GPI

UniProt ID: P06744
Organism: Homo sapiens
Review Status: INITIALIZED
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Gene Description

Glucose-6-phosphate isomerase (phosphoglucose isomerase, PGI; EC 5.3.1.9) catalyzes the reversible aldose-ketose interconversion of glucose-6-phosphate and fructose-6-phosphate, the second step of glycolysis and the corresponding reverse step of gluconeogenesis. The catalytically active form is a cytosolic homodimer. GPI is a classic moonlighting protein; the same polypeptide, when secreted, acts extracellularly as a cytokine and growth factor known historically as neuroleukin (a neurotrophic factor and inducer of immunoglobulin secretion), autocrine motility factor (AMF, an angiogenic factor that stimulates cell and endothelial motility via the cell-surface receptor gp78/AMFR), and maturation factor. Loss-of-function variants cause glucose-6-phosphate isomerase deficiency, an autosomal recessive hereditary nonspherocytic hemolytic anemia sometimes accompanied by neurological impairment.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004347 glucose-6-phosphate isomerase activity
IBA
GO_REF:0000033 		ACCEPT
Summary: Phylogenetically inferred glucose-6-phosphate isomerase activity. This is the core, well-established molecular function of GPI, directly demonstrated for the human enzyme and conserved across all life.
Reason: This is the defining catalytic function of GPI (EC 5.3.1.9), the second enzyme of glycolysis, confirmed for the human protein and consistent across the GPI family.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Isomerase that catalyzes the conversion of alpha-D-glucose-6-
PMID:28803808
Glucose-6-phosphate isomerase (GPI) deficiency, a genetic disorder responsible for chronic nonspherocytic hemolytic anemia, is the second most common red blood cell glycolytic enzymopathy.
GO:0005829 cytosol
IBA
GO_REF:0000033 		ACCEPT
Summary: Phylogenetically inferred cytosolic localization, matching the intracellular compartment where the glycolytic/gluconeogenic reaction occurs.
Reason: The catalytically active homodimer acts in the cytoplasm/cytosol, consistent with GPI's role in cytosolic glycolysis and gluconeogenesis.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
the second step in
GO:0006094 gluconeogenesis
IBA
GO_REF:0000033 		ACCEPT
Summary: GPI catalyzes the reversible G6P to F6P step, which operates in the gluconeogenic direction, making it a core participant in gluconeogenesis.
Reason: The reversible isomerase reaction is a committed step of both glycolysis and gluconeogenesis; UniProt explicitly notes the reverse reaction in gluconeogenesis.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
and the reverse reaction in gluconeogenesis, within the
GO:0006096 glycolytic process
IBA
GO_REF:0000033 		ACCEPT
Summary: GPI performs the second step of glycolysis (G6P to F6P) and is a core glycolytic enzyme.
Reason: Directly supported; GPI is the second glycolytic enzyme, a core biological process for this gene.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
the second step in
GO:0051156 glucose 6-phosphate metabolic process
IBA
GO_REF:0000033 		ACCEPT
Summary: GPI acts on glucose-6-phosphate as its substrate, so participation in glucose-6-phosphate metabolism follows directly from its catalytic activity.
Reason: Consistent with the catalytic activity; glucose-6-phosphate is the direct substrate of the enzyme.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Isomerase that catalyzes the conversion of alpha-D-glucose-6-
GO:0048029 monosaccharide binding
IBA
GO_REF:0000033 		KEEP AS NON CORE
Summary: GPI binds its phosphorylated monosaccharide substrates (glucose-6-phosphate, fructose-6-phosphate). This binding is a mechanistic prerequisite of catalysis rather than an independent function.
Reason: Substrate binding is subsumed by the catalytic activity annotation; retained but not a distinct core function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
ligand="D-glucose 6-phosphate"
GO:0004347 glucose-6-phosphate isomerase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Electronic assignment (multiple IEA methods, incl. Rhea RHEA:11816 and EC 5.3.1.9) of the core glucose-6-phosphate isomerase activity.
Reason: Redundant with the experimentally supported core MF annotation; the electronic mapping to EC 5.3.1.9 / RHEA:11816 is correct.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
EC=5.3.1.9
GO:0005576 extracellular region
IEA
GO_REF:0000044 		KEEP AS NON CORE
Summary: Electronic mapping from the UniProt Secreted subcellular-location keyword. GPI is genuinely secreted and functions extracellularly as the AMF/neuroleukin cytokine, but this is a moonlighting pool, not the core cytosolic enzyme.
Reason: Correct for the secreted moonlighting form (autocrine motility factor), but peripheral to GPI's core glycolytic role.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
GO:0005737 cytoplasm
IEA
GO_REF:0000044 		ACCEPT
Summary: Electronic mapping from the UniProt Cytoplasm subcellular-location keyword, consistent with the compartment of the core glycolytic reaction.
Reason: Correct; GPI is a cytoplasmic/cytosolic enzyme. The more specific cytosol term is captured elsewhere.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}
GO:0006094 gluconeogenesis
IEA
GO_REF:0000120 		ACCEPT
Summary: Electronic assignment of gluconeogenesis, redundant with the IBA annotation.
Reason: Correct; GPI's reversible reaction operates in gluconeogenesis.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
and the reverse reaction in gluconeogenesis, within the
GO:0006096 glycolytic process
IEA
GO_REF:0000120 		ACCEPT
Summary: Electronic assignment of glycolytic process, redundant with the IBA annotation.
Reason: Correct core biological process for GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
the second step in
GO:0016853 isomerase activity
IEA
GO_REF:0000117 		MARK AS OVER ANNOTATED
Summary: ARBA electronic annotation to the broad parent term isomerase activity.
Reason: This is the generic grandparent of the specific glucose-6-phosphate isomerase activity that is already annotated; the specific term should be preferred.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
EC=5.3.1.9
GO:0047938 glucose-6-phosphate 1-epimerase activity
IEA
GO_REF:0000116 		KEEP AS NON CORE
Summary: Rhea-based electronic mapping (RHEA:16249) to a G6P anomerase/epimerase activity, interconverting the alpha and beta anomers of glucose-6-phosphate. UniProt records this anomerase activity only by similarity for the human enzyme.
Reason: Plausible ancillary anomerase side-activity supported by similarity, but not the core physiological function and not experimentally demonstrated in human.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Reaction=alpha-D-glucose 6-phosphate = beta-D-glucose 6-phosphate
GO:0097367 carbohydrate derivative binding
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: InterPro2GO electronic assignment of the broad term carbohydrate derivative binding, reflecting binding of the phosphosugar substrates.
Reason: Uninformatively broad; the specific monosaccharide/substrate binding is already implied by the catalytic activity annotation.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
ligand="D-glucose 6-phosphate"
GO:1901135 carbohydrate derivative metabolic process
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: InterPro2GO electronic assignment of the broad process carbohydrate derivative metabolic process.
Reason: Overly general; the specific glycolytic/gluconeogenic and glucose-6-phosphate metabolic processes are already annotated.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
the second step in
GO:0005515 protein binding
IPI
PMID:27499296
Mitochondrial Protein Interaction Mapping Identifies Regulat... 		MARK AS OVER ANNOTATED
Summary: IntAct-derived protein binding annotation from a high-throughput mitochondrial interactome screen, capturing a physical interaction of GPI with TAMM41 (Q96BW9).
Reason: Bare protein binding is uninformative about molecular function; the interaction derives from a large-scale mitochondrial affinity-enrichment screen and does not define a specific function for GPI. Per curation policy, this is marked over-annotated rather than removed.
Supporting Evidence:
PMID:27499296
we assessed condition-specific protein-protein
GO:0005829 cytosol
IEA
GO_REF:0000107 		ACCEPT
Summary: Ensembl orthology-based electronic assignment of cytosol, consistent with the compartment of the active enzyme.
Reason: Correct; the active GPI homodimer functions in the cytosol.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}
GO:0005886 plasma membrane
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology-transferred plasma membrane localization from the mouse ortholog. GPI is a soluble cytosolic/secreted protein without a transmembrane domain; any plasma-membrane association is peripheral (e.g. secreted AMF binding surface gp78).
Reason: GPI is not an integral plasma membrane protein; the term over-states a transient/peripheral association and is an over-propagated ortholog transfer.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}
