{"gene":"VAPA","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":2002,"finding":"VAPA (VAP-A) interacts with oxysterol-binding protein (OSBP) through a region in OSBP spanning amino acids 351-442; C- and N-terminal truncations of VAP-A prevent OSBP binding but not VAP multimerization. The VAP-A/OSBP complex localizes to ER-associated structures and its disruption impairs ceramide transport from ER to Golgi, as measured by reduced sphingomyelin synthesis.","method":"Yeast two-hybrid screen, GST pulldown, co-immunoprecipitation, functional transport assay (ts045-VSVG-GFP, fluorescent ceramide)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, pulldown, domain mapping, and functional consequence with multiple orthogonal assays in single study","pmids":["12023275"],"is_preprint":false},{"year":2001,"finding":"VAPA is a resident of the ER/Golgi intermediate compartment and binds promiscuously to both v- and t-SNAREs including VAMP, syntaxin 1A, rbet1, rsec22, αSNAP, and NSF. Both N- and C-terminal domains of VAPA are required for VAMP binding and VAP dimerization.","method":"Subcellular fractionation, in vitro binding assays, domain deletion analysis in COS-7 cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and binding assays, single lab","pmids":["11511104"],"is_preprint":false},{"year":2004,"finding":"hVAP-33 (VAPA) binds to HCV nonstructural proteins NS5A and NS5B and is required for the formation of the HCV RNA replication complex on lipid rafts (detergent-resistant membranes). Expression of dominant-negative VAPA mutants or siRNA knockdown of hVAP-33 caused NS5B to relocate from detergent-resistant to detergent-sensitive membranes and reduced HCV RNA and protein levels.","method":"Co-immunoprecipitation, siRNA knockdown, dominant-negative mutants, detergent-resistant membrane fractionation, HCV replicon system","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches (Co-IP, DN mutant, siRNA, fractionation) with functional readout; highly cited","pmids":["15016871"],"is_preprint":false},{"year":2003,"finding":"Norwalk virus nonstructural protein p48 directly interacts with VAPA and forms a stable complex in mammalian cells, and this interaction inhibits cell-surface expression of vesicular stomatitis virus G protein, implicating VAPA-mediated disruption of intracellular protein trafficking.","method":"Yeast two-hybrid, co-immunoprecipitation, surface protein transport assay","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — yeast two-hybrid confirmed by Co-IP plus functional transport assay","pmids":["14557663"],"is_preprint":false},{"year":2008,"finding":"Overexpression of wild-type VAPA (but not VAPB) inhibits ER-to-Golgi transport by decreasing segregation of membrane cargo into ER vesicles and inhibiting lateral diffusion of membrane proteins, likely through stable VAPA association with microtubules. The FFAT motif peptide relieves this block and restores ER vesicle budding and disrupts VAP-microtubule association in vitro.","method":"Cargo transport assays, in vitro ER vesicle budding assay, lateral diffusion measurements, FFAT peptide competition","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro budding reconstitution combined with live-cell functional transport assays and mechanistic peptide competition","pmids":["18713837"],"is_preprint":false},{"year":2009,"finding":"Glycolipid transfer protein (GLTP) contains an FFAT-like motif and directly interacts with VAPA; mutation of the FFAT-like motif abolishes this interaction, as determined by GST pulldown.","method":"GST pulldown, FFAT motif mutagenesis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — single pulldown method with mutagenesis confirmation, single lab","pmids":["19665998"],"is_preprint":false},{"year":2010,"finding":"VAPA interacts with the cochlear motor protein prestin, confirmed by co-immunoprecipitation; VAPA expression is reduced in prestin-knockout OHCs, and co-expression of VAPA with prestin increases prestin abundance at the plasma membrane, suggesting VAPA facilitates prestin trafficking to the membrane.","method":"Yeast two-hybrid (membrane-based), co-immunoprecipitation, prestin-KO mouse comparison, surface expression assay","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP confirmed by KO model and functional overexpression, single lab","pmids":["20359505"],"is_preprint":false},{"year":2010,"finding":"The ALS-linked VAPB P56S mutation phenotype (ER aggregation) can be recapitulated in VAPA by mutating the equivalent proline distribution in the conserved region; VAPA normally requires three properly distributed prolines in this region for correct function, explaining why wild-type VAPA is resistant to the equivalent of the P56S mutation.","method":"Site-directed mutagenesis, fluorescence microscopy of aggregation phenotype","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis with defined phenotypic readout, single lab","pmids":["21144830"],"is_preprint":false},{"year":2011,"finding":"Viperin inhibits HCV replication by binding to VAPA through its C-terminus, competitively disrupting the VAPA-NS5A interaction; competitive co-immunoprecipitation showed that viperin and NS5A compete for the same region on VAPA.","method":"Co-immunoprecipitation, competitive co-immunoprecipitation, mutagenesis, confocal microscopy","journal":"The Journal of general virology","confidence":"Medium","confidence_rationale":"Tier 2 — competitive binding established by Co-IP with mutagenesis support","pmids":["21957124"],"is_preprint":false},{"year":2013,"finding":"GPS2 acts as a bridging factor between HCV NS5A and VAPA; overexpression of GPS2 enhances NS5A-VAPA association while GPS2 knockdown disrupts this interaction and suppresses HCV RNA replication.","method":"Co-immunoprecipitation, siRNA knockdown, domain mutagenesis, HCV replicon replication assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with mutagenesis, KD with functional readout","pmids":["24223774"],"is_preprint":false},{"year":2015,"finding":"Sterol ligand-induced changes in ORP-VAPA complex subcellular distribution were demonstrated using BiFC in HuH7 cells: cholesterol depletion concentrated OSBP-VAPA complexes at juxtanuclear position reversible by LDL; ORP2-VAPA complexes redistribute upon ORP2 ligand treatment; sterol-binding-deficient ORP4L localizes predominantly to plasma membrane. This demonstrates that sterol occupancy controls ORP-VAPA complex localization.","method":"Bimolecular fluorescence complementation (BiFC), sterol manipulation, sterol-binding deficient mutants","journal":"Steroids","confidence":"Medium","confidence_rationale":"Tier 2 — BiFC with pharmacological and mutagenesis controls, single lab","pmids":["25681634"],"is_preprint":false},{"year":2016,"finding":"VAP proteins (VAPA and VAPB) act as ER-resident receptors for FFAT-motif-containing proteins; approximately 50% of the ~100-protein VAP interactome (VAPome) in humans and yeast binds directly or indirectly via the VAP-FFAT interaction, as determined by systematic motif analysis and literature review of binding experiments.","method":"Bioinformatic FFAT motif analysis of confirmed interactors, review of binding experimental data","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — synthesis of extensive experimental literature with algorithmic motif validation; strong preponderance across labs","pmids":["26898182"],"is_preprint":false},{"year":2017,"finding":"Murine and human norovirus NS1/2 protein directly binds the MSP domain of VAPA through an FFAT motif mimic in the NS1 domain; mutations within this mimic disrupt VAPA binding and reduce viral replication efficiency at a step after cytoplasmic RNA entry but before minus-strand RNA synthesis; VAPA/B-deficient cells show reduced norovirus replication.","method":"Structural analysis of NS1 domain, co-immunoprecipitation, VAPA/B-knockout cells, mutagenesis of FFAT mimic, replication cycle stage analysis","journal":"mBio","confidence":"High","confidence_rationale":"Tier 1-2 — structure plus mutagenesis plus KO cells with defined replication step, multiple