{"gene":"UNC13B","run_date":"2026-04-28T21:43:01","timeline":{"discoveries":[{"year":1991,"finding":"The UNC-13 protein contains a cysteine-rich C1 domain that binds phorbol esters in a phospholipid- and calcium-dependent manner, and diacylglycerol competitively inhibits phorbol ester binding, identifying UNC-13/Munc13-2 as a DAG-binding protein in the diacylglycerol second-messenger pathway.","method":"Recombinant domain expression in E. coli, radioligand phorbol ester binding assay, competitive inhibition with diacylglycerol","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro biochemical assay with recombinant protein, confirmed by multiple binding studies across labs","pmids":["2062851","1445255","7537738"],"is_preprint":false},{"year":1995,"finding":"Mammalian Munc13-2 (UNC13B) is a brain-expressed peripheral membrane protein enriched in synaptosomes and localized to presynaptic plasma membranes but absent from synaptic vesicles, containing conserved C1 and C2 domains consistent with roles in diacylglycerol and calcium signaling during neurotransmitter release.","method":"Molecular cloning, specific antibody immunolocalization, subcellular fractionation/synaptosome preparation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — subcellular fractionation plus immunolocalization with specific antibodies, foundational paper >300 citations","pmids":["7559667"],"is_preprint":false},{"year":1997,"finding":"Munc13-1 (the rat UNC-13 homolog most closely related to Munc13-2/UNC13B) directly interacts with the N-terminal coiled-coil domain of syntaxin via its C-terminus, and through this interaction associates with a subpopulation of the exocytotic core complex (syntaxin/SNAP-25/synaptobrevin); the syntaxin-binding site overlaps with the Munc18 binding site.","method":"Three independent methods: GST pulldown, co-immunoprecipitation, and yeast two-hybrid; the interaction was demonstrated for Munc13-1 but directly relevant to the Munc13 family mechanism conserved in Munc13-2/UNC13B","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1/2 — three orthogonal binding methods, >230 citations, foundational mechanistic paper for Munc13 family","pmids":["8999968"],"is_preprint":false},{"year":1999,"finding":"UNC-13 is required for synaptic vesicle priming (the step after docking that renders vesicles fusion-competent): unc-13 null mutants in C. elegans have morphologically docked vesicles that are not competent for evoked release or for release by hyperosmotic saline, indicating a post-docking, pre-fusion priming role.","method":"Whole-cell voltage-clamp electrophysiology at C. elegans NMJ, electron microscopy, genetic null alleles","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 — clean null mutant with electrophysiology and EM, replicated in Drosophila same year, >490 citations","pmids":["10526333"],"is_preprint":false},{"year":1999,"finding":"Neurotransmitter release at C. elegans NMJs is facilitated by a presynaptic pathway: Gqα (EGL-30) → PLCβ (EGL-8) → DAG → DAG binding to UNC-13. A mutation eliminating phorbol ester/DAG binding to UNC-13 blocks this facilitation, and a constitutively membrane-tethered UNC-13 rescues PLCβ mutants, placing UNC-13 as the downstream DAG effector in this pathway.","method":"Genetic epistasis, phorbol ester binding site point mutation, constitutively membrane-bound UNC-13 transgenic rescue, acetylcholine release assays in C. elegans","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with multiple alleles plus functional rescue, >270 citations","pmids":["10571228"],"is_preprint":false},{"year":1999,"finding":"Serotonin inhibits synaptic transmission by activating Gα0 (GOA-1) and diacylglycerol kinase (DGK-1) to decrease DAG levels, which reduces the abundance of UNC-13 at presynaptic release sites; loss of GOA-1 causes abnormally high accumulation of UNC-13 at nerve terminals.","method":"Genetic epistasis in C. elegans, immunostaining of UNC-13 at synapses in pathway mutants, aldicarb sensitivity assay for acetylcholine release","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — genetic pathway dissection with direct localization readout, >260 citations","pmids":["10677040"],"is_preprint":false},{"year":1999,"finding":"UNC-13 transiently interacts with the UNC-18–syntaxin complex and promotes displacement of UNC-18 from syntaxin, providing a biochemical mechanism for UNC-13's role in regulating the priming step of synaptic vesicle exocytosis.","method":"Co-immunoprecipitation, in vitro binding assay, genetic double mutant analysis in C. elegans","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal biochemical and genetic evidence, single lab","pmids":["10366611"],"is_preprint":false},{"year":2001,"finding":"UNC-13 primes synaptic vesicles for fusion by promoting the open conformation of syntaxin: an engineered open-conformation syntaxin bypasses the requirement for UNC-13 in vesicle priming at C. elegans NMJs, demonstrating that the mechanistic function of UNC-13 is to convert syntaxin from closed to open.","method":"Constitutively open syntaxin mutant transgenic rescue of unc-13 null, electrophysiology, genetic epistasis in C. elegans","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1/2 — direct mechanistic test with engineered syntaxin mutant, rigorous genetic and electrophysiological validation, >320 citations","pmids":["11460165"],"is_preprint":false},{"year":2003,"finding":"In Drosophila, the synaptic abundance of DUNC-13 (UNC13B ortholog) is regulated by antagonistic G-protein pathways (GαS/cAMP/PKA increases, Gαq/PLC/DAG also increases abundance) through proteasome-mediated protein degradation, rather than translocation or transport.","method":"Immunostaining of DUNC-13 at NMJ boutons in pathway mutants, pharmacological modulation of cAMP and DAG, proteasome inhibitor experiments in Drosophila","journal":"Journal of neurobiology","confidence":"Medium","confidence_rationale":"Tier 2/3 — multiple pathway perturbations with quantitative immunostaining, single lab","pmids":["12532395"],"is_preprint":false},{"year":2005,"finding":"The UNC-13/syntaxin interaction (via MHD2 domain residues F1000/K1002) is required for nerve-evoked vesicle fusion at C. elegans synapses but not for synaptic vesicle priming per se, as MHD2 double mutants have normal primed vesicle pools but reduced evoked EPSCs.","method":"Site-directed mutagenesis of MHD2, electrophysiology at C. elegans NMJ, transgenic rescue of unc-13 mutants","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1/2 — mutagenesis combined with electrophysiology and defined phenotypic readout","pmids":["16271476"],"is_preprint":false},{"year":2005,"finding":"DAG-activated Munc13-2 (hmunc13/UNC13B) translocates to the Golgi and interacts with GTP-bound Rab34 via its MHD2 domain, functioning as an effector of Rab34 in intracellular lysosome-Golgi trafficking in kidney cells.","method":"Bacterial two-hybrid screen, co-immunoprecipitation, GST pulldown with GTPase mutants (Q111L/T66N), subcellular localization by fluorescence microscopy","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2/3 — multiple binding assays and localization, but single lab and non-neuronal context","pmids":["16138900"],"is_preprint":false},{"year":2006,"finding":"UNC-13 localizes to the presynaptic plasma membrane within ~100 nm of the dense projection (active zone) at C. elegans NMJs, and in unc-13 null mutants, synaptic vesicle contacts with the plasma membrane are dramatically reduced, identifying morphologically primed vesicles and defining the priming domain.","method":"High-pressure freeze fixation, immunogold electron microscopy, morphometric analysis in C. elegans","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1/2 — ultrastructural localization with immunogold EM and null mutant comparison, rigorous morphometric analysis","pmids":["16885217"],"is_preprint":false},{"year":2007,"finding":"hMunc13-4 (UNC13D) mediates priming of cytotoxic granule exocytosis in cytotoxic T lymphocytes and NK cells by independently facilitating the assembly of Rab11+ recycling endosomes and Rab27+ late endosomal vesicles, and by priming cytotoxic granule fusion through interaction with active Rab27a.","method":"Genetic deficiency models, co-immunoprecipitation, subcellular fractionation, fluorescence imaging of organelle trafficking in primary lymphocytes","journal":"Nature immunology","confidence":"Medium","confidence_rationale":"Tier 2/3 — multiple organelle-level functional assays in primary immune cells, but this is UNC13D not UNC13B","pmids":["17237785"],"is_preprint":false},{"year":2008,"finding":"Munc13-2 (UNC13B) is required for baseline/constitutive priming of a specific population of secretory granules in airway Clara cells; Munc13-2-deficient mouse airways accumulate Muc5b mucin in Clara cells, while agonist-stimulated secretion via Munc13-4 remains intact, demonstrating isoform-specific priming of distinct granule pools.","method":"Munc13-2 knockout mouse, histochemistry (AB/PAS staining), mucin immunostaining, electron microscopy of Clara cell ultrastructure, BAL cell counts","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with specific functional phenotype and ultrastructural validation in vivo","pmids":["18258655"],"is_preprint":false},{"year":2009,"finding":"High glucose-induced upregulation of munc13-2 (UNC13B) increases constitutive protein secretion in mesangial cells through interaction with GTP-bound Rab34 via the MHD2 domain; siRNA knockdown of munc13-2 or Rab34 abolishes high-glucose-stimulated fibronectin secretion, and an MHD2-deleted mutant fails to stimulate secretion.","method":"siRNA knockdown, domain deletion mutant transfection, VSVG-GFP secretion assay, fibronectin secretion assay in rat mesangial cells","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2/3 — multiple perturbations (KD of two proteins + domain deletion mutant) with functional secretion readout, single lab","pmids":["19641095"],"is_preprint":false},{"year":2009,"finding":"Munc13-2 (UNC13B) is essential for normal release probability at hippocampal mossy fiber synapses; Munc13-2-deficient mice show strongly increased paired-pulse and frequency facilitation at mossy fiber synapses but unaffected transmission at other hippocampal synapse types, demonstrating synapse-type specific roles.","method":"Munc13-2 knockout mouse, patch-clamp electrophysiology at hippocampal slices, paired-pulse and frequency facilitation protocols","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with rigorous electrophysiological characterization at multiple synapse types","pmids":["19700493"],"is_preprint":false},{"year":2013,"finding":"The N-terminal C2A domain of UNC-13 regulates the probability of evoked release and precise active zone localization in C. elegans; C2A-domain-mediated proximity of UNC-13 to Ca2+ entry sites accelerates neurotransmitter release kinetics, and the C2A domain is specifically required for spontaneous release.","method":"C2A domain deletion mutants, electrophysiology at C. elegans NMJ, kinetics analysis, EGTA sensitivity assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1/2 — domain deletion with electrophysiology and kinetic analysis, multiple functional phenotypes","pmids":["24220508"],"is_preprint":false},{"year":2015,"finding":"NLP-12 neuropeptide potentiates tonic ACh release specifically through DAG binding to UNC-13L (the long isoform), via a pathway independent of EGL-30 Gαq and EGL-8 PLCβ; evoked release potentiation uses both short and long UNC-13 isoforms through the canonical Gαq→PLCβ→DAG pathway, demonstrating isoform-specific signal integration.","method":"Genetic epistasis with isoform-specific mutants, aldicarb assays and electrophysiology in C. elegans, DAG-binding domain mutants","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with multiple isoform-specific alleles and functional readouts","pmids":["25609620"],"is_preprint":false},{"year":2016,"finding":"At Drosophila glutamatergic synapses, Unc13B isoform is recruited to nascent active zones by scaffolding proteins Syd-1 and Liprin-α and localizes ~120 nm from Ca2+ channels, while Unc13A is positioned ~70 nm from Ca2+ channels by Bruchpilot and Rim-binding protein. Unc13A is responsible for docking SVs at the closer distance and mediates efficient, fast release; Unc13A null mutants show inefficient, delayed, EGTA-supersensitive release.","method":"Super-resolution STED microscopy, intravital two-photon imaging, isoform-specific null mutants, electrophysiology, mathematical modeling at Drosophila NMJ","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 1/2 — super-resolution imaging, genetic nulls, electrophysiology, and mathematical modeling in a single study; >165 citations","pmids":["27526206"],"is_preprint":false},{"year":2016,"finding":"Munc13-2 (UNC13B) expression level determines release probability and short-term plasticity phenotype at basolateral amygdala glutamatergic synapses: B6 mice expressing higher Munc13-2 show lower release probability and more facilitation; shRNA knockdown of Munc13-2 in B6 mice recapitulates the D2 presynaptic phenotype.","method":"shRNA knockdown in vivo, patch-clamp electrophysiology, phorbol ester sensitivity assays, Western blot, strain comparison (B6 vs D2)","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — shRNA loss-of-function with electrophysiological phenotype recapitulating genetic strain difference","pmids":["27798178"],"is_preprint":false},{"year":2017,"finding":"Doc2B acts as a calcium sensor in vesicle priming in a step that requires interaction with ubMunc13-2 (UNC13B): Doc2B C2B-domain Ca2+-binding and interaction with ubMunc13-2 are required for a downstream priming step, as shown by Ca2+-coordinating aspartate mutations and Munc13-2-deficient chromaffin cells.","method":"C2-domain point mutations, overexpression in chromaffin cells, Munc13-2 KO mouse cells, capacitance measurements of exocytosis","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis and KO with functional exocytosis readout, but indirect for UNC13B itself","pmids":["29274147"],"is_preprint":false},{"year":2017,"finding":"UNC-18/Munc18-1 primes synaptic vesicle fusion downstream of UNC-13/Munc13-1; a gain-of-function UNC-18(P334A) mutation partially bypasses the requirement for UNC-13, and this bypass is synergistically enhanced by loss of TOM-1/Tomosyn, placing UNC-13 upstream of UNC-18-mediated SNARE complex templating.","method":"Genetic epistasis in C. elegans, electrophysiology, liposome fusion assay, SNARE complex assembly assay with Munc18-1(P335A)","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1/2 — genetic epistasis plus in vitro biochemical reconstitution and liposome fusion assays","pmids":["28821673"],"is_preprint":false},{"year":2018,"finding":"Ethanol binds to the C1 domain of Munc13-1/Dunc13 and reduces diacylglycerol binding; in Drosophila, sedating concentrations of ethanol reduce synaptic vesicle release in olfactory neurons without affecting membrane depolarization or Ca2+ influx, and Dunc13 haploinsufficiency confers resistance to ethanol-induced presynaptic inhibition and sedation.","method":"In vitro C1-domain DAG binding competition assay with ethanol, two-photon calcium imaging, electrophysiology, Dunc13 haploinsufficient mutants, RNAi, Munc13-1 transgenic rescue in Drosophila","journal":"eNeuro","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro binding assay plus in vivo functional genetics, but primarily Drosophila ortholog","pmids":["29911175"],"is_preprint":false},{"year":2019,"finding":"UNC-13L has three inhibitory domains (X region between C2A and C1, C1, and C2B) that suppress synaptic vesicle exocytosis; deleting all three produces hyperactive UNC-13 with dramatically increased release, Ca2+ sensitivity, and release probability. The hyperactive form enhances tonic release by increasing syntaxin open probability and has additional functions in evoked release.","method":"Systematic domain deletion mutagenesis, electrophysiology at C. elegans NMJ, genetic double mutant analysis with syntaxin alleles","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1/2 — systematic mutagenesis of multiple domains with electrophysiology and genetic epistasis","pmids":["31509756"],"is_preprint":false},{"year":2021,"finding":"Synaptotagmin-7 promotes Ca2+-dependent priming and inhibits depriming by placing dense-core vesicles within 6 nm of the plasma membrane, and this priming effect requires ubMunc13-2 (UNC13B) and phorbol ester-dependent pathways; without synaptotagmin-7, vesicles accumulate 20–40 nm from the membrane, out of reach of the fusion complex.","method":"TIRF microscopy with EGFP-tagged vesicle markers, synaptotagmin-7 KO in mouse chromaffin cells, Munc13-2 KO chromaffin cells, capacitance and amperometry measurements","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — imaging with nm-scale resolution plus KO with functional readout, but UNC13B role is indirect/epistatic","pmids":["33749593"],"is_preprint":false},{"year":2022,"finding":"Endogenous Unc-13 in Drosophila undergoes nanoscale reorganization at active zones during presynaptic homeostatic potentiation (PHP): super-resolution microscopy