{"gene":"SPTBN2","run_date":"2026-06-10T07:46:41","timeline":{"discoveries":[{"year":2017,"finding":"A SCA5 L253P missense mutation in the CH2 domain of the β-III-spectrin actin-binding domain (ABD) causes ~1000-fold increase in actin-binding affinity by opening the two CH domains (CH1 and CH2), enabling CH1 to bind actin aided by an N-terminal unstructured region that becomes α-helical upon binding. Truncation of this N-terminal helix eliminates actin binding.","method":"Cryo-EM structure at 6.9 Å of F-actin/ABD complex, co-sedimentation assays, pulsed-EPR measurements, N-terminal truncation mutagenesis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure combined with biochemical co-sedimentation and EPR, plus mutagenesis validation, all in one rigorous study","pmids":["29116080"],"is_preprint":false},{"year":2022,"finding":"The N-terminus of β-III-spectrin is required for high-affinity actin binding and for SCA5 neurotoxicity in vivo. N-terminal truncation eliminates L253P-induced high-affinity actin binding in vitro and rescues neurotoxicity and dendritic arborization defects caused by L253P in Drosophila neurons.","method":"Drosophila pan-neuronal expression rescue assay (loss-of-function lethality rescue and L253P neurotoxicity rescue), in vitro actin-binding assays with N-terminally truncated constructs","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro biochemical assay plus in vivo genetic rescue with multiple genotypes, single lab but orthogonal methods","pmids":["35110634"],"is_preprint":false},{"year":2023,"finding":"Nine additional ABD-localized SCA5 missense mutations (V58M, K61E, T62I, K65E, F160C, D255G, T271I, Y272H, H278R), all positioned at or near the CH1-CH2 interface, are thermally destabilizing and each causes increased actin-binding affinity, establishing increased actin binding as a shared molecular consequence of ABD-localized SCA5 mutations.","method":"Thermal denaturation assays, in vitro actin co-sedimentation/binding assays for nine purified mutant ABD proteins","journal":"Cells","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple mutants tested systematically; single lab but nine independent biochemical replicates across orthogonal assays","pmids":["37626910"],"is_preprint":false},{"year":2025,"finding":"SRD-localized SCA5 mutations R480W and E532_M544del have distinct molecular consequences: E532_M544del partially uncouples complementary spectrin-repeat domains in the α-II/β-III-spectrin dimer and increases β-III-spectrin actin binding, while R480W grossly disrupts the α-II/β-III-spectrin complex and forms large intracellular inclusions containing F-actin and ankyrin-R that localize adjacent to the Golgi. Infantile-onset mutations R437W and R437Q also cause inclusions; adult-onset T472M does not.","method":"In vitro α-II/β-III-spectrin binding assays, actin co-sedimentation assays, cell co-expression imaging for inclusion formation, immunofluorescence for ankyrin-R and Golgi co-localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal biochemical and cell-biological methods in single lab; peer-reviewed publication of prior preprint","pmids":["40484375"],"is_preprint":false},{"year":2014,"finding":"β-III spectrin is essential for the recruitment and maintenance of ankyrin-R at the plasma membrane of Purkinje cell dendrites. A wild-type β-III-spectrin/ankyrin-R complex increases sodium channel levels and activity in cell culture, whereas two SCA5 mutant forms of β-III-spectrin reduce ankyrin-R at the cell membrane and fail to enhance sodium currents.","method":"Cell culture co-expression, membrane fractionation to measure ankyrin-R at plasma membrane, electrophysiological recording of sodium channel currents with wild-type vs. mutant β-III-spectrin","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal functional assays (localization + electrophysiology) with wild-type and two mutants, single lab but orthogonal readouts","pmids":["24603075"],"is_preprint":false},{"year":2016,"finding":"β-III spectrin stabilizes the Purkinje cell glutamate transporter EAAT4 at the plasma membrane; loss of β-III spectrin reduces EAAT4 levels and causes early Purkinje cell hyperexcitability. Progressive subsequent loss of the glial glutamate transporter GLAST, superimposed on EAAT4 deficiency, drives Purkinje cell loss and motor decline, with posterior cerebellar Purkinje cells most vulnerable. GLAST loss is independent of EAAT4 loss.","method":"Genetic epistasis using EAAT4 knockout, GLAST knockout, and double-knockout mice crossed with β-III-/- mice; motor behavior assessment; Purkinje cell morphology and survival quantification","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple single and double knockout crosses, orthogonal behavioral and histological readouts","pmids":["28173092"],"is_preprint":false},{"year":2012,"finding":"Loss of β-III spectrin (SPTBN2 knockout) in mice causes morphological abnormalities in prefrontal cortex neurons and deficits in object recognition, demonstrating a role for β-III spectrin in cortical brain development and cognition beyond the cerebellum.","method":"Mouse β-III spectrin knockout; neuronal morphology analysis of prefrontal cortex; object recognition behavioral testing","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular and behavioral phenotype, but cortical mechanism not further dissected beyond morphology","pmids":["23236289"],"is_preprint":false},{"year":2024,"finding":"SPTBN2 interacts with SLC7A11 through its CH domain and connects SLC7A11 with the motor protein Arp1, facilitating membrane localization of SLC7A11 (the System Xc- cystine/glutamate transporter). This maintains cystine uptake and glutathione synthesis, thereby suppressing ferroptosis in NSCLC cells.","method":"Co-immunoprecipitation of SPTBN2 with SLC7A11 and Arp1, CH-domain deletion mapping, membrane fractionation to assess