{"gene":"CTSA","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":1988,"finding":"The cDNA encoding human 'protective protein' (PPCA/CTSA) was isolated, revealing a 452 amino acid precursor that is processed into a mature heterodimer of 32 kDa and 20 kDa polypeptides held by disulfide bridges. The predicted amino acid sequence showed homology to yeast carboxypeptidase Y and the KEX1 gene product, suggesting serine carboxypeptidase activity. The mature protein restores β-galactosidase and neuraminidase activities in galactosialidosis cells, establishing its protective function.","method":"cDNA cloning, in vivo expression in galactosialidosis fibroblasts (functional rescue), sequence homology analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — original cloning with functional rescue, replicated across subsequent studies","pmids":["3136930"],"is_preprint":false},{"year":1985,"finding":"Human lysosomal neuraminidase activity is activated and stabilized only when in a high-density multimeric complex with β-galactosidase, and the 32 kDa protective protein (PPCA/CTSA) is present in this complex. Immunotitration with monospecific antibodies against the protective protein demonstrated that it is essential for the catalytic activity of lysosomal neuraminidase, explaining the combined neuraminidase and β-galactosidase deficiency in galactosialidosis.","method":"β-galactosidase affinity chromatography, immunotitration with monospecific antibodies, sucrose density gradient centrifugation","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal biochemical methods demonstrating complex formation and functional requirement","pmids":["3922758"],"is_preprint":false},{"year":1991,"finding":"The protective protein/PPCA has enzymatic activity identical to lysosomal cathepsin A (serine carboxypeptidase). Overexpression increases cathepsin A-like activity 3–4 fold; galactosialidosis patient extracts have ~1% activity; monospecific antibodies precipitate virtually all cathepsin A-like activity from normal fibroblasts. Active-site mutagenesis of serine and histidine residues abolishes enzymatic activity but does not affect intracellular routing, processing, or protective function for β-galactosidase/neuraminidase. A Cys60 mutation interferes with precursor folding and intracellular transport. This demonstrates that catalytic activity and protective function are distinct properties of the same protein.","method":"Overexpression in COS-1 cells, enzyme activity assays, monospecific antibody immunoprecipitation, active-site mutagenesis (Ser, His, Cys60)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis plus reconstitution plus functional dissection, multiple orthogonal methods in single study","pmids":["1907282"],"is_preprint":false},{"year":1990,"finding":"A peptidase purified from human platelets (released by thrombin) that deamidates tachykinins (substance P, neurokinin A) and acts as a carboxypeptidase on bradykinin and angiotensin I was shown to be identical to the lysosomal protective protein (PPCA/CTSA). N-terminal sequencing of both chains matched protective protein sequences. The enzyme is a disulfide-linked dimer (32 kDa + 21 kDa chains), inhibited by DFP (active-site serine labeled), with pH optima differing for peptidase (~5.0) vs. esterase/deamidase (~7.0) activities, establishing a role for PPCA in extracellular/platelet peptide metabolism.","method":"Enzyme purification to homogeneity, N-terminal protein sequencing, DFP active-site labeling, biochemical activity assays, gel filtration","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — purification to homogeneity, direct sequence identification, active-site labeling","pmids":["1694176"],"is_preprint":false},{"year":2003,"finding":"The serine carboxypeptidase activity of PPCA/cathepsin A (CTSA) directly triggers degradation of LAMP2a, the lysosomal receptor for chaperone-mediated autophagy (CMA). PPCA associates with LAMP2a on the lysosomal membrane and cleaves it near the luminal/transmembrane domain boundary. Cells deficient in PPCA show reduced LAMP2a degradation, elevated lysosomal LAMP2a levels, and increased CMA rates; restoration of PPCA protease activity reverses these effects, reducing LAMP2a and CMA.","method":"Cell lines deficient in PPCA, restoration of PPCA protease activity, co-association assay (PPCA with LAMP2a), cleavage site mapping, measurement of CMA rates and LAMP2a levels","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — loss-of-function and gain-of-function with specific phenotypic readout, co-association and cleavage assay","pmids":["12505983"],"is_preprint":false},{"year":1991,"finding":"The human PPGB/CTSA gene was mapped by fluorescence in situ hybridization (FISH) to the long arm of chromosome 20, using both a 1.8-kb protective protein cDNA and a 12-kb genomic fragment as probes, confirmed by hybridization with whole chromosome DNA libraries.","method":"Fluorescence in situ hybridization (single- and double-color) on normal lymphocyte prometaphase chromosome spreads","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 — direct cytogenetic localization confirmed by two independent probes and chromosome libraries","pmids":["2071143"],"is_preprint":false},{"year":2020,"finding":"In canine inflammatory mammary adenocarcinoma cells, leptin downregulates cathepsin A (CTSA) expression at both transcript and protein levels, leading to reduced degradation of LAMP2a (the rate-limiting CMA receptor). Leptin also promoted LAMP2a multimerization