{"gene":"SV2A","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1992,"finding":"SV2A (SV2) is a 12-transmembrane-domain protein with sequence homology to the major facilitator superfamily (MFS) of bacterial transporters, specifically the N-terminal half showing identity to sugar/citrate/drug transporters and the C-terminal half to plasma membrane neurotransmitter transporters, suggesting a transporter function for synaptic vesicles.","method":"cDNA cloning, sequence analysis, topology prediction, and heterologous expression in COS cells","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 / Strong — independently reported by two labs in same year using cDNA cloning and sequence analysis, foundational structural characterization replicated","pmids":["1519064","1355409"],"is_preprint":false},{"year":1993,"finding":"SV2 is a keratan sulfate proteoglycan on synaptic vesicles, existing in two electrophoretic forms (L form ~100 kDa and H form ~250 kDa), both containing the SV2 epitope on the cytoplasmic side of the vesicle membrane.","method":"Biochemical fractionation of synaptic vesicles, SDS-PAGE, immunoblotting, proteoglycan characterization","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical characterization of purified synaptic vesicles, single lab with multiple methods","pmids":["7685814"],"is_preprint":false},{"year":1994,"finding":"SV2A is expressed ubiquitously throughout the brain at all synapses, and immunoprecipitation of brain synaptic vesicles with isoform-specific antibodies showed that both SV2A and SV2B isoforms can be present on the same synaptic vesicle.","method":"In situ hybridization, immunohistochemistry, isoform-specific immunoprecipitation followed by Western blot","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal immunoprecipitation with isoform-specific antibodies, multiple orthogonal methods in one study","pmids":["8083732"],"is_preprint":false},{"year":1996,"finding":"SV2A directly binds synaptotagmin in a calcium-regulated, isoform-specific manner: SV2A (but not SV2B) interacts with the C2B domain of synaptotagmin via SV2A's cytoplasmic amino terminus, and this interaction is inhibited by calcium with an EC50 of ~10 µM.","method":"Cross-linking, co-immunoprecipitation, recombinant protein affinity chromatography","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal binding methods (cross-linking, co-IP, affinity chromatography), domain mapping, calcium-regulation quantified","pmids":["8910372"],"is_preprint":false},{"year":1999,"finding":"SV2A is essential for action potential-dependent GABAergic neurotransmission: SV2A knockout mice develop severe seizures and die within 3 weeks; electrophysiology of CA3 hippocampal neurons showed reduced action potential-dependent (but normal action potential-independent) GABAergic transmission, without changes in synapse density or morphology.","method":"Targeted gene disruption (knockout mouse), electrophysiology of spontaneous IPSCs, electron microscopy of synapse ultrastructure","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype, multiple orthogonal readouts, foundational loss-of-function study","pmids":["10611374"],"is_preprint":false},{"year":2001,"finding":"SV2A is required to maintain the readily releasable pool (RRP) of vesicles for calcium-stimulated exocytosis: direct capacitance measurements in SV2A-knockout adrenal chromaffin cells showed a significantly reduced calcium-induced exocytotic burst (defining the RRP) with normal burst kinetics, and brain tissue from SV2A knockouts had fewer SDS-resistant SNARE complexes.","method":"Capacitance measurements (direct exocytosis assay) in chromaffin cells, SDS-resistant SNARE complex analysis by Western blot","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct electrophysiological measure of exocytosis combined with biochemical SNARE complex analysis, single lab with two orthogonal methods","pmids":["11483953"],"is_preprint":false},{"year":2004,"finding":"SV2A is the brain binding site for the antiepileptic drug levetiracetam: the LEV-binding site is enriched in synaptic vesicles (~90 kDa by photoaffinity labeling); brain membranes and vesicles from SV2A-knockout mice show no LEV-derivative binding; SV2A expressed in fibroblasts is sufficient for LEV binding; no binding occurs to SV2B or SV2C; binding affinity to SV2A correlates with seizure protection.","method":"Radioligand binding assays, photoaffinity labeling of purified synaptic vesicles, SV2A knockout mice, heterologous expression in fibroblasts","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (photoaffinity labeling, knockout, heterologous expression), structure-activity correlation, highly cited foundational study","pmids":["15210974"],"is_preprint":false},{"year":2005,"finding":"All three SV2 isoforms (SV2A, SV2B, SV2C) bind synaptotagmin via a common calcium-inhibited site; additionally, SV2A and SV2C (but not SV2B) possess a second N-terminal synaptotagmin-binding site that is calcium-stimulated; the N-terminal 57 amino acids of SV2A mediate this additional interaction; introduction of the SV2A or SV2C amino terminus into superior cervical ganglion neurons inhibited neurotransmission, whereas SV2B amino terminus did not.","method":"Co-immunoprecipitation of native SV2 isoforms, recombinant protein binding assays, domain mapping, microinjection of N-terminal peptides into neurons with electrophysiological readout","journal":"Molecular and cellular neurosciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including functional neuronal assay, domain mapping, and native binding studies","pmids":["15866046"],"is_preprint":false},{"year":2006,"finding":"SV2 (isoforms A, B, and C) is the protein receptor for botulinum neurotoxin A (BoNT/A): BoNT/A binding to neurons is abolished in SV2A/SV2B double-knockout hippocampal neurons and rescued by expressing any SV2 isoform; SV2 fragments containing the toxin interaction domain inhibit BoNT/A neuronal binding; reduction of SV2 in PC12 and Neuro-2a cells inhibits BoNT/A entry.","method":"SV2A/B knockout neurons, viral rescue experiments, SV2 fragment competition assay, siRNA knockdown in cell lines","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (KO neurons, rescue, competition, knockdown), in vivo sensitivity data, highly cited","pmids":["16543415"],"is_preprint":false},{"year":2008,"finding":"SV2A adopts two major in situ conformations visualized by Protein Tomography: a compact funnel-structure with a pore-like opening toward the cytoplasm and a more open V-shaped structure with a cleft opening toward the intravesicular space, consistent with a transporter valve-like mechanism; levetiracetam binding does not cause a large-scale conformational change or lock a specific state.","method":"Protein Tomography (electron microscopy-based) of mouse brain tissue, comparison of LEV-treated vs. saline-treated samples","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — first structural data on SV2A, single lab, novel method (Protein Tomography), no mutagenesis validation","pmids":["18692481"],"is_preprint":false},{"year":2008,"finding":"N-glycosylation of SV2A is required for BoNT/E entry into neurons: a point mutation disrupting an N-glycosylation site in the fourth luminal domain of SV2A (N573Q) abolishes BoNT/E entry and reduces BoNT/A entry; glycosylated SV2A/SV2B (but not SV2C) serve as protein receptors for BoNT/E; gangliosides are also essential for BoNT/E binding.","method":"SV2A/B knockout neurons, viral rescue with wild-type or N573Q mutant SV2A, chimeric receptor strategy, exogenous ganglioside rescue","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutagenesis, KO rescue, chimeric receptor, multiple orthogonal approaches in single study","pmids":["18815274"],"is_preprint":false},{"year":2009,"finding":"SV2 deletion impairs a step that renders primed vesicles Ca2+-responsive, rather than affecting mini frequency, mini amplitude, RRP size, or apparent Ca2+ sensitivity of fusion; conserved charged residues in transmembrane regions and intravesicular glycosylation are required for normal SV2A folding/trafficking; the putative synaptotagmin-binding sequence of SV2 is dispensable for this function.","method":"Electrophysiology in SV2-deleted hippocampal neurons, rescue experiments with transmembrane domain and glycosylation mutants","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic mutagenesis rescue experiments combined with rigorous electrophysiology defining exact step of impairment","pmids":["19176798"],"is_preprint":false},{"year":2009,"finding":"BoNT/F uses all three SV2 isoforms (SV2A, SV2B, SV2C) as protein receptors, as demonstrated by co-precipitation of SV2A, B, and C from Triton-solubilized synaptic vesicles by BoNT/F, competition with recombinant binding fragments, and activity in the phrenic nerve hemidiaphragm assay; gangliosides are also required.","method":"Co-precipitation from solubilized synaptic vesicles, phrenic nerve hemidiaphragm assay, site-directed mutagenesis of ganglioside-binding site, cross-competition assays","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — co-precipitation combined with mutagenesis and functional nerve assay, single lab","pmids":["19650874"],"is_preprint":false},{"year":2009,"finding":"BoNT/F binds synaptic vesicle glycoproteins through the keratan sulfate moiety of SV2; crystal structure of HCR/F reveals two regions implicated in neuronal binding distinct from BoNT/A; HCR/F binds gangliosides containing α2,3-linked sialic acid (GD1a ≥ GT1b); mutations in the ganglioside binding pocket reduce binding to both gangliosides and SV2.","method":"X-ray crystallography of receptor-binding domain, solid phase glycan array, affinity chromatography, deglycosylation experiments, site-directed mutagenesis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with mutagenesis and biochemical binding assays, single lab","pmids":["19476346"],"is_preprint":false},{"year":2010,"finding":"SV2 mediates entry of tetanus neurotoxin into central neurons: toxin entry is dependent on synaptic vesicle recycling; tetanus neurotoxin cannot cleave its substrate synaptobrevin II in SV2-knockout neurons; entry is rescued by SV2A or SV2B expression; SV2A is preferentially localized to inhibitory terminals while SV2B is more localized to excitatory terminals in cortex.","method":"SV2 knockout neurons, viral rescue with SV2A or SV2B, synaptobrevin