{"gene":"PIGQ","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1998,"finding":"PIGQ (hGPI1) forms a protein complex in the endoplasmic reticulum membrane with PIG-A, PIG-H, and PIG-C; this four-component complex mediates GPI-GlcNAc transferase (GPI-GnT) activity in vitro, catalyzing the first step of GPI biosynthesis (transfer of N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol). The complex did not mediate the second reaction (GlcNAc-PI de-N-acetylation), and the complex showed ~100-fold preference for bovine PI over soybean PI, suggesting the enzyme recognizes the fatty acyl chains of PI.","method":"Co-immunoprecipitation, in vitro GPI-GnT enzymatic assay, subcellular fractionation (ER membrane localization)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic reconstitution of the complex combined with Co-IP and substrate specificity assays; foundational paper replicated by subsequent studies","pmids":["9463366"],"is_preprint":false},{"year":1996,"finding":"Yeast GPI1 (ortholog of human PIGQ) is required for N-acetylglucosaminylphosphatidylinositol synthesis (first step of GPI anchor assembly). Disruption of GPI1 in S. cerevisiae abolished in vitro N-acetylglucosaminylphosphatidylinositol synthetic activity and blocked inositol incorporation into protein. Loss of Gpi1p caused a cell separation defect and defective ascospore wall maturation, demonstrating a role in morphogenesis.","method":"Gene disruption/knockout, in vitro enzymatic assay, radiolabeled inositol incorporation, complementation cloning","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — genetic disruption combined with in vitro enzymatic assay and multiple phenotypic readouts; foundational yeast ortholog study replicated by subsequent work","pmids":["8910381"],"is_preprint":false},{"year":1999,"finding":"GPI1 stabilizes the GPI-GnT complex by tying PIG-C into the PIG-A/PIG-H/PIG-C/GPI1 complex. Disruption of mouse GPI1 in F9 cells caused near-complete loss of the PIG-A/PIG-H/PIG-C trimeric complex (though the PIG-A/PIG-H binary complex was still detectable) and partial decreases in PIG-C and PIG-H protein levels, indicating a scaffolding/stabilization role for GPI1 rather than direct catalysis.","method":"Gene disruption by homologous recombination in mouse F9 cells, co-immunoprecipitation of complex components, Western blot quantification of subunit levels","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP with genetic knockout, multiple subunit quantification; independently consistent with complex biochemistry established in PMID:9463366","pmids":["10373468"],"is_preprint":false},{"year":2001,"finding":"Human GPI1 (PIGQ) is required for efficient GPI biosynthesis in human cells. Antisense RNA-mediated knockdown of GPI1 in HEK293 cells caused a marked but incomplete decrease in expression of a GPI-linked reporter protein, confirming GPI1's role in GPI anchor biosynthesis. The GPI1 locus was mapped to chromosome 16p13.3. Heterozygous deletion of one GPI1 allele (in alpha-thalassaemia/mental retardation syndrome patients) does not produce an overt defect in GPI-linked protein expression.","method":"Antisense RNA knockdown, GPI-reporter protein expression assay (flow cytometry), chromosomal mapping, analysis of patient cell lines","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — antisense knockdown with reporter assay; single lab, partial mechanistic follow-up confirming essentiality but limited by incomplete knockdown","pmids":["11418246"],"is_preprint":false},{"year":2002,"finding":"The Plasmodium falciparum GPI1 homolog (PfGPI1) functionally complements a S. cerevisiae gpi1 mutant, rescuing GPI anchor synthesis defects, establishing conservation of the GPI1 scaffolding/complex function across kingdoms.","method":"Heterologous complementation of yeast gpi1 mutant by P. falciparum GPI1","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic complementation in yeast, single study, provides functional conservation data but limited mechanistic detail for the human protein","pmids":["11849707"],"is_preprint":false},{"year":2020,"finding":"Biallelic pathogenic variants in human PIGQ cause reduced expression of GPI-anchored proteins on granulocytes and fibroblasts (demonstrated by flow cytometry). Transfection of wild-type PIGQ cDNA into patient fibroblasts rescued