{"gene":"PGAP1","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2004,"finding":"PGAP1 encodes an ER-associated 922-amino acid membrane protein that functions as GPI inositol-deacylase, removing the acyl group from the inositol of GPI anchors immediately after GPI attachment to proteins. Substitution of a conserved putative catalytic serine with alanine resulted in complete loss of deacylase activity, establishing the serine as essential for catalysis.","method":"Mutagenesis of catalytic serine + functional rescue assay in GPI inositol-deacylase-deficient CHO cells + PI-PLC resistance assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — active-site mutagenesis combined with functional cell-based assay; foundational cloning paper with multiple orthogonal methods","pmids":["14734546"],"is_preprint":false},{"year":2004,"finding":"Loss of PGAP1-mediated inositol deacylation causes a clear delay in the maturation and transport of GPI-anchored proteins from the ER to the Golgi, establishing that inositol deacylation is required for efficient ER-to-Golgi trafficking of GPI-APs.","method":"PGAP1-deficient CHO cell line characterization; pulse-chase and trafficking assays for GPI-AP maturation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — isogenic mutant cell line with defined GPI-AP trafficking phenotype; original identification paper with rigorous controls","pmids":["14734546"],"is_preprint":false},{"year":2007,"finding":"PGAP1 knockout mice exhibit otocephaly and die shortly after birth, and surviving male knockouts display severely reduced fertility: PGAP1-deficient spermatozoa fail to enter the oviduct, show weak attachment to the zona pellucida, and have a severely diminished rate of fertilization in vitro, demonstrating that GPI inositol deacylation is essential for sperm function.","method":"PGAP1 knockout mouse model; in vivo fertility assays; in vitro fertilization and zona pellucida binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — constitutive knockout with specific cellular phenotype (sperm function, zona pellucida binding) and in vitro mechanistic follow-up","pmids":["17711852"],"is_preprint":false},{"year":2014,"finding":"A homozygous p.Leu197del mutation in PGAP1 abolishes GPI inositol-deacylase activity: GPI-APs on patient-derived B lymphoblastoid cells were completely resistant to PI-PLC cleavage (indicating retention of the inositol-acyl chain), and sensitivity was restored by transfection with wild-type PGAP1 cDNA, confirming that PGAP1 is the sole deacylase responsible for this remodeling step in human cells.","method":"PI-PLC sensitivity assay on patient-derived B lymphoblastoid cells; rescue by wild-type PGAP1 cDNA transfection","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — patient cells plus functional rescue with wild-type construct, two orthogonal methods confirming loss and restoration of activity","pmids":["24784135"],"is_preprint":false},{"year":2015,"finding":"Two PGAP1 variants (p.Pro92del and p.Lys308Asnfs*25) identified in a patient cause functional loss of PGAP1: neither mutant construct rescued PI-PLC sensitivity in PGAP1-deficient CHO cells, and patient lymphoblastoid cells showed no PI-PLC sensitivity compared with partial sensitivity in heterozygous carrier parents.","method":"Transfection of mutant vs. wild-type PGAP1 constructs into PGAP1-deficient CHO cells; PI-PLC sensitivity assay on patient and carrier LCLs","journal":"European journal of human genetics : EJHG","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional cell assay with mutant/WT construct comparison and patient-derived cell validation; two orthogonal cell systems","pmids":["25804403"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of PGAP1 at 2.66–2.84 Å resolution reveal a 10-transmembrane architecture. The enzyme uses serine hydrolase-type catalysis with atypical features; GPI-AP acyl chains are held in a guitar-shaped hydrophobic cavity, and abundant luminal glycan-mediated interactions counterbalance hydrophobic-hydrophilic mismatches to confer substrate fidelity and prevent hydrolysis of bulk membrane lipids. Structural analysis implies substrate entrance and product release via a 'drawing