{"gene":"PREPL","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2005,"finding":"PREPL is localized in the cytosol and possesses a catalytic triad (Ser470, Asp556, His601); substitution of these predicted catalytic residues by alanines resulted in loss of reactivity with a serine hydrolase-specific activity-based probe, confirming an intact but unique catalytic machinery. Unlike prolyl oligopeptidase and oligopeptidase B, PREPL activity depends only on the carboxyterminal domain.","method":"Activity-based probe labeling with catalytic-residue alanine mutagenesis; subcellular fractionation","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct active-site mutagenesis combined with activity-based probe, single lab but multiple orthogonal methods","pmids":["16385448"],"is_preprint":false},{"year":2005,"finding":"PREPL A (638-residue splice variant) was purified from E. coli and shown to have secondary structure similar to oligopeptidase B; it reacted with diisopropyl fluorophosphate and slowly hydrolyzed an activated ester substrate, confirming a reactive catalytic serine. However, PREPL A did not cleave peptide substrates with a P1 basic residue (Arg/Lys), indicating negligible canonical peptidase activity and suggesting a non-peptidase biological function. Dimerization was observed and may account for enhanced conformational stability.","method":"Recombinant protein expression and purification, differential-scanning calorimetry, enzyme activity assays with peptide and activated ester substrates, DFP inhibitor labeling","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple substrate assays and inhibitor labeling, single lab with orthogonal biochemical methods","pmids":["16143824"],"is_preprint":false},{"year":2013,"finding":"PREPL (cytoplasmic) was identified as a direct interaction partner of the N-terminal 70 amino acids of AP-1 complex subunit μ1A via yeast two-hybrid screen. PREPL overexpression reduced AP-1 membrane binding, while reduced PREPL expression increased AP-1 membrane binding and impaired AP-1 recycling. PREPL-deficient patient cell lines displayed an expanded trans-Golgi network that was rescued by PREPL re-expression. PREPL colocalizes with residual membrane-bound AP-1, functioning as an AP-1 effector regulating AP-1 membrane association and TGN morphology.","method":"Yeast two-hybrid screen; AP-1 membrane binding assays; PREPL overexpression and knockdown; colocalization by fluorescence microscopy; patient cell line complementation","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid identification plus functional overexpression/knockdown and rescue in patient cell lines, multiple orthogonal methods","pmids":["23321636"],"is_preprint":false},{"year":2014,"finding":"PREPL deficiency causes a congenital myasthenic syndrome with decreased quantal content of the endplate potential and reduced miniature endplate potential amplitude without acetylcholine receptor deficiency or altered endplate geometry, indicating both pre- and postsynaptic defects. The myasthenia is attributed to abrogated PREPL interaction with adaptor protein 1 (AP-1). No PREPL expression was detected in patient muscle and endplates.","method":"Electrophysiology (in vitro neuromuscular transmission studies), immunoblot, histochemistry, ultrastructural studies in patient with isolated PREPL deficiency","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct electrophysiology in patient tissue, single lab, pathway placement inferred from AP-1 interaction data from separate study","pmids":["24610330"],"is_preprint":false},{"year":2014,"finding":"Deletion of exon 11 from the mouse Prepl gene (which encodes key catalytic amino acids) leads to loss of PREPL protein and reduced Prepl mRNA. PREPL-null mice exhibit significantly reduced growth (shorter and lighter) and neonatal hypotonia as measured by a righting reflex assay, establishing that PREPL is required for normal growth and neonatal muscle tone in vivo.","method":"PREPL knockout mouse model (exon 11 deletion); body measurement; righting assay for neonatal hypotonia","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO mouse with defined phenotypic readouts, single lab, no molecular mechanism identified beyond loss of protein","pmids":["24586561"],"is_preprint":false},{"year":2011,"finding":"A fluorescence polarization activity-based protein profiling (fluopol-ABPP) screen identified selective small-molecule inhibitors of PREPL serine hydrolase activity that block PREPL activity in cells. One inhibitor (1-isobutyl-3-oxo-3,5,6,7-tetrahydro-2H-cyclopenta[c]pyridine-4-carbonitrile) distributed