orthogonal methods","pmids":["28698274"],"is_preprint":false},{"year":2018,"finding":"VAPA and VAPB interact with Kv2.1 and Kv2.2 potassium channels via a noncanonical VAP-binding motif on the channel C-terminus, recruiting VAPs to ER-PM junctions; the interaction depends on Kv2's PRC/clustering motif and the FFAT-binding domain on VAPA; VAPA knockout reduces Kv2.1 clustering at ER-PM junctions.","method":"Proximity biotinylation (BioID), colocalization/redistribution assays, siRNA knockdown, FRET, CD4 chimeras, VAPA-KO mammalian cells, affinity immunopurification/mass spectrometry from mouse brain","journal":"Proceedings of the National Academy of Sciences / The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (BioID, FRET, siRNA, KO, chimeric proteins), replicated across two independent labs in same year","pmids":["29941597","30012696"],"is_preprint":false},{"year":2018,"finding":"VAPA and VAPB interact with the ATG proteins FIP200, ULK1, and WIPI2 via FFAT motifs to stabilize the ULK1/FIP200 complex at autophagosome formation sites on the ER, contributing to ER-isolation membrane (IM) contact site formation during autophagosome biogenesis; VAPA/B depletion impairs IM progression into autophagosomes and reduces ULK1 puncta formation.","method":"Depletion (RNAi), direct binding assays, co-immunoprecipitation, fluorescence imaging of autophagosome formation, VAPB P56S ALS mutant analysis","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 2 — direct binding, Co-IP, KD with defined cellular phenotype, disease mutant validation","pmids":["29628370"],"is_preprint":false},{"year":2018,"finding":"VAP-A/B are required at Aichi virus RNA replication sites: they interact with viral proteins 2B, 2BC, 2C, 3A, and 3AB as well as host factors OSBP and SAC1, and siRNA knockdown of VAPA/B inhibits AiV RNA replication and cholesterol accumulation at replication organelles.","method":"Co-immunoprecipitation, siRNA knockdown, cholesterol accumulation assay, electron microscopy","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP network and siRNA knockdown with multiple functional readouts, single lab","pmids":["29367253"],"is_preprint":false},{"year":2020,"finding":"Disruption of Kv2.1-VAPA association using a membrane-permeable peptide (TAT-DP-2) derived from Kv2.2 C-terminus disperses Kv2.1 surface clusters, prevents pro-apoptotic potassium current enhancement after injury, and is neuroprotective in a murine ischemia-reperfusion model by reducing infarct size and improving neurological function.","method":"Peptide-mediated declustering, in vitro neuronal injury model, in vivo murine stroke model (infarct measurement, behavioral scoring)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 — mechanistic peptide targeting with in vitro and in vivo functional validation, defined molecular target","pmids":["32937450"],"is_preprint":false},{"year":2021,"finding":"Cryo-tomography of a reconstituted in vitro MCS revealed that VAP-A is a highly flexible ER transmembrane protein enabling formation of MCS of variable intermembrane distances; the tethering portion of its partner OSBP forms a central dimeric T-shaped helical region whose geometry facilitates lipid transfer domain movement between membranes.","method":"In vitro MCS reconstitution with two membranes, cryo-electron tomography, structural analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — direct structural determination of in vitro reconstituted complex by cryo-tomography","pmids":["34103503"],"is_preprint":false},{"year":2021,"finding":"The MSP domain of VAPA binds FFAT-like motifs from diverse proteins including SARS-CoV-2 RNA-dependent RNA polymerase, as determined by solution NMR; specific binding requires defined sequence elements in the FFAT-like motif, with six of eight tested peptides binding specifically.","method":"Solution NMR","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — NMR structural analysis of binding, multiple ligands tested with clear specificity determination","pmids":["34312846"],"is_preprint":false},{"year":2021,"finding":"CDIP1 binds VAPA and VAPB through an FFAT-like motif in its C-terminal region; mutations in this motif reduce CDIP1-induced caspase-3/7-mediated cell death, indicating that VAPA/B interaction contributes to CDIP1-mediated apoptosis.","method":"Co-immunoprecipitation, FFAT motif mutagenesis, caspase-3/7 activity assay","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with mutagenesis and functional cell death readout, single lab","pmids":["33503978"],"is_preprint":false},{"year":2022,"finding":"VAP-A drives biogenesis of a ceramide-dependent, RNA-containing subpopulation of small extracellular vesicles; VAP-A knockdown reduces EV RNA content and ceramide levels in EVs; the VAP-A binding partner CERT (ceramide transfer protein) localizes to MVBs and its knockdown phenocopies VAP-A knockdown; neutral sphingomyelinase 2 colocalizes with VAP-A-positive ER, and VAP-A promotes luminal filling of MVBs.","method":"VAP-A knockdown, lipid analysis, imaging (CERT/MVB colocalization, nSMase2 colocalization), EV RNA quantification, in vivo tumor formation assay","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KD, lipid analysis, imaging, functional assays), mechanistic model supported by partner KD phenocopy","pmids":["35421371"],"is_preprint":false},{"year":2023,"finding":"VAP-A, hyperphosphorylated ORP3, and Rab7 form a VOR complex at the outer nuclear membrane; this complex promotes the formation of nuclear envelope invaginations (NEIs) exploited by HIV-1 for nuclear entry; silencing VAPA or ORP3 inhibits nuclear transfer of HIV-1 components and productive infection.","method":"siRNA knockdown, co-immunoprecipitation, imaging of nuclear envelope invaginations, HIV-1 infection assay in HeLa and CD4+ T cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — Co-IP, KD with defined functional outcome, replicated in multiple cell types","pmids":["37563144"],"is_preprint":false},{"year":2023,"finding":"VAP-A localization to different membrane contact sites (ER-mitochondria and ER-Golgi) depends on its intrinsically disordered regions (IDRs); removing IDRs restricts VAP-A to ER-mitochondria MCS exclusively. VAP-A interacts with PTPIP51 and VPS13A at ER-mitochondria MCS to promote mitochondrial fusion through lipid transfer and cardiolipin buildup, and with OSBP and CERT at ER-Golgi MCS for lipid exchange.","method":"IDR deletion mutants, fluorescence imaging of VAP-A distribution, mitochondrial fusion assay, lipid analysis (cardiolipin), co-immunoprecipitation","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays with domain mutants, defined functional consequences at multiple MCS types","pmids":["36693319"],"is_preprint":false},{"year":2024,"finding":"VAPA is required for proper cell motility; VAPA-depleted CaCo2 cells show collective and individual motility defects, disorganized actin cytoskeleton, and altered protrusive activity. VAPA maintains PI(4)P and PI(4,5)P2 levels at the plasma membrane during migration via its MSP domain. VAPA stabilizes and anchors ventral ER-PM contact sites to focal adhesions and mediates microtubule-dependent focal adhesion disassembly.","method":"VAPA depletion (siRNA), live-cell migration assays, phosphoinositide imaging, focal adhesion dynamics imaging, ER-PM contact site visualization","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — KD with multiple defined phenotypic readouts (migration, PI levels, FA dynamics), domain-level mechanism identified","pmids":["38446032"],"is_preprint":false},{"year":2025,"finding":"VAPA promotes degradation of JAK1 by facilitating the interaction between the E3 ubiquitin ligase NEDD4 and JAK1, enhancing JAK1 ubiquitination and proteasomal degradation, thereby negatively regulating IFN-I (JAK-STAT) signaling during viral infection.