{"gene":"EIF2B4","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1993,"finding":"GSK-3 phosphorylates the largest (epsilon) subunit of eIF2B and is rapidly inactivated by insulin, linking insulin signaling to eIF2B regulation via GSK-3 inactivation.","method":"Kinase activity assay with Mono-S chromatography fractions, immunoblotting with GSK-3 isoform-specific antibodies, phosphatase-2A reversal experiment","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (kinase assay, immunoblotting, phosphatase reversal), replicated in subsequent studies","pmids":["8397507"],"is_preprint":false},{"year":1998,"finding":"GSK-3 phosphorylates Ser540 (Ser535 in rat) of the eIF2Bε subunit in intact cells, and this phosphorylation inhibits eIF2B activity; insulin causes dephosphorylation of this site in a PI 3-kinase-dependent manner.","method":"In vitro kinase assay, phosphorylation site identification, PI 3-kinase inhibitor studies in intact cells","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1-2 — site-specific phosphorylation identified in vitro and confirmed in cells, PI3K pathway dissection, replicated across labs","pmids":["9468292"],"is_preprint":false},{"year":1997,"finding":"Insulin activates eIF2B through a PI 3-kinase-dependent pathway that leads to inhibition of GSK-3; dominant negative PI 3-kinase blocks both eIF2B activation and GSK-3 inhibition, while dominant negative Sos (MAP kinase pathway) does not.","method":"Dominant negative PI 3-kinase expression, dominant negative Sos expression, rapamycin treatment, kinase activity assays","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with dominant negatives and pharmacological inhibitors, reciprocal regulation confirmed","pmids":["9237674"],"is_preprint":false},{"year":1996,"finding":"eIF2B is rapidly activated following T-cell mitogenic stimulation coincident with inactivation of GSK-3; phosphorylation of eIF2Bε by GSK-3 inhibits nucleotide exchange activity in vitro, providing a mechanism for rapid eIF2B activation.","method":"eIF2B activity assay, GSK-3 kinase assay, in vitro nucleotide exchange inhibition assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro inhibition demonstrated, correlated with in-cell GSK-3 inactivation","pmids":["8626696"],"is_preprint":false},{"year":1998,"finding":"eIF2B is a heteropentameric GEF composed of two functionally distinct subcomplexes: a regulatory subcomplex (GCN3/α, GCD7/β, GCD2/δ) that binds eIF2(αP) with high affinity but lacks exchange activity, and a catalytic subcomplex (GCD1/γ, GCD6/ε) that has exchange activity insensitive to eIF2(αP). Binding of eIF2(αP) to the regulatory subcomplex prevents productive interaction with the catalytic subcomplex.","method":"In vitro nucleotide exchange assay, affinity binding assay, yeast regulatory mutants","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro exchange assay with purified subcomplexes, genetic and biochemical corroboration","pmids":["9472020"],"is_preprint":false},{"year":1998,"finding":"The α- and δ-subunits of eIF2B mediate sensitivity to inhibition by phosphorylated eIF2(αP): recombinant five-subunit eIF2B is inhibited by eIF2(αP), but four-subunit eIF2B lacking the α-subunit is insensitive; a point mutation in the δ-subunit also confers insensitivity.","method":"Baculovirus expression and purification of recombinant eIF2B holoprotein and subunit-deletion complexes, in vitro GEF activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted activity with purified recombinant complexes, mutagenesis, first direct biochemical evidence","pmids":["9582312"],"is_preprint":false},{"year":1996,"finding":"The GCN3(α), GCD7(β), and GCD2(δ) subunits of eIF2B form a stable trimeric regulatory subcomplex (confirmed by co-immunoprecipitation); this subcomplex interacts with eIF2(αP) and mediates inhibition of eIF2B GEF activity but lacks exchange activity itself.","method":"Co-immunoprecipitation of overexpressed subunits, in vivo suppression assays, genetic analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus genetic epistasis, replicated biochemically in subsequent studies","pmids":["8887689"],"is_preprint":false},{"year":2001,"finding":"Phosphorylated eIF2α (Ser51) tightly binds the eIF2B regulatory subcomplex (GCN3/GCD7/GCD2) in vitro in a phosphorylation-stimulated manner; this tight binding is required for inhibition of eIF2B GEF activity. Mutations in eIF2α and in GCD7 that abolish eIF2B inhibition also impair this binding.","method":"GST pulldown with recombinant phosphorylated eIF2α and eIF2B subunits, genetic suppressor analysis, in vivo competition assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro binding assay combined with genetic epistasis and mutagenesis","pmids":["11438658"],"is_preprint":false},{"year":2000,"finding":"Phosphorylation of Ser51 of eIF2α promotes complex formation between eIF2α(P) and eIF2B and inhibits eIF2B GEF activity; the Ser51→Asp phosphomimetic mutant recapitulates these effects, while the Ser51→Ala mutant does not.","method":"Baculovirus expression of eIF2α mutants, in vitro GEF inhibition assay, eIF2–eIF2B complex formation in reticulocyte lysate","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted biochemistry with phosphomimetic mutants, causal link between phosphorylation and inhibition established","pmids":["11041858"],"is_preprint":false},{"year":2002,"finding":"The catalytic domain of eIF2Bε (yeast GCD6) resides in residues 518–712; residues 518–581 are required for nucleotide exchange activity beyond eIF2 binding, and deletion of C-terminal 61 residues abolishes both functions. N-terminal half of eIF2Bε mediates complex formation with other subunits and an activation function stimulated by that complex formation.","method":"N- and C-terminal deletion analysis, in vitro GEF assay, in vivo complementation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — systematic deletion mutagenesis with in vitro reconstitution and in vivo validation","pmids":["12356745"],"is_preprint":false},{"year":2000,"finding":"eIF2 binds specifically to the δ- and ε-subunits of eIF2B; eIF2B binds to the β-subunit of eIF2, with the binding site located in the C-terminal ~70 amino acids of eIF2β. Phosphorylation of eIF2α does not promote binding of isolated eIF2α to eIF2B but increases overall eIF2B–eIF2 affinity.","method":"Far-Western blot analysis with individual subunits","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — far-Western blot, single method, but identifies specific subunit contacts","pmids":["9446619"],"is_preprint":false},{"year":2001,"finding":"Mammalian eIF2B acts as a GDP dissociation stimulator (releases eIF2-bound GDP even without free nucleotide); the β-subunit of eIF2B interacts with GTP; addition of eIF2Bα to preparations lacking it markedly enhances GEF activity.","method":"In vitro nucleotide release assay, GTP-binding assay, reconstitution with recombinant eIF2Bα","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro biochemistry defining catalytic mechanism and subunit requirements","pmids":["11323413"],"is_preprint":false},{"year":2005,"finding":"eIF2B and eIF2 co-localize to a specific cytoplasmic body in yeast; eIF2 dynamically cycles into these foci while eIF2B remains largely resident (FRAP); three distinct strategies to reduce eIF2B GEF function all inhibit eIF2 shuttling into foci, implicating this cytoplasmic body as the site of guanine nucleotide exchange.","method":"Fluorescence microscopy co-localization, FRAP (fluorescence recovery after photobleaching), genetic and pharmacological inhibition of eIF2B","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — live imaging with FRAP, multiple perturbations, functional consequence established","pmids":["16157703"],"is_preprint":false},{"year":2013,"finding":"eIF2B possesses a second activity as a GDI displacement factor (GDF): the eIF2Bγ and eIF2Bε subunits displace eIF5 (a GDI) from the eIF2•GDP/eIF5 complex prior to GEF action. GDF activity is insensitive to eIF2α