Affinage

PIGH

Phosphatidylinositol N-acetylglucosaminyltransferase subunit H · UniProt Q14442

Length
188 aa
Mass
21.1 kDa
Annotated
2026-06-10
32 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PIGH is an essential, cytoplasmically oriented ER-associated subunit of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the first committed step of GPI-anchor biosynthesis—transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol on the cytoplasmic face of the ER (PMID:8900170, PMID:9463366). PIG-H forms a core protein complex with the catalytic-class subunit PIG-A in the ER, and together with PIG-C and GPI1 constitutes a four-protein complex with reconstituted GPI-GnT activity in vitro that preferentially recognizes specific PI fatty-acyl species (PMID:8900170, PMID:9463366). Within this assembly GPI1 stabilizes the enzyme by bridging PIG-C to the PIG-A/PIG-H core, while a stable PIG-A/PIG-H dimer persists in its absence, defining PIG-H as part of the irreducible catalytic scaffold (PMID:10373468). The complex is further completed by the essential component PIG-P and regulated by DPM2, which enhances activity without being required for catalysis (PMID:10944123). Loss of PIGH function—through start-codon disruption that removes the essential N-terminal 62 residues, epigenetic silencing of its mRNA, or splice-disrupting variants—abolishes surface expression of GPI-anchored proteins and the downstream signaling they support, including CD14-mediated LPS/TLR4 activation (PMID:29573052, PMID:30370942, PMID:34294787). A loss-of-function splice variant in bovine PIGH causes autosomal recessive arthrogryposis, establishing PIGH as essential for normal mammalian development (PMID:25895751).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1996 High

    Established that PIG-H is a cytoplasmically oriented ER-associated protein that physically partners with PIG-A, defining the topology and subunit pairing of the GPI GlcNAc transferase before its activity was reconstituted.

    Evidence Subcellular fractionation, topology studies, immunofluorescence, and co-immunoprecipitation in mammalian cells

    PMID:8900170

    Open questions at the time
    • Did not reconstitute enzymatic activity
    • Catalytic versus structural role of PIG-H within the complex not resolved
  2. 1998 High

    Showed that PIG-A, PIG-H, PIG-C and GPI1 together form a four-protein complex carrying GPI-GnT activity, placing PIG-H in a defined enzyme rather than an inferred association.

    Evidence Co-immunoprecipitation plus in vitro GPI-GnT activity assay with PI substrate-specificity analysis

    PMID:9463366

    Open questions at the time
    • Which subunit performs catalysis not assigned
    • Did not test whether additional components are required for full activity
  3. 1999 High

    Resolved the internal architecture of the complex by showing GPI1 bridges PIG-C to a stable PIG-A/PIG-H core, defining PIG-H as part of the irreducible catalytic dimer.

    Evidence GPI1 gene disruption in F9 cells with co-IP and Western blot analysis of remaining subassemblies

    PMID:10373468

    Open questions at the time
    • Structural basis of the PIG-A/PIG-H interaction not determined
    • Did not establish whether PIG-A/PIG-H dimer alone has residual activity
  4. 2000 High

    Expanded the complex to five essential subunits plus a regulator, showing PIG-P is required and DPM2 enhances but is dispensable for activity, contextualizing PIG-H within a larger regulated machine.

    Evidence Co-IP, flow-cytometry GPI-anchor expression assays in loss-of-function cells, and in vitro GPI-GnT activity assays

    PMID:10944123

    Open questions at the time
    • Specific contribution of PIG-H to substrate binding or catalysis still undefined
    • No structural model of the assembled complex
  5. 2000 Medium

    Localized the catalytic-class subunit to perinuclear and mitochondria-associated ER lamellae and proposed a topological model, refining where the PIG-H-containing complex operates.

    Evidence Immunofluorescence, immunoelectron microscopy, affinity chromatography, and computational sequence alignment

    PMID:10716631

    Open questions at the time
    • Predicted active-site residues not validated by mutagenesis
    • Single-lab topological model
  6. 2015 Medium

    Demonstrated that loss-of-function PIGH is incompatible with normal development, linking a splice-disrupting variant to autosomal recessive arthrogryposis in cattle.

