{"gene":"ADAM22","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2006,"finding":"ADAM22 serves as a postsynaptic receptor for the secreted neuronal protein LGI1, and LGI1 binding to ADAM22 enhances AMPA receptor-mediated synaptic transmission in hippocampal slices. ADAM22 is anchored to the postsynaptic density via cytoskeletal scaffolds containing stargazin.","method":"Co-immunoprecipitation, cell-surface binding assay, hippocampal slice electrophysiology, postsynaptic density fractionation","journal":"Science","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (binding, electrophysiology, fractionation), high citation count, foundational study replicated by many subsequent labs","pmids":["16990550"],"is_preprint":false},{"year":2005,"finding":"ADAM22 knockout mice display severe ataxia, lethal seizures, and marked hypomyelination of peripheral nerves, establishing an essential in vivo role for ADAM22 in nervous system function and peripheral nerve myelination.","method":"Gene targeting (knockout mice), histological analysis, behavioral observation","journal":"BMC Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — clean KO with specific neurological and myelination phenotype, replicated/confirmed by multiple subsequent studies","pmids":["15876356"],"is_preprint":false},{"year":2010,"finding":"ADAM22 is a component of the Kv1 potassium channel complex at juxtaparanodes of myelinated axons, axon initial segments, and cerebellar basket cell terminals. ADAM22 co-immunoprecipitates Kv1.2 and the MAGUKs PSD-93 and PSD-95, and is required for recruitment of MAGUKs to juxtaparanodes (but not for Kv1.2 or Caspr2 clustering there). Clustering of ADAM22 at cerebellar basket cell terminals requires PSD-95.","method":"Immunoprecipitation of Kv1.2 followed by mass spectrometry, co-immunoprecipitation, analysis of multiple null mouse lines (Caspr-null, Caspr2-null, PSD-93-null, PSD-95-null, ADAM22-null), heterologous cell coexpression","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP/MS plus multiple genetic null mouse models with specific subcellular localization phenotypes","pmids":["20089912"],"is_preprint":false},{"year":2010,"finding":"Axonal ADAM22 is the principal neuronal receptor for Schwann cell-secreted LGI4, mediating a paracrine signaling axis that drives Schwann cell differentiation and peripheral nerve myelination. LGI4 binds directly to ADAM22 without requirement for additional membrane-associated factors.","method":"Direct binding assay, cell-type-specific conditional knockout mice, heterotypic Schwann cell–sensory neuron co-cultures","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding reconstitution plus cell-type-specific genetic epistasis in vivo","pmids":["20220021"],"is_preprint":false},{"year":2008,"finding":"LGI1 and LGI4 both bind specifically to ADAM22 (as well as ADAM11 and ADAM23), as demonstrated by immunoprecipitation from mouse brain and quantitative cell-ELISA, identifying ADAM22 as a receptor for multiple LGI family members.","method":"Immunoprecipitation from mouse brain, mass spectrometry, quantitative cell-ELISA","journal":"International Journal of Biological Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP from native tissue plus quantitative binding assay, single lab","pmids":["18974846"],"is_preprint":false},{"year":2009,"finding":"Crystal structure of the full ectodomain of mature human ADAM22 reveals a compact four-leaf clover arrangement in which the metalloproteinase-like domain is held in the concave face of a rigid module formed by disintegrin, cysteine-rich, and EGF-like domains. The metalloproteinase activity is abolished by absence of critical catalytic residues, filling of the substrate groove, and steric hindrance by the cysteine-rich domain. Three putative calcium ions are bound: one regulatory (metalloproteinase-like domain) and two structural (disintegrin domain).","method":"X-ray crystallography, isothermal titration calorimetry","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with calorimetric functional validation","pmids":["19692335"],"is_preprint":false},{"year":2015,"finding":"LGI1 acts as a paracrine signal from both pre- and postsynaptic neurons that acts specifically through ADAM22 to set postsynaptic strength. ADAM22 maintains excitatory synapses through PDZ domain interactions, and in the absence of LGI1, PSD-95 (but not SAP102) cannot potentiate synaptic transmission, revealing LGI1-ADAM22 as a complex that coordinates maturation of excitatory synapses.","method":"Single-cell electroporation, hippocampal slice electrophysiology, genetic knockout and rescue experiments","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — epistasis via genetic KO/rescue combined with electrophysiology, multiple orthogonal approaches","pmids":["26178195"],"is_preprint":false},{"year":2018,"finding":"Crystal structure of the human LGI1-ADAM22 complex reveals a 2:2 heterotetrameric assembly in which the hydrophobic pocket of the C-terminal EPTP domain of LGI1 binds to the metalloprotease-like domain of ADAM22. The N-terminal LRR and EPTP domains of LGI1 mediate intermolecular LGI1-LGI1 interaction. The pathogenic R474Q mutation of LGI1 disrupts this LGI1-LGI1 interface and the higher-order assembly in vitro and in a mouse model.","method":"X-ray crystallography, mutagenesis, mouse model of familial epilepsy","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and in vivo validation in mouse model","pmids":["29670100"],"is_preprint":false},{"year":2021,"finding":"The LGI1-ADAM22-MAGUK complex governs transsynaptic nanoalignment between presynaptic release machinery and postsynaptic AMPA/NMDA receptors. ADAM22 knock-in mice lacking the ADAM22-MAGUK interaction develop lethal epilepsy with less-condensed PSD-95 nanodomains and decreased excitatory synaptic transmission. Without ADAM22, PSD-95 cannot potentiate AMPA receptor-mediated synaptic transmission. Forced coexpression of ADAM22 and PSD-95 reconstitutes nano-condensates in non-neuronal cells.","method":"ADAM22 knock-in mouse model (PDZ-binding motif ablation), super-resolution microscopy, electrophysiology, reconstitution in non-neuronal cells","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1-2 — knock-in mouse with specific mechanistic rescue, super-resolution imaging, electrophysiology, and heterologous cell reconstitution","pmids":["33397806"],"is_preprint":false},{"year":2013,"finding":"LGI1 autoantibodies in limbic encephalitis specifically block the LGI1-ADAM22/23 interaction by targeting the EPTP repeat domain of LGI1, and disruption of LGI1-ADAM22 interaction by the soluble ADAM22 ectodomain is sufficient to reduce synaptic AMPA receptor clusters in hippocampal neurons. LGI1 knockout mice show greatly reduced AMPA receptor levels in hippocampal dentate gyrus.","method":"ELISA, cell-surface binding assay, co-immunoprecipitation, live hippocampal neuron imaging, LGI1 knockout mouse analysis","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including dominant-negative ectodomain experiment and KO mouse, strong mechanistic evidence","pmids":["24227725"],"is_preprint":false},{"year":2021,"finding":"PKA-dependent dual phosphorylation of ADAM22 mediates high-affinity binding to dimerized 14-3-3 