{"gene":"DOC2B","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2010,"finding":"Doc2b acts as a high-affinity Ca2+ sensor for spontaneous (miniature) neurotransmitter release. Although cytosolic, Doc2b functions analogously to synaptotagmin-1 but with higher Ca2+ sensitivity, and it binds to SNARE complexes in competition with synaptotagmin-1.","method":"Knockout mouse analysis, electrophysiology, Co-IP/competitive binding assays with SNARE complexes","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal binding assays and genetic KO with defined electrophysiological phenotype, highly cited foundational paper replicated across labs","pmids":["20150444"],"is_preprint":false},{"year":2008,"finding":"The C2A domain of DOC2B interacts directly with the plasma membrane in a Ca2+-dependent manner, causing translocation of DOC2B to the plasma membrane upon small elevations in intracellular Ca2+. At the plasma membrane, DOC2B acts as a priming factor increasing the number of fusion-competent vesicles, affects fusion pore expansion kinetics, and interacts with plasma membrane SNAREs.","method":"Biochemical binding assays, TIRF microscopy, electrophysiology, FRAP, mutagenesis of Ca2+-binding DOC2B","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biophysical, electrophysiological, morphological, live imaging) in a single study with mutagenesis controls","pmids":["18596155"],"is_preprint":false},{"year":2008,"finding":"DOC2b directly associates with syntaxin-4 (a target-SNARE) in an intracellular Ca2+-dependent manner, and this interaction is essential for triggering GLUT4 vesicle fusion in adipocytes upon insulin stimulation.","method":"Yeast two-hybrid screening, co-immunoprecipitation, GST pulldown, confocal immunofluorescence microscopy, siRNA knockdown with GLUT4 translocation assay","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Y2H, Co-IP, GST pulldown, functional KD) with defined cellular phenotype","pmids":["19033398"],"is_preprint":false},{"year":2004,"finding":"A rise in intracellular Ca2+ is sufficient (independent of Munc13) to recruit DOC2B to the target membrane. Purified DOC2B binds phospholipids in a Ca2+-dependent manner, and depolarization of neurons induces complete translocation of DOC2B-EGFP to the plasma membrane within 5 seconds.","method":"Phospholipid-binding assay with purified protein, live fluorescence imaging of DOC2B-EGFP in neurons, mutagenesis (Munc13-binding mutants)","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — in vitro lipid-binding reconstitution combined with live-cell imaging and mutagenesis","pmids":["15033971"],"is_preprint":false},{"year":2013,"finding":"Doc2b binds GLUT4 exocytic SNAREs and potently accelerates SNARE-dependent membrane fusion kinetics in a reconstituted proteoliposome system. This activity requires intact Ca2+-binding sites on both C2A and C2B domains. Doc2b also strongly bends membrane bilayers, and this membrane-bending activity is essential to its stimulatory function in fusion.","method":"Reconstituted proteoliposome fusion assay, electron microscopy, mutagenesis of Ca2+-binding sites","journal":"Molecular Biology of the Cell","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro fusion system with mutagenesis and EM structural validation","pmids":["23427263"],"is_preprint":false},{"year":2013,"finding":"Crystal structures of isolated DOC2B C2A and C2B domains were determined, revealing that C2B binds Ca2+ with considerably higher affinity than C2A. The C2AB solution structure (by SAXS) shows two domains with highly flexible orientation unaffected by Ca2+. In cells, C2B translocates to the plasma membrane at ~400 nM Ca2+ (EC50) while C2A does not at submicromolar Ca2+; C2AB translocates with ~2-fold lower EC50 than C2B alone, establishing C2B as the primary Ca2+-sensing unit.","method":"X-ray crystallography of C2A and C2B domains, SAXS of C2AB, Ca2+-binding kinetics, live-cell fluorescence imaging with isolated domain constructs","journal":"Journal of Molecular Biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structures combined with functional live-cell imaging and kinetic biochemistry in one study","pmids":["23994332"],"is_preprint":false},{"year":2015,"finding":"The C2AB domain of Doc2b stabilizes a membrane hemifusion intermediate (lipid mixing without content mixing) in a strictly Ca2+- and phosphatidylserine-dependent manner, directly acting on membranes without SNAREs. Doc2b-coated membrane stalks resist forces up to 600 pN.","method":"Dual optical trap assay with SNARE-free synthetic membranes, real-time fluorescence lipid/content mixing assay","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 — cell-free reconstitution with optical trapping and fluorescence imaging; direct mechanistic demonstration","pmids":["26395669"],"is_preprint":false},{"year":2012,"finding":"Doc2b is required for both phases of glucose-stimulated insulin secretion from pancreatic islets and for insulin-stimulated GLUT4 vesicle translocation in skeletal muscle, acting as a positive regulator of Munc18c-syntaxin 4-mediated SNARE complex assembly.","method":"Doc2b knockout mouse analysis, ex vivo islet secretion assay, skeletal muscle GLUT4 translocation assay, SNARE complex formation biochemical assay","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined phenotypic readouts and pathway placement via SNARE complex assay","pmids":["22698913"],"is_preprint":false},{"year":2014,"finding":"Doc2b serves as a scaffolding platform that simultaneously binds both Munc18-1 (via C2A domain) and Munc18c (via C2B domain), bridging their interaction. Macromolecular complexes of Munc18c-Doc2b-Munc18-1 exist in β-cells, and Munc18c and Munc18-1 fail to associate in the absence of Doc2b.","method":"Co-immunoprecipitation from β-cells, in vitro GST-Doc2b pulldown competition assays","journal":"The Biochemical Journal","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP and pulldown from single lab, but domain-specific interaction with mutagenesis/competition controls","pmids":["25190515"],"is_preprint":false},{"year":2013,"finding":"Doc2b plays distinct roles in two sequential priming steps in chromaffin cells. Mutating Ca2+-coordinating aspartates in C2A permanently localizes Doc2b at the plasma membrane and renders an upstream priming step Ca2+-independent. A downstream priming step depends on SNARE-binding and Ca2+-binding to C2B, interaction with ubMunc13-2, and presence of synaptotagmin-1. Doc2b also inhibits release during sustained Ca2+ elevations via its MID-domain.","method":"Site-directed mutagenesis of Ca2+-binding sites, overexpression/KO in chromaffin cells, capacitance measurements, genetic epistasis with ubMunc13-2 and synaptotagmin-1","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis of multiple domains, genetic epistasis with defined priming-step phenotypes, multiple orthogonal readouts","pmids":["29274147"],"is_preprint":false},{"year":2013,"finding":"In chromaffin cells, Doc2b overexpression inhibits the sustained release component and augments the readily releasable pool, while Doc2b KO shifts release from the readily releasable pool to the sustained component and accelerates (but makes incomplete) refilling of the readily releasable pool. Doc2b thus inhibits vesicle priming during prolonged Ca2+ elevations, protecting unprimed vesicles and favoring synchronized fast release.","method":"Doc2b knockout and overexpression in mouse chromaffin cells, high-temporal-resolution capacitance measurements, electron microscopy","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic KO and OE with multiple orthogonal