through the lysosomal mTORC2/PHLPP1/AKT1 pathway, increasing CMA activity and metastatic capacity.","method":"RT-PCR, Western blot, immunocytochemistry, lysosome isolation in canine mammary carcinoma cell line (CHMp) treated with leptin","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple methods but single lab, canine cell model, no mutagenesis","pmids":["33255835"],"is_preprint":false},{"year":2018,"finding":"miR-106b-5p directly binds the 3′ UTR of CTSA mRNA (confirmed by luciferase assay) and suppresses CTSA expression, thereby inhibiting colorectal cancer cell migration and invasion in vitro and lung metastasis in vivo. Rescue experiments confirmed that CTSA is the functional downstream target mediating miR-106b-5p's anti-metastatic effects.","method":"Luciferase 3′UTR reporter assay, transwell migration/invasion assays, mouse tail-vein metastasis model, rescue experiments","journal":"OncoTargets and therapy","confidence":"Medium","confidence_rationale":"Tier 2 — direct 3′UTR targeting confirmed by luciferase assay and rescue experiment, in vivo validation","pmids":["30013364"],"is_preprint":false},{"year":2025,"finding":"A novel homozygous CTSA missense variant (p.Gln436Arg) was identified in Thai patients with galactosialidosis showing undetectable PPCA activity. In vitro functional analysis indicated the variant impairs the dimerization process of PPCA, potentially disrupting proper protein maturation and function.","method":"Exome sequencing, Sanger sequencing, in vitro functional analysis of dimerization, lysosomal enzyme activity assay","journal":"Annals of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro functional analysis of a specific variant with mechanistic interpretation (dimerization impairment)","pmids":["40165614"],"is_preprint":false}],"current_model":"CTSA (protective protein/cathepsin A, PPCA) is a lysosomal serine carboxypeptidase that forms a multiprotein complex with β-galactosidase and neuraminidase to protect and stabilize their activities; its catalytic and protective functions are mechanistically distinct, as shown by active-site mutagenesis. PPCA cleaves LAMP2a near its luminal/transmembrane boundary to regulate chaperone-mediated autophagy rates, acts as a deamidase and carboxypeptidase on bioactive peptides (e.g., substance P, bradykinin) when released from platelets, and its expression is post-transcriptionally regulated by miR-106b-5p targeting its 3′ UTR, with upstream modulation by leptin signaling affecting its control of LAMP2a turnover."},"narrative":{"teleology":[{"year":1985,"claim":"Establishing that neuraminidase and β-galactosidase require a third protein for activity answered the fundamental question of why both enzymes are simultaneously deficient in galactosialidosis.","evidence":"Affinity chromatography, immunotitration, and density gradient sedimentation in human fibroblast lysates","pmids":["3922758"],"confidence":"High","gaps":["Identity and sequence of the protective protein were unknown","Whether the protective protein had intrinsic enzymatic activity was untested"]},{"year":1988,"claim":"Cloning of the PPCA cDNA revealed a 452-residue precursor with homology to serine carboxypeptidases, providing the molecular identity of the protective protein and predicting catalytic function.","evidence":"cDNA cloning and functional rescue of β-galactosidase/neuraminidase in galactosialidosis fibroblasts","pmids":["3136930"],"confidence":"High","gaps":["Whether the predicted carboxypeptidase activity was real and whether it was separable from the protective function","Endogenous substrates of the carboxypeptidase were unknown"]},{"year":1990,"claim":"Identification of platelet-derived deamidase/carboxypeptidase as PPCA established that the enzyme acts on bioactive peptides (substance P, bradykinin) outside the lysosome, broadening its functional repertoire beyond lysosomal housekeeping.","evidence":"Purification to homogeneity from human platelets, N-terminal sequencing matching PPCA, DFP active-site labeling","pmids":["1694176"],"confidence":"High","gaps":["Physiological significance of extracellular peptide metabolism in vivo was not demonstrated","Mechanism of PPCA sorting to platelet secretory granules was unknown"]},{"year":1991,"claim":"Active-site mutagenesis separated catalytic activity from protective function, proving PPCA uses distinct mechanisms for enzyme stabilization versus substrate hydrolysis — a key conceptual advance for understanding galactosialidosis pathogenesis.","evidence":"Ser/His active-site and Cys60 mutants expressed in COS-1 cells with quantitation of cathepsin A activity and β-galactosidase/neuraminidase stabilization","pmids":["1907282"],"confidence":"High","gaps":["Structural basis of the protective interaction with β-galactosidase/neuraminidase was not resolved","Whether protective function requires specific PPCA domains beyond Cys60-dependent folding was unexplored"]},{"year":2003,"claim":"Discovery that PPCA cleaves LAMP2a to control chaperone-mediated autophagy revealed a previously unknown lysosomal quality-control circuit and provided the first identified endogenous protein substrate for cathepsin A's carboxypeptidase activity in the lysosome.","evidence":"PPCA-deficient cells show elevated LAMP2a and CMA; restoration of protease activity reverses phenotype; co-association and cleavage site mapping","pmids":["12505983"],"confidence":"High","gaps":["Exact cleavage site residues on LAMP2a were mapped but structural context of the protease–substrate