{"gene":"PALS2","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2000,"finding":"PALS2 was identified as a novel MAGUK protein that binds to the amino terminus of mLin-7 (Lin-7) through a conserved mLin-7 binding domain. Site-directed mutagenesis identified conserved residues crucial for mLin-7 binding. PALS2 localizes to the lateral membrane in MDCK cells and represents a new subfamily of MAGUKs allowing for multiple targeting complexes containing mLin-7.","method":"Far Western overlay assay, bacterial expression cloning, site-directed mutagenesis, immunofluorescence localization in MDCK cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Far Western, mutagenesis, subcellular localization) in a focused mechanistic study of PALS2","pmids":["10753959"],"is_preprint":false},{"year":2001,"finding":"VAM-1 (PALS2) was shown to bind to Veli-1 (human LIN-7 homologue) through a conserved domain, as demonstrated by GST pull-down experiments and blot overlay assays in heterologous transfection systems. The vam-1 gene encodes a 540 amino acid MAGUK with PDZ, SH3, and GUK domains, localizes to chromosome 7p15-21, and is expressed in testis, brain, and kidney.","method":"GST pull-down, blot overlay assay, heterologous transfection, FISH chromosomal localization","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal binding assays (GST pulldown + blot overlay) in a single lab","pmids":["11311936"],"is_preprint":false},{"year":2003,"finding":"PALS2 was identified as a binding partner of Necl-2 (nectin-like molecule-2/IGSF4/SynCAM1) at the basolateral plasma membrane in epithelial cells. Unlike nectins, Necl-2 did not bind afadin but bound PALS2, a MAGUK family member known to bind Lin-7, suggesting PALS2 involvement in transmembrane protein localization.","method":"Protein binding assays (pulldown/interaction assays), immunofluorescence localization in mouse gall bladder epithelium","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct binding assay plus localization data, single lab, supporting mechanistic inference","pmids":["12826663"],"is_preprint":false},{"year":2002,"finding":"SAP97 does NOT interact with PALS2, despite interacting with the closely related MAGUKs DLG3 and DLG2. This negative result distinguishes PALS2 from other MAGUK family members in terms of SAP97 complex formation.","method":"Co-immunoprecipitation and binding assays in rat brain lysates and MDCK cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay with negative result, single lab, reciprocal controls with related MAGUKs","pmids":["12351654"],"is_preprint":false},{"year":2004,"finding":"PALS2 was identified as one of eight MAGUK family proteins associated with the Kir2.2 potassium channel C-terminal PDZ binding motif in rat brain, suggesting PALS2 participates in channel trafficking/anchoring protein complexes.","method":"Affinity chromatography from rat brain detergent extracts using Kir2.2 C-terminal matrix, multidimensional HPLC-ESI-MS/MS, immunoblotting","journal":"The Journal of biological chemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — proteomics identification in a large-scale screen, single method, no functional follow-up specific to PALS2","pmids":["15024025"],"is_preprint":false},{"year":2005,"finding":"The C-terminal cytoplasmic region of Necl-1/TSLL1/SynCAM3 was shown to bind PALS2 (along with Dlg3 and CASK), identifying PALS2 as a binding partner for this neural-tissue-specific cell adhesion molecule at non-junctional contact sites.","method":"Binding assays (pulldown/interaction assays) with Necl-1 C-terminal cytoplasmic region","journal":"Journal of cell science","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single binding assay, single lab, no functional validation specific to PALS2","pmids":["15741237"],"is_preprint":false},{"year":2007,"finding":"Phylogenetic analysis established that Drosophila Varicose (Vari) defines a new MAGUK subgroup that includes mammalian PALS2. Both Vari and PALS2 are basolateral proteins, and the interaction of Vari with Neurexin IV parallels PALS2 interaction with Necl-2, indicating that PALS2 is part of a conserved basolateral cell-adhesion complex distinct from the polarity complex.","method":"Phylogenetic analysis, in vivo localization studies in Drosophila, genetic loss-of-function analysis","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phylogenetic plus functional in vivo evidence in Drosophila ortholog with direct parallel drawn to PALS2; Drosophila ortholog study","pmids":["17267446"],"is_preprint":false},{"year":2022,"finding":"PALS2/MPP6 