to the brain after administration to mice, confirming PREPL is a functional serine hydrolase amenable to pharmacological inhibition.","method":"Fluopol-ABPP high-throughput screen (~300,000 compounds); cell-based activity assay; mouse pharmacokinetics","journal":"Journal of the American Chemical Society","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — activity-based probe assay confirmed in cells and in vivo, single lab but multiple assay levels","pmids":["21692504"],"is_preprint":false},{"year":2009,"finding":"NRF-2 and YY-1 transcription factors cooperatively bind a 243-bp GC-rich bidirectional minimal promoter within the 405-bp intergenic region between PREPL and C2ORF34, driving expression of both genes in an additive manner. Cis-acting repressive elements within this region also contribute to tissue-specific expression.","method":"Promoter deletion/reporter assays, transcription factor binding studies (gel shift/ChIP implied), expression analysis across tissues","journal":"BMC molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional promoter assays with transcription factor identification, single lab with multiple reporter and binding experiments","pmids":["19575798"],"is_preprint":false},{"year":2024,"finding":"Missense variants in PREPL from CMS22 patients do not impair hydrolase activity but reduce binding to known interactors, and structural analysis indicates the variants affect regions involved in intraprotein or protein-protein interactions. Catalytically inactive PREPL p.Ser559Ala cell lines showed that hydrolytic activity of PREPL is required for normal mitochondrial function but NOT for regulating AP-1-mediated transport in the trans-Golgi network, demonstrating that PREPL has separable enzymatic and non-enzymatic functions.","method":"Biochemical hydrolase activity assays; structural analysis; protein-protein interaction assays; CRISPR catalytic-dead knock-in (Ser559Ala) cell lines; mitochondrial function assays; AP-1 transport assays","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 1 / Moderate — catalytic-dead mutagenesis combined with functional cellular assays (mitochondria and TGN transport), structural analysis, and interaction studies in single rigorous study","pmids":["39078710"],"is_preprint":false},{"year":2025,"finding":"In PREPL KO HEK293T cells and Prepl KO mouse brains, global phospholipid composition was largely unchanged, arguing against a direct lipase role for PREPL in (lyso)phospholipid turnover. However, PREPL KO cells accumulated triacylglycerols (TAGs) and increased lipid droplets. PREPL does not localize to peroxisomes, and peroxisome numbers and protein levels were largely unaffected, but KO cells showed elongated peroxisomes. The TAG accumulation and peroxisome elongation are interpreted as secondary consequences of mitochondrial dysfunction (impaired fatty acid β-oxidation) caused by PREPL loss, not a direct lipase function.","method":"Unbiased lipidomics in KO mouse brain and CRISPR-Cas9 KO cell lines; lipid droplet imaging; peroxisome morphology and protein level analysis; PREPL localization studies","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — unbiased lipidomics and CRISPR KO with multiple readouts, preprint not yet peer-reviewed, single lab","pmids":["bio_10.1101_2025.10.28.685080"],"is_preprint":true}],"current_model":"PREPL is a cytosolic serine hydrolase of the prolyl oligopeptidase family with a reactive catalytic triad (Ser470/Ser559, Asp556, His601) that confers esterase activity but negligible canonical peptidase activity toward basic-residue substrates; it functions as an effector of the AP-1 clathrin adaptor complex by binding the μ1A subunit to regulate AP-1 membrane cycling and trans-Golgi network morphology (a non-enzymatic function), while its hydrolytic activity is separately required for normal mitochondrial respiratory function, with loss of PREPL causing triacylglycerol accumulation as a secondary metabolic consequence of mitochondrial dysfunction."