GPI-anchored protein expression, providing the first functional evidence in human cells that PIGQ variants directly impair GPI anchoring.","method":"Flow cytometry of GPI-anchored proteins on patient-derived cells, rescue by wild-type PIGQ cDNA transfection","journal":"Journal of inherited metabolic disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue experiment with patient-derived cells and wild-type cDNA transfection; two orthogonal methods (flow cytometry + rescue), single study","pmids":["32588908"],"is_preprint":false},{"year":2025,"finding":"A novel PIGQ missense variant (c.1370T>G, p.Leu457Arg) was validated as pathogenic by functional study in Chinese hamster ovarian cells, confirming that this variant impairs GPI biosynthesis.","method":"Functional complementation assay in CHO cells","journal":"Frontiers in genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single functional assay in CHO cells, single study, minimal mechanistic detail in abstract","pmids":["40718141"],"is_preprint":false}],"current_model":"PIGQ (hGPI1) is a subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex in the endoplasmic reticulum membrane, where it forms a stoichiometric complex with PIG-A, PIG-H, and PIG-C to catalyze the first step of GPI anchor biosynthesis (transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol); rather than contributing catalytic activity directly, PIGQ serves a scaffolding/stabilization role by bridging PIG-C into the PIG-A/PIG-H sub-complex, and loss of PIGQ leads to near-complete destabilization of the trimeric PIG-A/PIG-H/PIG-C complex and deficient surface expression of GPI-anchored proteins."},"narrative":{"mechanistic_narrative":"PIGQ (hGPI1) is a subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex in the endoplasmic reticulum membrane, where it acts with PIG-A, PIG-H, and PIG-C to catalyze the first committed step of glycosylphosphatidylinositol (GPI) anchor biosynthesis — transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol [PMID:9463366]. The reconstituted four-component complex carries out GlcNAc transfer but not the subsequent de-N-acetylation step, and recognizes the fatty acyl chains of phosphatidylinositol substrate [PMID:9463366]. Rather than contributing catalytic activity, PIGQ serves a scaffolding/stabilization role: it ties PIG-C into the PIG-A/PIG-H sub-complex, and its loss causes near-complete destabilization of the trimeric PIG-A/PIG-H/PIG-C complex while the PIG-A/PIG-H binary complex persists [PMID:10373468]. Loss of PIGQ function reduces surface expression of GPI-anchored proteins in human cells [PMID:11418246, PMID:32588908], and the gene's role is conserved across kingdoms, with yeast and Plasmodium orthologs supporting GPI assembly [PMID:8910381, PMID:11849707]. Biallelic pathogenic PIGQ variants cause an inherited GPI-deficiency disorder, established by reduced GPI-anchored protein expression on patient cells and rescue with wild-type PIGQ cDNA [PMID:32588908].","teleology":[{"year":1996,"claim":"Establishing whether GPI1 is genetically required for the first step of GPI anchor assembly, which was needed to place the gene in the biosynthetic pathway.","evidence":"Gene disruption in S. cerevisiae with in vitro enzymatic assay and radiolabeled inositol incorporation","pmids":["8910381"],"confidence":"High","gaps":["Did not define whether Gpi1p is catalytic or structural","Worked in yeast ortholog, not human protein","Did not identify the partner subunits of the complex"]},{"year":1998,"claim":"Defining the physical composition and enzymatic output of the human GPI-GnT complex, which assigned PIGQ to a specific multi-subunit enzyme.","evidence":"Co-immunoprecipitation, in vitro GPI-GnT enzymatic assay, and ER fractionation","pmids":["9463366"],"confidence":"High","gaps":["Did not resolve which subunit carries catalysis","Did not establish stoichiometry or assembly order","No structural model of the complex"]},{"year":1999,"claim":"Resolving PIGQ's role within the complex — scaffolding versus catalysis — by testing how its loss affects complex integrity.","evidence":"Homologous-recombination knockout of GPI1 in mouse F9 cells with reciprocal Co-IP and subunit Western quantification","pmids":["10373468"],"confidence":"High","gaps":["Did not map the PIGQ surface that contacts PIG-C","Mechanism by