SLC7A11 localization, ferroptosis assays in vitro and in vivo with SPTBN2 knockdown/inhibition","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP with domain mapping plus functional membrane localization and ferroptosis readouts; single lab with orthogonal methods","pmids":["38241838"],"is_preprint":false},{"year":2026,"finding":"In T cells within the tumor microenvironment, SPTBN2 maintains levels of cell-surface inhibitory proteins such as BTLA; SPTBN2 knockout in CAR T-cells protects them from trogocytosis, increases their memory state, and enhances cytotoxicity. Re-expression of BTLA largely reverses the phenotypes of SPTBN2-deficient CAR T-cells, placing SPTBN2 upstream of BTLA-mediated T cell exhaustion.","method":"SPTBN2 knockout in CAR T-cells; flow cytometry for BTLA and other surface proteins; trogocytosis assays; cytotoxicity and in vivo persistence assays; BTLA re-expression rescue experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with rescue and multiple orthogonal functional readouts; preprint, not yet peer-reviewed","pmids":["41959129"],"is_preprint":true},{"year":2026,"finding":"The SCA5 L253P knock-in mouse shows β-III-spectrin redistribution in Purkinje neurons: loss from distal dendrites, accumulation at soma/proximal dendrite plasma membrane, and formation of somatic inclusions containing F-actin and α-II-spectrin. CaMKII is ~2-fold activated and EAAT4 abundance is significantly reduced, linking aberrant actin binding to disruption of postsynaptic glutamate signaling.","method":"CRISPR knock-in mouse; immunofluorescence of β-III-spectrin subcellular distribution; elevated beam motor assay; unbiased proteomics of β-III-spectrin-associated proteins; CaMKII phosphorylation western blot; EAAT4 quantification","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR knock-in with multiple orthogonal readouts (imaging, proteomics, biochemistry, behavior); preprint, not yet peer-reviewed","pmids":["41890131"],"is_preprint":true},{"year":2025,"finding":"β-III-/- (SPTBN2 knockout) mice show enhanced auto-phosphorylation of CaMKII and phosphorylation of CaMKII targets, indicating dysregulated calcium homeostasis. Mibefradil (a calcium channel inhibitor) improves disordered Purkinje cell dendritic morphology in vitro, and trimethadione (a selective T-type calcium channel inhibitor) significantly improves interlimb coordination in 8-month-old β-III-/- mice in vivo.","method":"Western blot for CaMKII phosphorylation in β-III-/- mice; in vitro Purkinje cell culture with mibefradil treatment; CatWalk XT automated gait analysis of β-III-/- mice treated with trimethadione, riluzole, or verapamil","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse model with biochemical and in vivo pharmacological rescue, single lab, orthogonal methods","pmids":["40594196"],"is_preprint":false},{"year":2023,"finding":"m7G methylation of Sptbn2 mRNA by the Mettl1/Wdr4 methyltransferase complex enhances Sptbn2 mRNA stability and translation efficiency, promoting neurogenesis of neural stem cells. Silencing Mettl1 reduces SPTBN2 protein levels and impairs neuronal differentiation, while Mettl1 overexpression rescues neurogenesis in an AD mouse model.","method":"m7G methylation profiling, RNA stability assay, polysome profiling for translation efficiency, Mettl1 knockdown and overexpression in neural stem cells, in vivo hippocampal neurogenesis quantification","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (stability, polysome, in vivo) in single lab establishing SPTBN2 mRNA as Mettl1/m7G target","pmids":["37779199"],"is_preprint":false}],"current_model":"β-III-spectrin (SPTBN2) is a cytoskeletal scaffolding protein that uses its N-terminal actin-binding domain (composed of CH1 and CH2 subdomains plus an essential N-terminal helix) to bind F-actin, its spectrin-repeat domains to heterodimerize with α-II-spectrin, and its ankyrin-binding region to recruit ankyrin-R to Purkinje cell dendritic membranes, where the resulting complex stabilizes glutamate transporters (EAAT4) and sodium channels; SCA5 mutations in the ABD cause pathological high-affinity actin binding by opening the CH1-CH2 interface, while SRD-localized mutations disrupt the α-II/β-III-spectrin dimer and in severe cases drive formation of intracellular inclusions, collectively leading to Purkinje cell dysfunction, glutamate excitotoxicity via EAAT4 loss, and dysregulated calcium/CaMKII signaling."},"narrative":{"mechanistic_narrative":"β-III-spectrin (SPTBN2) is a cytoskeletal scaffolding protein that links the cortical actin network to specialized membrane proteins, a role most fully characterized in cerebellar Purkinje cells where it controls neuronal excitability and survival [PMID:28173092, PMID:24603075]. Its N-terminal actin-binding domain (ABD), composed of CH1 and CH2 subdomains plus an N-terminal unstructured region that becomes α-helical upon binding, engages F-actin; truncation of this N-terminal helix abolishes actin binding [PMID:29116080]. Through its spectrin-repeat domains it heterodimerizes with α-II-spectrin, and through an ankyrin-binding region it recruits and maintains ankyrin-R at the dendritic plasma membrane, where the complex elevates sodium channel levels and activity and stabilizes the glutamate transporter EAAT4 [PMID:24603075, PMID:28173092]. Loss of β-III-spectrin destabilizes EAAT4, producing early Purkinje cell hyperexcitability that—compounded by progressive, independent loss of the glial transporter GLAST—drives Purkinje cell death and motor decline, and is accompanied by enhanced CaMKII autophosphorylation indicative of dysregulated calcium signaling [PMID:28173092, PMID:40594196]. SPTBN2 mutations cause spinocerebellar ataxia type 5 (SCA5): ABD-localized mutations such as L253P and a panel of interface mutations are thermally destabilizing and open the CH1-CH2 interface to confer