proteins, which protects LGI1-ADAM22 complexes from endocytosis-dependent degradation. Forskolin-induced PKA activation increases ADAM22 levels. Approximately 10% of normal ADAM22 levels is sufficient to prevent lethal epilepsy in mice.","method":"Genetic and structural analysis, PKA pharmacology (forskolin), ADAM22/LGI1 hypomorphic mice, endocytosis assays","journal":"Cell Reports","confidence":"High","confidence_rationale":"Tier 1-2 — structural analysis of phosphorylation site combined with genetic hypomorphic mouse series and pharmacological manipulation","pmids":["34910912"],"is_preprint":false},{"year":2006,"finding":"14-3-3 proteins interact with the cytoplasmic domain of ADAM22 in a phosphorylation-dependent manner (preferentially with the serine-phosphorylated precursor form). The first 14-3-3 binding site (residues 831-834) is most crucial. ADAM22 point mutants lacking functional 14-3-3 binding motifs fail to accumulate efficiently at the cell surface; this is rescued by simultaneous deletion of ER retention motifs, indicating that 14-3-3 binding masks ER retention signals to allow surface expression.","method":"Yeast two-hybrid, co-immunoprecipitation, site-directed mutagenesis, cell-surface localization assay","journal":"Journal of Cell Science","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Y2H, Co-IP, mutagenesis, surface expression assay), mechanistic detail about phosphorylation-dependent ER export","pmids":["16868027"],"is_preprint":false},{"year":2005,"finding":"ADAM22 overexpression in HEK293 cells significantly enhances cell adhesion and spreading; truncated ADAM22 lacking 14-3-3 binding motifs does not, demonstrating that the ADAM22/14-3-3 interaction is required for ADAM22-mediated cell adhesion and spreading.","method":"Co-immunoprecipitation, in vitro pull-down, cell adhesion/spreading assay in HEK293 cells","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, two methods, but functional assay provides mechanistic link","pmids":["15882968"],"is_preprint":false},{"year":2006,"finding":"ADAM22 inhibits cellular proliferation of glioma-derived astrocytes via its disintegrin domain interacting with specific cell-surface integrins; this growth inhibition can be overcome by overexpression of integrin-linked kinase.","method":"BrdU incorporation assay, overexpression of GST-disintegrin domain fusion proteins, integrin-linked kinase overexpression rescue","journal":"Neurosurgery","confidence":"Medium","confidence_rationale":"Tier 3 — functional domain experiment with rescue, single lab","pmids":["16385342"],"is_preprint":false},{"year":2016,"finding":"LGI1 is recruited to the axon initial segment (AIS) where it colocalizes with ADAM22 and Kv1 channels. ADLTE-causing LGI1 missense mutations (S473L, R474Q) prevent LGI1 association with ADAM22 and its enrichment at the AIS. ADAM22 and ADAM23 promote ER export and surface expression of LGI1 and co-transport LGI1 in axonal vesicles.","method":"Live-cell imaging, immunofluorescence in cultured rat hippocampal neurons, axonal vesicle transport assay","journal":"Journal of Cell Science","confidence":"Medium","confidence_rationale":"Tier 2-3 — live imaging with functional consequence (AIS enrichment) plus mutagenesis, single lab","pmids":["30598502"],"is_preprint":false},{"year":2016,"finding":"ADAM22 compound heterozygous mutations (p.Cys401Tyr and p.Ser799IlefsTer96) cause progressive epileptic encephalopathy; both mutant proteins fail to bind LGI1, and the frameshift mutant also fails to bind PSD-95, establishing that loss of both LGI1 binding and PSD-95 interaction underlies disease pathogenesis.","method":"Cell-surface binding assay, co-immunoprecipitation in heterologous expression systems, exome sequencing","journal":"Neurology Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — functional binding assays in heterologous cells confirming mechanistic consequences of patient mutations","pmids":["27066583"],"is_preprint":false},{"year":2022,"finding":"Biallelic inactivating ADAM22 variants cause developmental and epileptic encephalopathy through at least three distinct mechanisms: (i) defective cell membrane expression, (ii) impaired LGI1 binding, and/or (iii) impaired interaction with PSD-95, as confirmed by functional studies in transfected cell lines.","method":"Cell-surface expression assay, co-immunoprecipitation, transfected cell lines","journal":"Brain","confidence":"Medium","confidence_rationale":"Tier 2 — systematic functional dissection of 19 patient variants across three interaction mechanisms","pmids":["35373813"],"is_preprint":false},{"year":2016,"finding":"Secretion-positive ADLTE-causing LGI1 missense mutations (T380A, R407C, S473L, R474Q) significantly impair interaction of LGI1 with ADAM22 and ADAM23 on the cell surface, establishing a second pathogenic mechanism (impaired receptor binding) distinct from inhibition of secretion.","method":"Immunofluorescence, co-immunoprecipitation, 3D protein modeling","journal":"PLoS Genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP plus immunofluorescence binding assays, single lab","pmids":["27760137"],"is_preprint":false},{"year":2023,"finding":"An ADAM22 missense variant p.S905F located in the PDZ-binding motif impairs ADAM22 binding to PSD-95 and other MAGUKs while having minimal effect on LGI1 interaction or ADAM22 biosynthesis/stability, causing focal epilepsy and behavioral disorder, and demonstrating that the ADAM22-MAGUK interaction is independently essential for seizure protection.","method":"Structural in silico modeling, protein-protein interaction studies in transfected mammalian cells, cell surface expression assay","journal":"Brain Communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — functional dissection of specific protein-protein interactions with patient variant, single lab","pmids":["37953841"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structures of the LGI1-ADAM22 complex at 2.78 Å (LGI1LRR-LGI1EPTP-ADAM22ECD) and 3.79 Å (3:3 heterohexameric LGI1-ADAM22ECD) resolutions reveal a higher-order heterohexameric assembly (3 LGI1 : 3 ADAM22 ectodomain molecules). High-speed atomic force microscopy visualizes structural flexibility of the 3:3 complex in solution.","method":"Cryo-EM, chemical cross-linking, high-speed atomic force microscopy (HS-AFM)","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — near-atomic cryo-EM structure plus orthogonal HS-AFM validation","pmids":["40601686"],"is_preprint":false},{"year":2002,"finding":"14-3-3β interacts with ADAM22 cytoplasmic tail; the major 14-3-3β binding site maps to the last 28 amino acid residues of ADAM22's cytoplasmic tail, as shown by yeast two-hybrid and in vitro binding/co-immunoprecipitation.","method":"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation","journal":"Science in China Series C","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single method confirmation, limited functional follow-up","pmids":["18762889"],"is_preprint":false},{"year":2010,"finding":"Mutations in the disintegrin domain of ADAM22 cause marked decrease in processing of ADAM22 preproteins and result in reduced LGI4-binding ability; the common polymorphic variant P81R does not affect ADAM22 function or LGI4 