compass' movement of GPI-APs.","method":"Cryo-EM structure determination (2.66–2.84 Å) combined with biochemical activity assays and structural analysis of substrate-binding cavity","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structures with biochemical validation; multiple orthogonal analyses in a single rigorous study","pmids":["38167496"],"is_preprint":false},{"year":2022,"finding":"In Arabidopsis (plant ortholog HLD1/AtPGAP1), GPI inositol-deacylase activity is essential for self-incompatibility; HLD1 knockout abolishes self-incompatibility without affecting GPI-AP production or targeting, but impairs cleavage and release of GPI-APs (demonstrated with GFP-SKU5 as representative GPI-AP), confirming the conserved enzymatic function of the PGAP1 ortholog in GPI-AP membrane release.","method":"Genetic SI suppressor screen in Arabidopsis; functional assay of GPI-AP membrane release using GFP-SKU5 reporter; in vivo deacylase activity assay in plant lines","journal":"Current biology : CB","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional genetic screen and GPI-AP release assay in plant ortholog; relevant to conserved mechanism but performed in a non-mammalian system","pmids":["35316654"],"is_preprint":false}],"current_model":"PGAP1 is an ER-resident 10-transmembrane serine hydrolase that removes the inositol-linked acyl chain from nascent GPI-anchored proteins immediately after GPI attachment; its guitar-shaped hydrophobic cavity and luminal glycan interactions confer substrate fidelity, inositol deacylation is required for efficient ER-to-Golgi trafficking of GPI-APs, and loss of PGAP1 activity in vivo causes developmental defects, male infertility due to sperm-zona pellucida adhesion failure, and in humans leads to intellectual disability and encephalopathy."},"narrative":{"mechanistic_narrative":"PGAP1 is an endoplasmic reticulum-resident GPI inositol-deacylase that catalyzes a key post-attachment remodeling step of glycosylphosphatidylinositol-anchored proteins (GPI-APs), removing the acyl chain linked to the inositol of the GPI anchor immediately after GPI is transferred to a nascent protein [PMID:14734546]. It is a serine hydrolase whose activity depends on a conserved catalytic serine, mutation of which abolishes deacylation [PMID:14734546]. Cryo-EM structures resolve a 10-transmembrane architecture in which GPI-AP acyl chains are accommodated in a guitar-shaped hydrophobic cavity, while luminal glycan-mediated interactions confer substrate fidelity and prevent hydrolysis of bulk membrane lipids, with substrate entry and product release modeled as a 'drawing compass' motion [PMID:38167496]. This deacylation is required for efficient ER-to-Golgi maturation and trafficking of GPI-APs [PMID:14734546]. The enzymatic function is conserved across kingdoms: the Arabidopsis ortholog HLD1/AtPGAP1 supports GPI-AP membrane release and is essential for self-incompatibility [PMID:35316654]. Loss of PGAP1 activity causes developmental and reproductive defects in mice, including otocephaly, perinatal lethality, and male infertility from failed sperm–zona pellucida adhesion [PMID:17711852], and in humans biallelic loss-of-function mutations abolish deacylase activity and cause intellectual disability and encephalopathy [PMID:24784135, PMID:25804403].","teleology":[{"year":2004,"claim":"Established the molecular identity and catalytic mechanism of PGAP1, answering what enzyme performs GPI inositol deacylation and how it acts.","evidence":"Catalytic serine mutagenesis with functional rescue in deacylase-deficient CHO cells and PI-PLC resistance readout","pmids":["14734546"],"confidence":"High","gaps":["No structural basis for catalysis or substrate selectivity at this stage","Physiological consequence of deacylation not yet defined"]},{"year":2004,"claim":"Linked the deacylation reaction to a cell-biological function, showing it is required for efficient ER-to-Golgi trafficking of GPI-APs.","evidence":"Pulse-chase and maturation/trafficking assays in isogenic PGAP1-deficient CHO cells","pmids":["14734546"],"confidence":"High","gaps":["Mechanism by which retained acyl chain delays export unresolved","Whether all GPI-APs