin-1 stimulates vesicle docking, while a distinct Munc18-1 interaction mode regulates the subsequent vesicle priming step in chromaffin cells; Munc18-1 null chromaffin cells show abolished vesicle docking and reduced syntaxin levels that are restored by Munc18-1 variants.\",\n      \"method\": \"Expression of Munc18 variants in Munc18-1 null chromaffin cells; electron microscopy for vesicle docking; capacitance recordings for exocytosis; syntaxin-1 immunoblot\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — null background rescue with structure-function variants, multiple readouts, replicated concept\",\n      \"pmids\": [\"17687045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Rab3a promotes secretory vesicle docking in chromaffin cells in a manner that requires Munc18-1; GTP- or GDP-locked Rab3a mutants fail to support docking, and wild-type Rab3a cannot promote docking in Munc18-1 null cells, placing Rab3a upstream of Munc18-1 in the docking cascade.\",\n      \"method\": \"Expression of Rab3a conformation-locked mutants in wild-type and munc18-1 null chromaffin cells; electron microscopy vesicle distribution analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with null background, morphological readout, single lab\",\n      \"pmids\": [\"17637832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"S-nitrosylation of syntaxin 1a at Cys145 disrupts binding of Munc18-1 to the closed conformation of syntaxin 1a in vitro without affecting SNARE complex formation or Munc18-1/SNARE complex binding; nitrosomimetic Cys145 mutants alter Munc18-1 localization and exocytosis kinetics in cells.\",\n      \"method\": \"In vitro NO treatment; site-directed mutagenesis (C145S, nitrosomimetic mutants); Munc18-1 binding assays; live-cell imaging; carbon fiber amperometry\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro mechanism with mutagenesis plus functional cell assays, multiple methods\",\n      \"pmids\": [\"18452404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"C. elegans UNC-18 (STXBP1 ortholog) acts as a molecular chaperone for syntaxin-1 (UNC-64) in neurons, promoting its anterograde ER-to-plasma-membrane transport; this chaperone function requires both closed-syntaxin binding and N-terminal syntaxin binding modes, while N-terminal binding is especially important for locomotion behavior.\",\n      \"method\": \"unc-18 mutant analysis; colocalization with ER markers; carbohydrate modification assays for ER retention; double mutants disrupting syntaxin binding modes; behavioral assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis in C. elegans with multiple orthogonal methods, strong mechanistic dissection\",\n      \"pmids\": [\"18596236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Presynaptic metabotropic glutamate receptor 4 (mGluR4) binds Munc18-1 at resting Ca2+ levels and releases it upon Ca2+-calmodulin activation; sequestration of Munc18-1 by mGluR4 suppresses basal synaptic vesicle release, and release of Munc18-1 from mGluR4 mediates paired-pulse facilitation.\",\n      \"method\": \"Co-immunoprecipitation; Ca2+-binding assay (EC50 determination); permeabilized PC12 cell secretion assay; electrophysiology (paired-pulse facilitation); mGluR4 domain peptide experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including electrophysiology, biochemistry, and secretion assays\",\n      \"pmids\": [\"19822743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Munc18-1 binds directly to synaptobrevin (VAMP2) and to the SNARE four-helix bundle with low-micromolar affinity through the same cavity that binds syntaxin-1; the Munc18-1 binding site on synaptobrevin is at the C-terminus of its SNARE motif, placing Munc18-1 at the site of membrane fusion.\",\n      \"method\": \"NMR; isothermal titration calorimetry; fluorescence anisotropy; analytical ultracentrifugation — multiple biophysical approaches\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple independent biophysical methods demonstrating direct binding, rigorous quantitative analysis\",\n      \"pmids\": [\"20102228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The SNARE four-helix bundle and the syntaxin N-peptide constitute a minimal complement for Munc18-1 activation of membrane fusion; the syntaxin Habc domain is dispensable for Munc18-1 stimulation of fusion, and the central cavity of Munc18-1 is required for fusion stimulation.\",\n      \"method\": \"Reconstituted membrane fusion assay; Munc18-1 and syntaxin domain deletion mutants; liposome fusion\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro fusion assay with systematic domain deletions\",\n      \"pmids\": [\"20603329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Munc18-1 stimulates neuronal SNARE-mediated membrane fusion via its interaction with the SNARE core even when both the Habc domain and N-peptide of syntaxin are absent, as shown by single-vesicle FRET fusion assay and EPR analysis of SNARE core/Munc18 interaction.