phosphorylation (unlike GEF), and eIF2Bγ mutations impair GDF but not GEF function.","method":"Protein-protein interaction assays, nucleotide exchange kinetic assays, mutagenesis of eIF2Bγ","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — novel activity defined by in vitro kinetics and mutagenesis, GDF and GEF activities dissociated","pmids":["24352424"],"is_preprint":false},{"year":2014,"finding":"eIF2B is a decamer (dimer of pentamers) rather than a pentamer; assembly occurs through the catalytic γ- and ε-subunits forming a tetrameric core, with regulatory subunits arranged asymmetrically; GTP binds to eIF2Bγ.","method":"Native mass spectrometry, chemical cross-linking, surface accessibility measurements, homology modelling","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — orthogonal MS methods with cross-linking, validated by subsequent cryo-EM structures","pmids":["24852487"],"is_preprint":false},{"year":2014,"finding":"Mammalian eIF2B is a decamer (dimer of eIF2B(βγδε) tetramers) stabilized by two copies of eIF2Bα; eIF2Bδ is pivotal for tetramer formation; decamers show greater eIF2 binding and activity than tetramers alone.","method":"Mass spectrometry, co-immunoprecipitation of overexpressed complexes, subunit deletion analysis","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — MS plus reciprocal co-IP, functional comparison of decamer vs tetramer","pmids":["24532666"],"is_preprint":false},{"year":2015,"finding":"ISRIB is an activator of eIF2B that stabilizes eIF2B dimers; eIF2B4 (δ-subunit) contributes to the ISRIB binding site. ISRIB renders cells insensitive to eIF2α phosphorylation by enhancing eIF2B activity.","method":"Reporter-based shRNA screen, biochemical stabilization assays, ISRIB analog structure-activity relationship, cell-based translation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — genetic screen plus biochemical validation, followed up by structural studies","pmids":["25875391"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM structures of eIF2 bound to eIF2B (dephosphorylated) reveal that the eIF2B decamer is a static platform on which one or two flexible eIF2 trimers bind and align with eIF2B's bipartite catalytic centers; phosphorylation refolds eIF2α, allowing it to contact eIF2B at a different interface and sequester it into a nonproductive complex.","method":"Cryo-electron microscopy structural determination","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures of both productive and inhibited complexes, mechanistic interpretation validated","pmids":["31048491"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM and crystallographic structures of eIF2B in complex with unphosphorylated or phosphorylated eIF2 show that the two forms bind eIF2B in completely different manners: unphosphorylated eIF2 binds in a nucleotide exchange-active mode, whereas phosphorylated eIF2 binds in an inactive mode, explaining dominant inhibition.","method":"Cryo-electron microscopy, X-ray crystallography","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — two independent structural methods, functional validation included","pmids":["31048492"],"is_preprint":false},{"year":2020,"finding":"ISRIB antagonizes the ISR by allosteric antagonism: ISRIB and eIF2(αP) bind distinct sites on eIF2B; eIF2(αP) engagement of both eIF2B regulatory sites remodels the ISRIB-binding pocket, reducing ISRIB binding affinity, and vice versa. Cryo-EM shows eIF2(αP) binding converts eIF2B into a conformation unfavorable for productive eIF2 engagement.","method":"Cryo-electron microscopy, in vitro nucleotide exchange assay with mutations, cell-based ISR reporter assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM plus in vitro reconstitution with mutagenesis, mechanistic model of allosteric antagonism","pmids":["33220178"],"is_preprint":false},{"year":2021,"finding":"eIF2B assembly state regulates ISR: without the α-subunit, unassembled eIF2B tetramers accumulate and induce the ISR. ISRIB promotes tetramer-to-octamer assembly and also allosterically antagonizes the ISR within fully assembled decamers via a rocking conformational motion coupling eIF2, eIF2-P, and ISRIB binding sites. eIF2-P binding converts eIF2B decamers into 'conjoined tetramers' with reduced substrate binding and activity.","method":"In vitro assembly monitoring, cryo-EM structural analysis, ISRIB treatment of cells lacking eIF2Bα, ISR reporter assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 — cryo-EM plus in vitro/in vivo assembly experiments, mechanistic model validated","pmids":["33688831"],"is_preprint":false},{"year":2018,"finding":"ISRIB stabilizes VWM disease mutant eIF2B in the decameric form and restores residual catalytic GEF activity to wild-type levels; various VWM mutations (including in EIF2B4/δ-subunit) destabilize the decameric holoenzyme.","method":"Biochemical stability assays, GEF activity assays of recombinant VWM mutant eIF2B complexes, cell-based ISR activation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 — purified recombinant complexes with multiple VWM mutations, orthogonal biochemical and cellular assays","pmids":["29489452"],"is_preprint":false},{"year":2017,"finding":"NMR, fluorescence spectroscopy, and mutagenesis reveal that eIF2α phosphorylation inhibits eIF2B by destabilizing an autoregulatory intramolecular interaction within eIF2α; the first structural model for eIF2B in complex with eIF2-GDP and intermediates was proposed.","method":"NMR spectroscopy, fluorescence spectroscopy, site-directed mutagenesis, thermodynamic analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal biophysical and biochemical methods in one study","pmids":["29036434"],"is_preprint":false},{"year":2012,"finding":"TLR-TRIF signaling activates eIF2B GEF activity through PP2A-mediated dephosphorylation of the eIF2Bε subunit; PP2A is itself activated by decreased Src-family-kinase-mediated tyrosine phosphorylation of its catalytic subunit, counteracting the inhibitory effect of p-eIF2α and preventing CHOP induction.","method":"eIF2B GEF activity assay, PP2A activity assay, pharmacological inhibitors, in vitro and in vivo (mouse) experiments","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods with in vitro and in vivo corroboration, epistasis established","pmids":["22231169"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of the eIF2B regulatory subcomplex (eIF2B RSC): eIF2Bβ and eIF2Bδ form a tetramer (βδ)2, and combined with a homodimer of eIF2Bα2, create a hexameric regulatory subcomplex. eIF2Bα specifically binds AMP and GMP as ligands in the ancestral catalytic site, revealing evolutionary relation to sugar isomerases.","method":"X-ray crystallography, mutational analysis, biochemical binding assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with functional mutagenesis and biochemical assays","pmids":["26384431"],"is_preprint":false},{"year":2007,"finding":"The universally conserved residue E569 and W699 in the eIF2Bε catalytic (GEF) domain are critical for exchange activity; W699 is required for interaction with eIF2β, while E569/L568 and W699 are all required for interaction with eIF2γ, establishing that multiple contacts between eIF2γ and eIF2Bε mediate nucleotide exchange.","method":"Site-directed mutagenesis, in vitro binding assays, yeast genetic complementation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with binding and activity assays, in vivo validation","pmids":["17526738"],"is_preprint":false},{"year":2021,"finding":"Sugar phosphates (e.g., glucose-6-phosphate) bind the ancestral catalytic site in the eIF2Bα subunit, promote eIF2B holoenzyme formation, and enhance GEF activity toward eIF2. A VWM disease mutation in the eIF2Bα ligand pocket abolishes sugar phosphate binding and stimulation.","method":"Unbiased binding and activity screens, X-ray crystallography of sugar phosphate-bound eIF2B, mutagenesis of ligand pocket, VWM mutant functional analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus biochemical