interaction is lacking","Whether PPCA regulates CMA in vivo under physiological stress was not tested"]},{"year":2018,"claim":"Identification of miR-106b-5p as a direct post-transcriptional repressor of CTSA via its 3′ UTR established a regulatory layer controlling CTSA abundance with functional consequences for cancer cell metastasis.","evidence":"Luciferase 3′ UTR reporter, rescue experiments, in vivo tail-vein metastasis model in colorectal cancer","pmids":["30013364"],"confidence":"Medium","gaps":["Relevance to endogenous miR-106b-5p levels in non-cancer physiology was not addressed","Whether CTSA's pro-metastatic effect operates through LAMP2a/CMA or another substrate was not dissected"]},{"year":2020,"claim":"Leptin-mediated suppression of CTSA expression in mammary carcinoma cells linked extracellular metabolic signaling to LAMP2a stability and CMA activation, contextualizing CTSA's role in obesity-associated tumor biology.","evidence":"RT-PCR, Western blot, immunocytochemistry, lysosome isolation in canine mammary carcinoma cells treated with leptin","pmids":["33255835"],"confidence":"Medium","gaps":["Findings are from a single canine cell line; human relevance is unconfirmed","Mechanism by which leptin transcriptionally or post-transcriptionally downregulates CTSA was not defined"]},{"year":2025,"claim":"A novel CTSA p.Gln436Arg variant causing galactosialidosis was shown to impair PPCA dimerization, linking specific residue-level defects to loss of both enzymatic and protective functions through disrupted protein maturation.","evidence":"Exome/Sanger sequencing in Thai patients, in vitro dimerization and enzyme activity assays","pmids":["40165614"],"confidence":"Medium","gaps":["Structural modeling of how Gln436Arg disrupts dimerization interface is lacking","Whether partial dimerization rescue could restore protective function independently of catalytic activity was not tested"]},{"year":null,"claim":"The structural basis of the PPCA–β-galactosidase–neuraminidase ternary complex, the full repertoire of endogenous PPCA substrates, and the in vivo physiological consequences of PPCA-regulated CMA remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of the ternary complex exists","Comprehensive substrate profiling (e.g., degradomics) for cathepsin A has not been performed","In vivo genetic models testing CMA-dependent phenotypes of CTSA loss are limited"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,3,4]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[2,3,4]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,1,2,4]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4,6]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2,8]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,8]}],"complexes":["β-galactosidase–neuraminidase–PPCA complex"],"partners":["GLB1","NEU1","LAMP2"],"other_free_text":[]},"mechanistic_narrative":"CTSA (protective protein/cathepsin A, PPCA) is a lysosomal serine carboxypeptidase that serves dual roles as a catalytic enzyme and as an essential stabilizer of β-galactosidase and neuraminidase within a multienzyme complex. Active-site mutagenesis demonstrates that its carboxypeptidase activity and its protective/stabilizing function are mechanistically separable: catalytic-dead mutants still rescue β-galactosidase and neuraminidase activities in galactosialidosis cells, whereas folding-defective mutants abolish both functions [PMID:1907282, PMID:3136930]. PPCA cleaves LAMP2a at the lysosomal membrane, thereby controlling chaperone-mediated autophagy rates; cells lacking PPCA accumulate LAMP2a and exhibit elevated CMA, a phenotype reversed by restoring protease activity [PMID:12505983]. Loss-of-function mutations in CTSA cause galactosialidosis, a lysosomal storage disorder characterized by combined deficiency of neuraminidase and β-galactosidase [PMID:40165614, PMID:3922758]."},"prefetch_data":{"uniprot":{"accession":"P10619","full_name":"Lysosomal protective protein","aliases":["Carboxypeptidase C","Carboxypeptidase L","Cathepsin A","Protective protein cathepsin A","PPCA","Protective protein for beta-galactosidase"],"length_aa":480,"mass_kda":54.5,"function":"Protective protein appears to be essential for both the activity of beta-galactosidase and neuraminidase, it associates with these enzymes and exerts a protective function necessary for their stability and activity. This protein is also a carboxypeptidase and can deamidate tachykinins","subcellular_location":"Lysosome","url":"https://www.uniprot.org/uniprotkb/P10619/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CTSA","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CTSA","total_profiled":1310},"omim":[{"mim_id":"621394","title":"BRAIN SMALL VESSEL DISEASE 6 WITH LEUKOENCEPHALOPATHY; BSVD6","url":"https://www.omim.org/entry/621394"},{"mim_id":"619723","title":"SERINE CARBOXYPEPTIDASE 1; SCPEP1","url":"https://www.omim.org/entry/619723"},{"mim_id":"613111","title":"CATHEPSIN A; CTSA","url":"https://www.omim.org/entry/613111"},{"mim_id":"611458","title":"GALACTOSIDASE, BETA-1; GLB1","url":"https://www.omim.org/entry/611458"},{"mim_id":"608272","title":"NEURAMINIDASE 1; NEU1","url":"https://www.omim.org/entry/608272"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Vesicles","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"adrenal gland","ntpm":312.4}],"url":"https://www.proteinatlas.org/search/CTSA"},"hgnc":{"alias_symbol":[],"prev_symbol":["GSL","PPGB"]},"alphafold":{"accession":"P10619","domains":[{"cath_id":"3.40.50.1820","chopping":"32-211_375-477","consensus_level":"high","plddt":98.3371,"start":32,"end":477},{"cath_id":"3.40.50.1820","chopping":"213-330","consensus_level":"medium","plddt":92.289,"start":213,"end":330}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P10619","model_url":"https://alphafold.ebi.ac.uk/files/AF-P10619-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P10619-F1-predicted_aligned_error_v6.png","plddt_mean":94.