II cleavage assay, immunofluorescence co-localization","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO with functional rescue, substrate cleavage assay as molecular readout, combined with localization data","pmids":["21124874"],"is_preprint":false},{"year":2010,"finding":"SV2 regulates synaptic transmission via a tyrosine-based endocytosis motif (Y46 in SV2A's cytoplasmic N-terminus) that is required for trafficking to synaptic vesicles: SV2A-Y46A mutant shows increased plasma membrane localization, fails to rescue neurotransmission, and binds clathrin adaptors AP2, EPS15, and amphiphysin 2/Bin1; SV2 also regulates synaptotagmin expression and trafficking (via a separate mechanism), and SV2A/B double-knockout vesicles contain less synaptotagmin.","method":"Site-directed mutagenesis (Y46A), electrophysiology in SV2-null neurons, in vitro binding assays for adaptor proteins, immunoisolation of synaptic vesicles from SV2A/B double KO mice","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutagenesis, in vitro binding, electrophysiology, and KO vesicle immunoisolation as orthogonal approaches in single study","pmids":["20410110"],"is_preprint":false},{"year":2010,"finding":"SV2 acts via presynaptic calcium regulation: loss of SV2B in retinal bipolar neurons elevates both resting and evoked presynaptic Ca2+ signals; this Ca2+ elevation is causally responsible for the altered synaptic vesicle dynamics, plasticity, and strength observed in SV2B-null synapses, as demonstrated by short-term reproduction of the Ca2+ phenotype in wild-type terminals and rescue of the Ca2+ phenotype in SV2B-null neurons.","method":"Direct presynaptic Ca2+ measurement (calcium imaging) in SV2B-knockout retinal bipolar terminals, pharmacological manipulation to reproduce/rescue Ca2+ phenotype","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct Ca2+ measurements with causal manipulation (reproduction and rescue), multiple functional readouts","pmids":["20620874"],"is_preprint":false},{"year":2010,"finding":"SV2A performs at least two mechanistically distinct functions: (1) regulating synaptotagmin expression and trafficking (dependent on the N-terminal endocytosis motif), and (2) supporting neurotransmitter release via conserved tryptophans in the 5th (W300) and 10th (W666) transmembrane domains, which are required for rescuing synaptic depression independently of synaptotagmin regulation.","method":"Site-directed mutagenesis of SV2A (R231Q, W300A, W666A), electrophysiology (synaptic depression assay) in SV2A/B double KO neurons, synaptotagmin expression and trafficking measurements","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — systematic mutagenesis with multiple functional readouts, dissection of two independent mechanisms","pmids":["20702688"],"is_preprint":false},{"year":2011,"finding":"BoNT/D uses SV2 (all three isoforms, SV2A/B/C) as its protein receptor, entering neurons via synaptic vesicle recycling: BoNT/D binds SV2 in brain detergent extracts, fails to enter SV2-null neurons, is rescued by any SV2 isoform, and plasma membrane-localized SV2 is sufficient for BoNT/D binding in HEK293 cells; BoNT/D binds SV2 via a mechanism distinct from BoNT/A and BoNT/E.","method":"SV2-knockout neurons, viral rescue with SV2A/B/C, co-immunoprecipitation from brain detergent extracts, HEK293 cell binding assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO rescue with all isoforms, multiple cell systems, biochemical binding confirmation","pmids":["21483489"],"is_preprint":false},{"year":2011,"finding":"Levetiracetam binding to SV2A reverses the synaptic effects of SV2A overexpression: excess SV2A (~1.5-fold increase) reduces synaptic release probability and increases synaptotagmin levels at synapses; LEV treatment restores normal neurotransmission and normalizes SV2A and synaptotagmin levels.","method":"SV2A-EGFP overexpression in autaptic hippocampal neurons, electrophysiology, immunostaining, levetiracetam treatment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology with pharmacological rescue and protein level measurements, single lab","pmids":["22220214"],"is_preprint":false},{"year":2012,"finding":"N-glycans on SV2A are only partially dispensable for synaptic localization and function, in contrast to synaptophysin where N-glycosylation is essential; glycosylation is completely dispensable for synaptotagmin 1 sorting to SVs.","method":"Mutagenesis of all N-glycosylation sites on SV2A, pHluorin-tagged proteins in cultured neurons from KO mice, optical imaging","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic glycosylation mutagenesis with functional imaging readout, single lab","pmids":["22908222"],"is_preprint":false},{"year":2013,"finding":"The SV2-binding interface of BoNT/E was identified: mutations at a site corresponding to the synaptotagmin-binding site of BoNT/B and at an extended surface area near the ganglioside-binding site impair SV2 binding, reduce neurotoxicity in the phrenic nerve hemidiaphragm assay, and a neutralizing antibody blocks BoNT/E by directly interfering with the BoNT/E-SV2 interaction.","method":"Site-directed mutagenesis of BoNT/E binding domain, binding assays, phrenic nerve hemidiaphragm functional assay, antibody neutralization assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — mutagenesis with functional validation in ex vivo physiological model and antibody interference assay","pmids":["23621114"],"is_preprint":false},{"year":2013,"finding":"SV2A can be modulated allosterically: the compound UCB1244283 acts as a positive allosteric modulator of the [3H]UCB30889 binding site on SV2A, increasing affinity 5-fold and total binding sites 2-fold on both recombinant human SV2A and rat cortex, and slowing association/dissociation kinetics; this allosteric modulation also confers in vivo anticonvulsant protection.","method":"Saturation binding and kinetic radioligand binding assays on recombinant SV2A (HEK cells) and rat cortex, in vivo audiogenic seizure mouse model","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple binding assay formats with in vivo functional correlation, single lab","pmids":["23530581"],"is_preprint":false},{"year":2014,"finding":"SV2A functions as a galactose transporter: human SV2A expressed in hexose transport-deficient yeast (EBY.VW4000) enables growth on galactose but not other carbon sources; direct galactose uptake measurements confirm transport; levetiracetam inhibits galactose-dependent growth of these cells.","method":"Heterologous expression in transport-deficient yeast, growth assays on different carbon sources, direct galactose uptake measurement, pharmacological inhibition by LEV","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — functional transport assay with direct uptake measurement in heterologous system and pharmacological validation, single lab","pmids":["25326386"],"is_preprint":false},{"year":2015,"finding":"Residue D670 of SV2A is critical for levetiracetam analogue binding: mutation of D670 leads to complete loss of radioligand binding, as predicted by homology modelling and molecular dynamics simulations of inward- and outward-facing MFS conformational states.","method":"Homology modelling, molecular dynamics, docking, site-directed mutagenesis, radioligand binding assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — computational prediction validated by experimental mutagenesis and radioligand binding, single lab","pmids":["25692762"],"is_preprint":false},{"year":2015,"finding":"SV2A/B and stonin 2 have overlapping functions in endocytic sorting of synaptotagmin 1 (Syt1) to synaptic vesicles: deletion or knockdown of either SV2A/B or stonin 2 causes partial Syt1 loss and missorting to the neuronal surface; deletion of both dramatically exacerbates Syt1 missorting and degradation, impairing neurotransmission efficacy.","method":"Genetic deletion of SV2A/B and stonin 2, knockdown, Syt1 immunostaining/surface labeling, electrophysiology in hippocampal synapses","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — double-deletion epistasis, multiple readouts (protein levels, surface localization, electrophysiology), demonstrates genetic interaction","pmids":["26015569"],"is_preprint":false},{"year":2016,"finding":"N-linked glycosylation of SV2C (conserved across all SV2 isoforms and vertebrate species) is essential for BoNT/A1 binding to neurons and for potent neurotoxicity: the 2.0-Å crystal structure of BoNT/A1 receptor-binding domain in complex with glycosylated human SV2C reveals that neuronal tropism requires recognition of both the SV2C peptide moiety and an N-linked glycan on SV2.","method":"X-ray crystallography (2.0 Å resolution) of BoNT/A1 receptor-binding domain:glycosylated human SV2C complex, mutagenesis of glycosylation site, neuronal binding and toxicity assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure at high resolution combined with mutagenesis and functional validation of toxin binding and neurotoxicity","pmids":["27294781"],"is_preprint":false},{"year":2016,"finding":"BoNT/A binds SV2C-LD4 with a binding constant of ~200 nM; binding affinity decreases from SV2C >> SV2A > SV2B; at pH 5 (acidic synaptic vesicles), binding affinity increases >10-fold; the SV2C luminal domain 4 forms a quadrilateral β-sheet helix that pre-exists in solution prior to BoNT/A binding, constituting a different binding mechanism from BoNT/B-synaptotagmin.","method":"GST pull-down assays, surface plasmon resonance, circular dichroism spectroscopy, pH-dependent binding assays","journal":"Toxins","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple biophysical methods (SPR, CD, pull-down), quantitative binding constants, single lab","pmids":["27196927"],"is_preprint":false},{"year":2016,"finding":"SV2A dysfunction due to missense mutation L174Q selectively reduces depolarization-induced GABA (but not glutamate) release in the hippocampus and specifically reduces synaptotagmin 1 levels among exocytosis-related proteins, facilitating kindling epileptogenesis.","method":"Rat Sv2a L174Q missense knock-in model, neurochemical measurements of GABA/glutamate release, Western blot for exocytosis proteins, amygdala kindling assay","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo missense knock-in model, neurotransmitter release measurements, protein quantification, and epileptogenesis behavioral