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GPAA1

GPI-anchor transamidase component GPAA1 · UniProt O43292

Length
621 aa
Mass
67.6 kDa
Annotated
2026-06-10
22 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/5 claims corpus-supported (80%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

GPAA1 (GAA1) is a core subunit of the endoplasmic reticulum GPI transamidase complex, the multiprotein machinery that cleaves the C-terminal signal peptide of precursor proteins and covalently attaches a preformed GPI anchor, and it is essential for cell-surface display of GPI-anchored proteins in human, mouse, and zebrafish cells (PMID:11483512, PMID:9468317, PMID:10898732, PMID:29100095). It is a polytopic ER membrane glycoprotein with a cytoplasmic N terminus and a lumenal C terminus; its large lumenal domain between the first and second transmembrane segments mediates assembly with the other transamidase subunits, while the C-terminal transmembrane segments are dispensable for subunit interaction but required for catalytic function (PMID:12052837). A conserved proline within the C-terminal transmembrane span is specifically required for recognition of the GPI lipid substrate: GPAA1 mutants lacking this residue retain all complex subunits and still bind proprotein substrate yet fail to co-immunoprecipitate GPI (PMID:14660601). Bi-allelic loss-of-function mutations in GPAA1 cause a human inherited GPI-anchor deficiency disorder, with reduced surface abundance of multiple GPI-anchored proteins in patient cells that is partially rescued by wild-type GPAA1 (PMID:29100095). Through its control of GPI-anchored substrates such as CD24, GPAA1 modulates cell-surface signaling and immune evasion, and its abundance is regulated post-translationally by RCBTB2-mediated ubiquitin-proteasomal degradation (PMID:38573857, PMID:41244118).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 1998 Medium

    Established that human GPAA1 is functionally required for GPI anchor attachment, moving it from a candidate to a necessary factor in the pathway.

    Evidence Antisense overexpression of hGAA1 in K562 cells with cell-surface GPI-anchored reporter readout

    PMID:9468317

    Open questions at the time
    • Single loss-of-function method
    • No biochemical mechanism or complex membership defined
  2. 2000 Medium

    Confirmed the requirement for GPAA1 in GPI anchoring across species, generalizing the human finding to murine cells.

    Evidence Antisense mGPAA1 expression in 3T3 cells with cell-surface GPI-anchored protein assay

    PMID:10898732

    Open questions at the time
    • Single method
    • Does not define molecular role within the complex
  3. 2001 High

    Defined GPAA1 as a core subunit of a multiprotein GPI transamidase complex and placed it among GPI8, PIG-S, and PIG-T, establishing the assembly that performs anchor transfer.

    Evidence Homologous-recombination knockouts in mouse F9 cells, reciprocal co-IP, and carbonyl-intermediate formation assay

    PMID:11483512

    Open questions at the time
    • Stoichiometry and catalytic subunit identity not resolved
    • GPAA1's specific catalytic contribution unclear
  4. 2002 High

    Mapped GPAA1 membrane topology and domain architecture, showing the lumenal domain drives complex assembly while C-terminal transmembrane segments are required for catalysis but not assembly.

    Evidence Topology assays, subcellular fractionation, sedimentation, co-IP, and complementation in Gaa1-deficient cells with epitope-tagged mutants

    PMID:12052837

    Open questions at the time
    • Function of the C-terminal segments not mechanistically explained
    • No atomic structure
  5. 2003 High

    Identified a conserved proline in the C-terminal transmembrane span as the determinant for GPI lipid substrate recognition, separating lipid binding from subunit assembly and proprotein binding.

    Evidence Site-directed mutagenesis with co-IP of GPI and proprotein substrates

    PMID:14660601

    Open questions at the time
    • How the proline mediates GPI contact at structural level is unknown
  6. 2005 Medium

    Resolved how GPAA1 reaches the ER, showing passive signalless retention rather than an active sorting motif.

    Evidence Fluorescence localization, deletion/fusion constructs, and N-glycosylation mapping

    PMID:15713669

    Open questions at the time
    • Retention mechanism remains indirect
    • Single lab
  7. 2017 Medium

    Provided in vitro evidence that the GPAA1 and GPI8 lumenal domains form a defined core heterotetramer, identifying a minimal assembly unit of the transamidase.

    Evidence Recombinant yeast ortholog lumenal domains analyzed by GST pulldown, native PAGE, and size-exclusion chromatography

    PMID:28893510

    Open questions at the time
    • Yeast orthologs, not human proteins
    • Does not include other subunits or lipid substrate
  8. 2017 High

    Established GPAA1 as the cause of a human Mendelian GPI-anchor deficiency disorder via bi-allelic loss-of-function mutations.

