{"gene":"CASKIN2","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":2016,"finding":"The crystal structure of the CASKIN2 SAM domain tandem (SAM1-SAM2) revealed a novel oligomerization mode where the minimal repeating unit is a dimer (rather than the monomer unit seen in CASKIN1). Analytical ultracentrifugation confirmed monomer/dimer equilibria for wild-type and a structure-directed double mutant that abolished oligomerization. EGFP-tagged SAM tandem proteins expressed in Neuro2a cells produced punctae distinct in shape and size from CASKIN1.","method":"X-ray crystallography, analytical ultracentrifugation sedimentation velocity, site-directed mutagenesis, fluorescence microscopy in Neuro2a cells","journal":"Cell communication and signaling : CCS","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis plus orthogonal biophysical method (AUC) in a single rigorous study","pmids":["27549312"],"is_preprint":false},{"year":2016,"finding":"The CASKIN2 SH3 domain has two non-canonical basic residues (K290/R319) in its peptide-binding cleft that prevent binding of typical polyproline ligands. An NMR structure confirmed the fold is intact but functionally impaired; a K290Y/R319W double mutant restoring canonical aromatic residues increased thermal stability by ~20°C, indicating the native SH3 domain is likely vestigial and non-functional for canonical SH3-mediated protein-protein interactions.","method":"NMR structure determination, site-directed mutagenesis, thermal stability assay","journal":"BMC structural biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure plus mutagenesis with functional readout (thermal stability and peptide-binding absence) in a single rigorous study","pmids":["27619958"],"is_preprint":false},{"year":2011,"finding":"The SAM domain of CASKIN2 was identified as a potential polymer-forming SAM domain using a negGFP-SAM fusion native gel screen followed by electron microscopy verification.","method":"negGFP-SAM fusion native gel screen, electron microscopy","journal":"Protein science : a publication of the Protein Society","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single screening method; listed among many SAM domains, limited functional follow-up on CASKIN2 specifically","pmids":["21805519"],"is_preprint":false},{"year":2019,"finding":"Deletion of both Caskin1 and Caskin2 in mice impairs LTP induction in hippocampal slices and reduces dendritic spine area and synaptic profiles in CA1 pyramidal neurons. Overexpressed Caskin1 in knockout hippocampal neurons increased mushroom-shaped spines. Immunoprecipitation showed Caskin1 co-localizes and co-precipitates with Shank2 within the same postsynaptic complex. Caskin deficiency specifically altered AMPA receptor phosphorylation, and cLTP-mediated spine enlargement was augmented in the knockout.","method":"Double knockout mouse model, electrophysiology (LTP, mEPSCs), ultrastructural analysis (EM), immunocytochemistry, co-immunoprecipitation, overexpression rescue","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (genetic KO, electrophysiology, EM, Co-IP) in a single lab; note findings attribute shared functions to Caskin1 and Caskin2 together, making CASKIN2-specific contributions partly indirect","pmids":["31727973"],"is_preprint":false},{"year":2024,"finding":"CASKIN2 directly interacts with the R8 domain of talin through its C-terminal LD motif. CASKIN2 also associates with the WAVE regulatory complex via Abi1 to promote cell migration. Growth factor-induced phosphorylation of CASKIN2 on serine 878 regulates the CASKIN2-Abi1 interaction. In MCF7 and UACC893 cells (which amplify CASKIN2), CASKIN2 localizes in plasma membrane-associated plaques and around focal adhesions in cortical microtubule stabilization complexes.","method":"Direct binding assay, co-immunoprecipitation, phosphorylation analysis (growth factor stimulation), cell migration assay (Abi1-dependent), fluorescence localization in cancer cell lines","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding and Co-IP with functional migration readout and phosphorylation regulation; single lab with multiple orthogonal methods","pmids":["38587458"],"is_preprint":false},{"year":2025,"finding":"CASKIN2, but not CASKIN1, is critical for proper synaptic transmission, synaptic strength, and active zone protein arrangement at glutamatergic synapses (shown in conditional knockout mice). Presynaptic CASKIN2 at CA3 neurons specifically regulates postsynaptic NMDAR-mediated responses, NMDAR surface expression, and LTP in CA1 neurons. PTPσ-mediated tyrosine dephosphorylation and multimerization of CASKIN2 are required for CASKIN2 to regulate excitatory synaptic transmission, NMDAR functions, and