{"gene":"PIGP","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2000,"finding":"PIGP (PIG-P) is an essential component of GPI-N-acetylglucosaminyltransferase (GPI-GnT), the enzyme that initiates GPI anchor biosynthesis by transferring N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol. PIG-P associates with PIG-A and GPI1 within the complex, and cells lacking PIG-P are GPI-anchor negative.","method":"Co-immunoprecipitation, cell-based complementation assay, GPI-anchor negative cell line generation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP establishing complex membership, loss-of-function cell line with defined GPI-anchor negative phenotype, replicated across organisms","pmids":["10944123"],"is_preprint":false},{"year":2000,"finding":"DPM2, a regulator of dolichol-phosphate-mannose synthase, associates with GPI-GnT through interactions with PIG-A, PIG-C, and GPI1 (not directly with PIG-P), and enhances GPI-GnT enzyme activity approximately 3-fold, indicating a regulatory role distinct from PIGP's essential structural role.","method":"Co-immunoprecipitation, in vitro enzyme activity assay","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzyme activity assay and co-IP, single lab, two orthogonal methods","pmids":["10944123"],"is_preprint":false},{"year":2005,"finding":"Gpi19p, the S. cerevisiae homolog of human PIG-P, is an essential subunit of the yeast GPI-GlcNAc transferase complex. It associates with the Gpi2 subunit in vivo, is required for GPI-GlcNAc transferase activity in vitro, and has a defined topology within the ER membrane. Temperature-sensitive gpi19 mutants display cell wall defects and hyperactive Ras phenotypes.","method":"Co-immunoprecipitation, in vitro enzyme activity assay, topology analysis, temperature-sensitive mutant phenotypic analysis","journal":"Eukaryotic cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro enzyme activity assay combined with co-IP and genetic mutant phenotypes, orthologous gene with conserved function confirmed","pmids":["16278447"],"is_preprint":false},{"year":2010,"finding":"CaGpi19p, the Candida albicans homolog of PIG-P, is the functional equivalent of S. cerevisiae Gpi19p and is essential for GPI anchor biosynthesis. An N-terminal truncation mutant of CaGpi19p complements a conditionally lethal S. cerevisiae gpi19 mutant. Repression of CaGPI19 causes growth defects, cell wall biogenesis aberrations, azole sensitivity, and hyperfilamentation, with a gene dosage effect observed in heterozygotes.","method":"Cross-species complementation assay, conditional null mutant (MET3 promoter control), phenotypic analysis","journal":"Microbiology (Reading, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cross-species complementation and conditional KO with multiple defined phenotypic readouts, single lab","pmids":["20576690"],"is_preprint":false},{"year":2009,"finding":"The Aspergillus nidulans pigP gene encodes a subunit of GPI-GnT; pigP mutants have significantly decreased GPI synthesis, display a 'button' phenotype with hyperbranched hyphae and impaired septation, and aberrantly secrete a 33-kDa alkaline serine protease into the medium, establishing PIGP's role in GPI-dependent protein membrane anchoring and secretion.","method":"Mutant analysis, GPI synthesis measurement, phenotypic characterization, protein secretion assay","journal":"Current genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with biochemical measurement of GPI synthesis and defined cellular phenotypes, single lab","pmids":["19421754"],"is_preprint":false},{"year":2017,"finding":"Compound heterozygous mutations in human PIGP (c.74T>C;p.Met25Thr and c.456delA;p.Glu153AsnFs*34) cause reduced PIGP mRNA levels and reduced GPI-anchored cell surface proteins. Wild-type PIGP expression rescued GPI-anchored protein levels in patient cells, confirming PIGP's essential role in the first step of GPI anchor biosynthesis in humans.","method":"Patient cell functional study, flow cytometry of GPI-anchored proteins, exogenous wild-type PIGP rescue experiment","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue experiment plus flow cytometry quantification in patient cells, single lab, two complementary methods","pmids":["28334793"],"is_preprint":false},{"year":2019,"finding":"A homozygous frameshift mutation (c.456delA;p.Glu153Asnfs*34) in PIGP causes reduced expression of GPI-anchored proteins on patient granulocytes, as confirmed by flow cytometry, independently replicating