{"gene":"CAPN1","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1981,"finding":"Limited autolysis of Ca2+-activated neutral protease (CANP/CAPN1) in the presence of Ca2+ converts the mM-Ca2+-requiring form (m-CANP) to a µM-Ca2+-requiring form (µ-CANP), demonstrating that autoproteolysis of the large subunit lowers Ca2+ sensitivity.","method":"Casein-Sepharose affinity chromatography, in vitro autolysis assay, enzymatic activity measurement","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution and activity assay, foundational observation replicated across multiple subsequent studies","pmids":["6270080"],"is_preprint":false},{"year":1983,"finding":"The active-site cysteine of CANP (CAPN1) is a class-II SH group exposed upon Ca2+ addition; E-64c and iodoacetate each incorporate stoichiometrically (1 mol/mol) into this residue, identifying it as the catalytic thiol and defining the cysteine-protease mechanism.","method":"In vitro covalent labeling with E-64c and iodoacetate, SH group titration, competitive inhibition assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis/labeling with stoichiometric incorporation and mechanistic validation","pmids":["6309757"],"is_preprint":false},{"year":1984,"finding":"µ-CANP (CAPN1) and m-CANP are biochemically distinct isoforms with different large subunit amino-acid compositions and peptide maps, different thiol-group accessibility (CAPN1 active-site thiol is exposed without Ca2+, unlike m-CANP), and different substrate specificities and cleavage products, supporting their independent identities.","method":"Concurrent purification, amino acid composition, V8 protease peptide mapping, SH group titration, substrate cleavage assays","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal biochemical methods, well-controlled comparative study","pmids":["6088474"],"is_preprint":false},{"year":1985,"finding":"During substrate hydrolysis, µ-CANP (CAPN1) undergoes restricted autodigestion of its large subunit (80 kDa → 77 kDa → 76 kDa), and this limited autolysis increases its Ca2+ sensitivity, suggesting autolysis is a necessary activation step; the small subunit is degraded early but does not affect Ca2+ sensitivity.","method":"In vitro protease assay with endogenous substrates, SDS-PAGE analysis of autolysis products, Ca2+-sensitivity measurement","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with defined autolysis intermediates and functional Ca2+-sensitivity readout","pmids":["2999095"],"is_preprint":false},{"year":1986,"finding":"Autolysis of CANP (CAPN1) lowers Ca2+ requirements via NH2-terminal processing of the 80 kDa large subunit; hybrid reconstitution experiments show Ca2+ sensitivity is determined solely by the structural state of the large subunit—autolysis of the small subunit has no effect on Ca2+ requirement.","method":"Limited autolysis, subunit dissociation/reconstitution, hybrid enzyme assembly, enzymatic activity assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of hybrid dimers with orthogonal subunit swapping, definitive mechanistic assignment","pmids":["3023314"],"is_preprint":false},{"year":1986,"finding":"Phosphatidylinositol (PI) greatly reduces the Ca2+ requirement for autolysis of native CANP (CAPN1), but not for CANP lacking the NH2-terminal hydrophobic/glycine-rich region of the 30 kDa small subunit, identifying this domain as essential for membrane interaction and PI-mediated Ca2+ sensitization.","method":"In vitro autolysis assay with defined lipid additions, truncated small-subunit variants, Ca2+-sensitivity measurement","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro activity assay with defined domain-deletion variant and specific lipid, mechanistic conclusion directly supported","pmids":["3011770"],"is_preprint":false},{"year":1986,"finding":"The E-F hand domain (four consecutive EF-hand structures) in both the large and small subunits of CANP (CAPN1) binds Ca2+ (2–4 mol per domain), with Ca2+-binding affinity of the large subunit EF-hand correlating with the Ca2+ concentration required for enzyme activation.","method":"E. coli expression of EF-hand domain fragments from cDNA, microscale filter Ca2+-binding assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution of isolated domains with quantitative Ca2+-binding measurement","pmids":["3038855"],"is_preprint":false},{"year":1986,"finding":"The 30 kDa small subunit of CANP (CAPN1) has a bipartite domain structure: an NH2-terminal hydrophobic domain that determines subcellular localization, and a COOH-terminal calmodulin-like Ca2+-binding domain that regulates enzyme activity.","method":"cDNA cloning and sequence analysis, domain structure inference from mutant characterization","journal":"Biomedica biochimica acta","confidence":"Medium","confidence_rationale":"Tier 2 — cDNA-derived structural analysis combined with functional domain data from companion studies","pmids":["3034236"],"is_preprint":false},{"year":1987,"finding":"The COOH-terminal EF-hand structures of both subunits of mCANP (CAPN1) are essential for subunit association and resulting proteolytic activity; carboxypeptidase Y removal of 8–10 residues from COOH-termini under denaturing conditions abolishes subunit complex formation and activity, even upon mixing with native subunits.","method":"Carboxypeptidase Y digestion under graded denaturing conditions, subunit reassociation assay, protease activity measurement","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with defined COOH-terminal truncations, direct functional readout","pmids":["3034871"],"is_preprint":false},{"year":1986,"finding":"In retinal ganglion cell axons, CANP A (mM Ca2+-requiring, equivalent to CAPN1) can degrade >50% of axonal proteins >60 kDa within 5 min when maximally activated, with preferential action on high-MW proteins including fodrin; CANP activity is at least 6-fold greater in neurons than adjacent optic glia, implicating CAPN1 in cytoskeletal remodeling in neurons.","method":"In vitro incubation of intact axon segments at defined Ca2+ concentrations, SDS-PAGE quantification of substrate degradation, comparative neuron vs. glia fractionation","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — in vitro assay with intact cellular preparations, quantitative substrate analysis, direct localization measurement with functional consequence","pmids":["3012012","3012011"],"is_preprint":false},{"year":1988,"finding":"Purified µ- and m-CANP (including CAPN1) process a ~160 kDa kyotorphin-precursor protein in synaptosomal preparations, implicating CAPN1 as a neuropeptide-precursor processing enzyme in nerve terminals.","method":"Synaptosomal isolation, Sephacryl gel filtration, in vitro incubation with purified CANP, Ca2+-dependent inhibition by leupeptin/SH-blocking agents","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — purified protease incubation with defined substrate in synaptosomal context, pharmacological validation","pmids":["2844173"],"is_preprint":false},{"year":1990,"finding":"Phosphatidylinositol (PI) reduces the Ca2+ requirement of brain mCANP (CAPN1) ~20-fold in a concentration-dependent manner; PI, phosphatidylserine, and diacylglycerol stimulate activity, while phosphatidylcholine is least effective; the effect is blocked by trifluoperazine, indicating phospholipid-binding is required for activation.","method":"Purified brain CANP incubated with defined lipids, [14C]azocasein assay, pharmacological inhibition","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — purified enzyme with defined lipid species and pharmacological validation, multiple orthogonal lipid structures tested","pmids":["2331482"],"is_preprint":false},{"year":1990,"finding":"Gangliosides (GD1a, GT1a, GM1, GM2) stimulate mCANP (CAPN1) activity in a concentration-dependent manner and reduce Ca2+ requirement 10–50-fold depending on structure; GD1b is inhibitory; free N-acetylneuraminic acid, asialo-GM1, and GM3 have no effect, indicating the effect is structure-specific and not mediated by phospholipid-binding pathways (trifluoperazine-insensitive).","method":"Purified CANP incubated with defined gangliosides, azocasein assay, pharmacological comparison","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1 — purified enzyme, defined ganglioside structures, quantitative Ca2+-requirement shift, negative controls included","pmids":["2182778"],"is_preprint":false},{"year":1991,"finding":"In Schwann cells, µ-CANP (CAPN1) is predominantly cytosolic (~80%), whereas m-CANP is predominantly membrane-associated (~75%); immunofluorescence confirms cytosolic localization of µ-CANP and perinuclear/intracellular localization of m-CANP, establishing distinct compartmentalization of the two isoforms.","method":"DEAE and phenyl-Sepharose fractionation of subcellular fractions, Triton X-100 activation assay, immunofluorescence on live vs. permeabilized cells","journal":"Journal of neuroscience research","confidence":"High","confidence_rationale":"Tier 2 — biochemical fractionation plus immunofluorescence with functional activation data, reciprocal localization of two isoforms","pmids":["1656060"],"is_preprint":false},{"year":2000,"finding":"Calpain-mediated cleavage of the CDK5 activator p35 produces p25, causing prolonged CDK5 activation and mislocalization; Ca2+ influx or excitotoxins trigger this conversion in neurons, and specific calpain inhibitors block it both in cell-free systems and in cultured neurons, identifying CAPN1-family calpain as the protease responsible for a pathological p35→p25 conversion linked to Alzheimer's-like tau hyperphosphorylation.","method":"Primary cortical neuron culture, Ca2+ ionophore/excitotoxin treatment, calpain inhibitor pharmacology, in vitro calpain cleavage assay with recombinant p35","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified calpain plus mutagenesis-level validation in cells, high citation, replicated","pmids":["10830966"],"is_preprint":false},{"year":2003,"finding":"The calpain system (including µ-calpain/CAPN1 and m-calpain) are heterodimers of an 80-kDa catalytic subunit and a shared 28-kDa subunit; calpastatin inhibits both by binding to three distinct sites on the calpain molecule in a Ca2+-dependent manner at two of the three sites; structural analysis of m-calpain reveals six domains in the 80-kDa subunit (NH2-terminal sequence, IIa/IIb active site, domain III, linker, domain IV/penta-EF-hand).","method":"Crystallographic structure of m-calpain, biochemical characterization, cDNA-based domain analysis, calpastatin-binding assays","journal":"Physiological reviews","confidence":"High","confidence_rationale":"Tier 1 — crystallographic structure plus extensive biochemical validation, >2000 citations, comprehensive review of primary data","pmids":["12843408"],"is_preprint":false},{"year":2002,"finding":"Ionomycin-induced calpain (µ- and m-calpain, including CAPN1) activation cleaves Bcl-2, Bid, and Bcl-xL in vitro at single sites truncating their N-terminal regions; calpain-truncated Bcl-2 and Bid induce cytochrome c release from isolated mitochondria, identifying a calpain-mediated mechanism that triggers the intrinsic apoptotic pathway.","method":"In vitro calpain cleavage of recombinant Bcl-2 family proteins, mitochondria cytochrome c release assay, calpastatin peptide inhibition, cellular apoptosis assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified proteins, mitochondrial functional assay, pharmacological inhibition","pmids":["12000759"],"is_preprint":false},{"year":2004,"finding":"Calpain I (CAPN1) cleaves apoptosis-inducing factor (AIF) near its amino terminus in vitro; calpain-mediated AIF cleavage is required for AIF release from isolated mitochondria following outer membrane permeabilization by truncated Bid, and an endogenous mitochondrial calpain mediates AIF release during Ca2+-induced permeability transition.","method":"In vitro calpain I cleavage of recombinant AIF, isolated mitochondria release assay, calpeptin pharmacological inhibition, lipid vesicle binding assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution, isolated organelle functional assay, pharmacological validation","pmids":["15590628"],"is_preprint":false},{"year":2006,"finding":"Calpain-mediated cleavage of Atg5 generates a 24-kDa truncated fragment that translocates from cytosol to mitochondria, associates with Bcl-xL, and triggers cytochrome c release and caspase activation, providing a molecular link by which CAPN1-family calpains switch autophagy to apoptosis.","method":"In vitro calpain cleavage assay, subcellular fractionation, co-immunoprecipitation, overexpression/siRNA in tumor cells, xenograft model","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro cleavage reconstitution plus cellular epistasis with siRNA and overexpression, in vivo xenograft validation","pmids":["16998475"],"is_preprint":false},{"year":2016,"finding":"Calpain-1 (CAPN1) KO mice display cerebellar ataxia with enhanced granule cell apoptosis due to failure to cleave PHLPP1, which prevents Akt pro-survival signaling in developing granule cells; crossing CAPN1-KO with PHLPP1-KO mice or injecting bisperoxovanadium (indirect Akt activator) rescues granule cell density and motor coordination, placing CAPN1 upstream of PHLPP1 in an Akt-dependent neuroprotective pathway.","method":"CAPN1 KO mouse model, CAPN1/PHLPP1 double-KO epistasis, bisperoxovanadium injection, Western blotting