\",\n      \"method\": \"Single-molecule FRET vesicle fusion assay; electron paramagnetic resonance (EPR)\",\n      \"journal\": \"ACS chemical neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with EPR structural validation\",\n      \"pmids\": [\"20300453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Munc18-1 modulates fusion pore properties via distinct interactions: the R39C mutation (disrupting syntaxin-1 binding) and P242S (disrupting Mint interaction) stabilize narrow fusion pores and increase fusion event amplitude; wild-type Munc18-1 abrogates synaptobrevin2/syntaxin-1 binary trans-complex formation, providing a proofreading function that favors vesicle tethering to preformed syntaxin-SNAP-25 binary cis-complexes.\",\n      \"method\": \"Patch-clamp capacitance recordings; STED microscopy; single-molecule atomic force microscopy; transfection of Munc18-1 mutants in lactotrophs\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple high-resolution methods with defined mutants and functional readouts\",\n      \"pmids\": [\"21677188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Munc18-1 inhibition of membrane fusion requires syntaxin-1 in a closed conformation; concurrent incubation with VAMP2 liposomes and SNAP-25 releases the inhibition and stimulates fusion specifically for VAMP2 (not VAMP8), requiring N-terminal syntaxin binding for robust stimulation, demonstrating Munc18-1 as a stage-specific off/on switch.\",\n      \"method\": \"Reconstituted sequential t-SNARE/v-SNARE assembly assay; liposome lipid mixing assay; temperature-controlled incubations; SNARE and Munc18-1 mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — fully reconstituted fusion assay with molecular specificity controls\",\n      \"pmids\": [\"21730064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Munc18-1 dual roles (chaperone of syntaxin-1A vs. SNARE complex activation) rely on distinct binding modes of its central cavity; a novel cavity mutant shows reduced syntaxin-1A binding and impaired chaperone function while retaining SNARE complex binding and ability to stimulate liposome fusion and secretion in neuroendocrine cells.\",\n      \"method\": \"Site-directed mutagenesis; co-immunoprecipitation; liposome fusion assay; secretion assay in neuroendocrine cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution plus cell-based rescue with structure-function mutants\",\n      \"pmids\": [\"21900493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Vesicle docking by synaptotagmin-1 is a prerequisite for Munc18-1 to accelerate trans-SNARE (SNAREpin) assembly and membrane fusion in a reconstituted giant unilamellar vesicle system; Munc18-1 was positioned as central to a sequential cascade: docking → priming → fusion.\",\n      \"method\": \"Reconstituted giant unilamellar vesicle docking/fusion assay with synaptotagmin-1, Munc18-1, complexin II, and Ca2+\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — fully reconstituted system with sequential epistasis\",\n      \"pmids\": [\"22810233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Domain 3a of Munc18-1 plays a crucial role in vesicle priming (downstream of docking) independently of its syntaxin-1 chaperoning activity; insertion mutations in domain 3a abolish secretion rescue while fully restoring syntaxin-1 plasma membrane expression and vesicle docking, and these mutants show impaired binding to the assembled SNARE complex.\",\n      \"method\": \"Munc18-1 null/knockdown PC12 cell rescue with domain 3a insertion mutants; exocytosis assay; electron microscopy for vesicle docking; SNARE complex binding assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — null-background rescue with domain-specific mutants, multiple functional readouts\",\n      \"pmids\": [\"23525015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The Munc18-1 domain 3a loop (residues 317-333) is essential for neuroexocytosis but dispensable for syntaxin-1A chaperoning and plasma membrane delivery; deletion of this loop fully rescues syntaxin-1A transport but not secretory granule fusion, and reduces SNARE complex binding at the cell surface.\",\n      \"method\": \"Munc18-1 deletion mutant (Δ317-333) expressed in DKD-PC12 cells; exocytosis assay; immunofluorescence; in vitro binding\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean domain separation of two functions, null-like background, replicated by same group and others\",\n      \"pmids\": [\"23761923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Munc18-1 allosterically controls syntaxin-1a conformational exchange between closed and open states; EPR shows that Munc18-1 binding shifts syntaxin H3 toward the ordered, folded state, suppresses the minor open population, and narrows H3-Habc distance distributions.