reveals Unc-13 subclusters move toward the active zone center during PHP with unaltered total protein levels, indicating spatial redistribution rather than abundance change as the plasticity mechanism.","method":"MiMIC-based endogenous GFSTF tagging, structured illumination microscopy, HDBSCAN cluster analysis, TEVC electrophysiology at Drosophila NMJ","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — endogenous tagging with super-resolution imaging and electrophysiology, single lab","pmids":["36589286"],"is_preprint":false},{"year":2023,"finding":"CLA-1 (Clarinet) recruits UNC-13 to active zones through a RIMB-1-independent mechanism in C. elegans; cla-1 null mutants show mislocalized UNC-13 and reduced priming, while CLA-1 acts in concert with UNC-10/RIM to organize the active zone scaffold.","method":"Quantitative fluorescence imaging, electron microscopy, electrophysiology at C. elegans NMJ, genetic double mutants","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods (EM, imaging, electrophysiology) in genetic null backgrounds","pmids":["37186867"],"is_preprint":false},{"year":2025,"finding":"Monoamine/octopamine signaling via Gαq→PLCβ→DAG causes rapid (within ~1 minute) nanoscale immobilization and compaction of Unc13A into synaptic clusters, potentiating evoked neurotransmitter release; a point mutation in the C1 (DAG-binding) domain of Unc13 blocks plasticity-induced nanoscale enrichment and synaptic potentiation, and also reduces calcium sensitivity and causes short-term depression.","method":"Live single-molecule imaging of endogenously tagged Unc13 at Drosophila NMJ, C1-domain point mutation (endogenous knockin), electrophysiology, phorbol ester pharmacology","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 1/2 — endogenous knockin point mutation with single-molecule live imaging and electrophysiology; Drosophila Unc13B isoform studied","pmids":["40833403"],"is_preprint":false}],"current_model":"UNC13B (Munc13-2) is a presynaptic peripheral membrane protein that primes synaptic vesicles for fusion by converting syntaxin from its default closed conformation to an open conformation compatible with SNARE complex assembly, a function regulated by diacylglycerol binding to its C1 domain (downstream of Gq→PLCβ signaling), by Ca2+-sensing through its C2 domains, and by its precise nanoscale positioning within active zone subdomains—with its N-terminal C2A domain and scaffold interactions (with Syd-1/Liprin-α/Clarinet) determining its distance from Ca2+ channels to tune release probability, kinetics, and short-term plasticity at specific synapse types."},"narrative":{"teleology":[{"year":1991,"claim":"Establishing that UNC-13 family members are direct DAG effectors resolved the question of how phorbol ester/DAG second-messenger signaling could modulate vesicle release machinery, identifying the C1 domain as the DAG-responsive element.","evidence":"Recombinant C1 domain expression with radioligand phorbol ester binding and DAG competition assays in vitro","pmids":["2062851","1445255","7537738"],"confidence":"High","gaps":["Whether DAG binding is sufficient to activate the full-length protein or only one regulatory input","Structural basis of C1 domain selectivity for DAG versus phorbol esters"]},{"year":1995,"claim":"Cloning and subcellular localization of mammalian Munc13-2 established that UNC13B is a presynaptic plasma membrane protein enriched in synaptosomes but absent from synaptic vesicles, placing it at the site of vesicle fusion rather than on the vesicles themselves.","evidence":"Molecular cloning, immunolocalization with specific antibodies, and synaptosome fractionation","pmids":["7559667"],"confidence":"High","gaps":["Sub-synaptic localization relative to active zone structures","Whether Munc13-2 and Munc13-1 occupy identical or distinct presynaptic positions"]},{"year":1997,"claim":"Demonstration that Munc13 family members directly bind syntaxin's N-terminal coiled-coil at a site overlapping the Munc18 binding region provided a molecular link between UNC-13 and the SNARE fusion machinery, suggesting a mechanism involving Munc18 displacement.","evidence":"GST pulldown, co-immunoprecipitation, and yeast two-hybrid for Munc13-1–syntaxin interaction","pmids":["8999968"],"confidence":"High","gaps":["Whether Munc13-2 uses an identical syntaxin-binding interface","Whether UNC-13 actively displaces Munc18 or captures an equilibrium intermediate"]},{"year":1999,"claim":"Convergent genetic, electrophysiological, and biochemical evidence in C. elegans established that UNC-13 is essential for a post-docking priming step, acts as the downstream DAG effector of the Gαq→PLCβ→DAG pathway, and promotes displacement of UNC-18 from syntaxin to enable vesicle fusion competence.","evidence":"unc-13 null mutants with EM and electrophysiology showing docked but unprimed vesicles; genetic epistasis placing UNC-13 downstream of EGL-30/EGL-8; DAG-binding point mutation and constitutive membrane-tethered rescue; co-IP showing UNC-13/UNC-18/syntaxin complex dynamics","pmids":["10526333","10571228","10677040","10366611"],"confidence":"High","gaps":["Molecular mechanism by which UNC-13 opens syntaxin not yet directly tested","Relative contributions of DAG-dependent membrane translocation versus allosteric activation"]},{"year":2001,"claim":"The central mechanistic question—how UNC-13 primes vesicles—was resolved by showing that a constitutively open syntaxin mutant fully bypasses the requirement for UNC-13, proving that UNC-13's essential function is converting syntaxin from closed to open conformation.","evidence":"Constitutively open syntaxin transgene rescuing unc-13 null phenotype in C. elegans, with electrophysiology","pmids":["11460165"],"confidence":"High","gaps":["Whether UNC-13 directly catalyzes syntaxin opening or acts through an intermediate","Structural basis of the closed-to-open transition"]},{"year":2005,"claim":"Dissection of the UNC-13/syntaxin interaction via MHD2 mutagenesis revealed that the direct syntaxin-binding interface is required for efficient evoked fusion but not for the priming step itself, separating priming from fusion coupling as distinct UNC-13 functions; separately, an unexpected non-neuronal role as a Rab34 effector in Golgi-lysosome trafficking was identified.","evidence":"MHD2 F1000/K1002 point mutations with electrophysiology at C. elegans NMJ; bacterial two-hybrid, co-IP, and GST pulldown for Rab34–MHD2 interaction with fluorescence microscopy in kidney cells","pmids":["16271476","16138900"],"confidence":"High","gaps":["Structural model of MHD2–syntaxin versus MHD2–Rab34 interfaces","Whether Rab34-dependent trafficking function is conserved across Munc13 isoforms"]},{"year":2006,"claim":"Immunogold EM localized UNC-13 within ~100 nm of the dense projection and showed that unc-13 nulls lack membrane-contacting (morphologically primed) vesicles, defining the nanoscale spatial domain where priming occurs.","evidence":"High-pressure freeze fixation with immunogold EM and morphometric analysis in C. elegans","pmids":["16885217"],"confidence":"High","gaps":["Whether the ~100 nm distance reflects UNC-13's direct scaffold association or indirect positioning","Resolution insufficient to distinguish Munc13 isoform-specific sub-positions"]},{"year":2008,"claim":"Munc13-2 knockout mice revealed a non-neuronal, isoform-specific role: Munc13-2 is required for constitutive (but not agonist-stimulated) mucin granule priming in airway Clara cells, demonstrating that UNC13B priming function extends beyond synapses.","evidence":"Munc13-2 KO mouse with histochemistry, mucin immunostaining, and EM of Clara cell ultrastructure","pmids":["18258655"],"confidence":"High","gaps":["Whether Munc13-2 uses the same syntaxin-opening mechanism in non-neuronal secretory cells","Identity of the target syntaxin isoform in Clara cells"]},{"year":2009,"claim":"Synapse-type specificity was established: Munc13-2 KO selectively altered release probability and short-term plasticity at hippocampal mossy fiber synapses without affecting other hippocampal synapse types, showing that Munc13-2 expression level is a determinant of synapse-specific release properties.","evidence":"Munc13-2 KO mouse with patch-clamp electrophysiology at hippocampal slices, paired-pulse and frequency facilitation protocols","pmids":["19700493"],"confidence":"High","gaps":["Whether Munc13-1 compensates at non-mossy fiber synapses or is simply absent","Transcriptional regulation determining synapse-specific Munc13-2 expression"]},{"year":2013,"claim":"The N-terminal C2A domain was identified as