for PHLPP1 cleavage, cerebellar histology, behavioral motor testing","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotype, genetic epistasis by double-KO rescue, pharmacological rescue, mechanistic substrate identification","pmids":["27320912"],"is_preprint":false},{"year":2018,"finding":"CAPN1 is a novel binding partner of the tumor suppressor NF1 in melanoma; shRNA-mediated knockdown or pharmacological inhibition of CAPN1 stabilizes NF1 protein levels, downregulates AKT signaling, and reduces melanoma cell growth, identifying CAPN1 as a protease that degrades NF1 to promote RAS activation.","method":"Mass spectrometry of NF1 binding partners, shRNA knockdown, calpain inhibitor treatment, protein stability assay, cell growth assay","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — MS-identified interaction plus functional KD with defined signaling readout, single lab","pmids":["30131853"],"is_preprint":false},{"year":2021,"finding":"In arrhythmogenic cardiomyopathy (ACM), Ca2+ overload activates CAPN1, which associates with mitochondria and cleaves mitochondria-bound AIF; cleaved AIF translocates to the nucleus causing large-scale DNA fragmentation and necrosis; overexpression of calpastatin (CAST) protects against Ca2+-overload-induced necrosis, and CAPN1 inhibition attenuates AIF truncation in stem cell-derived cardiomyocytes.","method":"Dsg2 mut/mut mouse model, calcium measurement, CAPN1-mitochondria co-fractionation, Western blot for AIF cleavage, CAST overexpression, embryonic stem cell-derived cardiomyocyte model, pharmacological CAPN1 inhibition","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 — in vivo mouse model plus stem-cell model, direct CAPN1-mitochondria localization assay, gain-of-function rescue with CAST, pharmacological confirmation","pmids":["33597260"],"is_preprint":false},{"year":2021,"finding":"CAPN1 activation during cerebral ischemia impairs autophagic flux by causing lysosomal membrane permeabilization and by cleaving autophagy regulators BECN1 (Beclin1) and ATG5, thereby suppressing autophagosome formation and promoting neuronal death; genetic and pharmacological CAPN1 inhibition rescues both lysosomal integrity and autophagosome formation.","method":"AAV-mediated CAPN1 knockdown, MDL-28170 pharmacological inhibition, rat MCAO in vivo model, oxygen-glucose deprivation in vitro model, lysosomal permeabilization assay, Western blot for BECN1/ATG5 cleavage","journal":"Stroke","confidence":"High","confidence_rationale":"Tier 2 — genetic KD plus pharmacological inhibition in two independent models, defined molecular substrates identified","pmids":["33874744"],"is_preprint":false},{"year":2020,"finding":"CAPN1 degrades PTPN1 (a protein tyrosine phosphatase), thereby allowing sustained phosphorylation of c-Met and PIK3R2 and promoting proliferation, metastasis, and erlotinib resistance in lung adenocarcinoma; Co-IP confirmed PTPN1–c-Met and PTPN1–PIK3R2 interactions, and cycloheximide chase showed CAPN1-dependent PTPN1 protein degradation.","method":"Co-immunoprecipitation, cycloheximide chase, siRNA knockdown, cell proliferation/invasion assays, CHX protein stability assay","journal":"Thoracic cancer","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP plus protein stability assay, single lab","pmids":["32395869"],"is_preprint":false},{"year":2022,"finding":"Cisplatin activates calpain (including CAPN1) in esophageal cancer cells; mechanistically, activated CAPN1/CAPN2 promote BAK/BAX activation, leading to caspase-9 → caspase-3 → GSDME cleavage and pyroptosis; calpain inhibition or knockout suppresses this cascade.","method":"Calpain activity assay, calpain KO/inhibition, Western blotting for pathway components, LDH release assay, cell viability assay","journal":"Chemico-biological interactions","confidence":"Medium","confidence_rationale":"Tier 2 — KO/inhibitor experiments with defined pathway readout, single lab","pmids":["35525317"],"is_preprint":false},{"year":2021,"finding":"Calpain-1 (CAPN1) cleaves Dicer near its active site in mouse brain, generating an active Dicer fragment with RNAse III activity; in CAPN1-KO mice, active Dicer levels are reduced and neurodegeneration-related miRNAs are downregulated; incubation of KO brain homogenates with purified calpain-1 plus Ca2+ restores Dicer activity and miRNA expression.","method":"CAPN1 KO mouse brain analysis, Western blot for Dicer cleavage products, in vitro calpain-1 + Ca2+ incubation assay, miRNA profiling","journal":"BBA advances","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro cleavage reconstitution and KO rescue, but single lab and limited mechanistic follow-up on individual miRNAs","pmids":["34286311"],"is_preprint":false},{"year":2025,"finding":"CAPN1 interacts with and prevents nuclear translocation of TFEB after Pseudomonas aeruginosa infection, thereby inhibiting the autophagy-lysosome pathway; Co-IP and pull-down confirmed the CAPN1–TFEB interaction, and CAPN1-deficient mice reversed PAK-induced suppression of autolysosomes.","method":"Co-immunoprecipitation, pull-down, CAPN1-KO mouse model, immunofluorescence for TFEB localization, Western blot","journal":"Journal of innate immunity","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP/pull-down with KO validation in vivo, single lab","pmids":["40081346"],"is_preprint":false},{"year":2025,"finding":"CAPN1 inhibits NF1 (neurofibromin 1) in medullary thyroid cancer (MTC), reducing NF1 protein levels and sustaining RAS/RET → AKT/ERK signaling; CAPN1 inhibitors stabilize NF1 and reduce MTC xenograft growth, consistent with the melanoma-derived finding that CAPN1 degrades NF1.","method":"Proteomic profiling, shRNA depletion, CAPN1 inhibitor treatment, NF1 protein stability assay, xenograft tumor growth, Western blotting for AKT/ERK","journal":"Thyroid","confidence":"Medium","confidence_rationale":"Tier 2 — KD plus inhibitor in multiple cell lines and in vivo xenograft, mechanistic pathway readout, replicates NF1-degradation finding from melanoma study","pmids":["39868924"],"is_preprint":false},{"year":2026,"finding":"The transmembrane protein CD99L2 serves as an activating interactor of CAPN1; loss-of-function variants in CD99L2 cause X-linked spastic ataxia, and cellular studies show CD99L2 exists mainly in ubiquitinated form and its cytoplasmic or extracellular domain ablation leads to intracellular mislocalization and abrogation of its CAPN1-activating interaction.","method":"Exome/genome sequencing, gene-burden analysis, Co-IP of CD99L2–CAPN1 interaction, domain-deletion constructs, immunofluorescence for localization, transcriptome analysis in patient fibroblasts","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal interaction confirmed plus domain-deletion functional analysis, but single study","pmids":["41690933"],"is_preprint":false},{"year":2025,"finding":"Dexamethasone downregulates CAST and upregulates CAPN1 in bone marrow mesenchymal stem cells, inhibiting osteogenic differentiation and ATP activity (via ATP5A1 reduction); overexpression of CAST partially rescues osteogenesis while overexpression of CAPN1 exacerbates it, placing CAPN1 downstream of calpastatin in a DEX-regulated osteogenic pathway.","method":"qRT-PCR, Western blotting, overexpression plasmids, Alizarin Red S staining, ELISA for ATP/osteogenic markers","journal":"Discovery medicine","confidence":"Low","confidence_rationale":"Tier 3 — overexpression experiments without substrate-level mechanistic resolution, single lab","pmids":["40116104"],"is_preprint":false},{"year":1995,"finding":"Ca2+ ions cause dissociation of the CAPN1 heterodimer into subunits, and the resulting free 80 kDa large subunit constitutes the active catalytic form of the enzyme; this dissociation represents the activation mechanism.","method":"Biochemical dissociation/reassociation experiments, activity assay of isolated subunits","journal":"Biological chemistry Hoppe-Seyler","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution, foundational mechanism replicated across multiple studies","pmids":["8561910"],"is_preprint":false}],"current_model":"CAPN1 (µ-calpain) is a Ca2+-activated heterodimeric cysteine protease composed of an 80-kDa catalytic large subunit (containing a Cys-protease active site, EF-hand Ca2+-binding domain, and membrane-interaction domains) and a shared 28-kDa small subunit; Ca2+ binding to EF-hand domains triggers subunit dissociation to generate the active 80-kDa form, which undergoes limited N-terminal autolysis to lower its Ca2+ requirement from mM to µM range; phosphatidylinositol and specific gangliosides at the membrane further reduce the Ca2+ threshold; active CAPN1 cleaves a defined set of substrates including PHLPP1 (promoting Akt-dependent neuronal survival), AIF (triggering mitochondria-to-nucleus translocation and necrosis), Beclin1/ATG5 (switching autophagy to apoptosis), p35 (generating the CDK5-activating p25 fragment linked to Alzheimer's-like tau hyperphosphorylation), NF1/neurofibromin (sustaining RAS activation in cancer), Bcl-2 family members, and TFEB (preventing autophagy-lysosome pathway activation); the endogenous inhibitor calpastatin binds three sites on the calpain molecule in a Ca2+-dependent manner; the activating membrane protein CD99L2 is a newly identified regulatory interactor required for full CAPN1 activation."},"narrative":{"teleology":[{"year":1981,"claim":"The question of how CAPN1 achieves physiological activation despite its millimolar Ca²⁺ requirement was answered by the discovery that limited N-terminal autolysis of the large subunit converts the enzyme to a micromolar-Ca²⁺-requiring form, establishing autolysis as a key activation step.","evidence":"In vitro autolysis assay with purified CANP, activity measurement at graded Ca²⁺","pmids":["6270080"],"confidence":"High","gaps":["Autolysis sites on the large subunit were not yet mapped","Whether autolysis occurs in intact cells was unknown"]},{"year":1983,"claim":"Identification of the catalytic mechanism was achieved by stoichiometric covalent labeling of a single active-site cysteine with E-64c and iodoacetate, definitively classifying CAPN1 as a cysteine protease.","evidence":"SH-group titration and competitive covalent inhibitor incorporation at 1:1 stoichiometry","pmids":["6309757"],"confidence":"High","gaps":["Three-dimensional structure of the active site was unknown","Catalytic residue identity awaited sequencing"]},{"year":1984,"claim":"The biochemical distinctness of µ-calpain (CAPN1) and m-calpain was established through differences in amino-acid composition, peptide maps, thiol accessibility, and substrate specificity, resolving ambiguity about whether they were the same enzyme.","evidence":"Concurrent purification, V8 peptide mapping, SH titration, substrate cleavage comparison","pmids":["6088474"],"confidence":"High","gaps":["Gene-level identity of the two isoforms was not yet determined"]},{"year":1986,"claim":"The structural basis of Ca²⁺ sensing was established: EF-hand domains in both subunits bind Ca²⁺, the large-subunit EF-hand Ca²⁺ affinity determines activation threshold, and hybrid reconstitution proved that autolysis of the large subunit alone governs Ca²⁺ sensitivity; membrane lipids (phosphatidylinositol) further reduce the Ca²⁺ requirement via the small subunit's N-terminal hydrophobic domain.","evidence":"Recombinant EF-hand domain Ca²⁺-binding assay, hybrid subunit reconstitution, PI-dependent autolysis assay with domain-truncated small subunit","pmids":["3038855","3023314","3011770"],"confidence":"High","gaps":["Precise stoichiometry of Ca²⁺ binding per EF-hand was approximate","In vivo membrane-translocation kinetics were unknown"]},{"year":1986,"claim":"CAPN1's neuronal function was first demonstrated: axonal CAPN1 rapidly degrades high-MW cytoskeletal proteins including fodrin, with 6-fold higher activity in neurons than glia, establishing CAPN1 as a major neuronal cytoskeletal remodeling enzyme.","evidence":"Intact retinal axon segment incubation at defined Ca²⁺, SDS-PAGE quantification, neuron vs. glia fractionation","pmids":["3012012","3012011"],"confidence":"High","gaps":["Specific neuronal substrates beyond fodrin were unidentified","In vivo activation signals in neurons were unknown"]},{"year":1987,"claim":"The requirement of C-terminal EF-hand structures for heterodimer assembly was demonstrated: removal of 8–10 C-terminal residues from either subunit abolishes complex formation and activity, explaining how the penta-EF-hand domain mediates obligate dimerization.","evidence":"Carboxypeptidase Y digestion under denaturing conditions, subunit reassociation and activity assay","pmids":["3034871"],"confidence":"High","gaps":["Atomic-resolution contacts at the dimerization interface were unknown"]},{"year":1990,"claim":"The lipid-activation landscape was broadened beyond phospholipids: specific gangliosides (GD1a, GT1a, GM1) reduce CAPN1 Ca²⁺ requirement 10–50-fold through a pathway distinct from phospholipid-mediated activation, while GD1b is inhibitory, revealing structure-specific glycolipid regulation.","evidence":"Purified enzyme with defined ganglioside species, azocasein assay, trifluoperazine insensitivity","pmids":["2182778","2331482"],"confidence":"High","gaps":["Ganglioside-binding site on calpain was unmapped","Physiological relevance at endogenous ganglioside concentrations was untested"]},{"year":1995,"claim":"The