},"narrative":{"mechanistic_narrative":"PREPL is a cytosolic serine hydrolase of the prolyl oligopeptidase family that performs two genetically separable functions—an enzymatic activity required for normal mitochondrial respiration and a non-enzymatic role as an effector of the AP-1 clathrin adaptor complex [PMID:39078710]. Its catalytic machinery comprises a serine hydrolase triad (Ser470, Asp556, His601) localized to the C-terminal domain; mutation of these residues abolishes labeling by serine hydrolase-directed probes, and recombinant PREPL reacts with active-site inhibitors and slowly hydrolyzes activated esters yet fails to cleave peptides bearing a P1 basic residue, defining it as an esterase with negligible canonical peptidase activity [PMID:16385448, PMID:16143824]. The non-enzymatic function arises through direct binding to the N-terminus of the AP-1 μ1A subunit, where PREPL regulates AP-1 membrane cycling: it limits AP-1 membrane association and is required for AP-1 recycling, and its loss expands the trans-Golgi network in patient cells, a defect rescued by PREPL re-expression [PMID:23321636]. Catalytically dead PREPL (Ser559Ala) retains normal AP-1-mediated TGN transport while failing to support mitochondrial function, and CMS22 patient missense variants disrupt interactor binding rather than hydrolase activity, cementing the division between the two roles [PMID:39078710]. Loss of PREPL causes triacylglycerol and lipid-droplet accumulation as a secondary consequence of mitochondrial dysfunction rather than a direct lipase activity [PMID:bio_10.1101_2025.10.28.685080]. PREPL deficiency causes a congenital myasthenic syndrome with combined pre- and postsynaptic neuromuscular transmission defects, and PREPL-null mice show reduced growth and neonatal hypotonia [PMID:24610330, PMID:24586561].","teleology":[{"year":2005,"claim":"Established that PREPL is a genuine but atypical serine hydrolase, resolving whether its predicted prolyl-oligopeptidase-family triad is catalytically functional.","evidence":"Activity-based probe labeling with catalytic-residue alanine mutagenesis and subcellular fractionation; recombinant protein with DSC, inhibitor labeling, and peptide/ester substrate assays","pmids":["16385448","16143824"],"confidence":"High","gaps":["No physiological substrate of the esterase activity identified","Biological consequence of catalysis not connected to a cellular process at this stage"]},{"year":2009,"claim":"Defined the transcriptional control of PREPL, showing it shares a bidirectional GC-rich promoter with C2ORF34 driven cooperatively by NRF-2 and YY-1.","evidence":"Promoter deletion/reporter assays and transcription factor binding analysis across tissues","pmids":["19575798"],"confidence":"Medium","gaps":["Does not link transcriptional regulation to a specific physiological stimulus","Tissue-specific repressive elements not mapped to defined factors"]},{"year":2011,"claim":"Demonstrated PREPL is a druggable functional serine hydrolase in cells and in vivo, providing tools to probe its enzymatic role.","evidence":"Fluopol-ABPP high-throughput screen (~300,000 compounds), cell-based activity assay, and mouse pharmacokinetics","pmids":["21692504"],"confidence":"Medium","gaps":["Inhibitor phenotype on cellular function not assessed","No endogenous substrate revealed by inhibition"]},{"year":2013,"claim":"Identified the first defined cellular function of PREPL as a non-enzymatic AP-1 effector controlling adaptor membrane cycling and TGN morphology.","evidence":"Yeast two-hybrid screen against μ1A, AP-1 membrane binding assays, overexpression/knockdown, and patient cell line complementation","pmids":["23321636"],"confidence":"High","gaps":["Whether the interaction depends on catalytic activity not tested here","Mechanism by which PREPL displaces AP-1 from membranes unresolved"]},{"year":2014,"claim":"Connected PREPL loss to neuromuscular disease, showing combined pre- and postsynaptic transmission defects and an organismal growth/tone phenotype.","evidence":"Neuromuscular electrophysiology in patient tissue with immunoblot/histochemistry; exon-11-deletion PREPL knockout mouse with body measurements and righting reflex assay","pmids":["24610330","24586561"],"confidence":"Medium","gaps":["Molecular cause of the synaptic defect inferred from AP-1 interaction rather than directly demonstrated","Mouse phenotype not mechanistically tied to AP-1 versus enzymatic function"]},{"year":2024,"claim":"Dissected PREPL's two activities, proving hydrolase function is required for mitochondrial function but dispensable for AP-1-mediated TGN transport, and that disease variants act by disrupting interactions.","evidence":"CRISPR catalytic-dead (Ser559Ala) knock-in cell lines, mitochondrial and AP-1 transport assays, hydrolase activity assays, structural analysis, and interaction studies of CMS22 variants","pmids":["39078710"],"confidence":"High","gaps":["Substrate and molecular mechanism linking PREPL catalysis to mitochondrial respiration unknown","Specific interactors lost by CMS22 variants not fully enumerated"]},{"year":2025,"claim":"Clarified the lipid phenotype of PREPL loss, arguing against a direct lipase role and attributing