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CTSA","jax_strain_url":"https://www.jax.org/strain/search?query=CTSA"},"sequence":{"accession":"P10619","fasta_url":"https://rest.uniprot.org/uniprotkb/P10619.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P10619/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P10619"}},"corpus_meta":[{"pmid":"2071143","id":"PMC_2071143","title":"The 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Probable identity with the lysosomal \"protective protein\".","date":"1990","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1694176","citation_count":153,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23533145","id":"PMC_23533145","title":"In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.","date":"2013","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/23533145","citation_count":138,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"1907282","id":"PMC_1907282","title":"Human lysosomal protective protein has cathepsin A-like activity distinct from its protective function.","date":"1991","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1907282","citation_count":137,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"31871319","id":"PMC_31871319","title":"Mapping the proximity interaction network of the Rho-family GTPases reveals signalling pathways and regulatory mechanisms.","date":"2019","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/31871319","citation_count":137,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"3922758","id":"PMC_3922758","title":"Human placental neuraminidase. Activation, stabilization and association with beta-galactosidase and its protective protein.","date":"1985","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/3922758","citation_count":134,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16546,"output_tokens":1237,"usd":0.034097},"stage2":{"model":"claude-opus-4-6","input_tokens":4471,"output_tokens":1742,"usd":0.098858},"total_usd":0.328555,"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":28685,"output_tokens":2571,"usd":0.06231},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":6137,"output_tokens":2327,"usd":0.13329}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"Mutations in the CTSA gene, encoding protective protein/cathepsin A (PPCA), cause secondary deficiency of both β-galactosidase (GLB1) and neuraminidase 1 (NEU1), establishing PPCA as a protective protein required for the functional integrity of this lysosomal enzyme complex.\",\n      \"method\": \"Clinical mutation analysis, biochemical enzyme activity assays in patient fibroblasts, in silico functional prediction of missense mutations\",\n      \"journal\": \"Orphanet journal of rare diseases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replicated across multiple independent clinical/biochemical studies consistently demonstrating the same mechanistic relationship\",\n      \"pmids\": [\"23915561\", \"31044084\", \"28555253\", \"29876240\", \"29333829\", \"40165614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The gene encoding human protective protein (PPGB/CTSA) is localized on the long arm of chromosome 20, established by in situ fluorescence hybridization with cDNA and genomic probes.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH) on normal lymphocyte prometaphase chromosome spreads using PPGB cDNA and genomic fragment probes\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct chromosomal localization by two independent probe types with confirmation by whole chromosome library hybridization\",\n      \"pmids\": [\"2071143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel homozygous missense CTSA variant (p.Gln436Arg) impairs the dimerization process of PPCA, disrupting proper protein maturation or function, leading to significantly reduced PPCA activity; demonstrated by in vitro functional analysis.\",\n      \"method\": \"In vitro functional analysis of recombinant CTSA variant; PPCA activity assay\",\n      \"journal\": \"Annals of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab, in vitro functional assay directly linking variant to dimerization defect and loss of enzymatic activity\",\n      \"pmids\": [\"40165614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cathepsin A (CTSA) is responsible for degradation of LAMP2a (lysosomal-associated membrane protein 2a), a rate-limiting factor in chaperone-mediated autophagy; leptin downregulates CTSA expression, thereby stabilizing LAMP2a and promoting its multimerization through the lysosomal mTORC2/PHLPP1/AKT1 pathway.\",\n      \"method\": \"Western blot, real-time PCR, immunocytochemistry, lysosome isolation in canine inflammatory mammary adenocarcinoma (CHMp) cells with leptin treatment\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple orthogonal methods in a single lab establishing CTSA as LAMP2a protease and its regulation by leptin/mTORC2 pathway\",\n      \"pmids\": [\"33255835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"miR-106b-5p directly binds to the 3' UTR of CTSA mRNA and suppresses CTSA expression, thereby inhibiting colorectal cancer cell migration and invasion; rescue experiments confirmed that CTSA is the functional target mediating miR-106b-5p's anti-metastatic effects.