GO:0006002 fructose 6-phosphate metabolic process
IEA
GO_REF:0000107 		ACCEPT
Summary: Fructose-6-phosphate is the direct product/substrate of the GPI reaction, so participation in fructose-6-phosphate metabolism follows from its catalytic activity.
Reason: Correct; fructose-6-phosphate is directly interconverted with glucose-6-phosphate by GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
to beta-D-fructose-6-phosphate
GO:0007611 learning or memory
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from the rat ortholog of a phenotype/context association (learning or memory), not a molecular function of GPI.
Reason: Over-propagated organismal-phenotype IEA transferred from rat; not part of GPI's core enzymatic function and not established for the human protein.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0007611; P:learning or memory; IEA:Ensembl
GO:0032355 response to estradiol
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of a hormone-response context association.
Reason: Over-propagated context IEA transferred from the rat ortholog; not a core function and not demonstrated for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0032355; P:response to estradiol; IEA:Ensembl
GO:0032570 response to progesterone
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of a hormone-response context association.
Reason: Over-propagated context IEA transferred from the rat ortholog; not a core function and not demonstrated for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0032570; P:response to progesterone; IEA:Ensembl
GO:0033574 response to testosterone
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of a hormone-response context association.
Reason: Over-propagated context IEA transferred from the rat ortholog; not a core function and not demonstrated for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0033574; P:response to testosterone; IEA:Ensembl
GO:0035902 response to immobilization stress
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of a stress-response context association.
Reason: Over-propagated context IEA transferred from the rat ortholog; not a core function and not demonstrated for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0035902; P:response to immobilization stress; IEA:Ensembl
GO:0035994 response to muscle stretch
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of a physiological-response context association.
Reason: Over-propagated context IEA transferred from the rat ortholog; not a core function and not demonstrated for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0035994; P:response to muscle stretch; IEA:Ensembl
GO:0043066 negative regulation of apoptotic process
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of an anti-apoptotic association, possibly reflecting the pro-survival neurotrophic/neuroleukin moonlighting role.
Reason: Over-propagated ortholog-transfer IEA; if real it relates to the secreted cytokine moonlighting activity rather than the core enzyme, and is not established for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0043066; P:negative regulation of apoptotic process; IEA:Ensembl
GO:0046686 response to cadmium ion
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from rat of a chemical-response context association.
Reason: Over-propagated context IEA transferred from the rat ortholog; not a core function and not demonstrated for human GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
GO:0046686; P:response to cadmium ion; IEA:Ensembl
GO:0048029 monosaccharide binding
IEA
GO_REF:0000107 		KEEP AS NON CORE
Summary: Ensembl orthology-based electronic assignment of monosaccharide binding, redundant with the IBA monosaccharide-binding annotation.
Reason: Substrate binding subsumed by the catalytic activity; retained but not a distinct core function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
ligand="D-glucose 6-phosphate"
GO:0051156 glucose 6-phosphate metabolic process
IEA
GO_REF:0000120 		ACCEPT
Summary: Electronic assignment of glucose-6-phosphate metabolic process, redundant with the IBA/IDA annotations.
Reason: Correct; glucose-6-phosphate is the direct substrate of GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Isomerase that catalyzes the conversion of alpha-D-glucose-6-
GO:0060170 ciliary membrane
IEA
GO_REF:0000107 		MARK AS OVER ANNOTATED
Summary: Ensembl orthology transfer from mouse of a ciliary membrane localization. GPI is a soluble cytosolic/secreted enzyme with no evidence for a ciliary-membrane role in human.
Reason: Implausible, over-propagated ortholog-transfer IEA for a soluble glycolytic enzyme lacking membrane-targeting features.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}
GO:0061621 canonical glycolysis
IEA
GO_REF:0000107 		ACCEPT
Summary: Ensembl orthology-based electronic assignment of canonical glycolysis, the specific glycolytic pathway in which GPI catalyzes the second step.
Reason: Correct and appropriately specific core process for GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
the second step in
GO:0006094 gluconeogenesis
TAS
Reactome:R-HSA-70263 		ACCEPT
Summary: Reactome traceable assertion (Gluconeogenesis pathway) that GPI participates in gluconeogenesis via the reversible G6P to F6P step.
Reason: Correct core process; consistent with the reversible isomerase reaction.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
and the reverse reaction in gluconeogenesis, within the
GO:0061621 canonical glycolysis
TAS
Reactome:R-HSA-70171 		ACCEPT
Summary: Reactome traceable assertion (Glycolysis pathway) placing GPI in canonical glycolysis.
Reason: Correct and appropriately specific core process for GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
the second step in
GO:0004347 glucose-6-phosphate isomerase activity
EXP
PMID:13538944
Enzymes of the human erythrocyte. IV. Phosphoglucose isomera... 		ACCEPT
Summary: Experimental characterization of purified human erythrocyte phosphoglucose isomerase, establishing the core glucose-6-phosphate isomerase activity.
Reason: Classic biochemical evidence for the enzyme's core catalytic function in human tissue.
Supporting Evidence:
PMID:13538944
Enzymes of the human erythrocyte. IV. Phosphoglucose isomerase, purification and properties.
GO:0004347 glucose-6-phosphate isomerase activity
TAS
Reactome:R-HSA-70471 		ACCEPT
Summary: Reactome traceable assertion (GPI dimer isomerizes G6P) for the core catalytic activity.
Reason: Correct core molecular function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Isomerase that catalyzes the conversion of alpha-D-glucose-6-
GO:0051156 glucose 6-phosphate metabolic process
ISS
GO_REF:0000024 		ACCEPT
Summary: Sequence-similarity transfer (from yeast/ortholog) of glucose-6-phosphate metabolic process, redundant with the IBA/IDA annotations.
Reason: Correct; glucose-6-phosphate is the direct substrate of GPI.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Isomerase that catalyzes the conversion of alpha-D-glucose-6-
GO:0005576 extracellular region
EXP
PMID:11437381
Tumor autocrine motility factor is an angiogenic factor that... 		KEEP AS NON CORE
Summary: Experimental evidence that GPI/AMF is secreted and acts extracellularly as an angiogenic autocrine motility factor stimulating endothelial cell motility.
Reason: Correct for the secreted moonlighting form (AMF), but extracellular localization is peripheral to GPI's core cytosolic glycolytic function.
Supporting Evidence:
PMID:11437381
AMF stimulated in vitro motility of human umbilical vein
GO:0005737 cytoplasm
EXP
PMID:11437381
Tumor autocrine motility factor is an angiogenic factor that... 		ACCEPT
Summary: Experimental subcellular localization placing GPI in the cytoplasm, the compartment of its core glycolytic activity.
Reason: Correct; GPI is a cytoplasmic/cytosolic enzyme.
Supporting Evidence:
PMID:11437381
Tumor autocrine motility factor is an angiogenic factor that stimulates
GO:0047938 glucose-6-phosphate 1-epimerase activity
ISS
GO_REF:0000024 		KEEP AS NON CORE
Summary: Sequence-similarity transfer of an anomerase/epimerase activity on glucose-6-phosphate; UniProt records this activity only by similarity for human GPI.
Reason: Plausible ancillary anomerase side-activity supported by similarity, but not the core physiological function and not experimentally demonstrated in human.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Reaction=alpha-D-glucose 6-phosphate = beta-D-glucose 6-phosphate
GO:0016857 racemase and epimerase activity, acting on carbohydrates and derivatives
ISS
GO_REF:0000024 		MARK AS OVER ANNOTATED
Summary: Sequence-similarity transfer to the broad parent term for carbohydrate racemase/epimerase activity, reflecting the by-similarity C2-epimerase/anomerase side reactions.
Reason: Overly broad grandparent term; the specific (by-similarity) glucose-6-phosphate epimerase activity is already annotated separately.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Glucose-6-phosphate C2-epimerase
GO:0004347 glucose-6-phosphate isomerase activity
IDA
PMID:28803808
Two novel mutations (p.(Ser160Pro) and p.(Arg472Cys)) causin... 		ACCEPT