reconstitution and mutagenesis, disease relevance validated","pmids":["34103529"],"is_preprint":false},{"year":2020,"finding":"eIF2B forms enzymatically inactive filaments in starving yeast cells, triggered by starvation-induced cytosolic acidification; filament assembly (not Gcn2 kinase) is required for rapid translational downregulation and promotes stress survival and fast recovery.","method":"Live fluorescence microscopy, pH measurement, translation assays, site-specific variants, Gcn2 mutant epistasis","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization, functional consequence of filament formation shown; ortholog in S. cerevisiae","pmids":["32554487"],"is_preprint":false},{"year":2010,"finding":"A specific isoform of eIF2Bδ (variant 1/V1) attenuates the ER stress/unfolded protein response: replacement of total eIF2Bδ with V1 renders cells insensitive to eIF2α phosphorylation (no ATF4 upregulation, no translational suppression); V1 does not interact with eIF2, unlike the canonical variant 2.","method":"Isoform-specific expression in cancer cell lines, eIF2B-eIF2 interaction assay, translation and ATF4 reporter assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — interaction assay plus functional readouts, single lab but multiple orthogonal methods","pmids":["20709751"],"is_preprint":false},{"year":2011,"finding":"eIF2Bα (α-subunit) is required for eIF2-mediated translational suppression in response to eIF2α phosphorylation; loss of eIF2Bα or a T41A point mutation is sufficient to overcome translational inhibition from eIF2α phosphorylation and renders normal cells susceptible to viral infection.","method":"Yeast functional complementation, mammalian cell knockdown/expression of eIF2Bα variants, virus infection susceptibility assay","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic and cellular loss-of-function with defined phenotypic readout across two model systems","pmids":["21795329"],"is_preprint":false},{"year":2020,"finding":"Viral proteins (from a coronavirus and a picornavirus) independently acquired the ability to act as competitive inhibitors of p-eIF2–eIF2B interaction, allowing continued eIF2-GTP formation and global translation at high p-eIF2 levels that would otherwise halt translation.","method":"In vitro competition binding assay, translation assays in infected cells, viral protein expression","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 — competition binding assay plus cell-based translation assays, independent discovery in two viral proteins","pmids":["32690955"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM reveals that SFSV NSs viral protein binds to the α-subunit of eIF2B in a manner competitive with eIF2(αP); in the presence of NSs, eIF2B retains GEF activity even with bound eIF2(αP), allowing unimpeded translation.","method":"Cryo-electron microscopy structural analysis, in vitro nucleotide exchange assay, ribosome profiling in cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure plus in vitro activity assay and genome-wide ribosome profiling","pmids":["34876589"],"is_preprint":false},{"year":2000,"finding":"Drosophila eIF2Bε shows guanine nucleotide exchange activity and is phosphorylated by GSK-3 and casein kinase II; GSK-3 phosphorylation inhibits Drosophila eIF2B activity; Drosophila eIF2Bα confers regulation by phosphorylated eIF2α in yeast, and eIF2B activity in S2 cells is regulated by serum and ER stress via eIF2α phosphorylation.","method":"Cloning, in vitro GEF assay, GSK-3 and CK2 kinase assay, yeast complementation, S2 cell serum starvation and ER stress experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro kinase and GEF assays with mutagenic validation, ortholog confirmed functional","pmids":["11060303"],"is_preprint":false},{"year":2008,"finding":"RNAi inactivation of eIF2Bδ (F11A3.2) in adult C. elegans reduces global protein synthesis and extends lifespan in a DAF-16 (FOXO)-dependent manner, also conferring thermal and oxidative stress resistance.","method":"Adult-onset RNAi, 35S-methionine incorporation assay, genetic epistasis with daf-16 deletion mutant","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — RNAi with direct translation measurement and genetic epistasis, C. elegans ortholog","pmids":["18728216"],"is_preprint":false},{"year":2001,"finding":"Fusel alcohols (butanol, isoamyl alcohol) inhibit translation initiation in yeast by targeting eIF2B; a Pro180Ser variation in GCD1 (γ-subunit of eIF2B) determines sensitivity to fusel alcohol-induced translational regulation.","method":"Genetic mapping, yeast strain-specific translational inhibition assay, identification of GCD1 allelic variation","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — genetic mapping with functional translation assay in yeast, identifies eIF2B γ-subunit as target","pmids":["11707417"],"is_preprint":false},{"year":1998,"finding":"EGF and NGF activate eIF2B in PC12 cells via PI 3-kinase; EGF activation additionally requires FRAP/mTOR signaling; GSK-3 inactivation by EGF/NGF is not rapamycin-sensitive despite eIF2B activation being rapamycin-sensitive, indicating additional regulatory inputs beyond GSK-3.","method":"PI3K inhibitor (wortmannin), rapamycin, GSK-3 and CKII kinase assays, eIF2B activity assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection of pathway, corroborated by multiple inhibitors","pmids":["9488678"],"is_preprint":false}],"current_model":"EIF2B4 (δ-subunit) is a regulatory component of the heterodecameric eIF2B guanine nucleotide exchange factor for eIF2: within the eIF2B decamer (dimer of pentamers), the δ-subunit participates in the regulatory subcomplex (α/β/δ) that mediates sensitivity to phosphorylated eIF2(αP), contributes to the ISRIB small-molecule binding site, is pivotal for βγδε tetramer formation, interacts with eIF2 directly, and harbors a variant (V1 isoform) that can uncouple eIF2B from eIF2α phosphorylation-mediated inhibition; mutations in EIF2B4 cause Vanishing White Matter disease by destabilizing the decameric holoenzyme and impairing GEF activity."},"narrative":{"teleology":[{"year":1993,"claim":"Identifying how growth-factor signaling reaches the translational machinery, GSK-3 was shown to phosphorylate eIF2Bε and to be rapidly inactivated by insulin, establishing the first kinase-mediated regulatory input into eIF2B.","evidence":"Kinase activity assay with chromatographic fractions and phosphatase-2A reversal in cell extracts","pmids":["8397507"],"confidence":"High","gaps":["Phosphorylation site on eIF2Bε not yet identified","Direct role of the δ-subunit in this regulation unknown"]},{"year":1998,"claim":"Defining eIF2B's subunit architecture and functional division, the complex was resolved into a regulatory subcomplex (α/β/δ) that binds eIF2α(P) without exchange activity, and a catalytic subcomplex (γ/ε) that performs nucleotide exchange but is insensitive to phosphorylation; a δ-subunit mutation was shown to confer insensitivity to eIF2α(P), directly implicating the δ-subunit in phospho-regulation.","evidence":"Reconstituted in vitro GEF assays with purified recombinant subcomplexes, baculovirus-expressed deletion complexes, yeast genetic suppressor analysis","pmids":["9472020","9582312","8887689"],"confidence":"High","gaps":["Structural basis for δ-subunit's role in phospho-sensing unresolved","Stoichiometry of the holoenzyme not yet established"]},{"year":2001,"claim":"Mapping the eIF2–eIF2B interaction surface revealed that the δ- and ε-subunits of eIF2B directly contact eIF2, while phosphorylated eIF2α binds the regulatory subcomplex in a phosphorylation-stimulated manner; binding of eIF2α(P) is required for inhibition of GEF activity.","evidence":"Far-Western blots of individual subunits, GST pulldown with phosphorylated eIF2α, genetic suppressor analysis","pmids":["9446619","11438658"],"confidence":"High","gaps":["Atomic-resolution contacts between δ-subunit and eIF2 unknown","How phospho-eIF2α binding to regulatory subcomplex