binding.","method":"Site-directed mutagenesis, cell surface expression assay, LGI4-binding assay","journal":"Journal of Receptor and Signal Transduction Research","confidence":"Medium","confidence_rationale":"Tier 2-3 — mutagenesis with functional binding readout, single lab","pmids":["20156119"],"is_preprint":false}],"current_model":"ADAM22 is a catalytically inactive transmembrane receptor that functions at neuronal synapses and juxtaparanodes: extracellularly, its metalloprotease-like domain binds the EPTP domain of secreted LGI1 (forming 2:2 and 3:3 trans-synaptic complexes) and also LGI4/LGI3; intracellularly, its PDZ-binding motif recruits PSD-95-family MAGUKs to organize a transsynaptic nanoarchitecture that positions AMPA and NMDA receptors and Kv1 channels, thereby supporting excitatory synaptic transmission and preventing epilepsy. ADAM22 surface expression is regulated by PKA-dependent dual phosphorylation that promotes high-affinity 14-3-3 binding to mask ER retention signals and protect ADAM22 from endocytic degradation, while axonal targeting of LGI1 depends on co-transport with ADAM22/ADAM23."},"narrative":{"teleology":[{"year":2002,"claim":"Identification of 14-3-3β as a cytoplasmic binding partner of ADAM22 provided the first clue that intracellular signaling or trafficking regulation controls ADAM22 function.","evidence":"Yeast two-hybrid and co-immunoprecipitation mapping 14-3-3β binding to the last 28 residues of ADAM22's cytoplasmic tail","pmids":["18762889"],"confidence":"Low","gaps":["Binding confirmed by yeast two-hybrid and Co-IP only; no independent lab replication","Functional consequence of 14-3-3 binding on ADAM22 trafficking unknown at this stage"]},{"year":2005,"claim":"Genetic ablation of ADAM22 in mice established that it is essential for nervous system function, causing lethal seizures, ataxia, and peripheral nerve hypomyelination — defining the physiological processes requiring ADAM22.","evidence":"ADAM22 knockout mice with histological, behavioral, and myelination analysis","pmids":["15876356"],"confidence":"High","gaps":["Molecular mechanism by which ADAM22 prevents seizures and promotes myelination unknown","Whether ADAM22 acts cell-autonomously in neurons vs. glia not resolved"]},{"year":2006,"claim":"Discovery that ADAM22 is the postsynaptic receptor for secreted LGI1 and that this interaction enhances AMPA receptor–mediated synaptic transmission provided the core functional paradigm for the gene.","evidence":"Co-immunoprecipitation, cell-surface binding, and hippocampal slice electrophysiology","pmids":["16990550"],"confidence":"High","gaps":["Structural basis of LGI1–ADAM22 binding not yet known","Whether LGI1 is the only relevant ligand at synapses unresolved"]},{"year":2006,"claim":"Phosphorylation-dependent 14-3-3 binding was shown to mask ER retention signals, explaining how ADAM22 surface expression is regulated — answering the trafficking mechanism question.","evidence":"Yeast two-hybrid, Co-IP, mutagenesis, and cell-surface localization assays showing 14-3-3 binding site mutants fail to reach the surface unless ER retention motifs are simultaneously deleted","pmids":["16868027"],"confidence":"High","gaps":["Kinase identity responsible for phosphorylation not yet identified","In vivo relevance of the trafficking mechanism not tested"]},{"year":2008,"claim":"Demonstration that both LGI1 and LGI4 bind ADAM22 expanded the receptor's ligand repertoire beyond a single LGI family member, suggesting a broader role for ADAM22 in LGI-mediated signaling.","evidence":"Immunoprecipitation from mouse brain and quantitative cell-ELISA","pmids":["18974846"],"confidence":"Medium","gaps":["Physiological contexts in which LGI4–ADAM22 interaction matters not yet defined"]},{"year":2009,"claim":"The crystal structure of the ADAM22 ectodomain revealed a compact four-domain arrangement and explained why the metalloprotease domain is catalytically inactive — the active site is occluded and lacks catalytic residues.","evidence":"X-ray crystallography and isothermal titration calorimetry","pmids":["19692335"],"confidence":"High","gaps":["Structure of the ADAM22–LGI1 complex not yet resolved","Roles of bound calcium ions in vivo unknown"]},{"year":2010,"claim":"Two studies resolved ADAM22's roles outside the synapse: at juxtaparanodes it recruits MAGUKs to Kv1 channel complexes, and on axons it serves as the receptor for Schwann cell–secreted LGI4 to drive peripheral myelination.","evidence":"IP-MS of Kv1.2 complexes plus multiple null mouse lines (juxtaparanode study); direct binding assays plus conditional knockout mice and neuron–Schwann cell co-cultures (myelination study)","pmids":["20089912","20220021"],"confidence":"High","gaps":["Whether ADAM22 acts differently at juxtaparanodes vs. AIS vs. synapses mechanistically","How ADAM22 cooperates with Caspr2 at juxtaparanodes unclear"]},{"year":2013,"claim":"LGI1 autoantibodies in limbic encephalitis were shown to disrupt LGI1–ADAM22 interaction specifically, and a soluble ADAM22 ectodomain acting as a dominant negative reduced synaptic AMPA receptor clusters — linking autoimmune disruption of the ADAM22 pathway to disease.","evidence":"ELISA, cell-surface binding, dominant-negative ectodomain experiments in hippocampal neurons, LGI1 KO mouse analysis","pmids":["24227725"],"confidence":"High","gaps":["Whether ADAM22 is itself a direct autoantibody target not fully resolved","Downstream signaling events after LGI1–ADAM22 disruption not characterized"]},{"year":2015,"claim":"Genetic epistasis experiments established that LGI1 signals exclusively through ADAM22 to set postsynaptic strength and that the ADAM22-PDZ interaction is required for PSD-95 to potentiate synaptic transmission, clarifying the receptor–scaffold signaling hierarchy.","evidence":"Single-cell electroporation, hippocampal slice electrophysiology, and KO/rescue experiments","pmids":["26178195"],"confidence":"High","gaps":["How LGI1 binding to ADAM22 transduces a signal intracellularly remains uncharacterized","Whether ADAM22 signals through any pathway independent of MAGUKs unknown"]},{"year":2016,"claim":"Patient mutations and ADLTE-causing LGI1 variants converged to show that disruption of the LGI1–ADAM22 binding interface or the ADAM22–PSD-95 interface individually suffice to cause epilepsy, genetically dissecting the two functional arms of ADAM22.","evidence":"Exome sequencing with functional binding assays for ADAM22 patient variants; immunofluorescence and Co-IP for LGI1 ADLTE missense mutations; live-cell imaging of LGI1–ADAM22 co-transport to the AIS","pmids":["27066583","27760137","30598502"],"confidence":"Medium","gaps":["Genotype-phenotype correlation across the full mutation spectrum incomplete","Whether partial loss of one interaction arm has a milder phenotype than loss of both not systematically tested in vivo"]},{"year":2018,"claim":"The crystal structure of the LGI1–ADAM22 complex revealed a 2:2 heterotetrameric assembly mediated by the LGI1-EPTP domain contacting the ADAM22 metalloprotease domain, and showed that the pathogenic R474Q mutation disrupts the LGI1–LGI1 interface needed for higher-order assembly.","evidence":"X-ray crystallography, mutagenesis, and a mouse model of familial