\",\n      \"method\": \"Luciferase reporter assay, transwell migration/invasion assays, in vivo mouse tail vein injection model, rescue experiments\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase assay directly confirms 3' UTR binding; rescue experiment confirms CTSA as functional target; multiple orthogonal methods\",\n      \"pmids\": [\"30013364\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CTSA encodes protective protein/cathepsin A (PPCA), a lysosomal serine protease that forms a protective complex with β-galactosidase and neuraminidase 1, preventing their degradation and maintaining their enzymatic activity; PPCA also degrades LAMP2a to regulate chaperone-mediated autophagy, and its expression is post-transcriptionally regulated by miR-106b-5p and modulated by leptin signaling through mTORC2/PHLPP1/AKT1.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1988,\n      \"finding\": \"The cDNA encoding human 'protective protein' (PPCA/CTSA) was isolated, revealing a 452 amino acid precursor that is processed into a mature heterodimer of 32 kDa and 20 kDa polypeptides held by disulfide bridges. The predicted amino acid sequence showed homology to yeast carboxypeptidase Y and the KEX1 gene product, suggesting serine carboxypeptidase activity. The mature protein restores β-galactosidase and neuraminidase activities in galactosialidosis cells, establishing its protective function.\",\n      \"method\": \"cDNA cloning, in vivo expression in galactosialidosis fibroblasts (functional rescue), sequence homology analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning with functional rescue, replicated across subsequent studies\",\n      \"pmids\": [\"3136930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"Human lysosomal neuraminidase activity is activated and stabilized only when in a high-density multimeric complex with β-galactosidase, and the 32 kDa protective protein (PPCA/CTSA) is present in this complex. Immunotitration with monospecific antibodies against the protective protein demonstrated that it is essential for the catalytic activity of lysosomal neuraminidase, explaining the combined neuraminidase and β-galactosidase deficiency in galactosialidosis.\",\n      \"method\": \"β-galactosidase affinity chromatography, immunotitration with monospecific antibodies, sucrose density gradient centrifugation\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal biochemical methods demonstrating complex formation and functional requirement\",\n      \"pmids\": [\"3922758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The protective protein/PPCA has enzymatic activity identical to lysosomal cathepsin A (serine carboxypeptidase). Overexpression increases cathepsin A-like activity 3–4 fold; galactosialidosis patient extracts have ~1% activity; monospecific antibodies precipitate virtually all cathepsin A-like activity from normal fibroblasts. Active-site mutagenesis of serine and histidine residues abolishes enzymatic activity but does not affect intracellular routing, processing, or protective function for β-galactosidase/neuraminidase. A Cys60 mutation interferes with precursor folding and intracellular transport. This demonstrates that catalytic activity and protective function are distinct properties of the same protein.\",\n      \"method\": \"Overexpression in COS-1 cells, enzyme activity assays, monospecific antibody immunoprecipitation, active-site mutagenesis (Ser, His, Cys60)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis plus reconstitution plus functional dissection, multiple orthogonal methods in single study\",\n      \"pmids\": [\"1907282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"A peptidase purified from human platelets (released by thrombin) that deamidates tachykinins (substance P, neurokinin A) and acts as a carboxypeptidase on bradykinin and angiotensin I was shown to be identical to the lysosomal protective protein (PPCA/CTSA). N-terminal sequencing of both chains matched protective protein sequences. The enzyme is a disulfide-linked dimer (32 kDa + 21 kDa chains), inhibited by DFP (active-site serine labeled), with pH optima differing for peptidase (~5.0) vs. esterase/deamidase (~7.0) activities, establishing a role for PPCA in extracellular/platelet peptide metabolism.\",\n      \"method\": \"Enzyme purification to homogeneity, N-terminal protein sequencing, DFP active-site labeling, biochemical activity assays, gel filtration\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purification to homogeneity, direct sequence identification, active-site labeling\",\n      \"pmids\": [\"1694176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The serine carboxypeptidase activity of PPCA/cathepsin A (CTSA) directly triggers degradation of LAMP2a, the lysosomal receptor for chaperone-mediated autophagy (CMA). PPCA associates with LAMP2a on the lysosomal membrane and cleaves it near the luminal/transmembrane domain boundary. Cells deficient in PPCA show reduced LAMP2a degradation, elevated lysosomal LAMP2a levels, and increased CMA rates; restoration of PPCA protease activity reverses these effects, reducing LAMP2a and CMA.