\",\n      \"method\": \"Electron paramagnetic resonance (EPR) spectroscopy on spin-labeled syntaxin; membrane-reconstituted full-length syntaxin ± Munc18-1\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — EPR structural analysis with and without Munc18-1, membrane-reconstituted system\",\n      \"pmids\": [\"23561535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Disease-linked Munc18-1 C180Y mutation renders the protein unstable at 37°C (but functional at permissive temperature), and undergoes K48-linked polyubiquitination leading to proteasomal (not lysosomal) degradation; mutant protein retains t-SNARE chaperone function but cannot support neuroexocytosis, which is rescued at lower temperature.\",\n      \"method\": \"Temperature-sensitive exocytosis assay in Munc18-null PC12 cells; ubiquitination assay; proteasome/lysosome inhibitor experiments; in vitro stability assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including proteasome inhibition, temperature rescue, and ubiquitination assays\",\n      \"pmids\": [\"25284778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Munc18-1 rapidly redistributes from synapses during stimulation and reclusters within minutes; reclustering is independent of syntaxin-1 but requires Ca2+ influx and PKC activity; a PKC-insensitive Munc18-1 mutant fails to recluster; synaptic Munc18-1 levels correlate with synaptic strength and releasable vesicle pool size.\",\n      \"method\": \"FRAP on fluorescently tagged endogenous Munc18-1 knock-in mouse neurons; PKC inhibitors; Ca2+ chelation; PKC phosphorylation site mutant\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — endogenous knock-in FRAP, pharmacological dissection, mutant analysis, functional correlation\",\n      \"pmids\": [\"24590174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Pro335 in Munc18-1 domain 3a plays a pivotal role balancing syntaxin-1 chaperoning vs. exocytic priming functions; P335A mutation reduces syntaxin-1 binding but enhances exocytosis rescue, while combination with flanking mutations abolishes both functions; the hinged/extended helix conformation controls the balance.\",\n      \"method\": \"Site-directed mutagenesis of domain 3a residues; rescue of exocytosis and syntaxin-1 expression in Munc18-1/2 double-knockdown PC12 cells; pulldown binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutagenesis with dual functional readouts in null-like background\",\n      \"pmids\": [\"25326390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Heterozygous STXBP1 loss-of-function mutations reduce Munc18-1 protein levels by ~30% and also reduce its binding partner Syntaxin-1 by ~30%, decreasing spontaneous and evoked neurotransmitter release by ~50% in isogenic human ES cell-derived neurons.\",\n      \"method\": \"Conditional heterozygous/homozygous STXBP1 knockin human ES cells; human neuron differentiation; immunoblot; electrophysiology (spontaneous and evoked release)\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — isogenic human neuron model with electrophysiology and biochemistry, rigorous genetic controls\",\n      \"pmids\": [\"26280581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The trans-SNARE-regulating function of Munc18-1 (promoting SNARE complex zippering) is essential for both spontaneous and evoked neurotransmitter release in neurons; v-SNARE mutations that selectively impair Munc18-1's ability to promote trans-SNARE zippering strongly inhibit release; and an Ohtahara Syndrome-associated Munc18-1 mutation compromises this trans-SNARE-regulating function.\",\n      \"method\": \"Reconstituted SNARE zippering assay; cultured neuron electrophysiology with v-SNARE mutants; disease variant analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution plus neuronal electrophysiology linking molecular mechanism to disease\",\n      \"pmids\": [\"26572858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Extension of helix 12 in Munc18-1 domain 3a is required for vesicle priming but not docking or syntaxin-1 chaperoning; gain-of-function P335A mutation (extended helix) markedly increases priming and secretory amplitude, while disruptive mutations (L348R, Δ324-339) reduce priming; effects are consistent in chromaffin cells and in an in vitro fusion assay.\",\n      \"method\": \"Expression of Munc18-1 helix-12 mutants in null chromaffin cells; capacitance recordings; electron microscopy; in vitro fusion assay\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — null-background rescue, multiple loss-of-function and gain-of-function mutants, in vitro corroboration\",\n      \"pmids\": [\"27358447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The Munc18-1 domain 3a hinge-loop controls syntaxin-1A nanodomain assembly and single-molecule dynamics; upon stimulation, wild-type Munc18-1 mobility increases while syntaxin-1A becomes less mobile (confinement); hinge-loop deletion (Δ317-333) blocks both diffusional switches and prolongs vesicle docking, establishing the loop as a conformational switch coupling Munc18-1 to syntaxin-1A SNARE complex assembly during priming.