    Evidence GWAS mapping, NGS, RNA-Seq, and RT-PCR confirmation of exon-2 skipping in Belgian Blue cattle

    PMID:25895751

    Open questions at the time
    • Functional consequence inferred from domain loss rather than direct enzyme assay
    • Single study; mechanism linking GPI deficiency to arthrogryposis not detailed
  7. 2018 Medium

    Mapped a functionally essential region of PIGH by showing that start-codon disruption removing the N-terminal 62 residues yields a truncated protein unable to restore GPI-anchor expression.

    Evidence FACS of GPI-AP surface expression in PIGH-deficient CHO cells complemented with c.1A>T cDNA, with Sanger sequencing

    PMID:29573052

    Open questions at the time
    • Single-lab cell-based complementation only
    • Molecular reason the N-terminus is required not defined
  8. 2018 Medium

    Showed that PIGH loss can be epigenetic rather than genetic, with mRNA silencing causing defective first-step GPI biosynthesis and loss of GPI-anchored proteins such as CD52.

    Evidence RT-PCR/mRNA expression, methylation analysis, and flow cytometry for GPI-AP surface expression in B-ALL cells

    PMID:30370942

    Open questions at the time
    • Mechanism of silencing not fully defined
    • Single lab
  9. 2021 Medium

    Connected PIGH-dependent GPI synthesis to a specific signaling output by showing silencing abolishes CD14 surface expression and LPS/TLR4 responses, rescued by PIGH overexpression.

    Evidence Flow cytometry for GPI-AP/CD14, LPS stimulation assays, and PIGH overexpression rescue in BLaER1 monocyte-model cells

    PMID:34294787

    Open questions at the time
    • Specificity to TLR4 versus broader GPI-AP loss not fully dissected
    • Single-lab functional model

Open questions

Synthesis pass · forward-looking unresolved questions
  • The precise catalytic contribution of PIG-H within the GPI-GnT complex and a structural model of how it scaffolds PIG-A remain unresolved.
  • No atomic structure of the PIG-A/PIG-H core
  • Whether PIG-H contributes residues to catalysis or only stabilizes the complex is unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 3
Localization
GO:0005783 endoplasmic reticulum 3 GO:0005829 cytosol 1
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-392499 Metabolism of proteins 2
Partners
DPM2GPI1PIGAPIGCPIGP
Complex memberships
GPI-GlcNAc transferase (GPI-GnT) complex