activity-dependent presynaptic F-actin rearrangement. CASKIN2 and PTPσ at Schaffer collateral circuits are required for novel object location memory.","method":"Conditional knockout mice (CASKIN1 and/or CASKIN2 cKO), electrophysiology (synaptic transmission, LTP), NMDAR surface expression assay, F-actin rearrangement assay, genetic epistasis with PTPσ, behavioral testing","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional knockout with multiple rigorous orthogonal readouts (electrophysiology, surface expression, F-actin dynamics, behavior), genetic epistasis with PTPσ, distinguishing CASKIN2-specific from CASKIN1 functions","pmids":["41223222"],"is_preprint":false}],"current_model":"CASKIN2 is a multidomain neuronal and non-neuronal scaffold protein whose SAM domain tandem forms dimeric oligomers via a unique mode distinct from CASKIN1, whose SH3 domain is structurally folded but functionally vestigial (unable to bind polyproline ligands), and which acts presynaptically at glutamatergic synapses where PTPσ-mediated tyrosine dephosphorylation and multimerization of CASKIN2 orchestrate transsynaptic NMDAR regulation and active zone organization; outside the synapse, CASKIN2 directly binds the talin R8 domain through an LD motif and associates with the WAVE regulatory complex via Abi1 (regulated by phosphorylation on S878) to promote cell migration."},"narrative":{"mechanistic_narrative":"CASKIN2 is a multidomain scaffold protein that organizes glutamatergic synaptic transmission presynaptically and also operates in cell migration machinery outside the synapse [PMID:41223222, PMID:38587458]. Its tandem SAM domains (SAM1-SAM2) mediate oligomerization through a distinctive mode whose minimal repeating unit is a dimer, generating cellular punctae morphologically distinct from the related CASKIN1 [PMID:27549312], while its SH3 domain, though correctly folded, carries non-canonical basic residues (K290/R319) in the binding cleft that abolish polyproline-ligand binding, rendering it functionally vestigial [PMID:27619958]. At Schaffer collateral synapses, presynaptic CASKIN2 — but not CASKIN1 — is required for synaptic strength, active zone protein arrangement, and regulation of postsynaptic NMDAR surface expression and LTP; PTPσ-mediated tyrosine dephosphorylation and multimerization of CASKIN2 are necessary for these functions and for activity-dependent presynaptic F-actin rearrangement and object-location memory [PMID:41223222]. Beyond the synapse, CASKIN2 binds the talin R8 domain via a C-terminal LD motif and associates with the WAVE regulatory complex through Abi1 to promote cell migration, an interaction controlled by growth factor-induced phosphorylation on serine 878 [PMID:38587458].","teleology":[{"year":2011,"claim":"Whether the CASKIN2 SAM domain could polymerize was unknown; an initial screen placed it among candidate self-associating SAM modules, framing oligomerization as a structural feature to test.","evidence":"negGFP-SAM fusion native gel screen with electron microscopy verification","pmids":["21805519"],"confidence":"Low","gaps":["Single screening method, no CASKIN2-specific quantitative biophysics","Did not define the oligomerization mode or interface","No functional consequence established"]},{"year":2016,"claim":"Resolved how the CASKIN2 SAM tandem self-associates, establishing a dimer-based oligomerization mode distinct from CASKIN1 and providing a structural basis for distinct cellular assemblies.","evidence":"X-ray crystallography of SAM1-SAM2, analytical ultracentrifugation, structure-directed mutagenesis, and fluorescence imaging in Neuro2a cells","pmids":["27549312"],"confidence":"High","gaps":["Physiological binding partners recruited to SAM oligomers not identified","Functional role of dimeric versus monomeric state in vivo undefined"]},{"year":2016,"claim":"Addressed whether the CASKIN2 SH3 domain mediates canonical interactions, showing the fold is intact but its binding cleft cannot engage polyproline ligands, marking the domain as vestigial.","evidence":"NMR structure determination, site-directed mutagenesis restoring canonical aromatic residues, and thermal stability assay","pmids":["27619958"],"confidence":"High","gaps":["Whether the SH3 domain has any non-canonical function is untested","No alternative ligand identified"]},{"year":2019,"claim":"Tested the role of CASKIN proteins in synaptic plasticity, showing combined Caskin1/Caskin2 loss impairs hippocampal LTP and spine structure and that CASKIN proteins reside in postsynaptic complexes with Shank2 and influence AMPAR phosphorylation.","evidence":"Caskin1/Caskin2 double-knockout mice with electrophysiology, EM ultrastructure, immunocytochemistry, co-immunoprecipitation, and