that PIGP is required for GPI anchor biosynthesis in humans.","method":"Flow cytometry of GPI-anchored proteins on patient granulocytes","journal":"Annals of clinical and translational neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — flow cytometry functional confirmation in second independent family, single method","pmids":["31139695"],"is_preprint":false},{"year":2020,"finding":"A homozygous PIGP frameshift variant (c.384del) results in a longer-than-wild-type protein predicted to have impaired functionality, and is associated with reduced expression of the GPI-anchored protein CD16 on granulocyte membranes, establishing CD16 as a functional marker for PIGP-related inherited GPI deficiency.","method":"Flow cytometry of GPI-anchored protein CD16 on patient granulocytes","journal":"Neurology. Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — flow cytometry functional readout in multiple affected individuals from a large family, single method","pmids":["32042915"],"is_preprint":false},{"year":2021,"finding":"PIGP is an autosomal gene essential for GPI-anchor biosynthesis; deletion of one PIGP allele followed by introduction of a truncating mutation in the other abolished GPI anchor display on the cell membrane, as detected by flow cytometry. This was rescued by correction of the PIGP mutation via targeted knock-in, directly demonstrating that PIGP function is required for GPI anchor surface expression.","method":"CRISPR/Cas9-based PIGP allele deletion, flow cytometry of GPI anchors, targeted knock-in rescue","journal":"Bioscience reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — engineered cell lines with allele-specific mutations and rescue, two orthogonal readouts, single lab","pmids":["34750615"],"is_preprint":false}],"current_model":"PIGP (also known as DSCR5/DCRC) encodes an essential small transmembrane subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex, which catalyzes the first committed step of GPI anchor biosynthesis at the ER membrane; PIGP directly associates with PIG-A and GPI1 within this complex, is indispensable for enzymatic activity, and loss of PIGP function in human patients reduces GPI-anchored protein surface expression, causing inherited GPI deficiency with developmental and epileptic encephalopathy."},"narrative":{"mechanistic_narrative":"PIGP encodes an essential subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex, which catalyzes the first committed step of glycosylphosphatidylinositol (GPI) anchor biosynthesis at the ER membrane by transferring N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol [PMID:10944123]. Within this complex PIGP physically associates with PIG-A and GPI1, and cells lacking PIGP are rendered GPI-anchor negative, defining PIGP as an indispensable structural component rather than a regulatory one—a role distinct from DPM2, which associates with other complex subunits and enhances enzyme activity without binding PIGP directly [PMID:10944123]. The essential, conserved function is corroborated by the yeast and fungal homologs, which associate with the GPI2 subunit, are required for in vitro GPI-GlcNAc transferase activity, and whose loss produces cell wall and GPI synthesis defects [PMID:16278447, PMID:19421754]. In humans, biallelic loss-of-function mutations in PIGP reduce surface expression of GPI-anchored proteins, and reintroduction of wild-type PIGP rescues this deficit, causing an inherited GPI deficiency presenting as developmental and epileptic encephalopathy [PMID:28334793, PMID:34750615].","teleology":[{"year":2000,"claim":"Established that PIGP is a bona fide, essential subunit of the GPI-GnT complex rather than an accessory factor, defining the molecular machine that initiates GPI anchor synthesis.","evidence":"Co-immunoprecipitation with PIG-A and GPI1, plus a GPI-anchor-negative loss-of-function cell line and complementation","pmids":["10944123"],"confidence":"High","gaps":["Catalytic contribution of PIGP versus its scaffolding role within the complex not resolved","No structure of the assembled complex"]},{"year":2000,"claim":"Distinguished PIGP's essential structural role from regulatory inputs by showing DPM2 enhances GPI-GnT activity ~3-fold via PIG-A, PIG-C, and GPI1 but not through PIGP.","evidence":"Co-immunoprecipitation and in vitro enzyme activity assay","pmids":["10944123"],"confidence":"Medium","gaps":["Mechanism by which DPM2 enhances activity not defined","Whether regulation occurs in human cells the same