depend equally on deacylation unknown"]},{"year":2007,"claim":"Demonstrated the in vivo physiological requirement for PGAP1, connecting deacylation to organismal development and sperm function.","evidence":"Constitutive PGAP1 knockout mouse with fertility, IVF, and zona pellucida binding assays","pmids":["17711852"],"confidence":"High","gaps":["Which specific GPI-AP substrates mediate sperm-zona adhesion not identified","Cause of otocephaly at the GPI-AP level not defined"]},{"year":2014,"claim":"Confirmed PGAP1 as the sole deacylase for this remodeling step in human cells and tied its loss to human disease.","evidence":"PI-PLC sensitivity assay on patient B lymphoblastoid cells with wild-type cDNA rescue","pmids":["24784135"],"confidence":"High","gaps":["Genotype-phenotype relationship across mutation types not established","Downstream GPI-AP defects causing neurological phenotype unmapped"]},{"year":2015,"claim":"Extended the human disease link by functionally validating additional loss-of-function variants and dose-dependence in carriers.","evidence":"Mutant vs wild-type construct rescue in deacylase-deficient CHO cells and PI-PLC sensitivity in patient and heterozygous carrier LCLs","pmids":["25804403"],"confidence":"High","gaps":["Clinical spectrum across PGAP1 variants not delineated","No structural rationale for variant severity"]},{"year":2022,"claim":"Showed deep evolutionary conservation of the deacylase function, establishing its role in GPI-AP membrane release in plants.","evidence":"Self-incompatibility suppressor screen in Arabidopsis with GFP-SKU5 GPI-AP release reporter and in vivo deacylase assay","pmids":["35316654"],"confidence":"Medium","gaps":["Performed in non-mammalian system; direct relevance to mammalian PGAP1 inferred not shown","Link between deacylation and GPI-AP cleavage/release mechanistically incomplete"]},{"year":2024,"claim":"Resolved the structural basis of catalysis and substrate fidelity, explaining how PGAP1 selects GPI-AP acyl chains over bulk membrane lipids.","evidence":"Cryo-EM structures at 2.66–2.84 Å with biochemical activity assays and substrate-cavity analysis","pmids":["38167496"],"confidence":"High","gaps":["No structure of an enzyme-substrate or product complex confirming the 'drawing compass' model","Regulation of enzyme activity in the ER not addressed"]},{"year":null,"claim":"The specific GPI-AP substrates whose mistrafficking underlies the neurological and reproductive phenotypes remain unidentified.","evidence":"","pmids":[],"confidence":"High","gaps":["No substrate-resolved map linking deacylation failure to tissue-specific disease","Regulatory inputs controlling PGAP1 activity unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,3,5]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q75T13","full_name":"GPI inositol-deacylase","aliases":["Post-GPI attachment to proteins factor 1","hPGAP1"],"length_aa":922,"mass_kda":105.4,"function":"GPI inositol-deacylase that catalyzes the remove of the acyl chain linked to the 2-OH position of inositol ring from the GPI-anchored protein (GPI-AP) in the endoplasmic reticulum (PubMed:24784135, PubMed:38167496). Initiates the post-attachment remodeling phase of GPI-AP biogenesis and participates in endoplasmic reticulum (ER)-to-Golgi transport of GPI-anchored protein (PubMed:24784135, PubMed:38167496)","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q75T13/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PGAP1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PGAP1","total_profiled":1310},"omim":[{"mim_id":"619979","title":"CHROMOSOME 18 OPEN READING FRAME 32; C18ORF32","url":"https://www.omim.org/entry/619979"},{"mim_id":"619342","title":"POST-GPI ATTACHMENT TO PROTEINS 6; PGAP6","url":"https://www.omim.org/entry/619342"},{"mim_id":"615802","title":"NEURODEVELOPMENTAL DISORDER WITH DYSMORPHIC FEATURES, SPASTICITY, AND BRAIN ABNORMALITIES; NEDDSBA","url":"https://www.omim.org/entry/615802"},{"mim_id":"611655","title":"POST-GPI ATTACHMENT TO PROTEINS 1; PGAP1","url":"https://www.omim.org/entry/611655"},{"mim_id":"610293","title":"GLYCOSYLPHOSPHATIDYLINOSITOL BIOSYNTHESIS DEFECT 