triacylglycerol and peroxisome changes to secondary mitochondrial dysfunction.","evidence":"Unbiased lipidomics in KO mouse brain and CRISPR KO cells, lipid droplet imaging, peroxisome morphology/protein analysis, and localization studies (preprint)","pmids":["bio_10.1101_2025.10.28.685080"],"confidence":"Medium","gaps":["Preprint not yet peer-reviewed","Direct biochemical link between PREPL catalysis and fatty acid β-oxidation not established"]},{"year":null,"claim":"The endogenous physiological substrate of PREPL's esterase activity and the molecular mechanism coupling that activity to mitochondrial respiration remain unidentified.","evidence":"","pmids":[],"confidence":"High","gaps":["No in vivo substrate identified despite confirmed esterase activity","Mechanism by which PREPL binding regulates AP-1 membrane release is undefined","Causal chain from catalytic loss to mitochondrial dysfunction not reconstituted"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,5,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[2]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[7,8]}],"complexes":[],"partners":["AP1M1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q4J6C6","full_name":"Prolyl endopeptidase-like","aliases":["Prolylendopeptidase-like"],"length_aa":727,"mass_kda":83.9,"function":"Serine peptidase whose precise substrate specificity remains unclear (PubMed:16143824, PubMed:16385448, PubMed:28726805). Does not cleave peptides after a arginine or lysine residue (PubMed:16143824). Regulates trans-Golgi network morphology and sorting by regulating the membrane binding of the AP-1 complex (PubMed:23321636). May play a role in the regulation of synaptic vesicle exocytosis (PubMed:24610330)","subcellular_location":"Cytoplasm, cytosol; Golgi apparatus, trans-Golgi network; Cytoplasm, cytoskeleton; Golgi apparatus; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q4J6C6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PREPL","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":[],"url":"https://opencell.sf.czbiohub.org/search/PREPL","total_profiled":1310},"omim":[{"mim_id":"616224","title":"MYASTHENIC SYNDROME, CONGENITAL, 22; CMS22","url":"https://www.omim.org/entry/616224"},{"mim_id":"609557","title":"PROLYL ENDOPEPTIDASE-LIKE; PREPL","url":"https://www.omim.org/entry/609557"},{"mim_id":"606407","title":"HYPOTONIA-CYSTINURIA SYNDROME","url":"https://www.omim.org/entry/606407"},{"mim_id":"601462","title":"MYASTHENIC SYNDROME, CONGENITAL, 1A, SLOW-CHANNEL; CMS1A","url":"https://www.omim.org/entry/601462"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PREPL"},"hgnc":{"alias_symbol":["KIAA0436"],"prev_symbol":[]},"alphafold":{"accession":"Q4J6C6","domains":[{"cath_id":"3.40.50.1820","chopping":"441-725","consensus_level":"high","plddt":94.2346,"start":441,"end":725},{"cath_id":"2.20.25","chopping":"112-201","consensus_level":"medium","plddt":88.3093,"start":112,"end":201}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4J6C6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q4J6C6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q4J6C6-F1-predicted_aligned_error_v6.png","plddt_mean":82.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PREPL","jax_strain_url":"https://www.jax.org/strain/search?query=PREPL"},"sequence":{"accession":"Q4J6C6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q4J6C6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q4J6C6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4J6C6"}},"corpus_meta":[{"pmid":"16385448","id":"PMC_16385448","title":"Deletion of PREPL, a gene encoding a putative serine oligopeptidase, in patients with hypotonia-cystinuria syndrome.","date":"2005","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16385448","citation_count":69,"is_preprint":false},{"pmid":"24610330","id":"PMC_24610330","title":"PREPL deficiency with or without cystinuria causes a novel myasthenic syndrome.","date":"2014","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/24610330","citation_count":48,"is_preprint":false},{"pmid":"18234729","id":"PMC_18234729","title":"Deletion of C2orf34, PREPL and SLC3A1 causes atypical hypotonia-cystinuria syndrome.","date":"2008","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18234729","citation_count":37,"is_preprint":false},{"pmid":"16913837","id":"PMC_16913837","title":"PREPL: a putative novel oligopeptidase propelled into the limelight.","date":"2006","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16913837","citation_count":30,"is_preprint":false},{"pmid":"16143824","id":"PMC_16143824","title":"The PREPL A protein, a new member of the