the key determinant of UNC-13's proximity to Ca²⁺ entry sites: C2A deletion slowed release kinetics, increased EGTA sensitivity, and abolished spontaneous release, establishing that C2A-mediated positioning tunes release probability.","evidence":"C2A domain deletion mutants with electrophysiology and kinetics analysis at C. elegans NMJ","pmids":["24220508"],"confidence":"High","gaps":["Whether C2A binds a specific scaffold protein or lipid to achieve positioning","Ca²⁺ dependence of C2A domain contribution"]},{"year":2016,"claim":"Super-resolution imaging resolved the nanoscale architecture: Unc13B localizes ~120 nm from Ca²⁺ channels (recruited by Syd-1/Liprin-α) while Unc13A sits ~70 nm away (recruited by Bruchpilot/RBP), with each isoform independently docking vesicles at its respective distance to create functionally distinct release pools with different coupling efficiencies.","evidence":"STED super-resolution microscopy, isoform-specific null mutants, electrophysiology, and mathematical modeling at Drosophila NMJ","pmids":["27526206"],"confidence":"High","gaps":["Whether mammalian Munc13-2 occupies an analogous distal position relative to Munc13-1","Structural basis of Syd-1/Liprin-α recruitment of Unc13B"]},{"year":2017,"claim":"The epistatic hierarchy was clarified: UNC-18/Munc18 functions downstream of UNC-13 in SNARE complex templating, as a gain-of-function UNC-18 mutation partially bypasses UNC-13 requirement, and Doc2B acts as a calcium sensor in a priming step that requires interaction with ubMunc13-2.","evidence":"Genetic epistasis and liposome fusion reconstitution in C. elegans/in vitro; Doc2B C2-domain mutagenesis in Munc13-2 KO chromaffin cells with capacitance measurements","pmids":["28821673","29274147"],"confidence":"High","gaps":["Direct structural evidence for UNC-13 catalyzing Munc18-mediated SNARE templating","Stoichiometry of the Doc2B–Munc13-2 interaction"]},{"year":2019,"claim":"Systematic domain deletion revealed three intramolecular inhibitory domains (X region, C1, C2B) that suppress UNC-13 activity: removal of all three creates a hyperactive protein with dramatically increased release probability and Ca²⁺ sensitivity, establishing that UNC-13 is tonically autoinhibited and that DAG/Ca²⁺ signals relieve this inhibition.","evidence":"Systematic domain deletion mutagenesis with electrophysiology and genetic epistasis with syntaxin alleles in C. elegans","pmids":["31509756"],"confidence":"High","gaps":["Structural mechanism by which each inhibitory domain suppresses activity","Whether autoinhibition is relieved sequentially or cooperatively by DAG and Ca²⁺"]},{"year":2022,"claim":"During presynaptic homeostatic potentiation, Unc-13 undergoes nanoscale spatial redistribution toward active zone centers without changes in total abundance, identifying spatial reorganization rather than protein level as the plasticity mechanism.","evidence":"Endogenous GFSTF tagging with structured illumination microscopy and HDBSCAN cluster analysis at Drosophila NMJ","pmids":["36589286"],"confidence":"Medium","gaps":["Molecular trigger for spatial redistribution during PHP","Whether Unc13A and Unc13B subclusters redistribute differently","Single-lab finding awaiting independent replication"]},{"year":2023,"claim":"CLA-1/Clarinet was identified as a scaffold that recruits UNC-13 to active zones independently of RIM-binding protein, with cla-1 null mutants showing mislocalized UNC-13 and reduced priming, revealing a parallel active-zone recruitment pathway.","evidence":"Quantitative fluorescence imaging, EM, electrophysiology, and genetic double mutants in C. elegans","pmids":["37186867"],"confidence":"Medium","gaps":["Direct physical interaction between CLA-1 and UNC-13 not demonstrated biochemically","Whether CLA-1 recruits specifically UNC-13L versus UNC-13S isoforms"]},{"year":2025,"claim":"Live single-molecule imaging showed that Gαq→PLCβ→DAG signaling causes rapid (~1 min) immobilization and compaction of Unc13 into nanoscale synaptic clusters, and a C1-domain point mutation blocking DAG binding abolishes this plasticity-induced enrichment, reduces Ca²⁺ sensitivity, and converts facilitation into depression—directly linking DAG-dependent nanoscale dynamics to short-term plasticity.","evidence":"Endogenous C1-domain knockin point mutation with live single-molecule imaging and electrophysiology at Drosophila NMJ","pmids":["40833403"],"confidence":"Medium","gaps":["Whether DAG directly immobilizes Unc13 or acts through conformational change affecting scaffold interactions","Generalizability to mammalian Munc13-2"]},{"year":null,"claim":"A high-resolution structural model of full-length UNC-13B in its autoinhibited and activated states, and the precise mechanism by which it catalyzes the syntaxin closed-to-open transition in the context of Munc18 and the SNARE complex, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length Munc13-2 structure available","Whether Munc13-2 directly templates SNARE complex assembly or solely opens syntaxin for Munc18-mediated templating","Mammalian in vivo confirmation of isoform-specific nanoscale positioning observed in Drosophila"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,4,27]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[7,23,9]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,6,21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,11,18]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[10]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[3,7,15,16,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,5,17,27]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,7,13,24]}],"complexes":["SNARE priming complex (with syntaxin/Munc18)"],"partners":["STX1A","UNC18","RAB34","DOC2B","SYD1","PPFIA1","CLA1"],"other_free_text":[]},"mechanistic_narrative":"UNC13B (Munc13-2) is a presynaptic priming factor that renders docked synaptic vesicles fusion-competent by converting syntaxin from a closed to an open conformation, thereby enabling SNARE complex assembly and neurotransmitter release [PMID:11460165, PMID:10526333]. Its activity is regulated by diacylglycerol binding to its C1 domain downstream of the Gαq→PLCβ→DAG signaling cascade, which controls both its membrane association and nanoscale positioning within active zones; DAG binding drives rapid clustering of UNC13 at release sites to potentiate evoked transmission, while inhibitory intramolecular domains (X, C1, C2B) restrain basal activity [PMID:10571228, PMID:31509756, PMID:40833403]. The N-terminal C2A domain and active-zone scaffolds (Syd-1/Liprin-α, CLA-1/Clarinet) determine UNC13B's nanoscale distance from calcium channels, tuning release probability, kinetics, and short-term plasticity in a synapse-type-specific manner—Munc13-2 knockout selectively increases facilitation at hippocampal mossy fiber and amygdala synapses [PMID:27526206, PMID:24220508, PMID:19700493, PMID:37186867]. Beyond neurons, Munc13-2 mediates constitutive granule priming in airway Clara cells and Rab34-dependent Golgi trafficking in non-neuronal cells [PMID:18258655, PMID:16138900]."},"prefetch_data":{"uniprot":{"accession":"O14795","full_name":"Protein unc-13 homolog B","aliases":["Munc13-2","munc13"],"length_aa":1591,"mass_kda":180.7,"function":"Plays a role in vesicle maturation during exocytosis as a target of the diacylglycerol second messenger pathway. Is involved in neurotransmitter release by acting in synaptic vesicle priming prior to vesicle fusion and participates in the activity-depending refilling of readily releasable vesicle pool (RRP) (By similarity). Essential for synaptic vesicle maturation in a subset of excitatory/glutamatergic but not inhibitory/GABA-mediated synapses (By similarity). In collaboration with UNC13A, facilitates neuronal dense core vesicles fusion as well as controls the location and efficiency of their synaptic release (By similarity)","subcellular_location":"Cytoplasm; Membrane; Cell membrane; Synapse","url":"https://www.uniprot.org/uniprotkb/O14795/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UNC13B","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CALM1","stoichiometry":0.2},{"gene":"CALM2","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/UNC13B","total_profiled":1310},"omim":[{"mim_id":"610917","title":"RAS-ASSOCIATED PROTEIN 34; RAB34","url":"https://www.omim.org/entry/610917"},{"mim_id":"609112","title":"F-BOX 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inhibits phorbol ester binding, identifying UNC-13/Munc13-2 as a DAG-binding protein in the diacylglycerol second-messenger pathway.