epilepsy","pmids":["29670100"],"confidence":"High","gaps":["Whether trans-synaptic bridging involves higher-order assemblies beyond 2:2 unknown","Structural basis of ADAM22 interaction with other LGI family members not determined"]},{"year":2021,"claim":"Two discoveries resolved the downstream consequence and upstream regulation of ADAM22: knock-in mice lacking the ADAM22–MAGUK interaction showed that ADAM22 governs transsynaptic nanoalignment of PSD-95 condensates with release sites, and PKA-dependent dual phosphorylation was identified as the signal promoting 14-3-3 binding that protects ADAM22–LGI1 complexes from endocytic degradation.","evidence":"ADAM22 PDZ-binding motif knock-in mice with super-resolution imaging and electrophysiology; PKA pharmacology and ADAM22/LGI1 hypomorphic mouse series with endocytosis assays","pmids":["33397806","34910912"],"confidence":"High","gaps":["Whether PKA regulation of ADAM22 is activity-dependent at synapses not shown","How approximately 10% of ADAM22 suffices to prevent seizures mechanistically unexplained"]},{"year":2022,"claim":"Systematic functional analysis of 19 patient ADAM22 variants confirmed biallelic loss-of-function causes developmental and epileptic encephalopathy through three distinct molecular mechanisms: defective surface expression, impaired LGI1 binding, and/or impaired PSD-95 interaction.","evidence":"Cell-surface expression and Co-IP assays across 19 transfected patient variants","pmids":["35373813"],"confidence":"Medium","gaps":["Patient variants tested only in heterologous cells, not in neuronal systems","Quantitative thresholds of each interaction arm needed to prevent seizures not defined"]},{"year":2025,"claim":"Cryo-EM structures revealed a 3:3 heterohexameric LGI1–ADAM22 assembly at near-atomic resolution, extending the 2:2 model and demonstrating structural flexibility of the complex in solution.","evidence":"Cryo-EM at 2.78 Å and 3.79 Å resolution with high-speed atomic force microscopy validation","pmids":["40601686"],"confidence":"High","gaps":["Whether the 3:3 complex forms in vivo at synapses not demonstrated","How the flexible 3:3 assembly bridges pre- and postsynaptic membranes structurally unresolved"]},{"year":null,"claim":"Key unresolved questions include how LGI1 binding to the ADAM22 ectodomain transduces an intracellular signal beyond scaffold recruitment, whether the 3:3 complex operates as the physiological trans-synaptic bridge, and whether activity-dependent regulation of ADAM22 phosphorylation tunes synaptic strength.","evidence":"","pmids":[],"confidence":"Low","gaps":["No intracellular signaling cascade downstream of LGI1–ADAM22 binding identified","In vivo stoichiometry and architecture of the trans-synaptic complex unknown","Whether ADAM22 has synaptic functions independent of LGI ligands not tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,3,7,19]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,11,14]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[11]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,2,6,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6,10]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[11,10,14]}],"complexes":["LGI1-ADAM22 trans-synaptic complex","Kv1 channel juxtaparanodal complex","ADAM22-PSD-95 postsynaptic complex"],"partners":["LGI1","LGI4","DLG4","DLG2","YWHAB","ADAM23","KCNB2","CACNG2"],"other_free_text":[]},"mechanistic_narrative":"ADAM22 is a catalytically inactive transmembrane member of the ADAM family that functions as a postsynaptic receptor for secreted LGI-family ligands, organizing synaptic nanoarchitecture and supporting myelination in the peripheral nervous system. Its metalloprotease-like ectodomain binds the EPTP domain of LGI1, forming 2:2 and 3:3 trans-synaptic assemblies that enhance AMPA receptor–mediated transmission and establish transsynaptic nanoalignment of release machinery with postsynaptic receptor clusters, while its cytoplasmic PDZ-binding motif recruits PSD-95-family MAGUKs to condense postsynaptic density nanodomains [PMID:16990550, PMID:33397806, PMID:29670100, PMID:40601686]. On myelinated axons, ADAM22 serves as the neuronal receptor for Schwann cell–secreted LGI4, driving peripheral nerve myelination, and localizes to juxtaparanodes and axon initial segments where it recruits MAGUKs to Kv1 channel complexes [PMID:20220021, PMID:20089912]. Surface expression is controlled by PKA-dependent phosphorylation that promotes 14-3-3 binding, masking ER retention signals and protecting ADAM22–LGI1 complexes from endocytic degradation [PMID:16868027, PMID:34910912]. Biallelic loss-of-function ADAM22 variants cause developmental and epileptic encephalopathy through defective surface expression, impaired LGI1 binding, and/or loss of PSD-95 interaction [PMID:27066583, PMID:35373813]."},"prefetch_data":{"uniprot":{"accession":"Q9P0K1","full_name":"Disintegrin and metalloproteinase domain-containing protein 22","aliases":["Metalloproteinase-disintegrin ADAM22-3","Metalloproteinase-like, disintegrin-like, and cysteine-rich protein 2"],"length_aa":906,"mass_kda":100.4,"function":"Probable ligand for integrin in the brain. This is a non catalytic metalloprotease-like protein (PubMed:19692335). Involved in regulation of cell adhesion and spreading and in inhibition of cell proliferation. Neuronal receptor for LGI1","subcellular_location":"Cell membrane; Cell projection, axon","url":"https://www.uniprot.org/uniprotkb/Q9P0K1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ADAM22","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2},{"gene":"TUBB4B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ADAM22","total_profiled":1310},"omim":[{"mim_id":"621475","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 121; DEE121","url":"https://www.omim.org/entry/621475"},{"mim_id":"617933","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 61; DEE61","url":"https://www.omim.org/entry/617933"},{"mim_id":"608303","title":"LEUCINE-RICH GENE, GLIOMA-INACTIVATED, 4; LGI4","url":"https://www.omim.org/entry/608303"},{"mim_id":"608302","title":"LEUCINE-RICH GENE, GLIOMA-INACTIVATED, 3; LGI3","url":"https://www.omim.org/entry/608302"},{"mim_id":"604619","title":"LEUCINE-RICH GENE, GLIOMA-INACTIVATED, 1; LGI1","url":"https://www.omim.org/entry/604619"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cell Junctions","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":48.2}],"url":"https://www.proteinatlas.org/search/ADAM22"},"hgnc":{"alias_symbol":["MDC2"],"prev_symbol":[]},"alphafold":{"accession":"Q9P0K1","domains":[{"cath_id":"3.40.390.10","chopping":"48-193_234-429","consensus_level":"medium","plddt":84.4978,"start":48,"end":429},{"cath_id":"4.10.70.10","chopping":"446-516","consensus_level":"medium","plddt":87.2155,"start":446,"end":516},{"cath_id":"-","chopping":"534-677","consensus_level":"high","plddt":93.7686,"start":534,"end":677}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P0K1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P0K1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P0K1-F1-predicted_aligned_error_v6.png","plddt_mean":73.