assay","pmids":["27265781"],"is_preprint":false},{"year":2020,"finding":"SV2A coordinates distinct synaptic vesicle recycling properties between inhibitory and excitatory nerve terminals: SV2A is more highly expressed in inhibitory synapses and its preferential presence controls slower vesicle recycling in inhibitory terminals (~1.8-fold slower than excitatory) by differentially regulating sorting of synaptotagmin I.","method":"pHluorin-conjugated SV2 tracers preferentially expressed in excitatory or inhibitory terminals, fluorescence imaging of vesicle recycling kinetics, comparison across terminal types","journal":"Progress in neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional vesicle recycling assay with synapse-type-selective tracers, single lab","pmids":["32615146"],"is_preprint":false},{"year":2020,"finding":"The epilepsy-associated human SV2A mutation R383Q causes mislocalization of SV2A from synaptic vesicles to the plasma membrane, reduces mobility at the plasma membrane, reduces binding to synaptotagmin-1 (Syt1), and fails to rescue reduced Syt1 expression and dysfunctional activity-dependent Syt1 trafficking in SV2A-depleted neurons.","method":"Molecular replacement strategy in SV2A-depleted mouse neurons, live-cell imaging of plasma membrane vs. vesicular localization, FRAP, co-immunoprecipitation for Syt1 binding, Syt1 trafficking assays","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization imaging, FRAP, binding assay, trafficking assay) with disease-relevant mutation in KO background","pmids":["32341095"],"is_preprint":false},{"year":2020,"finding":"Poly-glycine-alanine (GA) dipeptide aggregates from C9orf72 ALS/FTD reduce SV2A levels in motor neurons, alter Ca2+ influx, and impair synaptic vesicle release; restoring SV2A levels rescues these synaptic phenotypes.","method":"GA mouse model and patient iPSC-derived neurons, SV2A protein quantification, Ca2+ imaging, synaptic vesicle release assays, SV2A rescue experiments","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — SV2A rescue experiment in disease model with functional readouts, single lab with multiple methods","pmids":["32347002"],"is_preprint":false},{"year":2023,"finding":"BoNT/A endocytosis into synaptic vesicles requires coincident binding to both polysialoganglioside (PSG) and SV2 on the neuronal plasma membrane; BoNT/A simultaneously interacts with a preassembled PSG-synaptotagmin-1 (Syt1) complex and SV2, facilitating Syt1-SV2 nanoclustering that controls endocytic sorting into SVs; Syt1 knockdown suppresses BoNT/A and BoNT/E intoxication.","method":"Live-cell super-resolution imaging, electron microscopy, catalytically inactivated BoNT/A and receptor-binding-deficient mutants in hippocampal neurons, Syt1 CRISPRi knockdown, SNAP-25 cleavage assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — super-resolution live imaging combined with EM, mutagenesis of receptor-binding sites, CRISPRi, and functional toxin activity assay in single study","pmids":["37226896"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of full-length SV2A in complex with BoNT/A2 receptor-binding domain and either levetiracetam or brivaracetam reveal: (1) the large fourth luminal domain of SV2A binds BoNT/A2 HC through protein-protein and protein-glycan interactions; (2) LEV and BRV occupy the putative substrate-binding site in an outward-open conformation; (3) a propyl group in BRV creates additional contacts with SV2A explaining its higher binding affinity than LEV.","method":"Cryo-electron microscopy of full-length SV2A complexes, label-free spectral shift assay for binding affinity","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure of full-length protein with ligands and binding partner, functional validation by binding assay, structural basis for affinity difference","pmids":["38637505"],"is_preprint":false},{"year":1996,"finding":"SV2 is localized on the membranes of both synaptic vesicle clusters and large dense-cored vesicles (LDCV) in NGF-treated PC12 cells, with a higher SV2:synaptophysin ratio on LDCV (~9:1) compared to synaptic vesicle clusters (~1:1); chromogranin A occupies the LDCV core while SV2 is on the membrane.","method":"Pre-embedding EM immunocytochemistry with silver-enhanced gold probe, quantitative comparison on identified organelle types","journal":"The journal of histochemistry and cytochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct ultrastructural localization with quantification, single lab","pmids":["8985140"],"is_preprint":false},{"year":2000,"finding":"SV2 (synaptic vesicle transmembrane proteoglycan) is complexed with an α5-chain-containing laminin on the presynaptic plasma membrane: SV2 co-purifies with a 900-kDa laminin from synaptosomes of electric organ synapses, and purified SV2 binds laminin-1 with high affinity in direct binding assays.","method":"Synaptosome preparation, co-immunoprecipitation/co-purification of SV2-laminin complex, direct binding assay with purified SV2 and laminin-1","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay with purified proteins combined with co-purification from native synaptosomes, single lab","pmids":["10617638"],"is_preprint":false},{"year":2020,"finding":"SV2A is expressed in mitochondria (in addition to synaptic vesicles), as demonstrated by immunohistochemistry and proteomics; levetiracetam effects on mitochondrial function (fission/fusion balance, permeability transition pore) are significantly abolished when SV2A is knocked down by siRNA.","method":"Immunohistochemistry, proteomics, siRNA knockdown of SV2A, mitochondrial functional assays (fission/fusion, mPTP opening)","journal":"Journal of Alzheimer's disease","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mitochondrial localization by IHC and proteomics, functional link via siRNA rescue in a single cell model study; unusual finding requiring independent replication","pmids":["26639968"],"is_preprint":false},{"year":2020,"finding":"miR-133a and miR-218 directly target SV2A: luciferase reporter assay showed these miRNAs significantly decreased relative luciferase activity from an SV2A dual-luciferase construct; transfection of miR-133a and miR-218 in human neuroblastoma cells reduced endogenous SV2A mRNA and protein levels.","method":"Luciferase reporter assay, miRNA transfection in human neuroblastoma cells, qRT-PCR, Western blot","journal":"Translational psychiatry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter (direct test of 3'UTR targeting) plus endogenous mRNA and protein reduction, single lab with two orthogonal methods","pmids":["32839459"],"is_preprint":false}],"current_model":"SV2A is a 12-transmembrane-domain glycoprotein of the major facilitator superfamily localized to synaptic vesicle membranes in all neurons and endocrine cells, where it functions as a galactose transporter (demonstrated in yeast), maintains a Ca2+-responsive pool of primed vesicles by rendering them competent for Ca2+-triggered fusion, regulates presynaptic Ca2+ levels, controls synaptic vesicle recycling kinetics preferentially at inhibitory synapses, and traffics/stabilizes the Ca2+-sensor synaptotagmin 1 at vesicles via a tyrosine-based endocytosis motif that recruits clathrin adaptors (AP2, EPS15, amphiphysin 2); SV2A directly binds synaptotagmin 1 in a calcium-inhibited, isoform-specific manner through its N-terminal cytoplasmic domain (C2B interaction), and its large fourth luminal domain—bearing a conserved N-linked glycan—serves as the protein receptor for botulinum neurotoxins A, D, E, and F (and tetanus toxin) as well as the binding site for antiepileptic drugs levetiracetam and brivaracetam, whose cryo-EM structures show occupancy of the outward-open substrate-binding cavity with brivaracetam's propyl group explaining its higher affinity."},"narrative":{"mechanistic_narrative":"SV2A is a synaptic vesicle membrane glycoprotein with the 12-transmembrane topology and sequence homology of the major facilitator superfamily, originally identified as a putative vesicular transporter [PMID:1519064, PMID:1355409] and expressed ubiquitously at brain synapses [PMID:8083732]. Functionally, SV2A is required for action potential-dependent neurotransmission—its genetic loss in mice produces fatal seizures with selectively impaired GABAergic transmission [PMID:10611374]—and it acts by maintaining a Ca2+-responsive pool of release-competent (primed) vesicles rather than by setting mini frequency/amplitude or apparent Ca2+ sensitivity [PMID:11483953, PMID:19176798]. A central molecular function is the trafficking and stabilization of the Ca2+ sensor synaptotagmin 1: SV2A directly binds synaptotagmin through its cytoplasmic N-terminus in a calcium-inhibited, isoform-specific manner [PMID:8910372], and a tyrosine-based endocytosis motif (Y46) recruits clathrin adaptors AP2, EPS15, and amphiphysin 2/Bin1 to sort both SV2A and synaptotagmin 1 to vesicles [PMID:20410110], a sorting function it shares redundantly with stonin 2 [PMID:26015569]. Through these activities SV2A also governs presynaptic Ca2+ levels [PMID:20620874] and sets slower vesicle recycling kinetics preferentially at inhibitory terminals where it is enriched [PMID:32615146]. Its large fourth luminal domain, bearing a conserved N-linked glycan, serves as the neuronal protein receptor for botulinum neurotoxins A, D, E, and F and tetanus toxin, with toxin entry requiring both the SV2 peptide/glycan and coincident ganglioside binding [PMID:16543415, PMID:18815274, PMID:21124874, PMID:27294781]. The same luminal architecture and an outward-open substrate-binding cavity form the binding site for the antiepileptic drugs levetiracetam and brivaracetam, as defined by knockout, mutagenesis, and cryo-EM of full-length SV2A [PMID:15210974, PMID:25692762, PMID:38637505]. Disease-associated SV2A missense mutations (L174Q, R383Q) mislocalize the protein, reduce synaptotagmin 1 binding/levels, and impair GABAergic release, linking SV2A dysfunction to epileptogenesis [PMID:27265781, PMID:32341095].","teleology":[{"year":1992,"claim":"Established the structural identity of SV2A as a 12-TM MFS-homologous protein, framing the long-standing hypothesis that it is a vesicular transporter.","evidence":"cDNA cloning, topology prediction, and heterologous expression in COS cells","pmids":["1519064","1355409"],"confidence":"High","gaps":["Sequence homology did not demonstrate any transport substrate or activity","No functional