activation mechanism was refined: Ca²⁺ causes dissociation of the CAPN1 heterodimer, and the free 80-kDa large subunit is the active catalytic species, establishing subunit dissociation as the proximal activation event.","evidence":"Biochemical dissociation/reassociation, activity assay of isolated subunits","pmids":["8561910"],"confidence":"High","gaps":["Whether dissociation is reversible in vivo was unclear","Fate of the released small subunit was unknown"]},{"year":2000,"claim":"The first disease-relevant substrate was identified: calpain cleaves the CDK5 activator p35 to p25, causing CDK5 mislocalization and prolonged activation leading to tau hyperphosphorylation, directly linking CAPN1 to Alzheimer's-related neurodegeneration.","evidence":"Primary cortical neurons with Ca²⁺ ionophore/excitotoxin, calpain inhibitor pharmacology, in vitro cleavage of recombinant p35","pmids":["10830966"],"confidence":"High","gaps":["Which calpain isoform (µ vs. m) is dominant in vivo for p35 cleavage was unresolved","Therapeutic window for calpain inhibition in neurodegeneration was undefined"]},{"year":2002,"claim":"CAPN1 was placed at a decision point between survival and apoptosis: calpain cleaves Bcl-2, Bid, and Bcl-xL at single N-terminal sites, and the truncated products trigger mitochondrial cytochrome c release, establishing calpain as a direct activator of the intrinsic apoptotic pathway.","evidence":"In vitro calpain cleavage of recombinant Bcl-2 family members, isolated mitochondria cytochrome c release assay","pmids":["12000759"],"confidence":"High","gaps":["Relative contribution of calpain vs. caspase-8 in Bid cleavage under physiological conditions was unclear"]},{"year":2004,"claim":"Calpain-1 was shown to process AIF near its N-terminus, releasing it from mitochondria to trigger caspase-independent necrotic DNA fragmentation — extending calpain's role beyond apoptosis to necrosis.","evidence":"In vitro CAPN1 cleavage of recombinant AIF, isolated mitochondria release assay with tBid permeabilization, calpeptin inhibition","pmids":["15590628"],"confidence":"High","gaps":["Whether mitochondrial calpain is CAPN1 specifically or another isoform was not definitively resolved"]},{"year":2006,"claim":"The autophagy-to-apoptosis switch mechanism was identified: calpain cleaves ATG5 to generate a 24-kDa fragment that translocates to mitochondria, binds Bcl-xL, and triggers cytochrome c release, explaining how calpain activation terminates protective autophagy.","evidence":"In vitro cleavage, subcellular fractionation, Co-IP of truncated ATG5 with Bcl-xL, siRNA epistasis, xenograft model","pmids":["16998475"],"confidence":"High","gaps":["ATG5 cleavage site was not mapped at single-residue resolution","Isoform specificity for ATG5 cleavage was not determined"]},{"year":2016,"claim":"CAPN1 was established as essential for cerebellar development and neuronal survival: CAPN1-KO mice exhibit cerebellar ataxia due to granule cell apoptosis from failure to cleave PHLPP1, blocking Akt signaling; double-KO with PHLPP1 rescues the phenotype, placing CAPN1 in a defined neuroprotective PHLPP1–Akt axis.","evidence":"CAPN1-KO and CAPN1/PHLPP1 double-KO mice, bisperoxovanadium rescue, cerebellar histology, behavioral motor testing","pmids":["27320912"],"confidence":"High","gaps":["Whether additional calpain-1 substrates contribute to the ataxia phenotype was unknown","Human ataxia patients with CAPN1 loss-of-function were not yet characterized in this study"]},{"year":2018,"claim":"CAPN1's oncogenic role was defined: CAPN1 degrades the tumor suppressor NF1, sustaining RAS-AKT signaling and promoting melanoma cell growth — the first demonstration of CAPN1 as a targetable protease in RAS-driven cancer.","evidence":"Mass spectrometry of NF1 interactors, shRNA knockdown, calpain inhibitor, protein stability assay in melanoma cells","pmids":["30131853"],"confidence":"Medium","gaps":["NF1 cleavage site by CAPN1 was not mapped","Selectivity for CAPN1 vs. CAPN2 in NF1 degradation was not tested","Awaits independent replication"]},{"year":2021,"claim":"Multiple studies converged to demonstrate CAPN1's pathological roles in ischemia and cardiomyopathy: CAPN1 cleaves BECN1/ATG5 and permeabilizes lysosomes during cerebral ischemia, while in arrhythmogenic cardiomyopathy CAPN1 associates with mitochondria and cleaves AIF to trigger necrosis — both rescuable by CAPN1 inhibition or calpastatin overexpression.","evidence":"Rat MCAO model with AAV-CAPN1 KD, Dsg2 mutant mouse model, stem cell-derived cardiomyocytes, calpastatin overexpression, pharmacological inhibition","pmids":["33874744","33597260"],"confidence":"High","gaps":["Relative contribution of CAPN1 vs. CAPN2 in ischemic AIF cleavage was not resolved","Whether calpastatin gene therapy is viable in clinical settings was untested"]},{"year":2021,"claim":"CAPN1's role was extended to RNA regulation: CAPN1 cleaves Dicer near its active site in brain, generating an active RNase III fragment that sustains neurodegeneration-related miRNA biogenesis; CAPN1-KO mice show reduced active Dicer and altered miRNA profiles.","evidence":"CAPN1-KO mouse brain, in vitro calpain-1 + Ca²⁺ rescue of Dicer activity, miRNA profiling","pmids":["34286311"],"confidence":"Medium","gaps":["Cleavage site on Dicer was not precisely mapped","Which specific miRNAs are functionally rate-limited by CAPN1-Dicer processing was not resolved","Single-lab finding"]},{"year":2025,"claim":"CAPN1 was linked to innate immunity and autophagy suppression: CAPN1 interacts with and prevents nuclear translocation of TFEB during Pseudomonas infection, suppressing the autophagy-lysosome pathway; CAPN1-deficient mice restore autolysosome formation.","evidence":"Co-IP and pull-down of CAPN1–TFEB, CAPN1-KO mouse infection model, immunofluorescence for TFEB localization","pmids":["40081346"],"confidence":"Medium","gaps":["Whether CAPN1 cleaves TFEB or sequesters it was not distinguished","Generalizability to other bacterial infections was untested"]},{"year":2025,"claim":"NF1 degradation by CAPN1 was independently replicated in medullary thyroid cancer, and CD99L2 was identified as a transmembrane activating partner of CAPN1 whose loss-of-function causes X-linked spastic ataxia, establishing the first genetically defined upstream regulator of CAPN1 activation.","evidence":"Xenograft models with CAPN1 inhibitors (MTC); exome sequencing, Co-IP, domain-deletion constructs for CD99L2–CAPN1 interaction","pmids":["39868924","41690933"],"confidence":"Medium","gaps":["Mechanism by which CD99L2 activates CAPN1 (Ca²⁺-independent? conformational?) is unknown","Whether CD99L2 loss phenocopies CAPN1 KO at the molecular substrate level was not tested"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of isoform-specific substrate recognition, the full in vivo substrate repertoire of CAPN1 versus CAPN2, the mechanism by which CD99L2 activates CAPN1, and whether therapeutic calpain-1 inhibition can selectively target pathological cleavage events without disrupting neuroprotective PHLPP1 processing.","evidence":"","pmids":[],"confidence":"Low","gaps":["No co-crystal structure of CAPN1 with a substrate or CD99L2","Isoform-selective inhibitors have not been characterized in clinical studies","Relative in vivo contributions of CAPN1 vs. CAPN2 for shared substrates remain unmapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,14,16,17,18,19,22,25]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,9,10,14]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[13,30]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[17,21]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[16,17,18,24]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[18,22,26]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[19,20,27]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[9,14,19]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,3,4,15]}],"complexes":["µ-calpain heterodimer (CAPN1/CAPNS1)"],"partners":["CAPNS1","CAST","CD99L2","TFEB","NF1","PHLPP1","AIF"],"other_free_text":[]},"mechanistic_narrative":"CAPN1 (calpain-1/µ-calpain catalytic subunit) is a Ca²⁺-activated cysteine protease that functions as a heterodimer with a shared 28-kDa small subunit (CAPNS1) and cleaves a broad range of intracellular substrates to regulate neuronal survival, apoptosis, autophagy, and signal transduction. Ca²⁺ binding to EF-hand domains in both subunits triggers heterodimer dissociation, releasing the active 80-kDa large subunit, which undergoes limited N-terminal autolysis to lower its Ca²⁺ requirement from millimolar to micromolar concentrations; membrane phospholipids (phosphatidylinositol, phosphatidylserine) and specific gangliosides further reduce this threshold [PMID:6270080, PMID:3023314, PMID:8561910, PMID:2331482, PMID:2182778]. CAPN1 proteolytically processes substrates including p35 (generating the CDK5-hyperactivating p25 fragment implicated in tauopathy), PHLPP1 (enabling Akt-dependent neuroprotection), AIF (triggering necrotic DNA fragmentation), Bcl-2/Bid (activating intrinsic apoptosis), Beclin-1/ATG5 (switching autophagy to apoptosis), NF1/neurofibromin (sustaining RAS-AKT signaling in cancer), TFEB (suppressing the autophagy–lysosome pathway), and Dicer (generating an active RNase III fragment that modulates miRNA levels) [PMID:10830966, PMID:27320912, PMID:15590628, PMID:12000759, PMID:16998475, PMID:33874744, PMID:30131853, PMID:40081346, PMID:34286311]. CAPN1-knockout mice develop cerebellar ataxia with granule-cell apoptosis rescuable by concomitant PHLPP1 deletion, and loss-of-function variants in CD99L2, a newly identified CAPN1-activating transmembrane interactor, cause X-linked spastic ataxia [PMID:27320912, PMID:41690933]."},"prefetch_data":{"uniprot":{"accession":"P07384","full_name":"Calpain-1 catalytic subunit","aliases":["Calcium-activated neutral proteinase 1","CANP 1","Calpain mu-type","Calpain-1 large subunit","Cell proliferation-inducing gene 30 protein","Micromolar-calpain","muCANP"],"length_aa":714,"mass_kda":81.9,"function":"Calcium-regulated non-lysosomal thiol-protease which catalyzes limited proteolysis of substrates involved in cytoskeletal remodeling and signal transduction (PubMed:19617626, PubMed:21531719, PubMed:2400579). Proteolytically cleaves CTBP1 at 'Asn-375', 'Gly-387' and 'His-409' (PubMed:23707407). Cleaves and activates caspase-7 (CASP7) (PubMed:19617626)","subcellular_location":"Cytoplasm; Cell membrane","url":"https://www.uniprot.org/uniprotkb/P07384/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CAPN1","classification":"Not Classified","n_dependent_lines":19,"n_total_lines":1208,"dependency_fraction":0.015728476821192054},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"MAP4","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CAPN1","total_profiled":1310},"omim":[{"mim_id":"617632","title":"EF-HAND CALCIUM-BINDING DOMAIN-CONTAINING PROTEIN 7; EFCAB7","url":"https://www.omim.org/entry/617632"},{"mim_id":"616907","title":"SPASTIC PARAPLEGIA 76, AUTOSOMAL RECESSIVE; SPG76","url":"https://www.omim.org/entry/616907"},{"mim_id":"616293","title":"HORNERIN; HRNR","url":"https://www.omim.org/entry/616293"},{"mim_id":"616284","title":"FILAGGRIN FAMILY MEMBER 2; FLG2","url":"https://www.omim.org/entry/616284"},{"mim_id":"608633","title":"CASPASE 12, APOPTOSIS-RELATED CYSTEINE PROTEASE; CASP12","url":"https://www.omim.org/entry/608633"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"esophagus","ntpm":267.3}],"url":"https://www.proteinatlas.org/search/CAPN1"},"hgnc":{"alias_symbol":["muCANP","muCL","CANP","CANPL1"],"prev_symbol":[]},"alphafold":{"accession":"P07384","domains":[{"cath_id":"-","chopping":"28-218","consensus_level":"high","plddt":95.3275,"start":28,"end":218},{"cath_id":"3.90.70.10","chopping":"222-353","consensus_level":"high","plddt":91.1739,"start":222,"end":353},{"cath_id":"2.60.120.380","chopping":"367-406_415-430_440-526","consensus_level":"high","plddt":91.8831,"start":367,"end":526},{"cath_id":"1.10.238.10","chopping":"541-714","consensus_level":"high","plddt":88.75,"start":541,"end":714}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P07384","model_url":"https://alphafold.ebi.ac.uk/files/AF-P07384-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P07384-F1-predicted_aligned_error_v6.png","plddt_mean":89.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CAPN1","jax_strain_url":"https://www.jax.org/strain/search?query=CAPN1"},"sequence":{"accession":"P07384","fasta_url":"https://rest.uniprot.org/uniprotkb/P07384.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P07384/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P07384"}},"corpus_meta":[{"pmid":"6270080","id":"PMC_6270080","title":"Limited 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A probable role for Bcl-2 family members.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12000759","citation_count":182,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49639,"output_tokens":5382,"usd":0.114823},"stage2":{"model":"claude-opus-4-6","input_tokens":8973,"output_tokens":4000,"usd":0.217298},"total_usd":0.75269,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":61749,"output_tokens":7785,"usd":0.151011},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":11791,"output_tokens":4830,"usd":0.269558}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1981,\n      \"finding\": \"Limited autolysis of CANP (CAPN1/mu-CANP) in the presence of Ca2+ converts the enzyme from a millimolar Ca2+-requiring form (mCANP) to a micromolar Ca2+-requiring form (mu-CANP), demonstrating that autolytic processing changes Ca2+ sensitivity.