\",\n      \"method\": \"Recombinant domain expression in E. coli, radioligand phorbol ester binding assay, competitive inhibition with diacylglycerol\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro biochemical assay with recombinant protein, confirmed by multiple binding studies across labs\",\n      \"pmids\": [\"2062851\", \"1445255\", \"7537738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Mammalian Munc13-2 (UNC13B) is a brain-expressed peripheral membrane protein enriched in synaptosomes and localized to presynaptic plasma membranes but absent from synaptic vesicles, containing conserved C1 and C2 domains consistent with roles in diacylglycerol and calcium signaling during neurotransmitter release.\",\n      \"method\": \"Molecular cloning, specific antibody immunolocalization, subcellular fractionation/synaptosome preparation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — subcellular fractionation plus immunolocalization with specific antibodies, foundational paper >300 citations\",\n      \"pmids\": [\"7559667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Munc13-1 (the rat UNC-13 homolog most closely related to Munc13-2/UNC13B) directly interacts with the N-terminal coiled-coil domain of syntaxin via its C-terminus, and through this interaction associates with a subpopulation of the exocytotic core complex (syntaxin/SNAP-25/synaptobrevin); the syntaxin-binding site overlaps with the Munc18 binding site.\",\n      \"method\": \"Three independent methods: GST pulldown, co-immunoprecipitation, and yeast two-hybrid; the interaction was demonstrated for Munc13-1 but directly relevant to the Munc13 family mechanism conserved in Munc13-2/UNC13B\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — three orthogonal binding methods, >230 citations, foundational mechanistic paper for Munc13 family\",\n      \"pmids\": [\"8999968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UNC-13 is required for synaptic vesicle priming (the step after docking that renders vesicles fusion-competent): unc-13 null mutants in C. elegans have morphologically docked vesicles that are not competent for evoked release or for release by hyperosmotic saline, indicating a post-docking, pre-fusion priming role.\",\n      \"method\": \"Whole-cell voltage-clamp electrophysiology at C. elegans NMJ, electron microscopy, genetic null alleles\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean null mutant with electrophysiology and EM, replicated in Drosophila same year, >490 citations\",\n      \"pmids\": [\"10526333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Neurotransmitter release at C. elegans NMJs is facilitated by a presynaptic pathway: Gqα (EGL-30) → PLCβ (EGL-8) → DAG → DAG binding to UNC-13. A mutation eliminating phorbol ester/DAG binding to UNC-13 blocks this facilitation, and a constitutively membrane-tethered UNC-13 rescues PLCβ mutants, placing UNC-13 as the downstream DAG effector in this pathway.\",\n      \"method\": \"Genetic epistasis, phorbol ester binding site point mutation, constitutively membrane-bound UNC-13 transgenic rescue, acetylcholine release assays in C. elegans\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple alleles plus functional rescue, >270 citations\",\n      \"pmids\": [\"10571228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Serotonin inhibits synaptic transmission by activating Gα0 (GOA-1) and diacylglycerol kinase (DGK-1) to decrease DAG levels, which reduces the abundance of UNC-13 at presynaptic release sites; loss of GOA-1 causes abnormally high accumulation of UNC-13 at nerve terminals.\",\n      \"method\": \"Genetic epistasis in C. elegans, immunostaining of UNC-13 at synapses in pathway mutants, aldicarb sensitivity assay for acetylcholine release\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic pathway dissection with direct localization readout, >260 citations\",\n      \"pmids\": [\"10677040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UNC-13 transiently interacts with the UNC-18–syntaxin complex and promotes displacement of UNC-18 from syntaxin, providing a biochemical mechanism for UNC-13's role in regulating the priming step of synaptic vesicle exocytosis.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assay, genetic double mutant analysis in C. elegans\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal biochemical and genetic evidence, single lab\",\n      \"pmids\": [\"10366611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"UNC-13 primes synaptic vesicles for fusion by promoting the open conformation of syntaxin: an engineered open-conformation syntaxin bypasses the requirement for UNC-13 in vesicle priming at C. elegans NMJs, demonstrating that the mechanistic function of UNC-13 is to convert syntaxin from closed to open.\",\n      \"method\": \"Constitutively open syntaxin mutant transgenic rescue of unc-13 null, electrophysiology, genetic epistasis in C. elegans\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — direct mechanistic test with engineered syntaxin mutant, rigorous genetic and electrophysiological validation, >320 citations\",\n      \"pmids\": [\"11460165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In Drosophila, the synaptic abundance of DUNC-13 (UNC13B ortholog) is regulated by antagonistic G-protein pathways (GαS/cAMP/PKA increases, Gαq/PLC/DAG also increases abundance) through proteasome-mediated protein degradation, rather than translocation or transport.\",\n      \"method\": \"Immunostaining of DUNC-13 at NMJ boutons in pathway mutants, pharmacological modulation of cAMP and DAG, proteasome inhibitor experiments in Drosophila\",\n      \"journal\": \"Journal of neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple pathway perturbations with quantitative immunostaining, single lab\",\n      \"pmids\": [\"12532395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The UNC-13/syntaxin interaction (via MHD2 domain residues F1000/K1002) is required for nerve-evoked vesicle fusion at C. elegans synapses but not for synaptic vesicle priming per se, as MHD2 double mutants have normal primed vesicle pools but reduced evoked EPSCs.\",\n      \"method\": \"Site-directed mutagenesis of MHD2, electrophysiology at C. elegans NMJ, transgenic rescue of unc-13 mutants\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — mutagenesis combined with electrophysiology and defined phenotypic readout\",\n      \"pmids\": [\"16271476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"DAG-activated Munc13-2 (hmunc13/UNC13B) translocates to the Golgi and interacts with GTP-bound Rab34 via its MHD2 domain, functioning as an effector of Rab34 in intracellular lysosome-Golgi trafficking in kidney cells.\",\n      \"method\": \"Bacterial two-hybrid screen, co-immunoprecipitation, GST pulldown with GTPase mutants (Q111L/T66N), subcellular localization by fluorescence microscopy\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple binding assays and localization, but single lab and non-neuronal context\",\n      \"pmids\": [\"16138900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"UNC-13 localizes to the presynaptic plasma membrane within ~100 nm of the dense projection (active zone) at C. elegans NMJs, and in unc-13 null mutants, synaptic vesicle contacts with the plasma membrane are dramatically reduced, identifying morphologically primed vesicles and defining the priming domain.\",\n      \"method\": \"High-pressure freeze fixation, immunogold electron microscopy, morphometric analysis in C. elegans\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — ultrastructural localization with immunogold EM and null mutant comparison, rigorous morphometric analysis\",\n      \"pmids\": [\"16885217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"hMunc13-4 (UNC13D) mediates priming of cytotoxic granule exocytosis in cytotoxic T lymphocytes and NK cells by independently facilitating the assembly of Rab11+ recycling endosomes and Rab27+ late endosomal vesicles, and by priming cytotoxic granule fusion through interaction with active Rab27a.\",\n      \"method\": \"Genetic deficiency models, co-immunoprecipitation, subcellular fractionation, fluorescence imaging of organelle trafficking in primary lymphocytes\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple organelle-level functional assays in primary immune cells, but this is UNC13D not UNC13B\",\n      \"pmids\": [\"17237785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Munc13-2 (UNC13B) is required for baseline/constitutive priming of a specific population of secretory granules in airway Clara cells; Munc13-2-deficient mouse airways accumulate Muc5b mucin in Clara cells, while agonist-stimulated secretion via Munc13-4 remains intact, demonstrating isoform-specific priming of distinct granule pools.