overexpression rescue","pmids":["31727973"],"confidence":"Medium","gaps":["Phenotypes attributed to both paralogs jointly; CASKIN2-specific contribution not isolated","Shank2 co-IP not reciprocally validated or mapped to a domain"]},{"year":2024,"claim":"Defined a non-synaptic role for CASKIN2 in cell migration, identifying direct talin R8 binding via an LD motif and a phosphorylation-regulated link to the WAVE complex through Abi1.","evidence":"Direct binding assay, co-immunoprecipitation, growth factor-induced phosphorylation analysis, Abi1-dependent migration assay, and localization in CASKIN2-amplified cancer cell lines","pmids":["38587458"],"confidence":"Medium","gaps":["Kinase responsible for S878 phosphorylation not identified","Migration role established in cancer cell lines only; in vivo relevance unaddressed"]},{"year":2025,"claim":"Distinguished CASKIN2-specific synaptic function from CASKIN1, establishing presynaptic CASKIN2 as a transsynaptic regulator of NMDAR responses requiring PTPσ-mediated dephosphorylation and multimerization.","evidence":"Conditional CASKIN1/CASKIN2 knockout mice with electrophysiology, NMDAR surface expression and F-actin rearrangement assays, genetic epistasis with PTPσ, and behavioral memory testing","pmids":["41223222"],"confidence":"High","gaps":["Molecular link between PTPσ dephosphorylation, CASKIN2 multimerization, and active zone F-actin not structurally resolved","Tyrosine residues dephosphorylated by PTPσ not mapped","Presynaptic effectors transducing CASKIN2 state to postsynaptic NMDARs unidentified"]},{"year":null,"claim":"How CASKIN2's structurally defined SAM-mediated multimerization is mechanistically coupled to PTPσ-dependent dephosphorylation to control active zone organization and transsynaptic NMDAR signaling remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of CASKIN2 multimers in the dephosphorylated active state","Direct presynaptic-to-postsynaptic signaling intermediary unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,5]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[5,3]}],"complexes":["WAVE regulatory complex"],"partners":["TLN1","ABI1","PTPRS","SHANK2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8WXE0","full_name":"Caskin-2","aliases":["CASK-interacting protein 2"],"length_aa":1202,"mass_kda":126.8,"function":"","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q8WXE0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CASKIN2","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CASKIN2","total_profiled":1310},"omim":[{"mim_id":"612185","title":"CASK-INTERACTING PROTEIN 2; CASKIN2","url":"https://www.omim.org/entry/612185"},{"mim_id":"612184","title":"CASK-INTERACTING PROTEIN 1; CASKIN1","url":"https://www.omim.org/entry/612184"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CASKIN2"},"hgnc":{"alias_symbol":["KIAA1139","FLJ21609","ANKS5B"],"prev_symbol":[]},"alphafold":{"accession":"Q8WXE0","domains":[{"cath_id":"1.25.40.20","chopping":"4-31_39-281","consensus_level":"medium","plddt":87.6032,"start":4,"end":281},{"cath_id":"2.30.30.40","chopping":"282-350","consensus_level":"medium","plddt":76.2687,"start":282,"end":350},{"cath_id":"1.10.150.50","chopping":"490-553","consensus_level":"medium","plddt":87.2175,"start":490,"end":553},{"cath_id":"1.10.150.50","chopping":"557-628","consensus_level":"medium","plddt":87.0754,"start":557,"end":628}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WXE0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WXE0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WXE0-F1-predicted_aligned_error_v6.png","plddt_mean":57.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CASKIN2","jax_strain_url":"https://www.jax.org/strain/search?query=CASKIN2"},"sequence":{"accession":"Q8WXE0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WXE0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WXE0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WXE0"}},"corpus_meta":[{"pmid":"21805519","id":"PMC_21805519","title":"A human sterile alpha motif domain polymerizome.","date":"2011","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/21805519","citation_count":89,"is_preprint":false},{"pmid":"31727973","id":"PMC_31727973","title":"Dendritic spine morphology and memory formation depend on postsynaptic Caskin proteins.