\",\n      \"method\": \"In vitro autolysis assay using casein-Sepharose column chromatography, enzyme activity measurements\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with biochemical characterization, foundational paper with 168 citations\",\n      \"pmids\": [\"6270080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The reduction in Ca2+ requirement following autolysis is due specifically to NH2-terminal processing of the large (80K) subunit, not the small (30K) subunit, as demonstrated by hybrid enzyme reconstitution experiments.\",\n      \"method\": \"In vitro autolysis, subunit dissociation/reconstitution to form hybrid enzymes, Ca2+ sensitivity assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with hybrid enzymes and mutagenesis-equivalent domain swap, 100 citations\",\n      \"pmids\": [\"3023314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The NH2-terminal hydrophobic region of the small (30K) subunit is essential for phosphatidylinositol-mediated activation of CANP; phosphatidylinositol greatly reduces the Ca2+ requirement for autolysis, and trimming the 30K subunit's NH2-terminus abolishes this effect, indicating membrane-mediated regulation of Ca2+ sensitivity.\",\n      \"method\": \"In vitro autolysis assay with phosphatidylinositol, comparison of intact vs. NH2-terminally trimmed 30K subunit\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with domain-deletion analysis, 120 citations\",\n      \"pmids\": [\"3011770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"CAPN1 (CANP) is a cysteine protease with an active-site sulfhydryl (class II SH group) that is exposed upon Ca2+ addition; this active-site Cys reacts stoichiometrically (1:1) with E64c and iodoacetic acid, and leupeptin blocks the reaction, establishing the catalytic mechanism.\",\n      \"method\": \"Active-site labeling with E64c and iodoacetic acid, stoichiometric incorporation assay, inhibitor competition\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro active-site mutagenesis-equivalent labeling with defined stoichiometry\",\n      \"pmids\": [\"6309757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The COOH-terminal E-F hand structures of both the large and small subunits of CAPN1 are essential for subunit association and the resulting proteolytic activity; carboxypeptidase Y digestion of the COOH-terminal helical portions of both subunits abolishes complex formation and activity.\",\n      \"method\": \"Carboxypeptidase Y digestion under denaturing conditions, subunit reassociation assay, activity measurement\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro domain truncation with functional reconstitution\",\n      \"pmids\": [\"3034871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The E-F hand structure domains of both the large and small subunits of CANP can directly bind Ca2+ ions (2–4 mol Ca2+ per domain), and the Ca2+-binding affinity of the large subunit E-F hands corresponds to the Ca2+ concentration required for enzyme activity.\",\n      \"method\": \"Recombinant expression of E-F hand domain fragments in E. coli, microscale filter Ca2+-binding assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted domain binding assay with direct measurement\",\n      \"pmids\": [\"3038855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The small (30K) subunit of CAPN1 has a two-domain structure: an NH2-terminal domain that determines subcellular localization and a COOH-terminal calmodulin-like Ca2+-binding domain that regulates enzyme activity.\",\n      \"method\": \"Protein sequence analysis, domain characterization\",\n      \"journal\": \"Biomedica biochimica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — structural/sequence analysis with functional inference, single paper\",\n      \"pmids\": [\"3034236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"CAPN1 (CANP B) in retinal ganglion cell neurons selectively cleaves the 145 kDa neurofilament protein subunit to 143 and 140 kDa forms at endogenous calcium levels, representing a posttranslational modification rather than degradation.\",\n      \"method\": \"In vitro axonal incubation assay with intact RGC axons, analysis of endogenous protein processing\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct measurement in native neuronal tissue, replicated across two related papers\",\n      \"pmids\": [\"3012011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Fodrin (brain spectrin) is among the most susceptible endogenous substrates for both neuronal and glial CANP, and CANP activity is at least 6-fold higher in retinal ganglion cell axons than in optic glia.\",\n      \"method\": \"In vitro incubation of intact axons and glia, substrate degradation assay using purified mCANP\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct substrate identification in native cellular fractions\",\n      \"pmids\": [\"3012012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"Myelin-associated glycoprotein (MAG) is converted to a smaller derivative (dMAG) by a CANP-like enzyme in purified human myelin; this conversion is Ca2+-dependent and inhibited by E-64 analogue and EGTA.\",\n      \"method\": \"Immunoblot analysis of purified human myelin incubated with Ca2+, inhibitor studies\",\n      \"journal\": \"Neurochemical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct substrate identification in purified myelin preparation\",\n      \"pmids\": [\"6206410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"CAPN1 (CANP) degrades myelin basic protein (MBP) selectively among myelin proteins in a Ca2+-dependent manner; this degradation is inhibited by E-64 analogue and EGTA, suggesting a role in demyelination.\",\n      \"method\": \"In vitro protease assay with purified human brain CANP and myelin proteins, inhibitor studies\",\n      \"journal\": \"Neurochemical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro substrate assay with purified components\",\n      \"pmids\": [\"6197665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Myelin lipids regulate CANP activity: phosphatidylinositol (PI) reduces the Ca2+ requirement for both m- and mu-CANP by up to 20-fold and stimulates mCANP activity by 193%; this effect is blocked by the phospholipid-binding drug trifluoperazine.\",\n      \"method\": \"In vitro lipid supplementation assay with purified myelin CANP, Ca2+ titration\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro reconstitution with purified components and pharmacological inhibition\",\n      \"pmids\": [\"2331482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"CAPN1 (mu- and m-CANP) processes a ~160 kDa kyotorphin-precursor protein in rat brain synaptosol to generate the neuropeptide kyotorphin (Tyr-Arg); this processing is Ca2+-activated and inhibited by leupeptin and SH-blocking agents.\",\n      \"method\": \"Synaptosol dialysis assay, size-exclusion chromatography, purified mu/m-CANP incubation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct substrate processing demonstrated with purified enzyme\",\n      \"pmids\": [\"2844173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"In Schwann cells, ~80% of mu-CANP (CAPN1) activity is cytosolic while ~75% of mCANP activity is membrane-associated; Triton X-100 stimulates membrane-associated but not cytosolic CANP activity.\",\n      \"method\": \"Subcellular fractionation, DEAE and phenyl Sepharose chromatography, immunohistochemistry of permeabilized and non-permeabilized cells\",\n      \"journal\": \"Journal of neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — fractionation combined with immunohistochemical localization\",\n      \"pmids\": [\"1656060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Calpain-1 (CAPN1) knockout in mice causes cerebellar ataxia due to enhanced apoptosis of cerebellar granule cells, resulting from failure to cleave PHLPP1, which leads to inhibition of the Akt pro-survival pathway; crossing KO mice with PHLPP1 KO mice rescues granule cell density and motor coordination.\",\n      \"method\": \"Calpain-1 KO mice, genetic epistasis (double KO), neonatal Akt activator injection, cerebellar histology, apoptosis assays, synaptic transmission recording\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genetic epistasis with double KO rescue, pharmacological rescue, multiple orthogonal readouts\",\n      \"pmids\": [\"27320912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In arrhythmogenic cardiomyopathy, Ca2+ overload activates CAPN1, which associates with mitochondria and cleaves mitochondrial-bound AIF; truncated AIF translocates to the nucleus triggering DNA fragmentation and myocyte necrosis; calpastatin (CAST) overexpression protects against this pathway.\",\n      \"method\": \"Ca2+ overload in Dsg2 mutant mouse hearts, Co-IP of CAPN1 with mitochondria, CAPN1 inhibition, AIF cleavage assay, CAST overexpression, β-adrenergic stimulation of ES-CMs\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including genetic and pharmacological rescue, substrate cleavage demonstrated in multiple models\",\n      \"pmids\": [\"33597260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CAPN1 activation under cerebral ischemia impairs autophagic flux by causing lysosomal membrane permeabilization and by cleaving autophagy regulators BECN1 and ATG5, thereby suppressing autophagosome formation and contributing to neuronal death.\",\n      \"method\": \"AAV-mediated CAPN1 knockdown, pharmacological inhibition (MDL-28170) in rat MCAO model and OGD neurons, Western blot for BECN1/ATG5 cleavage, lysosomal integrity assay\",\n      \"journal\": \"Stroke\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological inhibition with substrate cleavage demonstration, single lab\",\n      \"pmids\": [\"33874744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CAPN1 binds to and degrades NF1 (neurofibromin) in melanoma cells; shRNA-mediated CAPN1 knockdown or CAPN1 inhibitor treatment stabilizes NF1 protein, downregulates AKT signaling, and reduces melanoma cell growth.\",\n      \"method\": \"Mass spectrometry interactome, shRNA knockdown, CAPN1 inhibitor treatment, Western blot for NF1 protein stability, AKT signaling assays, cell growth assays\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — MS interactome plus functional validation with KD and inhibitor, single lab\",\n      \"pmids\": [\"30131853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CAPN1 degrades PTPN1 (PTP1B) protein, and loss of PTPN1 (a dephosphorylase of c-Met and PIK3R2) leads to hyperphosphorylation of c-Met and PIK3R2, enhancing malignant behavior and erlotinib resistance in lung adenocarcinoma cells.\",\n      \"method\": \"Co-IP, cycloheximide chase assay for protein stability, CAPN1 KD, cell proliferation/migration/invasion assays\",\n      \"journal\": \"Thoracic cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP plus CHX chase plus functional KD, single lab\",\n      \"pmids\": [\"32395869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CAPN1 and CAPN2 activate a CAPN1/CAPN2-BAK/BAX-caspase-9-caspase-3-GSDME signaling axis in response to cisplatin, leading to pyroptosis in esophageal cancer cells; calpain inhibition or knockout suppresses cisplatin-induced pyroptosis.\",\n      \"method\": \"CAPN1/CAPN2 knockout, calpain activity assay, LDH release, Western blot for pathway components, cell viability assays\",\n      \"journal\": \"Chemico-biological interactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO plus pathway component Western blots establishing signaling sequence, single lab\",\n      \"pmids\": [\"35525317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CAPN1 interacts with and prevents nuclear entry of TFEB after Pseudomonas aeruginosa infection, thereby inhibiting the autophagy-lysosome pathway and promoting bacterial infection; CAPN1-deficient mice show restored autolysosome formation.\",\n      \"method\": \"Co-immunoprecipitation, pull-down assay, CAPN1 KO mice, immunofluorescence for TFEB localization, Western blot, bacterial infection models\",\n      \"journal\": \"Journal of innate immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP/pulldown plus KO rescue, single lab\",\n      \"pmids\": [\"40081346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Calpain-1 cleaves Dicer in mouse brain, generating an active Dicer fragment with RNAse III activity; CAPN1 KO mice show reduced active Dicer levels and altered neurodegeneration-related miRNA expression, which is rescued by incubation with calpain-1 and calcium.\",\n      \"method\": \"In vitro calpain-1 + Ca2+ incubation with Dicer, Western blot for Dicer cleavage products, miRNA profiling in CAPN1 KO vs. WT brain\",\n      \"journal\": \"BBA advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro cleavage assay plus KO validation, single lab\",\n      \"pmids\": [\"34286311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CAPN1 missense mutation (Cys115Tyr) in the catalytic triad abolishes enzymatic activity of calpain-1 and causes spinocerebellar ataxia in Parson Russell Terrier dogs, establishing that the catalytic Cys115 is essential for calpain-1 function in vivo.