    Evidence Whole-exome sequencing across families, flow cytometry of patient leukocytes/fibroblasts, and lentiviral wild-type rescue

    PMID:29100095

    Open questions at the time
    • Genotype-phenotype correlation across mutation classes incomplete
    • Rescue only partial
  9. 2020 Low

    Computational analyses proposed GPAA1 as a single-zinc M28 metallopeptidase whose lumenal active site catalyzes the transamidation peptide bond, offering a candidate catalytic mechanism.

    Evidence Homology modeling, molecular dynamics simulation, and phylogenetic analysis (also idx 4, 2014)

    PMID:24743167 PMID:32993792

    Open questions at the time
    • Computational only, no in vitro biochemical or mutagenesis validation
    • Metal coordination unproven experimentally
  10. 2019 Medium

    Linked GPAA1 abundance to oncogenic signaling, showing its upregulation enhances surface GPI-anchored proteins and lipid raft formation to promote EGFR-ERBB2 dimerization.

    Evidence Co-IP, in situ proximity ligation assay, and stable GPAA1 deletion/overexpression with in vitro and in vivo proliferation/metastasis assays in gastric cancer

    PMID:31118109

    Open questions at the time
    • Causal chain from raft changes to EGFR dimerization indirect
    • Single lab
  11. 2024 High

    Identified CD24 as a specific GPAA1-dependent surface substrate with immune consequences and demonstrated a small-molecule (bestatin) that binds GPAA1 to block GPI attachment.

    Evidence Genome-wide CRISPR screen, genetic ablation, phagocytosis assay, in vivo ovarian tumor model, and bestatin drug-binding assay

    PMID:38573857

    Open questions at the time
    • Bestatin binding site on GPAA1 not mapped
    • Substrate selectivity rules not defined
  12. 2025 Medium

    Revealed post-translational regulation of GPAA1 by the E3 ligase RCBTB2 through ubiquitin-proteasomal degradation, connecting GPAA1 turnover to cancer cell behavior.

    Evidence Co-IP, immunofluorescence co-localization, multi-omics, RCBTB2 overexpression, and GPAA1 knockdown functional assays in prostate cancer cells

    PMID:41244118

    Open questions at the time
    • Ubiquitination sites on GPAA1 not identified
    • Single lab; reciprocal validation limited

Open questions

Synthesis pass · forward-looking unresolved questions
  • The catalytic mechanism of GPAA1 within the transamidase remains experimentally unproven, and a high-resolution structure of the human complex with bound GPI and proprotein substrate is lacking.
  • No in vitro reconstitution of GPAA1 catalysis
  • No experimental zinc-coordination data
  • No atomic structure of the assembled human transamidase

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 3
Localization
GO:0005783 endoplasmic reticulum 3
Pathway
R-HSA-392499 Metabolism of proteins 3
Partners
PIGKPIGSPIGTRCBTB2
Complex memberships
GPI transamidase complex