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibition, NEDD4-deficient cells, viral replication assay","journal":"Veterinary microbiology","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic pathway (writer-substrate-reader) established by Co-IP and KO functional assay, single lab","pmids":["40080976"],"is_preprint":false},{"year":2025,"finding":"VAPA is required for sphingolipid transport to Leishmania-containing parasitophorous vacuoles in macrophages and for bi-directional lipid exchange between the parasite vacuole and ER; VAPA knockdown prevents L. amazonensis replication and vacuole expansion; L. amazonensis hijacks VAPA by disrupting its interactions with lipid transfer proteins CERT and ORP1L.","method":"siRNA knockdown, fluorescent ceramide tracking, proximity-ligation assay, co-immunoprecipitation, intracellular parasite replication assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays (KD, lipid tracking, PLA, Co-IP) with defined functional outcome in infection model","pmids":["40163521"],"is_preprint":false},{"year":2026,"finding":"VAPA localizes to the inner nuclear membrane (INM) in proximity to nuclear lamins, emerin, LAP2 isoforms, and Nup153; VAPA depletion reduces nuclear lamin levels, causes aberrant nuclear morphology (membrane invaginations and tunnels), and alters histone acetylation levels.","method":"RAPIDS proximity proteomics (rapamycin/APEX-SILAC), fluorescence imaging, VAPA depletion with nuclear morphology readout, lamin Western blot","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — novel localization established by proximity proteomics plus depletion phenotype, single lab, recently published","pmids":["41537431"],"is_preprint":false},{"year":2025,"finding":"VAPA:ORP1L:RAB7 multi-protein complex forms membrane contact sites between the ER and RAB7/LAMP1-positive endolysosomes; this complex participates in ER-to-lysosome-associated degradation (ERLAD) of misfolded ATZ polymers by engaging the CNX-FAM134B-LC3 segregation complex and facilitating STX17/VAMP8-mediated membrane fusion for ATZ delivery to endolysosomes.","method":"Co-immunoprecipitation, fluorescence imaging of MCS, functional ERLAD assay with ATZ client","journal":"Autophagy reports","confidence":"Medium","confidence_rationale":"Tier 2 — complex characterization with functional client degradation assay, single lab","pmids":["41179805"],"is_preprint":false}],"current_model":"VAPA is an ER-resident transmembrane protein whose cytoplasmic MSP domain acts as a universal ER scaffold by binding FFAT and FFAT-like motifs on ~100 diverse cytoplasmic and organelle-tethered proteins, thereby organizing membrane contact sites between the ER and plasma membrane, Golgi, mitochondria, endolysosomes, and autophagosomes; at these contacts VAPA recruits lipid transfer proteins (OSBP, CERT, ORP1L) to mediate non-vesicular lipid exchange, regulates phosphoinositide levels at the plasma membrane to support cell migration and focal adhesion dynamics, scaffolds ion channel clustering (Kv2.1/2.2) at ER-PM junctions, promotes ceramide-dependent RNA-containing extracellular vesicle biogenesis, participates in autophagosome formation by stabilizing the ULK1/FIP200 complex, and forms a nuclear envelope complex (with ORP3 and Rab7) involved in HIV-1 nuclear entry, while also modulating IFN-I signaling by facilitating NEDD4-mediated JAK1 ubiquitination and degradation."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing VAPA as an ER/ERGIC-resident protein with broad SNARE-binding capacity raised the question of whether it functions primarily in vesicular trafficking or as a more general ER scaffold.","evidence":"Subcellular fractionation and in vitro binding assays in COS-7 cells","pmids":["11511104"],"confidence":"Medium","gaps":["Functional consequence of SNARE binding unresolved","No in vivo validation","Specificity versus VAPB not addressed"]},{"year":2002,"claim":"The discovery that VAPA binds OSBP and that disruption of this complex impairs ceramide transport and sphingomyelin synthesis established VAPA as a functional scaffold for non-vesicular lipid transfer at ER–Golgi contacts.","evidence":"Yeast two-hybrid, GST pulldown, Co-IP, and ceramide transport assays","pmids":["12023275"],"confidence":"High","gaps":["Whether VAPA directly affects lipid transfer kinetics or only tethering was not resolved","Role of VAPB redundancy unknown"]},{"year":2004,"claim":"Demonstrating that HCV co-opts VAPA to assemble its RNA replication complex on lipid rafts revealed that the VAPA scaffolding interface is a common target for pathogen exploitation, a theme later extended to norovirus, Aichi virus, and SARS-CoV-2.","evidence":"Co-IP, siRNA, dominant-negative mutants, detergent-resistant membrane fractionation in HCV replicon system; later extended by norovirus FFAT-mimic mutagenesis and knockout cells, Aichi virus Co-IP/knockdown, and NMR binding of SARS-CoV-2 RdRp peptide","pmids":["15016871","14557663","28698274","29367253","34312846","24223774","21957124"],"confidence":"High","gaps":["Structural basis of how viral FFAT mimics compete with host FFAT proteins not fully resolved","Therapeutic targeting of the MSP–FFAT interface remains unexplored"]},{"year":2008,"claim":"Showing that VAPA overexpression blocks ER-to-Golgi transport through microtubule association—reversed by FFAT peptide competition—established that FFAT-motif occupancy regulates VAPA's functional state and distinguishes it from VAPB.","evidence":"In vitro ER vesicle budding reconstitution, cargo transport assays, FFAT peptide competition","pmids":["18713837"],"confidence":"High","gaps":["Physiological stoichiometry of VAPA:FFAT partners not determined","Whether microtubule association is direct or adaptor-mediated unclear"]},{"year":2016,"claim":"Systematic analysis revealing that ~100 proteins constitute the VAP interactome, roughly half binding through FFAT motifs, redefined VAPA as a universal ER hub rather than a pathway-specific factor.","evidence":"Bioinformatic FFAT motif analysis across confirmed experimental interactors","pmids":["26898182"],"confidence":"High","gaps":["Relative affinities and competition among FFAT clients unknown","How VAPA discriminates among simultaneous FFAT partners not addressed"]},{"year":2018,"claim":"Two independent studies demonstrated that VAPA scaffolds Kv2.1/Kv2.2 channel clusters at ER–PM junctions through a noncanonical VAP-binding motif, extending VAPA's role from lipid transfer to ion channel organization at MCS.","evidence":"BioID, FRET, siRNA, VAPA-KO cells, affinity purification/MS from mouse brain","pmids":["29941597","30012696"],"confidence":"High","gaps":["Whether VAPA modulates Kv2 channel gating directly was not tested","In vivo neuronal consequences of VAPA loss at ER–PM junctions uncharacterized at this point"]},{"year":2018,"claim":"Establishing that VAPA/B bind FIP200, ULK1, and WIPI2 via FFAT motifs to stabilize the autophagy initiation complex at ER sites broadened VAPA's role to autophagosome biogenesis.","evidence":"Direct binding assays, Co-IP, RNAi depletion with autophagosome formation imaging, VAPB P56S mutant analysis","pmids":["29628370"],"confidence":"High","gaps":["Relative contributions of VAPA versus VAPB to autophagosome initiation not separated","Lipid transfer function at autophagy MCS not demonstrated"]},{"year":2020,"claim":"Peptide-mediated disruption of the Kv2.1–VAPA interaction was neuroprotective in a murine stroke model, demonstrating that the VAPA scaffolding interface has therapeutic relevance.","evidence":"Membrane-permeable declustering peptide tested in neuronal injury model in vitro and murine ischemia-reperfusion in vivo","pmids":["32937450"],"confidence":"High","gaps":["Long-term effects of chronic Kv2–VAPA disruption unknown","Specificity of peptide for VAPA versus VAPB interaction not distinguished"]},{"year":2021,"claim":"Cryo-electron tomography of reconstituted VAPA–OSBP contact sites revealed that VAPA's flexibility enables variable intermembrane spacing, providing the first structural explanation for how VAPA accommodates diverse MCS geometries.","evidence":"In vitro reconstituted MCS with two membranes, cryo-ET","pmids":["34103503"],"confidence":"High","gaps":["Full-length VAPA structure including transmembrane domain not resolved","How IDR regions contribute