\",\n      \"method\": \"Single-molecule tracking of Munc18-1 and syntaxin-1A; TIRF microscopy; electron microscopy for docking; BoNT/E control\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — single-molecule live imaging plus electron microscopy, loss-of-function mutant, mechanistic specificity controls\",\n      \"pmids\": [\"27646276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Munc18-1 is autoinhibited in its synaptobrevin-binding activity via a 'furled conformation' of a loop; D326K mutation disrupting this conformation enhances specific synaptobrevin binding and stimulates Munc18-1 activity in Munc18-1/Munc13-1-dependent reconstitution assays, enables Munc13-1-independent fusion, and produces gain-of-function in C. elegans unc-18 nulls; conversely, L348R inhibits binding and activity.\",\n      \"method\": \"NMR (specific vs. non-specific synaptobrevin binding); reconstituted membrane fusion assay (with/without Munc13-1); C. elegans rescue experiments with gain/loss-of-function mutants\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural data combined with reconstitution and in vivo epistasis in two systems\",\n      \"pmids\": [\"28477408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Tyrosine phosphorylation of Munc18-1 at Y473 by neuronal Src family kinases abolishes its SNARE-templating activity and prevents vesicle priming (but not docking) in hippocampal null neurons; the mechanism involves occlusion of the synaptobrevin/VAMP2 binding groove and hindrance of domain 3a conformational changes.\",\n      \"method\": \"Phosphomimetic Y473D mutant; in vitro SNARE complex formation assay; hippocampal munc18-1 null neuron rescue; electrophysiology; high-frequency stimulation rescue\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro assay plus null-background neuronal rescue with electrophysiology, mechanistic interpretation supported by structural reasoning\",\n      \"pmids\": [\"29150433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Munc18-1/UNC-18 primes vesicle fusion downstream of Munc13-1/UNC-13 by templating SNARE complex assembly; UNC-18 P334A (gain-of-function) partially bypasses UNC-13 requirement, and this bypass is synergistically augmented by tom-1 (tomosyn) null mutation; P335A Munc18-1 shows enhanced SNARE complex formation and SNARE complex binding in vitro.\",\n      \"method\": \"C. elegans behavioral and electrophysiology assays; mammalian neuron electrophysiology; liposome fusion assay; biochemical SNARE assembly assays\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — epistasis genetics combined with reconstitution and electrophysiology in two systems\",\n      \"pmids\": [\"28821673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"At least five disease-linked Munc18-1 missense mutations cause protein destabilization and aggregation; mutant Munc18-1 aggregates sequester wild-type Munc18-1, depleting functional protein beyond hemizygous levels; chemical chaperones (4-phenylbutyrate, sorbitol, trehalose) reverse these deficits in vitro and in vivo in yeast, C. elegans, and mouse neurons.\",\n      \"method\": \"S. cerevisiae, C. elegans, and conditional Munc18-1 KO mouse neurons; aggregation assays; western blot; behavioral rescue; chemical chaperone treatment\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple organisms and multiple orthogonal methods, Strong evidence across systems\",\n      \"pmids\": [\"30266908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"STXBP1 disease variants have severely decreased protein stability; heterozygous STXBP1 mutations do not reduce exocytosis when overexpressed on a heterozygous background, indicating haploinsufficiency (not dominant-negative) as the primary cellular mechanism; GABAergic neuron-specific Stxbp1 haploinsufficiency causes cortical hyperexcitability.\",\n      \"method\": \"Allelic series of seven STXBP1 mutants in null and heterozygous mouse neurons; EEG recordings in four mouse models; c-Fos staining; conditional GABAergic neuron-specific knockout\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants, null and heterozygous backgrounds, in vivo EEG, conditional genetics\",\n      \"pmids\": [\"29538625\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The MUN domain of Munc13-1 stabilizes the Munc18-1/syntaxin-1/VAMP2 template complex by ~2.1 kBT, as measured by single-molecule force spectroscopy; this MUN-bound template complex enhances SNAP-25 binding and full SNARE assembly; mutational disruption of the complex impairs SNARE assembly and neurotransmitter release.