blocks catalytic subcomplex action is unclear"]},{"year":2005,"claim":"Demonstrating spatial organization of GEF activity in vivo, eIF2B was found to reside in dedicated cytoplasmic foci where eIF2 dynamically shuttles for nucleotide exchange; disrupting eIF2B function by three independent strategies blocked eIF2 cycling into these foci.","evidence":"Live fluorescence co-localization and FRAP in yeast with genetic/pharmacological perturbations","pmids":["16157703"],"confidence":"High","gaps":["Whether mammalian eIF2B forms analogous exchange bodies unknown","Role of individual subunits in body formation unresolved"]},{"year":2010,"claim":"An alternative δ-subunit isoform (V1) was discovered to uncouple eIF2B from the integrated stress response: cells expressing only V1 showed no eIF2α phosphorylation–dependent translational suppression and no ATF4 induction, because V1 cannot interact with eIF2.","evidence":"Isoform-specific expression in cancer cell lines, eIF2B–eIF2 interaction assays, ATF4 reporter and translation assays","pmids":["20709751"],"confidence":"Medium","gaps":["Structural basis for V1's inability to bind eIF2 not determined","Physiological contexts where V1 predominates unclear","Single-lab observation without independent replication"]},{"year":2014,"claim":"Resolving a longstanding stoichiometric question, native mass spectrometry established that eIF2B is a decamer (dimer of pentamers), with the δ-subunit pivotal for βγδε tetramer formation; decameric assemblies showed greater eIF2 binding and GEF activity than tetramers.","evidence":"Native MS, chemical cross-linking, co-immunoprecipitation of overexpressed subunit-deletion complexes","pmids":["24852487","24532666"],"confidence":"High","gaps":["High-resolution structure of complete decamer not yet available","How δ-subunit drives tetramer formation at atomic level unresolved"]},{"year":2015,"claim":"Identifying the drug target explaining ISRIB's mechanism, the δ-subunit was shown to contribute to the ISRIB-binding pocket; ISRIB stabilizes decameric assembly and overcomes eIF2α phosphorylation-mediated translational inhibition. Crystal structure of the regulatory subcomplex revealed that β and δ form a (βδ)₂ tetramer related to sugar isomerases.","evidence":"shRNA screen, ISRIB analog SAR, X-ray crystallography of eIF2B regulatory subcomplex, mutational analysis","pmids":["25875391","26384431"],"confidence":"High","gaps":["Precise atomic contacts between ISRIB and δ-subunit residues not yet mapped","Whether ISRIB acts identically in all cell types unknown"]},{"year":2018,"claim":"Linking eIF2B biochemistry to human disease, VWM disease mutations across eIF2B subunits (including EIF2B4/δ) were shown to destabilize the decamer and reduce GEF activity; ISRIB could stabilize mutant decamers and partially restore catalytic function.","evidence":"GEF activity and stability assays of recombinant VWM mutant eIF2B complexes, cell-based ISR activation assays","pmids":["29489452"],"confidence":"High","gaps":["In vivo efficacy of ISRIB for VWM disease not established","Mutation-specific effects on δ-subunit folding or intersubunit contacts uncharacterized"]},{"year":2019,"claim":"Cryo-EM structures of eIF2B with unphosphorylated and phosphorylated eIF2 revealed two completely different binding modes: productive (exchange-active) versus nonproductive (inhibitory), with phosphorylation-induced refolding of eIF2α creating a new interface that sequesters eIF2B.","evidence":"Cryo-EM and X-ray crystallography of eIF2B–eIF2 complexes in both phosphorylation states","pmids":["31048491","31048492"],"confidence":"High","gaps":["Dynamic transitions between productive and nonproductive modes not captured","Contribution of individual δ-subunit residues to either binding mode not dissected"]},{"year":2021,"claim":"Integrating assembly, allostery, and metabolic sensing, studies showed that eIF2B assembly state itself regulates the ISR (tetramers activate ISR), ISRIB antagonizes eIF2α(P) through allosteric rocking of the decamer, and sugar phosphates bind the α-subunit to promote holoenzyme formation and enhance GEF activity.","evidence":"Cryo-EM of assembly intermediates, X-ray crystallography of sugar phosphate–bound eIF2B, in vitro activity screens, ISR reporter assays, VWM mutant analysis","pmids":["33688831","34103529"],"confidence":"High","gaps":["Physiological sugar phosphate concentrations that regulate eIF2B in vivo uncharacterized","Whether δ-subunit conformational changes contribute to the rocking mechanism remains undefined"]},{"year":null,"claim":"The precise structural determinants within the δ-subunit that drive tetramer nucleation, the atomic contacts mediating ISRIB binding to δ-subunit residues, and the structural basis for V1 isoform dysfunction remain undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["High-resolution structure of ISRIB bound specifically at δ-subunit interface needed","Isoform-specific structural comparisons lacking","In vivo therapeutic relevance of ISRIB for EIF2B4-mutant VWM disease untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,5,6,7,16,28]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[12]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,5,9,17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,3,23]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[4,13]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[21]}],"complexes":["eIF2B decamer","eIF2B regulatory subcomplex (α/β/δ)","eIF2B βγδε tetramer"],"partners":["EIF2B1","EIF2B2","EIF2B3","EIF2B5","EIF2S1","EIF2S2","EIF2S3"],"other_free_text":[]},"mechanistic_narrative":"EIF2B4 encodes the δ-subunit of eIF2B, the essential heterodecameric guanine nucleotide exchange factor (GEF) that catalyzes GDP-to-GTP exchange on eIF2 to sustain translation initiation. Within the decamer (a dimer of αβγδε pentamers), the δ-subunit is a core component of the regulatory subcomplex (α/β/δ) that senses phosphorylated eIF2α(P) and transmits inhibitory signals to the catalytic γ/ε subcomplex; a point mutation in the δ-subunit can render eIF2B insensitive to eIF2α phosphorylation, and an alternative δ-subunit isoform (V1) uncouples eIF2B from the integrated stress response by abolishing eIF2 interaction [PMID:9582312, PMID:20709751]. The δ-subunit is pivotal for βγδε tetramer formation and contributes to the binding pocket of ISRIB, a small molecule that stabilizes the decameric assembly and restores GEF activity in Vanishing White Matter (VWM) disease mutants [PMID:24532666, PMID:25875391, PMID:29489452]. Mutations in EIF2B4, along with those in other eIF2B subunit genes, cause VWM disease by destabilizing the decameric holoenzyme and impairing nucleotide exchange [PMID:29489452]."},"prefetch_data":{"uniprot":{"accession":"Q9UI10","full_name":"Translation initiation factor eIF2B subunit delta","aliases":["eIF2B GDP-GTP exchange factor subunit delta"],"length_aa":523,"mass_kda":57.6,"function":"Acts as a component of the translation initiation factor 2B (eIF2B) complex, which catalyzes the exchange of GDP for GTP on eukaryotic initiation factor 2 (eIF2) gamma subunit (PubMed:25858979, PubMed:27023709, PubMed:31048492). Its guanine nucleotide exchange factor activity is repressed when bound to eIF2 complex phosphorylated on the alpha subunit, thereby limiting the amount of methionyl-initiator methionine tRNA available to the ribosome and consequently global translation is repressed (PubMed:25858979, PubMed:31048492)","subcellular_location":"Cytoplasm, cytosol","url":"https://www.uniprot.org/uniprotkb/Q9UI10/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/EIF2B4","classification":"Common 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rapidly inactivated by insulin, linking insulin signaling to eIF2B regulation via GSK-3 inactivation.