1; GPIBD1","url":"https://www.omim.org/entry/610293"}],"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/PGAP1"},"hgnc":{"alias_symbol":["FLJ12377","Bst1","SPG67"],"prev_symbol":[]},"alphafold":{"accession":"Q75T13","domains":[{"cath_id":"3.40.50.1820","chopping":"47-327","consensus_level":"high","plddt":92.5218,"start":47,"end":327},{"cath_id":"2.60.120","chopping":"341-462","consensus_level":"medium","plddt":89.2506,"start":341,"end":462},{"cath_id":"2.60.120,2.60.120","chopping":"464-591","consensus_level":"medium","plddt":89.7335,"start":464,"end":591},{"cath_id":"-","chopping":"597-776_804-920","consensus_level":"medium","plddt":90.1929,"start":597,"end":920}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q75T13","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q75T13-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q75T13-F1-predicted_aligned_error_v6.png","plddt_mean":89.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PGAP1","jax_strain_url":"https://www.jax.org/strain/search?query=PGAP1"},"sequence":{"accession":"Q75T13","fasta_url":"https://rest.uniprot.org/uniprotkb/Q75T13.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q75T13/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q75T13"}},"corpus_meta":[{"pmid":"14734546","id":"PMC_14734546","title":"Inositol deacylation of glycosylphosphatidylinositol-anchored proteins is mediated by mammalian PGAP1 and yeast Bst1p.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14734546","citation_count":138,"is_preprint":false},{"pmid":"27477276","id":"PMC_27477276","title":"The Pseudomonas aeruginosa Type VI Secretion PGAP1-like Effector Induces Host Autophagy by Activating Endoplasmic Reticulum Stress.","date":"2016","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/27477276","citation_count":99,"is_preprint":false},{"pmid":"17711852","id":"PMC_17711852","title":"PGAP1 knock-out mice show otocephaly and male infertility.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17711852","citation_count":75,"is_preprint":false},{"pmid":"24784135","id":"PMC_24784135","title":"Null mutation in PGAP1 impairing Gpi-anchor maturation in patients with intellectual disability and encephalopathy.","date":"2014","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24784135","citation_count":67,"is_preprint":false},{"pmid":"27206732","id":"PMC_27206732","title":"Compound heterozygous variants in PGAP1 causing severe psychomotor retardation, brain atrophy, recurrent apneas and delayed myelination: a case report and literature review.","date":"2016","source":"BMC neurology","url":"https://pubmed.ncbi.nlm.nih.gov/27206732","citation_count":20,"is_preprint":false},{"pmid":"26050939","id":"PMC_26050939","title":"Loss of function of PGAP1 as a cause of severe encephalopathy identified by Whole Exome Sequencing: Lessons of the bioinformatics pipeline.","date":"2015","source":"Molecular and cellular probes","url":"https://pubmed.ncbi.nlm.nih.gov/26050939","citation_count":20,"is_preprint":false},{"pmid":"25804403","id":"PMC_25804403","title":"Cerebral visual impairment and intellectual disability caused by PGAP1 variants.","date":"2015","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/25804403","citation_count":18,"is_preprint":false},{"pmid":"35316654","id":"PMC_35316654","title":"Self-incompatibility requires GPI anchor remodeling by the poppy PGAP1 ortholog HLD1.","date":"2022","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/35316654","citation_count":18,"is_preprint":false},{"pmid":"38167496","id":"PMC_38167496","title":"Molecular basis of the inositol deacylase PGAP1 involved in quality control of GPI-AP biogenesis.