readouts including EM and electrophysiology","pmids":["24133251"],"is_preprint":false},{"year":2013,"finding":"Munc13-1 co-translocates to the plasma membrane in a Doc2B- and Ca2+-dependent manner. Without co-expressed Doc2B, Munc13-1 does not translocate. Munc13-1 accumulation at the PM after repeated stimulations depends on DAG levels (via Munc13-1 H567K DAG-binding mutant), suggesting Doc2B recruits Munc13-1 to the PM where DAG stabilizes it.","method":"Fluorescent protein co-expression in PC12 cells, live-cell imaging, mutagenesis of Munc13-1 DAG-binding site","journal":"Frontiers in Endocrinology","confidence":"Medium","confidence_rationale":"Tier 3 — live imaging with mutagenesis controls, single lab, functional consequence inferred","pmids":["24062723"],"is_preprint":false},{"year":2009,"finding":"DOC2b associates with insulin vesicles and translocates to the plasma membrane upon high-glucose stimulation, where it interacts specifically with syntaxin-4 (not syntaxin-1), and is required for delayed (second-phase) but not rapid insulin secretion.","method":"Confocal microscopy of DOC2b localization, co-immunoprecipitation with syntaxins, siRNA knockdown with biphasic insulin secretion assay in MIN6 cells","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP and KD with defined secretory phenotype, single lab","pmids":["19410553"],"is_preprint":false},{"year":2005,"finding":"The intracellular Ca2+ concentration threshold for EGFP-DOC2B translocation to the plasma membrane is approximately 200 nM in the bulk cytoplasm of Aplysia neurons. DOC2B translocation kinetics are slower than Ca2+ elevation rate, and detachment is faster than Ca2+ removal.","method":"Live-cell imaging of EGFP-DOC2B in Aplysia neurons with simultaneous Ca2+ measurement","journal":"Cell Calcium","confidence":"Medium","confidence_rationale":"Tier 2 — direct quantitative live imaging with Ca2+ measurement, but single model system","pmids":["16305808"],"is_preprint":false},{"year":2019,"finding":"DOC2B is phosphorylated at tyrosine Y301 upon insulin stimulation in skeletal muscle cells. This phosphorylation enhances DOC2B's interaction with the microtubule motor protein kinesin light chain 1 (KLC1), and is required for insulin-stimulated GLUT4 accumulation at the plasma membrane. Mutation of Y301 blocks phosphorylation, KLC1 interaction, and blunts GLUT4 translocation.","method":"Site-directed mutagenesis of Y301, co-immunoprecipitation, mass spectrometry, GLUT4 translocation assay in L6-GLUT4-myc cells and skeletal-muscle-specific transgenic mice","journal":"Diabetologia","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis of specific phosphosite, Co-IP, MS identification, in vivo transgenic confirmation, multiple orthogonal methods","pmids":["30707251"],"is_preprint":false},{"year":2022,"finding":"DOC2b is tyrosine phosphorylated at Y301 within 2 min of glucose stimulation in β-cells, with YES kinase (Src family) responsible for this modification. Y301 phosphorylation is required for DOC2b's interaction with YES kinase and with ERM (Ezrin-Radixin-Moesin) family proteins, and ERM activation by Y301-phosphorylated DOC2b is required for VAMP2-containing insulin granule localization to the plasma membrane and enhancement of glucose-stimulated insulin secretion.","method":"Biochemical phosphorylation analysis, Co-immunoprecipitation with YES and ERM proteins, site-directed mutagenesis of Y301, ERM knockdown, VAMP2 PM localization assay, GSIS assay in human islets and clonal β-cells","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 — identified kinase (YES), phosphosite (Y301), downstream effectors (ERM), multiple orthogonal methods in human primary islets and cell lines","pmids":["35377441"],"is_preprint":false},{"year":2019,"finding":"Synaptotagmin-1 and Doc2b exhibit distinct membrane-remodeling mechanisms: Doc2b is more effective when loaded on both membranes, while Syt1 is more effective from a single membrane. Both C2AB fragments can induce hemifusion and reduce membrane bending modulus (as measured by AFM), but significantly higher Syt1 concentrations are required for hemifusion.","method":"Dual optical trap with SNARE-free membranes, lipid-mixing confocal assay, atomic force microscopy bending modulus measurement","journal":"Biophysical Journal","confidence":"High","confidence_rationale":"Tier 1 — cell-free reconstitution with multiple biophysical methods directly comparing Doc2b and Syt1 membrane activities","pmids":["31952804"],"is_preprint":false},{"year":2025,"finding":"DOC2b associates with IKKβ, NF-κB p65, and STAT-1 in cytokine-challenged β-cells. DOC2b enrichment attenuates cytokine-induced IKKβ activation and total IKKβ protein levels, increases IκBβ protein, and reduces STAT-1 activation and expression, resulting in decreased CXCL10 expression.","method":"Co-immunoprecipitation, qPCR, proteomics, immunoconfocal microscopy in DOC2b-enriched/depleted human islets and β-cell lines challenged with proinflammatory cytokines","journal":"Metabolism: Clinical and Experimental","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP association with signaling components, functional enrichment/depletion, single lab, pathway placement inferred","pmids":["39805534"],"is_preprint":false},{"year":2014,"finding":"DOC2B overexpression in cervical cancer cells impairs AKT1 and ERK1/2 signaling and induces actin cytoskeleton remodeling in a calcium-dependent manner, correlating with reduced cell migration, invasion, and tumor growth in xenograft models.","method":"DOC2B overexpression in SiHa cells, Western blotting for pAKT1/pERK1/2, actin staining, xenograft tumor model","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — overexpression with signaling readouts and in vivo xenograft, pathway placement partially defined, single lab","pmids":["24570007"],"is_preprint":false},{"year":2021,"finding":"DOC2B inhibits epithelial-mesenchymal transition (EMT) and promotes senescence via a calcium-dependent interaction with CDH1 (E-cadherin). This DOC2B-calcium-EMT-senescence axis is required for DOC2B's metastasis-suppressive function in cancer cells.","method":"DOC2B overexpression/knockdown in cancer cells, co-immunoprecipitation of DOC2B with CDH1, nude mice xenograft and liver metastasis models, EMT marker analysis","journal":"Cell Biology and Toxicology","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP with CDH1, functional KD/OE with in vivo confirmation, single lab","pmids":["33758996"],"is_preprint":false}],"current_model":"DOC2B is a cytosolic, double-C2-domain Ca2+ sensor (with C2B as the primary Ca2+-sensing unit) that, upon Ca2+ binding, translocates to the plasma membrane via C2 domain-phosphatidylserine interaction, where it promotes vesicle priming and fusion by binding SNARE complexes (competing with synaptotagmin-1), inducing membrane curvature/hemifusion, and scaffolding Munc18 isoforms and Munc13-1; it is post-translationally regulated by YES kinase-mediated phosphorylation at Y301, which drives interaction with KLC1 (in muscle) and ERM proteins (in β-cells) to facilitate GLUT4 and insulin granule trafficking to the plasma membrane, while also modulating inflammatory signaling via association with IKKβ and STAT-1."