\",\n      \"method\": \"Cell lines deficient in PPCA, restoration of PPCA protease activity, co-association assay (PPCA with LAMP2a), cleavage site mapping, measurement of CMA rates and LAMP2a levels\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — loss-of-function and gain-of-function with specific phenotypic readout, co-association and cleavage assay\",\n      \"pmids\": [\"12505983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The human PPGB/CTSA gene was mapped by fluorescence in situ hybridization (FISH) to the long arm of chromosome 20, using both a 1.8-kb protective protein cDNA and a 12-kb genomic fragment as probes, confirmed by hybridization with whole chromosome DNA libraries.\",\n      \"method\": \"Fluorescence in situ hybridization (single- and double-color) on normal lymphocyte prometaphase chromosome spreads\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct cytogenetic localization confirmed by two independent probes and chromosome libraries\",\n      \"pmids\": [\"2071143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In canine inflammatory mammary adenocarcinoma cells, leptin downregulates cathepsin A (CTSA) expression at both transcript and protein levels, leading to reduced degradation of LAMP2a (the rate-limiting CMA receptor). Leptin also promoted LAMP2a multimerization through the lysosomal mTORC2/PHLPP1/AKT1 pathway, increasing CMA activity and metastatic capacity.\",\n      \"method\": \"RT-PCR, Western blot, immunocytochemistry, lysosome isolation in canine mammary carcinoma cell line (CHMp) treated with leptin\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple methods but single lab, canine cell model, no mutagenesis\",\n      \"pmids\": [\"33255835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"miR-106b-5p directly binds the 3′ UTR of CTSA mRNA (confirmed by luciferase assay) and suppresses CTSA expression, thereby inhibiting colorectal cancer cell migration and invasion in vitro and lung metastasis in vivo. Rescue experiments confirmed that CTSA is the functional downstream target mediating miR-106b-5p's anti-metastatic effects.\",\n      \"method\": \"Luciferase 3′UTR reporter assay, transwell migration/invasion assays, mouse tail-vein metastasis model, rescue experiments\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct 3′UTR targeting confirmed by luciferase assay and rescue experiment, in vivo validation\",\n      \"pmids\": [\"30013364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel homozygous CTSA missense variant (p.Gln436Arg) was identified in Thai patients with galactosialidosis showing undetectable PPCA activity. In vitro functional analysis indicated the variant impairs the dimerization process of PPCA, potentially disrupting proper protein maturation and function.\",\n      \"method\": \"Exome sequencing, Sanger sequencing, in vitro functional analysis of dimerization, lysosomal enzyme activity assay\",\n      \"journal\": \"Annals of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro functional analysis of a specific variant with mechanistic interpretation (dimerization impairment)\",\n      \"pmids\": [\"40165614\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CTSA (protective protein/cathepsin A, PPCA) is a lysosomal serine carboxypeptidase that forms a multiprotein complex with β-galactosidase and neuraminidase to protect and stabilize their activities; its catalytic and protective functions are mechanistically distinct, as shown by active-site mutagenesis. PPCA cleaves LAMP2a near its luminal/transmembrane boundary to regulate chaperone-mediated autophagy rates, acts as a deamidase and carboxypeptidase on bioactive peptides (e.g., substance P, bradykinin) when released from platelets, and its expression is post-transcriptionally regulated by miR-106b-5p targeting its 3′ UTR, with upstream modulation by leptin signaling affecting its control of LAMP2a turnover.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CTSA encodes protective protein/cathepsin A (PPCA), a lysosomal serine protease that forms a multimeric complex with β-galactosidase (GLB1) and neuraminidase 1 (NEU1), protecting both enzymes from premature intralysosomal degradation; loss-of-function mutations in CTSA cause galactosialidosis, characterized by secondary deficiency of both GLB1 and NEU1 [PMID:23915561, PMID:40165614]. PPCA dimerization is required for proper maturation and catalytic activity, as demonstrated by a p.Gln436Arg variant that disrupts dimerization and abolishes enzyme function [PMID:40165614]. Beyond its protective role, CTSA degrades LAMP2a, a rate-limiting receptor in chaperone-mediated autophagy, and its expression is regulated by the leptin/mTORC2/PHLPP1/AKT1 signaling axis and post-transcriptionally by miR-106b-5p [PMID:33255835, PMID:30013364].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Establishing the chromosomal location of CTSA on chromosome 20q provided the physical framework for subsequent mutation and linkage studies in galactosialidosis.\",\n      \"evidence\": \"FISH with cDNA and genomic probes on human lymphocyte prometaphase chromosomes\",\n      \"pmids\": [\"2071143\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Gene structure and exon-intron organization not defined in this study\",\n        \"No functional characterization of the encoded protein\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identification of pathogenic CTSA mutations in galactosialidosis patients, coupled with demonstration of secondary GLB1 and NEU1 deficiency, established that PPCA is the essential protective subunit of the lysosomal multienzyme complex.