prolyl oligopeptidase family, lacking catalytic activity.","date":"2005","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/16143824","citation_count":29,"is_preprint":false},{"pmid":"28726805","id":"PMC_28726805","title":"PREPL deficiency: delineation of the phenotype and development of a functional blood assay.","date":"2017","source":"Genetics in medicine : official journal of the American College of Medical Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28726805","citation_count":28,"is_preprint":false},{"pmid":"21692504","id":"PMC_21692504","title":"A substrate-free activity-based protein profiling screen for the discovery of selective PREPL inhibitors.","date":"2011","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/21692504","citation_count":23,"is_preprint":false},{"pmid":"23321636","id":"PMC_23321636","title":"Trans-Golgi network morphology and sorting is regulated by prolyl-oligopeptidase-like protein PREPL and the AP-1 complex subunit μ1A.","date":"2013","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/23321636","citation_count":22,"is_preprint":false},{"pmid":"21222627","id":"PMC_21222627","title":"PREPL, a prolyl endopeptidase-like enzyme by name only?--Lessons from patients.","date":"2011","source":"CNS & neurological disorders drug targets","url":"https://pubmed.ncbi.nlm.nih.gov/21222627","citation_count":19,"is_preprint":false},{"pmid":"24586561","id":"PMC_24586561","title":"Deletion of PREPl causes growth impairment and hypotonia in mice.","date":"2014","source":"PloS 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genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32218803","citation_count":11,"is_preprint":false},{"pmid":"21686663","id":"PMC_21686663","title":"Deletion of C2orf34, PREPL and SLC3A1 causes atypical hypotonia-cystinuria syndrome.","date":"2009","source":"BMJ case reports","url":"https://pubmed.ncbi.nlm.nih.gov/21686663","citation_count":9,"is_preprint":false},{"pmid":"31985178","id":"PMC_31985178","title":"First maternal uniparental disomy for chromosome 2 with PREPL novel frameshift mutation of congenital myasthenic syndrome 22 in an infant.","date":"2020","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31985178","citation_count":8,"is_preprint":false},{"pmid":"33225564","id":"PMC_33225564","title":"Cleavage of PrePL by Lon promotes growth and pathogenesis in Magnaporthe oryzae.","date":"2021","source":"Environmental 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defects","date":"2025-10-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.28.685080","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11832,"output_tokens":2642,"usd":0.037563,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9940,"output_tokens":2875,"usd":0.060788,"stage2_stop_reason":"end_turn"},"total_usd":0.098351,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"PREPL is localized in the cytosol and possesses a catalytic triad (Ser470, Asp556, His601); substitution of these predicted catalytic residues by alanines resulted in loss of reactivity with a serine hydrolase-specific activity-based probe, confirming an intact but unique catalytic machinery. Unlike prolyl oligopeptidase and oligopeptidase B, PREPL activity depends only on the carboxyterminal domain.\",\n      \"method\": \"Activity-based probe labeling with catalytic-residue alanine mutagenesis; subcellular fractionation\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct active-site mutagenesis combined with activity-based probe, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"16385448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PREPL A (638-residue splice variant) was purified from E. coli and shown to have secondary structure similar to oligopeptidase B; it reacted with diisopropyl fluorophosphate and slowly hydrolyzed an activated ester substrate, confirming a reactive catalytic serine. However, PREPL A did not cleave peptide substrates with a P1 basic residue (Arg/Lys), indicating negligible canonical peptidase activity and suggesting a non-peptidase biological function. Dimerization was observed and may account for enhanced conformational stability.