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing the basic translocation mechanism: it was unknown how DOC2B reaches its site of action; direct lipid-binding assays and live imaging showed that a rise in intracellular Ca²⁺ is sufficient to recruit DOC2B to the plasma membrane via phospholipid interaction, independent of Munc13.","evidence":"Purified protein phospholipid-binding assay and DOC2B-EGFP live imaging in neurons with Munc13-binding mutants","pmids":["15033971"],"confidence":"High","gaps":["Specific phospholipid species preference not fully defined","Kinetics of membrane association/dissociation not quantified at this stage"]},{"year":2005,"claim":"Quantifying the Ca²⁺ sensitivity of translocation: the threshold intracellular Ca²⁺ concentration for DOC2B plasma membrane recruitment was determined to be ~200 nM, placing it as a sensor of modest Ca²⁺ fluctuations.","evidence":"Simultaneous EGFP-DOC2B imaging and Ca²⁺ measurement in Aplysia neurons","pmids":["16305808"],"confidence":"Medium","gaps":["Measured in invertebrate neurons only","Translocation kinetics slower than Ca²⁺ rise—mechanism not resolved"]},{"year":2008,"claim":"Defining DOC2B as a vesicle priming factor and identifying its SNARE interactions: DOC2B was shown to increase the number of fusion-competent vesicles at the plasma membrane, affect fusion pore kinetics, and interact with plasma membrane SNAREs—in neurons via C2A-dependent translocation, and in adipocytes via direct Ca²⁺-dependent binding to syntaxin-4 to trigger GLUT4 vesicle fusion.","evidence":"TIRF, FRAP, electrophysiology, and mutagenesis in neurons; yeast two-hybrid, Co-IP, GST pulldown, and siRNA knockdown with GLUT4 assay in adipocytes","pmids":["18596155","19033398"],"confidence":"High","gaps":["Whether priming and fusion pore effects are separable functions","Whether syntaxin-4 interaction applies to all peripheral secretory cell types"]},{"year":2009,"claim":"Linking DOC2B to biphasic insulin secretion: DOC2B was found on insulin vesicles, translocating to the plasma membrane upon glucose stimulation and specifically engaging syntaxin-4 to support second-phase insulin release.","evidence":"Confocal microscopy, Co-IP, siRNA knockdown with biphasic insulin secretion assay in MIN6 β-cells","pmids":["19410553"],"confidence":"Medium","gaps":["Only second-phase role demonstrated in this study; first-phase role unclear at this point","Single cell line (MIN6)"]},{"year":2010,"claim":"Identifying DOC2B as the high-affinity Ca²⁺ sensor for spontaneous neurotransmitter release: it was unknown what Ca²⁺ sensor drives miniature release; knockout analysis and competitive binding assays showed DOC2B binds SNARE complexes in competition with synaptotagmin-1 and is required for normal spontaneous release frequency.","evidence":"Doc2b knockout mice, electrophysiology, Co-IP and competitive SNARE-binding assays","pmids":["20150444"],"confidence":"High","gaps":["Whether Doc2b is the sole Ca²⁺ sensor for minis or acts redundantly with Doc2a","Structural basis of Syt1–Doc2b competition on SNAREs unresolved"]},{"year":2012,"claim":"Extending the in vivo role to whole-animal glucose homeostasis: Doc2b knockout mice showed impaired glucose-stimulated insulin secretion from islets and defective GLUT4 translocation in skeletal muscle, with Doc2b acting as a positive regulator of Munc18c–syntaxin-4 SNARE assembly.","evidence":"Doc2b knockout mouse, ex vivo islet secretion, skeletal muscle GLUT4 assay, SNARE complex formation biochemistry","pmids":["22698913"],"confidence":"High","gaps":["Whether Doc2b loss affects other SNARE-dependent trafficking in vivo","Contribution to type 2 diabetes pathogenesis not directly tested"]},{"year":2013,"claim":"Resolving the molecular mechanism of fusion acceleration and identifying C2B as the primary Ca²⁺-sensing unit: reconstituted systems and crystal structures showed that Doc2b accelerates SNARE-dependent fusion by bending membranes (requiring both C2 domains' Ca²⁺ sites), and C2B binds Ca²⁺ with higher affinity and translocates at ~400 nM Ca²⁺, establishing it as the dominant sensor.","evidence":"Proteoliposome fusion assays, EM, X-ray crystallography of C2A/C2B, SAXS of C2AB, live-cell translocation of isolated domains","pmids":["23427263","23994332"],"confidence":"High","gaps":["Full-length DOC2B structure not determined","How the flexible C2A–C2B orientation contributes to membrane bending is unclear"]},{"year":2013,"claim":"Delineating sequential priming roles and inhibitory function in chromaffin cells: Doc2b was found to participate in two sequential vesicle priming steps—an upstream step governed by C2A membrane attachment and a downstream step requiring C2B-SNARE and Munc13-2 interaction—while its MID domain inhibits release during sustained Ca²⁺, protecting the readily releasable pool.","evidence":"Site-directed mutagenesis of Ca²⁺-binding and MID domains, Doc2b KO/OE in chromaffin cells, capacitance measurements, genetic epistasis with Munc13-2 and Syt1","pmids":["29274147","24133251"],"confidence":"High","gaps":["Molecular basis of MID-domain inhibitory action unknown","Whether dual priming mechanism applies to neurons"]},{"year":2013,"claim":"Establishing DOC2B as a recruiter of Munc13-1 to the plasma membrane: Munc13-1 was shown to co-translocate with Doc2b in a Ca²⁺-dependent manner, with subsequent DAG-dependent stabilization at the membrane.","evidence":"Fluorescent protein co-expression and live imaging in PC12 cells, Munc13-1 DAG-binding mutant","pmids":["24062723"],"confidence":"Medium","gaps":["Functional consequence of Munc13-1 recruitment by Doc2b on secretion not directly measured","Observed in overexpression system only"]},{"year":2014,"claim":"Identifying DOC2B as a scaffolding hub bridging Munc18-1 and Munc18c: in β-cells, Doc2b simultaneously binds Munc18-1 (via C2A) and Munc18c (via C2B), and these two Munc18 isoforms fail to associate in the absence of Doc2b.","evidence":"Co-IP from β-cells, in vitro GST-Doc2b pulldown with competition assays","pmids":["25190515"],"confidence":"Medium","gaps":["Awaits reconstitution with purified components to confirm direct tripartite complex","Functional consequence of the Munc18-1/Munc18c bridging complex on secretion not directly tested"]},{"year":2015,"claim":"Demonstrating that Doc2b directly induces hemifusion without SNAREs: it was unknown whether Doc2b's membrane-remodeling activity required SNAREs; SNARE-free reconstitution showed Doc2b stabilizes hemifusion intermediates in a Ca²⁺/PS-dependent manner with stalks resisting ~600 pN.","evidence":"Dual optical trap with SNARE-free synthetic membranes, real-time lipid/content mixing fluorescence","pmids":["26395669"],"confidence":"High","gaps":["How SNARE-independent hemifusion integrates with SNARE-dependent fusion in vivo is unresolved","Lipid composition dependence beyond PS not explored"]},{"year":2019,"claim":"Revealing post-translational regulation of DOC2B by Y301 phosphorylation for GLUT4 trafficking: insulin-stimulated phosphorylation of DOC2B at Y301 was shown to enable interaction with kinesin light chain 1 (KLC1), coupling DOC2B to microtubule-based vesicle transport required for GLUT4 plasma membrane accumulation.","evidence":"Y301 mutagenesis, Co-IP, mass spectrometry, GLUT4 translocation assay in L6 cells and skeletal-muscle-specific transgenic mice","pmids":["30707251"],"confidence":"High","gaps":["Kinase responsible for Y301 phosphorylation in muscle not identified in this study","Whether KLC1 interaction applies in β-cells"]},{"year":2019,"claim":"Distinguishing Doc2b and Syt1 membrane-remodeling mechanisms: biophysical comparison showed Doc2b is more effective at hemifusion when present on both apposed membranes, while Syt1 acts preferentially from one membrane, clarifying their non-redundant roles.","evidence":"Dual optical trap with SNARE-free membranes, AFM bending modulus measurements","pmids":["31952804"],"confidence":"High","gaps":["Physiological relevance of bilateral versus unilateral membrane