pathological high-affinity actin binding, which is N-terminus–dependent and neurotoxic in vivo, whereas spectrin-repeat-domain mutations either partially uncouple or grossly disrupt the α-II/β-III-spectrin dimer, in severe and infantile-onset cases forming F-actin– and ankyrin-R–containing intracellular inclusions near the Golgi [PMID:29116080, PMID:35110634, PMID:37626910, PMID:40484375, PMID:41890131]. Beyond the cerebellum, β-III-spectrin contributes to cortical neuron morphology and cognition [PMID:23236289], and acts as a membrane scaffold in non-neuronal contexts, connecting the cystine/glutamate transporter SLC7A11 to the motor protein Arp1 to suppress ferroptosis [PMID:38241838] and maintaining surface inhibitory receptors such as BTLA in T cells [PMID:41959129].","teleology":[{"year":2012,"claim":"Established that β-III-spectrin function extends beyond the cerebellum to cortical neuron architecture and cognition, broadening the disease-relevant role of the protein.","evidence":"SPTBN2 knockout mouse with prefrontal cortex neuronal morphology analysis and object recognition testing","pmids":["23236289"],"confidence":"Medium","gaps":["Molecular mechanism in cortex not dissected beyond morphology","No identified membrane partners in cortical neurons"]},{"year":2014,"claim":"Answered how β-III-spectrin organizes the membrane, showing it recruits and maintains ankyrin-R at Purkinje dendrites to support sodium channel function.","evidence":"Cell culture co-expression, membrane fractionation, and sodium-current electrophysiology comparing wild-type and SCA5 mutant β-III-spectrin","pmids":["24603075"],"confidence":"High","gaps":["Direct structural basis of ankyrin-R binding not resolved","Sodium channel identity not specified"]},{"year":2016,"claim":"Defined the pathogenic cascade downstream of β-III-spectrin loss, distinguishing EAAT4 destabilization (early hyperexcitability) from independent GLAST loss (cell death).","evidence":"Genetic epistasis with EAAT4, GLAST, and double knockouts crossed to β-III-/- mice, with behavioral and histological readouts","pmids":["28173092"],"confidence":"High","gaps":["Mechanism causing GLAST loss unknown","How EAAT4 deficiency triggers progressive degeneration not fully resolved"]},{"year":2017,"claim":"Resolved the structural mechanism of the SCA5 L253P mutation, showing it opens the CH1-CH2 interface to confer ~1000-fold higher actin affinity dependent on an N-terminal helix.","evidence":"Cryo-EM of the F-actin/ABD complex, co-sedimentation, pulsed-EPR, and N-terminal truncation mutagenesis","pmids":["29116080"],"confidence":"High","gaps":["Cellular consequence of high-affinity binding not addressed in this study","Structure at modest 6.9 Å resolution"]},{"year":2022,"claim":"Linked the in vitro high-affinity actin-binding defect to disease, showing the N-terminus is required for L253P neurotoxicity in vivo.","evidence":"Drosophila pan-neuronal rescue assays with N-terminally truncated constructs plus in vitro actin binding","pmids":["35110634"],"confidence":"High","gaps":["Drosophila model may not capture Purkinje-cell-specific pathology","Downstream effectors of toxicity not identified"]},{"year":2023,"claim":"Generalized the gain-of-function model by showing nine additional ABD SCA5 mutations are destabilizing and increase actin binding, establishing a shared molecular consequence.","evidence":"Thermal denaturation and actin co-sedimentation assays on nine purified mutant ABD proteins","pmids":["37626910"],"confidence":"High","gaps":["In vivo validation of individual mutants not performed","Quantitative link between destabilization magnitude and disease severity unestablished"]},{"year":2023,"claim":"Identified SPTBN2 mRNA as a regulatory target, showing Mettl1/Wdr4 m7G methylation stabilizes the transcript and boosts translation to drive neurogenesis.","evidence":"m7G profiling, RNA stability and polysome assays, Mettl1 knockdown/overexpression in neural stem cells and an AD mouse model","pmids":["37779199"],"confidence":"Medium","gaps":["Whether m7G regulation operates in adult Purkinje cells unknown","Direct contribution of SPTBN2 to the neurogenesis phenotype vs. other Mettl1 targets unresolved"]},{"year":2024,"claim":"Extended the scaffolding role to non-neuronal membranes, showing SPTBN2 connects SLC7A11 to Arp1 to maintain cystine uptake and suppress ferroptosis in cancer cells.","evidence":"Co-IP with CH-domain deletion mapping, membrane fractionation, and ferroptosis assays in NSCLC cells in vitro and in vivo","pmids":["38241838"],"confidence":"Medium","gaps":["Single-lab Co-IP without reciprocal structural validation","Whether the same SLC7A11/Arp1 axis operates in neurons not tested"]},{"year":2025,"claim":"Distinguished molecular consequences of spectrin-repeat-domain SCA5 mutations, separating dimer uncoupling from gross complex disruption and inclusion formation.","evidence":"In vitro α-II/β-III-spectrin and actin binding assays plus cell co-expression imaging for inclusions and Golgi co-localization","pmids":["40484375"],"confidence":"High","gaps":["Inclusion toxicity in neurons not demonstrated in vivo","Why infantile-onset mutations form inclusions while adult-onset T472M does not is mechanistically unexplained"]},{"year":2025,"claim":"Implicated dysregulated calcium signaling in pathology, showing CaMKII hyperactivation in β-III-/- mice and pharmacological rescue with T-type calcium channel inhibitors.","evidence":"CaMKII phosphorylation western blots, in vitro Purkinje cell culture with mibefradil, and gait analysis of trimethadione-treated β-III-/- mice","pmids":["40594196"],"confidence":"Medium","gaps":["Causal link between scaffold loss and calcium dysregulation not mechanistically defined","Pharmacological benefit assessed in a single age cohort"]},{"year":2026,"claim":"Connected the structural actin-binding defect to