\",\n      \"method\": \"Munc13-2 knockout mouse, histochemistry (AB/PAS staining), mucin immunostaining, electron microscopy of Clara cell ultrastructure, BAL cell counts\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with specific functional phenotype and ultrastructural validation in vivo\",\n      \"pmids\": [\"18258655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"High glucose-induced upregulation of munc13-2 (UNC13B) increases constitutive protein secretion in mesangial cells through interaction with GTP-bound Rab34 via the MHD2 domain; siRNA knockdown of munc13-2 or Rab34 abolishes high-glucose-stimulated fibronectin secretion, and an MHD2-deleted mutant fails to stimulate secretion.\",\n      \"method\": \"siRNA knockdown, domain deletion mutant transfection, VSVG-GFP secretion assay, fibronectin secretion assay in rat mesangial cells\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple perturbations (KD of two proteins + domain deletion mutant) with functional secretion readout, single lab\",\n      \"pmids\": [\"19641095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Munc13-2 (UNC13B) is essential for normal release probability at hippocampal mossy fiber synapses; Munc13-2-deficient mice show strongly increased paired-pulse and frequency facilitation at mossy fiber synapses but unaffected transmission at other hippocampal synapse types, demonstrating synapse-type specific roles.\",\n      \"method\": \"Munc13-2 knockout mouse, patch-clamp electrophysiology at hippocampal slices, paired-pulse and frequency facilitation protocols\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with rigorous electrophysiological characterization at multiple synapse types\",\n      \"pmids\": [\"19700493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The N-terminal C2A domain of UNC-13 regulates the probability of evoked release and precise active zone localization in C. elegans; C2A-domain-mediated proximity of UNC-13 to Ca2+ entry sites accelerates neurotransmitter release kinetics, and the C2A domain is specifically required for spontaneous release.\",\n      \"method\": \"C2A domain deletion mutants, electrophysiology at C. elegans NMJ, kinetics analysis, EGTA sensitivity assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — domain deletion with electrophysiology and kinetic analysis, multiple functional phenotypes\",\n      \"pmids\": [\"24220508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NLP-12 neuropeptide potentiates tonic ACh release specifically through DAG binding to UNC-13L (the long isoform), via a pathway independent of EGL-30 Gαq and EGL-8 PLCβ; evoked release potentiation uses both short and long UNC-13 isoforms through the canonical Gαq→PLCβ→DAG pathway, demonstrating isoform-specific signal integration.\",\n      \"method\": \"Genetic epistasis with isoform-specific mutants, aldicarb assays and electrophysiology in C. elegans, DAG-binding domain mutants\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple isoform-specific alleles and functional readouts\",\n      \"pmids\": [\"25609620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"At Drosophila glutamatergic synapses, Unc13B isoform is recruited to nascent active zones by scaffolding proteins Syd-1 and Liprin-α and localizes ~120 nm from Ca2+ channels, while Unc13A is positioned ~70 nm from Ca2+ channels by Bruchpilot and Rim-binding protein. Unc13A is responsible for docking SVs at the closer distance and mediates efficient, fast release; Unc13A null mutants show inefficient, delayed, EGTA-supersensitive release.\",\n      \"method\": \"Super-resolution STED microscopy, intravital two-photon imaging, isoform-specific null mutants, electrophysiology, mathematical modeling at Drosophila NMJ\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — super-resolution imaging, genetic nulls, electrophysiology, and mathematical modeling in a single study; >165 citations\",\n      \"pmids\": [\"27526206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Munc13-2 (UNC13B) expression level determines release probability and short-term plasticity phenotype at basolateral amygdala glutamatergic synapses: B6 mice expressing higher Munc13-2 show lower release probability and more facilitation; shRNA knockdown of Munc13-2 in B6 mice recapitulates the D2 presynaptic phenotype.\",\n      \"method\": \"shRNA knockdown in vivo, patch-clamp electrophysiology, phorbol ester sensitivity assays, Western blot, strain comparison (B6 vs D2)\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — shRNA loss-of-function with electrophysiological phenotype recapitulating genetic strain difference\",\n      \"pmids\": [\"27798178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Doc2B acts as a calcium sensor in vesicle priming in a step that requires interaction with ubMunc13-2 (UNC13B): Doc2B C2B-domain Ca2+-binding and interaction with ubMunc13-2 are required for a downstream priming step, as shown by Ca2+-coordinating aspartate mutations and Munc13-2-deficient chromaffin cells.\",\n      \"method\": \"C2-domain point mutations, overexpression in chromaffin cells, Munc13-2 KO mouse cells, capacitance measurements of exocytosis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis and KO with functional exocytosis readout, but indirect for UNC13B itself\",\n      \"pmids\": [\"29274147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"UNC-18/Munc18-1 primes synaptic vesicle fusion downstream of UNC-13/Munc13-1; a gain-of-function UNC-18(P334A) mutation partially bypasses the requirement for UNC-13, and this bypass is synergistically enhanced by loss of TOM-1/Tomosyn, placing UNC-13 upstream of UNC-18-mediated SNARE complex templating.\",\n      \"method\": \"Genetic epistasis in C. elegans, electrophysiology, liposome fusion assay, SNARE complex assembly assay with Munc18-1(P335A)\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — genetic epistasis plus in vitro biochemical reconstitution and liposome fusion assays\",\n      \"pmids\": [\"28821673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ethanol binds to the C1 domain of Munc13-1/Dunc13 and reduces diacylglycerol binding; in Drosophila, sedating concentrations of ethanol reduce synaptic vesicle release in olfactory neurons without affecting membrane depolarization or Ca2+ influx, and Dunc13 haploinsufficiency confers resistance to ethanol-induced presynaptic inhibition and sedation.\",\n      \"method\": \"In vitro C1-domain DAG binding competition assay with ethanol, two-photon calcium imaging, electrophysiology, Dunc13 haploinsufficient mutants, RNAi, Munc13-1 transgenic rescue in Drosophila\",\n      \"journal\": \"eNeuro\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro binding assay plus in vivo functional genetics, but primarily Drosophila ortholog\",\n      \"pmids\": [\"29911175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UNC-13L has three inhibitory domains (X region between C2A and C1, C1, and C2B) that suppress synaptic vesicle exocytosis; deleting all three produces hyperactive UNC-13 with dramatically increased release, Ca2+ sensitivity, and release probability. The hyperactive form enhances tonic release by increasing syntaxin open probability and has additional functions in evoked release.\",\n      \"method\": \"Systematic domain deletion mutagenesis, electrophysiology at C. elegans NMJ, genetic double mutant analysis with syntaxin alleles\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — systematic mutagenesis of multiple domains with electrophysiology and genetic epistasis\",\n      \"pmids\": [\"31509756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Synaptotagmin-7 promotes Ca2+-dependent priming and inhibits depriming by placing dense-core vesicles within 6 nm of the plasma membrane, and this priming effect requires ubMunc13-2 (UNC13B) and phorbol ester-dependent pathways; without synaptotagmin-7, vesicles accumulate 20–40 nm from the membrane, out of reach of the fusion complex.\",\n      \"method\": \"TIRF microscopy with EGFP-tagged vesicle markers, synaptotagmin-7 KO in mouse chromaffin cells, Munc13-2 KO chromaffin cells, capacitance and amperometry measurements\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — imaging with nm-scale resolution plus KO with functional readout, but UNC13B role is indirect/epistatic\",\n      \"pmids\": [\"33749593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Endogenous Unc-13 in Drosophila undergoes nanoscale reorganization at active zones during presynaptic homeostatic potentiation (PHP): super-resolution microscopy reveals Unc-13 subclusters move toward the active zone center during PHP with unaltered total protein levels, indicating spatial redistribution rather than abundance change as the plasticity mechanism.