to flexibility was not structurally addressed at this time"]},{"year":2022,"claim":"Demonstrating that VAPA drives biogenesis of ceramide-dependent RNA-containing extracellular vesicles through CERT recruitment to MVBs revealed an unexpected role for ER–endosome MCS in EV composition.","evidence":"VAPA knockdown with EV RNA/lipid quantification, CERT–MVB colocalization, nSMase2 colocalization imaging","pmids":["35421371"],"confidence":"High","gaps":["Cargo selectivity mechanism for RNA loading into EVs unknown","Whether VAPB compensates for VAPA in EV biogenesis not tested"]},{"year":2023,"claim":"Discovery that intrinsically disordered regions direct VAPA to distinct MCS (ER–Golgi vs. ER–mitochondria), with VAPA promoting mitochondrial fusion through PTPIP51/VPS13A-mediated cardiolipin buildup, established that IDRs encode MCS selectivity and linked VAPA to mitochondrial dynamics.","evidence":"IDR deletion mutants, mitochondrial fusion assays, cardiolipin lipid analysis, Co-IP","pmids":["36693319"],"confidence":"High","gaps":["How IDR post-translational modifications regulate MCS targeting is unexplored","Whether cardiolipin transfer is direct through VPS13A or indirect not resolved"]},{"year":2023,"claim":"Identification of the VAPA–ORP3–Rab7 (VOR) complex at the outer nuclear membrane promoting nuclear envelope invaginations exploited by HIV-1 for nuclear entry connected VAPA to nuclear import and viral pathogenesis.","evidence":"Co-IP, siRNA knockdown, imaging of NEIs, HIV-1 infection assay in HeLa and CD4+ T cells","pmids":["37563144"],"confidence":"High","gaps":["Whether VOR complex has non-viral physiological roles at the nuclear envelope unknown","Mechanism by which NEI formation facilitates HIV capsid translocation not structurally defined"]},{"year":2025,"claim":"Multiple recent studies extended VAPA's MCS functions: to ER–endolysosome contacts for ERLAD of misfolded proteins, to parasitophorous vacuole contacts hijacked by Leishmania, to inner nuclear membrane organization affecting lamins and chromatin, and to innate immune regulation via NEDD4-mediated JAK1 degradation.","evidence":"Co-IP and ERLAD functional assays for ATZ degradation; siRNA/ceramide tracking/PLA in Leishmania infection; RAPIDS proximity proteomics at INM; ubiquitination assays and NEDD4-KO viral replication","pmids":["41179805","40163521","41537431","40080976"],"confidence":"Medium","gaps":["Inner nuclear membrane localization established by proximity proteomics only, awaits orthogonal confirmation","JAK1 regulation finding is from a single lab and cell system","ERLAD MCS architecture not structurally resolved"]},{"year":null,"claim":"Key open questions include: how VAPA prioritizes among its ~100 FFAT-motif clients under physiological conditions, whether IDR post-translational modifications dynamically redistribute VAPA across MCS, and what the full extent of VAPA's nuclear functions is beyond the nuclear envelope.","evidence":"","pmids":[],"confidence":"Low","gaps":["No quantitative model of competitive FFAT-client binding exists","In vivo tissue-specific phenotypes of VAPA loss in mammals remain poorly characterized","Whether VAPA and VAPB have truly non-redundant functions at specific MCS types is unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,11,13,14,17,22]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[11,14,24]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,22,25]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,4,17,22,23]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[13,23]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1,22]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[22]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[27]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[21,26]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,22,25]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[14,27]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[4,20]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[22]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[13,23]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[24]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,12,21]}],"complexes":["VAPA-OSBP ER-Golgi MCS complex","VAPA-ORP3-Rab7 (VOR) nuclear envelope complex","VAPA-ORP1L-Rab7 ER-endolysosome MCS complex"],"partners":["OSBP","CERT","ORP1L","ORP3","KCNB1","FIP200","PTPIP51","NEDD4"],"other_free_text":[]},"mechanistic_narrative":"VAPA is an ER-resident transmembrane protein that functions as a universal scaffold for membrane contact site (MCS) formation by engaging FFAT and FFAT-like motifs on diverse cytoplasmic and organelle-tethered proteins through its MSP domain, thereby tethering the ER to the plasma membrane, Golgi, mitochondria, endolysosomes, nuclear envelope, and autophagosomes [PMID:26898182, PMID:36693319]. At these contact sites, VAPA recruits lipid transfer proteins—including OSBP, CERT, and ORP1L—to mediate non-vesicular exchange of sterols, ceramide, and phosphoinositides, supporting processes ranging from sphingomyelin synthesis and mitochondrial cardiolipin buildup to plasma membrane phosphoinositide homeostasis during cell migration and focal adhesion turnover [PMID:12023275, PMID:36693319, PMID:38446032, PMID:35421371]. VAPA also scaffolds Kv2.1/Kv2.2 potassium channel clusters at ER–PM junctions with neuroprotective significance, stabilizes the ULK1/FIP200 complex during autophagosome biogenesis, participates in ER-to-lysosome-associated degradation of misfolded proteins, and forms a nuclear envelope complex with ORP3 and Rab7 that is exploited by HIV-1 for nuclear entry [PMID:29941597, PMID:29628370, PMID:41179805, PMID:37563144]. Multiple pathogenic organisms—including HCV, norovirus, Aichi virus, SARS-CoV-2, and Leishmania—hijack the VAPA FFAT-binding interface to establish replication platforms or nutrient acquisition, while VAPA additionally modulates innate immune signaling by facilitating NEDD4-mediated JAK1 ubiquitination and degradation [PMID:15016871, PMID:28698274, PMID:40163521, PMID:40080976]."},"prefetch_data":{"uniprot":{"accession":"Q9P0L0","full_name":"Vesicle-associated membrane protein-associated protein A","aliases":["33 kDa VAMP-associated protein","VAP-33"],"length_aa":249,"mass_kda":27.9,"function":"Endoplasmic reticulum (ER)-anchored protein that mediates the formation of contact sites between the ER and endosomes via interaction with FFAT motif-containing proteins such as STARD3 or WDR44 (PubMed:32344433, PubMed:33124732). STARD3-VAPA interaction enables cholesterol transfer from the ER to endosomes (PubMed:33124732). Via interaction with WDR44 participates in neosynthesized protein export (PubMed:32344433). In addition, recruited to the plasma membrane through OSBPL3 binding (PubMed:25447204). The OSBPL3-VAPA complex stimulates RRAS signaling which in turn attenuates integrin beta-1 (ITGB1) activation at the cell surface (PubMed:25447204). With OSBPL3, may regulate ER morphology (PubMed:16143324). 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NEDHSF","url":"https://www.omim.org/entry/616351"},{"mim_id":"606737","title":"OXYSTEROL-BINDING PROTEIN-LIKE PROTEIN 9; OSBPL9","url":"https://www.omim.org/entry/606737"},{"mim_id":"605704","title":"VAMP-ASSOCIATED PROTEIN B AND C; VAPB","url":"https://www.omim.org/entry/605704"},{"mim_id":"605703","title":"VAMP-ASSOCIATED PROTEIN A; VAPA","url":"https://www.omim.org/entry/605703"},{"mim_id":"604677","title":"CERAMIDE TRANSPORTER 1; CERT1","url":"https://www.omim.org/entry/604677"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Endoplasmic reticulum","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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science","url":"https://pubmed.ncbi.nlm.nih.gov/40754416","citation_count":2,"is_preprint":false},{"pmid":"33493378","id":"PMC_33493378","title":"Development of diagnostic assays for differentiation of atypical Aeromonas salmonicida vapA type V and type VI in ballan wrasse (Labrus bergylta, Ascanius).","date":"2021","source":"Journal of fish diseases","url":"https://pubmed.ncbi.nlm.nih.gov/33493378","citation_count":2,"is_preprint":false},{"pmid":"38421980","id":"PMC_38421980","title":"The N-terminal domain is required for cell surface localisation of VapA, a member of the Vap family of Rhodococcus equi virulence proteins.","date":"2024","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/38421980","citation_count":2,"is_preprint":false},{"pmid":"30252885","id":"PMC_30252885","title":"Molecular analysis of the chromosomal 16S rRNA gene and vapA plasmid gene of Polish field strains of R. equi.","date":"2018","source":"PloS 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The VAP-A/OSBP complex localizes to ER-associated structures and its disruption impairs ceramide transport from ER to Golgi, as measured by reduced sphingomyelin synthesis.