way as in vitro untested"]},{"year":2005,"claim":"Confirmed functional conservation by showing the yeast homolog Gpi19p is an essential GPI-GlcNAc transferase subunit with defined ER membrane topology, linking GPI synthesis to cell wall and Ras-pathway phenotypes.","evidence":"Co-IP with Gpi2, in vitro enzyme activity assay, topology analysis, and temperature-sensitive mutant phenotyping in S. cerevisiae","pmids":["16278447"],"confidence":"High","gaps":["Human PIGP membrane topology not directly mapped","Connection between GPI deficiency and Ras hyperactivity mechanistically unexplained"]},{"year":2009,"claim":"Connected loss of PIGP function to downstream secretory consequences by showing fungal pigP mutants have decreased GPI synthesis and aberrant secretion of a normally membrane-anchored protease.","evidence":"Mutant analysis with GPI synthesis measurement and protein secretion assay in Aspergillus nidulans","pmids":["19421754"],"confidence":"Medium","gaps":["Findings in filamentous fungus may not transfer to human cell biology","Specific anchored substrates affected in humans not enumerated"]},{"year":2010,"claim":"Extended conservation and demonstrated gene-dosage sensitivity, showing the Candida homolog is essential and that even partial reduction produces cell wall, drug-sensitivity, and morphogenesis defects.","evidence":"Cross-species complementation and conditional null (MET3 promoter) phenotyping in Candida albicans","pmids":["20576690"],"confidence":"Medium","gaps":["Whether dosage sensitivity applies to human heterozygotes untested here","Single lab"]},{"year":2017,"claim":"Established PIGP as a human disease gene by linking biallelic mutations to reduced GPI-anchored surface protein levels and demonstrating rescue by wild-type PIGP.","evidence":"Patient cell functional study, flow cytometry of GPI-anchored proteins, and wild-type PIGP rescue","pmids":["28334793"],"confidence":"Medium","gaps":["Genotype-phenotype correlation across mutation types not established","Tissue-specific effects of GPI deficiency not addressed"]},{"year":2019,"claim":"Independently replicated the human requirement for PIGP in a second family, reinforcing the causal link between PIGP loss and GPI-anchored protein deficiency.","evidence":"Flow cytometry of GPI-anchored proteins on patient granulocytes","pmids":["31139695"],"confidence":"Medium","gaps":["Single method","No mechanistic dissection beyond surface marker quantification"]},{"year":2020,"claim":"Identified a clinically usable functional readout by establishing reduced granulocyte CD16 as a marker of PIGP-related inherited GPI deficiency.","evidence":"Flow cytometry of CD16 on patient granulocytes from a large family","pmids":["32042915"],"confidence":"Medium","gaps":["Predicted impaired functionality of elongated mutant protein not biochemically confirmed","Single method"]},{"year":2021,"claim":"Provided direct causal proof in engineered human cells that PIGP function is required for GPI anchor surface display, with knock-in correction restoring the anchor.","evidence":"CRISPR/Cas9 allele deletion plus truncation, flow cytometry of GPI anchors, and targeted knock-in rescue","pmids":["34750615"],"confidence":"Medium","gaps":["Stoichiometry and assembly order of PIGP within the human GPI-GnT complex unresolved","Single lab"]},{"year":null,"claim":"How PIGP contributes structurally or mechanistically to GPI-GnT catalysis—its precise position, stoichiometry, and topology within the human complex—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of the human GPI-GnT complex","Catalytic versus scaffolding contribution of PIGP undefined","Regulatory inputs governing complex activity in human cells uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,5]}],"complexes":["GPI-N-acetylglucosaminyltransferase (GPI-GnT)"],"partners":["PIGA","GPI1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P57054","full_name":"Phosphatidylinositol N-acetylglucosaminyltransferase subunit P","aliases":["Down syndrome critical region protein 5","Down syndrome critical region protein C","Phosphatidylinositol-glycan biosynthesis class P protein","PIG-P"],"length_aa":158,"mass_kda":18.1,"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/P57054/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PIGP","classification":"Not Classified","n_dependent_lines":20,"n_total_lines":1208,"dependency_fraction":0.016556291390728478},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PIGP","total_profiled":1310},"omim":[{"mim_id":"617599","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 