was identified by mass spectrometry-based proteomics as part of a complex with Cadm4, Lin7, and band 4.1G (Epb41l2) at Schmidt-Lanterman incisures (SLIs) in peripheral nerve myelin. This complex was increased in Fa2h-deficient mouse sciatic nerves at 17 months of age.","method":"Mass spectrometry-based proteomics of purified myelin from sciatic nerves of Fa2h-/- mice","journal":"Molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative proteomics with subcellular localization context; single study, single method for this complex identification","pmids":["35445918"],"is_preprint":false},{"year":2024,"finding":"PALS2 was shown to form a complex with GSDME by co-immunoprecipitation in vascular smooth muscle cells (VSMCs). Knockdown of PALS2 attenuated activated caspase-3 and GSDME fragmentation, placing PALS2 upstream of caspase-3 activation and GSDME cleavage in VSMC apoptosis.","method":"Co-immunoprecipitation (protein co-IP), siRNA knockdown with Western blot readout for activated caspase-3 and GSDME fragmentation in VSMCs","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus functional KD with specific molecular readouts, single lab","pmids":["38851795"],"is_preprint":false},{"year":2025,"finding":"PALS2/MPP6 was identified as a pan-cone photoreceptor protein absent in rod photoreceptors by quantitative DIA mass spectrometry proteomics of FACS-sorted mouse retinal cells, establishing cone-specific subcellular localization.","method":"Fluorescence-activated cell sorting of rod and cone photoreceptors, data-independent acquisition (DIA) mass spectrometry proteomics","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single rigorous proteomics study establishing cell-type-specific localization, no functional follow-up","pmids":["41396450"],"is_preprint":false}],"current_model":"PALS2 (also known as VAM-1, p55T, MPP6) is a basolateral MAGUK scaffolding protein that binds Lin-7/Veli family members through a conserved L27-type domain, interacts with cell-adhesion molecules Necl-1 and Necl-2 at the basolateral membrane, participates in Kir2 channel-associated protein complexes in brain, forms a complex with GSDME to regulate caspase-3-dependent apoptosis in vascular smooth muscle cells, and localizes specifically to cone photoreceptors and Schmidt-Lanterman incisures in myelin, where it associates with Cadm4 and Lin7 as part of a membrane skeletal complex."},"narrative":{"mechanistic_narrative":"PALS2 (MPP6/VAM-1/p55T) is a basolateral membrane-associated guanylate kinase (MAGUK) scaffolding protein that nucleates multiprotein complexes linking cell-adhesion molecules to the membrane cytoskeleton [PMID:10753959, PMID:17267446]. It was first defined by its ability to bind the amino terminus of the Lin-7/Veli family of adaptor proteins through a conserved Lin-7-binding (L27-type) domain, with site-directed mutagenesis identifying the residues required for this interaction, and it localizes to the lateral membrane of polarized epithelial cells [PMID:10753959, PMID:11311936]. PALS2 engages the cytoplasmic tails of nectin-like cell-adhesion molecules Necl-2 (SynCAM1) and Necl-1 (SynCAM3) at non-junctional basolateral contact sites, behaving as a conserved adhesion-complex scaffold distinct from the apical polarity machinery — a role mirrored by its Drosophila ortholog Varicose binding Neurexin IV [PMID:12826663, PMID:15741237, PMID:17267446]. In peripheral nerve myelin it assembles with Cadm4, Lin7, and band 4.1G (Epb41l2) into a membrane-skeletal complex at Schmidt-Lanterman incisures, and it marks cone but not rod photoreceptors [PMID:35445918, PMID:41396450]. Beyond scaffolding, PALS2 forms a complex with GSDME in vascular smooth muscle cells and acts upstream of caspase-3 activation and GSDME cleavage during apoptosis [PMID:38851795]. Its specificity among MAGUKs is underscored by its failure to interact with SAP97 despite SAP97 binding the related MAGUKs DLG2 and DLG3 [PMID:12351654].","teleology":[{"year":2000,"claim":"Established PALS2 as a distinct MAGUK that selectively recruits the Lin-7 adaptor, defining the molecular basis for a new class of lateral-membrane targeting complexes.","evidence":"Far Western overlay, expression cloning, and site-directed mutagenesis with immunofluorescence in MDCK cells","pmids":["10753959"],"confidence":"High","gaps":["Functional consequence of the Lin-7 interaction not tested","No physiological ligand of the PDZ/SH3/GUK module identified"]},{"year":2001,"claim":"Confirmed the conserved Lin-7/Veli-binding domain and provided domain architecture and