\",\n      \"method\": \"Kinase activity assay with Mono-S chromatography fractions, immunoblotting with GSK-3 isoform-specific antibodies, phosphatase-2A reversal experiment\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (kinase assay, immunoblotting, phosphatase reversal), replicated in subsequent studies\",\n      \"pmids\": [\"8397507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"GSK-3 phosphorylates Ser540 (Ser535 in rat) of the eIF2Bε subunit in intact cells, and this phosphorylation inhibits eIF2B activity; insulin causes dephosphorylation of this site in a PI 3-kinase-dependent manner.\",\n      \"method\": \"In vitro kinase assay, phosphorylation site identification, PI 3-kinase inhibitor studies in intact cells\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — site-specific phosphorylation identified in vitro and confirmed in cells, PI3K pathway dissection, replicated across labs\",\n      \"pmids\": [\"9468292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Insulin activates eIF2B through a PI 3-kinase-dependent pathway that leads to inhibition of GSK-3; dominant negative PI 3-kinase blocks both eIF2B activation and GSK-3 inhibition, while dominant negative Sos (MAP kinase pathway) does not.\",\n      \"method\": \"Dominant negative PI 3-kinase expression, dominant negative Sos expression, rapamycin treatment, kinase activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with dominant negatives and pharmacological inhibitors, reciprocal regulation confirmed\",\n      \"pmids\": [\"9237674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"eIF2B is rapidly activated following T-cell mitogenic stimulation coincident with inactivation of GSK-3; phosphorylation of eIF2Bε by GSK-3 inhibits nucleotide exchange activity in vitro, providing a mechanism for rapid eIF2B activation.\",\n      \"method\": \"eIF2B activity assay, GSK-3 kinase assay, in vitro nucleotide exchange inhibition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro inhibition demonstrated, correlated with in-cell GSK-3 inactivation\",\n      \"pmids\": [\"8626696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"eIF2B is a heteropentameric GEF composed of two functionally distinct subcomplexes: a regulatory subcomplex (GCN3/α, GCD7/β, GCD2/δ) that binds eIF2(αP) with high affinity but lacks exchange activity, and a catalytic subcomplex (GCD1/γ, GCD6/ε) that has exchange activity insensitive to eIF2(αP). Binding of eIF2(αP) to the regulatory subcomplex prevents productive interaction with the catalytic subcomplex.\",\n      \"method\": \"In vitro nucleotide exchange assay, affinity binding assay, yeast regulatory mutants\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro exchange assay with purified subcomplexes, genetic and biochemical corroboration\",\n      \"pmids\": [\"9472020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The α- and δ-subunits of eIF2B mediate sensitivity to inhibition by phosphorylated eIF2(αP): recombinant five-subunit eIF2B is inhibited by eIF2(αP), but four-subunit eIF2B lacking the α-subunit is insensitive; a point mutation in the δ-subunit also confers insensitivity.\",\n      \"method\": \"Baculovirus expression and purification of recombinant eIF2B holoprotein and subunit-deletion complexes, in vitro GEF activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted activity with purified recombinant complexes, mutagenesis, first direct biochemical evidence\",\n      \"pmids\": [\"9582312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The GCN3(α), GCD7(β), and GCD2(δ) subunits of eIF2B form a stable trimeric regulatory subcomplex (confirmed by co-immunoprecipitation); this subcomplex interacts with eIF2(αP) and mediates inhibition of eIF2B GEF activity but lacks exchange activity itself.\",\n      \"method\": \"Co-immunoprecipitation of overexpressed subunits, in vivo suppression assays, genetic analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus genetic epistasis, replicated biochemically in subsequent studies\",\n      \"pmids\": [\"8887689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Phosphorylated eIF2α (Ser51) tightly binds the eIF2B regulatory subcomplex (GCN3/GCD7/GCD2) in vitro in a phosphorylation-stimulated manner; this tight binding is required for inhibition of eIF2B GEF activity. Mutations in eIF2α and in GCD7 that abolish eIF2B inhibition also impair this binding.\",\n      \"method\": \"GST pulldown with recombinant phosphorylated eIF2α and eIF2B subunits, genetic suppressor analysis, in vivo competition assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro binding assay combined with genetic epistasis and mutagenesis\",\n      \"pmids\": [\"11438658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Phosphorylation of Ser51 of eIF2α promotes complex formation between eIF2α(P) and eIF2B and inhibits eIF2B GEF activity; the Ser51→Asp phosphomimetic mutant recapitulates these effects, while the Ser51→Ala mutant does not.\",\n      \"method\": \"Baculovirus expression of eIF2α mutants, in vitro GEF inhibition assay, eIF2–eIF2B complex formation in reticulocyte lysate\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted biochemistry with phosphomimetic mutants, causal link between phosphorylation and inhibition established\",\n      \"pmids\": [\"11041858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The catalytic domain of eIF2Bε (yeast GCD6) resides in residues 518–712; residues 518–581 are required for nucleotide exchange activity beyond eIF2 binding, and deletion of C-terminal 61 residues abolishes both functions. N-terminal half of eIF2Bε mediates complex formation with other subunits and an activation function stimulated by that complex formation.\",\n      \"method\": \"N- and C-terminal deletion analysis, in vitro GEF assay, in vivo complementation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic deletion mutagenesis with in vitro reconstitution and in vivo validation\",\n      \"pmids\": [\"12356745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"eIF2 binds specifically to the δ- and ε-subunits of eIF2B; eIF2B binds to the β-subunit of eIF2, with the binding site located in the C-terminal ~70 amino acids of eIF2β. Phosphorylation of eIF2α does not promote binding of isolated eIF2α to eIF2B but increases overall eIF2B–eIF2 affinity.\",\n      \"method\": \"Far-Western blot analysis with individual subunits\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — far-Western blot, single method, but identifies specific subunit contacts\",\n      \"pmids\": [\"9446619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Mammalian eIF2B acts as a GDP dissociation stimulator (releases eIF2-bound GDP even without free nucleotide); the β-subunit of eIF2B interacts with GTP; addition of eIF2Bα to preparations lacking it markedly enhances GEF activity.\",\n      \"method\": \"In vitro nucleotide release assay, GTP-binding assay, reconstitution with recombinant eIF2Bα\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro biochemistry defining catalytic mechanism and subunit requirements\",\n      \"pmids\": [\"11323413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"eIF2B and eIF2 co-localize to a specific cytoplasmic body in yeast; eIF2 dynamically cycles into these foci while eIF2B remains largely resident (FRAP); three distinct strategies to reduce eIF2B GEF function all inhibit eIF2 shuttling into foci, implicating this cytoplasmic body as the site of guanine nucleotide exchange.\",\n      \"method\": \"Fluorescence microscopy co-localization, FRAP (fluorescence recovery after photobleaching), genetic and pharmacological inhibition of eIF2B\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — live imaging with FRAP, multiple perturbations, functional consequence established\",\n      \"pmids\": [\"16157703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"eIF2B possesses a second activity as a GDI displacement factor (GDF): the eIF2Bγ and eIF2Bε subunits displace eIF5 (a GDI) from the eIF2•GDP/eIF5 complex prior to GEF action. GDF activity is insensitive to eIF2α phosphorylation (unlike GEF), and eIF2Bγ mutations impair GDF but not GEF function.