\",\n      \"method\": \"MiMIC-based endogenous GFSTF tagging, structured illumination microscopy, HDBSCAN cluster analysis, TEVC electrophysiology at Drosophila NMJ\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — endogenous tagging with super-resolution imaging and electrophysiology, single lab\",\n      \"pmids\": [\"36589286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CLA-1 (Clarinet) recruits UNC-13 to active zones through a RIMB-1-independent mechanism in C. elegans; cla-1 null mutants show mislocalized UNC-13 and reduced priming, while CLA-1 acts in concert with UNC-10/RIM to organize the active zone scaffold.\",\n      \"method\": \"Quantitative fluorescence imaging, electron microscopy, electrophysiology at C. elegans NMJ, genetic double mutants\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods (EM, imaging, electrophysiology) in genetic null backgrounds\",\n      \"pmids\": [\"37186867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Monoamine/octopamine signaling via Gαq→PLCβ→DAG causes rapid (within ~1 minute) nanoscale immobilization and compaction of Unc13A into synaptic clusters, potentiating evoked neurotransmitter release; a point mutation in the C1 (DAG-binding) domain of Unc13 blocks plasticity-induced nanoscale enrichment and synaptic potentiation, and also reduces calcium sensitivity and causes short-term depression.\",\n      \"method\": \"Live single-molecule imaging of endogenously tagged Unc13 at Drosophila NMJ, C1-domain point mutation (endogenous knockin), electrophysiology, phorbol ester pharmacology\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — endogenous knockin point mutation with single-molecule live imaging and electrophysiology; Drosophila Unc13B isoform studied\",\n      \"pmids\": [\"40833403\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UNC13B (Munc13-2) is a presynaptic peripheral membrane protein that primes synaptic vesicles for fusion by converting syntaxin from its default closed conformation to an open conformation compatible with SNARE complex assembly, a function regulated by diacylglycerol binding to its C1 domain (downstream of Gq→PLCβ signaling), by Ca2+-sensing through its C2 domains, and by its precise nanoscale positioning within active zone subdomains—with its N-terminal C2A domain and scaffold interactions (with Syd-1/Liprin-α/Clarinet) determining its distance from Ca2+ channels to tune release probability, kinetics, and short-term plasticity at specific synapse types.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"UNC13B (Munc13-2) is a presynaptic priming factor that renders docked synaptic vesicles fusion-competent by converting syntaxin from a closed to an open conformation, thereby enabling SNARE complex assembly and neurotransmitter release [PMID:11460165, PMID:10526333]. Its activity is regulated by diacylglycerol binding to its C1 domain downstream of the Gαq→PLCβ→DAG signaling cascade, which controls both its membrane association and nanoscale positioning within active zones; DAG binding drives rapid clustering of UNC13 at release sites to potentiate evoked transmission, while inhibitory intramolecular domains (X, C1, C2B) restrain basal activity [PMID:10571228, PMID:31509756, PMID:40833403]. The N-terminal C2A domain and active-zone scaffolds (Syd-1/Liprin-α, CLA-1/Clarinet) determine UNC13B's nanoscale distance from calcium channels, tuning release probability, kinetics, and short-term plasticity in a synapse-type-specific manner—Munc13-2 knockout selectively increases facilitation at hippocampal mossy fiber and amygdala synapses [PMID:27526206, PMID:24220508, PMID:19700493, PMID:37186867]. Beyond neurons, Munc13-2 mediates constitutive granule priming in airway Clara cells and Rab34-dependent Golgi trafficking in non-neuronal cells [PMID:18258655, PMID:16138900].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Establishing that UNC-13 family members are direct DAG effectors resolved the question of how phorbol ester/DAG second-messenger signaling could modulate vesicle release machinery, identifying the C1 domain as the DAG-responsive element.\",\n      \"evidence\": \"Recombinant C1 domain expression with radioligand phorbol ester binding and DAG competition assays in vitro\",\n      \"pmids\": [\"2062851\", \"1445255\", \"7537738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DAG binding is sufficient to activate the full-length protein or only one regulatory input\", \"Structural basis of C1 domain selectivity for DAG versus phorbol esters\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Cloning and subcellular localization of mammalian Munc13-2 established that UNC13B is a presynaptic plasma membrane protein enriched in synaptosomes but absent from synaptic vesicles, placing it at the site of vesicle fusion rather than on the vesicles themselves.\",\n      \"evidence\": \"Molecular cloning, immunolocalization with specific antibodies, and synaptosome fractionation\",\n      \"pmids\": [\"7559667\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sub-synaptic localization relative to active zone structures\", \"Whether Munc13-2 and Munc13-1 occupy identical or distinct presynaptic positions\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstration that Munc13 family members directly bind syntaxin's N-terminal coiled-coil at a site overlapping the Munc18 binding region provided a molecular link between UNC-13 and the SNARE fusion machinery, suggesting a mechanism involving Munc18 displacement.\",\n      \"evidence\": \"GST pulldown, co-immunoprecipitation, and yeast two-hybrid for Munc13-1–syntaxin interaction\",\n      \"pmids\": [\"8999968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Munc13-2 uses an identical syntaxin-binding interface\", \"Whether UNC-13 actively displaces Munc18 or captures an equilibrium intermediate\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Convergent genetic, electrophysiological, and biochemical evidence in C. elegans established that UNC-13 is essential for a post-docking priming step, acts as the downstream DAG effector of the Gαq→PLCβ→DAG pathway, and promotes displacement of UNC-18 from syntaxin to enable vesicle fusion competence.\",\n      \"evidence\": \"unc-13 null mutants with EM and electrophysiology showing docked but unprimed vesicles; genetic epistasis placing UNC-13 downstream of EGL-30/EGL-8; DAG-binding point mutation and constitutive membrane-tethered rescue; co-IP showing UNC-13/UNC-18/syntaxin complex dynamics\",\n      \"pmids\": [\"10526333\", \"10571228\", \"10677040\", \"10366611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which UNC-13 opens syntaxin not yet directly tested\", \"Relative contributions of DAG-dependent membrane translocation versus allosteric activation\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The central mechanistic question—how UNC-13 primes vesicles—was resolved by showing that a constitutively open syntaxin mutant fully bypasses the requirement for UNC-13, proving that UNC-13's essential function is converting syntaxin from closed to open conformation.\",\n      \"evidence\": \"Constitutively open syntaxin transgene rescuing unc-13 null phenotype in C. elegans, with electrophysiology\",\n      \"pmids\": [\"11460165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether UNC-13 directly catalyzes syntaxin opening or acts through an intermediate\", \"Structural basis of the closed-to-open transition\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Dissection of the UNC-13/syntaxin interaction via MHD2 mutagenesis revealed that the direct syntaxin-binding interface is required for efficient evoked fusion but not for the priming step itself, separating priming from fusion coupling as distinct UNC-13 functions; separately, an unexpected non-neuronal role as a Rab34 effector in Golgi-lysosome trafficking was identified.