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1996 PIG-A is an ER transmembrane protein with a large cytoplasmic domain homologous to a bacterial GlcNAc transferase and a small lumenal domain; PIG-H is a cytoplasmically oriented, ER-associated protein; both form a protein complex in the endoplasmic reticulum, indicating they are subunits of the GPI GlcNAc transferase that transfers GlcNAc to PI on the cytoplasmic side of the ER. Subcellular fractionation, immunofluorescence, topology studies, co-immunoprecipitation The Journal of biological chemistry High 8900170
1998 PIG-A, PIG-H, PIG-C, and human GPI1 form a four-protein complex in the ER membrane that has GPI-GlcNAc transferase (GPI-GnT) activity in vitro, catalyzing transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol; PIG-L (involved in the second GPI synthesis step) did not associate with this complex. The complex preferentially utilizes bovine PI (~100-fold) over soybean PI, suggesting recognition of specific fatty acyl chains. Co-immunoprecipitation, in vitro GPI-GnT activity assay with substrate specificity analysis The EMBO journal High 9463366
1999 GPI1 stabilizes the GPI-GnT enzyme complex by tying PIG-C to a core PIG-A/PIG-H complex; disruption of GPI1 in F9 cells caused nearly undetectable PIG-A/PIG-H/PIG-C trimeric complex while PIG-A/PIG-H dimeric complex remained detectable, and caused partial decreases in PIG-C and PIG-H protein levels. Gene disruption (KO) in F9 embryonal carcinoma cells, co-immunoprecipitation, Western blot The Journal of biological chemistry High 10373468
2000 GPI-GnT requires a fifth component, PIG-P, which associates with PIG-A and GPI1; a cell lacking PIG-P is GPI-anchor negative, establishing PIG-P as essential. DPM2 associates with GPI-GnT (through interactions with PIG-A, PIG-C, and GPI1) and enhances enzyme activity 3-fold, but is not essential for the reaction. PIG-H is thus a subunit of this larger, regulated complex. Co-immunoprecipitation, cell-based GPI-anchor expression assay (flow cytometry), in vitro GPI-GnT activity assay The EMBO journal High 10944123
2000 PIG-A (the proposed catalytic subunit of the GPI-GnT complex) localizes to both perinuclear and mitochondria-associated lamellae of the ER; computer-aided alignment identified highly conserved residues in the membrane-proximal cytoplasmic domain (residues 230–340) of PIG-A potentially involved in catalysis. A topological model of the four partners (PIG-A, PIG-H, PIG-C, GPI1) was proposed. Immunofluorescence, immunoelectron microscopy, affinity chromatography, computational sequence comparison The international journal of biochemistry & cell biology Medium 10716631
2018 A homozygous c.1A>T transversion in PIGH (disrupting the start codon) results in utilization of an in-frame start site at codon 63, producing a truncated protein that cannot efficiently restore GPI-anchored protein expression in PIGH-deficient CHO cells, demonstrating that the N-terminal 62 residues of PIGH are essential for GPI-GnT function. FACS analysis of GPI-AP surface expression in PIGH-deficient CHO cells transfected with cDNA bearing c.1A>T, Sanger sequencing Human mutation Medium 29573052
2018 Loss of GPI-anchor–negative phenotype in B-ALL cells results from epigenetic silencing of PIGH mRNA expression (rather than gene mutation or deletion), leading to defective first-step GPI biosynthesis and loss of GPI-anchored protein (including CD52) surface expression. RT-PCR/mRNA expression analysis, flow cytometry for GPI-AP surface expression, methylation/epigenetic analysis American journal of hematology Medium 30370942
2021 Epigenetic silencing of PIGH in BLaER1 monocyte-model cells causes GPI-anchor deficiency, loss of CD14 surface expression, and diminished LPS/TLR4 signaling (but not TLR7/TLR8 signaling); overexpressing PIGH restored GPI-anchored protein (including CD14) expression and LPS responsiveness, placing PIGH upstream of CD14-dependent TLR4 activation. Flow cytometry for GPI-AP/CD14 surface expression, LPS stimulation assay, PIGH overexpression rescue experiment Scientific reports Medium 34294787
2015 A splice-site variant (c211-10C>G) in bovine PIGH causes skipping of exon 2, producing a non-functional PIGH protein lacking essential domains; this loss-of-function is associated with autosomal recessive arthrogryposis in Belgian Blue cattle, confirming PIGH is essential for normal development in mammals. Genome-wide association mapping, next-generation DNA sequencing, RNA-Seq, RT-PCR confirmation of exon skipping BMC genomics Medium 25895751