\",\n      \"method\": \"Single-molecule force spectroscopy; mutagenesis of MUN-template interface; SNARE assembly assay; neurotransmitter release assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — single-molecule force spectroscopy with mutagenesis and functional validation\",\n      \"pmids\": [\"31888993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Stxbp1 haploinsufficiency specifically reduces cortical inhibitory neurotransmission from both parvalbumin-expressing and somatostatin-expressing interneurons via distinct mechanisms, contributing to cortical hyperexcitability and seizures in mice.\",\n      \"method\": \"Stxbp1+/- mouse; in vivo EEG; whole-cell patch clamp of inhibitory synaptic transmission; conditional interneuron-specific knockouts; behavioral assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional genetics, in vivo electrophysiology, multiple inhibitory neuron subtypes characterized\",\n      \"pmids\": [\"32073399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A homozygous Munc18-1 L446F mutation causes a gain-of-function in synaptic transmission (2-fold increased evoked release probability) with minor impact on protein stability compared to heterozygous disease mutants, demonstrating that STXBP1 mutations can produce divergent cellular effects (loss vs. gain of function) leading to different clinical features.\",\n      \"method\": \"Patch clamp recordings in Munc18-1 null mouse neurons expressing L446F; protein stability assays; morphological analysis\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — null-background electrophysiology with biochemical validation, clear gain-of-function result\",\n      \"pmids\": [\"31855252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"STXBP1 protein variants associated with epilepsy in humanized C. elegans unc-18 null strains show reduced protein levels (20-30% of wild-type) despite normal mRNA levels, indicating that the mutations cause protein instability rather than transcriptional defects.\",\n      \"method\": \"CRISPR/Cas9 unc-18 null rescue with human STXBP1 variants; behavioral assays; electrophysiology; western blot; RT-PCR\",\n      \"journal\": \"Epilepsia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — humanized in vivo model with biochemical, electrophysiological, and behavioral readouts\",\n      \"pmids\": [\"32112430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Munc18-1 is essential specifically for neuropeptide/dense-core vesicle (DCV) secretion in CNS neurons; MUNC18-2 and MUNC18-3 cannot substitute; heterozygous Munc18-1 reduction impairs DCV exocytosis especially during initial high-frequency stimulation.\",\n      \"method\": \"Conditional Munc18-1 null neurons; pHluorin/mCherry-tagged NPY and BDNF single-vesicle imaging; action potential train stimulation; rescue with MUNC18-1/2/3\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional null, single-vesicle resolution, isoform-specificity rescue, strong mechanistic conclusion\",\n      \"pmids\": [\"34103363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"STXBP1 physically interacts with the phospholipase A1 enzyme DDHD2 (via pulldown-mass spectrometry); STXBP1 controls DDHD2 targeting to the plasma membrane and the generation of saturated free fatty acids (especially myristic acid C14:0) in the brain during neuronal stimulation and memory acquisition.\",\n      \"method\": \"Pulldown-mass spectrometry; DDHD2 knockout mice; STXBP1+/- haploinsufficient mice; lipidomics; behavioral memory assays; STXBP1/2 knockout neurosecretory cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal pulldown-MS, multiple genetic models, lipidomics, behavioral readouts\",\n      \"pmids\": [\"38316990\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"STXBP1/Munc18-1 is a neural-specific SM (Sec1/Munc18) protein that orchestrates every step of SNARE-dependent exocytosis: it binds the closed conformation of syntaxin-1 to act as a molecular chaperone for syntaxin-1 trafficking from ER to plasma membrane, then undergoes conformational changes in its domain 3a helix 12 to template SNARE complex assembly (syntaxin-1/VAMP2/SNAP-25) cooperatively with Munc13-1, promotes sequential trans-SNARE zippering to drive vesicle priming and membrane fusion, and modulates fusion pore properties; its activity is regulated by PKC-mediated phosphorylation (at Ser306/313) that disrupts syntaxin binding, by Src kinase phosphorylation at Y473 that blocks SNARE templating, by S-nitrosylation of syntaxin-1 Cys145, and by Ca2+-calmodulin–dependent release from presynaptic mGluRs, while disease-causing mutations primarily destabilize the protein leading to haploinsufficiency, impaired inhibitory synaptic transmission, and epileptic encephalopathy.