which loss reduces PIG-C/PIG-H protein levels not defined","No structural basis for stabilization"]},{"year":2001,"claim":"Confirming PIGQ is required for GPI biosynthesis in human cells and mapping the locus, extending the model beyond yeast and mouse.","evidence":"Antisense RNA knockdown with GPI-reporter flow cytometry and chromosomal mapping in HEK293 cells","pmids":["11418246"],"confidence":"Medium","gaps":["Knockdown was incomplete, so null phenotype not fully resolved","Heterozygous deletion produced no overt phenotype, leaving dosage sensitivity unclear","Single lab"]},{"year":2002,"claim":"Testing cross-kingdom conservation of PIGQ function by heterologous complementation.","evidence":"Complementation of yeast gpi1 mutant by P. falciparum GPI1","pmids":["11849707"],"confidence":"Medium","gaps":["Provides conservation evidence but no mechanistic detail for the human protein","Single study"]},{"year":2020,"claim":"Demonstrating that human PIGQ variants are directly causal for impaired GPI anchoring, linking the gene to inherited disease.","evidence":"Flow cytometry of GPI-anchored proteins on patient cells with wild-type PIGQ cDNA rescue","pmids":["32588908"],"confidence":"Medium","gaps":["Single study","Genotype-phenotype correlation across variants not established","Residual GPI synthesis in patient cells not quantified mechanistically"]},{"year":2025,"claim":"Extending the catalogue of pathogenic PIGQ alleles by validating a novel missense variant.","evidence":"Functional complementation assay in CHO cells","pmids":["40718141"],"confidence":"Low","gaps":["Single functional assay, single study, minimal mechanistic detail","Effect on complex stability not assessed","No structural interpretation of the missense substitution"]},{"year":null,"claim":"A structural model of how PIGQ bridges PIG-C into the PIG-A/PIG-H complex, and the molecular basis by which individual missense variants destabilize the GPI-GnT complex, remains undefined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No atomic structure of the GPI-GnT complex or PIGQ contact surfaces","Variant-specific effects on complex assembly uncharacterized","Substrate acyl-chain recognition mechanism not mapped to a subunit"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,5]}],"complexes":["GPI-GlcNAc transferase (GPI-GnT) complex"],"partners":["PIGA","PIGH","PIGC"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BRB3","full_name":"Phosphatidylinositol N-acetylglucosaminyltransferase subunit Q","aliases":["N-acetylglucosamyl transferase component GPI1","Phosphatidylinositol-glycan biosynthesis class Q protein","PIG-Q"],"length_aa":760,"mass_kda":84.1,"function":"Part of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol and participates in the first step of GPI biosynthesis","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q9BRB3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PIGQ","classification":"Not Classified","n_dependent_lines":12,"n_total_lines":1208,"dependency_fraction":0.009933774834437087},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PIGQ","total_profiled":1310},"omim":[{"mim_id":"618548","title":"MULTIPLE CONGENITAL ANOMALIES-HYPOTONIA-SEIZURES SYNDROME 4; MCAHS4","url":"https://www.omim.org/entry/618548"},{"mim_id":"614080","title":"MULTIPLE CONGENITAL ANOMALIES-HYPOTONIA-SEIZURES SYNDROME 1; MCAHS1","url":"https://www.omim.org/entry/614080"},{"mim_id":"610293","title":"GLYCOSYLPHOSPHATIDYLINOSITOL BIOSYNTHESIS DEFECT 1; GPIBD1","url":"https://www.omim.org/entry/610293"},{"mim_id":"605754","title":"PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS CLASS Q PROTEIN; PIGQ","url":"https://www.omim.org/entry/605754"},{"mim_id":"601730","title":"PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS CLASS C PROTEIN; PIGC","url":"https://www.omim.org/entry/601730"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PIGQ"},"hgnc":{"alias_symbol":["hGPI1","GPI1"],"prev_symbol":[]},"alphafold":{"accession":"Q9BRB3","domains":[{"cath_id":"3.40.140","chopping":"3-115_122-144_158-195","consensus_level":"high","plddt":70.6633,"start":3,"end":195},{"cath_id":"-","chopping":"290-505","consensus_level":"high","plddt":90.2564,"start":290,"end":505},{"cath_id":"1.20.5","chopping":"196-265","consensus_level":"medium","plddt":76.75,"start":196,"end":265}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BRB3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BRB3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BRB3-F1-predicted_aligned_error_v6.png","plddt_mean":64.