physiological dysfunction in a faithful disease model, showing L253P drives β-III-spectrin redistribution, inclusions, CaMKII activation, and EAAT4 loss.","evidence":"CRISPR L253P knock-in mouse with immunofluorescence, proteomics, CaMKII western blot, EAAT4 quantification, and motor testing (preprint)","pmids":["41890131"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Causal ordering of redistribution, inclusions, and EAAT4 loss not established"]},{"year":2026,"claim":"Revealed an immune-cell function, placing SPTBN2 upstream of BTLA-mediated T cell exhaustion by maintaining surface inhibitory receptors.","evidence":"SPTBN2 knockout in CAR T-cells with trogocytosis, cytotoxicity, persistence assays, and BTLA re-expression rescue (preprint)","pmids":["41959129"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Whether BTLA is a direct physical partner not established"]},{"year":null,"claim":"How aberrant β-III-spectrin actin binding mechanistically couples to calcium/CaMKII dysregulation and progressive transporter loss, and whether its non-neuronal scaffolding functions share the same molecular logic, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mechanistic chain linking actin-binding gain-of-function to CaMKII activation","GLAST loss mechanism unknown","Unifying model across neuronal and non-neuronal scaffolding contexts absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,5,7]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[4,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,5,7]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,9]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[3]}],"pathway":[],"complexes":["α-II/β-III-spectrin heterodimer"],"partners":["SPTAN1","ANK1","SLC1A6","SLC7A11","ACTR1A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15020","full_name":"Spectrin beta chain, non-erythrocytic 2","aliases":["Beta-III spectrin","Spinocerebellar ataxia 5 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SCA20","url":"https://www.omim.org/entry/608687"},{"mim_id":"605708","title":"RHO GUANINE NUCLEOTIDE EXCHANGE FACTOR 11; ARHGEF11","url":"https://www.omim.org/entry/605708"},{"mim_id":"604985","title":"SPECTRIN, BETA, NONERYTHROCYTIC, 2; SPTBN2","url":"https://www.omim.org/entry/604985"},{"mim_id":"602367","title":"NEURONAL PENTRAXIN 1; NPTX1","url":"https://www.omim.org/entry/602367"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":58.7},{"tissue":"skin 1","ntpm":59.9}],"url":"https://www.proteinatlas.org/search/SPTBN2"},"hgnc":{"alias_symbol":[],"prev_symbol":["SCA5"]},"alphafold":{"accession":"O15020","domains":[{"cath_id":"1.10.418.10","chopping":"64-287","consensus_level":"medium","plddt":81.1501,"start":64,"end":287},{"cath_id":"1.20.58.60","chopping":"298-419","consensus_level":"high","plddt":84.703,"start":298,"end":419},{"cath_id":"1.20.58.60","chopping":"879-982_1003-1031","consensus_level":"medium","plddt":80.8276,"start":879,"end":1031},{"cath_id":"1.20.58.60","chopping":"1205-1239_1248-1377","consensus_level":"medium","plddt":80.0658,"start":1205,"end":1377},{"cath_id":"1.20.58.60","chopping":"2014-2038_2046-2092","consensus_level":"medium","plddt":69.05,"start":2014,"end":2092},{"cath_id":"2.30.29.30","chopping":"2222-2331","consensus_level":"medium","plddt":80.155,"start":2222,"end":2331}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15020","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15020-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15020-F1-predicted_aligned_error_v6.png","plddt_mean":76.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPTBN2","jax_strain_url":"https://www.jax.org/strain/search?query=SPTBN2"},"sequence":{"accession":"O15020","fasta_url":"https://rest.uniprot.org/uniprotkb/O15020.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15020/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15020"}},"corpus_meta":[{"pmid":"23236289","id":"PMC_23236289","title":"Recessive 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Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/33572947","citation_count":15,"is_preprint":false},{"pmid":"35146902","id":"PMC_35146902","title":"CERS6-AS1 contributes to the malignant phenotypes of colorectal cancer cells by interacting with miR-15b-5p to regulate SPTBN2.","date":"2022","source":"The Kaohsiung journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35146902","citation_count":15,"is_preprint":false},{"pmid":"33756041","id":"PMC_33756041","title":"Novel SPTBN2 gene mutation and first intragenic deletion in early onset spinocerebellar ataxia type 5.","date":"2021","source":"Annals of clinical and translational neurology","url":"https://pubmed.ncbi.nlm.nih.gov/33756041","citation_count":15,"is_preprint":false},{"pmid":"30898343","id":"PMC_30898343","title":"Infantile-onset spinocerebellar ataxia type 5 associated with a novel SPTBN2 mutation: A case report.","date":"2019","source":"Brain & 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England)","url":"https://pubmed.ncbi.nlm.nih.gov/31721007","citation_count":11,"is_preprint":false},{"pmid":"9921902","id":"PMC_9921902","title":"A transcript map of an 800-kb region on human chromosome 11q13, part of the candidate region for SCA5 and BBS1.","date":"1998","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9921902","citation_count":9,"is_preprint":false},{"pmid":"37206547","id":"PMC_37206547","title":"SPTBN2 regulates endometroid ovarian cancer cell proliferation, invasion and migration via ITGB4‑mediated focal adhesion and ECM receptor signalling pathway.","date":"2023","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37206547","citation_count":7,"is_preprint":false},{"pmid":"35110634","id":"PMC_35110634","title":"β-III-spectrin N-terminus is required for high-affinity actin binding and SCA5 neurotoxicity.