tissue-expression context, generalizing the interaction across species homologues.","evidence":"GST pull-down and blot overlay in heterologous transfection, FISH chromosomal mapping","pmids":["11311936"],"confidence":"Medium","gaps":["Interaction shown in heterologous systems only","No endogenous complex demonstrated"]},{"year":2003,"claim":"Connected PALS2 to a transmembrane adhesion molecule by showing it binds Necl-2 at the basolateral membrane, implicating PALS2 in localizing cell-adhesion proteins.","evidence":"Protein binding assays plus immunofluorescence in mouse gall bladder epithelium","pmids":["12826663"],"confidence":"Medium","gaps":["Direct vs indirect binding to Necl-2 not fully resolved","No loss-of-function test of trafficking role"]},{"year":2002,"claim":"Defined the binding specificity of PALS2 within the MAGUK family by demonstrating it does not associate with SAP97, distinguishing it from DLG2/DLG3.","evidence":"Co-immunoprecipitation and binding assays in rat brain lysates and MDCK cells","pmids":["12351654"],"confidence":"Medium","gaps":["Negative result; structural basis of exclusion not defined"]},{"year":2004,"claim":"Placed PALS2 among MAGUKs associated with a potassium channel C-terminal motif, raising a possible channel-anchoring role in brain.","evidence":"Affinity chromatography on Kir2.2 C-terminal matrix with HPLC-ESI-MS/MS and immunoblotting from rat brain","pmids":["15024025"],"confidence":"Low","gaps":["Proteomic co-isolation only; no direct PALS2-Kir2.2 interaction or functional follow-up","PALS2-specific contribution not isolated from eight co-purifying MAGUKs"]},{"year":2005,"claim":"Extended the adhesion-scaffold role to the nervous system by showing PALS2 binds the neural cell-adhesion molecule Necl-1 at non-junctional contacts.","evidence":"Binding assays with the Necl-1 C-terminal cytoplasmic region","pmids":["15741237"],"confidence":"Low","gaps":["Single binding assay without reciprocal or functional validation","Endogenous complex not demonstrated"]},{"year":2007,"claim":"Used the Drosophila ortholog Varicose to establish PALS2 as part of a conserved basolateral cell-adhesion complex separable from the apical polarity complex.","evidence":"Phylogenetic analysis with in vivo localization and genetic loss-of-function in Drosophila","pmids":["17267446"],"confidence":"Medium","gaps":["Functional parallel inferred from ortholog rather than mammalian loss-of-function","Mammalian PALS2 phenotype not tested"]},{"year":2022,"claim":"Defined a membrane-skeletal complex containing PALS2, Cadm4, Lin7, and band 4.1G at Schmidt-Lanterman incisures of peripheral myelin, anchoring PALS2 in a specific subcellular myelin domain.","evidence":"Mass spectrometry proteomics of purified myelin from Fa2h-/- mouse sciatic nerves","pmids":["35445918"],"confidence":"Medium","gaps":["Complex composition from co-purification; direct binding not mapped","Functional role of the complex in myelin maintenance not established"]},{"year":2024,"claim":"Revealed a non-scaffolding apoptotic function by showing PALS2 complexes with GSDME and acts upstream of caspase-3 activation and GSDME cleavage in vascular smooth muscle cells.","evidence":"Reciprocal co-immunoprecipitation and siRNA knockdown with Western readout for activated caspase-3 and GSDME fragmentation in VSMCs","pmids":["38851795"],"confidence":"Medium","gaps":["Mechanism by which PALS2 promotes caspase-3 activation unknown","Single cell type and single lab"]},{"year":2025,"claim":"Established cell-type-specific expression by identifying PALS2 as a pan-cone, rod-absent photoreceptor protein, suggesting a specialized role in cone photoreceptors.","evidence":"FACS-sorted mouse retinal cells with DIA mass spectrometry proteomics","pmids":["41396450"],"confidence":"Medium","gaps":["Localization only; no functional role in cones tested","Binding partners in cones not identified"]},{"year":null,"claim":"How PALS2's scaffolding activity mechanistically connects to its apoptotic role with GSDME, and what its function is in cone photoreceptors and myelin incisures, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of PALS2 in its complexes","No mammalian loss-of-function phenotype linking scaffolding to physiology","Mechanism linking PALS2 to caspase-3 activation undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,2,5,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,6]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[8]}],"complexes":["Cadm4-Lin7-band 4.1G membrane-skeletal complex (Schmidt-Lanterman