55; DEE55","url":"https://www.omim.org/entry/617599"},{"mim_id":"610293","title":"GLYCOSYLPHOSPHATIDYLINOSITOL BIOSYNTHESIS DEFECT 1; GPIBD1","url":"https://www.omim.org/entry/610293"},{"mim_id":"605938","title":"PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS CLASS P PROTEIN; PIGP","url":"https://www.omim.org/entry/605938"},{"mim_id":"311770","title":"PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS CLASS A PROTEIN; PIGA","url":"https://www.omim.org/entry/311770"},{"mim_id":"308350","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 1; DEE1","url":"https://www.omim.org/entry/308350"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PIGP"},"hgnc":{"alias_symbol":["DCRC","DSRC"],"prev_symbol":["DSCR5"]},"alphafold":{"accession":"P57054","domains":[{"cath_id":"1.20.5","chopping":"37-72","consensus_level":"medium","plddt":91.9822,"start":37,"end":72},{"cath_id":"1.20.5","chopping":"75-106","consensus_level":"medium","plddt":94.8122,"start":75,"end":106}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P57054","model_url":"https://alphafold.ebi.ac.uk/files/AF-P57054-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P57054-F1-predicted_aligned_error_v6.png","plddt_mean":82.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PIGP","jax_strain_url":"https://www.jax.org/strain/search?query=PIGP"},"sequence":{"accession":"P57054","fasta_url":"https://rest.uniprot.org/uniprotkb/P57054.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P57054/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P57054"}},"corpus_meta":[{"pmid":"25294943","id":"PMC_25294943","title":"Analysis of the expression patterns, subcellular localisations and interaction partners of Drosophila proteins using a pigP protein trap library.","date":"2014","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/25294943","citation_count":130,"is_preprint":false},{"pmid":"18829451","id":"PMC_18829451","title":"The crystal structure of Desulfovibrio vulgaris dissimilatory sulfite reductase bound to DsrC provides novel insights into the mechanism of sulfate respiration.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18829451","citation_count":125,"is_preprint":false},{"pmid":"24662917","id":"PMC_24662917","title":"The \"bacterial heterodisulfide\" DsrC is a key protein in dissimilatory sulfur metabolism.","date":"2014","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/24662917","citation_count":123,"is_preprint":false},{"pmid":"10944123","id":"PMC_10944123","title":"Initial enzyme for glycosylphosphatidylinositol biosynthesis requires PIG-P and is regulated by DPM2.","date":"2000","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/10944123","citation_count":110,"is_preprint":false},{"pmid":"21183667","id":"PMC_21183667","title":"PigS and PigP regulate prodigiosin biosynthesis in Serratia via differential control of divergent operons, which include predicted transporters of sulfur-containing molecules.","date":"2010","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/21183667","citation_count":55,"is_preprint":false},{"pmid":"22815818","id":"PMC_22815818","title":"Cytoplasmic sulfurtransferases in the purple sulfur bacterium Allochromatium vinosum: evidence for sulfur transfer from DsrEFH to DsrC.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22815818","citation_count":55,"is_preprint":false},{"pmid":"23469212","id":"PMC_23469212","title":"A Serratia marcescens PigP homolog controls prodigiosin 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the gamma subunit of dissimilatory sulfite reductase.","date":"2001","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11722571","citation_count":33,"is_preprint":false},{"pmid":"20576690","id":"PMC_20576690","title":"The Candida albicans homologue of PIG-P, CaGpi19p: gene dosage and role in growth and filamentation.","date":"2010","source":"Microbiology (Reading, England)","url":"https://pubmed.ncbi.nlm.nih.gov/20576690","citation_count":30,"is_preprint":false},{"pmid":"15221505","id":"PMC_15221505","title":"Protein levels of genes encoded on chromosome 21 in fetal Down Syndrome brain (Part V): overexpression of phosphatidyl-inositol-glycan class P protein (DSCR5).","date":"2004","source":"Amino acids","url":"https://pubmed.ncbi.nlm.nih.gov/15221505","citation_count":27,"is_preprint":false},{"pmid":"10814524","id":"PMC_10814524","title":"Isolation of two novel genes, DSCR5 and DSCR6, from Down syndrome critical region on human chromosome 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PIG-P associates with PIG-A and GPI1 within the complex, and cells lacking PIG-P are GPI-anchor negative.