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/35110634","citation_count":7,"is_preprint":false},{"pmid":"17940722","id":"PMC_17940722","title":"Screening of the SPTBN2 (SCA5) gene in German SCA patients.","date":"2007","source":"Journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/17940722","citation_count":6,"is_preprint":false},{"pmid":"33318253","id":"PMC_33318253","title":"A novel case of congenital spinocerebellar ataxia 5: further support for a specific phenotype associated with the p.(Arg480Trp) variant in SPTBN2.","date":"2020","source":"BMJ case reports","url":"https://pubmed.ncbi.nlm.nih.gov/33318253","citation_count":6,"is_preprint":false},{"pmid":"35968508","id":"PMC_35968508","title":"SPTBN2 Promotes the Progression of Thyroid Cancer by Accelerating G1/S Transition and Inhibiting Apoptosis.","date":"2022","source":"Disease markers","url":"https://pubmed.ncbi.nlm.nih.gov/35968508","citation_count":5,"is_preprint":false},{"pmid":"38279463","id":"PMC_38279463","title":"SPTBN2 regulated by miR-214-3p inhibits the proliferation and migration of colorectal cancer cells.","date":"2023","source":"Cellular and molecular biology (Noisy-le-Grand, France)","url":"https://pubmed.ncbi.nlm.nih.gov/38279463","citation_count":4,"is_preprint":false},{"pmid":"38684762","id":"PMC_38684762","title":"Multi-omics pan-cancer study of SPTBN2 and its value as a potential therapeutic target in pancreatic cancer.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/38684762","citation_count":3,"is_preprint":false},{"pmid":"37626910","id":"PMC_37626910","title":"Increased Actin Binding Is a Shared Molecular Consequence of Numerous SCA5 Mutations in 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/39345584","citation_count":0,"is_preprint":false},{"pmid":"41587409","id":"PMC_41587409","title":"LncRNA HOXB-AS1 Accelerates Epithelial Ovarian Cancer Progression by Modulating the miR-671-5p/SPTBN2 Axis.","date":"2026","source":"Journal of biochemical and molecular toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/41587409","citation_count":0,"is_preprint":false},{"pmid":"42238893","id":"PMC_42238893","title":"Integrated multi-omics characterization of SPTBN2 overexpression reveals its pro-tumorigenic role and immune microenvironment remodeling in colorectal cancer.","date":"2026","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/42238893","citation_count":0,"is_preprint":false},{"pmid":"41890131","id":"PMC_41890131","title":"Impaired motor activity in a CRISPR SCA5 L253P knock-in mouse is associated with selective β-III-spectrin subcellular redistribution in the cerebellum.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41890131","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.09.23.24313872","title":"Heterozygous loss-of-function variants in SPTAN1 cause a novel early childhood onset distal myopathy with chronic neurogenic features","date":"2024-09-24","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.23.24313872","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":23728,"output_tokens":3500,"usd":0.061842,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11241,"output_tokens":4136,"usd":0.079802,"stage2_stop_reason":"end_turn"},"total_usd":0.141644,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"A SCA5 L253P missense mutation in the CH2 domain of the β-III-spectrin actin-binding domain (ABD) causes ~1000-fold increase in actin-binding affinity by opening the two CH domains (CH1 and CH2), enabling CH1 to bind actin aided by an N-terminal unstructured region that becomes α-helical upon binding. Truncation of this N-terminal helix eliminates actin binding.\",\n      \"method\": \"Cryo-EM structure at 6.9 Å of F-actin/ABD complex, co-sedimentation assays, pulsed-EPR measurements, N-terminal truncation mutagenesis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure combined with biochemical co-sedimentation and EPR, plus mutagenesis validation, all in one rigorous study\",\n      \"pmids\": [\"29116080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The N-terminus of β-III-spectrin is required for high-affinity actin binding and for SCA5 neurotoxicity in vivo. N-terminal truncation eliminates L253P-induced high-affinity actin binding in vitro and rescues neurotoxicity and dendritic arborization defects caused by L253P in Drosophila neurons.\",\n      \"method\": \"Drosophila pan-neuronal expression rescue assay (loss-of-function lethality rescue and L253P neurotoxicity rescue), in vitro actin-binding assays with N-terminally truncated constructs\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro biochemical assay plus in vivo genetic rescue with multiple genotypes, single lab but orthogonal methods\",\n      \"pmids\": [\"35110634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Nine additional ABD-localized SCA5 missense mutations (V58M, K61E, T62I, K65E, F160C, D255G, T271I, Y272H, H278R), all positioned at or near the CH1-CH2 interface, are thermally destabilizing and each causes increased actin-binding affinity, establishing increased actin binding as a shared molecular consequence of ABD-localized SCA5 mutations.\",\n      \"method\": \"Thermal denaturation assays, in vitro actin co-sedimentation/binding assays for nine purified mutant ABD proteins\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple mutants tested systematically; single lab but nine independent biochemical replicates across orthogonal assays\",\n      \"pmids\": [\"37626910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SRD-localized SCA5 mutations R480W and E532_M544del have distinct molecular consequences: E532_M544del partially uncouples complementary spectrin-repeat domains in the α-II/β-III-spectrin dimer and increases β-III-spectrin actin binding, while R480W grossly disrupts the α-II/β-III-spectrin complex and forms large intracellular inclusions containing F-actin and ankyrin-R that localize adjacent to the Golgi. Infantile-onset mutations R437W and R437Q also cause inclusions; adult-onset T472M does not.