\",\n      \"method\": \"Recombinant protein expression and purification, differential-scanning calorimetry, enzyme activity assays with peptide and activated ester substrates, DFP inhibitor labeling\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple substrate assays and inhibitor labeling, single lab with orthogonal biochemical methods\",\n      \"pmids\": [\"16143824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PREPL (cytoplasmic) was identified as a direct interaction partner of the N-terminal 70 amino acids of AP-1 complex subunit μ1A via yeast two-hybrid screen. PREPL overexpression reduced AP-1 membrane binding, while reduced PREPL expression increased AP-1 membrane binding and impaired AP-1 recycling. PREPL-deficient patient cell lines displayed an expanded trans-Golgi network that was rescued by PREPL re-expression. PREPL colocalizes with residual membrane-bound AP-1, functioning as an AP-1 effector regulating AP-1 membrane association and TGN morphology.\",\n      \"method\": \"Yeast two-hybrid screen; AP-1 membrane binding assays; PREPL overexpression and knockdown; colocalization by fluorescence microscopy; patient cell line complementation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid identification plus functional overexpression/knockdown and rescue in patient cell lines, multiple orthogonal methods\",\n      \"pmids\": [\"23321636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PREPL deficiency causes a congenital myasthenic syndrome with decreased quantal content of the endplate potential and reduced miniature endplate potential amplitude without acetylcholine receptor deficiency or altered endplate geometry, indicating both pre- and postsynaptic defects. The myasthenia is attributed to abrogated PREPL interaction with adaptor protein 1 (AP-1). No PREPL expression was detected in patient muscle and endplates.\",\n      \"method\": \"Electrophysiology (in vitro neuromuscular transmission studies), immunoblot, histochemistry, ultrastructural studies in patient with isolated PREPL deficiency\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct electrophysiology in patient tissue, single lab, pathway placement inferred from AP-1 interaction data from separate study\",\n      \"pmids\": [\"24610330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Deletion of exon 11 from the mouse Prepl gene (which encodes key catalytic amino acids) leads to loss of PREPL protein and reduced Prepl mRNA. PREPL-null mice exhibit significantly reduced growth (shorter and lighter) and neonatal hypotonia as measured by a righting reflex assay, establishing that PREPL is required for normal growth and neonatal muscle tone in vivo.\",\n      \"method\": \"PREPL knockout mouse model (exon 11 deletion); body measurement; righting assay for neonatal hypotonia\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO mouse with defined phenotypic readouts, single lab, no molecular mechanism identified beyond loss of protein\",\n      \"pmids\": [\"24586561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A fluorescence polarization activity-based protein profiling (fluopol-ABPP) screen identified selective small-molecule inhibitors of PREPL serine hydrolase activity that block PREPL activity in cells. One inhibitor (1-isobutyl-3-oxo-3,5,6,7-tetrahydro-2H-cyclopenta[c]pyridine-4-carbonitrile) distributed to the brain after administration to mice, confirming PREPL is a functional serine hydrolase amenable to pharmacological inhibition.\",\n      \"method\": \"Fluopol-ABPP high-throughput screen (~300,000 compounds); cell-based activity assay; mouse pharmacokinetics\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — activity-based probe assay confirmed in cells and in vivo, single lab but multiple assay levels\",\n      \"pmids\": [\"21692504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NRF-2 and YY-1 transcription factors cooperatively bind a 243-bp GC-rich bidirectional minimal promoter within the 405-bp intergenic region between PREPL and C2ORF34, driving expression of both genes in an additive manner. Cis-acting repressive elements within this region also contribute to tissue-specific expression.\",\n      \"method\": \"Promoter deletion/reporter assays, transcription factor binding studies (gel shift/ChIP implied), expression analysis across tissues\",\n      \"journal\": \"BMC molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional promoter assays with transcription factor identification, single lab with multiple reporter and binding experiments\",\n      \"pmids\": [\"19575798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Missense variants in PREPL from CMS22 patients do not impair hydrolase activity but reduce binding to known interactors, and structural analysis indicates the variants affect regions involved in intraprotein or protein-protein interactions. Catalytically inactive PREPL p.Ser559Ala cell lines showed that hydrolytic activity of PREPL is required for normal mitochondrial function but NOT for regulating AP-1-mediated transport in the trans-Golgi network, demonstrating that PREPL has separable enzymatic and non-enzymatic functions.