\",\n      \"method\": \"Protein-protein interaction assays, nucleotide exchange kinetic assays, mutagenesis of eIF2Bγ\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — novel activity defined by in vitro kinetics and mutagenesis, GDF and GEF activities dissociated\",\n      \"pmids\": [\"24352424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"eIF2B is a decamer (dimer of pentamers) rather than a pentamer; assembly occurs through the catalytic γ- and ε-subunits forming a tetrameric core, with regulatory subunits arranged asymmetrically; GTP binds to eIF2Bγ.\",\n      \"method\": \"Native mass spectrometry, chemical cross-linking, surface accessibility measurements, homology modelling\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — orthogonal MS methods with cross-linking, validated by subsequent cryo-EM structures\",\n      \"pmids\": [\"24852487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mammalian eIF2B is a decamer (dimer of eIF2B(βγδε) tetramers) stabilized by two copies of eIF2Bα; eIF2Bδ is pivotal for tetramer formation; decamers show greater eIF2 binding and activity than tetramers alone.\",\n      \"method\": \"Mass spectrometry, co-immunoprecipitation of overexpressed complexes, subunit deletion analysis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS plus reciprocal co-IP, functional comparison of decamer vs tetramer\",\n      \"pmids\": [\"24532666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ISRIB is an activator of eIF2B that stabilizes eIF2B dimers; eIF2B4 (δ-subunit) contributes to the ISRIB binding site. ISRIB renders cells insensitive to eIF2α phosphorylation by enhancing eIF2B activity.\",\n      \"method\": \"Reporter-based shRNA screen, biochemical stabilization assays, ISRIB analog structure-activity relationship, cell-based translation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic screen plus biochemical validation, followed up by structural studies\",\n      \"pmids\": [\"25875391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM structures of eIF2 bound to eIF2B (dephosphorylated) reveal that the eIF2B decamer is a static platform on which one or two flexible eIF2 trimers bind and align with eIF2B's bipartite catalytic centers; phosphorylation refolds eIF2α, allowing it to contact eIF2B at a different interface and sequester it into a nonproductive complex.\",\n      \"method\": \"Cryo-electron microscopy structural determination\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures of both productive and inhibited complexes, mechanistic interpretation validated\",\n      \"pmids\": [\"31048491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM and crystallographic structures of eIF2B in complex with unphosphorylated or phosphorylated eIF2 show that the two forms bind eIF2B in completely different manners: unphosphorylated eIF2 binds in a nucleotide exchange-active mode, whereas phosphorylated eIF2 binds in an inactive mode, explaining dominant inhibition.\",\n      \"method\": \"Cryo-electron microscopy, X-ray crystallography\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — two independent structural methods, functional validation included\",\n      \"pmids\": [\"31048492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ISRIB antagonizes the ISR by allosteric antagonism: ISRIB and eIF2(αP) bind distinct sites on eIF2B; eIF2(αP) engagement of both eIF2B regulatory sites remodels the ISRIB-binding pocket, reducing ISRIB binding affinity, and vice versa. Cryo-EM shows eIF2(αP) binding converts eIF2B into a conformation unfavorable for productive eIF2 engagement.\",\n      \"method\": \"Cryo-electron microscopy, in vitro nucleotide exchange assay with mutations, cell-based ISR reporter assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM plus in vitro reconstitution with mutagenesis, mechanistic model of allosteric antagonism\",\n      \"pmids\": [\"33220178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"eIF2B assembly state regulates ISR: without the α-subunit, unassembled eIF2B tetramers accumulate and induce the ISR. ISRIB promotes tetramer-to-octamer assembly and also allosterically antagonizes the ISR within fully assembled decamers via a rocking conformational motion coupling eIF2, eIF2-P, and ISRIB binding sites. eIF2-P binding converts eIF2B decamers into 'conjoined tetramers' with reduced substrate binding and activity.\",\n      \"method\": \"In vitro assembly monitoring, cryo-EM structural analysis, ISRIB treatment of cells lacking eIF2Bα, ISR reporter assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — cryo-EM plus in vitro/in vivo assembly experiments, mechanistic model validated\",\n      \"pmids\": [\"33688831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ISRIB stabilizes VWM disease mutant eIF2B in the decameric form and restores residual catalytic GEF activity to wild-type levels; various VWM mutations (including in EIF2B4/δ-subunit) destabilize the decameric holoenzyme.\",\n      \"method\": \"Biochemical stability assays, GEF activity assays of recombinant VWM mutant eIF2B complexes, cell-based ISR activation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — purified recombinant complexes with multiple VWM mutations, orthogonal biochemical and cellular assays\",\n      \"pmids\": [\"29489452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NMR, fluorescence spectroscopy, and mutagenesis reveal that eIF2α phosphorylation inhibits eIF2B by destabilizing an autoregulatory intramolecular interaction within eIF2α; the first structural model for eIF2B in complex with eIF2-GDP and intermediates was proposed.\",\n      \"method\": \"NMR spectroscopy, fluorescence spectroscopy, site-directed mutagenesis, thermodynamic analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biophysical and biochemical methods in one study\",\n      \"pmids\": [\"29036434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TLR-TRIF signaling activates eIF2B GEF activity through PP2A-mediated dephosphorylation of the eIF2Bε subunit; PP2A is itself activated by decreased Src-family-kinase-mediated tyrosine phosphorylation of its catalytic subunit, counteracting the inhibitory effect of p-eIF2α and preventing CHOP induction.\",\n      \"method\": \"eIF2B GEF activity assay, PP2A activity assay, pharmacological inhibitors, in vitro and in vivo (mouse) experiments\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with in vitro and in vivo corroboration, epistasis established\",\n      \"pmids\": [\"22231169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of the eIF2B regulatory subcomplex (eIF2B RSC): eIF2Bβ and eIF2Bδ form a tetramer (βδ)2, and combined with a homodimer of eIF2Bα2, create a hexameric regulatory subcomplex. eIF2Bα specifically binds AMP and GMP as ligands in the ancestral catalytic site, revealing evolutionary relation to sugar isomerases.\",\n      \"method\": \"X-ray crystallography, mutational analysis, biochemical binding assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with functional mutagenesis and biochemical assays\",\n      \"pmids\": [\"26384431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The universally conserved residue E569 and W699 in the eIF2Bε catalytic (GEF) domain are critical for exchange activity; W699 is required for interaction with eIF2β, while E569/L568 and W699 are all required for interaction with eIF2γ, establishing that multiple contacts between eIF2γ and eIF2Bε mediate nucleotide exchange.\",\n      \"method\": \"Site-directed mutagenesis, in vitro binding assays, yeast genetic complementation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with binding and activity assays, in vivo validation\",\n      \"pmids\": [\"17526738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sugar phosphates (e.g., glucose-6-phosphate) bind the ancestral catalytic site in the eIF2Bα subunit, promote eIF2B holoenzyme formation, and enhance GEF activity toward eIF2. A VWM disease mutation in the eIF2Bα ligand pocket abolishes sugar phosphate binding and stimulation.