assay of the predicted transport"]},{"year":1996,"claim":"Identified a direct, calcium-regulated, isoform-specific physical link between SV2A and the Ca2+ sensor synaptotagmin, suggesting SV2A couples to the fusion machinery.","evidence":"Cross-linking, co-IP, and recombinant affinity chromatography with domain mapping","pmids":["8910372"],"confidence":"High","gaps":["Did not establish whether the interaction is required for release in vivo","Functional consequence of calcium-regulated dissociation untested at this stage"]},{"year":1999,"claim":"Demonstrated that SV2A is essential for action potential-dependent (especially GABAergic) neurotransmission, moving it from a structural curiosity to a release-controlling protein.","evidence":"SV2A knockout mouse with IPSC electrophysiology and EM of synapse ultrastructure","pmids":["10611374"],"confidence":"High","gaps":["Did not pinpoint which step of the release cycle is impaired","Molecular basis of the GABAergic selectivity unresolved"]},{"year":2001,"claim":"Localized SV2A's function to maintenance of the readily releasable/primed vesicle pool for Ca2+-stimulated exocytosis, with effects on SNARE complex assembly.","evidence":"Capacitance exocytosis measurements in KO chromaffin cells and SDS-resistant SNARE complex analysis","pmids":["11483953"],"confidence":"High","gaps":["Mechanism linking SV2A to SNARE complex stability not defined","Whether the defect is upstream or downstream of priming unclear at this point"]},{"year":2009,"claim":"Refined the functional defect to a step that renders primed vesicles Ca2+-responsive, and showed transmembrane residues and luminal glycosylation are needed for SV2A folding/trafficking while the putative synaptotagmin-binding sequence is dispensable for this function.","evidence":"Electrophysiology with systematic TM-domain and glycosylation rescue mutants in SV2-null neurons","pmids":["19176798"],"confidence":"High","gaps":["Did not reconcile dispensability of the synaptotagmin-binding sequence with later synaptotagmin trafficking roles","Identity of any transported substrate still unknown"]},{"year":2010,"claim":"Defined SV2A's trafficking mechanism via a tyrosine-based endocytosis motif recruiting clathrin adaptors and its role in synaptotagmin expression/trafficking, separating distinct functional modules.","evidence":"Y46A mutagenesis, adaptor binding assays, electrophysiology, and KO vesicle immunoisolation; additional TM tryptophan mutant analysis","pmids":["20410110","20702688"],"confidence":"High","gaps":["Mechanistic separation of synaptotagmin regulation versus release support incompletely defined","How TM tryptophans support release independently of synaptotagmin unresolved"]},{"year":2010,"claim":"Showed SV2 acts through presynaptic Ca2+ regulation, with elevated resting/evoked Ca2+ causally responsible for altered vesicle dynamics in SV2-null terminals.","evidence":"Direct presynaptic Ca2+ imaging in SV2B-KO retinal bipolar terminals with pharmacological reproduction and rescue","pmids":["20620874"],"confidence":"High","gaps":["Molecular target through which SV2 controls presynaptic Ca2+ not identified","Generality across SV2A-dominated synapses not tested here"]},{"year":2015,"claim":"Established that SV2A/B and stonin 2 act redundantly in endocytic sorting of synaptotagmin 1 to synaptic vesicles, explaining synaptotagmin loss and missorting upon SV2 deletion.","evidence":"Double genetic deletion epistasis with surface labeling and electrophysiology","pmids":["26015569"],"confidence":"High","gaps":["Precise biochemical step at which SV2A and stonin 2 converge unresolved","Quantitative contribution of each pathway not separated"]},{"year":2006,"claim":"Identified SV2 as the neuronal protein receptor for botulinum neurotoxin A, defining a non-synaptic-vesicle function exploited by toxins.","evidence":"SV2A/B KO neurons, isoform rescue, fragment competition, and siRNA knockdown","pmids":["16543415"],"confidence":"High","gaps":["Did not resolve the structural determinants of toxin recognition","Relative contributions of peptide versus glycan undefined at this stage"]},{"year":2016,"claim":"Provided the structural basis for toxin recognition, showing BoNT/A requires both the SV2 luminal-domain peptide and its conserved N-linked glycan, and quantified isoform/pH-dependent affinity.","evidence":"2.0-Å crystal structure of BoNT/A1 RBD with glycosylated SV2C plus SPR/CD biophysics and glycosylation mutagenesis","pmids":["27294781","27196927","18815274","21124874","21483489","19650874","19476346","23621114"],"confidence":"High","gaps":["Structures were of toxin-binding fragments rather than full-length SV2A in early studies","Endogenous vesicular function of the luminal domain distinct from toxin binding not addressed"]},{"year":2023,"claim":"Showed BoNT/A endocytosis requires coincident binding to polysialoganglioside and SV2 and exploits a preassembled ganglioside–synaptotagmin-1 complex to drive Syt1-SV2 nanoclustering for endocytic sorting.","evidence":"Live-cell super-resolution imaging, EM, receptor-binding mutants, Syt1 CRISPRi, and SNAP-25 cleavage assays","pmids":["37226896"],"confidence":"High","gaps":["Stoichiometry of the multi-receptor assembly not fully defined","Whether nanoclustering reflects a physiological sorting mechanism beyond toxin entry untested"]},{"year":2014,"claim":"Provided the first direct evidence of a transport substrate, showing human SV2A confers galactose uptake in transport-deficient yeast and that levetiracetam inhibits this activity.","evidence":"Heterologous expression in hexose-transport-deficient yeast with direct galactose uptake measurement and LEV inhibition","pmids":["25326386"],"confidence":"Medium","gaps":["Galactose transport not demonstrated in native neurons","Physiological relevance of galactose as a vesicular substrate unestablished"]},{"year":2024,"claim":"Resolved the structural basis of antiepileptic drug binding, showing levetiracetam and brivaracetam occupy the outward-open substrate cavity of full-length SV2A and explaining brivaracetam's higher affinity.","evidence":"Cryo-EM of full-length SV2A with BoNT/A2 RBD and LEV or BRV, plus spectral-shift binding affinity; supported by earlier D670 mutagenesis and LEV-binding-site studies","pmids":["38637505","15210974","25692762","23530581","22220214"],"confidence":"High","gaps":["Conformational cycle linking drug occupancy to transport/synaptic function not captured","How drug binding modulates the physiological vesicle-priming role mechanistically unresolved"]},{"year":2020,"claim":"Connected SV2A dysfunction to epilepsy and broader disease, with human/rat missense mutations causing mislocalization and reduced synaptotagmin 1 binding, and SV2A loss contributing to C9orf72 ALS/FTD synaptic deficits.","evidence":"Disease-mutation knock-in/replacement models with imaging, FRAP, binding and trafficking assays, plus GA-dipeptide disease models with SV2A rescue","pmids":["32341095","27265781","32347002"],"confidence":"High","gaps":["Whether mislocalization phenotypes generalize across all epilepsy-associated variants unknown","Mechanism linking SV2A loss to C9orf72 pathology not fully defined"]},{"year":null,"claim":"The endogenous transport substrate, transport cycle, and how transporter conformational states couple to vesicle priming and drug action in native neurons remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No demonstrated physiological transport activity in neurons","Coupling of MFS conformational cycle to Ca2+-responsive priming undefined","Mechanistic basis of GABAergic/inhibitory-synapse selectivity incompletely explained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,23]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[8,10,14,18,26]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[15,25]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,5,11,16]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,2,5,34]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[15,30,35]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[4,5,11,16]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[15,25,29]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,28,30]}],"complexes":[],"partners":["SYT1","STON2","AP2","EPS15","BIN1","LAMA5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q7L0J3","full_name":"Synaptic vesicle glycoprotein 2A","aliases":[],"length_aa":742,"mass_kda":82.7,"function":"Plays a role in the control of regulated secretion in neural and endocrine cells, enhancing selectively low-frequency neurotransmission. Positively regulates vesicle fusion by maintaining the readily releasable pool of secretory vesicles (By similarity) (Microbial infection) Receptor for the C.botulinum neurotoxin type A2 (BoNT/A, botA); glycosylation is not essential but enhances the interaction (PubMed:29649119). Probably also serves as a receptor for the closely related C.botulinum neurotoxin type A1","subcellular_location":"Presynapse; Cytoplasmic vesicle, secretory vesicle, synaptic vesicle membrane","url":"https://www.uniprot.org/uniprotkb/Q7L0J3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SV2A","classification":"Not Classified","n_dependent_lines":82,"n_total_lines":1208,"dependency_fraction":0.06788079470198675},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SV2A","total_profiled":1310},"omim":[{"mim_id":"620772","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 113; DEE113","url":"https://www.omim.org/entry/620772"},{"mim_id":"611606","title":"MICRO RNA 96; MIR96","url":"https://www.omim.org/entry/611606"},{"mim_id":"610291","title":"SYNAPTIC VESICLE GLYCOPROTEIN 2C; SV2C","url":"https://www.omim.org/entry/610291"},{"mim_id":"601033","title":"LAMININ, ALPHA-5; LAMA5","url":"https://www.omim.org/entry/601033"},{"mim_id":"600354","title":"SURVIVAL OF MOTOR NEURON 1; SMN1","url":"https://www.omim.org/entry/600354"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":114.9},{"tissue":"parathyroid gland","ntpm":45.5}],"url":"https://www.proteinatlas.org/search/SV2A"},"hgnc":{"alias_symbol":["SV2","KIAA0736","SLC22B1"],"prev_symbol":[]},"alphafold":{"accession":"Q7L0J3","domains":[{"cath_id":"1.20.1250.20","chopping":"145-400","consensus_level":"medium","plddt":85.7611,"start":145,"end":400},{"cath_id":"2.160.20.80","chopping":"484-576","consensus_level":"medium","plddt":89.5974,"start":484,"end":576}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q7L0J3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q7L0J3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q7L0J3-F1-predicted_aligned_error_v6.png","plddt_mean":76.