\",\n      \"method\": \"Biochemical hydrolase activity assays; structural analysis; protein-protein interaction assays; CRISPR catalytic-dead knock-in (Ser559Ala) cell lines; mitochondrial function assays; AP-1 transport assays\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — catalytic-dead mutagenesis combined with functional cellular assays (mitochondria and TGN transport), structural analysis, and interaction studies in single rigorous study\",\n      \"pmids\": [\"39078710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In PREPL KO HEK293T cells and Prepl KO mouse brains, global phospholipid composition was largely unchanged, arguing against a direct lipase role for PREPL in (lyso)phospholipid turnover. However, PREPL KO cells accumulated triacylglycerols (TAGs) and increased lipid droplets. PREPL does not localize to peroxisomes, and peroxisome numbers and protein levels were largely unaffected, but KO cells showed elongated peroxisomes. The TAG accumulation and peroxisome elongation are interpreted as secondary consequences of mitochondrial dysfunction (impaired fatty acid β-oxidation) caused by PREPL loss, not a direct lipase function.\",\n      \"method\": \"Unbiased lipidomics in KO mouse brain and CRISPR-Cas9 KO cell lines; lipid droplet imaging; peroxisome morphology and protein level analysis; PREPL localization studies\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — unbiased lipidomics and CRISPR KO with multiple readouts, preprint not yet peer-reviewed, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.10.28.685080\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PREPL is a cytosolic serine hydrolase of the prolyl oligopeptidase family with a reactive catalytic triad (Ser470/Ser559, Asp556, His601) that confers esterase activity but negligible canonical peptidase activity toward basic-residue substrates; it functions as an effector of the AP-1 clathrin adaptor complex by binding the μ1A subunit to regulate AP-1 membrane cycling and trans-Golgi network morphology (a non-enzymatic function), while its hydrolytic activity is separately required for normal mitochondrial respiratory function, with loss of PREPL causing triacylglycerol accumulation as a secondary metabolic consequence of mitochondrial dysfunction.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PREPL is a cytosolic serine hydrolase of the prolyl oligopeptidase family that performs two genetically separable functions—an enzymatic activity required for normal mitochondrial respiration and a non-enzymatic role as an effector of the AP-1 clathrin adaptor complex [#7]. Its catalytic machinery comprises a serine hydrolase triad (Ser470, Asp556, His601) localized to the C-terminal domain; mutation of these residues abolishes labeling by serine hydrolase-directed probes, and recombinant PREPL reacts with active-site inhibitors and slowly hydrolyzes activated esters yet fails to cleave peptides bearing a P1 basic residue, defining it as an esterase with negligible canonical peptidase activity [#0, #1]. The non-enzymatic function arises through direct binding to the N-terminus of the AP-1 μ1A subunit, where PREPL regulates AP-1 membrane cycling: it limits AP-1 membrane association and is required for AP-1 recycling, and its loss expands the trans-Golgi network in patient cells, a defect rescued by PREPL re-expression [#2]. Catalytically dead PREPL (Ser559Ala) retains normal AP-1-mediated TGN transport while failing to support mitochondrial function, and CMS22 patient missense variants disrupt interactor binding rather than hydrolase activity, cementing the division between the two roles [#7]. Loss of PREPL causes triacylglycerol and lipid-droplet accumulation as a secondary consequence of mitochondrial dysfunction rather than a direct lipase activity [#8]. PREPL deficiency causes a congenital myasthenic syndrome with combined pre- and postsynaptic neuromuscular transmission defects, and PREPL-null mice show reduced growth and neonatal hypotonia [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established that PREPL is a genuine but atypical serine hydrolase, resolving whether its predicted prolyl-oligopeptidase-family triad is catalytically functional.