incisures)"],"partners":["LIN7","NECL-2/CADM1","NECL-1/CADM3","CADM4","EPB41L2","GSDME"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NZW5","full_name":"Protein PALS2","aliases":["MAGUK p55 subfamily member 6","Membrane protein, palmitoylated 6","Veli-associated MAGUK 1","VAM-1"],"length_aa":540,"mass_kda":61.1,"function":"","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q9NZW5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PALS2","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"NUMA1","stoichiometry":0.2},{"gene":"SRP9","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PALS2","total_profiled":1310},"omim":[{"mim_id":"609743","title":"CELL ADHESION MOLECULE 3; CADM3","url":"https://www.omim.org/entry/609743"},{"mim_id":"606959","title":"PROTEIN ASSOCIATED WITH LIN7 2, MAGUK p55 FAMILY MEMBER; PALS2","url":"https://www.omim.org/entry/606959"},{"mim_id":"606958","title":"PROTEIN ASSOCIATED WITH LIN7 1, MAGUK p55 FAMILY MEMBER; PALS1","url":"https://www.omim.org/entry/606958"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"gallbladder","ntpm":17.9},{"tissue":"testis","ntpm":23.3}],"url":"https://www.proteinatlas.org/search/PALS2"},"hgnc":{"alias_symbol":["VAM-1","p55T"],"prev_symbol":["MPP6"]},"alphafold":{"accession":"Q9NZW5","domains":[{"cath_id":"2.30.42.10","chopping":"128-205","consensus_level":"high","plddt":86.3737,"start":128,"end":205},{"cath_id":"2.30.30.40","chopping":"217-285","consensus_level":"high","plddt":89.8609,"start":217,"end":285},{"cath_id":"3.40.50.300","chopping":"336-534","consensus_level":"medium","plddt":94.7576,"start":336,"end":534}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NZW5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NZW5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NZW5-F1-predicted_aligned_error_v6.png","plddt_mean":83.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PALS2","jax_strain_url":"https://www.jax.org/strain/search?query=PALS2"},"sequence":{"accession":"Q9NZW5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NZW5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NZW5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NZW5"}},"corpus_meta":[{"pmid":"12826663","id":"PMC_12826663","title":"Implications of nectin-like molecule-2/IGSF4/RA175/SgIGSF/TSLC1/SynCAM1 in cell-cell adhesion and transmembrane protein localization in epithelial cells.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12826663","citation_count":180,"is_preprint":false},{"pmid":"15024025","id":"PMC_15024025","title":"Protein trafficking and anchoring complexes revealed by proteomic analysis of inward rectifier potassium channel (Kir2.x)-associated proteins.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15024025","citation_count":172,"is_preprint":false},{"pmid":"10753959","id":"PMC_10753959","title":"Molecular cloning and characterization of Pals, proteins associated with mLin-7.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10753959","citation_count":147,"is_preprint":false},{"pmid":"15741237","id":"PMC_15741237","title":"Nectin-like molecule-1/TSLL1/SynCAM3: a neural tissue-specific immunoglobulin-like cell-cell adhesion molecule localizing at non-junctional contact sites of presynaptic nerve terminals, axons and glia cell processes.","date":"2005","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/15741237","citation_count":110,"is_preprint":false},{"pmid":"14719143","id":"PMC_14719143","title":"Identification and characterization of human MPP7 gene and mouse Mpp7 gene in silico.","date":"2004","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/14719143","citation_count":80,"is_preprint":false},{"pmid":"17267446","id":"PMC_17267446","title":"Drosophila Varicose, a member of a new subgroup of basolateral MAGUKs, is required for septate junctions and tracheal morphogenesis.","date":"2007","source":"Development (Cambridge, 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of mLin-7 (Lin-7) through a conserved mLin-7 binding domain. Site-directed mutagenesis identified conserved residues crucial for mLin-7 binding. PALS2 localizes to the lateral membrane in MDCK cells and represents a new subfamily of MAGUKs allowing for multiple targeting complexes containing mLin-7.