\",\n      \"method\": \"Yeast two-hybrid screen, GST pulldown, co-immunoprecipitation, functional transport assay (ts045-VSVG-GFP, fluorescent ceramide)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, pulldown, domain mapping, and functional consequence with multiple orthogonal assays in single study\",\n      \"pmids\": [\"12023275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"VAPA is a resident of the ER/Golgi intermediate compartment and binds promiscuously to both v- and t-SNAREs including VAMP, syntaxin 1A, rbet1, rsec22, αSNAP, and NSF. Both N- and C-terminal domains of VAPA are required for VAMP binding and VAP dimerization.\",\n      \"method\": \"Subcellular fractionation, in vitro binding assays, domain deletion analysis in COS-7 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and binding assays, single lab\",\n      \"pmids\": [\"11511104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"hVAP-33 (VAPA) binds to HCV nonstructural proteins NS5A and NS5B and is required for the formation of the HCV RNA replication complex on lipid rafts (detergent-resistant membranes). Expression of dominant-negative VAPA mutants or siRNA knockdown of hVAP-33 caused NS5B to relocate from detergent-resistant to detergent-sensitive membranes and reduced HCV RNA and protein levels.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, dominant-negative mutants, detergent-resistant membrane fractionation, HCV replicon system\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (Co-IP, DN mutant, siRNA, fractionation) with functional readout; highly cited\",\n      \"pmids\": [\"15016871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Norwalk virus nonstructural protein p48 directly interacts with VAPA and forms a stable complex in mammalian cells, and this interaction inhibits cell-surface expression of vesicular stomatitis virus G protein, implicating VAPA-mediated disruption of intracellular protein trafficking.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, surface protein transport assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — yeast two-hybrid confirmed by Co-IP plus functional transport assay\",\n      \"pmids\": [\"14557663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Overexpression of wild-type VAPA (but not VAPB) inhibits ER-to-Golgi transport by decreasing segregation of membrane cargo into ER vesicles and inhibiting lateral diffusion of membrane proteins, likely through stable VAPA association with microtubules. The FFAT motif peptide relieves this block and restores ER vesicle budding and disrupts VAP-microtubule association in vitro.\",\n      \"method\": \"Cargo transport assays, in vitro ER vesicle budding assay, lateral diffusion measurements, FFAT peptide competition\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro budding reconstitution combined with live-cell functional transport assays and mechanistic peptide competition\",\n      \"pmids\": [\"18713837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Glycolipid transfer protein (GLTP) contains an FFAT-like motif and directly interacts with VAPA; mutation of the FFAT-like motif abolishes this interaction, as determined by GST pulldown.\",\n      \"method\": \"GST pulldown, FFAT motif mutagenesis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single pulldown method with mutagenesis confirmation, single lab\",\n      \"pmids\": [\"19665998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"VAPA interacts with the cochlear motor protein prestin, confirmed by co-immunoprecipitation; VAPA expression is reduced in prestin-knockout OHCs, and co-expression of VAPA with prestin increases prestin abundance at the plasma membrane, suggesting VAPA facilitates prestin trafficking to the membrane.\",\n      \"method\": \"Yeast two-hybrid (membrane-based), co-immunoprecipitation, prestin-KO mouse comparison, surface expression assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP confirmed by KO model and functional overexpression, single lab\",\n      \"pmids\": [\"20359505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The ALS-linked VAPB P56S mutation phenotype (ER aggregation) can be recapitulated in VAPA by mutating the equivalent proline distribution in the conserved region; VAPA normally requires three properly distributed prolines in this region for correct function, explaining why wild-type VAPA is resistant to the equivalent of the P56S mutation.\",\n      \"method\": \"Site-directed mutagenesis, fluorescence microscopy of aggregation phenotype\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis with defined phenotypic readout, single lab\",\n      \"pmids\": [\"21144830\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Viperin inhibits HCV replication by binding to VAPA through its C-terminus, competitively disrupting the VAPA-NS5A interaction; competitive co-immunoprecipitation showed that viperin and NS5A compete for the same region on VAPA.\",\n      \"method\": \"Co-immunoprecipitation, competitive co-immunoprecipitation, mutagenesis, confocal microscopy\",\n      \"journal\": \"The Journal of general virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — competitive binding established by Co-IP with mutagenesis support\",\n      \"pmids\": [\"21957124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPS2 acts as a bridging factor between HCV NS5A and VAPA; overexpression of GPS2 enhances NS5A-VAPA association while GPS2 knockdown disrupts this interaction and suppresses HCV RNA replication.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, domain mutagenesis, HCV replicon replication assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with mutagenesis, KD with functional readout\",\n      \"pmids\": [\"24223774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Sterol ligand-induced changes in ORP-VAPA complex subcellular distribution were demonstrated using BiFC in HuH7 cells: cholesterol depletion concentrated OSBP-VAPA complexes at juxtanuclear position reversible by LDL; ORP2-VAPA complexes redistribute upon ORP2 ligand treatment; sterol-binding-deficient ORP4L localizes predominantly to plasma membrane. This demonstrates that sterol occupancy controls ORP-VAPA complex localization.\",\n      \"method\": \"Bimolecular fluorescence complementation (BiFC), sterol manipulation, sterol-binding deficient mutants\",\n      \"journal\": \"Steroids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — BiFC with pharmacological and mutagenesis controls, single lab\",\n      \"pmids\": [\"25681634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"VAP proteins (VAPA and VAPB) act as ER-resident receptors for FFAT-motif-containing proteins; approximately 50% of the ~100-protein VAP interactome (VAPome) in humans and yeast binds directly or indirectly via the VAP-FFAT interaction, as determined by systematic motif analysis and literature review of binding experiments.