\",\n      \"evidence\": \"Activity-based probe labeling with catalytic-residue alanine mutagenesis and subcellular fractionation; recombinant protein with DSC, inhibitor labeling, and peptide/ester substrate assays\",\n      \"pmids\": [\"16385448\", \"16143824\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No physiological substrate of the esterase activity identified\",\n        \"Biological consequence of catalysis not connected to a cellular process at this stage\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the transcriptional control of PREPL, showing it shares a bidirectional GC-rich promoter with C2ORF34 driven cooperatively by NRF-2 and YY-1.\",\n      \"evidence\": \"Promoter deletion/reporter assays and transcription factor binding analysis across tissues\",\n      \"pmids\": [\"19575798\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Does not link transcriptional regulation to a specific physiological stimulus\",\n        \"Tissue-specific repressive elements not mapped to defined factors\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated PREPL is a druggable functional serine hydrolase in cells and in vivo, providing tools to probe its enzymatic role.\",\n      \"evidence\": \"Fluopol-ABPP high-throughput screen (~300,000 compounds), cell-based activity assay, and mouse pharmacokinetics\",\n      \"pmids\": [\"21692504\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Inhibitor phenotype on cellular function not assessed\",\n        \"No endogenous substrate revealed by inhibition\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified the first defined cellular function of PREPL as a non-enzymatic AP-1 effector controlling adaptor membrane cycling and TGN morphology.\",\n      \"evidence\": \"Yeast two-hybrid screen against μ1A, AP-1 membrane binding assays, overexpression/knockdown, and patient cell line complementation\",\n      \"pmids\": [\"23321636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the interaction depends on catalytic activity not tested here\",\n        \"Mechanism by which PREPL displaces AP-1 from membranes unresolved\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected PREPL loss to neuromuscular disease, showing combined pre- and postsynaptic transmission defects and an organismal growth/tone phenotype.\",\n      \"evidence\": \"Neuromuscular electrophysiology in patient tissue with immunoblot/histochemistry; exon-11-deletion PREPL knockout mouse with body measurements and righting reflex assay\",\n      \"pmids\": [\"24610330\", \"24586561\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular cause of the synaptic defect inferred from AP-1 interaction rather than directly demonstrated\",\n        \"Mouse phenotype not mechanistically tied to AP-1 versus enzymatic function\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dissected PREPL's two activities, proving hydrolase function is required for mitochondrial function but dispensable for AP-1-mediated TGN transport, and that disease variants act by disrupting interactions.\",\n      \"evidence\": \"CRISPR catalytic-dead (Ser559Ala) knock-in cell lines, mitochondrial and AP-1 transport assays, hydrolase activity assays, structural analysis, and interaction studies of CMS22 variants\",\n      \"pmids\": [\"39078710\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Substrate and molecular mechanism linking PREPL catalysis to mitochondrial respiration unknown\",\n        \"Specific interactors lost by CMS22 variants not fully enumerated\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Clarified the lipid phenotype of PREPL loss, arguing against a direct lipase role and attributing triacylglycerol and peroxisome changes to secondary mitochondrial dysfunction.\",\n      \"evidence\": \"Unbiased lipidomics in KO mouse brain and CRISPR KO cells, lipid droplet imaging, peroxisome morphology/protein analysis, and localization studies (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.10.28.685080\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint not yet peer-reviewed\",\n        \"Direct biochemical link between PREPL catalysis and fatty acid β-oxidation not established\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous physiological substrate of PREPL's esterase activity and the molecular mechanism coupling that activity to mitochondrial respiration remain unidentified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No in vivo substrate identified despite confirmed esterase activity\",\n        \"Mechanism by which PREPL binding regulates AP-1 membrane release is undefined\",\n        \"Causal chain from catalytic loss to mitochondrial dysfunction not reconstituted\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 5, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [7, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"AP1M1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}