\",\n      \"method\": \"Unbiased binding and activity screens, X-ray crystallography of sugar phosphate-bound eIF2B, mutagenesis of ligand pocket, VWM mutant functional analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus biochemical reconstitution and mutagenesis, disease relevance validated\",\n      \"pmids\": [\"34103529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"eIF2B forms enzymatically inactive filaments in starving yeast cells, triggered by starvation-induced cytosolic acidification; filament assembly (not Gcn2 kinase) is required for rapid translational downregulation and promotes stress survival and fast recovery.\",\n      \"method\": \"Live fluorescence microscopy, pH measurement, translation assays, site-specific variants, Gcn2 mutant epistasis\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization, functional consequence of filament formation shown; ortholog in S. cerevisiae\",\n      \"pmids\": [\"32554487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A specific isoform of eIF2Bδ (variant 1/V1) attenuates the ER stress/unfolded protein response: replacement of total eIF2Bδ with V1 renders cells insensitive to eIF2α phosphorylation (no ATF4 upregulation, no translational suppression); V1 does not interact with eIF2, unlike the canonical variant 2.\",\n      \"method\": \"Isoform-specific expression in cancer cell lines, eIF2B-eIF2 interaction assay, translation and ATF4 reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — interaction assay plus functional readouts, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"20709751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"eIF2Bα (α-subunit) is required for eIF2-mediated translational suppression in response to eIF2α phosphorylation; loss of eIF2Bα or a T41A point mutation is sufficient to overcome translational inhibition from eIF2α phosphorylation and renders normal cells susceptible to viral infection.\",\n      \"method\": \"Yeast functional complementation, mammalian cell knockdown/expression of eIF2Bα variants, virus infection susceptibility assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and cellular loss-of-function with defined phenotypic readout across two model systems\",\n      \"pmids\": [\"21795329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Viral proteins (from a coronavirus and a picornavirus) independently acquired the ability to act as competitive inhibitors of p-eIF2–eIF2B interaction, allowing continued eIF2-GTP formation and global translation at high p-eIF2 levels that would otherwise halt translation.\",\n      \"method\": \"In vitro competition binding assay, translation assays in infected cells, viral protein expression\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — competition binding assay plus cell-based translation assays, independent discovery in two viral proteins\",\n      \"pmids\": [\"32690955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM reveals that SFSV NSs viral protein binds to the α-subunit of eIF2B in a manner competitive with eIF2(αP); in the presence of NSs, eIF2B retains GEF activity even with bound eIF2(αP), allowing unimpeded translation.\",\n      \"method\": \"Cryo-electron microscopy structural analysis, in vitro nucleotide exchange assay, ribosome profiling in cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure plus in vitro activity assay and genome-wide ribosome profiling\",\n      \"pmids\": [\"34876589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Drosophila eIF2Bε shows guanine nucleotide exchange activity and is phosphorylated by GSK-3 and casein kinase II; GSK-3 phosphorylation inhibits Drosophila eIF2B activity; Drosophila eIF2Bα confers regulation by phosphorylated eIF2α in yeast, and eIF2B activity in S2 cells is regulated by serum and ER stress via eIF2α phosphorylation.\",\n      \"method\": \"Cloning, in vitro GEF assay, GSK-3 and CK2 kinase assay, yeast complementation, S2 cell serum starvation and ER stress experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro kinase and GEF assays with mutagenic validation, ortholog confirmed functional\",\n      \"pmids\": [\"11060303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RNAi inactivation of eIF2Bδ (F11A3.2) in adult C. elegans reduces global protein synthesis and extends lifespan in a DAF-16 (FOXO)-dependent manner, also conferring thermal and oxidative stress resistance.\",\n      \"method\": \"Adult-onset RNAi, 35S-methionine incorporation assay, genetic epistasis with daf-16 deletion mutant\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNAi with direct translation measurement and genetic epistasis, C. elegans ortholog\",\n      \"pmids\": [\"18728216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Fusel alcohols (butanol, isoamyl alcohol) inhibit translation initiation in yeast by targeting eIF2B; a Pro180Ser variation in GCD1 (γ-subunit of eIF2B) determines sensitivity to fusel alcohol-induced translational regulation.\",\n      \"method\": \"Genetic mapping, yeast strain-specific translational inhibition assay, identification of GCD1 allelic variation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic mapping with functional translation assay in yeast, identifies eIF2B γ-subunit as target\",\n      \"pmids\": [\"11707417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"EGF and NGF activate eIF2B in PC12 cells via PI 3-kinase; EGF activation additionally requires FRAP/mTOR signaling; GSK-3 inactivation by EGF/NGF is not rapamycin-sensitive despite eIF2B activation being rapamycin-sensitive, indicating additional regulatory inputs beyond GSK-3.\",\n      \"method\": \"PI3K inhibitor (wortmannin), rapamycin, GSK-3 and CKII kinase assays, eIF2B activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection of pathway, corroborated by multiple inhibitors\",\n      \"pmids\": [\"9488678\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EIF2B4 (δ-subunit) is a regulatory component of the heterodecameric eIF2B guanine nucleotide exchange factor for eIF2: within the eIF2B decamer (dimer of pentamers), the δ-subunit participates in the regulatory subcomplex (α/β/δ) that mediates sensitivity to phosphorylated eIF2(αP), contributes to the ISRIB small-molecule binding site, is pivotal for βγδε tetramer formation, interacts with eIF2 directly, and harbors a variant (V1 isoform) that can uncouple eIF2B from eIF2α phosphorylation-mediated inhibition; mutations in EIF2B4 cause Vanishing White Matter disease by destabilizing the decameric holoenzyme and impairing GEF activity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EIF2B4 encodes the δ-subunit of eIF2B, the essential heterodecameric guanine nucleotide exchange factor (GEF) that catalyzes GDP-to-GTP exchange on eIF2 to sustain translation initiation. Within the decamer (a dimer of αβγδε pentamers), the δ-subunit is a core component of the regulatory subcomplex (α/β/δ) that senses phosphorylated eIF2α(P) and transmits inhibitory signals to the catalytic γ/ε subcomplex; a point mutation in the δ-subunit can render eIF2B insensitive to eIF2α phosphorylation, and an alternative δ-subunit isoform (V1) uncouples eIF2B from the integrated stress response by abolishing eIF2 interaction [PMID:9582312, PMID:20709751]. The δ-subunit is pivotal for βγδε tetramer formation and contributes to the binding pocket of ISRIB, a small molecule that stabilizes the decameric assembly and restores GEF activity in Vanishing White Matter (VWM) disease mutants [PMID:24532666, PMID:25875391, PMID:29489452]. Mutations in EIF2B4, along with those in other eIF2B subunit genes, cause VWM disease by destabilizing the decameric holoenzyme and impairing nucleotide exchange [PMID:29489452].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Identifying how growth-factor signaling reaches the translational machinery, GSK-3 was shown to phosphorylate eIF2Bε and to be rapidly inactivated by insulin, establishing the first kinase-mediated regulatory input into eIF2B.