\",\n      \"method\": \"Bioinformatic FFAT motif analysis of confirmed interactors, review of binding experimental data\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — synthesis of extensive experimental literature with algorithmic motif validation; strong preponderance across labs\",\n      \"pmids\": [\"26898182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Murine and human norovirus NS1/2 protein directly binds the MSP domain of VAPA through an FFAT motif mimic in the NS1 domain; mutations within this mimic disrupt VAPA binding and reduce viral replication efficiency at a step after cytoplasmic RNA entry but before minus-strand RNA synthesis; VAPA/B-deficient cells show reduced norovirus replication.\",\n      \"method\": \"Structural analysis of NS1 domain, co-immunoprecipitation, VAPA/B-knockout cells, mutagenesis of FFAT mimic, replication cycle stage analysis\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structure plus mutagenesis plus KO cells with defined replication step, multiple orthogonal methods\",\n      \"pmids\": [\"28698274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"VAPA and VAPB interact with Kv2.1 and Kv2.2 potassium channels via a noncanonical VAP-binding motif on the channel C-terminus, recruiting VAPs to ER-PM junctions; the interaction depends on Kv2's PRC/clustering motif and the FFAT-binding domain on VAPA; VAPA knockout reduces Kv2.1 clustering at ER-PM junctions.\",\n      \"method\": \"Proximity biotinylation (BioID), colocalization/redistribution assays, siRNA knockdown, FRET, CD4 chimeras, VAPA-KO mammalian cells, affinity immunopurification/mass spectrometry from mouse brain\",\n      \"journal\": \"Proceedings of the National Academy of Sciences / The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (BioID, FRET, siRNA, KO, chimeric proteins), replicated across two independent labs in same year\",\n      \"pmids\": [\"29941597\", \"30012696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"VAPA and VAPB interact with the ATG proteins FIP200, ULK1, and WIPI2 via FFAT motifs to stabilize the ULK1/FIP200 complex at autophagosome formation sites on the ER, contributing to ER-isolation membrane (IM) contact site formation during autophagosome biogenesis; VAPA/B depletion impairs IM progression into autophagosomes and reduces ULK1 puncta formation.\",\n      \"method\": \"Depletion (RNAi), direct binding assays, co-immunoprecipitation, fluorescence imaging of autophagosome formation, VAPB P56S ALS mutant analysis\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding, Co-IP, KD with defined cellular phenotype, disease mutant validation\",\n      \"pmids\": [\"29628370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"VAP-A/B are required at Aichi virus RNA replication sites: they interact with viral proteins 2B, 2BC, 2C, 3A, and 3AB as well as host factors OSBP and SAC1, and siRNA knockdown of VAPA/B inhibits AiV RNA replication and cholesterol accumulation at replication organelles.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, cholesterol accumulation assay, electron microscopy\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP network and siRNA knockdown with multiple functional readouts, single lab\",\n      \"pmids\": [\"29367253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Disruption of Kv2.1-VAPA association using a membrane-permeable peptide (TAT-DP-2) derived from Kv2.2 C-terminus disperses Kv2.1 surface clusters, prevents pro-apoptotic potassium current enhancement after injury, and is neuroprotective in a murine ischemia-reperfusion model by reducing infarct size and improving neurological function.\",\n      \"method\": \"Peptide-mediated declustering, in vitro neuronal injury model, in vivo murine stroke model (infarct measurement, behavioral scoring)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic peptide targeting with in vitro and in vivo functional validation, defined molecular target\",\n      \"pmids\": [\"32937450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-tomography of a reconstituted in vitro MCS revealed that VAP-A is a highly flexible ER transmembrane protein enabling formation of MCS of variable intermembrane distances; the tethering portion of its partner OSBP forms a central dimeric T-shaped helical region whose geometry facilitates lipid transfer domain movement between membranes.\",\n      \"method\": \"In vitro MCS reconstitution with two membranes, cryo-electron tomography, structural analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural determination of in vitro reconstituted complex by cryo-tomography\",\n      \"pmids\": [\"34103503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The MSP domain of VAPA binds FFAT-like motifs from diverse proteins including SARS-CoV-2 RNA-dependent RNA polymerase, as determined by solution NMR; specific binding requires defined sequence elements in the FFAT-like motif, with six of eight tested peptides binding specifically.\",\n      \"method\": \"Solution NMR\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural analysis of binding, multiple ligands tested with clear specificity determination\",\n      \"pmids\": [\"34312846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CDIP1 binds VAPA and VAPB through an FFAT-like motif in its C-terminal region; mutations in this motif reduce CDIP1-induced caspase-3/7-mediated cell death, indicating that VAPA/B interaction contributes to CDIP1-mediated apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, FFAT motif mutagenesis, caspase-3/7 activity assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with mutagenesis and functional cell death readout, single lab\",\n      \"pmids\": [\"33503978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"VAP-A drives biogenesis of a ceramide-dependent, RNA-containing subpopulation of small extracellular vesicles; VAP-A knockdown reduces EV RNA content and ceramide levels in EVs; the VAP-A binding partner CERT (ceramide transfer protein) localizes to MVBs and its knockdown phenocopies VAP-A knockdown; neutral sphingomyelinase 2 colocalizes with VAP-A-positive ER, and VAP-A promotes luminal filling of MVBs.\",\n      \"method\": \"VAP-A knockdown, lipid analysis, imaging (CERT/MVB colocalization, nSMase2 colocalization), EV RNA quantification, in vivo tumor formation assay\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, lipid analysis, imaging, functional assays), mechanistic model supported by partner KD phenocopy\",\n      \"pmids\": [\"35421371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"VAP-A, hyperphosphorylated ORP3, and Rab7 form a VOR complex at the outer nuclear membrane; this complex promotes the formation of nuclear envelope invaginations (NEIs) exploited by HIV-1 for nuclear entry; silencing VAPA or ORP3 inhibits nuclear transfer of HIV-1 components and productive infection.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, imaging of nuclear envelope invaginations, HIV-1 infection assay in HeLa and CD4+ T cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, KD with defined functional outcome, replicated in multiple cell types\",\n      \"pmids\": [\"37563144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"VAP-A localization to different membrane contact sites (ER-mitochondria and ER-Golgi) depends on its intrinsically disordered regions (IDRs); removing IDRs restricts VAP-A to ER-mitochondria MCS exclusively. VAP-A interacts with PTPIP51 and VPS13A at ER-mitochondria MCS to promote mitochondrial fusion through lipid transfer and cardiolipin buildup, and with OSBP and CERT at ER-Golgi MCS for lipid exchange.\",\n      \"method\": \"IDR deletion mutants, fluorescence imaging of VAP-A distribution, mitochondrial fusion assay, lipid analysis (cardiolipin), co-immunoprecipitation\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays with domain mutants, defined functional consequences at multiple MCS types\",\n      \"pmids\": [\"36693319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"VAPA is required for proper cell motility; VAPA-depleted CaCo2 cells show collective and individual motility defects, disorganized actin cytoskeleton, and altered protrusive activity. VAPA maintains PI(4)P and PI(4,5)P2 levels at the plasma membrane during migration via its MSP domain. VAPA stabilizes and anchors ventral ER-PM contact sites to focal adhesions and mediates microtubule-dependent focal adhesion disassembly.