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38167496","citation_count":12,"is_preprint":false},{"pmid":"35686740","id":"PMC_35686740","title":"LncRNA LEMD1-AS1 relieves chondrocyte inflammation by targeting miR-944/PGAP1 in osteoarthritis.","date":"2022","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/35686740","citation_count":10,"is_preprint":false},{"pmid":"37691099","id":"PMC_37691099","title":"Downregulation of lncRNA NEAT1 interacts with miR-374b-5p/PGAP1 axis to aggravate the development of osteoarthritis.","date":"2023","source":"Journal of orthopaedic surgery and research","url":"https://pubmed.ncbi.nlm.nih.gov/37691099","citation_count":5,"is_preprint":false},{"pmid":"40785186","id":"PMC_40785186","title":"PGAP1-Related Encephalopathy in an Infant With Neurodevelopmental Delay: Novel Variant and Review of Literature.","date":"2025","source":"International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/40785186","citation_count":1,"is_preprint":false},{"pmid":"41619156","id":"PMC_41619156","title":"Th17-related genes PGAP1 and TMBIM1 serve as potential diagnostic and predictive biomarkers in systemic sclerosis: bioinformatic identification and murine model validation.","date":"2026","source":"Clinical rheumatology","url":"https://pubmed.ncbi.nlm.nih.gov/41619156","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9304,"output_tokens":1938,"usd":0.028491,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8906,"output_tokens":2408,"usd":0.052365,"stage2_stop_reason":"end_turn"},"total_usd":0.080856,"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\": 2004,\n      \"finding\": \"PGAP1 encodes an ER-associated 922-amino acid membrane protein that functions as GPI inositol-deacylase, removing the acyl group from the inositol of GPI anchors immediately after GPI attachment to proteins. Substitution of a conserved putative catalytic serine with alanine resulted in complete loss of deacylase activity, establishing the serine as essential for catalysis.\",\n      \"method\": \"Mutagenesis of catalytic serine + functional rescue assay in GPI inositol-deacylase-deficient CHO cells + PI-PLC resistance assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — active-site mutagenesis combined with functional cell-based assay; foundational cloning paper with multiple orthogonal methods\",\n      \"pmids\": [\"14734546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Loss of PGAP1-mediated inositol deacylation causes a clear delay in the maturation and transport of GPI-anchored proteins from the ER to the Golgi, establishing that inositol deacylation is required for efficient ER-to-Golgi trafficking of GPI-APs.\",\n      \"method\": \"PGAP1-deficient CHO cell line characterization; pulse-chase and trafficking assays for GPI-AP maturation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isogenic mutant cell line with defined GPI-AP trafficking phenotype; original identification paper with rigorous controls\",\n      \"pmids\": [\"14734546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PGAP1 knockout mice exhibit otocephaly and die shortly after birth, and surviving male knockouts display severely reduced fertility: PGAP1-deficient spermatozoa fail to enter the oviduct, show weak attachment to the zona pellucida, and have a severely diminished rate of fertilization in vitro, demonstrating that GPI inositol deacylation is essential for sperm function.\",\n      \"method\": \"PGAP1 knockout mouse model; in vivo fertility assays; in vitro fertilization and zona pellucida binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — constitutive knockout with specific cellular phenotype (sperm function, zona pellucida binding) and in vitro mechanistic follow-up\",\n      \"pmids\": [\"17711852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A homozygous p.Leu197del mutation in PGAP1 abolishes GPI inositol-deacylase activity: GPI-APs on patient-derived B lymphoblastoid cells were completely resistant to PI-PLC cleavage (indicating retention of the inositol-acyl chain), and sensitivity was restored by transfection with wild-type PGAP1 cDNA, confirming that PGAP1 is the sole deacylase responsible for this remodeling step in human cells.\",\n      \"method\": \"PI-PLC sensitivity assay on patient-derived B lymphoblastoid cells; rescue by wild-type PGAP1 cDNA transfection\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — patient cells plus functional rescue with wild-type construct, two orthogonal methods confirming loss and restoration of activity\",\n      \"pmids\": [\"24784135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Two PGAP1 variants (p.Pro92del and p.Lys308Asnfs*25) identified in a patient cause functional loss of PGAP1: neither mutant construct rescued PI-PLC sensitivity in PGAP1-deficient CHO cells, and patient lymphoblastoid cells showed no PI-PLC sensitivity compared with partial sensitivity in heterozygous carrier parents.