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31727973","citation_count":26,"is_preprint":false},{"pmid":"26070167","id":"PMC_26070167","title":"Effects of 17 α-methyltestosterone on transcriptome, gonadal histology and sex steroid hormones in rare minnow Gobiocypris rarus.","date":"2015","source":"Comparative biochemistry and physiology. Part D, Genomics & proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/26070167","citation_count":21,"is_preprint":false},{"pmid":"27549312","id":"PMC_27549312","title":"A new mode of SAM domain mediated oligomerization observed in the CASKIN2 neuronal scaffolding protein.","date":"2016","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/27549312","citation_count":16,"is_preprint":false},{"pmid":"38156018","id":"PMC_38156018","title":"Long non-coding RNA expression in PBMCs of patients with active pulmonary tuberculosis.","date":"2023","source":"Frontiers in microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/38156018","citation_count":11,"is_preprint":false},{"pmid":"27619958","id":"PMC_27619958","title":"A lack of peptide binding and decreased thermostability suggests that the CASKIN2 scaffolding protein SH3 domain may be vestigial.","date":"2016","source":"BMC structural biology","url":"https://pubmed.ncbi.nlm.nih.gov/27619958","citation_count":9,"is_preprint":false},{"pmid":"38587458","id":"PMC_38587458","title":"Caskin2 is a novel talin- and Abi1-binding protein that promotes cell motility.","date":"2024","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/38587458","citation_count":4,"is_preprint":false},{"pmid":"41223222","id":"PMC_41223222","title":"CASKIN2 mediates PTPσ-orchestrated transsynaptic mechanisms at excitatory synapses.","date":"2025","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41223222","citation_count":1,"is_preprint":false},{"pmid":"41451349","id":"PMC_41451349","title":"Identification of CASKIN2 as a Novel Candidate Gene for Müllerian Duct Anomalies in Humans.","date":"2025","source":"International journal of women's health","url":"https://pubmed.ncbi.nlm.nih.gov/41451349","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6816,"output_tokens":1930,"usd":0.024699,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8904,"output_tokens":2510,"usd":0.053635,"stage2_stop_reason":"end_turn"},"total_usd":0.078334,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2016,\n      \"finding\": \"The crystal structure of the CASKIN2 SAM domain tandem (SAM1-SAM2) revealed a novel oligomerization mode where the minimal repeating unit is a dimer (rather than the monomer unit seen in CASKIN1). Analytical ultracentrifugation confirmed monomer/dimer equilibria for wild-type and a structure-directed double mutant that abolished oligomerization. EGFP-tagged SAM tandem proteins expressed in Neuro2a cells produced punctae distinct in shape and size from CASKIN1.\",\n      \"method\": \"X-ray crystallography, analytical ultracentrifugation sedimentation velocity, site-directed mutagenesis, fluorescence microscopy in Neuro2a cells\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis plus orthogonal biophysical method (AUC) in a single rigorous study\",\n      \"pmids\": [\"27549312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The CASKIN2 SH3 domain has two non-canonical basic residues (K290/R319) in its peptide-binding cleft that prevent binding of typical polyproline ligands. An NMR structure confirmed the fold is intact but functionally impaired; a K290Y/R319W double mutant restoring canonical aromatic residues increased thermal stability by ~20°C, indicating the native SH3 domain is likely vestigial and non-functional for canonical SH3-mediated protein-protein interactions.\",\n      \"method\": \"NMR structure determination, site-directed mutagenesis, thermal stability assay\",\n      \"journal\": \"BMC structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure plus mutagenesis with functional readout (thermal stability and peptide-binding absence) in a single rigorous study\",\n      \"pmids\": [\"27619958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SAM domain of CASKIN2 was identified as a potential polymer-forming SAM domain using a negGFP-SAM fusion native gel screen followed by electron microscopy verification.\",\n      \"method\": \"negGFP-SAM fusion native gel screen, electron microscopy\",\n      \"journal\": \"Protein science : a publication of the Protein Society\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single screening method; listed among many SAM domains, limited functional follow-up on CASKIN2 specifically\",\n      \"pmids\": [\"21805519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Deletion of both Caskin1 and Caskin2 in mice impairs LTP induction in hippocampal slices and reduces dendritic spine area and synaptic profiles in CA1 pyramidal neurons. Overexpressed Caskin1 in knockout hippocampal neurons increased mushroom-shaped spines. Immunoprecipitation showed Caskin1 co-localizes and co-precipitates with Shank2 within the same postsynaptic complex. Caskin deficiency specifically altered AMPA receptor phosphorylation, and cLTP-mediated spine enlargement was augmented in the knockout.