\",\n      \"evidence\": \"MHD2 F1000/K1002 point mutations with electrophysiology at C. elegans NMJ; bacterial two-hybrid, co-IP, and GST pulldown for Rab34–MHD2 interaction with fluorescence microscopy in kidney cells\",\n      \"pmids\": [\"16271476\", \"16138900\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural model of MHD2–syntaxin versus MHD2–Rab34 interfaces\", \"Whether Rab34-dependent trafficking function is conserved across Munc13 isoforms\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Immunogold EM localized UNC-13 within ~100 nm of the dense projection and showed that unc-13 nulls lack membrane-contacting (morphologically primed) vesicles, defining the nanoscale spatial domain where priming occurs.\",\n      \"evidence\": \"High-pressure freeze fixation with immunogold EM and morphometric analysis in C. elegans\",\n      \"pmids\": [\"16885217\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the ~100 nm distance reflects UNC-13's direct scaffold association or indirect positioning\", \"Resolution insufficient to distinguish Munc13 isoform-specific sub-positions\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Munc13-2 knockout mice revealed a non-neuronal, isoform-specific role: Munc13-2 is required for constitutive (but not agonist-stimulated) mucin granule priming in airway Clara cells, demonstrating that UNC13B priming function extends beyond synapses.\",\n      \"evidence\": \"Munc13-2 KO mouse with histochemistry, mucin immunostaining, and EM of Clara cell ultrastructure\",\n      \"pmids\": [\"18258655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Munc13-2 uses the same syntaxin-opening mechanism in non-neuronal secretory cells\", \"Identity of the target syntaxin isoform in Clara cells\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Synapse-type specificity was established: Munc13-2 KO selectively altered release probability and short-term plasticity at hippocampal mossy fiber synapses without affecting other hippocampal synapse types, showing that Munc13-2 expression level is a determinant of synapse-specific release properties.\",\n      \"evidence\": \"Munc13-2 KO mouse with patch-clamp electrophysiology at hippocampal slices, paired-pulse and frequency facilitation protocols\",\n      \"pmids\": [\"19700493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Munc13-1 compensates at non-mossy fiber synapses or is simply absent\", \"Transcriptional regulation determining synapse-specific Munc13-2 expression\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The N-terminal C2A domain was identified as the key determinant of UNC-13's proximity to Ca²⁺ entry sites: C2A deletion slowed release kinetics, increased EGTA sensitivity, and abolished spontaneous release, establishing that C2A-mediated positioning tunes release probability.\",\n      \"evidence\": \"C2A domain deletion mutants with electrophysiology and kinetics analysis at C. elegans NMJ\",\n      \"pmids\": [\"24220508\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether C2A binds a specific scaffold protein or lipid to achieve positioning\", \"Ca²⁺ dependence of C2A domain contribution\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Super-resolution imaging resolved the nanoscale architecture: Unc13B localizes ~120 nm from Ca²⁺ channels (recruited by Syd-1/Liprin-α) while Unc13A sits ~70 nm away (recruited by Bruchpilot/RBP), with each isoform independently docking vesicles at its respective distance to create functionally distinct release pools with different coupling efficiencies.\",\n      \"evidence\": \"STED super-resolution microscopy, isoform-specific null mutants, electrophysiology, and mathematical modeling at Drosophila NMJ\",\n      \"pmids\": [\"27526206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian Munc13-2 occupies an analogous distal position relative to Munc13-1\", \"Structural basis of Syd-1/Liprin-α recruitment of Unc13B\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The epistatic hierarchy was clarified: UNC-18/Munc18 functions downstream of UNC-13 in SNARE complex templating, as a gain-of-function UNC-18 mutation partially bypasses UNC-13 requirement, and Doc2B acts as a calcium sensor in a priming step that requires interaction with ubMunc13-2.\",\n      \"evidence\": \"Genetic epistasis and liposome fusion reconstitution in C. elegans/in vitro; Doc2B C2-domain mutagenesis in Munc13-2 KO chromaffin cells with capacitance measurements\",\n      \"pmids\": [\"28821673\", \"29274147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural evidence for UNC-13 catalyzing Munc18-mediated SNARE templating\", \"Stoichiometry of the Doc2B–Munc13-2 interaction\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Systematic domain deletion revealed three intramolecular inhibitory domains (X region, C1, C2B) that suppress UNC-13 activity: removal of all three creates a hyperactive protein with dramatically increased release probability and Ca²⁺ sensitivity, establishing that UNC-13 is tonically autoinhibited and that DAG/Ca²⁺ signals relieve this inhibition.\",\n      \"evidence\": \"Systematic domain deletion mutagenesis with electrophysiology and genetic epistasis with syntaxin alleles in C. elegans\",\n      \"pmids\": [\"31509756\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which each inhibitory domain suppresses activity\", \"Whether autoinhibition is relieved sequentially or cooperatively by DAG and Ca²⁺\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"During presynaptic homeostatic potentiation, Unc-13 undergoes nanoscale spatial redistribution toward active zone centers without changes in total abundance, identifying spatial reorganization rather than protein level as the plasticity mechanism.\",\n      \"evidence\": \"Endogenous GFSTF tagging with structured illumination microscopy and HDBSCAN cluster analysis at Drosophila NMJ\",\n      \"pmids\": [\"36589286\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular trigger for spatial redistribution during PHP\", \"Whether Unc13A and Unc13B subclusters redistribute differently\", \"Single-lab finding awaiting independent replication\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"CLA-1/Clarinet was identified as a scaffold that recruits UNC-13 to active zones independently of RIM-binding protein, with cla-1 null mutants showing mislocalized UNC-13 and reduced priming, revealing a parallel active-zone recruitment pathway.\",\n      \"evidence\": \"Quantitative fluorescence imaging, EM, electrophysiology, and genetic double mutants in C. elegans\",\n      \"pmids\": [\"37186867\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical interaction between CLA-1 and UNC-13 not demonstrated biochemically\", \"Whether CLA-1 recruits specifically UNC-13L versus UNC-13S isoforms\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Live single-molecule imaging showed that Gαq→PLCβ→DAG signaling causes rapid (~1 min) immobilization and compaction of Unc13 into nanoscale synaptic clusters, and a C1-domain point mutation blocking DAG binding abolishes this plasticity-induced enrichment, reduces Ca²⁺ sensitivity, and converts facilitation into depression—directly linking DAG-dependent nanoscale dynamics to short-term plasticity.\",\n      \"evidence\": \"Endogenous C1-domain knockin point mutation with live single-molecule imaging and electrophysiology at Drosophila NMJ\",\n      \"pmids\": [\"40833403\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether DAG directly immobilizes Unc13 or acts through conformational change affecting scaffold interactions\", \"Generalizability to mammalian Munc13-2\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structural model of full-length UNC-13B in its autoinhibited and activated states, and the precise mechanism by which it catalyzes the syntaxin closed-to-open transition in the context of Munc18 and the SNARE complex, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length Munc13-2 structure available\", \"Whether Munc13-2 directly templates SNARE complex assembly or solely opens syntaxin for Munc18-mediated templating\", \"Mammalian in vivo confirmation of isoform-specific nanoscale positioning observed in Drosophila\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 4, 27]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [7, 23, 9]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 6, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 11, 18]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3, 7, 15, 16, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 5, 17, 27]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 7, 13, 24]}\n    ],\n    \"complexes\": [\n      \"SNARE priming complex (with syntaxin/Munc18)\"\n    ],\n    \"partners\": [\n      \"STX1A\",\n      \"UNC18\",\n      \"RAB34\",\n      \"DOC2B\",\n      \"SYD1\",\n      \"PPFIA1\",\n      \"CLA1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}