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"STXBP1 (Munc18-1) is a neuron-enriched Sec1/Munc18-family protein that orchestrates every major step of SNARE-dependent synaptic vesicle exocytosis—from syntaxin-1 chaperoning and trafficking, through vesicle docking and priming, to membrane fusion and fusion-pore regulation. It binds the closed conformation of syntaxin-1 via its central cavity to chaperone syntaxin-1 from the ER to the plasma membrane, then undergoes a conformational transition in its domain 3a hinge-loop/helix 12 that templates SNARE complex assembly cooperatively with Munc13-1, directly engaging synaptobrevin/VAMP2 at the C-terminus of its SNARE motif and promoting sequential trans-SNARE zippering to drive fusion [PMID:8108429, PMID:18596236, PMID:28477408, PMID:31888993, PMID:27358447]. Its activity is dynamically regulated by PKC phosphorylation at Ser306/Ser313 (disrupting syntaxin binding and controlling synaptic reclustering), Src-family kinase phosphorylation at Y473 (blocking SNARE templating), S-nitrosylation of syntaxin-1 Cys145, and Ca²⁺-calmodulin–dependent release from presynaptic mGluR4 [PMID:8631738, PMID:24590174, PMID:29150433, PMID:18452404, PMID:19822743]. Heterozygous loss-of-function mutations in STXBP1 cause protein destabilization and haploinsufficiency that preferentially impairs inhibitory synaptic transmission, leading to epileptic encephalopathy (including Ohtahara syndrome), while rare mutations such as L446F produce gain-of-function effects on release probability [PMID:29538625, PMID:32073399, PMID:31855252, PMID:26572858].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Identification of STXBP1 as a neural syntaxin-binding protein established that a Sec1-family member directly and specifically engages the t-SNARE syntaxin (but not SNAP-25 or VAMP) at synapses, providing the first molecular handle on SM-protein function in neurotransmitter release.\",\n      \"evidence\": \"Pulldown assays with syntaxin fusion proteins and brain extracts in two independent laboratories\",\n      \"pmids\": [\"8108429\", \"8134339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No information on whether the interaction was direct or via a complex\", \"Binding mode (closed vs. open syntaxin) unknown\", \"Functional consequence for exocytosis not yet tested\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstration that PKC phosphorylates Munc18-1 at Ser306/Ser313 and that phosphorylation disrupts syntaxin binding revealed the first regulatory switch controlling the Munc18-1/syntaxin interaction, later confirmed in native nerve terminals and chromaffin cells.\",\n      \"evidence\": \"In vitro kinase assay with site mapping; subsequently validated in synaptosomes and chromaffin cells with phospho-specific antibodies and depolarization paradigms\",\n      \"pmids\": [\"8631738\", \"10651895\", \"12950453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo phosphorylation stoichiometry at individual sites not quantified\", \"Downstream effect on vesicle pool sizes not directly measured\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showing that Munc18-1 prevents syntaxin-1A–induced Golgi disruption and is required for syntaxin trafficking to the plasma membrane established a chaperone function distinct from a direct role in fusion, later confirmed in C. elegans neurons.\",\n      \"evidence\": \"Syntaxin-1A overexpression ± rbSec1 in non-neurosecretory cells; C. elegans unc-18 mutant ER-retention assays\",\n      \"pmids\": [\"10341206\", \"18596236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether chaperoning requires a specific closed-conformation lock or simply stoichiometric binding was initially unclear\", \"Chaperone function not reconstituted with purified components\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"FRET imaging in living cells demonstrated that Munc18-1 and syntaxin-1A first interact at the Golgi and then at the plasma membrane, and that PKC (Ser313) and Cdk5 (Thr574) phosphomimetic mutations reduce the interaction, linking phospho-regulation to the trafficking and exocytic pathways in real time.\",\n      \"evidence\": \"FRET/FLIM between CFP-Munc18-1 and YFP-syntaxin-1A in HEK293 and chromaffin cells with phosphomimetic mutants\",\n      \"pmids\": [\"15489225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cdk5-mediated phosphorylation at Thr574 not validated with phospho-specific antibodies in neurons\", \"Whether Golgi interaction is required for subsequent plasma membrane function not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery that Munc18-1 binds syntaxin in two modes—closed-conformation binding (promoting docking) and SNARE-complex binding via the syntaxin N-terminus (promoting priming/fusion)—and that disrupting the N-terminal interaction blocks neurotransmitter release at the calyx of Held, established a dual-mode framework for SM-protein function.