\",\n      \"method\": \"Co-immunoprecipitation, cell-based complementation assay, GPI-anchor negative cell line generation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP establishing complex membership, loss-of-function cell line with defined GPI-anchor negative phenotype, replicated across organisms\",\n      \"pmids\": [\"10944123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"DPM2, a regulator of dolichol-phosphate-mannose synthase, associates with GPI-GnT through interactions with PIG-A, PIG-C, and GPI1 (not directly with PIG-P), and enhances GPI-GnT enzyme activity approximately 3-fold, indicating a regulatory role distinct from PIGP's essential structural role.\",\n      \"method\": \"Co-immunoprecipitation, in vitro enzyme activity assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzyme activity assay and co-IP, single lab, two orthogonal methods\",\n      \"pmids\": [\"10944123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Gpi19p, the S. cerevisiae homolog of human PIG-P, is an essential subunit of the yeast GPI-GlcNAc transferase complex. It associates with the Gpi2 subunit in vivo, is required for GPI-GlcNAc transferase activity in vitro, and has a defined topology within the ER membrane. Temperature-sensitive gpi19 mutants display cell wall defects and hyperactive Ras phenotypes.\",\n      \"method\": \"Co-immunoprecipitation, in vitro enzyme activity assay, topology analysis, temperature-sensitive mutant phenotypic analysis\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro enzyme activity assay combined with co-IP and genetic mutant phenotypes, orthologous gene with conserved function confirmed\",\n      \"pmids\": [\"16278447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CaGpi19p, the Candida albicans homolog of PIG-P, is the functional equivalent of S. cerevisiae Gpi19p and is essential for GPI anchor biosynthesis. An N-terminal truncation mutant of CaGpi19p complements a conditionally lethal S. cerevisiae gpi19 mutant. Repression of CaGPI19 causes growth defects, cell wall biogenesis aberrations, azole sensitivity, and hyperfilamentation, with a gene dosage effect observed in heterozygotes.\",\n      \"method\": \"Cross-species complementation assay, conditional null mutant (MET3 promoter control), phenotypic analysis\",\n      \"journal\": \"Microbiology (Reading, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cross-species complementation and conditional KO with multiple defined phenotypic readouts, single lab\",\n      \"pmids\": [\"20576690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The Aspergillus nidulans pigP gene encodes a subunit of GPI-GnT; pigP mutants have significantly decreased GPI synthesis, display a 'button' phenotype with hyperbranched hyphae and impaired septation, and aberrantly secrete a 33-kDa alkaline serine protease into the medium, establishing PIGP's role in GPI-dependent protein membrane anchoring and secretion.\",\n      \"method\": \"Mutant analysis, GPI synthesis measurement, phenotypic characterization, protein secretion assay\",\n      \"journal\": \"Current genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with biochemical measurement of GPI synthesis and defined cellular phenotypes, single lab\",\n      \"pmids\": [\"19421754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Compound heterozygous mutations in human PIGP (c.74T>C;p.Met25Thr and c.456delA;p.Glu153AsnFs*34) cause reduced PIGP mRNA levels and reduced GPI-anchored cell surface proteins. Wild-type PIGP expression rescued GPI-anchored protein levels in patient cells, confirming PIGP's essential role in the first step of GPI anchor biosynthesis in humans.\",\n      \"method\": \"Patient cell functional study, flow cytometry of GPI-anchored proteins, exogenous wild-type PIGP rescue experiment\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue experiment plus flow cytometry quantification in patient cells, single lab, two complementary methods\",\n      \"pmids\": [\"28334793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous frameshift mutation (c.456delA;p.Glu153Asnfs*34) in PIGP causes reduced expression of GPI-anchored proteins on patient granulocytes, as confirmed by flow cytometry, independently replicating that PIGP is required for GPI anchor biosynthesis in humans.