\",\n      \"method\": \"GWAS, target-enriched sequencing, identification of catalytic triad mutation; conservation analysis across species\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function mutation at catalytic residue with defined neurological phenotype\",\n      \"pmids\": [\"23741357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The transmembrane protein CD99L2 acts as an activating interactor of CAPN1; loss-of-function variants in CD99L2 abrogate its interaction with CAPN1 and impair CAPN1 activation, causing X-linked spastic ataxia; mislocalization of CD99L2 through ablation of its cytoplasmic or extracellular domains disrupts the CD99L2-CAPN1 interplay.\",\n      \"method\": \"Cellular interaction studies, genetic burden analysis in patient cohort, domain deletion constructs, transcriptome analysis in patient fibroblasts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cellular interaction studies with domain mapping plus human genetic evidence\",\n      \"pmids\": [\"41690933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In medullary thyroid cancer, CAPN1 inhibits NF1 (neurofibromin) to promote RET/RAS-AKT/ERK signaling; CAPN1 depletion or inhibition stabilizes NF1 protein levels and reduces downstream RAS activation, reducing tumor growth.\",\n      \"method\": \"Proteomic profiling, shRNA knockdown, CAPN1 inhibitor treatment, xenograft tumor model, Western blot for NF1 and downstream signaling\",\n      \"journal\": \"Thyroid\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — shRNA KD plus pharmacological inhibition plus in vivo xenograft, single lab\",\n      \"pmids\": [\"39868924\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CAPN1 (calpain-1/mu-calpain) is a Ca2+-dependent cysteine protease that requires micromolar Ca2+ for activation; its activity is regulated by autolytic NH2-terminal processing of its large subunit, membrane phospholipids (especially phosphatidylinositol), and the endogenous inhibitor calpastatin, and it cleaves a broad range of substrates including cytoskeletal proteins (fodrin, neurofilaments, MBP, MAG), signaling regulators (PHLPP1, NF1/neurofibromin, PTPN1, AIF, BECN1, ATG5, Dicer, TFEB), and pro-apoptotic/pyroptotic effectors (BAK/BAX-caspase cascade) to modulate neuronal survival, synaptic plasticity, autophagy, and cell death in both physiological and pathological contexts.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1981,\n      \"finding\": \"Limited autolysis of Ca2+-activated neutral protease (CANP/CAPN1) in the presence of Ca2+ converts the mM-Ca2+-requiring form (m-CANP) to a µM-Ca2+-requiring form (µ-CANP), demonstrating that autoproteolysis of the large subunit lowers Ca2+ sensitivity.\",\n      \"method\": \"Casein-Sepharose affinity chromatography, in vitro autolysis assay, enzymatic activity measurement\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution and activity assay, foundational observation replicated across multiple subsequent studies\",\n      \"pmids\": [\"6270080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"The active-site cysteine of CANP (CAPN1) is a class-II SH group exposed upon Ca2+ addition; E-64c and iodoacetate each incorporate stoichiometrically (1 mol/mol) into this residue, identifying it as the catalytic thiol and defining the cysteine-protease mechanism.\",\n      \"method\": \"In vitro covalent labeling with E-64c and iodoacetate, SH group titration, competitive inhibition assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis/labeling with stoichiometric incorporation and mechanistic validation\",\n      \"pmids\": [\"6309757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"µ-CANP (CAPN1) and m-CANP are biochemically distinct isoforms with different large subunit amino-acid compositions and peptide maps, different thiol-group accessibility (CAPN1 active-site thiol is exposed without Ca2+, unlike m-CANP), and different substrate specificities and cleavage products, supporting their independent identities.\",\n      \"method\": \"Concurrent purification, amino acid composition, V8 protease peptide mapping, SH group titration, substrate cleavage assays\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biochemical methods, well-controlled comparative study\",\n      \"pmids\": [\"6088474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"During substrate hydrolysis, µ-CANP (CAPN1) undergoes restricted autodigestion of its large subunit (80 kDa → 77 kDa → 76 kDa), and this limited autolysis increases its Ca2+ sensitivity, suggesting autolysis is a necessary activation step; the small subunit is degraded early but does not affect Ca2+ sensitivity.\",\n      \"method\": \"In vitro protease assay with endogenous substrates, SDS-PAGE analysis of autolysis products, Ca2+-sensitivity measurement\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with defined autolysis intermediates and functional Ca2+-sensitivity readout\",\n      \"pmids\": [\"2999095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Autolysis of CANP (CAPN1) lowers Ca2+ requirements via NH2-terminal processing of the 80 kDa large subunit; hybrid reconstitution experiments show Ca2+ sensitivity is determined solely by the structural state of the large subunit—autolysis of the small subunit has no effect on Ca2+ requirement.\",\n      \"method\": \"Limited autolysis, subunit dissociation/reconstitution, hybrid enzyme assembly, enzymatic activity assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of hybrid dimers with orthogonal subunit swapping, definitive mechanistic assignment\",\n      \"pmids\": [\"3023314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Phosphatidylinositol (PI) greatly reduces the Ca2+ requirement for autolysis of native CANP (CAPN1), but not for CANP lacking the NH2-terminal hydrophobic/glycine-rich region of the 30 kDa small subunit, identifying this domain as essential for membrane interaction and PI-mediated Ca2+ sensitization.\",\n      \"method\": \"In vitro autolysis assay with defined lipid additions, truncated small-subunit variants, Ca2+-sensitivity measurement\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro activity assay with defined domain-deletion variant and specific lipid, mechanistic conclusion directly supported\",\n      \"pmids\": [\"3011770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The E-F hand domain (four consecutive EF-hand structures) in both the large and small subunits of CANP (CAPN1) binds Ca2+ (2–4 mol per domain), with Ca2+-binding affinity of the large subunit EF-hand correlating with the Ca2+ concentration required for enzyme activation.\",\n      \"method\": \"E. coli expression of EF-hand domain fragments from cDNA, microscale filter Ca2+-binding assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution of isolated domains with quantitative Ca2+-binding measurement\",\n      \"pmids\": [\"3038855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The 30 kDa small subunit of CANP (CAPN1) has a bipartite domain structure: an NH2-terminal hydrophobic domain that determines subcellular localization, and a COOH-terminal calmodulin-like Ca2+-binding domain that regulates enzyme activity.\",\n      \"method\": \"cDNA cloning and sequence analysis, domain structure inference from mutant characterization\",\n      \"journal\": \"Biomedica biochimica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cDNA-derived structural analysis combined with functional domain data from companion studies\",\n      \"pmids\": [\"3034236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The COOH-terminal EF-hand structures of both subunits of mCANP (CAPN1) are essential for subunit association and resulting proteolytic activity; carboxypeptidase Y removal of 8–10 residues from COOH-termini under denaturing conditions abolishes subunit complex formation and activity, even upon mixing with native subunits.\",\n      \"method\": \"Carboxypeptidase Y digestion under graded denaturing conditions, subunit reassociation assay, protease activity measurement\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with defined COOH-terminal truncations, direct functional readout\",\n      \"pmids\": [\"3034871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"In retinal ganglion cell axons, CANP A (mM Ca2+-requiring, equivalent to CAPN1) can degrade >50% of axonal proteins >60 kDa within 5 min when maximally activated, with preferential action on high-MW proteins including fodrin; CANP activity is at least 6-fold greater in neurons than adjacent optic glia, implicating CAPN1 in cytoskeletal remodeling in neurons.\",\n      \"method\": \"In vitro incubation of intact axon segments at defined Ca2+ concentrations, SDS-PAGE quantification of substrate degradation, comparative neuron vs. glia fractionation\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro assay with intact cellular preparations, quantitative substrate analysis, direct localization measurement with functional consequence\",\n      \"pmids\": [\"3012012\", \"3012011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Purified µ- and m-CANP (including CAPN1) process a ~160 kDa kyotorphin-precursor protein in synaptosomal preparations, implicating CAPN1 as a neuropeptide-precursor processing enzyme in nerve terminals.\",\n      \"method\": \"Synaptosomal isolation, Sephacryl gel filtration, in vitro incubation with purified CANP, Ca2+-dependent inhibition by leupeptin/SH-blocking agents\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — purified protease incubation with defined substrate in synaptosomal context, pharmacological validation\",\n      \"pmids\": [\"2844173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Phosphatidylinositol (PI) reduces the Ca2+ requirement of brain mCANP (CAPN1) ~20-fold in a concentration-dependent manner; PI, phosphatidylserine, and diacylglycerol stimulate activity, while phosphatidylcholine is least effective; the effect is blocked by trifluoperazine, indicating phospholipid-binding is required for activation.\",\n      \"method\": \"Purified brain CANP incubated with defined lipids, [14C]azocasein assay, pharmacological inhibition\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified enzyme with defined lipid species and pharmacological validation, multiple orthogonal lipid structures tested\",\n      \"pmids\": [\"2331482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Gangliosides (GD1a, GT1a, GM1, GM2) stimulate mCANP (CAPN1) activity in a concentration-dependent manner and reduce Ca2+ requirement 10–50-fold depending on structure; GD1b is inhibitory; free N-acetylneuraminic acid, asialo-GM1, and GM3 have no effect, indicating the effect is structure-specific and not mediated by phospholipid-binding pathways (trifluoperazine-insensitive).\",\n      \"method\": \"Purified CANP incubated with defined gangliosides, azocasein assay, pharmacological comparison\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified enzyme, defined ganglioside structures, quantitative Ca2+-requirement shift, negative controls included\",\n      \"pmids\": [\"2182778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"In Schwann cells, µ-CANP (CAPN1) is predominantly cytosolic (~80%), whereas m-CANP is predominantly membrane-associated (~75%); immunofluorescence confirms cytosolic localization of µ-CANP and perinuclear/intracellular localization of m-CANP, establishing distinct compartmentalization of the two isoforms.\",\n      \"method\": \"DEAE and phenyl-Sepharose fractionation of subcellular fractions, Triton X-100 activation assay, immunofluorescence on live vs. permeabilized cells\",\n      \"journal\": \"Journal of neuroscience research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical fractionation plus immunofluorescence with functional activation data, reciprocal localization of two isoforms\",\n      \"pmids\": [\"1656060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Calpain-mediated cleavage of the CDK5 activator p35 produces p25, causing prolonged CDK5 activation and mislocalization; Ca2+ influx or excitotoxins trigger this conversion in neurons, and specific calpain inhibitors block it both in cell-free systems and in cultured neurons, identifying CAPN1-family calpain as the protease responsible for a pathological p35→p25 conversion linked to Alzheimer's-like tau hyperphosphorylation.\",\n      \"method\": \"Primary cortical neuron culture, Ca2+ ionophore/excitotoxin treatment, calpain inhibitor pharmacology, in vitro calpain cleavage assay with recombinant p35\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified calpain plus mutagenesis-level validation in cells, high citation, replicated\",\n      \"pmids\": [\"10830966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The calpain system (including µ-calpain/CAPN1 and m-calpain) are heterodimers of an 80-kDa catalytic subunit and a shared 28-kDa subunit; calpastatin inhibits both by binding to three distinct sites on the calpain molecule in a Ca2+-dependent manner at two of the three sites; structural analysis of m-calpain reveals six domains in the 80-kDa subunit (NH2-terminal sequence, IIa/IIb active site, domain III, linker, domain IV/penta-EF-hand).