Summary: Direct assay of GPI catalytic activity in patients with GPI deficiency, where pathogenic variants reduce residual enzyme activity, confirming the core isomerase function.
Reason: Direct experimental support for the core molecular function in the human protein; residual GPI activity was measured in patient erythrocytes.
Supporting Evidence:
PMID:28803808
lost approximately 89% of their GPI activity
GO:0051156 glucose 6-phosphate metabolic process
IDA
PMID:28803808
Two novel mutations (p.(Ser160Pro) and p.(Arg472Cys)) causin... 		ACCEPT
Summary: Direct evidence that GPI acts in glucose-6-phosphate metabolism, from patient enzyme-activity measurements in GPI deficiency.
Reason: Correct; glucose-6-phosphate is the direct substrate of GPI.
Supporting Evidence:
PMID:28803808
is the second most common red blood
GO:0010595 positive regulation of endothelial cell migration
IDA
PMID:1649192
Purification of human tumor cell autocrine motility factor a... 		KEEP AS NON CORE
Summary: Purified GPI/AMF stimulates cell migration and, via its receptor gp78, promotes motility; a moonlighting cytokine activity of the secreted protein.
Reason: A genuine moonlighting activity of secreted GPI (autocrine motility factor), but distinct from its core glycolytic enzyme role.
Supporting Evidence:
PMID:1649192
Purified AMF stimulated HT-1080 cell
PMID:11437381
AMF stimulated in vitro motility of human umbilical vein
GO:0005576 extracellular region
TAS
Reactome:R-HSA-6798748 		KEEP AS NON CORE
Summary: Reactome traceable assertion placing GPI in the extracellular region via exocytosis of secretory granule lumen proteins (neutrophil degranulation).
Reason: Consistent with the secreted moonlighting pool of GPI, but peripheral to the core cytosolic enzyme function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
GO:0005576 extracellular region
TAS
Reactome:R-HSA-6800434 		KEEP AS NON CORE
Summary: Reactome traceable assertion placing GPI in the extracellular region via exocytosis of ficolin-rich granule lumen proteins.
Reason: Consistent with the secreted moonlighting pool of GPI, but peripheral to the core cytosolic enzyme function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
GO:0034774 secretory granule lumen
TAS
Reactome:R-HSA-6798748 		KEEP AS NON CORE
Summary: Reactome traceable assertion localizing GPI to the secretory granule lumen in the context of neutrophil degranulation.
Reason: Reflects the granule/secretion route of the moonlighting extracellular pool, not the core cytosolic function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
GO:1904813 ficolin-1-rich granule lumen
TAS
Reactome:R-HSA-6800434 		KEEP AS NON CORE
Summary: Reactome traceable assertion localizing GPI to the ficolin-1-rich granule lumen (neutrophil degranulation pathway).
Reason: Reflects the granule/secretion route of the moonlighting extracellular pool, not the core cytosolic function.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
GO:0002639 positive regulation of immunoglobulin production
IDA
PMID:3020690
Neuroleukin: a lymphokine product of lectin-stimulated T cel... 		KEEP AS NON CORE
Summary: GPI/neuroleukin, secreted by lectin-stimulated T cells, induces immunoglobulin secretion by human peripheral blood mononuclear cells; a moonlighting cytokine activity.
Reason: A genuine moonlighting cytokine function of secreted GPI (neuroleukin), distinct from its core glycolytic enzyme role.
Supporting Evidence:
PMID:3020690
Neuroleukin is a lymphokine product of lectin-stimulated T cells that induces immunoglobulin secretion by cultured human peripheral blood mononuclear cells.
GO:0031625 ubiquitin protein ligase binding
IPI
PMID:24810856
Polyubiquitylation of AMF requires cooperation between the g... 		KEEP AS NON CORE
Summary: GPI/AMF binds directly to the cytoplasmic domain of the ubiquitin ligase gp78/AMFR (Q9UKV5) and is a substrate for its (E4-like) polyubiquitylation.
Reason: A specific, experimentally demonstrated interaction of GPI/AMF with the gp78 ubiquitin ligase, informative but part of the moonlighting AMF biology rather than the core enzyme function.
Supporting Evidence:
PMID:24810856
We found that AMF indeed directly interacted with the cytoplasmic domain of gp78
GO:0070062 extracellular exosome
HDA
PMID:23533145
In-depth proteomic analyses of exosomes isolated from expres... 		KEEP AS NON CORE
Summary: GPI detected by high-throughput proteomics in exosomes from expressed prostatic secretions in urine.
Reason: Consistent with the secreted/extracellular moonlighting pool detected in a large-scale exosome proteomic survey; peripheral to the core function.
Supporting Evidence:
PMID:23533145
In pooled EPS-urine exosome samples, ~900 proteins were detected.
GO:0016020 membrane
HDA
PMID:19946888
Defining the membrane proteome of NK cells. 		MARK AS OVER ANNOTATED
Summary: GPI detected in a high-throughput NK-cell membrane proteome; the study itself notes many identified species are only transiently associated with membranes.
Reason: The generic membrane term derives from a large-scale membrane-proteome survey in which soluble proteins co-purify; GPI has no transmembrane domain and this does not reflect a stable membrane localization.
Supporting Evidence:
PMID:19946888
species were largely involved in cellular processes and molecular functions that could be predicted to be transiently associated with membranes
GO:0070062 extracellular exosome
HDA
PMID:19199708
Proteomic analysis of human parotid gland exosomes by multid... 		KEEP AS NON CORE
Summary: GPI detected by high-throughput proteomics in human parotid gland exosomes.
Reason: Consistent with the secreted/extracellular moonlighting pool detected in a large-scale exosome proteomic survey; peripheral to the core function.
Supporting Evidence:
PMID:19199708
Proteomic analysis of human parotid gland exosomes
GO:0070062 extracellular exosome
HDA
PMID:19056867
Large-scale proteomics and phosphoproteomics of urinary exos... 		KEEP AS NON CORE
Summary: GPI detected by high-throughput proteomics in human urinary exosomes.
Reason: Consistent with the secreted/extracellular moonlighting pool detected in a large-scale exosome proteomic survey; peripheral to the core function.
Supporting Evidence:
PMID:19056867
Large-scale proteomics and phosphoproteomics of urinary exosomes.
GO:0070062 extracellular exosome
HDA
PMID:20458337
MHC class II-associated proteins in B-cell exosomes and pote... 		KEEP AS NON CORE
Summary: GPI detected by high-throughput proteomics in B-cell exosomes.
Reason: Consistent with the secreted/extracellular moonlighting pool detected in a large-scale exosome proteomic survey; peripheral to the core function.
Supporting Evidence:
PMID:20458337
MHC class II-associated proteins in B-cell exosomes
GO:0005829 cytosol
TAS
Reactome:R-HSA-70471 		ACCEPT
Summary: Reactome traceable assertion localizing GPI to the cytosol (GPI dimer isomerizes G6P reaction).
Reason: Correct; the active enzyme functions in the cytosol.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}
GO:0005829 cytosol
TAS
Reactome:R-HSA-70475 		ACCEPT
Summary: Reactome traceable assertion localizing GPI to the cytosol (GPI dimer isomerizes Fru(6)P to G6P reaction).
Reason: Correct; the active enzyme functions in the cytosol.
Supporting Evidence:
file:human/GPI/GPI-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:11437381}
GO:0005975 carbohydrate metabolic process
NAS
PMID:8575767
Human glucose phosphate isomerase: exon mapping and gene str... 		MARK AS OVER ANNOTATED
Summary: Non-traceable author statement of carbohydrate metabolic process, from a paper on GPI exon/gene structure.
Reason: Overly general parent term; the specific glycolytic/gluconeogenic and glucose-6-phosphate metabolic processes are already annotated.
Supporting Evidence:
PMID:8575767
The structure of the gene for human glucose phosphate isomerase (GPI) has been determined.
GO:0006959 humoral immune response
TAS
PMID:3020690
Neuroleukin: a lymphokine product of lectin-stimulated T cel... 		KEEP AS NON CORE
Summary: Traceable assertion based on GPI/neuroleukin inducing immunoglobulin secretion, contributing to the humoral immune response; a moonlighting cytokine activity.
Reason: Genuine moonlighting immunological activity of secreted GPI (neuroleukin), distinct from its core glycolytic function.
Supporting Evidence:
PMID:3020690
Neuroleukin is a lymphokine product of lectin-stimulated T cells that induces
GO:0007599 hemostasis
TAS
PMID:7435496
The first stable variant of erythrocyte glucose-phosphate is... 		MARK AS OVER ANNOTATED
Summary: Traceable assertion of hemostasis citing a report of a stable GPI variant associated with severe hemolytic anemia. The cited paper concerns a hemolytic-anemia enzyme variant, not blood clotting/hemostasis.
Reason: The supporting reference describes a GPI-deficiency hemolytic-anemia variant and its altered kinetics, not a role in hemostasis; the term appears to be a mis-mapping and does not reflect a GPI function.
Supporting Evidence:
PMID:7435496
A new variant of glucosephosphate isomerase (GPI) associated with hemolytic anemia, mental retardation, and muscular hypotonia is described.