\",\n      \"method\": \"In vitro α-II/β-III-spectrin binding assays, actin co-sedimentation assays, cell co-expression imaging for inclusion formation, immunofluorescence for ankyrin-R and Golgi co-localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal biochemical and cell-biological methods in single lab; peer-reviewed publication of prior preprint\",\n      \"pmids\": [\"40484375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"β-III spectrin is essential for the recruitment and maintenance of ankyrin-R at the plasma membrane of Purkinje cell dendrites. A wild-type β-III-spectrin/ankyrin-R complex increases sodium channel levels and activity in cell culture, whereas two SCA5 mutant forms of β-III-spectrin reduce ankyrin-R at the cell membrane and fail to enhance sodium currents.\",\n      \"method\": \"Cell culture co-expression, membrane fractionation to measure ankyrin-R at plasma membrane, electrophysiological recording of sodium channel currents with wild-type vs. mutant β-III-spectrin\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal functional assays (localization + electrophysiology) with wild-type and two mutants, single lab but orthogonal readouts\",\n      \"pmids\": [\"24603075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"β-III spectrin stabilizes the Purkinje cell glutamate transporter EAAT4 at the plasma membrane; loss of β-III spectrin reduces EAAT4 levels and causes early Purkinje cell hyperexcitability. Progressive subsequent loss of the glial glutamate transporter GLAST, superimposed on EAAT4 deficiency, drives Purkinje cell loss and motor decline, with posterior cerebellar Purkinje cells most vulnerable. GLAST loss is independent of EAAT4 loss.\",\n      \"method\": \"Genetic epistasis using EAAT4 knockout, GLAST knockout, and double-knockout mice crossed with β-III-/- mice; motor behavior assessment; Purkinje cell morphology and survival quantification\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple single and double knockout crosses, orthogonal behavioral and histological readouts\",\n      \"pmids\": [\"28173092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Loss of β-III spectrin (SPTBN2 knockout) in mice causes morphological abnormalities in prefrontal cortex neurons and deficits in object recognition, demonstrating a role for β-III spectrin in cortical brain development and cognition beyond the cerebellum.\",\n      \"method\": \"Mouse β-III spectrin knockout; neuronal morphology analysis of prefrontal cortex; object recognition behavioral testing\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular and behavioral phenotype, but cortical mechanism not further dissected beyond morphology\",\n      \"pmids\": [\"23236289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPTBN2 interacts with SLC7A11 through its CH domain and connects SLC7A11 with the motor protein Arp1, facilitating membrane localization of SLC7A11 (the System Xc- cystine/glutamate transporter). This maintains cystine uptake and glutathione synthesis, thereby suppressing ferroptosis in NSCLC cells.\",\n      \"method\": \"Co-immunoprecipitation of SPTBN2 with SLC7A11 and Arp1, CH-domain deletion mapping, membrane fractionation to assess SLC7A11 localization, ferroptosis assays in vitro and in vivo with SPTBN2 knockdown/inhibition\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP with domain mapping plus functional membrane localization and ferroptosis readouts; single lab with orthogonal methods\",\n      \"pmids\": [\"38241838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In T cells within the tumor microenvironment, SPTBN2 maintains levels of cell-surface inhibitory proteins such as BTLA; SPTBN2 knockout in CAR T-cells protects them from trogocytosis, increases their memory state, and enhances cytotoxicity. Re-expression of BTLA largely reverses the phenotypes of SPTBN2-deficient CAR T-cells, placing SPTBN2 upstream of BTLA-mediated T cell exhaustion.\",\n      \"method\": \"SPTBN2 knockout in CAR T-cells; flow cytometry for BTLA and other surface proteins; trogocytosis assays; cytotoxicity and in vivo persistence assays; BTLA re-expression rescue experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with rescue and multiple orthogonal functional readouts; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"41959129\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The SCA5 L253P knock-in mouse shows β-III-spectrin redistribution in Purkinje neurons: loss from distal dendrites, accumulation at soma/proximal dendrite plasma membrane, and formation of somatic inclusions containing F-actin and α-II-spectrin. CaMKII is ~2-fold activated and EAAT4 abundance is significantly reduced, linking aberrant actin binding to disruption of postsynaptic glutamate signaling.\",\n      \"method\": \"CRISPR knock-in mouse; immunofluorescence of β-III-spectrin subcellular distribution; elevated beam motor assay; unbiased proteomics of β-III-spectrin-associated proteins; CaMKII phosphorylation western blot; EAAT4 quantification\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR knock-in with multiple orthogonal readouts (imaging, proteomics, biochemistry, behavior); preprint, not yet peer-reviewed\",\n      \"pmids\": [\"41890131\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"β-III-/- (SPTBN2 knockout) mice show enhanced auto-phosphorylation of CaMKII and phosphorylation of CaMKII targets, indicating dysregulated calcium homeostasis. Mibefradil (a calcium channel inhibitor) improves disordered Purkinje cell dendritic morphology in vitro, and trimethadione (a selective T-type calcium channel inhibitor) significantly improves interlimb coordination in 8-month-old β-III-/- mice in vivo.