\",\n      \"method\": \"Crystallographic structure of m-calpain, biochemical characterization, cDNA-based domain analysis, calpastatin-binding assays\",\n      \"journal\": \"Physiological reviews\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystallographic structure plus extensive biochemical validation, >2000 citations, comprehensive review of primary data\",\n      \"pmids\": [\"12843408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Ionomycin-induced calpain (µ- and m-calpain, including CAPN1) activation cleaves Bcl-2, Bid, and Bcl-xL in vitro at single sites truncating their N-terminal regions; calpain-truncated Bcl-2 and Bid induce cytochrome c release from isolated mitochondria, identifying a calpain-mediated mechanism that triggers the intrinsic apoptotic pathway.\",\n      \"method\": \"In vitro calpain cleavage of recombinant Bcl-2 family proteins, mitochondria cytochrome c release assay, calpastatin peptide inhibition, cellular apoptosis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified proteins, mitochondrial functional assay, pharmacological inhibition\",\n      \"pmids\": [\"12000759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Calpain I (CAPN1) cleaves apoptosis-inducing factor (AIF) near its amino terminus in vitro; calpain-mediated AIF cleavage is required for AIF release from isolated mitochondria following outer membrane permeabilization by truncated Bid, and an endogenous mitochondrial calpain mediates AIF release during Ca2+-induced permeability transition.\",\n      \"method\": \"In vitro calpain I cleavage of recombinant AIF, isolated mitochondria release assay, calpeptin pharmacological inhibition, lipid vesicle binding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution, isolated organelle functional assay, pharmacological validation\",\n      \"pmids\": [\"15590628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Calpain-mediated cleavage of Atg5 generates a 24-kDa truncated fragment that translocates from cytosol to mitochondria, associates with Bcl-xL, and triggers cytochrome c release and caspase activation, providing a molecular link by which CAPN1-family calpains switch autophagy to apoptosis.\",\n      \"method\": \"In vitro calpain cleavage assay, subcellular fractionation, co-immunoprecipitation, overexpression/siRNA in tumor cells, xenograft model\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro cleavage reconstitution plus cellular epistasis with siRNA and overexpression, in vivo xenograft validation\",\n      \"pmids\": [\"16998475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Calpain-1 (CAPN1) KO mice display cerebellar ataxia with enhanced granule cell apoptosis due to failure to cleave PHLPP1, which prevents Akt pro-survival signaling in developing granule cells; crossing CAPN1-KO with PHLPP1-KO mice or injecting bisperoxovanadium (indirect Akt activator) rescues granule cell density and motor coordination, placing CAPN1 upstream of PHLPP1 in an Akt-dependent neuroprotective pathway.\",\n      \"method\": \"CAPN1 KO mouse model, CAPN1/PHLPP1 double-KO epistasis, bisperoxovanadium injection, Western blotting for PHLPP1 cleavage, cerebellar histology, behavioral motor testing\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype, genetic epistasis by double-KO rescue, pharmacological rescue, mechanistic substrate identification\",\n      \"pmids\": [\"27320912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CAPN1 is a novel binding partner of the tumor suppressor NF1 in melanoma; shRNA-mediated knockdown or pharmacological inhibition of CAPN1 stabilizes NF1 protein levels, downregulates AKT signaling, and reduces melanoma cell growth, identifying CAPN1 as a protease that degrades NF1 to promote RAS activation.\",\n      \"method\": \"Mass spectrometry of NF1 binding partners, shRNA knockdown, calpain inhibitor treatment, protein stability assay, cell growth assay\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS-identified interaction plus functional KD with defined signaling readout, single lab\",\n      \"pmids\": [\"30131853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In arrhythmogenic cardiomyopathy (ACM), Ca2+ overload activates CAPN1, which associates with mitochondria and cleaves mitochondria-bound AIF; cleaved AIF translocates to the nucleus causing large-scale DNA fragmentation and necrosis; overexpression of calpastatin (CAST) protects against Ca2+-overload-induced necrosis, and CAPN1 inhibition attenuates AIF truncation in stem cell-derived cardiomyocytes.\",\n      \"method\": \"Dsg2 mut/mut mouse model, calcium measurement, CAPN1-mitochondria co-fractionation, Western blot for AIF cleavage, CAST overexpression, embryonic stem cell-derived cardiomyocyte model, pharmacological CAPN1 inhibition\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo mouse model plus stem-cell model, direct CAPN1-mitochondria localization assay, gain-of-function rescue with CAST, pharmacological confirmation\",\n      \"pmids\": [\"33597260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CAPN1 activation during cerebral ischemia impairs autophagic flux by causing lysosomal membrane permeabilization and by cleaving autophagy regulators BECN1 (Beclin1) and ATG5, thereby suppressing autophagosome formation and promoting neuronal death; genetic and pharmacological CAPN1 inhibition rescues both lysosomal integrity and autophagosome formation.\",\n      \"method\": \"AAV-mediated CAPN1 knockdown, MDL-28170 pharmacological inhibition, rat MCAO in vivo model, oxygen-glucose deprivation in vitro model, lysosomal permeabilization assay, Western blot for BECN1/ATG5 cleavage\",\n      \"journal\": \"Stroke\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KD plus pharmacological inhibition in two independent models, defined molecular substrates identified\",\n      \"pmids\": [\"33874744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CAPN1 degrades PTPN1 (a protein tyrosine phosphatase), thereby allowing sustained phosphorylation of c-Met and PIK3R2 and promoting proliferation, metastasis, and erlotinib resistance in lung adenocarcinoma; Co-IP confirmed PTPN1–c-Met and PTPN1–PIK3R2 interactions, and cycloheximide chase showed CAPN1-dependent PTPN1 protein degradation.\",\n      \"method\": \"Co-immunoprecipitation, cycloheximide chase, siRNA knockdown, cell proliferation/invasion assays, CHX protein stability assay\",\n      \"journal\": \"Thoracic cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP plus protein stability assay, single lab\",\n      \"pmids\": [\"32395869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cisplatin activates calpain (including CAPN1) in esophageal cancer cells; mechanistically, activated CAPN1/CAPN2 promote BAK/BAX activation, leading to caspase-9 → caspase-3 → GSDME cleavage and pyroptosis; calpain inhibition or knockout suppresses this cascade.\",\n      \"method\": \"Calpain activity assay, calpain KO/inhibition, Western blotting for pathway components, LDH release assay, cell viability assay\",\n      \"journal\": \"Chemico-biological interactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO/inhibitor experiments with defined pathway readout, single lab\",\n      \"pmids\": [\"35525317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Calpain-1 (CAPN1) cleaves Dicer near its active site in mouse brain, generating an active Dicer fragment with RNAse III activity; in CAPN1-KO mice, active Dicer levels are reduced and neurodegeneration-related miRNAs are downregulated; incubation of KO brain homogenates with purified calpain-1 plus Ca2+ restores Dicer activity and miRNA expression.\",\n      \"method\": \"CAPN1 KO mouse brain analysis, Western blot for Dicer cleavage products, in vitro calpain-1 + Ca2+ incubation assay, miRNA profiling\",\n      \"journal\": \"BBA advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro cleavage reconstitution and KO rescue, but single lab and limited mechanistic follow-up on individual miRNAs\",\n      \"pmids\": [\"34286311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CAPN1 interacts with and prevents nuclear translocation of TFEB after Pseudomonas aeruginosa infection, thereby inhibiting the autophagy-lysosome pathway; Co-IP and pull-down confirmed the CAPN1–TFEB interaction, and CAPN1-deficient mice reversed PAK-induced suppression of autolysosomes.\",\n      \"method\": \"Co-immunoprecipitation, pull-down, CAPN1-KO mouse model, immunofluorescence for TFEB localization, Western blot\",\n      \"journal\": \"Journal of innate immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP/pull-down with KO validation in vivo, single lab\",\n      \"pmids\": [\"40081346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CAPN1 inhibits NF1 (neurofibromin 1) in medullary thyroid cancer (MTC), reducing NF1 protein levels and sustaining RAS/RET → AKT/ERK signaling; CAPN1 inhibitors stabilize NF1 and reduce MTC xenograft growth, consistent with the melanoma-derived finding that CAPN1 degrades NF1.\",\n      \"method\": \"Proteomic profiling, shRNA depletion, CAPN1 inhibitor treatment, NF1 protein stability assay, xenograft tumor growth, Western blotting for AKT/ERK\",\n      \"journal\": \"Thyroid\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD plus inhibitor in multiple cell lines and in vivo xenograft, mechanistic pathway readout, replicates NF1-degradation finding from melanoma study\",\n      \"pmids\": [\"39868924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The transmembrane protein CD99L2 serves as an activating interactor of CAPN1; loss-of-function variants in CD99L2 cause X-linked spastic ataxia, and cellular studies show CD99L2 exists mainly in ubiquitinated form and its cytoplasmic or extracellular domain ablation leads to intracellular mislocalization and abrogation of its CAPN1-activating interaction.\",\n      \"method\": \"Exome/genome sequencing, gene-burden analysis, Co-IP of CD99L2–CAPN1 interaction, domain-deletion constructs, immunofluorescence for localization, transcriptome analysis in patient fibroblasts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction confirmed plus domain-deletion functional analysis, but single study\",\n      \"pmids\": [\"41690933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Dexamethasone downregulates CAST and upregulates CAPN1 in bone marrow mesenchymal stem cells, inhibiting osteogenic differentiation and ATP activity (via ATP5A1 reduction); overexpression of CAST partially rescues osteogenesis while overexpression of CAPN1 exacerbates it, placing CAPN1 downstream of calpastatin in a DEX-regulated osteogenic pathway.\",\n      \"method\": \"qRT-PCR, Western blotting, overexpression plasmids, Alizarin Red S staining, ELISA for ATP/osteogenic markers\",\n      \"journal\": \"Discovery medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — overexpression experiments without substrate-level mechanistic resolution, single lab\",\n      \"pmids\": [\"40116104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Ca2+ ions cause dissociation of the CAPN1 heterodimer into subunits, and the resulting free 80 kDa large subunit constitutes the active catalytic form of the enzyme; this dissociation represents the activation mechanism.\",\n      \"method\": \"Biochemical dissociation/reassociation experiments, activity assay of isolated subunits\",\n      \"journal\": \"Biological chemistry Hoppe-Seyler\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution, foundational mechanism replicated across multiple studies\",\n      \"pmids\": [\"8561910\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CAPN1 (µ-calpain) is a Ca2+-activated heterodimeric cysteine protease composed of an 80-kDa catalytic large subunit (containing a Cys-protease active site, EF-hand Ca2+-binding domain, and membrane-interaction domains) and a shared 28-kDa small subunit; Ca2+ binding to EF-hand domains triggers subunit dissociation to generate the active 80-kDa form, which undergoes limited N-terminal autolysis to lower its Ca2+ requirement from mM to µM range; phosphatidylinositol and specific gangliosides at the membrane further reduce the Ca2+ threshold; active CAPN1 cleaves a defined set of substrates including PHLPP1 (promoting Akt-dependent neuronal survival), AIF (triggering mitochondria-to-nucleus translocation and necrosis), Beclin1/ATG5 (switching autophagy to apoptosis), p35 (generating the CDK5-activating p25 fragment linked to Alzheimer's-like tau hyperphosphorylation), NF1/neurofibromin (sustaining RAS activation in cancer), Bcl-2 family members, and TFEB (preventing autophagy-lysosome pathway activation); the endogenous inhibitor calpastatin binds three sites on the calpain molecule in a Ca2+-dependent manner; the activating membrane protein CD99L2 is a newly identified regulatory interactor required for full CAPN1 activation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CAPN1 (calpain-1/µ-calpain) is a Ca²⁺-dependent cysteine protease that functions as a heterodimer of a catalytic large subunit and a regulatory small subunit, cleaving diverse substrates to regulate neuronal survival, cytoskeletal remodeling, autophagy, and cell death. Ca²⁺ binding to EF-hand domains on both subunits activates the enzyme, and autolytic processing of the large subunit's NH₂-terminus shifts the Ca²⁺ requirement from millimolar to micromolar concentrations, while membrane phosphatidylinositol further lowers this threshold [PMID:6270080, PMID:3023314, PMID:3011770]. CAPN1 cleaves cytoskeletal proteins (fodrin, neurofilaments), signaling regulators (PHLPP1, NF1, PTPN1, TFEB, Dicer), and pro-apoptotic effectors (AIF, BECN1, ATG5, BAK/BAX), thereby controlling Akt survival signaling in cerebellar neurons, autophagic flux, miRNA biogenesis, and pyroptotic cell death [PMID:27320912, PMID:33874744, PMID:34286311, PMID:35525317]. Loss-of-function mutations in CAPN1 cause cerebellar ataxia in mice and dogs, and disruption of the CAPN1-activating interactor CD99L2 causes X-linked spastic ataxia in humans [PMID:27320912, PMID:23741357, PMID:41690933].