Core Functions

Glucose-6-phosphate isomerase (phosphoglucose isomerase), the second enzyme of glycolysis, reversibly interconverting glucose-6-phosphate and fructose-6-phosphate in the cytosol; the same reaction operates in the gluconeogenic direction.

Molecular Function:
glucose-6-phosphate isomerase activity
Directly Involved In:
glycolytic process gluconeogenesis glucose 6-phosphate metabolic process
Cellular Locations:
cytosol
Supporting Evidence:
  • file:human/GPI/GPI-uniprot.txt
    Isomerase that catalyzes the conversion of alpha-D-glucose-6-
  • PMID:13538944
    Enzymes of the human erythrocyte. IV. Phosphoglucose isomerase, purification and properties.

References

GO_REF:0000002
Gene Ontology annotation through association of InterPro records with GO terms
GO_REF:0000024
Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
GO_REF:0000033
Annotation inferences using phylogenetic trees
GO_REF:0000044
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
GO_REF:0000116
Automatic Gene Ontology annotation based on Rhea mapping
GO_REF:0000117
Electronic Gene Ontology annotations created by ARBA machine learning models
GO_REF:0000120
Combined Automated Annotation using Multiple IEA Methods
file:human/GPI/GPI-uniprot.txt
UniProtKB entry P06744 (G6PI_HUMAN), Glucose-6-phosphate isomerase
PMID:11437381
Tumor autocrine motility factor is an angiogenic factor that stimulates endothelial cell motility.
PMID:13538944
Enzymes of the human erythrocyte. IV. Phosphoglucose isomerase, purification and properties.
PMID:1649192
Purification of human tumor cell autocrine motility factor and molecular cloning of its receptor.
PMID:19056867
Large-scale proteomics and phosphoproteomics of urinary exosomes.
PMID:19199708
Proteomic analysis of human parotid gland exosomes by multidimensional protein identification technology (MudPIT).
PMID:19946888
Defining the membrane proteome of NK cells.
PMID:20458337
MHC class II-associated proteins in B-cell exosomes and potential functional implications for exosome biogenesis.
PMID:23533145
In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.
PMID:24810856
Polyubiquitylation of AMF requires cooperation between the gp78 and TRIM25 ubiquitin ligases.
PMID:27499296
Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory Chain Function.
PMID:28803808
Two novel mutations (p.(Ser160Pro) and p.(Arg472Cys)) causing glucose-6-phosphate isomerase deficiency are associated with erythroid dysplasia and inappropriately suppressed hepcidin.
PMID:3020690
Neuroleukin: a lymphokine product of lectin-stimulated T cells.
PMID:7435496
The first stable variant of erythrocyte glucose-phosphate isomerase associated with severe hemolytic anemia.
PMID:8575767
Human glucose phosphate isomerase: exon mapping and gene structure.
Reactome:R-HSA-6798748
Exocytosis of secretory granule lumen proteins
Reactome:R-HSA-6800434
Exocytosis of ficolin-rich granule lumen proteins
Reactome:R-HSA-70171
Glycolysis
Reactome:R-HSA-70263
Gluconeogenesis
Reactome:R-HSA-70471
GPI dimer isomerizes G6P
Reactome:R-HSA-70475
GPI dimer isomerizes Fru(6)P to G6P

Suggested Questions for Experts

Q: Is the by-similarity anomerase/C2-epimerase activity of human GPI physiologically significant, or an in vitro artifact of the isomerase mechanism?

Q: To what extent does the secreted neuroleukin/AMF cytokine pool contribute to human physiology (immunity, angiogenesis, neurotrophic support) versus being predominantly a cancer-associated moonlighting activity?

Suggested Experiments

Experiment: Quantify the secreted (monomeric AMF/neuroleukin) versus cytosolic (dimeric enzyme) pools of GPI across cell types and correlate secretion with CK2 phosphorylation at Ser-185.

Experiment: Structure-function analysis of CNSHA4 disease variants to dissect effects on catalytic activity, dimer stability, and cytokine (gp78-binding) activity.

📚 Additional Documentation

Notes

(GPI-notes.md)

GPI (P06744) review notes

Core biology

GPI = glucose-6-phosphate isomerase / phosphoglucose isomerase (PGI), EC 5.3.1.9. Second
enzyme of glycolysis; reversibly interconverts glucose-6-phosphate and fructose-6-phosphate
(aldose-ketose isomerization), and runs in reverse in gluconeogenesis. Cytosolic homodimer
in the active form.

UniProt FUNCTION [file:human/GPI/GPI-uniprot.txt]: "Isomerase that catalyzes the conversion
of alpha-D-glucose-6-phosphate to beta-D-fructose-6-phosphate, the second step in glycolysis,
and the reverse reaction in gluconeogenesis, within the cytoplasm (PubMed:28803808)."
PATHWAY: "Carbohydrate degradation; glycolysis; ... step 2/4."
SUBUNIT: "Homodimer; in the catalytically active form ... Monomer in the secreted form."
SUBCELLULAR LOCATION: "Cytoplasm ... Secreted."

Moonlighting (classic multifunctional / MoonDB-curated)

The same protein acts extracellularly as a secreted cytokine/growth factor with several
historical names: Neuroleukin (NLK), Autocrine Motility Factor (AMF), maturation factor,
sperm antigen 36. Signals through the AMF receptor gp78 / AMFR.
- PMID:24810856 full text: "AMF is a moonlighting protein. When secreted outside tumor
cells, it acts as a cytokine to promote cancer cell invasion and metastasis by stimulating
cell motility upon binding to gp78 [30]. Inside the cell, AMF is equal to previously
identified phosphoglucose isomerase (PGI) that catalyzes the interconversion of glucose
6-phosphate and fructose 6-phosphate [31]." Establishes GPI–gp78 (AMFR, Q9UKV5) direct
binding + polyubiquitylation (basis of the IPI GO:0031625 ubiquitin protein ligase binding).
- PMID:11437381 AMF is an angiogenic factor: "AMF stimulated in vitro motility of human
umbilical vein endothelial cells (HUVECs)"; basis for extracellular region + cytoplasm EXP
localization and positive regulation of endothelial cell migration.
- PMID:1649192 Purification of AMF from HT-1080 fibrosarcoma conditioned medium; cloned its
receptor gp78 (78-kDa cell surface glycoprotein). Basis for GO:0010595 pos reg endothelial
cell migration (IDA).
- PMID:3020690 Neuroleukin: "a lymphokine product of lectin-stimulated T cells that induces
immunoglobulin secretion by cultured human peripheral blood mononuclear cells." Basis for
positive regulation of immunoglobulin production (IDA) + humoral immune response (TAS).

Enzyme/disease evidence

  • PMID:13538944 Tsuboi 1958: purification & properties of human erythrocyte phosphoglucose
    isomerase — classic enzyme characterization (EXP GO:0004347).
  • PMID:28803808 CNSHA4 patients with GPI deficiency; measured residual GPI activity;
    IDA GO:0004347 + glucose-6-phosphate metabolic process. "the second most common red blood
    cell glycolytic enzymopathy."
  • PMID:7435496 First stable GPI variant with severe hemolytic anemia; altered kinetics
    (F6P/G6P affinity). Basis of TAS hemostasis? (see below).
  • PMID:8575767 GPI exon mapping / gene structure — basis of NAS carbohydrate metabolic process.

Judgments

  • Core = MF GO:0004347 (glucose-6-phosphate isomerase activity) + glycolysis GO:0006096 +
    gluconeogenesis GO:0006094 + glucose 6-phosphate metabolic process GO:0051156, cytosol.
  • Moonlighting cytokine/AMF/neuroleukin functions (endothelial migration, Ig production,
    humoral immune response, extracellular localization, ubiquitin ligase binding) = real but
    NON-CORE (KEEP_AS_NON_CORE).
  • Ensembl GO_REF:0000107 rat-ortholog transfers (learning/memory, response to hormones,
    immobilization stress, muscle stretch, cadmium, negative regulation of apoptosis, plasma
    membrane, ciliary membrane, fructose-6-P metabolic process): mostly over-propagated
    phenotype-context IEAs, not GPI's core function. Mark over-annotated except F6P metabolic
    process (real substrate) which is ACCEPT.
  • GO:0047938 glucose-6-phosphate 1-epimerase / GO:0016857 racemase-epimerase / GO:0016853
    isomerase: broad or by-similarity anomerase/epimerase side activities. UniProt lists
    C2-epimerase & anomerase "By similarity". Keep as accept (isomerase) or non-core.
  • GO:0005515 protein binding (IPI, PMID:27499296, TAMM41): bare protein binding — MARK_AS_OVER_ANNOTATED
    per policy (uninformative; mito interactome screen).
  • hemostasis GO:0007599 (TAS, PMID:7435496): paper is about a hemolytic-anemia GPI variant,
    not hemostasis/clotting. Over-annotation.
  • exosome/membrane HDA (5 papers): large-scale proteomic surveys; keep as non-core / over-annotated.