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PIGQ","jax_strain_url":"https://www.jax.org/strain/search?query=PIGQ"},"sequence":{"accession":"Q9BRB3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BRB3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BRB3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BRB3"}},"corpus_meta":[{"pmid":"9463366","id":"PMC_9463366","title":"The first step of glycosylphosphatidylinositol biosynthesis is mediated by a complex of PIG-A, PIG-H, PIG-C and GPI1.","date":"1998","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9463366","citation_count":129,"is_preprint":false},{"pmid":"8910381","id":"PMC_8910381","title":"Gpi1, a Saccharomyces cerevisiae protein that participates in the first step in glycosylphosphatidylinositol anchor synthesis.","date":"1996","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8910381","citation_count":73,"is_preprint":false},{"pmid":"10373468","id":"PMC_10373468","title":"GPI1 stabilizes an enzyme essential in the first step of glycosylphosphatidylinositol biosynthesis.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10373468","citation_count":31,"is_preprint":false},{"pmid":"3996761","id":"PMC_3996761","title":"Onset of paternal and maternal Gpi-1 expression in preimplantation mouse embryos.","date":"1985","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/3996761","citation_count":25,"is_preprint":false},{"pmid":"32588908","id":"PMC_32588908","title":"Early infantile epileptic encephalopathy due to biallelic pathogenic variants in PIGQ: Report of seven new subjects and review of the literature.","date":"2020","source":"Journal of inherited metabolic disease","url":"https://pubmed.ncbi.nlm.nih.gov/32588908","citation_count":23,"is_preprint":false},{"pmid":"11849707","id":"PMC_11849707","title":"The GPI1 homologue from Plasmodium falciparum complements a Saccharomyces cerevisiae GPI1 anchoring mutant.","date":"2002","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/11849707","citation_count":17,"is_preprint":false},{"pmid":"7295293","id":"PMC_7295293","title":"Genetic variation for prolidase (PEP-4) in the mouse maps near the gene for glucosephosphate isomerase (GPI-1) on chromosome 7.","date":"1981","source":"Biochemical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/7295293","citation_count":14,"is_preprint":false},{"pmid":"31148362","id":"PMC_31148362","title":"PIGQ glycosylphosphatidylinositol-anchored protein deficiency: Characterizing the phenotype.","date":"2019","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/31148362","citation_count":12,"is_preprint":false},{"pmid":"11418246","id":"PMC_11418246","title":"The human GPI1 gene is required for efficient glycosylphosphatidylinositol biosynthesis.","date":"2001","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/11418246","citation_count":11,"is_preprint":false},{"pmid":"4084208","id":"PMC_4084208","title":"Glucosephosphate isomerase (GPI-1) expression in mouse ova: cis regulation of monomer realization.","date":"1985","source":"Biochemical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/4084208","citation_count":11,"is_preprint":false},{"pmid":"34089469","id":"PMC_34089469","title":"PIGQ-Related Glycophosphatidylinositol Deficiency Associated with Nonprogressive Congenital Ataxia.","date":"2021","source":"Cerebellum (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/34089469","citation_count":6,"is_preprint":false},{"pmid":"38571402","id":"PMC_38571402","title":"Perturbation of the insomnia WDR90 genome-wide association studies locus pinpoints rs3752495 as a causal variant influencing distal expression of neighboring gene, PIG-Q.","date":"2024","source":"Sleep","url":"https://pubmed.ncbi.nlm.nih.gov/38571402","citation_count":3,"is_preprint":false},{"pmid":"37645863","id":"PMC_37645863","title":"Perturbation of the insomnia WDR90 GWAS locus pinpoints rs3752495 as a causal variant influencing distal expression of neighboring gene, PIG-Q.