\",\n      \"method\": \"Double knockout mouse model, electrophysiology (LTP, mEPSCs), ultrastructural analysis (EM), immunocytochemistry, co-immunoprecipitation, overexpression rescue\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (genetic KO, electrophysiology, EM, Co-IP) in a single lab; note findings attribute shared functions to Caskin1 and Caskin2 together, making CASKIN2-specific contributions partly indirect\",\n      \"pmids\": [\"31727973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CASKIN2 directly interacts with the R8 domain of talin through its C-terminal LD motif. CASKIN2 also associates with the WAVE regulatory complex via Abi1 to promote cell migration. Growth factor-induced phosphorylation of CASKIN2 on serine 878 regulates the CASKIN2-Abi1 interaction. In MCF7 and UACC893 cells (which amplify CASKIN2), CASKIN2 localizes in plasma membrane-associated plaques and around focal adhesions in cortical microtubule stabilization complexes.\",\n      \"method\": \"Direct binding assay, co-immunoprecipitation, phosphorylation analysis (growth factor stimulation), cell migration assay (Abi1-dependent), fluorescence localization in cancer cell lines\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding and Co-IP with functional migration readout and phosphorylation regulation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"38587458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CASKIN2, but not CASKIN1, is critical for proper synaptic transmission, synaptic strength, and active zone protein arrangement at glutamatergic synapses (shown in conditional knockout mice). Presynaptic CASKIN2 at CA3 neurons specifically regulates postsynaptic NMDAR-mediated responses, NMDAR surface expression, and LTP in CA1 neurons. PTPσ-mediated tyrosine dephosphorylation and multimerization of CASKIN2 are required for CASKIN2 to regulate excitatory synaptic transmission, NMDAR functions, and activity-dependent presynaptic F-actin rearrangement. CASKIN2 and PTPσ at Schaffer collateral circuits are required for novel object location memory.\",\n      \"method\": \"Conditional knockout mice (CASKIN1 and/or CASKIN2 cKO), electrophysiology (synaptic transmission, LTP), NMDAR surface expression assay, F-actin rearrangement assay, genetic epistasis with PTPσ, behavioral testing\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional knockout with multiple rigorous orthogonal readouts (electrophysiology, surface expression, F-actin dynamics, behavior), genetic epistasis with PTPσ, distinguishing CASKIN2-specific from CASKIN1 functions\",\n      \"pmids\": [\"41223222\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CASKIN2 is a multidomain neuronal and non-neuronal scaffold protein whose SAM domain tandem forms dimeric oligomers via a unique mode distinct from CASKIN1, whose SH3 domain is structurally folded but functionally vestigial (unable to bind polyproline ligands), and which acts presynaptically at glutamatergic synapses where PTPσ-mediated tyrosine dephosphorylation and multimerization of CASKIN2 orchestrate transsynaptic NMDAR regulation and active zone organization; outside the synapse, CASKIN2 directly binds the talin R8 domain through an LD motif and associates with the WAVE regulatory complex via Abi1 (regulated by phosphorylation on S878) to promote cell migration.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CASKIN2 is a multidomain scaffold protein that organizes glutamatergic synaptic transmission presynaptically and also operates in cell migration machinery outside the synapse [#5, #4]. Its tandem SAM domains (SAM1-SAM2) mediate oligomerization through a distinctive mode whose minimal repeating unit is a dimer, generating cellular punctae morphologically distinct from the related CASKIN1 [#0], while its SH3 domain, though correctly folded, carries non-canonical basic residues (K290/R319) in the binding cleft that abolish polyproline-ligand binding, rendering it functionally vestigial [#1]. At Schaffer collateral synapses, presynaptic CASKIN2 — but not CASKIN1 — is required for synaptic strength, active zone protein arrangement, and regulation of postsynaptic NMDAR surface expression and LTP; PTPσ-mediated tyrosine dephosphorylation and multimerization of CASKIN2 are necessary for these functions and for activity-dependent presynaptic F-actin rearrangement and object-location memory [#5]. Beyond the synapse, CASKIN2 binds the talin R8 domain via a C-terminal LD motif and associates with the WAVE regulatory complex through Abi1 to promote cell migration, an interaction controlled by growth factor-induced phosphorylation on serine 878 [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Whether the CASKIN2 SAM domain could polymerize was unknown; an initial screen placed it among candidate self-associating SAM modules, framing oligomerization as a structural feature to test.