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ADAM22","jax_strain_url":"https://www.jax.org/strain/search?query=ADAM22"},"sequence":{"accession":"Q9P0K1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9P0K1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9P0K1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P0K1"}},"corpus_meta":[{"pmid":"16990550","id":"PMC_16990550","title":"Epilepsy-related ligand/receptor complex LGI1 and ADAM22 regulate synaptic transmission.","date":"2006","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/16990550","citation_count":310,"is_preprint":false},{"pmid":"24227725","id":"PMC_24227725","title":"Autoantibodies to epilepsy-related LGI1 in limbic encephalitis neutralize LGI1-ADAM22 interaction and reduce synaptic AMPA receptors.","date":"2013","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/24227725","citation_count":265,"is_preprint":false},{"pmid":"15876356","id":"PMC_15876356","title":"Ataxia and peripheral nerve hypomyelination in ADAM22-deficient mice.","date":"2005","source":"BMC neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/15876356","citation_count":131,"is_preprint":false},{"pmid":"20089912","id":"PMC_20089912","title":"ADAM22, a Kv1 channel-interacting protein, recruits membrane-associated guanylate kinases to 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ADAM22 is anchored to the postsynaptic density via cytoskeletal scaffolds containing stargazin.\",\n      \"method\": \"Co-immunoprecipitation, cell-surface binding assay, hippocampal slice electrophysiology, postsynaptic density fractionation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (binding, electrophysiology, fractionation), high citation count, foundational study replicated by many subsequent labs\",\n      \"pmids\": [\"16990550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ADAM22 knockout mice display severe ataxia, lethal seizures, and marked hypomyelination of peripheral nerves, establishing an essential in vivo role for ADAM22 in nervous system function and peripheral nerve myelination.\",\n      \"method\": \"Gene targeting (knockout mice), histological analysis, behavioral observation\",\n      \"journal\": \"BMC Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific neurological and myelination phenotype, replicated/confirmed by multiple subsequent studies\",\n      \"pmids\": [\"15876356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ADAM22 is a component of the Kv1 potassium channel complex at juxtaparanodes of myelinated axons, axon initial segments, and cerebellar basket cell terminals. ADAM22 co-immunoprecipitates Kv1.2 and the MAGUKs PSD-93 and PSD-95, and is required for recruitment of MAGUKs to juxtaparanodes (but not for Kv1.2 or Caspr2 clustering there). Clustering of ADAM22 at cerebellar basket cell terminals requires PSD-95.\",\n      \"method\": \"Immunoprecipitation of Kv1.2 followed by mass spectrometry, co-immunoprecipitation, analysis of multiple null mouse lines (Caspr-null, Caspr2-null, PSD-93-null, PSD-95-null, ADAM22-null), heterologous cell coexpression\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP/MS plus multiple genetic null mouse models with specific subcellular localization phenotypes\",\n      \"pmids\": [\"20089912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Axonal ADAM22 is the principal neuronal receptor for Schwann cell-secreted LGI4, mediating a paracrine signaling axis that drives Schwann cell differentiation and peripheral nerve myelination. LGI4 binds directly to ADAM22 without requirement for additional membrane-associated factors.\",\n      \"method\": \"Direct binding assay, cell-type-specific conditional knockout mice, heterotypic Schwann cell–sensory neuron co-cultures\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding reconstitution plus cell-type-specific genetic epistasis in vivo\",\n      \"pmids\": [\"20220021\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"LGI1 and LGI4 both bind specifically to ADAM22 (as well as ADAM11 and ADAM23), as demonstrated by immunoprecipitation from mouse brain and quantitative cell-ELISA, identifying ADAM22 as a receptor for multiple LGI family members.\",\n      \"method\": \"Immunoprecipitation from mouse brain, mass spectrometry, quantitative cell-ELISA\",\n      \"journal\": \"International Journal of Biological Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP from native tissue plus quantitative binding assay, single lab\",\n      \"pmids\": [\"18974846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structure of the full ectodomain of mature human ADAM22 reveals a compact four-leaf clover arrangement in which the metalloproteinase-like domain is held in the concave face of a rigid module formed by disintegrin, cysteine-rich, and EGF-like domains. The metalloproteinase activity is abolished by absence of critical catalytic residues, filling of the substrate groove, and steric hindrance by the cysteine-rich domain. Three putative calcium ions are bound: one regulatory (metalloproteinase-like domain) and two structural (disintegrin domain).\",\n      \"method\": \"X-ray crystallography, isothermal titration calorimetry\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with calorimetric functional validation\",\n      \"pmids\": [\"19692335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LGI1 acts as a paracrine signal from both pre- and postsynaptic neurons that acts specifically through ADAM22 to set postsynaptic strength. ADAM22 maintains excitatory synapses through PDZ domain interactions, and in the absence of LGI1, PSD-95 (but not SAP102) cannot potentiate synaptic transmission, revealing LGI1-ADAM22 as a complex that coordinates maturation of excitatory synapses.\",\n      \"method\": \"Single-cell electroporation, hippocampal slice electrophysiology, genetic knockout and rescue experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis via genetic KO/rescue combined with electrophysiology, multiple orthogonal approaches\",\n      \"pmids\": [\"26178195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structure of the human LGI1-ADAM22 complex reveals a 2:2 heterotetrameric assembly in which the hydrophobic pocket of the C-terminal EPTP domain of LGI1 binds to the metalloprotease-like domain of ADAM22. The N-terminal LRR and EPTP domains of LGI1 mediate intermolecular LGI1-LGI1 interaction. The pathogenic R474Q mutation of LGI1 disrupts this LGI1-LGI1 interface and the higher-order assembly in vitro and in a mouse model.\",\n      \"method\": \"X-ray crystallography, mutagenesis, mouse model of familial epilepsy\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and in vivo validation in mouse model\",\n      \"pmids\": [\"29670100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The LGI1-ADAM22-MAGUK complex governs transsynaptic nanoalignment between presynaptic release machinery and postsynaptic AMPA/NMDA receptors. ADAM22 knock-in mice lacking the ADAM22-MAGUK interaction develop lethal epilepsy with less-condensed PSD-95 nanodomains and decreased excitatory synaptic transmission. Without ADAM22, PSD-95 cannot potentiate AMPA receptor-mediated synaptic transmission. Forced coexpression of ADAM22 and PSD-95 reconstitutes nano-condensates in non-neuronal cells.