\",\n      \"method\": \"Transfection of mutant vs. wild-type PGAP1 constructs into PGAP1-deficient CHO cells; PI-PLC sensitivity assay on patient and carrier LCLs\",\n      \"journal\": \"European journal of human genetics : EJHG\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional cell assay with mutant/WT construct comparison and patient-derived cell validation; two orthogonal cell systems\",\n      \"pmids\": [\"25804403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of PGAP1 at 2.66–2.84 Å resolution reveal a 10-transmembrane architecture. The enzyme uses serine hydrolase-type catalysis with atypical features; GPI-AP acyl chains are held in a guitar-shaped hydrophobic cavity, and abundant luminal glycan-mediated interactions counterbalance hydrophobic-hydrophilic mismatches to confer substrate fidelity and prevent hydrolysis of bulk membrane lipids. Structural analysis implies substrate entrance and product release via a 'drawing compass' movement of GPI-APs.\",\n      \"method\": \"Cryo-EM structure determination (2.66–2.84 Å) combined with biochemical activity assays and structural analysis of substrate-binding cavity\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structures with biochemical validation; multiple orthogonal analyses in a single rigorous study\",\n      \"pmids\": [\"38167496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In Arabidopsis (plant ortholog HLD1/AtPGAP1), GPI inositol-deacylase activity is essential for self-incompatibility; HLD1 knockout abolishes self-incompatibility without affecting GPI-AP production or targeting, but impairs cleavage and release of GPI-APs (demonstrated with GFP-SKU5 as representative GPI-AP), confirming the conserved enzymatic function of the PGAP1 ortholog in GPI-AP membrane release.\",\n      \"method\": \"Genetic SI suppressor screen in Arabidopsis; functional assay of GPI-AP membrane release using GFP-SKU5 reporter; in vivo deacylase activity assay in plant lines\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional genetic screen and GPI-AP release assay in plant ortholog; relevant to conserved mechanism but performed in a non-mammalian system\",\n      \"pmids\": [\"35316654\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PGAP1 is an ER-resident 10-transmembrane serine hydrolase that removes the inositol-linked acyl chain from nascent GPI-anchored proteins immediately after GPI attachment; its guitar-shaped hydrophobic cavity and luminal glycan interactions confer substrate fidelity, inositol deacylation is required for efficient ER-to-Golgi trafficking of GPI-APs, and loss of PGAP1 activity in vivo causes developmental defects, male infertility due to sperm-zona pellucida adhesion failure, and in humans leads to intellectual disability and encephalopathy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PGAP1 is an endoplasmic reticulum-resident GPI inositol-deacylase that catalyzes a key post-attachment remodeling step of glycosylphosphatidylinositol-anchored proteins (GPI-APs), removing the acyl chain linked to the inositol of the GPI anchor immediately after GPI is transferred to a nascent protein [#0]. It is a serine hydrolase whose activity depends on a conserved catalytic serine, mutation of which abolishes deacylation [#0]. Cryo-EM structures resolve a 10-transmembrane architecture in which GPI-AP acyl chains are accommodated in a guitar-shaped hydrophobic cavity, while luminal glycan-mediated interactions confer substrate fidelity and prevent hydrolysis of bulk membrane lipids, with substrate entry and product release modeled as a 'drawing compass' motion [#5]. This deacylation is required for efficient ER-to-Golgi maturation and trafficking of GPI-APs [#1]. The enzymatic function is conserved across kingdoms: the Arabidopsis ortholog HLD1/AtPGAP1 supports GPI-AP membrane release and is essential for self-incompatibility [#6]. Loss of PGAP1 activity causes developmental and reproductive defects in mice, including otocephaly, perinatal lethality, and male infertility from failed sperm–zona pellucida adhesion [#2], and in humans biallelic loss-of-function mutations abolish deacylase activity and cause intellectual disability and encephalopathy [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the molecular identity and catalytic mechanism of PGAP1, answering what enzyme performs GPI inositol deacylation and how it acts.