\",\n  \"teleology\": [\n    {\n      \"year\": 1981,\n      \"claim\": \"Established that CAPN1 undergoes Ca²⁺-dependent autolysis that converts the enzyme from a high-Ca²⁺ to a low-Ca²⁺ form, revealing autoproteolytic regulation of its own activation threshold.\",\n      \"evidence\": \"In vitro autolysis assay with casein-Sepharose chromatography and Ca²⁺ titration\",\n      \"pmids\": [\"6270080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Autolysis site(s) not mapped at residue level\", \"Physiological relevance of autolysis in intact cells not demonstrated\"]\n    },\n    {\n      \"year\": 1983,\n      \"claim\": \"Demonstrated that CAPN1 is a cysteine protease with a single catalytic sulfhydryl that is exposed upon Ca²⁺ binding, defining its catalytic mechanism.\",\n      \"evidence\": \"Stoichiometric active-site labeling with E64c and iodoacetic acid, inhibitor competition\",\n      \"pmids\": [\"6309757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of catalytic residue inferred but not confirmed by mutagenesis at that time\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Resolved the structural basis of Ca²⁺ sensitivity regulation: autolysis of the large subunit's NH₂-terminus (not the small subunit) reduces Ca²⁺ requirement, while the small subunit's NH₂-terminal hydrophobic domain mediates phosphatidylinositol-dependent lowering of the Ca²⁺ threshold, establishing a dual membrane-and-autolysis regulatory mechanism.\",\n      \"evidence\": \"Hybrid enzyme reconstitution with autolyzed/intact subunits; phosphatidylinositol supplementation with domain-trimmed small subunit\",\n      \"pmids\": [\"3023314\", \"3011770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Membrane interaction mechanism at atomic resolution unknown\", \"In vivo membrane-dependent activation not shown\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"Showed that EF-hand domains on both subunits directly bind Ca²⁺ and are required for heterodimer assembly and catalytic activity, establishing the structural determinants of Ca²⁺ sensing.\",\n      \"evidence\": \"Recombinant EF-hand domain expression in E. coli with Ca²⁺ binding assay; carboxypeptidase Y trimming of C-termini abolishing subunit association\",\n      \"pmids\": [\"3038855\", \"3034871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Number of functional Ca²⁺ sites per subunit not precisely determined\", \"Cooperativity of Ca²⁺ binding not resolved\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Identified the first neuronal substrates of CAPN1—fodrin (brain spectrin) and the 145 kDa neurofilament subunit—showing that calpain performs limited, posttranslational cleavage rather than complete degradation, implicating it in cytoskeletal remodeling.\",\n      \"evidence\": \"In vitro incubation of intact retinal ganglion cell axons and optic glia; substrate processing assays\",\n      \"pmids\": [\"3012011\", \"3012012\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of neurofilament/fodrin cleavage on axonal physiology not established\", \"Distinction between CAPN1 and CAPN2 contributions in situ uncertain\"]\n    },\n    {\n      \"year\": 1984,\n      \"claim\": \"Extended CAPN1 substrate repertoire to myelin components—MBP and MAG—suggesting a role in demyelination processes.\",\n      \"evidence\": \"Ca²⁺-dependent processing of purified human myelin proteins inhibited by E-64 and EGTA\",\n      \"pmids\": [\"6206410\", \"6197665\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo demyelination role not demonstrated\", \"Isoform specificity (CAPN1 vs CAPN2) not resolved for myelin substrates\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A loss-of-function mutation at the catalytic Cys115 in CAPN1 causes spinocerebellar ataxia in dogs, providing the first genetic evidence that CAPN1 catalytic activity is essential for cerebellar function in vivo.\",\n      \"evidence\": \"GWAS and targeted sequencing in Parson Russell Terriers identifying C115Y catalytic triad mutation\",\n      \"pmids\": [\"23741357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No enzymatic activity assay on the mutant protein performed\", \"Mechanism connecting loss of calpain-1 to Purkinje/granule cell degeneration unknown at this point\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established CAPN1's neuroprotective role: CAPN1 knockout mice develop cerebellar ataxia because failure to cleave PHLPP1 leads to Akt pathway suppression and granule cell apoptosis; genetic removal of PHLPP1 rescues the phenotype, providing epistatic proof of this substrate axis.\",\n      \"evidence\": \"Calpain-1 KO mice, calpain-1/PHLPP1 double KO rescue, neonatal Akt activator injection, cerebellar histology and electrophysiology\",\n      \"pmids\": [\"27320912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other substrates contribute to the cerebellar phenotype not excluded\", \"Temporal dynamics of PHLPP1 cleavage during development not mapped\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that CAPN1 degrades the tumor suppressor NF1 (neurofibromin), linking calpain-1 to oncogenic RAS-AKT signaling in melanoma.\",\n      \"evidence\": \"Mass spectrometry interactome, shRNA knockdown, pharmacological inhibition stabilizing NF1\",\n      \"pmids\": [\"30131853\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cleavage site in NF1 not mapped\", \"Independent replication in non-melanoma context not available at that time\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended CAPN1 signaling-substrate repertoire to PTPN1 (PTP1B), whose degradation by CAPN1 hyperactivates c-Met and PIK3R2 phosphorylation, promoting drug resistance in lung cancer.\",\n      \"evidence\": \"Co-IP, cycloheximide chase, CAPN1 knockdown in lung adenocarcinoma cells\",\n      \"pmids\": [\"32395869\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct cleavage site not mapped\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed that CAPN1 mediates cardiomyocyte death in arrhythmogenic cardiomyopathy by cleaving mitochondrial AIF, whose truncated form translocates to the nucleus to trigger DNA fragmentation; calpastatin overexpression is protective.\",\n      \"evidence\": \"Dsg2 mutant mouse hearts, Co-IP of CAPN1 with mitochondria, calpastatin overexpression rescue, AIF cleavage assays\",\n      \"pmids\": [\"33597260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of CAPN1 recruitment to mitochondria not defined\", \"Relative contribution vs CAPN2 unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated that ischemia-activated CAPN1 impairs autophagic flux by cleaving BECN1 and ATG5 and permeabilizing lysosomes, establishing CAPN1 as a negative regulator of protective autophagy in neurons.\",\n      \"evidence\": \"AAV-mediated CAPN1 knockdown and MDL-28170 inhibition in rat MCAO stroke model and OGD neurons\",\n      \"pmids\": [\"33874744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cleavage sites in BECN1/ATG5 not mapped\", \"Whether CAPN1 directly permeabilizes lysosomes or acts indirectly unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed that CAPN1 cleaves Dicer in mouse brain to generate an active RNase III fragment, regulating miRNA biogenesis relevant to neurodegeneration.\",\n      \"evidence\": \"In vitro calpain-1/Ca²⁺ cleavage of Dicer, miRNA profiling in CAPN1 KO vs WT brain\",\n      \"pmids\": [\"34286311\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cleavage site in Dicer not precisely mapped\", \"Functional consequence on specific miRNA targets not fully characterized\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a CAPN1/CAPN2–BAK/BAX–caspase-9–caspase-3–GSDME signaling axis through which cisplatin triggers pyroptosis, extending CAPN1's role beyond apoptosis to inflammatory cell death.\",\n      \"evidence\": \"CAPN1/CAPN2 knockout in esophageal cancer cells, LDH release, Western blot for pathway components\",\n      \"pmids\": [\"35525317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CAPN1 directly cleaves BAK/BAX or acts indirectly not resolved\", \"Relative contributions of CAPN1 vs CAPN2 not fully separated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed that CAPN1 interacts with TFEB to prevent its nuclear translocation, thereby suppressing the autophagy-lysosome pathway during bacterial infection; CAPN1 KO restores autolysosome formation and bacterial clearance.\",\n      \"evidence\": \"Co-IP and pull-down in Pseudomonas-infected cells, CAPN1 KO mice, immunofluorescence for TFEB\",\n      \"pmids\": [\"40081346\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CAPN1 cleaves TFEB or sequesters it through binding alone not fully resolved\", \"Generalizability to other bacterial infections untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Independently confirmed NF1 as a CAPN1 substrate in medullary thyroid cancer, showing CAPN1 depletion stabilizes NF1 and suppresses RET/RAS-AKT/ERK tumor growth in vivo.\",\n      \"evidence\": \"Proteomic profiling, shRNA knockdown, pharmacological inhibition, xenograft tumor model\",\n      \"pmids\": [\"39868924\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct cleavage site in NF1 still not mapped\", \"Whether other calpain isoforms also target NF1 in thyroid cancer not tested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified CD99L2 as a transmembrane activating partner of CAPN1 whose loss-of-function causes X-linked spastic ataxia, revealing a previously unknown upstream regulatory input to CAPN1 activation at the cell membrane.\",\n      \"evidence\": \"Cellular interaction studies, domain deletion constructs, genetic burden analysis in patient cohort\",\n      \"pmids\": [\"41690933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biochemical mechanism by which CD99L2 activates CAPN1 not defined\", \"Whether CD99L2 affects CAPN1 Ca²⁺ sensitivity or membrane recruitment not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the precise structural basis of Ca²⁺-induced active-site exposure in the full-length heterodimer, the cleavage sites in most identified substrates, the mechanism by which CD99L2 activates CAPN1, and whether CAPN1 and CAPN2 have fully distinct or overlapping substrate repertoires in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length heterodimer structure with Ca²⁺-bound transition state\", \"Cleavage sites unmapped for PHLPP1, NF1, PTPN1, BECN1, ATG5, TFEB, Dicer\", \"In vivo isoform-specific substrate profiling not performed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3, 7, 8, 10, 14, 15, 16, 17, 18, 19, 21, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [14, 15, 19]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [16, 20]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 17, 18, 24]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [7, 8, 14, 22]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CAPNS1\",\n      \"PHLPP1\",\n      \"NF1\",\n      \"AIF\",\n      \"TFEB\",\n      \"CD99L2\",\n      \"PTPN1\",\n      \"DICER1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CAPN1 (calpain-1/µ-calpain catalytic subunit) is a Ca²⁺-activated cysteine protease that functions as a heterodimer with a shared 28-kDa small subunit (CAPNS1) and cleaves a broad range of intracellular substrates to regulate neuronal survival, apoptosis, autophagy, and signal transduction. Ca²⁺ binding to EF-hand domains in both subunits triggers heterodimer dissociation, releasing the active 80-kDa large subunit, which undergoes limited N-terminal autolysis to lower its Ca²⁺ requirement from millimolar to micromolar concentrations; membrane phospholipids (phosphatidylinositol, phosphatidylserine) and specific gangliosides further reduce this threshold [PMID:6270080, PMID:3023314, PMID:8561910, PMID:2331482, PMID:2182778]. CAPN1 proteolytically processes substrates including p35 (generating the CDK5-hyperactivating p25 fragment implicated in tauopathy), PHLPP1 (enabling Akt-dependent neuroprotection), AIF (triggering necrotic DNA fragmentation), Bcl-2/Bid (activating intrinsic apoptosis), Beclin-1/ATG5 (switching autophagy to apoptosis), NF1/neurofibromin (sustaining RAS-AKT signaling in cancer), TFEB (suppressing the autophagy–lysosome pathway), and Dicer (generating an active RNase III fragment that modulates miRNA levels) [PMID:10830966, PMID:27320912, PMID:15590628, PMID:12000759, PMID:16998475, PMID:33874744, PMID:30131853, PMID:40081346, PMID:34286311]. CAPN1-knockout mice develop cerebellar ataxia with granule-cell apoptosis rescuable by concomitant PHLPP1 deletion, and loss-of-function variants in CD99L2, a newly identified CAPN1-activating transmembrane interactor, cause X-linked spastic ataxia [PMID:27320912, PMID:41690933].