\",\n      \"method\": \"ADAM22 knock-in mouse model (PDZ-binding motif ablation), super-resolution microscopy, electrophysiology, reconstitution in non-neuronal cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — knock-in mouse with specific mechanistic rescue, super-resolution imaging, electrophysiology, and heterologous cell reconstitution\",\n      \"pmids\": [\"33397806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LGI1 autoantibodies in limbic encephalitis specifically block the LGI1-ADAM22/23 interaction by targeting the EPTP repeat domain of LGI1, and disruption of LGI1-ADAM22 interaction by the soluble ADAM22 ectodomain is sufficient to reduce synaptic AMPA receptor clusters in hippocampal neurons. LGI1 knockout mice show greatly reduced AMPA receptor levels in hippocampal dentate gyrus.\",\n      \"method\": \"ELISA, cell-surface binding assay, co-immunoprecipitation, live hippocampal neuron imaging, LGI1 knockout mouse analysis\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including dominant-negative ectodomain experiment and KO mouse, strong mechanistic evidence\",\n      \"pmids\": [\"24227725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PKA-dependent dual phosphorylation of ADAM22 mediates high-affinity binding to dimerized 14-3-3 proteins, which protects LGI1-ADAM22 complexes from endocytosis-dependent degradation. Forskolin-induced PKA activation increases ADAM22 levels. Approximately 10% of normal ADAM22 levels is sufficient to prevent lethal epilepsy in mice.\",\n      \"method\": \"Genetic and structural analysis, PKA pharmacology (forskolin), ADAM22/LGI1 hypomorphic mice, endocytosis assays\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structural analysis of phosphorylation site combined with genetic hypomorphic mouse series and pharmacological manipulation\",\n      \"pmids\": [\"34910912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"14-3-3 proteins interact with the cytoplasmic domain of ADAM22 in a phosphorylation-dependent manner (preferentially with the serine-phosphorylated precursor form). The first 14-3-3 binding site (residues 831-834) is most crucial. ADAM22 point mutants lacking functional 14-3-3 binding motifs fail to accumulate efficiently at the cell surface; this is rescued by simultaneous deletion of ER retention motifs, indicating that 14-3-3 binding masks ER retention signals to allow surface expression.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, site-directed mutagenesis, cell-surface localization assay\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Y2H, Co-IP, mutagenesis, surface expression assay), mechanistic detail about phosphorylation-dependent ER export\",\n      \"pmids\": [\"16868027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ADAM22 overexpression in HEK293 cells significantly enhances cell adhesion and spreading; truncated ADAM22 lacking 14-3-3 binding motifs does not, demonstrating that the ADAM22/14-3-3 interaction is required for ADAM22-mediated cell adhesion and spreading.\",\n      \"method\": \"Co-immunoprecipitation, in vitro pull-down, cell adhesion/spreading assay in HEK293 cells\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, two methods, but functional assay provides mechanistic link\",\n      \"pmids\": [\"15882968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ADAM22 inhibits cellular proliferation of glioma-derived astrocytes via its disintegrin domain interacting with specific cell-surface integrins; this growth inhibition can be overcome by overexpression of integrin-linked kinase.\",\n      \"method\": \"BrdU incorporation assay, overexpression of GST-disintegrin domain fusion proteins, integrin-linked kinase overexpression rescue\",\n      \"journal\": \"Neurosurgery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — functional domain experiment with rescue, single lab\",\n      \"pmids\": [\"16385342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LGI1 is recruited to the axon initial segment (AIS) where it colocalizes with ADAM22 and Kv1 channels. ADLTE-causing LGI1 missense mutations (S473L, R474Q) prevent LGI1 association with ADAM22 and its enrichment at the AIS. ADAM22 and ADAM23 promote ER export and surface expression of LGI1 and co-transport LGI1 in axonal vesicles.\",\n      \"method\": \"Live-cell imaging, immunofluorescence in cultured rat hippocampal neurons, axonal vesicle transport assay\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — live imaging with functional consequence (AIS enrichment) plus mutagenesis, single lab\",\n      \"pmids\": [\"30598502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ADAM22 compound heterozygous mutations (p.Cys401Tyr and p.Ser799IlefsTer96) cause progressive epileptic encephalopathy; both mutant proteins fail to bind LGI1, and the frameshift mutant also fails to bind PSD-95, establishing that loss of both LGI1 binding and PSD-95 interaction underlies disease pathogenesis.\",\n      \"method\": \"Cell-surface binding assay, co-immunoprecipitation in heterologous expression systems, exome sequencing\",\n      \"journal\": \"Neurology Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional binding assays in heterologous cells confirming mechanistic consequences of patient mutations\",\n      \"pmids\": [\"27066583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Biallelic inactivating ADAM22 variants cause developmental and epileptic encephalopathy through at least three distinct mechanisms: (i) defective cell membrane expression, (ii) impaired LGI1 binding, and/or (iii) impaired interaction with PSD-95, as confirmed by functional studies in transfected cell lines.\",\n      \"method\": \"Cell-surface expression assay, co-immunoprecipitation, transfected cell lines\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic functional dissection of 19 patient variants across three interaction mechanisms\",\n      \"pmids\": [\"35373813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Secretion-positive ADLTE-causing LGI1 missense mutations (T380A, R407C, S473L, R474Q) significantly impair interaction of LGI1 with ADAM22 and ADAM23 on the cell surface, establishing a second pathogenic mechanism (impaired receptor binding) distinct from inhibition of secretion.\",\n      \"method\": \"Immunofluorescence, co-immunoprecipitation, 3D protein modeling\",\n      \"journal\": \"PLoS Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus immunofluorescence binding assays, single lab\",\n      \"pmids\": [\"27760137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"An ADAM22 missense variant p.S905F located in the PDZ-binding motif impairs ADAM22 binding to PSD-95 and other MAGUKs while having minimal effect on LGI1 interaction or ADAM22 biosynthesis/stability, causing focal epilepsy and behavioral disorder, and demonstrating that the ADAM22-MAGUK interaction is independently essential for seizure protection.\",\n      \"method\": \"Structural in silico modeling, protein-protein interaction studies in transfected mammalian cells, cell surface expression assay\",\n      \"journal\": \"Brain Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — functional dissection of specific protein-protein interactions with patient variant, single lab\",\n      \"pmids\": [\"37953841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structures of the LGI1-ADAM22 complex at 2.78 Å (LGI1LRR-LGI1EPTP-ADAM22ECD) and 3.79 Å (3:3 heterohexameric LGI1-ADAM22ECD) resolutions reveal a higher-order heterohexameric assembly (3 LGI1 : 3 ADAM22 ectodomain molecules). High-speed atomic force microscopy visualizes structural flexibility of the 3:3 complex in solution.