\",\n      \"method\": \"Far Western overlay assay, bacterial expression cloning, site-directed mutagenesis, immunofluorescence localization in MDCK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Far Western, mutagenesis, subcellular localization) in a focused mechanistic study of PALS2\",\n      \"pmids\": [\"10753959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"VAM-1 (PALS2) was shown to bind to Veli-1 (human LIN-7 homologue) through a conserved domain, as demonstrated by GST pull-down experiments and blot overlay assays in heterologous transfection systems. The vam-1 gene encodes a 540 amino acid MAGUK with PDZ, SH3, and GUK domains, localizes to chromosome 7p15-21, and is expressed in testis, brain, and kidney.\",\n      \"method\": \"GST pull-down, blot overlay assay, heterologous transfection, FISH chromosomal localization\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal binding assays (GST pulldown + blot overlay) in a single lab\",\n      \"pmids\": [\"11311936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PALS2 was identified as a binding partner of Necl-2 (nectin-like molecule-2/IGSF4/SynCAM1) at the basolateral plasma membrane in epithelial cells. Unlike nectins, Necl-2 did not bind afadin but bound PALS2, a MAGUK family member known to bind Lin-7, suggesting PALS2 involvement in transmembrane protein localization.\",\n      \"method\": \"Protein binding assays (pulldown/interaction assays), immunofluorescence localization in mouse gall bladder epithelium\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct binding assay plus localization data, single lab, supporting mechanistic inference\",\n      \"pmids\": [\"12826663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SAP97 does NOT interact with PALS2, despite interacting with the closely related MAGUKs DLG3 and DLG2. This negative result distinguishes PALS2 from other MAGUK family members in terms of SAP97 complex formation.\",\n      \"method\": \"Co-immunoprecipitation and binding assays in rat brain lysates and MDCK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay with negative result, single lab, reciprocal controls with related MAGUKs\",\n      \"pmids\": [\"12351654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PALS2 was identified as one of eight MAGUK family proteins associated with the Kir2.2 potassium channel C-terminal PDZ binding motif in rat brain, suggesting PALS2 participates in channel trafficking/anchoring protein complexes.\",\n      \"method\": \"Affinity chromatography from rat brain detergent extracts using Kir2.2 C-terminal matrix, multidimensional HPLC-ESI-MS/MS, immunoblotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — proteomics identification in a large-scale screen, single method, no functional follow-up specific to PALS2\",\n      \"pmids\": [\"15024025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The C-terminal cytoplasmic region of Necl-1/TSLL1/SynCAM3 was shown to bind PALS2 (along with Dlg3 and CASK), identifying PALS2 as a binding partner for this neural-tissue-specific cell adhesion molecule at non-junctional contact sites.\",\n      \"method\": \"Binding assays (pulldown/interaction assays) with Necl-1 C-terminal cytoplasmic region\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single binding assay, single lab, no functional validation specific to PALS2\",\n      \"pmids\": [\"15741237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Phylogenetic analysis established that Drosophila Varicose (Vari) defines a new MAGUK subgroup that includes mammalian PALS2. Both Vari and PALS2 are basolateral proteins, and the interaction of Vari with Neurexin IV parallels PALS2 interaction with Necl-2, indicating that PALS2 is part of a conserved basolateral cell-adhesion complex distinct from the polarity complex.\",\n      \"method\": \"Phylogenetic analysis, in vivo localization studies in Drosophila, genetic loss-of-function analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phylogenetic plus functional in vivo evidence in Drosophila ortholog with direct parallel drawn to PALS2; Drosophila ortholog study\",\n      \"pmids\": [\"17267446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PALS2/MPP6 was identified by mass spectrometry-based proteomics as part of a complex with Cadm4, Lin7, and band 4.1G (Epb41l2) at Schmidt-Lanterman incisures (SLIs) in peripheral nerve myelin. This complex was increased in Fa2h-deficient mouse sciatic nerves at 17 months of age.\",\n      \"method\": \"Mass spectrometry-based proteomics of purified myelin from sciatic nerves of Fa2h-/- mice\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative proteomics with subcellular localization context; single study, single method for this complex identification\",\n      \"pmids\": [\"35445918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PALS2 was shown to form a complex with GSDME by co-immunoprecipitation in vascular smooth muscle cells (VSMCs). Knockdown of PALS2 attenuated activated caspase-3 and GSDME fragmentation, placing PALS2 upstream of caspase-3 activation and GSDME cleavage in VSMC apoptosis.