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37645863","citation_count":1,"is_preprint":false},{"pmid":"40718141","id":"PMC_40718141","title":"Two novel cases with PIGQ-CDG: expansion of the genotype-phenotype spectrum and evaluation of GestaltMatcher as a diagnostic tool.","date":"2025","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40718141","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.21.666043","title":"The Tricuspid Valve is Transcriptionally Active During Prolonged Pressure Overload, Right-Sided Heart Failure, and Valve Regurgitation","date":"2025-07-25","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.21.666043","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.13.648563","title":"Sustained Antigen Stimulation to Evoke and Study Negative feedback Systems responsible for Self-Tolerance/Tumor Immune Escape and transition to the M2 macrophage","date":"2025-04-18","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.13.648563","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11011,"output_tokens":2010,"usd":0.031592,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8988,"output_tokens":2478,"usd":0.053445,"stage2_stop_reason":"end_turn"},"total_usd":0.085037,"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\": 1998,\n      \"finding\": \"PIGQ (hGPI1) forms a protein complex in the endoplasmic reticulum membrane with PIG-A, PIG-H, and PIG-C; this four-component complex mediates GPI-GlcNAc transferase (GPI-GnT) activity in vitro, catalyzing the first step of GPI biosynthesis (transfer of N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol). The complex did not mediate the second reaction (GlcNAc-PI de-N-acetylation), and the complex showed ~100-fold preference for bovine PI over soybean PI, suggesting the enzyme recognizes the fatty acyl chains of PI.\",\n      \"method\": \"Co-immunoprecipitation, in vitro GPI-GnT enzymatic assay, subcellular fractionation (ER membrane localization)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic reconstitution of the complex combined with Co-IP and substrate specificity assays; foundational paper replicated by subsequent studies\",\n      \"pmids\": [\"9463366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Yeast GPI1 (ortholog of human PIGQ) is required for N-acetylglucosaminylphosphatidylinositol synthesis (first step of GPI anchor assembly). Disruption of GPI1 in S. cerevisiae abolished in vitro N-acetylglucosaminylphosphatidylinositol synthetic activity and blocked inositol incorporation into protein. Loss of Gpi1p caused a cell separation defect and defective ascospore wall maturation, demonstrating a role in morphogenesis.\",\n      \"method\": \"Gene disruption/knockout, in vitro enzymatic assay, radiolabeled inositol incorporation, complementation cloning\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — genetic disruption combined with in vitro enzymatic assay and multiple phenotypic readouts; foundational yeast ortholog study replicated by subsequent work\",\n      \"pmids\": [\"8910381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GPI1 stabilizes the GPI-GnT complex by tying PIG-C into the PIG-A/PIG-H/PIG-C/GPI1 complex. Disruption of mouse GPI1 in F9 cells caused near-complete loss of the PIG-A/PIG-H/PIG-C trimeric complex (though the PIG-A/PIG-H binary complex was still detectable) and partial decreases in PIG-C and PIG-H protein levels, indicating a scaffolding/stabilization role for GPI1 rather than direct catalysis.\",\n      \"method\": \"Gene disruption by homologous recombination in mouse F9 cells, co-immunoprecipitation of complex components, Western blot quantification of subunit levels\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP with genetic knockout, multiple subunit quantification; independently consistent with complex biochemistry established in PMID:9463366\",\n      \"pmids\": [\"10373468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Human GPI1 (PIGQ) is required for efficient GPI biosynthesis in human cells. Antisense RNA-mediated knockdown of GPI1 in HEK293 cells caused a marked but incomplete decrease in expression of a GPI-linked reporter protein, confirming GPI1's role in GPI anchor biosynthesis. The GPI1 locus was mapped to chromosome 16p13.3. Heterozygous deletion of one GPI1 allele (in alpha-thalassaemia/mental retardation syndrome patients) does not produce an overt defect in GPI-linked protein expression.