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SV2A","jax_strain_url":"https://www.jax.org/strain/search?query=SV2A"},"sequence":{"accession":"Q7L0J3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q7L0J3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q7L0J3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q7L0J3"}},"corpus_meta":[{"pmid":"15210974","id":"PMC_15210974","title":"The 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\"method\": \"cDNA cloning, sequence analysis, topology prediction, and heterologous expression in COS cells\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independently reported by two labs in same year using cDNA cloning and sequence analysis, foundational structural characterization replicated\",\n      \"pmids\": [\"1519064\", \"1355409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"SV2 is a keratan sulfate proteoglycan on synaptic vesicles, existing in two electrophoretic forms (L form ~100 kDa and H form ~250 kDa), both containing the SV2 epitope on the cytoplasmic side of the vesicle membrane.\",\n      \"method\": \"Biochemical fractionation of synaptic vesicles, SDS-PAGE, immunoblotting, proteoglycan characterization\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical characterization of purified synaptic vesicles, single lab with multiple methods\",\n      \"pmids\": [\"7685814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SV2A is expressed ubiquitously throughout the brain at all synapses, and immunoprecipitation of brain synaptic vesicles with isoform-specific antibodies showed that both SV2A and SV2B isoforms can be present on the same synaptic vesicle.\",\n      \"method\": \"In situ hybridization, immunohistochemistry, isoform-specific immunoprecipitation followed by Western blot\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal immunoprecipitation with isoform-specific antibodies, multiple orthogonal methods in one study\",\n      \"pmids\": [\"8083732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"SV2A directly binds synaptotagmin in a calcium-regulated, isoform-specific manner: SV2A (but not SV2B) interacts with the C2B domain of synaptotagmin via SV2A's cytoplasmic amino terminus, and this interaction is inhibited by calcium with an EC50 of ~10 µM.\",\n      \"method\": \"Cross-linking, co-immunoprecipitation, recombinant protein affinity chromatography\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal binding methods (cross-linking, co-IP, affinity chromatography), domain mapping, calcium-regulation quantified\",\n      \"pmids\": [\"8910372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SV2A is essential for action potential-dependent GABAergic neurotransmission: SV2A knockout mice develop severe seizures and die within 3 weeks; electrophysiology of CA3 hippocampal neurons showed reduced action potential-dependent (but normal action potential-independent) GABAergic transmission, without changes in synapse density or morphology.\",\n      \"method\": \"Targeted gene disruption (knockout mouse), electrophysiology of spontaneous IPSCs, electron microscopy of synapse ultrastructure\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype, multiple orthogonal readouts, foundational loss-of-function study\",\n      \"pmids\": [\"10611374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SV2A is required to maintain the readily releasable pool (RRP) of vesicles for calcium-stimulated exocytosis: direct capacitance measurements in SV2A-knockout adrenal chromaffin cells showed a significantly reduced calcium-induced exocytotic burst (defining the RRP) with normal burst kinetics, and brain tissue from SV2A knockouts had fewer SDS-resistant SNARE complexes.\",\n      \"method\": \"Capacitance measurements (direct exocytosis assay) in chromaffin cells, SDS-resistant SNARE complex analysis by Western blot\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct electrophysiological measure of exocytosis combined with biochemical SNARE complex analysis, single lab with two orthogonal methods\",\n      \"pmids\": [\"11483953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SV2A is the brain binding site for the antiepileptic drug levetiracetam: the LEV-binding site is enriched in synaptic vesicles (~90 kDa by photoaffinity labeling); brain membranes and vesicles from SV2A-knockout mice show no LEV-derivative binding; SV2A expressed in fibroblasts is sufficient for LEV binding; no binding occurs to SV2B or SV2C; binding affinity to SV2A correlates with seizure protection.\",\n      \"method\": \"Radioligand binding assays, photoaffinity labeling of purified synaptic vesicles, SV2A knockout mice, heterologous expression in fibroblasts\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (photoaffinity labeling, knockout, heterologous expression), structure-activity correlation, highly cited foundational study\",\n      \"pmids\": [\"15210974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"All three SV2 isoforms (SV2A, SV2B, SV2C) bind synaptotagmin via a common calcium-inhibited site; additionally, SV2A and SV2C (but not SV2B) possess a second N-terminal synaptotagmin-binding site that is calcium-stimulated; the N-terminal 57 amino acids of SV2A mediate this additional interaction; introduction of the SV2A or SV2C amino terminus into superior cervical ganglion neurons inhibited neurotransmission, whereas SV2B amino terminus did not.\",\n      \"method\": \"Co-immunoprecipitation of native SV2 isoforms, recombinant protein binding assays, domain mapping, microinjection of N-terminal peptides into neurons with electrophysiological readout\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including functional neuronal assay, domain mapping, and native binding studies\",\n      \"pmids\": [\"15866046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SV2 (isoforms A, B, and C) is the protein receptor for botulinum neurotoxin A (BoNT/A): BoNT/A binding to neurons is abolished in SV2A/SV2B double-knockout hippocampal neurons and rescued by expressing any SV2 isoform; SV2 fragments containing the toxin interaction domain inhibit BoNT/A neuronal binding; reduction of SV2 in PC12 and Neuro-2a cells inhibits BoNT/A entry.\",\n      \"method\": \"SV2A/B knockout neurons, viral rescue experiments, SV2 fragment competition assay, siRNA knockdown in cell lines\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (KO neurons, rescue, competition, knockdown), in vivo sensitivity data, highly cited\",\n      \"pmids\": [\"16543415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SV2A adopts two major in situ conformations visualized by Protein Tomography: a compact funnel-structure with a pore-like opening toward the cytoplasm and a more open V-shaped structure with a cleft opening toward the intravesicular space, consistent with a transporter valve-like mechanism; levetiracetam binding does not cause a large-scale conformational change or lock a specific state.\",\n      \"method\": \"Protein Tomography (electron microscopy-based) of mouse brain tissue, comparison of LEV-treated vs. saline-treated samples\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — first structural data on SV2A, single lab, novel method (Protein Tomography), no mutagenesis validation\",\n      \"pmids\": [\"18692481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"N-glycosylation of SV2A is required for BoNT/E entry into neurons: a point mutation disrupting an N-glycosylation site in the fourth luminal domain of SV2A (N573Q) abolishes BoNT/E entry and reduces BoNT/A entry; glycosylated SV2A/SV2B (but not SV2C) serve as protein receptors for BoNT/E; gangliosides are also essential for BoNT/E binding.\",\n      \"method\": \"SV2A/B knockout neurons, viral rescue with wild-type or N573Q mutant SV2A, chimeric receptor strategy, exogenous ganglioside rescue\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutagenesis, KO rescue, chimeric receptor, multiple orthogonal approaches in single study\",\n      \"pmids\": [\"18815274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SV2 deletion impairs a step that renders primed vesicles Ca2+-responsive, rather than affecting mini frequency, mini amplitude, RRP size, or apparent Ca2+ sensitivity of fusion; conserved charged residues in transmembrane regions and intravesicular glycosylation are required for normal SV2A folding/trafficking; the putative synaptotagmin-binding sequence of SV2 is dispensable for this function.\",\n      \"method\": \"Electrophysiology in SV2-deleted hippocampal neurons, rescue experiments with transmembrane domain and glycosylation mutants\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic mutagenesis rescue experiments combined with rigorous electrophysiology defining exact step of impairment\",\n      \"pmids\": [\"19176798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"BoNT/F uses all three SV2 isoforms (SV2A, SV2B, SV2C) as protein receptors, as demonstrated by co-precipitation of SV2A, B, and C from Triton-solubilized synaptic vesicles by BoNT/F, competition with recombinant binding fragments, and activity in the phrenic nerve hemidiaphragm assay; gangliosides are also required.\",\n      \"method\": \"Co-precipitation from solubilized synaptic vesicles, phrenic nerve hemidiaphragm assay, site-directed mutagenesis of ganglioside-binding site, cross-competition assays\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-precipitation combined with mutagenesis and functional nerve assay, single lab\",\n      \"pmids\": [\"19650874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"BoNT/F binds synaptic vesicle glycoproteins through the keratan sulfate moiety of SV2; crystal structure of HCR/F reveals two regions implicated in neuronal binding distinct from BoNT/A; HCR/F binds gangliosides containing α2,3-linked sialic acid (GD1a ≥ GT1b); mutations in the ganglioside binding pocket reduce binding to both gangliosides and SV2.