\",\n      \"method\": \"Cryo-EM, chemical cross-linking, high-speed atomic force microscopy (HS-AFM)\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — near-atomic cryo-EM structure plus orthogonal HS-AFM validation\",\n      \"pmids\": [\"40601686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"14-3-3β interacts with ADAM22 cytoplasmic tail; the major 14-3-3β binding site maps to the last 28 amino acid residues of ADAM22's cytoplasmic tail, as shown by yeast two-hybrid and in vitro binding/co-immunoprecipitation.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation\",\n      \"journal\": \"Science in China Series C\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method confirmation, limited functional follow-up\",\n      \"pmids\": [\"18762889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mutations in the disintegrin domain of ADAM22 cause marked decrease in processing of ADAM22 preproteins and result in reduced LGI4-binding ability; the common polymorphic variant P81R does not affect ADAM22 function or LGI4 binding.\",\n      \"method\": \"Site-directed mutagenesis, cell surface expression assay, LGI4-binding assay\",\n      \"journal\": \"Journal of Receptor and Signal Transduction Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — mutagenesis with functional binding readout, single lab\",\n      \"pmids\": [\"20156119\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ADAM22 is a catalytically inactive transmembrane receptor that functions at neuronal synapses and juxtaparanodes: extracellularly, its metalloprotease-like domain binds the EPTP domain of secreted LGI1 (forming 2:2 and 3:3 trans-synaptic complexes) and also LGI4/LGI3; intracellularly, its PDZ-binding motif recruits PSD-95-family MAGUKs to organize a transsynaptic nanoarchitecture that positions AMPA and NMDA receptors and Kv1 channels, thereby supporting excitatory synaptic transmission and preventing epilepsy. ADAM22 surface expression is regulated by PKA-dependent dual phosphorylation that promotes high-affinity 14-3-3 binding to mask ER retention signals and protect ADAM22 from endocytic degradation, while axonal targeting of LGI1 depends on co-transport with ADAM22/ADAM23.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ADAM22 is a catalytically inactive transmembrane member of the ADAM family that functions as a postsynaptic receptor for secreted LGI-family ligands, organizing synaptic nanoarchitecture and supporting myelination in the peripheral nervous system. Its metalloprotease-like ectodomain binds the EPTP domain of LGI1, forming 2:2 and 3:3 trans-synaptic assemblies that enhance AMPA receptor–mediated transmission and establish transsynaptic nanoalignment of release machinery with postsynaptic receptor clusters, while its cytoplasmic PDZ-binding motif recruits PSD-95-family MAGUKs to condense postsynaptic density nanodomains [PMID:16990550, PMID:33397806, PMID:29670100, PMID:40601686]. On myelinated axons, ADAM22 serves as the neuronal receptor for Schwann cell–secreted LGI4, driving peripheral nerve myelination, and localizes to juxtaparanodes and axon initial segments where it recruits MAGUKs to Kv1 channel complexes [PMID:20220021, PMID:20089912]. Surface expression is controlled by PKA-dependent phosphorylation that promotes 14-3-3 binding, masking ER retention signals and protecting ADAM22–LGI1 complexes from endocytic degradation [PMID:16868027, PMID:34910912]. Biallelic loss-of-function ADAM22 variants cause developmental and epileptic encephalopathy through defective surface expression, impaired LGI1 binding, and/or loss of PSD-95 interaction [PMID:27066583, PMID:35373813].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of 14-3-3β as a cytoplasmic binding partner of ADAM22 provided the first clue that intracellular signaling or trafficking regulation controls ADAM22 function.\",\n      \"evidence\": \"Yeast two-hybrid and co-immunoprecipitation mapping 14-3-3β binding to the last 28 residues of ADAM22's cytoplasmic tail\",\n      \"pmids\": [\"18762889\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Binding confirmed by yeast two-hybrid and Co-IP only; no independent lab replication\", \"Functional consequence of 14-3-3 binding on ADAM22 trafficking unknown at this stage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic ablation of ADAM22 in mice established that it is essential for nervous system function, causing lethal seizures, ataxia, and peripheral nerve hypomyelination — defining the physiological processes requiring ADAM22.\",\n      \"evidence\": \"ADAM22 knockout mice with histological, behavioral, and myelination analysis\",\n      \"pmids\": [\"15876356\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which ADAM22 prevents seizures and promotes myelination unknown\", \"Whether ADAM22 acts cell-autonomously in neurons vs. glia not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that ADAM22 is the postsynaptic receptor for secreted LGI1 and that this interaction enhances AMPA receptor–mediated synaptic transmission provided the core functional paradigm for the gene.\",\n      \"evidence\": \"Co-immunoprecipitation, cell-surface binding, and hippocampal slice electrophysiology\",\n      \"pmids\": [\"16990550\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of LGI1–ADAM22 binding not yet known\", \"Whether LGI1 is the only relevant ligand at synapses unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Phosphorylation-dependent 14-3-3 binding was shown to mask ER retention signals, explaining how ADAM22 surface expression is regulated — answering the trafficking mechanism question.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, mutagenesis, and cell-surface localization assays showing 14-3-3 binding site mutants fail to reach the surface unless ER retention motifs are simultaneously deleted\",\n      \"pmids\": [\"16868027\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase identity responsible for phosphorylation not yet identified\", \"In vivo relevance of the trafficking mechanism not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstration that both LGI1 and LGI4 bind ADAM22 expanded the receptor's ligand repertoire beyond a single LGI family member, suggesting a broader role for ADAM22 in LGI-mediated signaling.\",\n      \"evidence\": \"Immunoprecipitation from mouse brain and quantitative cell-ELISA\",\n      \"pmids\": [\"18974846\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological contexts in which LGI4–ADAM22 interaction matters not yet defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The crystal structure of the ADAM22 ectodomain revealed a compact four-domain arrangement and explained why the metalloprotease domain is catalytically inactive — the active site is occluded and lacks catalytic residues.