loading not tested in vivo"]},{"year":2021,"claim":"Linking DOC2B to metastasis suppression: DOC2B was found to interact with E-cadherin (CDH1) in a calcium-dependent manner, inhibiting EMT and promoting senescence to suppress metastasis.","evidence":"Co-IP of DOC2B with CDH1, OE/KD in cancer cells, xenograft and liver metastasis models","pmids":["33758996"],"confidence":"Medium","gaps":["Whether DOC2B-CDH1 interaction is direct or scaffolded","Mechanism by which DOC2B promotes senescence unknown"]},{"year":2022,"claim":"Identifying YES kinase as the DOC2B Y301 kinase and ERM proteins as downstream effectors in β-cells: glucose stimulation triggers rapid YES-mediated Y301 phosphorylation, which enables DOC2B–ERM interaction, ERM activation, and VAMP2-containing insulin granule delivery to the plasma membrane.","evidence":"Phosphorylation kinetics, Co-IP with YES and ERM, Y301 mutagenesis, ERM knockdown, GSIS in human islets and clonal β-cells","pmids":["35377441"],"confidence":"High","gaps":["Whether YES-DOC2B-ERM axis operates in neurons or other secretory cells","How ERM activation mechanistically promotes granule–PM docking"]},{"year":2025,"claim":"Extending DOC2B's role to inflammatory signaling: DOC2B was found to associate with IKKβ and STAT-1 in cytokine-challenged β-cells, attenuating NF-κB and STAT-1 activation and reducing CXCL10 expression.","evidence":"Co-IP, proteomics, qPCR, immunoconfocal in DOC2b-enriched/depleted human islets and β-cell lines","pmids":["39805534"],"confidence":"Medium","gaps":["Direct versus indirect association with IKKβ and STAT-1 not resolved","Whether this anti-inflammatory role is linked to DOC2B's vesicle trafficking function"]},{"year":null,"claim":"A full-length DOC2B structure in the context of membranes and SNARE complexes has not been determined, the molecular basis of the MID-domain's inhibitory function remains uncharacterized, and whether DOC2B's vesicle-trafficking and anti-inflammatory roles are mechanistically coupled is unknown.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length DOC2B atomic structure","MID-domain inhibitory mechanism unresolved","Integration of trafficking and signaling functions not tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1,3,5,6]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,5,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[8,14,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[9,10,17]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,3,5,12,13]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,9,10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,15,17]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,2,4,7,12]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17]}],"complexes":["Munc18c-Doc2b-Munc18-1 scaffold","SNARE complex (syntaxin-4/VAMP2-associated)"],"partners":["STX4","MUNC18C","MUNC18-1","SYT1","UNC13A","KLC1","YES1","EZR"],"other_free_text":[]},"mechanistic_narrative":"DOC2B is a double-C2-domain calcium sensor that functions as a key regulator of vesicle priming and membrane fusion across neuronal, neuroendocrine, and metabolic cell types. Upon submicromolar Ca²⁺ elevations, DOC2B translocates to the plasma membrane via Ca²⁺- and phosphatidylserine-dependent C2 domain–lipid interactions—with C2B serving as the primary Ca²⁺-sensing unit—where it binds SNARE complexes (syntaxin-4 in peripheral tissues, plasma membrane SNAREs in neurons), induces membrane curvature and hemifusion, and scaffolds Munc18 isoforms and Munc13-1 to promote vesicle competence for fusion [PMID:20150444, PMID:18596155, PMID:23994332, PMID:26395669, PMID:25190515]. In neurons, DOC2B acts as the high-affinity Ca²⁺ sensor for spontaneous neurotransmitter release, competing with synaptotagmin-1 for SNARE binding, and in chromaffin cells it orchestrates sequential priming steps while inhibiting release during sustained Ca²⁺ elevation to favor synchronized secretion [PMID:20150444, PMID:29274147, PMID:24133251]. In pancreatic β-cells and skeletal muscle, DOC2B is phosphorylated at Y301 by YES kinase upon glucose or insulin stimulation, enabling interactions with kinesin light chain 1 and ERM proteins that drive insulin granule and GLUT4 vesicle delivery to the plasma membrane [PMID:30707251, PMID:35377441, PMID:22698913]. DOC2B also attenuates cytokine-induced inflammatory signaling in β-cells by associating with IKKβ and STAT-1 to dampen NF-κB pathway activation [PMID:39805534]."},"prefetch_data":{"uniprot":{"accession":"Q14184","full_name":"Double C2-like domain-containing protein beta","aliases":[],"length_aa":412,"mass_kda":45.9,"function":"Calcium sensor which positively regulates SNARE-dependent fusion of vesicles with membranes. Binds phospholipids in a calcium-dependent manner and may act at the priming stage of fusion by modifying membrane curvature to stimulate fusion. Involved in calcium-triggered exocytosis in chromaffin cells and calcium-dependent spontaneous release of neurotransmitter in absence of action potentials in neuronal cells. Involved both in glucose-stimulated insulin secretion in pancreatic cells and insulin-dependent GLUT4 transport to the plasma membrane in adipocytes (By similarity)","subcellular_location":"Cytoplasm; Cytoplasmic granule; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q14184/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/DOC2B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":77,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/DOC2B","total_profiled":1310},"omim":[{"mim_id":"604568","title":"DOUBLE C2-LIKE DOMAIN-CONTAINING PROTEIN, BETA; DOC2B","url":"https://www.omim.org/entry/604568"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":53.3},{"tissue":"retina","ntpm":39.0}],"url":"https://www.proteinatlas.org/search/DOC2B"},"hgnc":{"alias_symbol":[],"prev_symbol":["DOC2BL"]},"alphafold":{"accession":"Q14184","domains":[{"cath_id":"2.60.40.150","chopping":"130-258","consensus_level":"high","plddt":93.9708,"start":130,"end":258},{"cath_id":"2.60.40.150","chopping":"267-402","consensus_level":"high","plddt":96.1555,"start":267,"end":402}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14184","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14184-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14184-F1-predicted_aligned_error_v6.png","plddt_mean":78.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DOC2B","jax_strain_url":"https://www.jax.org/strain/search?query=DOC2B"},"sequence":{"accession":"Q14184","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14184.