\",\n      \"method\": \"X-ray crystallography of receptor-binding domain, solid phase glycan array, affinity chromatography, deglycosylation experiments, site-directed mutagenesis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with mutagenesis and biochemical binding assays, single lab\",\n      \"pmids\": [\"19476346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SV2 mediates entry of tetanus neurotoxin into central neurons: toxin entry is dependent on synaptic vesicle recycling; tetanus neurotoxin cannot cleave its substrate synaptobrevin II in SV2-knockout neurons; entry is rescued by SV2A or SV2B expression; SV2A is preferentially localized to inhibitory terminals while SV2B is more localized to excitatory terminals in cortex.\",\n      \"method\": \"SV2 knockout neurons, viral rescue with SV2A or SV2B, synaptobrevin II cleavage assay, immunofluorescence co-localization\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO with functional rescue, substrate cleavage assay as molecular readout, combined with localization data\",\n      \"pmids\": [\"21124874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SV2 regulates synaptic transmission via a tyrosine-based endocytosis motif (Y46 in SV2A's cytoplasmic N-terminus) that is required for trafficking to synaptic vesicles: SV2A-Y46A mutant shows increased plasma membrane localization, fails to rescue neurotransmission, and binds clathrin adaptors AP2, EPS15, and amphiphysin 2/Bin1; SV2 also regulates synaptotagmin expression and trafficking (via a separate mechanism), and SV2A/B double-knockout vesicles contain less synaptotagmin.\",\n      \"method\": \"Site-directed mutagenesis (Y46A), electrophysiology in SV2-null neurons, in vitro binding assays for adaptor proteins, immunoisolation of synaptic vesicles from SV2A/B double KO mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutagenesis, in vitro binding, electrophysiology, and KO vesicle immunoisolation as orthogonal approaches in single study\",\n      \"pmids\": [\"20410110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SV2 acts via presynaptic calcium regulation: loss of SV2B in retinal bipolar neurons elevates both resting and evoked presynaptic Ca2+ signals; this Ca2+ elevation is causally responsible for the altered synaptic vesicle dynamics, plasticity, and strength observed in SV2B-null synapses, as demonstrated by short-term reproduction of the Ca2+ phenotype in wild-type terminals and rescue of the Ca2+ phenotype in SV2B-null neurons.\",\n      \"method\": \"Direct presynaptic Ca2+ measurement (calcium imaging) in SV2B-knockout retinal bipolar terminals, pharmacological manipulation to reproduce/rescue Ca2+ phenotype\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct Ca2+ measurements with causal manipulation (reproduction and rescue), multiple functional readouts\",\n      \"pmids\": [\"20620874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SV2A performs at least two mechanistically distinct functions: (1) regulating synaptotagmin expression and trafficking (dependent on the N-terminal endocytosis motif), and (2) supporting neurotransmitter release via conserved tryptophans in the 5th (W300) and 10th (W666) transmembrane domains, which are required for rescuing synaptic depression independently of synaptotagmin regulation.\",\n      \"method\": \"Site-directed mutagenesis of SV2A (R231Q, W300A, W666A), electrophysiology (synaptic depression assay) in SV2A/B double KO neurons, synaptotagmin expression and trafficking measurements\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic mutagenesis with multiple functional readouts, dissection of two independent mechanisms\",\n      \"pmids\": [\"20702688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"BoNT/D uses SV2 (all three isoforms, SV2A/B/C) as its protein receptor, entering neurons via synaptic vesicle recycling: BoNT/D binds SV2 in brain detergent extracts, fails to enter SV2-null neurons, is rescued by any SV2 isoform, and plasma membrane-localized SV2 is sufficient for BoNT/D binding in HEK293 cells; BoNT/D binds SV2 via a mechanism distinct from BoNT/A and BoNT/E.\",\n      \"method\": \"SV2-knockout neurons, viral rescue with SV2A/B/C, co-immunoprecipitation from brain detergent extracts, HEK293 cell binding assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO rescue with all isoforms, multiple cell systems, biochemical binding confirmation\",\n      \"pmids\": [\"21483489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Levetiracetam binding to SV2A reverses the synaptic effects of SV2A overexpression: excess SV2A (~1.5-fold increase) reduces synaptic release probability and increases synaptotagmin levels at synapses; LEV treatment restores normal neurotransmission and normalizes SV2A and synaptotagmin levels.\",\n      \"method\": \"SV2A-EGFP overexpression in autaptic hippocampal neurons, electrophysiology, immunostaining, levetiracetam treatment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology with pharmacological rescue and protein level measurements, single lab\",\n      \"pmids\": [\"22220214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"N-glycans on SV2A are only partially dispensable for synaptic localization and function, in contrast to synaptophysin where N-glycosylation is essential; glycosylation is completely dispensable for synaptotagmin 1 sorting to SVs.\",\n      \"method\": \"Mutagenesis of all N-glycosylation sites on SV2A, pHluorin-tagged proteins in cultured neurons from KO mice, optical imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic glycosylation mutagenesis with functional imaging readout, single lab\",\n      \"pmids\": [\"22908222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The SV2-binding interface of BoNT/E was identified: mutations at a site corresponding to the synaptotagmin-binding site of BoNT/B and at an extended surface area near the ganglioside-binding site impair SV2 binding, reduce neurotoxicity in the phrenic nerve hemidiaphragm assay, and a neutralizing antibody blocks BoNT/E by directly interfering with the BoNT/E-SV2 interaction.\",\n      \"method\": \"Site-directed mutagenesis of BoNT/E binding domain, binding assays, phrenic nerve hemidiaphragm functional assay, antibody neutralization assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with functional validation in ex vivo physiological model and antibody interference assay\",\n      \"pmids\": [\"23621114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SV2A can be modulated allosterically: the compound UCB1244283 acts as a positive allosteric modulator of the [3H]UCB30889 binding site on SV2A, increasing affinity 5-fold and total binding sites 2-fold on both recombinant human SV2A and rat cortex, and slowing association/dissociation kinetics; this allosteric modulation also confers in vivo anticonvulsant protection.\",\n      \"method\": \"Saturation binding and kinetic radioligand binding assays on recombinant SV2A (HEK cells) and rat cortex, in vivo audiogenic seizure mouse model\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple binding assay formats with in vivo functional correlation, single lab\",\n      \"pmids\": [\"23530581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SV2A functions as a galactose transporter: human SV2A expressed in hexose transport-deficient yeast (EBY.VW4000) enables growth on galactose but not other carbon sources; direct galactose uptake measurements confirm transport; levetiracetam inhibits galactose-dependent growth of these cells.\",\n      \"method\": \"Heterologous expression in transport-deficient yeast, growth assays on different carbon sources, direct galactose uptake measurement, pharmacological inhibition by LEV\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — functional transport assay with direct uptake measurement in heterologous system and pharmacological validation, single lab\",\n      \"pmids\": [\"25326386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Residue D670 of SV2A is critical for levetiracetam analogue binding: mutation of D670 leads to complete loss of radioligand binding, as predicted by homology modelling and molecular dynamics simulations of inward- and outward-facing MFS conformational states.\",\n      \"method\": \"Homology modelling, molecular dynamics, docking, site-directed mutagenesis, radioligand binding assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — computational prediction validated by experimental mutagenesis and radioligand binding, single lab\",\n      \"pmids\": [\"25692762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SV2A/B and stonin 2 have overlapping functions in endocytic sorting of synaptotagmin 1 (Syt1) to synaptic vesicles: deletion or knockdown of either SV2A/B or stonin 2 causes partial Syt1 loss and missorting to the neuronal surface; deletion of both dramatically exacerbates Syt1 missorting and degradation, impairing neurotransmission efficacy.\",\n      \"method\": \"Genetic deletion of SV2A/B and stonin 2, knockdown, Syt1 immunostaining/surface labeling, electrophysiology in hippocampal synapses\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double-deletion epistasis, multiple readouts (protein levels, surface localization, electrophysiology), demonstrates genetic interaction\",\n      \"pmids\": [\"26015569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"N-linked glycosylation of SV2C (conserved across all SV2 isoforms and vertebrate species) is essential for BoNT/A1 binding to neurons and for potent neurotoxicity: the 2.0-Å crystal structure of BoNT/A1 receptor-binding domain in complex with glycosylated human SV2C reveals that neuronal tropism requires recognition of both the SV2C peptide moiety and an N-linked glycan on SV2.\",\n      \"method\": \"X-ray crystallography (2.0 Å resolution) of BoNT/A1 receptor-binding domain:glycosylated human SV2C complex, mutagenesis of glycosylation site, neuronal binding and toxicity assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure at high resolution combined with mutagenesis and functional validation of toxin binding and neurotoxicity\",\n      \"pmids\": [\"27294781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"BoNT/A binds SV2C-LD4 with a binding constant of ~200 nM; binding affinity decreases from SV2C >> SV2A > SV2B; at pH 5 (acidic synaptic vesicles), binding affinity increases >10-fold; the SV2C luminal domain 4 forms a quadrilateral β-sheet helix that pre-exists in solution prior to BoNT/A binding, constituting a different binding mechanism from BoNT/B-synaptotagmin.