\",\n  \"teleology\": [\n    {\n      \"year\": 1981,\n      \"claim\": \"The question of how CAPN1 achieves physiological activation despite its millimolar Ca²⁺ requirement was answered by the discovery that limited N-terminal autolysis of the large subunit converts the enzyme to a micromolar-Ca²⁺-requiring form, establishing autolysis as a key activation step.\",\n      \"evidence\": \"In vitro autolysis assay with purified CANP, activity measurement at graded Ca²⁺\",\n      \"pmids\": [\"6270080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Autolysis sites on the large subunit were not yet mapped\", \"Whether autolysis occurs in intact cells was unknown\"]\n    },\n    {\n      \"year\": 1983,\n      \"claim\": \"Identification of the catalytic mechanism was achieved by stoichiometric covalent labeling of a single active-site cysteine with E-64c and iodoacetate, definitively classifying CAPN1 as a cysteine protease.\",\n      \"evidence\": \"SH-group titration and competitive covalent inhibitor incorporation at 1:1 stoichiometry\",\n      \"pmids\": [\"6309757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional structure of the active site was unknown\", \"Catalytic residue identity awaited sequencing\"]\n    },\n    {\n      \"year\": 1984,\n      \"claim\": \"The biochemical distinctness of µ-calpain (CAPN1) and m-calpain was established through differences in amino-acid composition, peptide maps, thiol accessibility, and substrate specificity, resolving ambiguity about whether they were the same enzyme.\",\n      \"evidence\": \"Concurrent purification, V8 peptide mapping, SH titration, substrate cleavage comparison\",\n      \"pmids\": [\"6088474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Gene-level identity of the two isoforms was not yet determined\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"The structural basis of Ca²⁺ sensing was established: EF-hand domains in both subunits bind Ca²⁺, the large-subunit EF-hand Ca²⁺ affinity determines activation threshold, and hybrid reconstitution proved that autolysis of the large subunit alone governs Ca²⁺ sensitivity; membrane lipids (phosphatidylinositol) further reduce the Ca²⁺ requirement via the small subunit's N-terminal hydrophobic domain.\",\n      \"evidence\": \"Recombinant EF-hand domain Ca²⁺-binding assay, hybrid subunit reconstitution, PI-dependent autolysis assay with domain-truncated small subunit\",\n      \"pmids\": [\"3038855\", \"3023314\", \"3011770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise stoichiometry of Ca²⁺ binding per EF-hand was approximate\", \"In vivo membrane-translocation kinetics were unknown\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"CAPN1's neuronal function was first demonstrated: axonal CAPN1 rapidly degrades high-MW cytoskeletal proteins including fodrin, with 6-fold higher activity in neurons than glia, establishing CAPN1 as a major neuronal cytoskeletal remodeling enzyme.\",\n      \"evidence\": \"Intact retinal axon segment incubation at defined Ca²⁺, SDS-PAGE quantification, neuron vs. glia fractionation\",\n      \"pmids\": [\"3012012\", \"3012011\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific neuronal substrates beyond fodrin were unidentified\", \"In vivo activation signals in neurons were unknown\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"The requirement of C-terminal EF-hand structures for heterodimer assembly was demonstrated: removal of 8–10 C-terminal residues from either subunit abolishes complex formation and activity, explaining how the penta-EF-hand domain mediates obligate dimerization.\",\n      \"evidence\": \"Carboxypeptidase Y digestion under denaturing conditions, subunit reassociation and activity assay\",\n      \"pmids\": [\"3034871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution contacts at the dimerization interface were unknown\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"The lipid-activation landscape was broadened beyond phospholipids: specific gangliosides (GD1a, GT1a, GM1) reduce CAPN1 Ca²⁺ requirement 10–50-fold through a pathway distinct from phospholipid-mediated activation, while GD1b is inhibitory, revealing structure-specific glycolipid regulation.\",\n      \"evidence\": \"Purified enzyme with defined ganglioside species, azocasein assay, trifluoperazine insensitivity\",\n      \"pmids\": [\"2182778\", \"2331482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ganglioside-binding site on calpain was unmapped\", \"Physiological relevance at endogenous ganglioside concentrations was untested\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The activation mechanism was refined: Ca²⁺ causes dissociation of the CAPN1 heterodimer, and the free 80-kDa large subunit is the active catalytic species, establishing subunit dissociation as the proximal activation event.\",\n      \"evidence\": \"Biochemical dissociation/reassociation, activity assay of isolated subunits\",\n      \"pmids\": [\"8561910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether dissociation is reversible in vivo was unclear\", \"Fate of the released small subunit was unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The first disease-relevant substrate was identified: calpain cleaves the CDK5 activator p35 to p25, causing CDK5 mislocalization and prolonged activation leading to tau hyperphosphorylation, directly linking CAPN1 to Alzheimer's-related neurodegeneration.\",\n      \"evidence\": \"Primary cortical neurons with Ca²⁺ ionophore/excitotoxin, calpain inhibitor pharmacology, in vitro cleavage of recombinant p35\",\n      \"pmids\": [\"10830966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which calpain isoform (µ vs. m) is dominant in vivo for p35 cleavage was unresolved\", \"Therapeutic window for calpain inhibition in neurodegeneration was undefined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"CAPN1 was placed at a decision point between survival and apoptosis: calpain cleaves Bcl-2, Bid, and Bcl-xL at single N-terminal sites, and the truncated products trigger mitochondrial cytochrome c release, establishing calpain as a direct activator of the intrinsic apoptotic pathway.\",\n      \"evidence\": \"In vitro calpain cleavage of recombinant Bcl-2 family members, isolated mitochondria cytochrome c release assay\",\n      \"pmids\": [\"12000759\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of calpain vs. caspase-8 in Bid cleavage under physiological conditions was unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Calpain-1 was shown to process AIF near its N-terminus, releasing it from mitochondria to trigger caspase-independent necrotic DNA fragmentation — extending calpain's role beyond apoptosis to necrosis.\",\n      \"evidence\": \"In vitro CAPN1 cleavage of recombinant AIF, isolated mitochondria release assay with tBid permeabilization, calpeptin inhibition\",\n      \"pmids\": [\"15590628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mitochondrial calpain is CAPN1 specifically or another isoform was not definitively resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The autophagy-to-apoptosis switch mechanism was identified: calpain cleaves ATG5 to generate a 24-kDa fragment that translocates to mitochondria, binds Bcl-xL, and triggers cytochrome c release, explaining how calpain activation terminates protective autophagy.\",\n      \"evidence\": \"In vitro cleavage, subcellular fractionation, Co-IP of truncated ATG5 with Bcl-xL, siRNA epistasis, xenograft model\",\n      \"pmids\": [\"16998475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ATG5 cleavage site was not mapped at single-residue resolution\", \"Isoform specificity for ATG5 cleavage was not determined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"CAPN1 was established as essential for cerebellar development and neuronal survival: CAPN1-KO mice exhibit cerebellar ataxia due to granule cell apoptosis from failure to cleave PHLPP1, blocking Akt signaling; double-KO with PHLPP1 rescues the phenotype, placing CAPN1 in a defined neuroprotective PHLPP1–Akt axis.\",\n      \"evidence\": \"CAPN1-KO and CAPN1/PHLPP1 double-KO mice, bisperoxovanadium rescue, cerebellar histology, behavioral motor testing\",\n      \"pmids\": [\"27320912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional calpain-1 substrates contribute to the ataxia phenotype was unknown\", \"Human ataxia patients with CAPN1 loss-of-function were not yet characterized in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"CAPN1's oncogenic role was defined: CAPN1 degrades the tumor suppressor NF1, sustaining RAS-AKT signaling and promoting melanoma cell growth — the first demonstration of CAPN1 as a targetable protease in RAS-driven cancer.\",\n      \"evidence\": \"Mass spectrometry of NF1 interactors, shRNA knockdown, calpain inhibitor, protein stability assay in melanoma cells\",\n      \"pmids\": [\"30131853\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"NF1 cleavage site by CAPN1 was not mapped\", \"Selectivity for CAPN1 vs. CAPN2 in NF1 degradation was not tested\", \"Awaits independent replication\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Multiple studies converged to demonstrate CAPN1's pathological roles in ischemia and cardiomyopathy: CAPN1 cleaves BECN1/ATG5 and permeabilizes lysosomes during cerebral ischemia, while in arrhythmogenic cardiomyopathy CAPN1 associates with mitochondria and cleaves AIF to trigger necrosis — both rescuable by CAPN1 inhibition or calpastatin overexpression.\",\n      \"evidence\": \"Rat MCAO model with AAV-CAPN1 KD, Dsg2 mutant mouse model, stem cell-derived cardiomyocytes, calpastatin overexpression, pharmacological inhibition\",\n      \"pmids\": [\"33874744\", \"33597260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of CAPN1 vs. CAPN2 in ischemic AIF cleavage was not resolved\", \"Whether calpastatin gene therapy is viable in clinical settings was untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CAPN1's role was extended to RNA regulation: CAPN1 cleaves Dicer near its active site in brain, generating an active RNase III fragment that sustains neurodegeneration-related miRNA biogenesis; CAPN1-KO mice show reduced active Dicer and altered miRNA profiles.\",\n      \"evidence\": \"CAPN1-KO mouse brain, in vitro calpain-1 + Ca²⁺ rescue of Dicer activity, miRNA profiling\",\n      \"pmids\": [\"34286311\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cleavage site on Dicer was not precisely mapped\", \"Which specific miRNAs are functionally rate-limited by CAPN1-Dicer processing was not resolved\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"CAPN1 was linked to innate immunity and autophagy suppression: CAPN1 interacts with and prevents nuclear translocation of TFEB during Pseudomonas infection, suppressing the autophagy-lysosome pathway; CAPN1-deficient mice restore autolysosome formation.\",\n      \"evidence\": \"Co-IP and pull-down of CAPN1–TFEB, CAPN1-KO mouse infection model, immunofluorescence for TFEB localization\",\n      \"pmids\": [\"40081346\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CAPN1 cleaves TFEB or sequesters it was not distinguished\", \"Generalizability to other bacterial infections was untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"NF1 degradation by CAPN1 was independently replicated in medullary thyroid cancer, and CD99L2 was identified as a transmembrane activating partner of CAPN1 whose loss-of-function causes X-linked spastic ataxia, establishing the first genetically defined upstream regulator of CAPN1 activation.\",\n      \"evidence\": \"Xenograft models with CAPN1 inhibitors (MTC); exome sequencing, Co-IP, domain-deletion constructs for CD99L2–CAPN1 interaction\",\n      \"pmids\": [\"39868924\", \"41690933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which CD99L2 activates CAPN1 (Ca²⁺-independent? conformational?) is unknown\", \"Whether CD99L2 loss phenocopies CAPN1 KO at the molecular substrate level was not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of isoform-specific substrate recognition, the full in vivo substrate repertoire of CAPN1 versus CAPN2, the mechanism by which CD99L2 activates CAPN1, and whether therapeutic calpain-1 inhibition can selectively target pathological cleavage events without disrupting neuroprotective PHLPP1 processing.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No co-crystal structure of CAPN1 with a substrate or CD99L2\", \"Isoform-selective inhibitors have not been characterized in clinical studies\", \"Relative in vivo contributions of CAPN1 vs. CAPN2 for shared substrates remain unmapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 14, 16, 17, 18, 19, 22, 25]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 9, 10, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [13, 30]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [17, 21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [16, 17, 18, 24]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [18, 22, 26]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [19, 20, 27]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [9, 14, 19]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 3, 4, 15]}\n    ],\n    \"complexes\": [\n      \"µ-calpain heterodimer (CAPN1/CAPNS1)\"\n    ],\n    \"partners\": [\n      \"CAPNS1\",\n      \"CAST\",\n      \"CD99L2\",\n      \"TFEB\",\n      \"NF1\",\n      \"PHLPP1\",\n      \"AIF\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}