\",\n      \"method\": \"Co-immunoprecipitation (protein co-IP), siRNA knockdown with Western blot readout for activated caspase-3 and GSDME fragmentation in VSMCs\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus functional KD with specific molecular readouts, single lab\",\n      \"pmids\": [\"38851795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PALS2/MPP6 was identified as a pan-cone photoreceptor protein absent in rod photoreceptors by quantitative DIA mass spectrometry proteomics of FACS-sorted mouse retinal cells, establishing cone-specific subcellular localization.\",\n      \"method\": \"Fluorescence-activated cell sorting of rod and cone photoreceptors, data-independent acquisition (DIA) mass spectrometry proteomics\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single rigorous proteomics study establishing cell-type-specific localization, no functional follow-up\",\n      \"pmids\": [\"41396450\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PALS2 (also known as VAM-1, p55T, MPP6) is a basolateral MAGUK scaffolding protein that binds Lin-7/Veli family members through a conserved L27-type domain, interacts with cell-adhesion molecules Necl-1 and Necl-2 at the basolateral membrane, participates in Kir2 channel-associated protein complexes in brain, forms a complex with GSDME to regulate caspase-3-dependent apoptosis in vascular smooth muscle cells, and localizes specifically to cone photoreceptors and Schmidt-Lanterman incisures in myelin, where it associates with Cadm4 and Lin7 as part of a membrane skeletal complex.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PALS2 (MPP6/VAM-1/p55T) is a basolateral membrane-associated guanylate kinase (MAGUK) scaffolding protein that nucleates multiprotein complexes linking cell-adhesion molecules to the membrane cytoskeleton [#0, #6]. It was first defined by its ability to bind the amino terminus of the Lin-7/Veli family of adaptor proteins through a conserved Lin-7-binding (L27-type) domain, with site-directed mutagenesis identifying the residues required for this interaction, and it localizes to the lateral membrane of polarized epithelial cells [#0, #1]. PALS2 engages the cytoplasmic tails of nectin-like cell-adhesion molecules Necl-2 (SynCAM1) and Necl-1 (SynCAM3) at non-junctional basolateral contact sites, behaving as a conserved adhesion-complex scaffold distinct from the apical polarity machinery — a role mirrored by its Drosophila ortholog Varicose binding Neurexin IV [#2, #5, #6]. In peripheral nerve myelin it assembles with Cadm4, Lin7, and band 4.1G (Epb41l2) into a membrane-skeletal complex at Schmidt-Lanterman incisures, and it marks cone but not rod photoreceptors [#7, #9]. Beyond scaffolding, PALS2 forms a complex with GSDME in vascular smooth muscle cells and acts upstream of caspase-3 activation and GSDME cleavage during apoptosis [#8]. Its specificity among MAGUKs is underscored by its failure to interact with SAP97 despite SAP97 binding the related MAGUKs DLG2 and DLG3 [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established PALS2 as a distinct MAGUK that selectively recruits the Lin-7 adaptor, defining the molecular basis for a new class of lateral-membrane targeting complexes.\",\n      \"evidence\": \"Far Western overlay, expression cloning, and site-directed mutagenesis with immunofluorescence in MDCK cells\",\n      \"pmids\": [\"10753959\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the Lin-7 interaction not tested\", \"No physiological ligand of the PDZ/SH3/GUK module identified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Confirmed the conserved Lin-7/Veli-binding domain and provided domain architecture and tissue-expression context, generalizing the interaction across species homologues.\",\n      \"evidence\": \"GST pull-down and blot overlay in heterologous transfection, FISH chromosomal mapping\",\n      \"pmids\": [\"11311936\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interaction shown in heterologous systems only\", \"No endogenous complex demonstrated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Connected PALS2 to a transmembrane adhesion molecule by showing it binds Necl-2 at the basolateral membrane, implicating PALS2 in localizing cell-adhesion proteins.