\",\n      \"method\": \"Antisense RNA knockdown, GPI-reporter protein expression assay (flow cytometry), chromosomal mapping, analysis of patient cell lines\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — antisense knockdown with reporter assay; single lab, partial mechanistic follow-up confirming essentiality but limited by incomplete knockdown\",\n      \"pmids\": [\"11418246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The Plasmodium falciparum GPI1 homolog (PfGPI1) functionally complements a S. cerevisiae gpi1 mutant, rescuing GPI anchor synthesis defects, establishing conservation of the GPI1 scaffolding/complex function across kingdoms.\",\n      \"method\": \"Heterologous complementation of yeast gpi1 mutant by P. falciparum GPI1\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic complementation in yeast, single study, provides functional conservation data but limited mechanistic detail for the human protein\",\n      \"pmids\": [\"11849707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Biallelic pathogenic variants in human PIGQ cause reduced expression of GPI-anchored proteins on granulocytes and fibroblasts (demonstrated by flow cytometry). Transfection of wild-type PIGQ cDNA into patient fibroblasts rescued GPI-anchored protein expression, providing the first functional evidence in human cells that PIGQ variants directly impair GPI anchoring.\",\n      \"method\": \"Flow cytometry of GPI-anchored proteins on patient-derived cells, rescue by wild-type PIGQ cDNA transfection\",\n      \"journal\": \"Journal of inherited metabolic disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue experiment with patient-derived cells and wild-type cDNA transfection; two orthogonal methods (flow cytometry + rescue), single study\",\n      \"pmids\": [\"32588908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel PIGQ missense variant (c.1370T>G, p.Leu457Arg) was validated as pathogenic by functional study in Chinese hamster ovarian cells, confirming that this variant impairs GPI biosynthesis.\",\n      \"method\": \"Functional complementation assay in CHO cells\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single functional assay in CHO cells, single study, minimal mechanistic detail in abstract\",\n      \"pmids\": [\"40718141\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PIGQ (hGPI1) is a subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex in the endoplasmic reticulum membrane, where it forms a stoichiometric complex with PIG-A, PIG-H, and PIG-C to catalyze the first step of GPI anchor biosynthesis (transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol); rather than contributing catalytic activity directly, PIGQ serves a scaffolding/stabilization role by bridging PIG-C into the PIG-A/PIG-H sub-complex, and loss of PIGQ leads to near-complete destabilization of the trimeric PIG-A/PIG-H/PIG-C complex and deficient surface expression of GPI-anchored proteins.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PIGQ (hGPI1) is a subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex in the endoplasmic reticulum membrane, where it acts with PIG-A, PIG-H, and PIG-C to catalyze the first committed step of glycosylphosphatidylinositol (GPI) anchor biosynthesis — transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol [#0]. The reconstituted four-component complex carries out GlcNAc transfer but not the subsequent de-N-acetylation step, and recognizes the fatty acyl chains of phosphatidylinositol substrate [#0]. Rather than contributing catalytic activity, PIGQ serves a scaffolding/stabilization role: it ties PIG-C into the PIG-A/PIG-H sub-complex, and its loss causes near-complete destabilization of the trimeric PIG-A/PIG-H/PIG-C complex while the PIG-A/PIG-H binary complex persists [#2]. Loss of PIGQ function reduces surface expression of GPI-anchored proteins in human cells [#3, #5], and the gene's role is conserved across kingdoms, with yeast and Plasmodium orthologs supporting GPI assembly [#1, #4]. Biallelic pathogenic PIGQ variants cause an inherited GPI-deficiency disorder, established by reduced GPI-anchored protein expression on patient cells and rescue with wild-type PIGQ cDNA [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Establishing whether GPI1 is genetically required for the first step of GPI anchor assembly, which was needed to place the gene in the biosynthetic pathway.