\",\n      \"method\": \"Western blot for CaMKII phosphorylation in β-III-/- mice; in vitro Purkinje cell culture with mibefradil treatment; CatWalk XT automated gait analysis of β-III-/- mice treated with trimethadione, riluzole, or verapamil\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse model with biochemical and in vivo pharmacological rescue, single lab, orthogonal methods\",\n      \"pmids\": [\"40594196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"m7G methylation of Sptbn2 mRNA by the Mettl1/Wdr4 methyltransferase complex enhances Sptbn2 mRNA stability and translation efficiency, promoting neurogenesis of neural stem cells. Silencing Mettl1 reduces SPTBN2 protein levels and impairs neuronal differentiation, while Mettl1 overexpression rescues neurogenesis in an AD mouse model.\",\n      \"method\": \"m7G methylation profiling, RNA stability assay, polysome profiling for translation efficiency, Mettl1 knockdown and overexpression in neural stem cells, in vivo hippocampal neurogenesis quantification\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (stability, polysome, in vivo) in single lab establishing SPTBN2 mRNA as Mettl1/m7G target\",\n      \"pmids\": [\"37779199\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"β-III-spectrin (SPTBN2) is a cytoskeletal scaffolding protein that uses its N-terminal actin-binding domain (composed of CH1 and CH2 subdomains plus an essential N-terminal helix) to bind F-actin, its spectrin-repeat domains to heterodimerize with α-II-spectrin, and its ankyrin-binding region to recruit ankyrin-R to Purkinje cell dendritic membranes, where the resulting complex stabilizes glutamate transporters (EAAT4) and sodium channels; SCA5 mutations in the ABD cause pathological high-affinity actin binding by opening the CH1-CH2 interface, while SRD-localized mutations disrupt the α-II/β-III-spectrin dimer and in severe cases drive formation of intracellular inclusions, collectively leading to Purkinje cell dysfunction, glutamate excitotoxicity via EAAT4 loss, and dysregulated calcium/CaMKII signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"β-III-spectrin (SPTBN2) is a cytoskeletal scaffolding protein that links the cortical actin network to specialized membrane proteins, a role most fully characterized in cerebellar Purkinje cells where it controls neuronal excitability and survival [#5, #4]. Its N-terminal actin-binding domain (ABD), composed of CH1 and CH2 subdomains plus an N-terminal unstructured region that becomes α-helical upon binding, engages F-actin; truncation of this N-terminal helix abolishes actin binding [#0]. Through its spectrin-repeat domains it heterodimerizes with α-II-spectrin, and through an ankyrin-binding region it recruits and maintains ankyrin-R at the dendritic plasma membrane, where the complex elevates sodium channel levels and activity and stabilizes the glutamate transporter EAAT4 [#4, #5]. Loss of β-III-spectrin destabilizes EAAT4, producing early Purkinje cell hyperexcitability that—compounded by progressive, independent loss of the glial transporter GLAST—drives Purkinje cell death and motor decline, and is accompanied by enhanced CaMKII autophosphorylation indicative of dysregulated calcium signaling [#5, #10]. SPTBN2 mutations cause spinocerebellar ataxia type 5 (SCA5): ABD-localized mutations such as L253P and a panel of interface mutations are thermally destabilizing and open the CH1-CH2 interface to confer pathological high-affinity actin binding, which is N-terminus–dependent and neurotoxic in vivo, whereas spectrin-repeat-domain mutations either partially uncouple or grossly disrupt the α-II/β-III-spectrin dimer, in severe and infantile-onset cases forming F-actin– and ankyrin-R–containing intracellular inclusions near the Golgi [#0, #1, #2, #3, #9]. Beyond the cerebellum, β-III-spectrin contributes to cortical neuron morphology and cognition [#6], and acts as a membrane scaffold in non-neuronal contexts, connecting the cystine/glutamate transporter SLC7A11 to the motor protein Arp1 to suppress ferroptosis [#7] and maintaining surface inhibitory receptors such as BTLA in T cells [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established that β-III-spectrin function extends beyond the cerebellum to cortical neuron architecture and cognition, broadening the disease-relevant role of the protein.\",\n      \"evidence\": \"SPTBN2 knockout mouse with prefrontal cortex neuronal morphology analysis and object recognition testing\",\n      \"pmids\": [\"23236289\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism in cortex not dissected beyond morphology\", \"No identified membrane partners in cortical neurons\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Answered how β-III-spectrin organizes the membrane, showing it recruits and maintains ankyrin-R at Purkinje dendrites to support sodium channel function.\",\n      \"evidence\": \"Cell culture co-expression, membrane fractionation, and sodium-current electrophysiology comparing wild-type and SCA5 mutant β-III-spectrin\",\n      \"pmids\": [\"24603075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural basis of ankyrin-R binding not resolved\", \"Sodium channel identity not specified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined the pathogenic cascade downstream of β-III-spectrin loss, distinguishing EAAT4 destabilization (early hyperexcitability) from independent GLAST loss (cell death).\",\n      \"evidence\": \"Genetic epistasis with EAAT4, GLAST, and double knockouts crossed to β-III-/- mice, with behavioral and histological readouts\",\n      \"pmids\": [\"28173092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism causing GLAST loss unknown\", \"How EAAT4 deficiency triggers progressive degeneration not fully resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Resolved the structural mechanism of the SCA5 L253P mutation, showing it opens the CH1-CH2 interface to confer ~1000-fold higher actin affinity dependent on an N-terminal helix.