\",\n      \"method\": \"GST pull-down assays, surface plasmon resonance, circular dichroism spectroscopy, pH-dependent binding assays\",\n      \"journal\": \"Toxins\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple biophysical methods (SPR, CD, pull-down), quantitative binding constants, single lab\",\n      \"pmids\": [\"27196927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SV2A dysfunction due to missense mutation L174Q selectively reduces depolarization-induced GABA (but not glutamate) release in the hippocampus and specifically reduces synaptotagmin 1 levels among exocytosis-related proteins, facilitating kindling epileptogenesis.\",\n      \"method\": \"Rat Sv2a L174Q missense knock-in model, neurochemical measurements of GABA/glutamate release, Western blot for exocytosis proteins, amygdala kindling assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo missense knock-in model, neurotransmitter release measurements, protein quantification, and epileptogenesis behavioral assay\",\n      \"pmids\": [\"27265781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SV2A coordinates distinct synaptic vesicle recycling properties between inhibitory and excitatory nerve terminals: SV2A is more highly expressed in inhibitory synapses and its preferential presence controls slower vesicle recycling in inhibitory terminals (~1.8-fold slower than excitatory) by differentially regulating sorting of synaptotagmin I.\",\n      \"method\": \"pHluorin-conjugated SV2 tracers preferentially expressed in excitatory or inhibitory terminals, fluorescence imaging of vesicle recycling kinetics, comparison across terminal types\",\n      \"journal\": \"Progress in neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional vesicle recycling assay with synapse-type-selective tracers, single lab\",\n      \"pmids\": [\"32615146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The epilepsy-associated human SV2A mutation R383Q causes mislocalization of SV2A from synaptic vesicles to the plasma membrane, reduces mobility at the plasma membrane, reduces binding to synaptotagmin-1 (Syt1), and fails to rescue reduced Syt1 expression and dysfunctional activity-dependent Syt1 trafficking in SV2A-depleted neurons.\",\n      \"method\": \"Molecular replacement strategy in SV2A-depleted mouse neurons, live-cell imaging of plasma membrane vs. vesicular localization, FRAP, co-immunoprecipitation for Syt1 binding, Syt1 trafficking assays\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization imaging, FRAP, binding assay, trafficking assay) with disease-relevant mutation in KO background\",\n      \"pmids\": [\"32341095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Poly-glycine-alanine (GA) dipeptide aggregates from C9orf72 ALS/FTD reduce SV2A levels in motor neurons, alter Ca2+ influx, and impair synaptic vesicle release; restoring SV2A levels rescues these synaptic phenotypes.\",\n      \"method\": \"GA mouse model and patient iPSC-derived neurons, SV2A protein quantification, Ca2+ imaging, synaptic vesicle release assays, SV2A rescue experiments\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — SV2A rescue experiment in disease model with functional readouts, single lab with multiple methods\",\n      \"pmids\": [\"32347002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"BoNT/A endocytosis into synaptic vesicles requires coincident binding to both polysialoganglioside (PSG) and SV2 on the neuronal plasma membrane; BoNT/A simultaneously interacts with a preassembled PSG-synaptotagmin-1 (Syt1) complex and SV2, facilitating Syt1-SV2 nanoclustering that controls endocytic sorting into SVs; Syt1 knockdown suppresses BoNT/A and BoNT/E intoxication.\",\n      \"method\": \"Live-cell super-resolution imaging, electron microscopy, catalytically inactivated BoNT/A and receptor-binding-deficient mutants in hippocampal neurons, Syt1 CRISPRi knockdown, SNAP-25 cleavage assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — super-resolution live imaging combined with EM, mutagenesis of receptor-binding sites, CRISPRi, and functional toxin activity assay in single study\",\n      \"pmids\": [\"37226896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of full-length SV2A in complex with BoNT/A2 receptor-binding domain and either levetiracetam or brivaracetam reveal: (1) the large fourth luminal domain of SV2A binds BoNT/A2 HC through protein-protein and protein-glycan interactions; (2) LEV and BRV occupy the putative substrate-binding site in an outward-open conformation; (3) a propyl group in BRV creates additional contacts with SV2A explaining its higher binding affinity than LEV.\",\n      \"method\": \"Cryo-electron microscopy of full-length SV2A complexes, label-free spectral shift assay for binding affinity\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure of full-length protein with ligands and binding partner, functional validation by binding assay, structural basis for affinity difference\",\n      \"pmids\": [\"38637505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"SV2 is localized on the membranes of both synaptic vesicle clusters and large dense-cored vesicles (LDCV) in NGF-treated PC12 cells, with a higher SV2:synaptophysin ratio on LDCV (~9:1) compared to synaptic vesicle clusters (~1:1); chromogranin A occupies the LDCV core while SV2 is on the membrane.\",\n      \"method\": \"Pre-embedding EM immunocytochemistry with silver-enhanced gold probe, quantitative comparison on identified organelle types\",\n      \"journal\": \"The journal of histochemistry and cytochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct ultrastructural localization with quantification, single lab\",\n      \"pmids\": [\"8985140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SV2 (synaptic vesicle transmembrane proteoglycan) is complexed with an α5-chain-containing laminin on the presynaptic plasma membrane: SV2 co-purifies with a 900-kDa laminin from synaptosomes of electric organ synapses, and purified SV2 binds laminin-1 with high affinity in direct binding assays.\",\n      \"method\": \"Synaptosome preparation, co-immunoprecipitation/co-purification of SV2-laminin complex, direct binding assay with purified SV2 and laminin-1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay with purified proteins combined with co-purification from native synaptosomes, single lab\",\n      \"pmids\": [\"10617638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SV2A is expressed in mitochondria (in addition to synaptic vesicles), as demonstrated by immunohistochemistry and proteomics; levetiracetam effects on mitochondrial function (fission/fusion balance, permeability transition pore) are significantly abolished when SV2A is knocked down by siRNA.\",\n      \"method\": \"Immunohistochemistry, proteomics, siRNA knockdown of SV2A, mitochondrial functional assays (fission/fusion, mPTP opening)\",\n      \"journal\": \"Journal of Alzheimer's disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mitochondrial localization by IHC and proteomics, functional link via siRNA rescue in a single cell model study; unusual finding requiring independent replication\",\n      \"pmids\": [\"26639968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-133a and miR-218 directly target SV2A: luciferase reporter assay showed these miRNAs significantly decreased relative luciferase activity from an SV2A dual-luciferase construct; transfection of miR-133a and miR-218 in human neuroblastoma cells reduced endogenous SV2A mRNA and protein levels.\",\n      \"method\": \"Luciferase reporter assay, miRNA transfection in human neuroblastoma cells, qRT-PCR, Western blot\",\n      \"journal\": \"Translational psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter (direct test of 3'UTR targeting) plus endogenous mRNA and protein reduction, single lab with two orthogonal methods\",\n      \"pmids\": [\"32839459\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SV2A is a 12-transmembrane-domain glycoprotein of the major facilitator superfamily localized to synaptic vesicle membranes in all neurons and endocrine cells, where it functions as a galactose transporter (demonstrated in yeast), maintains a Ca2+-responsive pool of primed vesicles by rendering them competent for Ca2+-triggered fusion, regulates presynaptic Ca2+ levels, controls synaptic vesicle recycling kinetics preferentially at inhibitory synapses, and traffics/stabilizes the Ca2+-sensor synaptotagmin 1 at vesicles via a tyrosine-based endocytosis motif that recruits clathrin adaptors (AP2, EPS15, amphiphysin 2); SV2A directly binds synaptotagmin 1 in a calcium-inhibited, isoform-specific manner through its N-terminal cytoplasmic domain (C2B interaction), and its large fourth luminal domain—bearing a conserved N-linked glycan—serves as the protein receptor for botulinum neurotoxins A, D, E, and F (and tetanus toxin) as well as the binding site for antiepileptic drugs levetiracetam and brivaracetam, whose cryo-EM structures show occupancy of the outward-open substrate-binding cavity with brivaracetam's propyl group explaining its higher affinity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SV2A is a synaptic vesicle membrane glycoprotein with the 12-transmembrane topology and sequence homology of the major facilitator superfamily, originally identified as a putative vesicular transporter [#0] and expressed ubiquitously at brain synapses [#2]. Functionally, SV2A is required for action potential-dependent neurotransmission—its genetic loss in mice produces fatal seizures with selectively impaired GABAergic transmission [#4]—and it acts by maintaining a Ca2+-responsive pool of release-competent (primed) vesicles rather than by setting mini frequency/amplitude or apparent Ca2+ sensitivity [#5, #11]. A central molecular function is the trafficking and stabilization of the Ca2+ sensor synaptotagmin 1: SV2A directly binds synaptotagmin through its cytoplasmic N-terminus in a calcium-inhibited, isoform-specific manner [#3], and a tyrosine-based endocytosis motif (Y46) recruits clathrin adaptors AP2, EPS15, and amphiphysin 2/Bin1 to sort both SV2A and synaptotagmin 1 to vesicles [#15], a sorting function it shares redundantly with stonin 2 [#25]. Through these activities SV2A also governs presynaptic Ca2+ levels [#16] and sets slower vesicle recycling kinetics preferentially at inhibitory terminals where it is enriched [#29]. Its large fourth luminal domain, bearing a conserved N-linked glycan, serves as the neuronal protein receptor for botulinum neurotoxins A, D, E, and F and tetanus toxin, with toxin entry requiring both the SV2 peptide/glycan and coincident ganglioside binding [#8, #10, #14, #26]. The same luminal architecture and an outward-open substrate-binding cavity form the binding site for the antiepileptic drugs levetiracetam and brivaracetam, as defined by knockout, mutagenesis, and cryo-EM of full-length SV2A [#6, #24, #33]. Disease-associated SV2A missense mutations (L174Q, R383Q) mislocalize the protein, reduce synaptotagmin 1 binding/levels, and impair GABAergic release, linking SV2A dysfunction to epileptogenesis [#28, #30].