\",\n      \"evidence\": \"Gene disruption in S. cerevisiae with in vitro enzymatic assay and radiolabeled inositol incorporation\",\n      \"pmids\": [\"8910381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not define whether Gpi1p is catalytic or structural\",\n        \"Worked in yeast ortholog, not human protein\",\n        \"Did not identify the partner subunits of the complex\"\n      ]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining the physical composition and enzymatic output of the human GPI-GnT complex, which assigned PIGQ to a specific multi-subunit enzyme.\",\n      \"evidence\": \"Co-immunoprecipitation, in vitro GPI-GnT enzymatic assay, and ER fractionation\",\n      \"pmids\": [\"9463366\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not resolve which subunit carries catalysis\",\n        \"Did not establish stoichiometry or assembly order\",\n        \"No structural model of the complex\"\n      ]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Resolving PIGQ's role within the complex — scaffolding versus catalysis — by testing how its loss affects complex integrity.\",\n      \"evidence\": \"Homologous-recombination knockout of GPI1 in mouse F9 cells with reciprocal Co-IP and subunit Western quantification\",\n      \"pmids\": [\"10373468\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not map the PIGQ surface that contacts PIG-C\",\n        \"Mechanism by which loss reduces PIG-C/PIG-H protein levels not defined\",\n        \"No structural basis for stabilization\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Confirming PIGQ is required for GPI biosynthesis in human cells and mapping the locus, extending the model beyond yeast and mouse.\",\n      \"evidence\": \"Antisense RNA knockdown with GPI-reporter flow cytometry and chromosomal mapping in HEK293 cells\",\n      \"pmids\": [\"11418246\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Knockdown was incomplete, so null phenotype not fully resolved\",\n        \"Heterozygous deletion produced no overt phenotype, leaving dosage sensitivity unclear\",\n        \"Single lab\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Testing cross-kingdom conservation of PIGQ function by heterologous complementation.\",\n      \"evidence\": \"Complementation of yeast gpi1 mutant by P. falciparum GPI1\",\n      \"pmids\": [\"11849707\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Provides conservation evidence but no mechanistic detail for the human protein\",\n        \"Single study\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that human PIGQ variants are directly causal for impaired GPI anchoring, linking the gene to inherited disease.\",\n      \"evidence\": \"Flow cytometry of GPI-anchored proteins on patient cells with wild-type PIGQ cDNA rescue\",\n      \"pmids\": [\"32588908\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single study\",\n        \"Genotype-phenotype correlation across variants not established\",\n        \"Residual GPI synthesis in patient cells not quantified mechanistically\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extending the catalogue of pathogenic PIGQ alleles by validating a novel missense variant.\",\n      \"evidence\": \"Functional complementation assay in CHO cells\",\n      \"pmids\": [\"40718141\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Single functional assay, single study, minimal mechanistic detail\",\n        \"Effect on complex stability not assessed\",\n        \"No structural interpretation of the missense substitution\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A structural model of how PIGQ bridges PIG-C into the PIG-A/PIG-H complex, and the molecular basis by which individual missense variants destabilize the GPI-GnT complex, remains undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No atomic structure of the GPI-GnT complex or PIGQ contact surfaces\",\n        \"Variant-specific effects on complex assembly uncharacterized\",\n        \"Substrate acyl-chain recognition mechanism not mapped to a subunit\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"complexes\": [\"GPI-GlcNAc transferase (GPI-GnT) complex\"],\n    \"partners\": [\"PIGA\", \"PIGH\", \"PIGC\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}