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14184/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14184"}},"corpus_meta":[{"pmid":"20150444","id":"PMC_20150444","title":"Doc2b 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calcium sensor for vesicle priming requiring synaptotagmin-1, Munc13-2 and SNAREs.","date":"2017","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/29274147","citation_count":27,"is_preprint":false},{"pmid":"30707251","id":"PMC_30707251","title":"DOC2B promotes insulin sensitivity in mice via a novel KLC1-dependent mechanism in skeletal muscle.","date":"2019","source":"Diabetologia","url":"https://pubmed.ncbi.nlm.nih.gov/30707251","citation_count":22,"is_preprint":false},{"pmid":"19410553","id":"PMC_19410553","title":"DOC2b is a SNARE regulator of glucose-stimulated delayed insulin secretion.","date":"2009","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/19410553","citation_count":22,"is_preprint":false},{"pmid":"33758996","id":"PMC_33758996","title":"Metastatic suppression by DOC2B is mediated by inhibition of epithelial-mesenchymal transition and induction of senescence.","date":"2021","source":"Cell biology and 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Translocates to the Plasma Membrane in a Doc2B- and Calcium-Dependent Manner.","date":"2013","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/24062723","citation_count":17,"is_preprint":false},{"pmid":"31952804","id":"PMC_31952804","title":"Synaptotagmin-1 and Doc2b Exhibit Distinct Membrane-Remodeling Mechanisms.","date":"2019","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/31952804","citation_count":16,"is_preprint":false},{"pmid":"16305808","id":"PMC_16305808","title":"Calcium concentration threshold and translocation kinetics of EGFP-DOC2B expressed in cultured Aplysia neurons.","date":"2005","source":"Cell calcium","url":"https://pubmed.ncbi.nlm.nih.gov/16305808","citation_count":16,"is_preprint":false},{"pmid":"29506054","id":"PMC_29506054","title":"Exocytosis Protein DOC2B as a Biomarker of Type 1 Diabetes.","date":"2018","source":"The Journal of clinical endocrinology and 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Diabetes.","date":"2026","source":"EJIFCC","url":"https://pubmed.ncbi.nlm.nih.gov/41659295","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":17796,"output_tokens":4984,"usd":0.064074},"stage2":{"model":"claude-opus-4-6","input_tokens":8524,"output_tokens":4363,"usd":0.227543},"total_usd":0.291617,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"Doc2b acts as a high-affinity Ca2+ sensor for spontaneous (miniature) neurotransmitter release. Although cytosolic, Doc2b functions analogously to synaptotagmin-1 but with higher Ca2+ sensitivity, and it binds to SNARE complexes in competition with synaptotagmin-1.\",\n      \"method\": \"Knockout mouse analysis, electrophysiology, Co-IP/competitive binding assays with SNARE complexes\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding assays and genetic KO with defined electrophysiological phenotype, highly cited foundational paper replicated across labs\",\n      \"pmids\": [\"20150444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The C2A domain of DOC2B interacts directly with the plasma membrane in a Ca2+-dependent manner, causing translocation of DOC2B to the plasma membrane upon small elevations in intracellular Ca2+. At the plasma membrane, DOC2B acts as a priming factor increasing the number of fusion-competent vesicles, affects fusion pore expansion kinetics, and interacts with plasma membrane SNAREs.\",\n      \"method\": \"Biochemical binding assays, TIRF microscopy, electrophysiology, FRAP, mutagenesis of Ca2+-binding DOC2B\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biophysical, electrophysiological, morphological, live imaging) in a single study with mutagenesis controls\",\n      \"pmids\": [\"18596155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"DOC2b directly associates with syntaxin-4 (a target-SNARE) in an intracellular Ca2+-dependent manner, and this interaction is essential for triggering GLUT4 vesicle fusion in adipocytes upon insulin stimulation.\",\n      \"method\": \"Yeast two-hybrid screening, co-immunoprecipitation, GST pulldown, confocal immunofluorescence microscopy, siRNA knockdown with GLUT4 translocation assay\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Y2H, Co-IP, GST pulldown, functional KD) with defined cellular phenotype\",\n      \"pmids\": [\"19033398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A rise in intracellular Ca2+ is sufficient (independent of Munc13) to recruit DOC2B to the target membrane. Purified DOC2B binds phospholipids in a Ca2+-dependent manner, and depolarization of neurons induces complete translocation of DOC2B-EGFP to the plasma membrane within 5 seconds.\",\n      \"method\": \"Phospholipid-binding assay with purified protein, live fluorescence imaging of DOC2B-EGFP in neurons, mutagenesis (Munc13-binding mutants)\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro lipid-binding reconstitution combined with live-cell imaging and mutagenesis\",\n      \"pmids\": [\"15033971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Doc2b binds GLUT4 exocytic SNAREs and potently accelerates SNARE-dependent membrane fusion kinetics in a reconstituted proteoliposome system. This activity requires intact Ca2+-binding sites on both C2A and C2B domains. Doc2b also strongly bends membrane bilayers, and this membrane-bending activity is essential to its stimulatory function in fusion.\",\n      \"method\": \"Reconstituted proteoliposome fusion assay, electron microscopy, mutagenesis of Ca2+-binding sites\",\n      \"journal\": \"Molecular Biology of the Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro fusion system with mutagenesis and EM structural validation\",\n      \"pmids\": [\"23427263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structures of isolated DOC2B C2A and C2B domains were determined, revealing that C2B binds Ca2+ with considerably higher affinity than C2A. The C2AB solution structure (by SAXS) shows two domains with highly flexible orientation unaffected by Ca2+. In cells, C2B translocates to the plasma membrane at ~400 nM Ca2+ (EC50) while C2A does not at submicromolar Ca2+; C2AB translocates with ~2-fold lower EC50 than C2B alone, establishing C2B as the primary Ca2+-sensing unit.\",\n      \"method\": \"X-ray crystallography of C2A and C2B domains, SAXS of C2AB, Ca2+-binding kinetics, live-cell fluorescence imaging with isolated domain constructs\",\n      \"journal\": \"Journal of Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures combined with functional live-cell imaging and kinetic biochemistry in one study\",\n      \"pmids\": [\"23994332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The C2AB domain of Doc2b stabilizes a membrane hemifusion intermediate (lipid mixing without content mixing) in a strictly Ca2+- and phosphatidylserine-dependent manner, directly acting on membranes without SNAREs. Doc2b-coated membrane stalks resist forces up to 600 pN.\",\n      \"method\": \"Dual optical trap assay with SNARE-free synthetic membranes, real-time fluorescence lipid/content mixing assay\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cell-free reconstitution with optical trapping and fluorescence imaging; direct mechanistic demonstration\",\n      \"pmids\": [\"26395669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Doc2b is required for both phases of glucose-stimulated insulin secretion from pancreatic islets and for insulin-stimulated GLUT4 vesicle translocation in skeletal muscle, acting as a positive regulator of Munc18c-syntaxin 4-mediated SNARE complex assembly.\",\n      \"method\": \"Doc2b knockout mouse analysis, ex vivo islet secretion assay, skeletal muscle GLUT4 translocation assay, SNARE complex formation biochemical assay\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined phenotypic readouts and pathway placement via SNARE complex assay\",\n      \"pmids\": [\"22698913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Doc2b serves as a scaffolding platform that simultaneously binds both Munc18-1 (via C2A domain) and Munc18c (via C2B domain), bridging their interaction. Macromolecular complexes of Munc18c-Doc2b-Munc18-1 exist in β-cells, and Munc18c and Munc18-1 fail to associate in the absence of Doc2b.