\",\n      \"evidence\": \"Kinase activity assay with chromatographic fractions and phosphatase-2A reversal in cell extracts\",\n      \"pmids\": [\"8397507\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation site on eIF2Bε not yet identified\", \"Direct role of the δ-subunit in this regulation unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining eIF2B's subunit architecture and functional division, the complex was resolved into a regulatory subcomplex (α/β/δ) that binds eIF2α(P) without exchange activity, and a catalytic subcomplex (γ/ε) that performs nucleotide exchange but is insensitive to phosphorylation; a δ-subunit mutation was shown to confer insensitivity to eIF2α(P), directly implicating the δ-subunit in phospho-regulation.\",\n      \"evidence\": \"Reconstituted in vitro GEF assays with purified recombinant subcomplexes, baculovirus-expressed deletion complexes, yeast genetic suppressor analysis\",\n      \"pmids\": [\"9472020\", \"9582312\", \"8887689\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for δ-subunit's role in phospho-sensing unresolved\", \"Stoichiometry of the holoenzyme not yet established\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mapping the eIF2–eIF2B interaction surface revealed that the δ- and ε-subunits of eIF2B directly contact eIF2, while phosphorylated eIF2α binds the regulatory subcomplex in a phosphorylation-stimulated manner; binding of eIF2α(P) is required for inhibition of GEF activity.\",\n      \"evidence\": \"Far-Western blots of individual subunits, GST pulldown with phosphorylated eIF2α, genetic suppressor analysis\",\n      \"pmids\": [\"9446619\", \"11438658\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution contacts between δ-subunit and eIF2 unknown\", \"How phospho-eIF2α binding to regulatory subcomplex blocks catalytic subcomplex action is unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating spatial organization of GEF activity in vivo, eIF2B was found to reside in dedicated cytoplasmic foci where eIF2 dynamically shuttles for nucleotide exchange; disrupting eIF2B function by three independent strategies blocked eIF2 cycling into these foci.\",\n      \"evidence\": \"Live fluorescence co-localization and FRAP in yeast with genetic/pharmacological perturbations\",\n      \"pmids\": [\"16157703\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian eIF2B forms analogous exchange bodies unknown\", \"Role of individual subunits in body formation unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"An alternative δ-subunit isoform (V1) was discovered to uncouple eIF2B from the integrated stress response: cells expressing only V1 showed no eIF2α phosphorylation–dependent translational suppression and no ATF4 induction, because V1 cannot interact with eIF2.\",\n      \"evidence\": \"Isoform-specific expression in cancer cell lines, eIF2B–eIF2 interaction assays, ATF4 reporter and translation assays\",\n      \"pmids\": [\"20709751\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis for V1's inability to bind eIF2 not determined\", \"Physiological contexts where V1 predominates unclear\", \"Single-lab observation without independent replication\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Resolving a longstanding stoichiometric question, native mass spectrometry established that eIF2B is a decamer (dimer of pentamers), with the δ-subunit pivotal for βγδε tetramer formation; decameric assemblies showed greater eIF2 binding and GEF activity than tetramers.\",\n      \"evidence\": \"Native MS, chemical cross-linking, co-immunoprecipitation of overexpressed subunit-deletion complexes\",\n      \"pmids\": [\"24852487\", \"24532666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of complete decamer not yet available\", \"How δ-subunit drives tetramer formation at atomic level unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying the drug target explaining ISRIB's mechanism, the δ-subunit was shown to contribute to the ISRIB-binding pocket; ISRIB stabilizes decameric assembly and overcomes eIF2α phosphorylation-mediated translational inhibition. Crystal structure of the regulatory subcomplex revealed that β and δ form a (βδ)₂ tetramer related to sugar isomerases.\",\n      \"evidence\": \"shRNA screen, ISRIB analog SAR, X-ray crystallography of eIF2B regulatory subcomplex, mutational analysis\",\n      \"pmids\": [\"25875391\", \"26384431\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise atomic contacts between ISRIB and δ-subunit residues not yet mapped\", \"Whether ISRIB acts identically in all cell types unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linking eIF2B biochemistry to human disease, VWM disease mutations across eIF2B subunits (including EIF2B4/δ) were shown to destabilize the decamer and reduce GEF activity; ISRIB could stabilize mutant decamers and partially restore catalytic function.\",\n      \"evidence\": \"GEF activity and stability assays of recombinant VWM mutant eIF2B complexes, cell-based ISR activation assays\",\n      \"pmids\": [\"29489452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo efficacy of ISRIB for VWM disease not established\", \"Mutation-specific effects on δ-subunit folding or intersubunit contacts uncharacterized\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Cryo-EM structures of eIF2B with unphosphorylated and phosphorylated eIF2 revealed two completely different binding modes: productive (exchange-active) versus nonproductive (inhibitory), with phosphorylation-induced refolding of eIF2α creating a new interface that sequesters eIF2B.\",\n      \"evidence\": \"Cryo-EM and X-ray crystallography of eIF2B–eIF2 complexes in both phosphorylation states\",\n      \"pmids\": [\"31048491\", \"31048492\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamic transitions between productive and nonproductive modes not captured\", \"Contribution of individual δ-subunit residues to either binding mode not dissected\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Integrating assembly, allostery, and metabolic sensing, studies showed that eIF2B assembly state itself regulates the ISR (tetramers activate ISR), ISRIB antagonizes eIF2α(P) through allosteric rocking of the decamer, and sugar phosphates bind the α-subunit to promote holoenzyme formation and enhance GEF activity.\",\n      \"evidence\": \"Cryo-EM of assembly intermediates, X-ray crystallography of sugar phosphate–bound eIF2B, in vitro activity screens, ISR reporter assays, VWM mutant analysis\",\n      \"pmids\": [\"33688831\", \"34103529\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological sugar phosphate concentrations that regulate eIF2B in vivo uncharacterized\", \"Whether δ-subunit conformational changes contribute to the rocking mechanism remains undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The precise structural determinants within the δ-subunit that drive tetramer nucleation, the atomic contacts mediating ISRIB binding to δ-subunit residues, and the structural basis for V1 isoform dysfunction remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"High-resolution structure of ISRIB bound specifically at δ-subunit interface needed\", \"Isoform-specific structural comparisons lacking\", \"In vivo therapeutic relevance of ISRIB for EIF2B4-mutant VWM disease untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 5, 6, 7, 16, 28]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 5, 9, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 3, 23]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [4, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"complexes\": [\n      \"eIF2B decamer\",\n      \"eIF2B regulatory subcomplex (α/β/δ)\",\n      \"eIF2B βγδε tetramer\"\n    ],\n    \"partners\": [\n      \"EIF2B1\",\n      \"EIF2B2\",\n      \"EIF2B3\",\n      \"EIF2B5\",\n      \"EIF2S1\",\n      \"EIF2S2\",\n      \"EIF2S3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}