\",\n      \"method\": \"Flow cytometry of GPI-anchored proteins on patient granulocytes\",\n      \"journal\": \"Annals of clinical and translational neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — flow cytometry functional confirmation in second independent family, single method\",\n      \"pmids\": [\"31139695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A homozygous PIGP frameshift variant (c.384del) results in a longer-than-wild-type protein predicted to have impaired functionality, and is associated with reduced expression of the GPI-anchored protein CD16 on granulocyte membranes, establishing CD16 as a functional marker for PIGP-related inherited GPI deficiency.\",\n      \"method\": \"Flow cytometry of GPI-anchored protein CD16 on patient granulocytes\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — flow cytometry functional readout in multiple affected individuals from a large family, single method\",\n      \"pmids\": [\"32042915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PIGP is an autosomal gene essential for GPI-anchor biosynthesis; deletion of one PIGP allele followed by introduction of a truncating mutation in the other abolished GPI anchor display on the cell membrane, as detected by flow cytometry. This was rescued by correction of the PIGP mutation via targeted knock-in, directly demonstrating that PIGP function is required for GPI anchor surface expression.\",\n      \"method\": \"CRISPR/Cas9-based PIGP allele deletion, flow cytometry of GPI anchors, targeted knock-in rescue\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — engineered cell lines with allele-specific mutations and rescue, two orthogonal readouts, single lab\",\n      \"pmids\": [\"34750615\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PIGP (also known as DSCR5/DCRC) encodes an essential small transmembrane subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex, which catalyzes the first committed step of GPI anchor biosynthesis at the ER membrane; PIGP directly associates with PIG-A and GPI1 within this complex, is indispensable for enzymatic activity, and loss of PIGP function in human patients reduces GPI-anchored protein surface expression, causing inherited GPI deficiency with developmental and epileptic encephalopathy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PIGP encodes an essential subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex, which catalyzes the first committed step of glycosylphosphatidylinositol (GPI) anchor biosynthesis at the ER membrane by transferring N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol [#0]. Within this complex PIGP physically associates with PIG-A and GPI1, and cells lacking PIGP are rendered GPI-anchor negative, defining PIGP as an indispensable structural component rather than a regulatory one—a role distinct from DPM2, which associates with other complex subunits and enhances enzyme activity without binding PIGP directly [#0, #1]. The essential, conserved function is corroborated by the yeast and fungal homologs, which associate with the GPI2 subunit, are required for in vitro GPI-GlcNAc transferase activity, and whose loss produces cell wall and GPI synthesis defects [#2, #4]. In humans, biallelic loss-of-function mutations in PIGP reduce surface expression of GPI-anchored proteins, and reintroduction of wild-type PIGP rescues this deficit, causing an inherited GPI deficiency presenting as developmental and epileptic encephalopathy [#5, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that PIGP is a bona fide, essential subunit of the GPI-GnT complex rather than an accessory factor, defining the molecular machine that initiates GPI anchor synthesis.\",\n      \"evidence\": \"Co-immunoprecipitation with PIG-A and GPI1, plus a GPI-anchor-negative loss-of-function cell line and complementation\",\n      \"pmids\": [\"10944123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic contribution of PIGP versus its scaffolding role within the complex not resolved\", \"No structure of the assembled complex\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Distinguished PIGP's essential structural role from regulatory inputs by showing DPM2 enhances GPI-GnT activity ~3-fold via PIG-A, PIG-C, and GPI1 but not through PIGP.