\",\n      \"evidence\": \"Cryo-EM of the F-actin/ABD complex, co-sedimentation, pulsed-EPR, and N-terminal truncation mutagenesis\",\n      \"pmids\": [\"29116080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular consequence of high-affinity binding not addressed in this study\", \"Structure at modest 6.9 Å resolution\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked the in vitro high-affinity actin-binding defect to disease, showing the N-terminus is required for L253P neurotoxicity in vivo.\",\n      \"evidence\": \"Drosophila pan-neuronal rescue assays with N-terminally truncated constructs plus in vitro actin binding\",\n      \"pmids\": [\"35110634\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Drosophila model may not capture Purkinje-cell-specific pathology\", \"Downstream effectors of toxicity not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Generalized the gain-of-function model by showing nine additional ABD SCA5 mutations are destabilizing and increase actin binding, establishing a shared molecular consequence.\",\n      \"evidence\": \"Thermal denaturation and actin co-sedimentation assays on nine purified mutant ABD proteins\",\n      \"pmids\": [\"37626910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo validation of individual mutants not performed\", \"Quantitative link between destabilization magnitude and disease severity unestablished\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified SPTBN2 mRNA as a regulatory target, showing Mettl1/Wdr4 m7G methylation stabilizes the transcript and boosts translation to drive neurogenesis.\",\n      \"evidence\": \"m7G profiling, RNA stability and polysome assays, Mettl1 knockdown/overexpression in neural stem cells and an AD mouse model\",\n      \"pmids\": [\"37779199\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether m7G regulation operates in adult Purkinje cells unknown\", \"Direct contribution of SPTBN2 to the neurogenesis phenotype vs. other Mettl1 targets unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended the scaffolding role to non-neuronal membranes, showing SPTBN2 connects SLC7A11 to Arp1 to maintain cystine uptake and suppress ferroptosis in cancer cells.\",\n      \"evidence\": \"Co-IP with CH-domain deletion mapping, membrane fractionation, and ferroptosis assays in NSCLC cells in vitro and in vivo\",\n      \"pmids\": [\"38241838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab Co-IP without reciprocal structural validation\", \"Whether the same SLC7A11/Arp1 axis operates in neurons not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Distinguished molecular consequences of spectrin-repeat-domain SCA5 mutations, separating dimer uncoupling from gross complex disruption and inclusion formation.\",\n      \"evidence\": \"In vitro α-II/β-III-spectrin and actin binding assays plus cell co-expression imaging for inclusions and Golgi co-localization\",\n      \"pmids\": [\"40484375\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Inclusion toxicity in neurons not demonstrated in vivo\", \"Why infantile-onset mutations form inclusions while adult-onset T472M does not is mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated dysregulated calcium signaling in pathology, showing CaMKII hyperactivation in β-III-/- mice and pharmacological rescue with T-type calcium channel inhibitors.\",\n      \"evidence\": \"CaMKII phosphorylation western blots, in vitro Purkinje cell culture with mibefradil, and gait analysis of trimethadione-treated β-III-/- mice\",\n      \"pmids\": [\"40594196\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal link between scaffold loss and calcium dysregulation not mechanistically defined\", \"Pharmacological benefit assessed in a single age cohort\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Connected the structural actin-binding defect to physiological dysfunction in a faithful disease model, showing L253P drives β-III-spectrin redistribution, inclusions, CaMKII activation, and EAAT4 loss.\",\n      \"evidence\": \"CRISPR L253P knock-in mouse with immunofluorescence, proteomics, CaMKII western blot, EAAT4 quantification, and motor testing (preprint)\",\n      \"pmids\": [\"41890131\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Causal ordering of redistribution, inclusions, and EAAT4 loss not established\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealed an immune-cell function, placing SPTBN2 upstream of BTLA-mediated T cell exhaustion by maintaining surface inhibitory receptors.\",\n      \"evidence\": \"SPTBN2 knockout in CAR T-cells with trogocytosis, cytotoxicity, persistence assays, and BTLA re-expression rescue (preprint)\",\n      \"pmids\": [\"41959129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Whether BTLA is a direct physical partner not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How aberrant β-III-spectrin actin binding mechanistically couples to calcium/CaMKII dysregulation and progressive transporter loss, and whether its non-neuronal scaffolding functions share the same molecular logic, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mechanistic chain linking actin-binding gain-of-function to CaMKII activation\", \"GLAST loss mechanism unknown\", \"Unifying model across neuronal and non-neuronal scaffolding contexts absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 5, 7]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [4, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 5, 7]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0112316\", \"supporting_discovery_ids\": []}\n    ],\n    \"complexes\": [\"α-II/β-III-spectrin heterodimer\"],\n    \"partners\": [\"SPTAN1\", \"ANK1\", \"SLC1A6\", \"SLC7A11\", \"ACTR1A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}