\",\n      \"evidence\": \"Clinical mutation analysis and biochemical enzyme activity assays in patient fibroblasts across multiple independent studies\",\n      \"pmids\": [\"23915561\", \"31044084\", \"28555253\", \"29876240\", \"29333829\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Precise stoichiometry and assembly pathway of the PPCA-GLB1-NEU1 complex not resolved\",\n        \"Contribution of PPCA catalytic activity versus chaperone-like function to enzyme protection unclear\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating that miR-106b-5p directly suppresses CTSA expression via 3′ UTR binding revealed a post-transcriptional regulatory layer and implicated CTSA in colorectal cancer cell migration and invasion.\",\n      \"evidence\": \"Luciferase reporter assay, transwell migration/invasion assays, in vivo mouse tail vein metastasis model, and CTSA rescue experiments in colorectal cancer cells\",\n      \"pmids\": [\"30013364\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which elevated CTSA promotes metastatic behavior not defined\",\n        \"Relevance of miR-106b-5p–CTSA axis in primary human tumors not validated\",\n        \"Single study without independent replication\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of CTSA as the protease responsible for LAMP2a degradation connected PPCA activity to regulation of chaperone-mediated autophagy and placed CTSA downstream of leptin/mTORC2/PHLPP1/AKT1 signaling.\",\n      \"evidence\": \"Western blot, RT-PCR, immunocytochemistry, and lysosome isolation in canine mammary adenocarcinoma cells treated with leptin\",\n      \"pmids\": [\"33255835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"LAMP2a cleavage site and kinetics of degradation by CTSA not characterized\",\n        \"Findings derived from a single canine cancer cell line; human cell confirmation lacking\",\n        \"Whether CTSA-mediated LAMP2a degradation operates under physiological (non-cancer) conditions not shown\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrating that the p.Gln436Arg variant disrupts PPCA dimerization established that dimer formation is a prerequisite for catalytic competence, linking protein quaternary structure to disease mechanism.\",\n      \"evidence\": \"In vitro functional analysis of recombinant CTSA variant with PPCA activity assays\",\n      \"pmids\": [\"40165614\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural basis of dimerization defect not resolved at atomic level\",\n        \"Single variant studied; generalizability of dimerization-disrupting mutations not tested\",\n        \"Effect on GLB1/NEU1 complex formation in patient cells not directly assessed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The relative contributions of PPCA's serine protease activity versus its chaperone/protective function to lysosomal multienzyme complex stability, and the physiological relevance of CTSA-mediated LAMP2a degradation in non-cancer human tissues, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No separation-of-function mutants distinguishing catalytic from protective roles\",\n        \"No structural model of the full PPCA-GLB1-NEU1 ternary complex\",\n        \"In vivo significance of CTSA in chaperone-mediated autophagy regulation in human systems not demonstrated\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\n      \"Lysosomal multienzyme complex (PPCA-GLB1-NEU1)\"\n    ],\n    \"partners\": [\n      \"GLB1\",\n      \"NEU1\",\n      \"LAMP2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CTSA (protective protein/cathepsin A, PPCA) is a lysosomal serine carboxypeptidase that serves dual roles as a catalytic enzyme and as an essential stabilizer of β-galactosidase and neuraminidase within a multienzyme complex. Active-site mutagenesis demonstrates that its carboxypeptidase activity and its protective/stabilizing function are mechanistically separable: catalytic-dead mutants still rescue β-galactosidase and neuraminidase activities in galactosialidosis cells, whereas folding-defective mutants abolish both functions [PMID:1907282, PMID:3136930]. PPCA cleaves LAMP2a at the lysosomal membrane, thereby controlling chaperone-mediated autophagy rates; cells lacking PPCA accumulate LAMP2a and exhibit elevated CMA, a phenotype reversed by restoring protease activity [PMID:12505983]. Loss-of-function mutations in CTSA cause galactosialidosis, a lysosomal storage disorder characterized by combined deficiency of neuraminidase and β-galactosidase [PMID:40165614, PMID:3922758].\",\n  \"teleology\": [\n    {\n      \"year\": 1985,\n      \"claim\": \"Establishing that neuraminidase and β-galactosidase require a third protein for activity answered the fundamental question of why both enzymes are simultaneously deficient in galactosialidosis.\",\n      \"evidence\": \"Affinity chromatography, immunotitration, and density gradient sedimentation in human fibroblast lysates\",\n      \"pmids\": [\"3922758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity and sequence of the protective protein were unknown\",\n        \"Whether the protective protein had intrinsic enzymatic activity was untested\"\n      ]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Cloning of the PPCA cDNA revealed a 452-residue precursor with homology to serine carboxypeptidases, providing the molecular identity of the protective protein and predicting catalytic function.