Source papers

Stage 0 corpus · 32 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Biosynthesis of the red antibiotic, prodigiosin, in Serratia: identification of a novel 2-methyl-3-n-amyl-pyrrole (MAP) assembly pathway, definition of the terminal condensing enzyme, and implications for undecylprodigiosin biosynthesis in Streptomyces. Molecular microbiology 168 15853884
1998 The first step of glycosylphosphatidylinositol biosynthesis is mediated by a complex of PIG-A, PIG-H, PIG-C and GPI1. The EMBO journal 129 9463366
2000 Initial enzyme for glycosylphosphatidylinositol biosynthesis requires PIG-P and is regulated by DPM2. The EMBO journal 110 10944123
1996 PIG-A and PIG-H, which participate in glycosylphosphatidylinositol anchor biosynthesis, form a protein complex in the endoplasmic reticulum. The Journal of biological chemistry 73 8900170
1996 PIG-C, one of the three human genes involved in the first step of glycosylphosphatidylinositol biosynthesis is a homologue of Saccharomyces cerevisiae GPI2. Biochemical and biophysical research communications 66 8806613
2006 Protein assembly line components in prodigiosin biosynthesis: characterization of PigA,G,H,I,J. Journal of the American Chemical Society 56 17002325
1994 Chromosomal assignment of genes involved in glycosylphosphatidylinositol anchor biosynthesis: implications for the pathogenesis of paroxysmal nocturnal hemoglobinuria. Blood 43 8204896
2006 Autoreactive marginal zone B cells are spontaneously activated but lymph node B cells require T cell help. The Journal of experimental medicine 37 16880262
1999 GPI1 stabilizes an enzyme essential in the first step of glycosylphosphatidylinositol biosynthesis. The Journal of biological chemistry 31 10373468
1998 Human and mouse Gpi1p homologues restore glycosylphosphatidylinositol membrane anchor biosynthesis in yeast mutants. The Biochemical journal 26 9729469
1994 Co-segregation of the malignant hyperthermia and the Arg615-Cys615 mutation in the skeletal muscle calcium release channel protein in five European Landrace and Pietrain pig breeds. Animal genetics 25 7943985
2005 Gpi19, the Saccharomyces cerevisiae homologue of mammalian PIG-P, is a subunit of the initial enzyme for glycosylphosphatidylinositol anchor biosynthesis. Eukaryotic cell 23 16278447
2000 Characterisation of the enzymatic complex for the first step in glycosylphosphatidylinositol biosynthesis. The international journal of biochemistry & cell biology 19 10716631
2018 A homozygous variant disrupting the PIGH start-codon is associated with developmental delay, epilepsy, and microcephaly. Human mutation 17 29573052
2018 A PIGH mutation leading to GPI deficiency is associated with developmental delay and autism. Human mutation 13 29603516
2015 Genome-wide next-generation DNA and RNA sequencing reveals a mutation that perturbs splicing of the phosphatidylinositol glycan anchor biosynthesis class H gene (PIGH) and causes arthrogryposis in Belgian Blue cattle. BMC genomics 13 25895751
2019 PIGQ glycosylphosphatidylinositol-anchored protein deficiency: Characterizing the phenotype. American journal of medical genetics. Part A 12 31148362
2001 The human GPI1 gene is required for efficient glycosylphosphatidylinositol biosynthesis. Gene 11 11418246
2020 PIGH deficiency can be associated with severe neurodevelopmental and skeletal manifestations. Clinical genetics 9 33156547
2009 Two populations of double minute chromosomes harbor distinct amplicons, the MYC locus at 8q24.2 and a 0.43-Mb region at 14q24.1, in the SW613-S human carcinoma cell line. Cytogenetic and genome research 9 19372663
1997 Structures and chromosomal localizations of the glycosylphosphatidylinositol synthesis gene PIGC and its pseudogene PIGCP1. Genomics 7 9325057
2018 Loss of the GPI-anchor in B-lymphoblastic leukemia by epigenetic downregulation of PIGH expression. American journal of hematology 6 30370942
2023 In silico exploration of Serratia sp. BRL41 genome for detecting prodigiosin Biosynthetic Gene Cluster (BGC) and in vitro antimicrobial activity assessment of secreted prodigiosin. PloS one 5 37967102
2024 Mining key circRNA-associated-ceRNA networks for milk fat metabolism in cows with varying milk fat percentages. BMC genomics 4 38561663
2021 Solution Structure and Conformational Dynamics of a Doublet Acyl Carrier Protein from Prodigiosin Biosynthesis. Biochemistry 4 33416314
2021 An epigenetic GPI anchor defect impairs TLR4 signaling in the B cell transdifferentiation model for primary human monocytes BLaER1. Scientific reports 4 34294787
2023 Expanding the phenotype of PIGP deficiency to multiple congenital anomalies-hypotonia-seizures syndrome. Clinical genetics 3 37125481
2023 Up- and Downregulated Genes after Long-Term Muscle Atrophy Induced by Denervation in Mice Detected Using RNA-Seq. Life (Basel, Switzerland) 3 37240756
2021 Acromegaly Cases Exhibiting Increased Growth Hormone Levels during Oral Glucose Loading with Preadministration of Dipeptidyl Peptidase-4 Inhibitor. Internal medicine (Tokyo, Japan) 3 34334589
2020 Multisystem disorders, severe developmental delay and seizures in two affected siblings, expanding the phenotype of PIGC deficiency. European journal of medical genetics 3 32707268
2025 Pathogenic glycosyltransferase genes and potential therapeutic drugs in pressure overload-induced heart failure. ESC heart failure 2 40903443
2025 Integrating machine learning and single-cell sequencing to identify shared biomarkers in type 1 diabetes mellitus and clear cell renal cell carcinoma. Frontiers in oncology 0 40098701

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