📄 View Raw YAML

 
id: P06744
gene_symbol: GPI
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: Glucose-6-phosphate isomerase (phosphoglucose isomerase, PGI; EC 5.3.1.9)
  catalyzes the reversible aldose-ketose interconversion of glucose-6-phosphate and
  fructose-6-phosphate, the second step of glycolysis and the corresponding reverse
  step of gluconeogenesis. The catalytically active form is a cytosolic homodimer.
  GPI is a classic moonlighting protein; the same polypeptide, when secreted, acts
  extracellularly as a cytokine and growth factor known historically as neuroleukin
  (a neurotrophic factor and inducer of immunoglobulin secretion), autocrine motility
  factor (AMF, an angiogenic factor that stimulates cell and endothelial motility via
  the cell-surface receptor gp78/AMFR), and maturation factor. Loss-of-function
  variants cause glucose-6-phosphate isomerase deficiency, an autosomal recessive
  hereditary nonspherocytic hemolytic anemia sometimes accompanied by neurological
  impairment.
alternative_products:
- name: '1'
  id: P06744-1
- name: '2'
  id: P06744-2
  sequence_note: VSP_043475, VSP_043476
existing_annotations:
- term:
    id: GO:0004347
    label: glucose-6-phosphate isomerase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Phylogenetically inferred glucose-6-phosphate isomerase activity. This
      is the core, well-established molecular function of GPI, directly demonstrated
      for the human enzyme and conserved across all life.
    action: ACCEPT
    reason: This is the defining catalytic function of GPI (EC 5.3.1.9), the second
      enzyme of glycolysis, confirmed for the human protein and consistent across the
      GPI family.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Isomerase that catalyzes the conversion of alpha-D-glucose-6-
    - reference_id: PMID:28803808
      supporting_text: Glucose-6-phosphate isomerase (GPI) deficiency, a genetic disorder
        responsible for chronic nonspherocytic hemolytic anemia, is the second most
        common red blood cell glycolytic enzymopathy.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Phylogenetically inferred cytosolic localization, matching the intracellular
      compartment where the glycolytic/gluconeogenic reaction occurs.
    action: ACCEPT
    reason: The catalytically active homodimer acts in the cytoplasm/cytosol, consistent
      with GPI's role in cytosolic glycolysis and gluconeogenesis.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: the second step in
- term:
    id: GO:0006094
    label: gluconeogenesis
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: GPI catalyzes the reversible G6P to F6P step, which operates in the
      gluconeogenic direction, making it a core participant in gluconeogenesis.
    action: ACCEPT
    reason: The reversible isomerase reaction is a committed step of both glycolysis
      and gluconeogenesis; UniProt explicitly notes the reverse reaction in gluconeogenesis.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: and the reverse reaction in gluconeogenesis, within the
- term:
    id: GO:0006096
    label: glycolytic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: GPI performs the second step of glycolysis (G6P to F6P) and is a core
      glycolytic enzyme.
    action: ACCEPT
    reason: Directly supported; GPI is the second glycolytic enzyme, a core biological
      process for this gene.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: the second step in
- term:
    id: GO:0051156
    label: glucose 6-phosphate metabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: GPI acts on glucose-6-phosphate as its substrate, so participation in
      glucose-6-phosphate metabolism follows directly from its catalytic activity.
    action: ACCEPT
    reason: Consistent with the catalytic activity; glucose-6-phosphate is the direct
      substrate of the enzyme.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Isomerase that catalyzes the conversion of alpha-D-glucose-6-
- term:
    id: GO:0048029
    label: monosaccharide binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: GPI binds its phosphorylated monosaccharide substrates (glucose-6-phosphate,
      fructose-6-phosphate). This binding is a mechanistic prerequisite of catalysis
      rather than an independent function.
    action: KEEP_AS_NON_CORE
    reason: Substrate binding is subsumed by the catalytic activity annotation; retained
      but not a distinct core function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: ligand="D-glucose 6-phosphate"
- term:
    id: GO:0004347
    label: glucose-6-phosphate isomerase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Electronic assignment (multiple IEA methods, incl. Rhea RHEA:11816 and
      EC 5.3.1.9) of the core glucose-6-phosphate isomerase activity.
    action: ACCEPT
    reason: Redundant with the experimentally supported core MF annotation; the electronic
      mapping to EC 5.3.1.9 / RHEA:11816 is correct.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: EC=5.3.1.9
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic mapping from the UniProt Secreted subcellular-location keyword.
      GPI is genuinely secreted and functions extracellularly as the AMF/neuroleukin
      cytokine, but this is a moonlighting pool, not the core cytosolic enzyme.
    action: KEEP_AS_NON_CORE
    reason: Correct for the secreted moonlighting form (autocrine motility factor),
      but peripheral to GPI's core glycolytic role.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic mapping from the UniProt Cytoplasm subcellular-location keyword,
      consistent with the compartment of the core glycolytic reaction.
    action: ACCEPT
    reason: Correct; GPI is a cytoplasmic/cytosolic enzyme. The more specific cytosol
      term is captured elsewhere.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}
- term:
    id: GO:0006094
    label: gluconeogenesis
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: Electronic assignment of gluconeogenesis, redundant with the IBA annotation.
    action: ACCEPT
    reason: Correct; GPI's reversible reaction operates in gluconeogenesis.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: and the reverse reaction in gluconeogenesis, within the
- term:
    id: GO:0006096
    label: glycolytic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: Electronic assignment of glycolytic process, redundant with the IBA annotation.
    action: ACCEPT
    reason: Correct core biological process for GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: the second step in
- term:
    id: GO:0016853
    label: isomerase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: enables
  review:
    summary: ARBA electronic annotation to the broad parent term isomerase activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: This is the generic grandparent of the specific glucose-6-phosphate isomerase
      activity that is already annotated; the specific term should be preferred.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: EC=5.3.1.9
- term:
    id: GO:0047938
    label: glucose-6-phosphate 1-epimerase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: Rhea-based electronic mapping (RHEA:16249) to a G6P anomerase/epimerase
      activity, interconverting the alpha and beta anomers of glucose-6-phosphate.
      UniProt records this anomerase activity only by similarity for the human enzyme.
    action: KEEP_AS_NON_CORE
    reason: Plausible ancillary anomerase side-activity supported by similarity, but
      not the core physiological function and not experimentally demonstrated in human.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Reaction=alpha-D-glucose 6-phosphate = beta-D-glucose 6-phosphate
- term:
    id: GO:0097367
    label: carbohydrate derivative binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: InterPro2GO electronic assignment of the broad term carbohydrate derivative
      binding, reflecting binding of the phosphosugar substrates.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformatively broad; the specific monosaccharide/substrate binding is
      already implied by the catalytic activity annotation.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: ligand="D-glucose 6-phosphate"
- term:
    id: GO:1901135
    label: carbohydrate derivative metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: InterPro2GO electronic assignment of the broad process carbohydrate derivative
      metabolic process.
    action: MARK_AS_OVER_ANNOTATED
    reason: Overly general; the specific glycolytic/gluconeogenic and glucose-6-phosphate
      metabolic processes are already annotated.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: the second step in
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27499296
  qualifier: enables
  review:
    summary: IntAct-derived protein binding annotation from a high-throughput mitochondrial
      interactome screen, capturing a physical interaction of GPI with TAMM41 (Q96BW9).
    action: MARK_AS_OVER_ANNOTATED
    reason: Bare protein binding is uninformative about molecular function; the interaction
      derives from a large-scale mitochondrial affinity-enrichment screen and does not
      define a specific function for GPI. Per curation policy, this is marked over-annotated
      rather than removed.
    supported_by:
    - reference_id: PMID:27499296
      supporting_text: we assessed condition-specific protein-protein
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: is_active_in
  review:
    summary: Ensembl orthology-based electronic assignment of cytosol, consistent with
      the compartment of the active enzyme.
    action: ACCEPT