\",\n      \"method\": \"VAPA depletion (siRNA), live-cell migration assays, phosphoinositide imaging, focal adhesion dynamics imaging, ER-PM contact site visualization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KD with multiple defined phenotypic readouts (migration, PI levels, FA dynamics), domain-level mechanism identified\",\n      \"pmids\": [\"38446032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"VAPA promotes degradation of JAK1 by facilitating the interaction between the E3 ubiquitin ligase NEDD4 and JAK1, enhancing JAK1 ubiquitination and proteasomal degradation, thereby negatively regulating IFN-I (JAK-STAT) signaling during viral infection.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, proteasome inhibition, NEDD4-deficient cells, viral replication assay\",\n      \"journal\": \"Veterinary microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway (writer-substrate-reader) established by Co-IP and KO functional assay, single lab\",\n      \"pmids\": [\"40080976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"VAPA is required for sphingolipid transport to Leishmania-containing parasitophorous vacuoles in macrophages and for bi-directional lipid exchange between the parasite vacuole and ER; VAPA knockdown prevents L. amazonensis replication and vacuole expansion; L. amazonensis hijacks VAPA by disrupting its interactions with lipid transfer proteins CERT and ORP1L.\",\n      \"method\": \"siRNA knockdown, fluorescent ceramide tracking, proximity-ligation assay, co-immunoprecipitation, intracellular parasite replication assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays (KD, lipid tracking, PLA, Co-IP) with defined functional outcome in infection model\",\n      \"pmids\": [\"40163521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"VAPA localizes to the inner nuclear membrane (INM) in proximity to nuclear lamins, emerin, LAP2 isoforms, and Nup153; VAPA depletion reduces nuclear lamin levels, causes aberrant nuclear morphology (membrane invaginations and tunnels), and alters histone acetylation levels.\",\n      \"method\": \"RAPIDS proximity proteomics (rapamycin/APEX-SILAC), fluorescence imaging, VAPA depletion with nuclear morphology readout, lamin Western blot\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel localization established by proximity proteomics plus depletion phenotype, single lab, recently published\",\n      \"pmids\": [\"41537431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"VAPA:ORP1L:RAB7 multi-protein complex forms membrane contact sites between the ER and RAB7/LAMP1-positive endolysosomes; this complex participates in ER-to-lysosome-associated degradation (ERLAD) of misfolded ATZ polymers by engaging the CNX-FAM134B-LC3 segregation complex and facilitating STX17/VAMP8-mediated membrane fusion for ATZ delivery to endolysosomes.\",\n      \"method\": \"Co-immunoprecipitation, fluorescence imaging of MCS, functional ERLAD assay with ATZ client\",\n      \"journal\": \"Autophagy reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — complex characterization with functional client degradation assay, single lab\",\n      \"pmids\": [\"41179805\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"VAPA is an ER-resident transmembrane protein whose cytoplasmic MSP domain acts as a universal ER scaffold by binding FFAT and FFAT-like motifs on ~100 diverse cytoplasmic and organelle-tethered proteins, thereby organizing membrane contact sites between the ER and plasma membrane, Golgi, mitochondria, endolysosomes, and autophagosomes; at these contacts VAPA recruits lipid transfer proteins (OSBP, CERT, ORP1L) to mediate non-vesicular lipid exchange, regulates phosphoinositide levels at the plasma membrane to support cell migration and focal adhesion dynamics, scaffolds ion channel clustering (Kv2.1/2.2) at ER-PM junctions, promotes ceramide-dependent RNA-containing extracellular vesicle biogenesis, participates in autophagosome formation by stabilizing the ULK1/FIP200 complex, and forms a nuclear envelope complex (with ORP3 and Rab7) involved in HIV-1 nuclear entry, while also modulating IFN-I signaling by facilitating NEDD4-mediated JAK1 ubiquitination and degradation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"VAPA is an ER-resident transmembrane protein that functions as a universal scaffold for membrane contact site (MCS) formation by engaging FFAT and FFAT-like motifs on diverse cytoplasmic and organelle-tethered proteins through its MSP domain, thereby tethering the ER to the plasma membrane, Golgi, mitochondria, endolysosomes, nuclear envelope, and autophagosomes [PMID:26898182, PMID:36693319]. At these contact sites, VAPA recruits lipid transfer proteins—including OSBP, CERT, and ORP1L—to mediate non-vesicular exchange of sterols, ceramide, and phosphoinositides, supporting processes ranging from sphingomyelin synthesis and mitochondrial cardiolipin buildup to plasma membrane phosphoinositide homeostasis during cell migration and focal adhesion turnover [PMID:12023275, PMID:36693319, PMID:38446032, PMID:35421371]. VAPA also scaffolds Kv2.1/Kv2.2 potassium channel clusters at ER–PM junctions with neuroprotective significance, stabilizes the ULK1/FIP200 complex during autophagosome biogenesis, participates in ER-to-lysosome-associated degradation of misfolded proteins, and forms a nuclear envelope complex with ORP3 and Rab7 that is exploited by HIV-1 for nuclear entry [PMID:29941597, PMID:29628370, PMID:41179805, PMID:37563144]. Multiple pathogenic organisms—including HCV, norovirus, Aichi virus, SARS-CoV-2, and Leishmania—hijack the VAPA FFAT-binding interface to establish replication platforms or nutrient acquisition, while VAPA additionally modulates innate immune signaling by facilitating NEDD4-mediated JAK1 ubiquitination and degradation [PMID:15016871, PMID:28698274, PMID:40163521, PMID:40080976].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing VAPA as an ER/ERGIC-resident protein with broad SNARE-binding capacity raised the question of whether it functions primarily in vesicular trafficking or as a more general ER scaffold.\",\n      \"evidence\": \"Subcellular fractionation and in vitro binding assays in COS-7 cells\",\n      \"pmids\": [\"11511104\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of SNARE binding unresolved\", \"No in vivo validation\", \"Specificity versus VAPB not addressed\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The discovery that VAPA binds OSBP and that disruption of this complex impairs ceramide transport and sphingomyelin synthesis established VAPA as a functional scaffold for non-vesicular lipid transfer at ER–Golgi contacts.\",\n      \"evidence\": \"Yeast two-hybrid, GST pulldown, Co-IP, and ceramide transport assays\",\n      \"pmids\": [\"12023275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether VAPA directly affects lipid transfer kinetics or only tethering was not resolved\", \"Role of VAPB redundancy unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that HCV co-opts VAPA to assemble its RNA replication complex on lipid rafts revealed that the VAPA scaffolding interface is a common target for pathogen exploitation, a theme later extended to norovirus, Aichi virus, and SARS-CoV-2.\",\n      \"evidence\": \"Co-IP, siRNA, dominant-negative mutants, detergent-resistant membrane fractionation in HCV replicon system; later extended by norovirus FFAT-mimic mutagenesis and knockout cells, Aichi virus Co-IP/knockdown, and NMR binding of SARS-CoV-2 RdRp peptide\",\n      \"pmids\": [\"15016871\", \"14557663\", \"28698274\", \"29367253\", \"34312846\", \"24223774\", \"21957124\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of how viral FFAT mimics compete with host FFAT proteins not fully resolved\", \"Therapeutic targeting of the MSP–FFAT interface remains unexplored\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showing that VAPA overexpression blocks ER-to-Golgi transport through microtubule association—reversed by FFAT peptide competition—established that FFAT-motif occupancy regulates VAPA's functional state and distinguishes it from VAPB.