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2001 GAA1/GPAA1 is a core subunit of the GPI transamidase complex; the complex additionally contains GPI8, PIG-S, and PIG-T. PIG-T maintains the complex by stabilizing the expression of GAA1 and GPI8, and loss of PIG-S or PIG-T abolishes formation of the carbonyl intermediate with substrate proteins during GPI anchor transfer. Gene disruption by homologous recombination in mouse F9 cells, co-immunoprecipitation, carbonyl-intermediate formation assay The EMBO journal High 11483512
2002 GAA1/GPAA1 is an ER-localized polytopic membrane glycoprotein with a cytoplasmically oriented N terminus and a lumenally oriented C terminus; it sediments at ~17 S in detergent extracts. The large lumenal domain between the first and second transmembrane segments mediates interaction with other GPI transamidase subunits. C-terminal transmembrane segments are dispensable for subunit interaction but are required for a functional GPI transamidase complex. The cytoplasmic N terminus is not required for complex formation but may act as a membrane-sorting determinant. Epitope-tagged Gaa1 mutant analysis, membrane topology assay, subcellular fractionation, co-immunoprecipitation, sedimentation/density gradient, complementation in Gaa1-deficient cells The Journal of biological chemistry High 12052837
2003 A conserved proline residue within the C-terminal transmembrane span of Gaa1/GPAA1 is required for GPI recognition by the GPI transamidase complex. GPIT complexes containing C-terminally truncated Gaa1 retain all subunits and can interact with a proprotein substrate but cannot co-immunoprecipitate GPI; mutation of the conserved proline alone abrogates GPI co-immunoprecipitation. Site-directed mutagenesis, co-immunoprecipitation with GPI and proprotein substrates The Journal of biological chemistry High 14660601
2005 GAA1/GPAA1 lacks dominant ER-sorting determinants and is passively retained in the ER by a signalless mechanism; removal of a triple arginine cluster near the N terminus does not affect ER localization. Fusion proteins bearing different Gaa1 domains can exit the ER, confirming the passive retention model. Subcellular localization by fluorescence microscopy/fractionation, deletion and fusion protein analysis, N-glycosylation mapping The Journal of biological chemistry Medium 15713669
2014 The ~300-amino-acid lumenal domain of GAA1/GPAA1 is predicted and computationally validated to be an M28 family metallo-peptide-synthetase with an α/β hydrolase fold; it coordinates a single metal ion (most likely zinc) via three conserved polar residues and is proposed to catalyze peptide bond formation between the substrate protein's omega-site carbonyl and the phosphoethanolamine moiety of the GPI anchor. Bioinformatic sequence analysis, structural homology modeling, evolutionary conservation analysis Cell cycle (Georgetown, Tex.) Low 24743167
2017 The soluble lumenal domains of Gpi8 and Gaa1 (yeast orthologs) directly interact to form an α2β2 heterotetramer in vitro, without requirement for other subunits, establishing a core assembly unit of the GPI transamidase. Recombinant protein expression, GST pulldown, native gel electrophoresis, size-exclusion chromatography Archives of biochemistry and biophysics Medium 28893510
2020 Structural modeling of the lumenal domain of human GPAA1 identifies two large flap loops surrounding the active site that undergo anti-correlated breathing-like dynamics; canonical zinc-binding sites 2 and 3 are the strongest binders for a single Zn ion, and substrate binding enhances interaction of site 5 with Zn1, consistent with a single zinc ion metallopeptidase mechanism. Comparative molecular dynamics simulation, homology modeling, phylogenetic analysis Biology direct Low 32993792
1998 Overexpression of antisense hGAA1 in human K562 cells significantly reduces production of a GPI-anchored reporter protein on the cell surface, establishing that hGAA1/GPAA1 is required for GPI anchor attachment in human cells. Antisense overexpression, flow cytometry/cell surface reporter assay FEBS letters Medium 9468317
2000 3T3 cell lines expressing antisense mGPAA1 fail to express GPI-anchored proteins on the cell surface membrane, confirming an essential role of GPAA1 in GPI anchor attachment in murine cells. Antisense expression, cell surface protein assay American journal of physiology. Cell physiology Medium 10898732
2017 Bi-allelic loss-of-function mutations in GPAA1 (frameshift, splicing, and missense) in humans cause reduced cell-surface abundance of multiple GPI-anchored proteins (FLAER, CD16, CD59, CD73, CD109) in patient leukocytes and fibroblasts; lentiviral transduction with wild-type GPAA1 partially rescues this GPI-anchor deficiency. Whole-exome sequencing, flow cytometry of patient cells, lentiviral rescue experiment American journal of human genetics High 29100095
2019 GPAA1 upregulation enhances GPI-anchored protein levels on the cell surface and intensifies lipid raft formation, which promotes EGFR–ERBB2 dimerization and downstream pro-proliferative signalling in gastric cancer cells. Co-immunoprecipitation, in situ proximity ligation assay, stable GPAA1 deletion/overexpression with proliferation and metastasis assays in vitro and in vivo Journal of experimental & clinical cancer research : CR Medium 31118109
2020 A missense variant (c.968A>G) in GPAA1 causes scarce expression of GPAA1 protein in vascular endothelium and shifts its localization from the ER membrane to the cytoplasm and nucleus; wild-type GPAA1 expression in endothelial cells inhibits proliferation and migration, whereas the variant causes overgrowth and overmigration. Whole-exome sequencing, immunofluorescence localization, cell proliferation/migration assays with WT vs. variant GPAA1, gpaa1-deficient zebrafish model Human genetics Medium 32533362
2024 GPAA1 catalyzes GPI anchor attachment to CD24; genetic ablation of GPAA1 abolishes CD24 cell surface expression, enhances macrophage-mediated phagocytosis, and inhibits ovarian tumor growth in mice. The aminopeptidase inhibitor bestatin binds to GPAA1 and blocks GPI attachment, reducing CD24 surface expression. Genome-wide CRISPR knockout screen, genetic ablation (KO), phagocytosis assay, in vivo tumor model, drug-binding assay with bestatin Cell reports High 38573857
2025 The E3 ubiquitin ligase RCBTB2 directly interacts with GPAA1 and promotes its ubiquitin-mediated proteasomal degradation (protein downregulation without mRNA change); GPAA1 knockdown suppresses malignant behaviors of prostate cancer cells and reduces expression of aggrephagy-related factor p62. Co-immunoprecipitation, immunofluorescence co-localization, multi-omics analysis, RCBTB2 overexpression cell line, GPAA1 knockdown functional assays American journal of cancer research Medium 41244118