\",\n      \"evidence\": \"negGFP-SAM fusion native gel screen with electron microscopy verification\",\n      \"pmids\": [\"21805519\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single screening method, no CASKIN2-specific quantitative biophysics\", \"Did not define the oligomerization mode or interface\", \"No functional consequence established\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolved how the CASKIN2 SAM tandem self-associates, establishing a dimer-based oligomerization mode distinct from CASKIN1 and providing a structural basis for distinct cellular assemblies.\",\n      \"evidence\": \"X-ray crystallography of SAM1-SAM2, analytical ultracentrifugation, structure-directed mutagenesis, and fluorescence imaging in Neuro2a cells\",\n      \"pmids\": [\"27549312\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological binding partners recruited to SAM oligomers not identified\", \"Functional role of dimeric versus monomeric state in vivo undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Addressed whether the CASKIN2 SH3 domain mediates canonical interactions, showing the fold is intact but its binding cleft cannot engage polyproline ligands, marking the domain as vestigial.\",\n      \"evidence\": \"NMR structure determination, site-directed mutagenesis restoring canonical aromatic residues, and thermal stability assay\",\n      \"pmids\": [\"27619958\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the SH3 domain has any non-canonical function is untested\", \"No alternative ligand identified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Tested the role of CASKIN proteins in synaptic plasticity, showing combined Caskin1/Caskin2 loss impairs hippocampal LTP and spine structure and that CASKIN proteins reside in postsynaptic complexes with Shank2 and influence AMPAR phosphorylation.\",\n      \"evidence\": \"Caskin1/Caskin2 double-knockout mice with electrophysiology, EM ultrastructure, immunocytochemistry, co-immunoprecipitation, and overexpression rescue\",\n      \"pmids\": [\"31727973\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phenotypes attributed to both paralogs jointly; CASKIN2-specific contribution not isolated\", \"Shank2 co-IP not reciprocally validated or mapped to a domain\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined a non-synaptic role for CASKIN2 in cell migration, identifying direct talin R8 binding via an LD motif and a phosphorylation-regulated link to the WAVE complex through Abi1.\",\n      \"evidence\": \"Direct binding assay, co-immunoprecipitation, growth factor-induced phosphorylation analysis, Abi1-dependent migration assay, and localization in CASKIN2-amplified cancer cell lines\",\n      \"pmids\": [\"38587458\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase responsible for S878 phosphorylation not identified\", \"Migration role established in cancer cell lines only; in vivo relevance unaddressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Distinguished CASKIN2-specific synaptic function from CASKIN1, establishing presynaptic CASKIN2 as a transsynaptic regulator of NMDAR responses requiring PTPσ-mediated dephosphorylation and multimerization.\",\n      \"evidence\": \"Conditional CASKIN1/CASKIN2 knockout mice with electrophysiology, NMDAR surface expression and F-actin rearrangement assays, genetic epistasis with PTPσ, and behavioral memory testing\",\n      \"pmids\": [\"41223222\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between PTPσ dephosphorylation, CASKIN2 multimerization, and active zone F-actin not structurally resolved\", \"Tyrosine residues dephosphorylated by PTPσ not mapped\", \"Presynaptic effectors transducing CASKIN2 state to postsynaptic NMDARs unidentified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CASKIN2's structurally defined SAM-mediated multimerization is mechanistically coupled to PTPσ-dependent dephosphorylation to control active zone organization and transsynaptic NMDAR signaling remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of CASKIN2 multimers in the dephosphorylated active state\", \"Direct presynaptic-to-postsynaptic signaling intermediary unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [5, 3]}\n    ],\n    \"complexes\": [\"WAVE regulatory complex\"],\n    \"partners\": [\"TLN1\", \"ABI1\", \"PTPRS\", \"SHANK2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":4,"faith_total":4,"faith_pct":100.0}}