\",\n      \"evidence\": \"In vitro ER vesicle budding reconstitution, cargo transport assays, FFAT peptide competition\",\n      \"pmids\": [\"18713837\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological stoichiometry of VAPA:FFAT partners not determined\", \"Whether microtubule association is direct or adaptor-mediated unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Systematic analysis revealing that ~100 proteins constitute the VAP interactome, roughly half binding through FFAT motifs, redefined VAPA as a universal ER hub rather than a pathway-specific factor.\",\n      \"evidence\": \"Bioinformatic FFAT motif analysis across confirmed experimental interactors\",\n      \"pmids\": [\"26898182\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative affinities and competition among FFAT clients unknown\", \"How VAPA discriminates among simultaneous FFAT partners not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Two independent studies demonstrated that VAPA scaffolds Kv2.1/Kv2.2 channel clusters at ER–PM junctions through a noncanonical VAP-binding motif, extending VAPA's role from lipid transfer to ion channel organization at MCS.\",\n      \"evidence\": \"BioID, FRET, siRNA, VAPA-KO cells, affinity purification/MS from mouse brain\",\n      \"pmids\": [\"29941597\", \"30012696\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether VAPA modulates Kv2 channel gating directly was not tested\", \"In vivo neuronal consequences of VAPA loss at ER–PM junctions uncharacterized at this point\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Establishing that VAPA/B bind FIP200, ULK1, and WIPI2 via FFAT motifs to stabilize the autophagy initiation complex at ER sites broadened VAPA's role to autophagosome biogenesis.\",\n      \"evidence\": \"Direct binding assays, Co-IP, RNAi depletion with autophagosome formation imaging, VAPB P56S mutant analysis\",\n      \"pmids\": [\"29628370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of VAPA versus VAPB to autophagosome initiation not separated\", \"Lipid transfer function at autophagy MCS not demonstrated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Peptide-mediated disruption of the Kv2.1–VAPA interaction was neuroprotective in a murine stroke model, demonstrating that the VAPA scaffolding interface has therapeutic relevance.\",\n      \"evidence\": \"Membrane-permeable declustering peptide tested in neuronal injury model in vitro and murine ischemia-reperfusion in vivo\",\n      \"pmids\": [\"32937450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term effects of chronic Kv2–VAPA disruption unknown\", \"Specificity of peptide for VAPA versus VAPB interaction not distinguished\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cryo-electron tomography of reconstituted VAPA–OSBP contact sites revealed that VAPA's flexibility enables variable intermembrane spacing, providing the first structural explanation for how VAPA accommodates diverse MCS geometries.\",\n      \"evidence\": \"In vitro reconstituted MCS with two membranes, cryo-ET\",\n      \"pmids\": [\"34103503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length VAPA structure including transmembrane domain not resolved\", \"How IDR regions contribute to flexibility was not structurally addressed at this time\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that VAPA drives biogenesis of ceramide-dependent RNA-containing extracellular vesicles through CERT recruitment to MVBs revealed an unexpected role for ER–endosome MCS in EV composition.\",\n      \"evidence\": \"VAPA knockdown with EV RNA/lipid quantification, CERT–MVB colocalization, nSMase2 colocalization imaging\",\n      \"pmids\": [\"35421371\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cargo selectivity mechanism for RNA loading into EVs unknown\", \"Whether VAPB compensates for VAPA in EV biogenesis not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that intrinsically disordered regions direct VAPA to distinct MCS (ER–Golgi vs. ER–mitochondria), with VAPA promoting mitochondrial fusion through PTPIP51/VPS13A-mediated cardiolipin buildup, established that IDRs encode MCS selectivity and linked VAPA to mitochondrial dynamics.\",\n      \"evidence\": \"IDR deletion mutants, mitochondrial fusion assays, cardiolipin lipid analysis, Co-IP\",\n      \"pmids\": [\"36693319\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IDR post-translational modifications regulate MCS targeting is unexplored\", \"Whether cardiolipin transfer is direct through VPS13A or indirect not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of the VAPA–ORP3–Rab7 (VOR) complex at the outer nuclear membrane promoting nuclear envelope invaginations exploited by HIV-1 for nuclear entry connected VAPA to nuclear import and viral pathogenesis.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, imaging of NEIs, HIV-1 infection assay in HeLa and CD4+ T cells\",\n      \"pmids\": [\"37563144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether VOR complex has non-viral physiological roles at the nuclear envelope unknown\", \"Mechanism by which NEI formation facilitates HIV capsid translocation not structurally defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multiple recent studies extended VAPA's MCS functions: to ER–endolysosome contacts for ERLAD of misfolded proteins, to parasitophorous vacuole contacts hijacked by Leishmania, to inner nuclear membrane organization affecting lamins and chromatin, and to innate immune regulation via NEDD4-mediated JAK1 degradation.\",\n      \"evidence\": \"Co-IP and ERLAD functional assays for ATZ degradation; siRNA/ceramide tracking/PLA in Leishmania infection; RAPIDS proximity proteomics at INM; ubiquitination assays and NEDD4-KO viral replication\",\n      \"pmids\": [\"41179805\", \"40163521\", \"41537431\", \"40080976\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inner nuclear membrane localization established by proximity proteomics only, awaits orthogonal confirmation\", \"JAK1 regulation finding is from a single lab and cell system\", \"ERLAD MCS architecture not structurally resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: how VAPA prioritizes among its ~100 FFAT-motif clients under physiological conditions, whether IDR post-translational modifications dynamically redistribute VAPA across MCS, and what the full extent of VAPA's nuclear functions is beyond the nuclear envelope.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No quantitative model of competitive FFAT-client binding exists\", \"In vivo tissue-specific phenotypes of VAPA loss in mammals remain poorly characterized\", \"Whether VAPA and VAPB have truly non-redundant functions at specific MCS types is unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 11, 13, 14, 17, 22]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [11, 14, 24]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 22, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 4, 17, 22, 23]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [13, 23]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 22]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [27]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [21, 26]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 22, 25]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [14, 27]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [4, 20]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [13, 23]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [24]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 12, 21]}\n    ],\n    \"complexes\": [\n      \"VAPA-OSBP ER-Golgi MCS complex\",\n      \"VAPA-ORP3-Rab7 (VOR) nuclear envelope complex\",\n      \"VAPA-ORP1L-Rab7 ER-endolysosome MCS complex\"\n    ],\n    \"partners\": [\n      \"OSBP\",\n      \"CERT\",\n      \"ORP1L\",\n      \"ORP3\",\n      \"KCNB1\",\n      \"FIP200\",\n      \"PTPIP51\",\n      \"NEDD4\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}