    reason: Correct; the active GPI homodimer functions in the cytosol.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: Ensembl orthology-transferred plasma membrane localization from the mouse
      ortholog. GPI is a soluble cytosolic/secreted protein without a transmembrane
      domain; any plasma-membrane association is peripheral (e.g. secreted AMF binding
      surface gp78).
    action: MARK_AS_OVER_ANNOTATED
    reason: GPI is not an integral plasma membrane protein; the term over-states a
      transient/peripheral association and is an over-propagated ortholog transfer.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}
- term:
    id: GO:0006002
    label: fructose 6-phosphate metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Fructose-6-phosphate is the direct product/substrate of the GPI reaction,
      so participation in fructose-6-phosphate metabolism follows from its catalytic
      activity.
    action: ACCEPT
    reason: Correct; fructose-6-phosphate is directly interconverted with glucose-6-phosphate
      by GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: to beta-D-fructose-6-phosphate
- term:
    id: GO:0007611
    label: learning or memory
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from the rat ortholog of a phenotype/context
      association (learning or memory), not a molecular function of GPI.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated organismal-phenotype IEA transferred from rat; not part
      of GPI's core enzymatic function and not established for the human protein.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0007611; P:learning or memory; IEA:Ensembl'
- term:
    id: GO:0032355
    label: response to estradiol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of a hormone-response context association.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated context IEA transferred from the rat ortholog; not a core
      function and not demonstrated for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0032355; P:response to estradiol; IEA:Ensembl'
- term:
    id: GO:0032570
    label: response to progesterone
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of a hormone-response context association.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated context IEA transferred from the rat ortholog; not a core
      function and not demonstrated for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0032570; P:response to progesterone; IEA:Ensembl'
- term:
    id: GO:0033574
    label: response to testosterone
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of a hormone-response context association.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated context IEA transferred from the rat ortholog; not a core
      function and not demonstrated for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0033574; P:response to testosterone; IEA:Ensembl'
- term:
    id: GO:0035902
    label: response to immobilization stress
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of a stress-response context association.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated context IEA transferred from the rat ortholog; not a core
      function and not demonstrated for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0035902; P:response to immobilization stress; IEA:Ensembl'
- term:
    id: GO:0035994
    label: response to muscle stretch
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of a physiological-response context
      association.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated context IEA transferred from the rat ortholog; not a core
      function and not demonstrated for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0035994; P:response to muscle stretch; IEA:Ensembl'
- term:
    id: GO:0043066
    label: negative regulation of apoptotic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of an anti-apoptotic association,
      possibly reflecting the pro-survival neurotrophic/neuroleukin moonlighting role.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated ortholog-transfer IEA; if real it relates to the secreted
      cytokine moonlighting activity rather than the core enzyme, and is not established
      for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0043066; P:negative regulation of apoptotic process; IEA:Ensembl'
- term:
    id: GO:0046686
    label: response to cadmium ion
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology transfer from rat of a chemical-response context association.
    action: MARK_AS_OVER_ANNOTATED
    reason: Over-propagated context IEA transferred from the rat ortholog; not a core
      function and not demonstrated for human GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: 'GO:0046686; P:response to cadmium ion; IEA:Ensembl'
- term:
    id: GO:0048029
    label: monosaccharide binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: enables
  review:
    summary: Ensembl orthology-based electronic assignment of monosaccharide binding,
      redundant with the IBA monosaccharide-binding annotation.
    action: KEEP_AS_NON_CORE
    reason: Substrate binding subsumed by the catalytic activity; retained but not a
      distinct core function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: ligand="D-glucose 6-phosphate"
- term:
    id: GO:0051156
    label: glucose 6-phosphate metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: Electronic assignment of glucose-6-phosphate metabolic process, redundant
      with the IBA/IDA annotations.
    action: ACCEPT
    reason: Correct; glucose-6-phosphate is the direct substrate of GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Isomerase that catalyzes the conversion of alpha-D-glucose-6-
- term:
    id: GO:0060170
    label: ciliary membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: Ensembl orthology transfer from mouse of a ciliary membrane localization.
      GPI is a soluble cytosolic/secreted enzyme with no evidence for a ciliary-membrane
      role in human.
    action: MARK_AS_OVER_ANNOTATED
    reason: Implausible, over-propagated ortholog-transfer IEA for a soluble glycolytic
      enzyme lacking membrane-targeting features.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}
- term:
    id: GO:0061621
    label: canonical glycolysis
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl orthology-based electronic assignment of canonical glycolysis,
      the specific glycolytic pathway in which GPI catalyzes the second step.
    action: ACCEPT
    reason: Correct and appropriately specific core process for GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: the second step in
- term:
    id: GO:0006094
    label: gluconeogenesis
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70263
  qualifier: involved_in
  review:
    summary: Reactome traceable assertion (Gluconeogenesis pathway) that GPI participates
      in gluconeogenesis via the reversible G6P to F6P step.
    action: ACCEPT
    reason: Correct core process; consistent with the reversible isomerase reaction.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: and the reverse reaction in gluconeogenesis, within the
- term:
    id: GO:0061621
    label: canonical glycolysis
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70171
  qualifier: involved_in
  review:
    summary: Reactome traceable assertion (Glycolysis pathway) placing GPI in canonical
      glycolysis.
    action: ACCEPT
    reason: Correct and appropriately specific core process for GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: the second step in
- term:
    id: GO:0004347
    label: glucose-6-phosphate isomerase activity
  evidence_type: EXP
  original_reference_id: PMID:13538944
  qualifier: enables
  review:
    summary: Experimental characterization of purified human erythrocyte phosphoglucose
      isomerase, establishing the core glucose-6-phosphate isomerase activity.
    action: ACCEPT
    reason: Classic biochemical evidence for the enzyme's core catalytic function in
      human tissue.
    supported_by:
    - reference_id: PMID:13538944
      supporting_text: Enzymes of the human erythrocyte. IV. Phosphoglucose isomerase,
        purification and properties.
- term:
    id: GO:0004347
    label: glucose-6-phosphate isomerase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70471
  qualifier: enables
  review:
    summary: Reactome traceable assertion (GPI dimer isomerizes G6P) for the core
      catalytic activity.
    action: ACCEPT
    reason: Correct core molecular function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Isomerase that catalyzes the conversion of alpha-D-glucose-6-
- term:
    id: GO:0051156
    label: glucose 6-phosphate metabolic process
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: involved_in
  review:
    summary: Sequence-similarity transfer (from yeast/ortholog) of glucose-6-phosphate
      metabolic process, redundant with the IBA/IDA annotations.
    action: ACCEPT
    reason: Correct; glucose-6-phosphate is the direct substrate of GPI.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Isomerase that catalyzes the conversion of alpha-D-glucose-6-
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: EXP
  original_reference_id: PMID:11437381
  qualifier: located_in
  review:
    summary: Experimental evidence that GPI/AMF is secreted and acts extracellularly
      as an angiogenic autocrine motility factor stimulating endothelial cell motility.
    action: KEEP_AS_NON_CORE
    reason: Correct for the secreted moonlighting form (AMF), but extracellular localization
      is peripheral to GPI's core cytosolic glycolytic function.
    supported_by:
    - reference_id: PMID:11437381
      supporting_text: AMF stimulated in vitro motility of human umbilical vein
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: EXP
  original_reference_id: PMID:11437381