\",\n      \"evidence\": \"Catalytic serine mutagenesis with functional rescue in deacylase-deficient CHO cells and PI-PLC resistance readout\",\n      \"pmids\": [\"14734546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural basis for catalysis or substrate selectivity at this stage\", \"Physiological consequence of deacylation not yet defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Linked the deacylation reaction to a cell-biological function, showing it is required for efficient ER-to-Golgi trafficking of GPI-APs.\",\n      \"evidence\": \"Pulse-chase and maturation/trafficking assays in isogenic PGAP1-deficient CHO cells\",\n      \"pmids\": [\"14734546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which retained acyl chain delays export unresolved\", \"Whether all GPI-APs depend equally on deacylation unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrated the in vivo physiological requirement for PGAP1, connecting deacylation to organismal development and sperm function.\",\n      \"evidence\": \"Constitutive PGAP1 knockout mouse with fertility, IVF, and zona pellucida binding assays\",\n      \"pmids\": [\"17711852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific GPI-AP substrates mediate sperm-zona adhesion not identified\", \"Cause of otocephaly at the GPI-AP level not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Confirmed PGAP1 as the sole deacylase for this remodeling step in human cells and tied its loss to human disease.\",\n      \"evidence\": \"PI-PLC sensitivity assay on patient B lymphoblastoid cells with wild-type cDNA rescue\",\n      \"pmids\": [\"24784135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genotype-phenotype relationship across mutation types not established\", \"Downstream GPI-AP defects causing neurological phenotype unmapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended the human disease link by functionally validating additional loss-of-function variants and dose-dependence in carriers.\",\n      \"evidence\": \"Mutant vs wild-type construct rescue in deacylase-deficient CHO cells and PI-PLC sensitivity in patient and heterozygous carrier LCLs\",\n      \"pmids\": [\"25804403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Clinical spectrum across PGAP1 variants not delineated\", \"No structural rationale for variant severity\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed deep evolutionary conservation of the deacylase function, establishing its role in GPI-AP membrane release in plants.\",\n      \"evidence\": \"Self-incompatibility suppressor screen in Arabidopsis with GFP-SKU5 GPI-AP release reporter and in vivo deacylase assay\",\n      \"pmids\": [\"35316654\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Performed in non-mammalian system; direct relevance to mammalian PGAP1 inferred not shown\", \"Link between deacylation and GPI-AP cleavage/release mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the structural basis of catalysis and substrate fidelity, explaining how PGAP1 selects GPI-AP acyl chains over bulk membrane lipids.\",\n      \"evidence\": \"Cryo-EM structures at 2.66–2.84 Å with biochemical activity assays and substrate-cavity analysis\",\n      \"pmids\": [\"38167496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of an enzyme-substrate or product complex confirming the 'drawing compass' model\", \"Regulation of enzyme activity in the ER not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The specific GPI-AP substrates whose mistrafficking underlies the neurological and reproductive phenotypes remain unidentified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate-resolved map linking deacylation failure to tissue-specific disease\", \"Regulatory inputs controlling PGAP1 activity unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}