\",\n      \"evidence\": \"Co-IP with truncated syntaxins; electrophysiology with competing N-terminal peptide at calyx of Held; Munc18-1 variant rescue in null chromaffin cells with EM and capacitance\",\n      \"pmids\": [\"17989281\", \"17687045\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how the two binding modes interconvert was not resolved\", \"Whether additional interaction surfaces beyond the N-peptide contribute was unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biophysical and reconstitution studies showed Munc18-1 directly binds synaptobrevin/VAMP2 and stimulates SNARE-mediated membrane fusion through its central cavity, even without the syntaxin Habc domain, positioning Munc18-1 as a direct fusion catalyst rather than merely a syntaxin clamp.\",\n      \"evidence\": \"NMR, ITC, and analytical ultracentrifugation for VAMP2 binding; reconstituted liposome fusion with domain-deletion mutants; single-vesicle FRET and EPR\",\n      \"pmids\": [\"20102228\", \"20603329\", \"20300453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Affinity for VAMP2 was low-micromolar—relevance at synaptic concentrations debated\", \"How Munc18-1 coordinates simultaneous binding to syntaxin and synaptobrevin structurally unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Reconstitution showed Munc18-1 acts as a stage-specific off/on switch: it inhibits fusion when bound to closed syntaxin, then stimulates fusion specifically upon VAMP2 and SNAP-25 addition, while also modulating fusion pore geometry through distinct interaction surfaces.\",\n      \"evidence\": \"Sequential t-SNARE/v-SNARE liposome fusion assay; patch-clamp capacitance and STED microscopy with Munc18-1 mutants in lactotrophs\",\n      \"pmids\": [\"21730064\", \"21677188\", \"21900493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the inhibitory-to-stimulatory transition is triggered at native synapses was not clear\", \"Whether fusion pore effects are direct or secondary to SNARE zippering kinetics not resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Domain 3a of Munc18-1—specifically its hinge-loop (residues 317–333) and helix 12—was identified as essential for vesicle priming and SNARE complex binding but dispensable for syntaxin chaperoning, cleanly separating the two major functions of the protein.\",\n      \"evidence\": \"Domain 3a insertion and deletion mutants rescuing Munc18-1 null/knockdown PC12 cells; exocytosis, EM docking, and SNARE binding assays; EPR of syntaxin conformational exchange\",\n      \"pmids\": [\"23525015\", \"23761923\", \"23561535\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of the extended helix 12 conformation not yet available\", \"Whether domain 3a conformational change is triggered by a specific signal (e.g., Munc13) was unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Heterozygous STXBP1 mutations reduce Munc18-1 and syntaxin-1 protein levels by ~30% each and decrease neurotransmitter release by ~50% in isogenic human neurons, establishing haploinsufficiency as the primary cellular disease mechanism for STXBP1 encephalopathy.\",\n      \"evidence\": \"Isogenic heterozygous/homozygous human ES cell-derived neurons; electrophysiology and immunoblot\",\n      \"pmids\": [\"26280581\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which neuron subtypes are most vulnerable to haploinsufficiency was not determined in the human model\", \"Whether protein aggregation contributes to haploinsufficiency in patient neurons was not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Structural and functional work revealed that Munc18-1 templates SNARE complex assembly via an autoinhibited domain 3a loop that, when unfurled (e.g., D326K), specifically binds synaptobrevin and can bypass the Munc13 requirement; Src kinase phosphorylation at Y473 blocks this templating without affecting docking, establishing two orthogonal regulatory inputs on the same priming step.\",\n      \"evidence\": \"NMR of specific vs. non-specific VAMP2 binding; reconstituted fusion ± Munc13; C. elegans rescue; phosphomimetic Y473D in null hippocampal neurons with electrophysiology\",\n      \"pmids\": [\"28477408\", \"29150433\", \"28821673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Munc13 physically unfurls the domain 3a loop was not structurally resolved\", \"Whether Y473 phosphorylation occurs under physiological stimulation patterns in vivo not shown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Multiple disease-associated Munc18-1 mutations were shown to cause protein aggregation that co-aggregates wild-type protein (dominant-negative at the protein level though functionally haploinsufficient), and GABAergic neuron-specific Stxbp1 haploinsufficiency was demonstrated to cause cortical hyperexcitability, pinpointing inhibitory neurons as the vulnerable population.