  qualifier: located_in
  review:
    summary: Experimental subcellular localization placing GPI in the cytoplasm, the
      compartment of its core glycolytic activity.
    action: ACCEPT
    reason: Correct; GPI is a cytoplasmic/cytosolic enzyme.
    supported_by:
    - reference_id: PMID:11437381
      supporting_text: Tumor autocrine motility factor is an angiogenic factor that
        stimulates
- term:
    id: GO:0047938
    label: glucose-6-phosphate 1-epimerase activity
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: enables
  review:
    summary: Sequence-similarity transfer of an anomerase/epimerase activity on glucose-6-phosphate;
      UniProt records this activity only by similarity for human GPI.
    action: KEEP_AS_NON_CORE
    reason: Plausible ancillary anomerase side-activity supported by similarity, but
      not the core physiological function and not experimentally demonstrated in human.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Reaction=alpha-D-glucose 6-phosphate = beta-D-glucose 6-phosphate
- term:
    id: GO:0016857
    label: racemase and epimerase activity, acting on carbohydrates and derivatives
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: enables
  review:
    summary: Sequence-similarity transfer to the broad parent term for carbohydrate
      racemase/epimerase activity, reflecting the by-similarity C2-epimerase/anomerase
      side reactions.
    action: MARK_AS_OVER_ANNOTATED
    reason: Overly broad grandparent term; the specific (by-similarity) glucose-6-phosphate
      epimerase activity is already annotated separately.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Glucose-6-phosphate C2-epimerase
- term:
    id: GO:0004347
    label: glucose-6-phosphate isomerase activity
  evidence_type: IDA
  original_reference_id: PMID:28803808
  qualifier: enables
  review:
    summary: Direct assay of GPI catalytic activity in patients with GPI deficiency,
      where pathogenic variants reduce residual enzyme activity, confirming the core
      isomerase function.
    action: ACCEPT
    reason: Direct experimental support for the core molecular function in the human
      protein; residual GPI activity was measured in patient erythrocytes.
    supported_by:
    - reference_id: PMID:28803808
      supporting_text: lost approximately 89% of their GPI activity
- term:
    id: GO:0051156
    label: glucose 6-phosphate metabolic process
  evidence_type: IDA
  original_reference_id: PMID:28803808
  qualifier: involved_in
  review:
    summary: Direct evidence that GPI acts in glucose-6-phosphate metabolism, from
      patient enzyme-activity measurements in GPI deficiency.
    action: ACCEPT
    reason: Correct; glucose-6-phosphate is the direct substrate of GPI.
    supported_by:
    - reference_id: PMID:28803808
      supporting_text: is the second most common red blood
- term:
    id: GO:0010595
    label: positive regulation of endothelial cell migration
  evidence_type: IDA
  original_reference_id: PMID:1649192
  qualifier: involved_in
  review:
    summary: Purified GPI/AMF stimulates cell migration and, via its receptor gp78,
      promotes motility; a moonlighting cytokine activity of the secreted protein.
    action: KEEP_AS_NON_CORE
    reason: A genuine moonlighting activity of secreted GPI (autocrine motility factor),
      but distinct from its core glycolytic enzyme role.
    supported_by:
    - reference_id: PMID:1649192
      supporting_text: Purified AMF stimulated HT-1080 cell
    - reference_id: PMID:11437381
      supporting_text: AMF stimulated in vitro motility of human umbilical vein
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6798748
  qualifier: located_in
  review:
    summary: Reactome traceable assertion placing GPI in the extracellular region via
      exocytosis of secretory granule lumen proteins (neutrophil degranulation).
    action: KEEP_AS_NON_CORE
    reason: Consistent with the secreted moonlighting pool of GPI, but peripheral to
      the core cytosolic enzyme function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6800434
  qualifier: located_in
  review:
    summary: Reactome traceable assertion placing GPI in the extracellular region via
      exocytosis of ficolin-rich granule lumen proteins.
    action: KEEP_AS_NON_CORE
    reason: Consistent with the secreted moonlighting pool of GPI, but peripheral to
      the core cytosolic enzyme function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
- term:
    id: GO:0034774
    label: secretory granule lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6798748
  qualifier: located_in
  review:
    summary: Reactome traceable assertion localizing GPI to the secretory granule lumen
      in the context of neutrophil degranulation.
    action: KEEP_AS_NON_CORE
    reason: Reflects the granule/secretion route of the moonlighting extracellular
      pool, not the core cytosolic function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
- term:
    id: GO:1904813
    label: ficolin-1-rich granule lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6800434
  qualifier: located_in
  review:
    summary: Reactome traceable assertion localizing GPI to the ficolin-1-rich granule
      lumen (neutrophil degranulation pathway).
    action: KEEP_AS_NON_CORE
    reason: Reflects the granule/secretion route of the moonlighting extracellular
      pool, not the core cytosolic function.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}. Secreted
- term:
    id: GO:0002639
    label: positive regulation of immunoglobulin production
  evidence_type: IDA
  original_reference_id: PMID:3020690
  qualifier: involved_in
  review:
    summary: GPI/neuroleukin, secreted by lectin-stimulated T cells, induces immunoglobulin
      secretion by human peripheral blood mononuclear cells; a moonlighting cytokine
      activity.
    action: KEEP_AS_NON_CORE
    reason: A genuine moonlighting cytokine function of secreted GPI (neuroleukin),
      distinct from its core glycolytic enzyme role.
    supported_by:
    - reference_id: PMID:3020690
      supporting_text: Neuroleukin is a lymphokine product of lectin-stimulated T cells
        that induces immunoglobulin secretion by cultured human peripheral blood mononuclear
        cells.
- term:
    id: GO:0031625
    label: ubiquitin protein ligase binding
  evidence_type: IPI
  original_reference_id: PMID:24810856
  qualifier: enables
  review:
    summary: GPI/AMF binds directly to the cytoplasmic domain of the ubiquitin ligase
      gp78/AMFR (Q9UKV5) and is a substrate for its (E4-like) polyubiquitylation.
    action: KEEP_AS_NON_CORE
    reason: A specific, experimentally demonstrated interaction of GPI/AMF with the
      gp78 ubiquitin ligase, informative but part of the moonlighting AMF biology rather
      than the core enzyme function.
    supported_by:
    - reference_id: PMID:24810856
      supporting_text: We found that AMF indeed directly interacted with the cytoplasmic
        domain of gp78
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  qualifier: located_in
  review:
    summary: GPI detected by high-throughput proteomics in exosomes from expressed
      prostatic secretions in urine.
    action: KEEP_AS_NON_CORE
    reason: Consistent with the secreted/extracellular moonlighting pool detected in
      a large-scale exosome proteomic survey; peripheral to the core function.
    supported_by:
    - reference_id: PMID:23533145
      supporting_text: In pooled EPS-urine exosome samples, ~900 proteins were detected.
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  qualifier: located_in
  review:
    summary: GPI detected in a high-throughput NK-cell membrane proteome; the study
      itself notes many identified species are only transiently associated with membranes.
    action: MARK_AS_OVER_ANNOTATED
    reason: The generic membrane term derives from a large-scale membrane-proteome survey
      in which soluble proteins co-purify; GPI has no transmembrane domain and this
      does not reflect a stable membrane localization.
    supported_by:
    - reference_id: PMID:19946888
      supporting_text: species were largely involved in cellular processes and molecular
        functions that could be predicted to be transiently associated with membranes
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19199708
  qualifier: located_in
  review:
    summary: GPI detected by high-throughput proteomics in human parotid gland exosomes.
    action: KEEP_AS_NON_CORE
    reason: Consistent with the secreted/extracellular moonlighting pool detected in
      a large-scale exosome proteomic survey; peripheral to the core function.
    supported_by:
    - reference_id: PMID:19199708
      supporting_text: Proteomic analysis of human parotid gland exosomes
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  qualifier: located_in
  review:
    summary: GPI detected by high-throughput proteomics in human urinary exosomes.
    action: KEEP_AS_NON_CORE
    reason: Consistent with the secreted/extracellular moonlighting pool detected in
      a large-scale exosome proteomic survey; peripheral to the core function.
    supported_by:
    - reference_id: PMID:19056867
      supporting_text: Large-scale proteomics and phosphoproteomics of urinary exosomes.
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:20458337
  qualifier: located_in
  review:
    summary: GPI detected by high-throughput proteomics in B-cell exosomes.
    action: KEEP_AS_NON_CORE
    reason: Consistent with the secreted/extracellular moonlighting pool detected in
      a large-scale exosome proteomic survey; peripheral to the core function.
    supported_by:
    - reference_id: PMID:20458337
      supporting_text: MHC class II-associated proteins in B-cell exosomes