\",\n      \"method\": \"Co-immunoprecipitation from β-cells, in vitro GST-Doc2b pulldown competition assays\",\n      \"journal\": \"The Biochemical Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP and pulldown from single lab, but domain-specific interaction with mutagenesis/competition controls\",\n      \"pmids\": [\"25190515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Doc2b plays distinct roles in two sequential priming steps in chromaffin cells. Mutating Ca2+-coordinating aspartates in C2A permanently localizes Doc2b at the plasma membrane and renders an upstream priming step Ca2+-independent. A downstream priming step depends on SNARE-binding and Ca2+-binding to C2B, interaction with ubMunc13-2, and presence of synaptotagmin-1. Doc2b also inhibits release during sustained Ca2+ elevations via its MID-domain.\",\n      \"method\": \"Site-directed mutagenesis of Ca2+-binding sites, overexpression/KO in chromaffin cells, capacitance measurements, genetic epistasis with ubMunc13-2 and synaptotagmin-1\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis of multiple domains, genetic epistasis with defined priming-step phenotypes, multiple orthogonal readouts\",\n      \"pmids\": [\"29274147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In chromaffin cells, Doc2b overexpression inhibits the sustained release component and augments the readily releasable pool, while Doc2b KO shifts release from the readily releasable pool to the sustained component and accelerates (but makes incomplete) refilling of the readily releasable pool. Doc2b thus inhibits vesicle priming during prolonged Ca2+ elevations, protecting unprimed vesicles and favoring synchronized fast release.\",\n      \"method\": \"Doc2b knockout and overexpression in mouse chromaffin cells, high-temporal-resolution capacitance measurements, electron microscopy\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO and OE with multiple orthogonal readouts including EM and electrophysiology\",\n      \"pmids\": [\"24133251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Munc13-1 co-translocates to the plasma membrane in a Doc2B- and Ca2+-dependent manner. Without co-expressed Doc2B, Munc13-1 does not translocate. Munc13-1 accumulation at the PM after repeated stimulations depends on DAG levels (via Munc13-1 H567K DAG-binding mutant), suggesting Doc2B recruits Munc13-1 to the PM where DAG stabilizes it.\",\n      \"method\": \"Fluorescent protein co-expression in PC12 cells, live-cell imaging, mutagenesis of Munc13-1 DAG-binding site\",\n      \"journal\": \"Frontiers in Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — live imaging with mutagenesis controls, single lab, functional consequence inferred\",\n      \"pmids\": [\"24062723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DOC2b associates with insulin vesicles and translocates to the plasma membrane upon high-glucose stimulation, where it interacts specifically with syntaxin-4 (not syntaxin-1), and is required for delayed (second-phase) but not rapid insulin secretion.\",\n      \"method\": \"Confocal microscopy of DOC2b localization, co-immunoprecipitation with syntaxins, siRNA knockdown with biphasic insulin secretion assay in MIN6 cells\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP and KD with defined secretory phenotype, single lab\",\n      \"pmids\": [\"19410553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The intracellular Ca2+ concentration threshold for EGFP-DOC2B translocation to the plasma membrane is approximately 200 nM in the bulk cytoplasm of Aplysia neurons. DOC2B translocation kinetics are slower than Ca2+ elevation rate, and detachment is faster than Ca2+ removal.\",\n      \"method\": \"Live-cell imaging of EGFP-DOC2B in Aplysia neurons with simultaneous Ca2+ measurement\",\n      \"journal\": \"Cell Calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct quantitative live imaging with Ca2+ measurement, but single model system\",\n      \"pmids\": [\"16305808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DOC2B is phosphorylated at tyrosine Y301 upon insulin stimulation in skeletal muscle cells. This phosphorylation enhances DOC2B's interaction with the microtubule motor protein kinesin light chain 1 (KLC1), and is required for insulin-stimulated GLUT4 accumulation at the plasma membrane. Mutation of Y301 blocks phosphorylation, KLC1 interaction, and blunts GLUT4 translocation.\",\n      \"method\": \"Site-directed mutagenesis of Y301, co-immunoprecipitation, mass spectrometry, GLUT4 translocation assay in L6-GLUT4-myc cells and skeletal-muscle-specific transgenic mice\",\n      \"journal\": \"Diabetologia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis of specific phosphosite, Co-IP, MS identification, in vivo transgenic confirmation, multiple orthogonal methods\",\n      \"pmids\": [\"30707251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DOC2b is tyrosine phosphorylated at Y301 within 2 min of glucose stimulation in β-cells, with YES kinase (Src family) responsible for this modification. Y301 phosphorylation is required for DOC2b's interaction with YES kinase and with ERM (Ezrin-Radixin-Moesin) family proteins, and ERM activation by Y301-phosphorylated DOC2b is required for VAMP2-containing insulin granule localization to the plasma membrane and enhancement of glucose-stimulated insulin secretion.\",\n      \"method\": \"Biochemical phosphorylation analysis, Co-immunoprecipitation with YES and ERM proteins, site-directed mutagenesis of Y301, ERM knockdown, VAMP2 PM localization assay, GSIS assay in human islets and clonal β-cells\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — identified kinase (YES), phosphosite (Y301), downstream effectors (ERM), multiple orthogonal methods in human primary islets and cell lines\",\n      \"pmids\": [\"35377441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Synaptotagmin-1 and Doc2b exhibit distinct membrane-remodeling mechanisms: Doc2b is more effective when loaded on both membranes, while Syt1 is more effective from a single membrane. Both C2AB fragments can induce hemifusion and reduce membrane bending modulus (as measured by AFM), but significantly higher Syt1 concentrations are required for hemifusion.\",\n      \"method\": \"Dual optical trap with SNARE-free membranes, lipid-mixing confocal assay, atomic force microscopy bending modulus measurement\",\n      \"journal\": \"Biophysical Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cell-free reconstitution with multiple biophysical methods directly comparing Doc2b and Syt1 membrane activities\",\n      \"pmids\": [\"31952804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DOC2b associates with IKKβ, NF-κB p65, and STAT-1 in cytokine-challenged β-cells. DOC2b enrichment attenuates cytokine-induced IKKβ activation and total IKKβ protein levels, increases IκBβ protein, and reduces STAT-1 activation and expression, resulting in decreased CXCL10 expression.\",\n      \"method\": \"Co-immunoprecipitation, qPCR, proteomics, immunoconfocal microscopy in DOC2b-enriched/depleted human islets and β-cell lines challenged with proinflammatory cytokines\",\n      \"journal\": \"Metabolism: Clinical and Experimental\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP association with signaling components, functional enrichment/depletion, single lab, pathway placement inferred\",\n      \"pmids\": [\"39805534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"DOC2B overexpression in cervical cancer cells impairs AKT1 and ERK1/2 signaling and induces actin cytoskeleton remodeling in a calcium-dependent manner, correlating with reduced cell migration, invasion, and tumor growth in xenograft models.