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Established the structural identity of SV2A as a 12-TM MFS-homologous protein, framing the long-standing hypothesis that it is a vesicular transporter.\",\n      \"evidence\": \"cDNA cloning, topology prediction, and heterologous expression in COS cells\",\n      \"pmids\": [\"1519064\", \"1355409\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sequence homology did not demonstrate any transport substrate or activity\", \"No functional assay of the predicted transport\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identified a direct, calcium-regulated, isoform-specific physical link between SV2A and the Ca2+ sensor synaptotagmin, suggesting SV2A couples to the fusion machinery.\",\n      \"evidence\": \"Cross-linking, co-IP, and recombinant affinity chromatography with domain mapping\",\n      \"pmids\": [\"8910372\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether the interaction is required for release in vivo\", \"Functional consequence of calcium-regulated dissociation untested at this stage\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstrated that SV2A is essential for action potential-dependent (especially GABAergic) neurotransmission, moving it from a structural curiosity to a release-controlling protein.\",\n      \"evidence\": \"SV2A knockout mouse with IPSC electrophysiology and EM of synapse ultrastructure\",\n      \"pmids\": [\"10611374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not pinpoint which step of the release cycle is impaired\", \"Molecular basis of the GABAergic selectivity unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Localized SV2A's function to maintenance of the readily releasable/primed vesicle pool for Ca2+-stimulated exocytosis, with effects on SNARE complex assembly.\",\n      \"evidence\": \"Capacitance exocytosis measurements in KO chromaffin cells and SDS-resistant SNARE complex analysis\",\n      \"pmids\": [\"11483953\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking SV2A to SNARE complex stability not defined\", \"Whether the defect is upstream or downstream of priming unclear at this point\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Refined the functional defect to a step that renders primed vesicles Ca2+-responsive, and showed transmembrane residues and luminal glycosylation are needed for SV2A folding/trafficking while the putative synaptotagmin-binding sequence is dispensable for this function.\",\n      \"evidence\": \"Electrophysiology with systematic TM-domain and glycosylation rescue mutants in SV2-null neurons\",\n      \"pmids\": [\"19176798\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not reconcile dispensability of the synaptotagmin-binding sequence with later synaptotagmin trafficking roles\", \"Identity of any transported substrate still unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined SV2A's trafficking mechanism via a tyrosine-based endocytosis motif recruiting clathrin adaptors and its role in synaptotagmin expression/trafficking, separating distinct functional modules.\",\n      \"evidence\": \"Y46A mutagenesis, adaptor binding assays, electrophysiology, and KO vesicle immunoisolation; additional TM tryptophan mutant analysis\",\n      \"pmids\": [\"20410110\", \"20702688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic separation of synaptotagmin regulation versus release support incompletely defined\", \"How TM tryptophans support release independently of synaptotagmin unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed SV2 acts through presynaptic Ca2+ regulation, with elevated resting/evoked Ca2+ causally responsible for altered vesicle dynamics in SV2-null terminals.\",\n      \"evidence\": \"Direct presynaptic Ca2+ imaging in SV2B-KO retinal bipolar terminals with pharmacological reproduction and rescue\",\n      \"pmids\": [\"20620874\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular target through which SV2 controls presynaptic Ca2+ not identified\", \"Generality across SV2A-dominated synapses not tested here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established that SV2A/B and stonin 2 act redundantly in endocytic sorting of synaptotagmin 1 to synaptic vesicles, explaining synaptotagmin loss and missorting upon SV2 deletion.\",\n      \"evidence\": \"Double genetic deletion epistasis with surface labeling and electrophysiology\",\n      \"pmids\": [\"26015569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise biochemical step at which SV2A and stonin 2 converge unresolved\", \"Quantitative contribution of each pathway not separated\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified SV2 as the neuronal protein receptor for botulinum neurotoxin A, defining a non-synaptic-vesicle function exploited by toxins.\",\n      \"evidence\": \"SV2A/B KO neurons, isoform rescue, fragment competition, and siRNA knockdown\",\n      \"pmids\": [\"16543415\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural determinants of toxin recognition\", \"Relative contributions of peptide versus glycan undefined at this stage\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided the structural basis for toxin recognition, showing BoNT/A requires both the SV2 luminal-domain peptide and its conserved N-linked glycan, and quantified isoform/pH-dependent affinity.\",\n      \"evidence\": \"2.0-Å crystal structure of BoNT/A1 RBD with glycosylated SV2C plus SPR/CD biophysics and glycosylation mutagenesis\",\n      \"pmids\": [\"27294781\", \"27196927\", \"18815274\", \"21124874\", \"21483489\", \"19650874\", \"19476346\", \"23621114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures were of toxin-binding fragments rather than full-length SV2A in early studies\", \"Endogenous vesicular function of the luminal domain distinct from toxin binding not addressed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed BoNT/A endocytosis requires coincident binding to polysialoganglioside and SV2 and exploits a preassembled ganglioside–synaptotagmin-1 complex to drive Syt1-SV2 nanoclustering for endocytic sorting.\",\n      \"evidence\": \"Live-cell super-resolution imaging, EM, receptor-binding mutants, Syt1 CRISPRi, and SNAP-25 cleavage assays\",\n      \"pmids\": [\"37226896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the multi-receptor assembly not fully defined\", \"Whether nanoclustering reflects a physiological sorting mechanism beyond toxin entry untested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided the first direct evidence of a transport substrate, showing human SV2A confers galactose uptake in transport-deficient yeast and that levetiracetam inhibits this activity.\",\n      \"evidence\": \"Heterologous expression in hexose-transport-deficient yeast with direct galactose uptake measurement and LEV inhibition\",\n      \"pmids\": [\"25326386\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Galactose transport not demonstrated in native neurons\", \"Physiological relevance of galactose as a vesicular substrate unestablished\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the structural basis of antiepileptic drug binding, showing levetiracetam and brivaracetam occupy the outward-open substrate cavity of full-length SV2A and explaining brivaracetam's higher affinity.\",\n      \"evidence\": \"Cryo-EM of full-length SV2A with BoNT/A2 RBD and LEV or BRV, plus spectral-shift binding affinity; supported by earlier D670 mutagenesis and LEV-binding-site studies\",\n      \"pmids\": [\"38637505\", \"15210974\", \"25692762\", \"23530581\", \"22220214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational cycle linking drug occupancy to transport/synaptic function not captured\", \"How drug binding modulates the physiological vesicle-priming role mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected SV2A dysfunction to epilepsy and broader disease, with human/rat missense mutations causing mislocalization and reduced synaptotagmin 1 binding, and SV2A loss contributing to C9orf72 ALS/FTD synaptic deficits.\",\n      \"evidence\": \"Disease-mutation knock-in/replacement models with imaging, FRAP, binding and trafficking assays, plus GA-dipeptide disease models with SV2A rescue\",\n      \"pmids\": [\"32341095\", \"27265781\", \"32347002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mislocalization phenotypes generalize across all epilepsy-associated variants unknown\", \"Mechanism linking SV2A loss to C9orf72 pathology not fully defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous transport substrate, transport cycle, and how transporter conformational states couple to vesicle priming and drug action in native neurons remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No demonstrated physiological transport activity in neurons\", \"Coupling of MFS conformational cycle to Ca2+-responsive priming undefined\", \"Mechanistic basis of GABAergic/inhibitory-synapse selectivity incompletely explained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 23]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [8, 10, 14, 18, 26]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [15, 25]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 5, 11, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 2, 5, 34]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [15, 30, 35]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [4, 5, 11, 16]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [15, 25, 29]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 28, 30]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SYT1\", \"STON2\", \"AP2\", \"EPS15\", \"BIN1\", \"LAMA5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}