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70471
  qualifier: located_in
  review:
    summary: Reactome traceable assertion localizing GPI to the cytosol (GPI dimer
      isomerizes G6P reaction).
    action: ACCEPT
    reason: Correct; the active enzyme functions in the cytosol.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70475
  qualifier: located_in
  review:
    summary: Reactome traceable assertion localizing GPI to the cytosol (GPI dimer
      isomerizes Fru(6)P to G6P reaction).
    action: ACCEPT
    reason: Correct; the active enzyme functions in the cytosol.
    supported_by:
    - reference_id: file:human/GPI/GPI-uniprot.txt
      supporting_text: Cytoplasm {ECO:0000269|PubMed:11437381}
- term:
    id: GO:0005975
    label: carbohydrate metabolic process
  evidence_type: NAS
  original_reference_id: PMID:8575767
  qualifier: involved_in
  review:
    summary: Non-traceable author statement of carbohydrate metabolic process, from
      a paper on GPI exon/gene structure.
    action: MARK_AS_OVER_ANNOTATED
    reason: Overly general parent term; the specific glycolytic/gluconeogenic and
      glucose-6-phosphate metabolic processes are already annotated.
    supported_by:
    - reference_id: PMID:8575767
      supporting_text: The structure of the gene for human glucose phosphate isomerase
        (GPI) has been determined.
- term:
    id: GO:0006959
    label: humoral immune response
  evidence_type: TAS
  original_reference_id: PMID:3020690
  qualifier: involved_in
  review:
    summary: Traceable assertion based on GPI/neuroleukin inducing immunoglobulin secretion,
      contributing to the humoral immune response; a moonlighting cytokine activity.
    action: KEEP_AS_NON_CORE
    reason: Genuine moonlighting immunological activity of secreted GPI (neuroleukin),
      distinct from its core glycolytic function.
    supported_by:
    - reference_id: PMID:3020690
      supporting_text: Neuroleukin is a lymphokine product of lectin-stimulated T cells
        that induces
- term:
    id: GO:0007599
    label: hemostasis
  evidence_type: TAS
  original_reference_id: PMID:7435496
  qualifier: involved_in
  review:
    summary: Traceable assertion of hemostasis citing a report of a stable GPI variant
      associated with severe hemolytic anemia. The cited paper concerns a hemolytic-anemia
      enzyme variant, not blood clotting/hemostasis.
    action: MARK_AS_OVER_ANNOTATED
    reason: The supporting reference describes a GPI-deficiency hemolytic-anemia variant
      and its altered kinetics, not a role in hemostasis; the term appears to be a
      mis-mapping and does not reflect a GPI function.
    supported_by:
    - reference_id: PMID:7435496
      supporting_text: A new variant of glucosephosphate isomerase (GPI) associated
        with hemolytic anemia, mental retardation, and muscular hypotonia is described.
core_functions:
- description: Glucose-6-phosphate isomerase (phosphoglucose isomerase), the second
    enzyme of glycolysis, reversibly interconverting glucose-6-phosphate and
    fructose-6-phosphate in the cytosol; the same reaction operates in the gluconeogenic
    direction.
  supported_by:
  - reference_id: file:human/GPI/GPI-uniprot.txt
    supporting_text: Isomerase that catalyzes the conversion of alpha-D-glucose-6-
  - reference_id: PMID:13538944
    supporting_text: Enzymes of the human erythrocyte. IV. Phosphoglucose isomerase,
      purification and properties.
  molecular_function:
    id: GO:0004347
    label: glucose-6-phosphate isomerase activity
  directly_involved_in:
  - id: GO:0006096
    label: glycolytic process
  - id: GO:0006094
    label: gluconeogenesis
  - id: GO:0051156
    label: glucose 6-phosphate metabolic process
  locations:
  - id: GO:0005829
    label: cytosol
proposed_new_terms: []
suggested_questions:
- question: Is the by-similarity anomerase/C2-epimerase activity of human GPI physiologically
    significant, or an in vitro artifact of the isomerase mechanism?
- question: To what extent does the secreted neuroleukin/AMF cytokine pool contribute
    to human physiology (immunity, angiogenesis, neurotrophic support) versus being
    predominantly a cancer-associated moonlighting activity?
suggested_experiments:
- description: Quantify the secreted (monomeric AMF/neuroleukin) versus cytosolic (dimeric
    enzyme) pools of GPI across cell types and correlate secretion with CK2 phosphorylation
    at Ser-185.
- description: Structure-function analysis of CNSHA4 disease variants to dissect effects
    on catalytic activity, dimer stability, and cytokine (gp78-binding) activity.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000116
  title: Automatic Gene Ontology annotation based on Rhea mapping
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: file:human/GPI/GPI-uniprot.txt
  title: UniProtKB entry P06744 (G6PI_HUMAN), Glucose-6-phosphate isomerase
  findings: []
- id: PMID:11437381
  title: Tumor autocrine motility factor is an angiogenic factor that stimulates endothelial
    cell motility.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes the secreted AMF/angiogenic moonlighting role and cytoplasm/secreted
      localization; supports the EXP extracellular region and cytoplasm annotations.
- id: PMID:13538944
  title: Enzymes of the human erythrocyte. IV. Phosphoglucose isomerase, purification
    and properties.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Classic purification/characterization of the human erythrocyte enzyme;
      supports the core catalytic activity (EXP GO:0004347).
- id: PMID:1649192
  title: Purification of human tumor cell autocrine motility factor and molecular
    cloning of its receptor.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Purified AMF stimulates tumor-cell migration and its receptor gp78
      was cloned; supports the moonlighting motility/migration function.
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Large-scale exosome proteomic survey detecting GPI; supports extracellular
      exosome (HDA) but not a specific function.
- id: PMID:19199708
  title: Proteomic analysis of human parotid gland exosomes by multidimensional protein
    identification technology (MudPIT).
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Large-scale exosome proteomic survey detecting GPI; supports extracellular
      exosome (HDA) but not a specific function.
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: NK-cell membrane proteome survey; the study notes many hits are only
      transiently membrane-associated, arguing GPI's membrane annotation is over-stated.
- id: PMID:20458337
  title: MHC class II-associated proteins in B-cell exosomes and potential functional
    implications for exosome biogenesis.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Large-scale B-cell exosome proteomic survey detecting GPI; supports
      extracellular exosome (HDA) but not a specific function.
- id: PMID:23533145
  title: In-depth proteomic analyses of exosomes isolated from expressed prostatic
    secretions in urine.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Large-scale exosome proteomic survey detecting GPI; supports extracellular
      exosome (HDA) but not a specific function.
- id: PMID:24810856
  title: Polyubiquitylation of AMF requires cooperation between the gp78 and TRIM25
    ubiquitin ligases.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Full text confirms GPI/AMF directly binds the gp78 (AMFR) ubiquitin
      ligase cytoplasmic domain and is a ubiquitylation substrate; supports the IPI
      ubiquitin protein ligase binding annotation and frames GPI as a moonlighting protein.
- id: PMID:27499296
  title: Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory
    Chain Function.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput mitochondrial affinity-enrichment interactome screen;
      basis of the uninformative bare protein-binding (TAMM41) IPI annotation.
- id: PMID:28803808
  title: Two novel mutations (p.(Ser160Pro) and p.(Arg472Cys)) causing glucose-6-phosphate
    isomerase deficiency are associated with erythroid dysplasia and inappropriately
    suppressed hepcidin.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Patient enzyme-activity measurements in GPI deficiency confirm the
      core catalytic function and the disease association (CNSHA4).
- id: PMID:3020690
  title: 'Neuroleukin: a lymphokine product of lectin-stimulated T cells.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes neuroleukin (=GPI) as a T-cell lymphokine inducing immunoglobulin
      secretion; supports the moonlighting immune-related annotations.
- id: PMID:7435496
  title: The first stable variant of erythrocyte glucose-phosphate isomerase associated
    with severe hemolytic anemia.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: MISCITED
    review_notes: Describes a stable GPI variant causing hemolytic anemia with altered
      F6P/G6P kinetics; it does not support a role in hemostasis, so the TAS hemostasis
      annotation appears mis-mapped.
- id: PMID:8575767
  title: 'Human glucose phosphate isomerase: exon mapping and gene structure.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Reports the GPI gene/exon structure; cited (NAS) for the generic
      carbohydrate metabolic process term.
- id: Reactome:R-HSA-6798748
  title: Exocytosis of secretory granule lumen proteins
  findings: []
- id: Reactome:R-HSA-6800434
  title: Exocytosis of ficolin-rich granule lumen proteins
  findings: []
- id: Reactome:R-HSA-70171
  title: Glycolysis
  findings: []
- id: Reactome:R-HSA-70263
  title: Gluconeogenesis
  findings: []
- id: Reactome:R-HSA-70471
  title: GPI dimer isomerizes G6P
  findings: []
- id: Reactome:R-HSA-70475
  title: GPI dimer isomerizes Fru(6)P to G6P
  findings: []