\",\n      \"method\": \"DOC2B overexpression in SiHa cells, Western blotting for pAKT1/pERK1/2, actin staining, xenograft tumor model\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — overexpression with signaling readouts and in vivo xenograft, pathway placement partially defined, single lab\",\n      \"pmids\": [\"24570007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DOC2B inhibits epithelial-mesenchymal transition (EMT) and promotes senescence via a calcium-dependent interaction with CDH1 (E-cadherin). This DOC2B-calcium-EMT-senescence axis is required for DOC2B's metastasis-suppressive function in cancer cells.\",\n      \"method\": \"DOC2B overexpression/knockdown in cancer cells, co-immunoprecipitation of DOC2B with CDH1, nude mice xenograft and liver metastasis models, EMT marker analysis\",\n      \"journal\": \"Cell Biology and Toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP with CDH1, functional KD/OE with in vivo confirmation, single lab\",\n      \"pmids\": [\"33758996\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DOC2B is a cytosolic, double-C2-domain Ca2+ sensor (with C2B as the primary Ca2+-sensing unit) that, upon Ca2+ binding, translocates to the plasma membrane via C2 domain-phosphatidylserine interaction, where it promotes vesicle priming and fusion by binding SNARE complexes (competing with synaptotagmin-1), inducing membrane curvature/hemifusion, and scaffolding Munc18 isoforms and Munc13-1; it is post-translationally regulated by YES kinase-mediated phosphorylation at Y301, which drives interaction with KLC1 (in muscle) and ERM proteins (in β-cells) to facilitate GLUT4 and insulin granule trafficking to the plasma membrane, while also modulating inflammatory signaling via association with IKKβ and STAT-1.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"DOC2B is a double-C2-domain calcium sensor that functions as a key regulator of vesicle priming and membrane fusion across neuronal, neuroendocrine, and metabolic cell types. Upon submicromolar Ca²⁺ elevations, DOC2B translocates to the plasma membrane via Ca²⁺- and phosphatidylserine-dependent C2 domain–lipid interactions—with C2B serving as the primary Ca²⁺-sensing unit—where it binds SNARE complexes (syntaxin-4 in peripheral tissues, plasma membrane SNAREs in neurons), induces membrane curvature and hemifusion, and scaffolds Munc18 isoforms and Munc13-1 to promote vesicle competence for fusion [PMID:20150444, PMID:18596155, PMID:23994332, PMID:26395669, PMID:25190515]. In neurons, DOC2B acts as the high-affinity Ca²⁺ sensor for spontaneous neurotransmitter release, competing with synaptotagmin-1 for SNARE binding, and in chromaffin cells it orchestrates sequential priming steps while inhibiting release during sustained Ca²⁺ elevation to favor synchronized secretion [PMID:20150444, PMID:29274147, PMID:24133251]. In pancreatic β-cells and skeletal muscle, DOC2B is phosphorylated at Y301 by YES kinase upon glucose or insulin stimulation, enabling interactions with kinesin light chain 1 and ERM proteins that drive insulin granule and GLUT4 vesicle delivery to the plasma membrane [PMID:30707251, PMID:35377441, PMID:22698913]. DOC2B also attenuates cytokine-induced inflammatory signaling in β-cells by associating with IKKβ and STAT-1 to dampen NF-κB pathway activation [PMID:39805534].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing the basic translocation mechanism: it was unknown how DOC2B reaches its site of action; direct lipid-binding assays and live imaging showed that a rise in intracellular Ca²⁺ is sufficient to recruit DOC2B to the plasma membrane via phospholipid interaction, independent of Munc13.\",\n      \"evidence\": \"Purified protein phospholipid-binding assay and DOC2B-EGFP live imaging in neurons with Munc13-binding mutants\",\n      \"pmids\": [\"15033971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phospholipid species preference not fully defined\", \"Kinetics of membrane association/dissociation not quantified at this stage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Quantifying the Ca²⁺ sensitivity of translocation: the threshold intracellular Ca²⁺ concentration for DOC2B plasma membrane recruitment was determined to be ~200 nM, placing it as a sensor of modest Ca²⁺ fluctuations.\",\n      \"evidence\": \"Simultaneous EGFP-DOC2B imaging and Ca²⁺ measurement in Aplysia neurons\",\n      \"pmids\": [\"16305808\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Measured in invertebrate neurons only\", \"Translocation kinetics slower than Ca²⁺ rise—mechanism not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defining DOC2B as a vesicle priming factor and identifying its SNARE interactions: DOC2B was shown to increase the number of fusion-competent vesicles at the plasma membrane, affect fusion pore kinetics, and interact with plasma membrane SNAREs—in neurons via C2A-dependent translocation, and in adipocytes via direct Ca²⁺-dependent binding to syntaxin-4 to trigger GLUT4 vesicle fusion.\",\n      \"evidence\": \"TIRF, FRAP, electrophysiology, and mutagenesis in neurons; yeast two-hybrid, Co-IP, GST pulldown, and siRNA knockdown with GLUT4 assay in adipocytes\",\n      \"pmids\": [\"18596155\", \"19033398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether priming and fusion pore effects are separable functions\", \"Whether syntaxin-4 interaction applies to all peripheral secretory cell types\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linking DOC2B to biphasic insulin secretion: DOC2B was found on insulin vesicles, translocating to the plasma membrane upon glucose stimulation and specifically engaging syntaxin-4 to support second-phase insulin release.\",\n      \"evidence\": \"Confocal microscopy, Co-IP, siRNA knockdown with biphasic insulin secretion assay in MIN6 β-cells\",\n      \"pmids\": [\"19410553\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Only second-phase role demonstrated in this study; first-phase role unclear at this point\", \"Single cell line (MIN6)\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying DOC2B as the high-affinity Ca²⁺ sensor for spontaneous neurotransmitter release: it was unknown what Ca²⁺ sensor drives miniature release; knockout analysis and competitive binding assays showed DOC2B binds SNARE complexes in competition with synaptotagmin-1 and is required for normal spontaneous release frequency.\",\n      \"evidence\": \"Doc2b knockout mice, electrophysiology, Co-IP and competitive SNARE-binding assays\",\n      \"pmids\": [\"20150444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Doc2b is the sole Ca²⁺ sensor for minis or acts redundantly with Doc2a\", \"Structural basis of Syt1–Doc2b competition on SNAREs unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extending the in vivo role to whole-animal glucose homeostasis: Doc2b knockout mice showed impaired glucose-stimulated insulin secretion from islets and defective GLUT4 translocation in skeletal muscle, with Doc2b acting as a positive regulator of Munc18c–syntaxin-4 SNARE assembly.\",\n      \"evidence\": \"Doc2b knockout mouse, ex vivo islet secretion, skeletal muscle GLUT4 assay, SNARE complex formation biochemistry\",\n      \"pmids\": [\"22698913\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Doc2b loss affects other SNARE-dependent trafficking in vivo\", \"Contribution to type 2 diabetes pathogenesis not directly tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolving the molecular mechanism of fusion acceleration and identifying C2B as the primary Ca²⁺-sensing unit: reconstituted systems and crystal structures showed that Doc2b accelerates SNARE-dependent fusion by bending membranes (requiring both C2 domains' Ca²⁺ sites), and C2B binds Ca²⁺ with higher affinity and translocates at ~400 nM Ca²⁺, establishing it as the dominant sensor.