\",\n      \"evidence\": \"X-ray crystallography and isothermal titration calorimetry\",\n      \"pmids\": [\"19692335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the ADAM22–LGI1 complex not yet resolved\", \"Roles of bound calcium ions in vivo unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Two studies resolved ADAM22's roles outside the synapse: at juxtaparanodes it recruits MAGUKs to Kv1 channel complexes, and on axons it serves as the receptor for Schwann cell–secreted LGI4 to drive peripheral myelination.\",\n      \"evidence\": \"IP-MS of Kv1.2 complexes plus multiple null mouse lines (juxtaparanode study); direct binding assays plus conditional knockout mice and neuron–Schwann cell co-cultures (myelination study)\",\n      \"pmids\": [\"20089912\", \"20220021\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ADAM22 acts differently at juxtaparanodes vs. AIS vs. synapses mechanistically\", \"How ADAM22 cooperates with Caspr2 at juxtaparanodes unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"LGI1 autoantibodies in limbic encephalitis were shown to disrupt LGI1–ADAM22 interaction specifically, and a soluble ADAM22 ectodomain acting as a dominant negative reduced synaptic AMPA receptor clusters — linking autoimmune disruption of the ADAM22 pathway to disease.\",\n      \"evidence\": \"ELISA, cell-surface binding, dominant-negative ectodomain experiments in hippocampal neurons, LGI1 KO mouse analysis\",\n      \"pmids\": [\"24227725\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ADAM22 is itself a direct autoantibody target not fully resolved\", \"Downstream signaling events after LGI1–ADAM22 disruption not characterized\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Genetic epistasis experiments established that LGI1 signals exclusively through ADAM22 to set postsynaptic strength and that the ADAM22-PDZ interaction is required for PSD-95 to potentiate synaptic transmission, clarifying the receptor–scaffold signaling hierarchy.\",\n      \"evidence\": \"Single-cell electroporation, hippocampal slice electrophysiology, and KO/rescue experiments\",\n      \"pmids\": [\"26178195\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How LGI1 binding to ADAM22 transduces a signal intracellularly remains uncharacterized\", \"Whether ADAM22 signals through any pathway independent of MAGUKs unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Patient mutations and ADLTE-causing LGI1 variants converged to show that disruption of the LGI1–ADAM22 binding interface or the ADAM22–PSD-95 interface individually suffice to cause epilepsy, genetically dissecting the two functional arms of ADAM22.\",\n      \"evidence\": \"Exome sequencing with functional binding assays for ADAM22 patient variants; immunofluorescence and Co-IP for LGI1 ADLTE missense mutations; live-cell imaging of LGI1–ADAM22 co-transport to the AIS\",\n      \"pmids\": [\"27066583\", \"27760137\", \"30598502\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genotype-phenotype correlation across the full mutation spectrum incomplete\", \"Whether partial loss of one interaction arm has a milder phenotype than loss of both not systematically tested in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The crystal structure of the LGI1–ADAM22 complex revealed a 2:2 heterotetrameric assembly mediated by the LGI1-EPTP domain contacting the ADAM22 metalloprotease domain, and showed that the pathogenic R474Q mutation disrupts the LGI1–LGI1 interface needed for higher-order assembly.\",\n      \"evidence\": \"X-ray crystallography, mutagenesis, and a mouse model of familial epilepsy\",\n      \"pmids\": [\"29670100\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether trans-synaptic bridging involves higher-order assemblies beyond 2:2 unknown\", \"Structural basis of ADAM22 interaction with other LGI family members not determined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Two discoveries resolved the downstream consequence and upstream regulation of ADAM22: knock-in mice lacking the ADAM22–MAGUK interaction showed that ADAM22 governs transsynaptic nanoalignment of PSD-95 condensates with release sites, and PKA-dependent dual phosphorylation was identified as the signal promoting 14-3-3 binding that protects ADAM22–LGI1 complexes from endocytic degradation.\",\n      \"evidence\": \"ADAM22 PDZ-binding motif knock-in mice with super-resolution imaging and electrophysiology; PKA pharmacology and ADAM22/LGI1 hypomorphic mouse series with endocytosis assays\",\n      \"pmids\": [\"33397806\", \"34910912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKA regulation of ADAM22 is activity-dependent at synapses not shown\", \"How approximately 10% of ADAM22 suffices to prevent seizures mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Systematic functional analysis of 19 patient ADAM22 variants confirmed biallelic loss-of-function causes developmental and epileptic encephalopathy through three distinct molecular mechanisms: defective surface expression, impaired LGI1 binding, and/or impaired PSD-95 interaction.\",\n      \"evidence\": \"Cell-surface expression and Co-IP assays across 19 transfected patient variants\",\n      \"pmids\": [\"35373813\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Patient variants tested only in heterologous cells, not in neuronal systems\", \"Quantitative thresholds of each interaction arm needed to prevent seizures not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cryo-EM structures revealed a 3:3 heterohexameric LGI1–ADAM22 assembly at near-atomic resolution, extending the 2:2 model and demonstrating structural flexibility of the complex in solution.\",\n      \"evidence\": \"Cryo-EM at 2.78 Å and 3.79 Å resolution with high-speed atomic force microscopy validation\",\n      \"pmids\": [\"40601686\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the 3:3 complex forms in vivo at synapses not demonstrated\", \"How the flexible 3:3 assembly bridges pre- and postsynaptic membranes structurally unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how LGI1 binding to the ADAM22 ectodomain transduces an intracellular signal beyond scaffold recruitment, whether the 3:3 complex operates as the physiological trans-synaptic bridge, and whether activity-dependent regulation of ADAM22 phosphorylation tunes synaptic strength.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No intracellular signaling cascade downstream of LGI1–ADAM22 binding identified\", \"In vivo stoichiometry and architecture of the trans-synaptic complex unknown\", \"Whether ADAM22 has synaptic functions independent of LGI ligands not tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 3, 7, 19]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 11, 14]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 2, 6, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6, 10]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [11, 10, 14]}\n    ],\n    \"complexes\": [\n      \"LGI1-ADAM22 trans-synaptic complex\",\n      \"Kv1 channel juxtaparanodal complex\",\n      \"ADAM22-PSD-95 postsynaptic complex\"\n    ],\n    \"partners\": [\n      \"LGI1\",\n      \"LGI4\",\n      \"DLG4\",\n      \"DLG2\",\n      \"YWHAB\",\n      \"ADAM23\",\n      \"KCNB2\",\n      \"CACNG2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}