\",\n      \"evidence\": \"cDNA cloning and functional rescue of β-galactosidase/neuraminidase in galactosialidosis fibroblasts\",\n      \"pmids\": [\"3136930\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the predicted carboxypeptidase activity was real and whether it was separable from the protective function\",\n        \"Endogenous substrates of the carboxypeptidase were unknown\"\n      ]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Identification of platelet-derived deamidase/carboxypeptidase as PPCA established that the enzyme acts on bioactive peptides (substance P, bradykinin) outside the lysosome, broadening its functional repertoire beyond lysosomal housekeeping.\",\n      \"evidence\": \"Purification to homogeneity from human platelets, N-terminal sequencing matching PPCA, DFP active-site labeling\",\n      \"pmids\": [\"1694176\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Physiological significance of extracellular peptide metabolism in vivo was not demonstrated\",\n        \"Mechanism of PPCA sorting to platelet secretory granules was unknown\"\n      ]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Active-site mutagenesis separated catalytic activity from protective function, proving PPCA uses distinct mechanisms for enzyme stabilization versus substrate hydrolysis — a key conceptual advance for understanding galactosialidosis pathogenesis.\",\n      \"evidence\": \"Ser/His active-site and Cys60 mutants expressed in COS-1 cells with quantitation of cathepsin A activity and β-galactosidase/neuraminidase stabilization\",\n      \"pmids\": [\"1907282\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the protective interaction with β-galactosidase/neuraminidase was not resolved\",\n        \"Whether protective function requires specific PPCA domains beyond Cys60-dependent folding was unexplored\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovery that PPCA cleaves LAMP2a to control chaperone-mediated autophagy revealed a previously unknown lysosomal quality-control circuit and provided the first identified endogenous protein substrate for cathepsin A's carboxypeptidase activity in the lysosome.\",\n      \"evidence\": \"PPCA-deficient cells show elevated LAMP2a and CMA; restoration of protease activity reverses phenotype; co-association and cleavage site mapping\",\n      \"pmids\": [\"12505983\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Exact cleavage site residues on LAMP2a were mapped but structural context of the protease–substrate interaction is lacking\",\n        \"Whether PPCA regulates CMA in vivo under physiological stress was not tested\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of miR-106b-5p as a direct post-transcriptional repressor of CTSA via its 3′ UTR established a regulatory layer controlling CTSA abundance with functional consequences for cancer cell metastasis.\",\n      \"evidence\": \"Luciferase 3′ UTR reporter, rescue experiments, in vivo tail-vein metastasis model in colorectal cancer\",\n      \"pmids\": [\"30013364\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Relevance to endogenous miR-106b-5p levels in non-cancer physiology was not addressed\",\n        \"Whether CTSA's pro-metastatic effect operates through LAMP2a/CMA or another substrate was not dissected\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Leptin-mediated suppression of CTSA expression in mammary carcinoma cells linked extracellular metabolic signaling to LAMP2a stability and CMA activation, contextualizing CTSA's role in obesity-associated tumor biology.\",\n      \"evidence\": \"RT-PCR, Western blot, immunocytochemistry, lysosome isolation in canine mammary carcinoma cells treated with leptin\",\n      \"pmids\": [\"33255835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Findings are from a single canine cell line; human relevance is unconfirmed\",\n        \"Mechanism by which leptin transcriptionally or post-transcriptionally downregulates CTSA was not defined\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A novel CTSA p.Gln436Arg variant causing galactosialidosis was shown to impair PPCA dimerization, linking specific residue-level defects to loss of both enzymatic and protective functions through disrupted protein maturation.\",\n      \"evidence\": \"Exome/Sanger sequencing in Thai patients, in vitro dimerization and enzyme activity assays\",\n      \"pmids\": [\"40165614\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural modeling of how Gln436Arg disrupts dimerization interface is lacking\",\n        \"Whether partial dimerization rescue could restore protective function independently of catalytic activity was not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of the PPCA–β-galactosidase–neuraminidase ternary complex, the full repertoire of endogenous PPCA substrates, and the in vivo physiological consequences of PPCA-regulated CMA remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of the ternary complex exists\",\n        \"Comprehensive substrate profiling (e.g., degradomics) for cathepsin A has not been performed\",\n        \"In vivo genetic models testing CMA-dependent phenotypes of CTSA loss are limited\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 4]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4, 6]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2, 8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"complexes\": [\n      \"β-galactosidase–neuraminidase–PPCA complex\"\n    ],\n    \"partners\": [\n      \"GLB1\",\n      \"NEU1\",\n      \"LAMP2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}