\",\n      \"evidence\": \"Proteoliposome fusion assays, EM, X-ray crystallography of C2A/C2B, SAXS of C2AB, live-cell translocation of isolated domains\",\n      \"pmids\": [\"23427263\", \"23994332\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length DOC2B structure not determined\", \"How the flexible C2A–C2B orientation contributes to membrane bending is unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Delineating sequential priming roles and inhibitory function in chromaffin cells: Doc2b was found to participate in two sequential vesicle priming steps—an upstream step governed by C2A membrane attachment and a downstream step requiring C2B-SNARE and Munc13-2 interaction—while its MID domain inhibits release during sustained Ca²⁺, protecting the readily releasable pool.\",\n      \"evidence\": \"Site-directed mutagenesis of Ca²⁺-binding and MID domains, Doc2b KO/OE in chromaffin cells, capacitance measurements, genetic epistasis with Munc13-2 and Syt1\",\n      \"pmids\": [\"29274147\", \"24133251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of MID-domain inhibitory action unknown\", \"Whether dual priming mechanism applies to neurons\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing DOC2B as a recruiter of Munc13-1 to the plasma membrane: Munc13-1 was shown to co-translocate with Doc2b in a Ca²⁺-dependent manner, with subsequent DAG-dependent stabilization at the membrane.\",\n      \"evidence\": \"Fluorescent protein co-expression and live imaging in PC12 cells, Munc13-1 DAG-binding mutant\",\n      \"pmids\": [\"24062723\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of Munc13-1 recruitment by Doc2b on secretion not directly measured\", \"Observed in overexpression system only\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying DOC2B as a scaffolding hub bridging Munc18-1 and Munc18c: in β-cells, Doc2b simultaneously binds Munc18-1 (via C2A) and Munc18c (via C2B), and these two Munc18 isoforms fail to associate in the absence of Doc2b.\",\n      \"evidence\": \"Co-IP from β-cells, in vitro GST-Doc2b pulldown with competition assays\",\n      \"pmids\": [\"25190515\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Awaits reconstitution with purified components to confirm direct tripartite complex\", \"Functional consequence of the Munc18-1/Munc18c bridging complex on secretion not directly tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrating that Doc2b directly induces hemifusion without SNAREs: it was unknown whether Doc2b's membrane-remodeling activity required SNAREs; SNARE-free reconstitution showed Doc2b stabilizes hemifusion intermediates in a Ca²⁺/PS-dependent manner with stalks resisting ~600 pN.\",\n      \"evidence\": \"Dual optical trap with SNARE-free synthetic membranes, real-time lipid/content mixing fluorescence\",\n      \"pmids\": [\"26395669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SNARE-independent hemifusion integrates with SNARE-dependent fusion in vivo is unresolved\", \"Lipid composition dependence beyond PS not explored\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealing post-translational regulation of DOC2B by Y301 phosphorylation for GLUT4 trafficking: insulin-stimulated phosphorylation of DOC2B at Y301 was shown to enable interaction with kinesin light chain 1 (KLC1), coupling DOC2B to microtubule-based vesicle transport required for GLUT4 plasma membrane accumulation.\",\n      \"evidence\": \"Y301 mutagenesis, Co-IP, mass spectrometry, GLUT4 translocation assay in L6 cells and skeletal-muscle-specific transgenic mice\",\n      \"pmids\": [\"30707251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for Y301 phosphorylation in muscle not identified in this study\", \"Whether KLC1 interaction applies in β-cells\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Distinguishing Doc2b and Syt1 membrane-remodeling mechanisms: biophysical comparison showed Doc2b is more effective at hemifusion when present on both apposed membranes, while Syt1 acts preferentially from one membrane, clarifying their non-redundant roles.\",\n      \"evidence\": \"Dual optical trap with SNARE-free membranes, AFM bending modulus measurements\",\n      \"pmids\": [\"31952804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of bilateral versus unilateral membrane loading not tested in vivo\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linking DOC2B to metastasis suppression: DOC2B was found to interact with E-cadherin (CDH1) in a calcium-dependent manner, inhibiting EMT and promoting senescence to suppress metastasis.\",\n      \"evidence\": \"Co-IP of DOC2B with CDH1, OE/KD in cancer cells, xenograft and liver metastasis models\",\n      \"pmids\": [\"33758996\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether DOC2B-CDH1 interaction is direct or scaffolded\", \"Mechanism by which DOC2B promotes senescence unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying YES kinase as the DOC2B Y301 kinase and ERM proteins as downstream effectors in β-cells: glucose stimulation triggers rapid YES-mediated Y301 phosphorylation, which enables DOC2B–ERM interaction, ERM activation, and VAMP2-containing insulin granule delivery to the plasma membrane.\",\n      \"evidence\": \"Phosphorylation kinetics, Co-IP with YES and ERM, Y301 mutagenesis, ERM knockdown, GSIS in human islets and clonal β-cells\",\n      \"pmids\": [\"35377441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether YES-DOC2B-ERM axis operates in neurons or other secretory cells\", \"How ERM activation mechanistically promotes granule–PM docking\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extending DOC2B's role to inflammatory signaling: DOC2B was found to associate with IKKβ and STAT-1 in cytokine-challenged β-cells, attenuating NF-κB and STAT-1 activation and reducing CXCL10 expression.\",\n      \"evidence\": \"Co-IP, proteomics, qPCR, immunoconfocal in DOC2b-enriched/depleted human islets and β-cell lines\",\n      \"pmids\": [\"39805534\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect association with IKKβ and STAT-1 not resolved\", \"Whether this anti-inflammatory role is linked to DOC2B's vesicle trafficking function\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length DOC2B structure in the context of membranes and SNARE complexes has not been determined, the molecular basis of the MID-domain's inhibitory function remains uncharacterized, and whether DOC2B's vesicle-trafficking and anti-inflammatory roles are mechanistically coupled is unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length DOC2B atomic structure\", \"MID-domain inhibitory mechanism unresolved\", \"Integration of trafficking and signaling functions not tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1, 3, 5, 6]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 5, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [8, 14, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9, 10, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 3, 5, 12, 13]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 9, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 15, 17]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 2, 4, 7, 12]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"complexes\": [\n      \"Munc18c-Doc2b-Munc18-1 scaffold\",\n      \"SNARE complex (syntaxin-4/VAMP2-associated)\"\n    ],\n    \"partners\": [\n      \"STX4\",\n      \"MUNC18C\",\n      \"MUNC18-1\",\n      \"SYT1\",\n      \"UNC13A\",\n      \"KLC1\",\n      \"YES1\",\n      \"EZR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}