\",\n      \"evidence\": \"Aggregation assays in yeast, C. elegans, and mouse neurons with chemical chaperone rescue; conditional GABAergic Stxbp1 knockout with EEG and c-Fos\",\n      \"pmids\": [\"30266908\", \"29538625\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether chemical chaperones are effective in patient-derived neurons not tested\", \"Relative contributions of parvalbumin vs. somatostatin interneurons not dissected in these studies\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Single-molecule force spectroscopy quantified Munc13-1 MUN domain stabilization of the Munc18-1/syntaxin-1/VAMP2 template complex by ~2.1 kBT, showing how Munc13 cooperatively promotes full SNARE assembly through this intermediate.\",\n      \"evidence\": \"Single-molecule force spectroscopy; mutagenesis of MUN-template interface; SNARE assembly and neurotransmitter release assays\",\n      \"pmids\": [\"31888993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional factors (e.g., synaptotagmin, complexin) modulate template stability not measured\", \"In vivo relevance of the ~2.1 kBT stabilization energy not confirmed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A homozygous L446F mutation demonstrated gain-of-function (2-fold increased release probability), showing that not all STXBP1 mutations cause loss of function and that the clinical spectrum includes divergent cellular mechanisms; independently, humanized C. elegans confirmed that most epilepsy-associated variants cause protein instability rather than transcriptional defects.\",\n      \"evidence\": \"Null-background electrophysiology with L446F; humanized C. elegans STXBP1 variant panel with western blot and RT-PCR\",\n      \"pmids\": [\"31855252\", \"32073399\", \"32112430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for L446F gain-of-function not determined\", \"Whether gain-of-function and loss-of-function variants require different therapeutic strategies not addressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Munc18-1 was shown to be uniquely required for dense-core vesicle (neuropeptide) exocytosis in CNS neurons, with no substitution by Munc18-2 or Munc18-3, extending the protein's essential role beyond synaptic vesicle fusion.\",\n      \"evidence\": \"Conditional Munc18-1 null neurons; single-vesicle pHluorin imaging of NPY and BDNF release; isoform rescue\",\n      \"pmids\": [\"34103363\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DCV secretion deficits contribute to STXBP1 encephalopathy phenotypes not tested\", \"Mechanism for isoform specificity not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Discovery of a physical interaction between STXBP1 and the phospholipase DDHD2 revealed an unexpected role in controlling plasma membrane lipid remodeling—specifically saturated free fatty acid generation during neuronal stimulation and memory acquisition—expanding STXBP1 function beyond SNARE-mediated fusion.\",\n      \"evidence\": \"Pulldown-mass spectrometry; DDHD2 KO and STXBP1+/- mice; lipidomics; behavioral memory assays\",\n      \"pmids\": [\"38316990\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DDHD2 interaction is direct or within a larger complex not confirmed by recombinant reconstitution\", \"How lipid remodeling feeds back on SNARE-dependent exocytosis unknown\", \"Relevance to STXBP1 encephalopathy not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structure of the fully assembled Munc18-1/Munc13-1/SNARE template complex, the precise mechanism by which Munc13 unfurls the domain 3a autoinhibitory loop, how STXBP1 gain-of-function mutations produce distinct clinical phenotypes from haploinsufficiency variants, and whether the DDHD2-dependent lipid remodeling pathway contributes to disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the Munc18-1/Munc13-MUN/SNARE template intermediate\", \"Therapeutic potential of chemical chaperones not validated in patient-derived neurons or clinical trials\", \"Gain-of-function vs. loss-of-function variant-specific therapeutic strategies undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 9, 15, 32]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [7, 13, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [18, 19, 24, 30, 37]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [16, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 10, 31, 42]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 26]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [10, 21, 41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 9, 28, 29, 38]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [10, 16, 19, 21, 41]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 14, 33]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [7, 13, 22]}\n    ],\n    \"complexes\": [\n      \"Munc18-1/syntaxin-1 binary complex\",\n      \"Munc18-1/SNARE core complex\",\n      \"Munc18-1/Munc13-1/SNARE template complex\"\n    ],\n    \"partners\": [\n      \"STX1A\",\n      \"VAMP2\",\n      \"SNAP25\",\n      \"UNC13A\",\n      \"GRM4\",\n      \"SYTL4\",\n      \"DDHD2\",\n      \"CDK5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}