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 PIG-S and PIG-T, essential for GPI anchor attachment to proteins, form a complex with GAA1 and GPI8. The EMBO journal 143 11483512
2017 Mutations in GPAA1, Encoding a GPI Transamidase Complex Protein, Cause Developmental Delay, Epilepsy, Cerebellar Atrophy, and Osteopenia. American journal of human genetics 56 29100095
2002 Structural requirements for the recruitment of Gaa1 into a functional glycosylphosphatidylinositol transamidase complex. The Journal of biological chemistry 43 12052837
1998 Molecular cloning of human homolog of yeast GAA1 which is required for attachment of glycosylphosphatidylinositols to proteins. FEBS letters 42 9468317
2014 Transamidase subunit GAA1/GPAA1 is a M28 family metallo-peptide-synthetase that catalyzes the peptide bond formation between the substrate protein's omega-site and the GPI lipid anchor's phosphoethanolamine. Cell cycle (Georgetown, Tex.) 38 24743167
2006 Increased expression of glycosyl-phosphatidylinositol anchor attachment protein 1 (GPAA1) is associated with gene amplification in hepatocellular carcinoma. International journal of cancer 34 16642471
2003 A conserved proline in the last transmembrane segment of Gaa1 is required for glycosylphosphatidylinositol (GPI) recognition by GPI transamidase. The Journal of biological chemistry 31 14660601
2016 The Glycosylphosphatidylinositol Anchor Biosynthesis Genes GPI12, GAA1, and GPI8 Are Essential for Cell-Wall Integrity and Pathogenicity of the Maize Anthracnose Fungus Colletotrichum graminicola. Molecular plant-microbe interactions : MPMI 25 27937175
2019 GPAA1 promotes gastric cancer progression via upregulation of GPI-anchored protein and enhancement of ERBB signalling pathway. Journal of experimental & clinical cancer research : CR 22 31118109
2024 Targeting the GPI transamidase subunit GPAA1 abrogates the CD24 immune checkpoint in ovarian cancer. Cell reports 14 38573857
2020 A novel variant in GPAA1, encoding a GPI transamidase complex protein, causes inherited vascular anomalies with various phenotypes. Human genetics 10 32533362
2005 Endoplasmic reticulum localization of Gaa1 and PIG-T, subunits of the glycosylphosphatidylinositol transamidase complex. The Journal of biological chemistry 9 15713669
2017 The soluble domains of Gpi8 and Gaa1, two subunits of glycosylphosphatidylinositol transamidase (GPI-T), assemble into a complex. Archives of biochemistry and biophysics 8 28893510
2022 GPAA1 promotes the proliferation, invasion and migration of hepatocellular carcinoma cells by binding to RNA-binding protein SF3B4. Oncology letters 6 35399327
2020 Structural modelling of the lumenal domain of human GPAA1, the metallo-peptide synthetase subunit of the transamidase complex, reveals zinc-binding mode and two flaps surrounding the active site. Biology direct 6 32993792
2000 Cloning of murine glycosyl phosphatidylinositol anchor attachment protein, GPAA1. American journal of physiology. Cell physiology 5 10898732
1999 Human and mouse GPAA1 (Glycosylphosphatidylinositol anchor attachment 1) genes: genomic structures, chromosome loci and the presence of a minor class intron. Cytogenetics and cell genetics 5 10393431
2020 GPAA1 promotes progression of childhood acute lymphoblastic leukemia through regulating c-myc. European review for medical and pharmacological sciences 3 32432756
2023 [Glycosylphosphatidylinositol biosynthesis deficiency 15 caused by GPAA1 gene mutation: a rare disease study]. Zhongguo dang dai er ke za zhi = Chinese journal of contemporary pediatrics 1 38112147
2026 Longitudinal analysis shows GAA1 length and baseline clinical status as robust predictors of progression in Friedreich ataxia. Journal of neurology 0 41954755
2025 The ubiquitin ligase RCBTB2 regulates aggrephagy and inhibits prostate cancer progression by targeting GPAA1 for degradation. American journal of cancer research 0 41244118
2025 Mechanistic insights into GPAA1-mediated cold tumor phenotype and immune evasion in colorectal cancer: integrative multi-omics analysis and experimental validation. Frontiers in oncology 0 41367867

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