\",\n      \"evidence\": \"Protein binding assays plus immunofluorescence in mouse gall bladder epithelium\",\n      \"pmids\": [\"12826663\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect binding to Necl-2 not fully resolved\", \"No loss-of-function test of trafficking role\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined the binding specificity of PALS2 within the MAGUK family by demonstrating it does not associate with SAP97, distinguishing it from DLG2/DLG3.\",\n      \"evidence\": \"Co-immunoprecipitation and binding assays in rat brain lysates and MDCK cells\",\n      \"pmids\": [\"12351654\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result; structural basis of exclusion not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Placed PALS2 among MAGUKs associated with a potassium channel C-terminal motif, raising a possible channel-anchoring role in brain.\",\n      \"evidence\": \"Affinity chromatography on Kir2.2 C-terminal matrix with HPLC-ESI-MS/MS and immunoblotting from rat brain\",\n      \"pmids\": [\"15024025\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Proteomic co-isolation only; no direct PALS2-Kir2.2 interaction or functional follow-up\", \"PALS2-specific contribution not isolated from eight co-purifying MAGUKs\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Extended the adhesion-scaffold role to the nervous system by showing PALS2 binds the neural cell-adhesion molecule Necl-1 at non-junctional contacts.\",\n      \"evidence\": \"Binding assays with the Necl-1 C-terminal cytoplasmic region\",\n      \"pmids\": [\"15741237\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single binding assay without reciprocal or functional validation\", \"Endogenous complex not demonstrated\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Used the Drosophila ortholog Varicose to establish PALS2 as part of a conserved basolateral cell-adhesion complex separable from the apical polarity complex.\",\n      \"evidence\": \"Phylogenetic analysis with in vivo localization and genetic loss-of-function in Drosophila\",\n      \"pmids\": [\"17267446\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional parallel inferred from ortholog rather than mammalian loss-of-function\", \"Mammalian PALS2 phenotype not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a membrane-skeletal complex containing PALS2, Cadm4, Lin7, and band 4.1G at Schmidt-Lanterman incisures of peripheral myelin, anchoring PALS2 in a specific subcellular myelin domain.\",\n      \"evidence\": \"Mass spectrometry proteomics of purified myelin from Fa2h-/- mouse sciatic nerves\",\n      \"pmids\": [\"35445918\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Complex composition from co-purification; direct binding not mapped\", \"Functional role of the complex in myelin maintenance not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a non-scaffolding apoptotic function by showing PALS2 complexes with GSDME and acts upstream of caspase-3 activation and GSDME cleavage in vascular smooth muscle cells.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation and siRNA knockdown with Western readout for activated caspase-3 and GSDME fragmentation in VSMCs\",\n      \"pmids\": [\"38851795\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which PALS2 promotes caspase-3 activation unknown\", \"Single cell type and single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established cell-type-specific expression by identifying PALS2 as a pan-cone, rod-absent photoreceptor protein, suggesting a specialized role in cone photoreceptors.\",\n      \"evidence\": \"FACS-sorted mouse retinal cells with DIA mass spectrometry proteomics\",\n      \"pmids\": [\"41396450\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Localization only; no functional role in cones tested\", \"Binding partners in cones not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PALS2's scaffolding activity mechanistically connects to its apoptotic role with GSDME, and what its function is in cone photoreceptors and myelin incisures, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of PALS2 in its complexes\", \"No mammalian loss-of-function phenotype linking scaffolding to physiology\", \"Mechanism linking PALS2 to caspase-3 activation undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [\n      \"Cadm4-Lin7-band 4.1G membrane-skeletal complex (Schmidt-Lanterman incisures)\"\n    ],\n    \"partners\": [\n      \"LIN7\",\n      \"Necl-2/CADM1\",\n      \"Necl-1/CADM3\",\n      \"CADM4\",\n      \"EPB41L2\",\n      \"GSDME\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}