\",\n      \"evidence\": \"Co-immunoprecipitation and in vitro enzyme activity assay\",\n      \"pmids\": [\"10944123\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which DPM2 enhances activity not defined\", \"Whether regulation occurs in human cells the same way as in vitro untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Confirmed functional conservation by showing the yeast homolog Gpi19p is an essential GPI-GlcNAc transferase subunit with defined ER membrane topology, linking GPI synthesis to cell wall and Ras-pathway phenotypes.\",\n      \"evidence\": \"Co-IP with Gpi2, in vitro enzyme activity assay, topology analysis, and temperature-sensitive mutant phenotyping in S. cerevisiae\",\n      \"pmids\": [\"16278447\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human PIGP membrane topology not directly mapped\", \"Connection between GPI deficiency and Ras hyperactivity mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Connected loss of PIGP function to downstream secretory consequences by showing fungal pigP mutants have decreased GPI synthesis and aberrant secretion of a normally membrane-anchored protease.\",\n      \"evidence\": \"Mutant analysis with GPI synthesis measurement and protein secretion assay in Aspergillus nidulans\",\n      \"pmids\": [\"19421754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Findings in filamentous fungus may not transfer to human cell biology\", \"Specific anchored substrates affected in humans not enumerated\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended conservation and demonstrated gene-dosage sensitivity, showing the Candida homolog is essential and that even partial reduction produces cell wall, drug-sensitivity, and morphogenesis defects.\",\n      \"evidence\": \"Cross-species complementation and conditional null (MET3 promoter) phenotyping in Candida albicans\",\n      \"pmids\": [\"20576690\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether dosage sensitivity applies to human heterozygotes untested here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established PIGP as a human disease gene by linking biallelic mutations to reduced GPI-anchored surface protein levels and demonstrating rescue by wild-type PIGP.\",\n      \"evidence\": \"Patient cell functional study, flow cytometry of GPI-anchored proteins, and wild-type PIGP rescue\",\n      \"pmids\": [\"28334793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genotype-phenotype correlation across mutation types not established\", \"Tissue-specific effects of GPI deficiency not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Independently replicated the human requirement for PIGP in a second family, reinforcing the causal link between PIGP loss and GPI-anchored protein deficiency.\",\n      \"evidence\": \"Flow cytometry of GPI-anchored proteins on patient granulocytes\",\n      \"pmids\": [\"31139695\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method\", \"No mechanistic dissection beyond surface marker quantification\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified a clinically usable functional readout by establishing reduced granulocyte CD16 as a marker of PIGP-related inherited GPI deficiency.\",\n      \"evidence\": \"Flow cytometry of CD16 on patient granulocytes from a large family\",\n      \"pmids\": [\"32042915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Predicted impaired functionality of elongated mutant protein not biochemically confirmed\", \"Single method\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Provided direct causal proof in engineered human cells that PIGP function is required for GPI anchor surface display, with knock-in correction restoring the anchor.\",\n      \"evidence\": \"CRISPR/Cas9 allele deletion plus truncation, flow cytometry of GPI anchors, and targeted knock-in rescue\",\n      \"pmids\": [\"34750615\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and assembly order of PIGP within the human GPI-GnT complex unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PIGP contributes structurally or mechanistically to GPI-GnT catalysis—its precise position, stoichiometry, and topology within the human complex—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of the human GPI-GnT complex\", \"Catalytic versus scaffolding contribution of PIGP undefined\", \"Regulatory inputs governing complex activity in human cells uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"complexes\": [\"GPI-N-acetylglucosaminyltransferase (GPI-GnT)\"],\n    \"partners\": [\"PIGA\", \"GPI1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}