id: P10253
gene_symbol: GAA
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  GAA encodes lysosomal acid alpha-glucosidase (acid maltase; EC 3.2.1.20), a
  glycoside-hydrolase-family-31 (GH31) enzyme that acts within the acidic
  lysosomal lumen to completely hydrolyse glycogen to glucose. It cleaves
  terminal, non-reducing alpha-1,4-glucosidic bonds with highest activity and,
  more slowly, alpha-1,6 branch linkages, degrading the glycogen delivered to
  lysosomes by autophagy (glycophagy). This lysosomal glycogenolysis is distinct
  from the cytosolic pathway carried out by glycogen phosphorylase and the
  debranching enzyme. The enzyme is synthesised as a ~110 kDa N-glycosylated
  precursor, tagged with mannose-6-phosphate for delivery to the lysosome via the
  mannose-6-phosphate receptor, and proteolytically matured into shorter (76 kDa
  and 70 kDa) forms. Catalysis proceeds by a retaining GH31 double-displacement
  mechanism using an aspartate nucleophile (Asp518) and an acid/base aspartate
  (Asp616). Loss of GAA activity causes Pompe disease (glycogen storage disease
  type II / acid maltase deficiency), an autosomal recessive lysosomal storage
  disorder in which glycogen accumulates in muscle, heart and other tissues;
  the infantile-onset form presents with hypertrophic cardiomyopathy and
  hypotonia, while late-onset disease manifests as a progressive limb-girdle and
  respiratory myopathy. Recombinant human GAA (alglucosidase alfa) is used for
  enzyme replacement therapy.
existing_annotations:
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetically inferred alpha-1,4-glucosidase activity. This is the
      well-established, experimentally supported core molecular function of GAA
      and is annotated at an appropriate level of specificity.
    action: ACCEPT
    reason: >-
      GAA is the lysosomal acid alpha-glucosidase; UniProt records EC 3.2.1.20
      with the catalytic reaction being hydrolysis of terminal, non-reducing
      (1->4)-linked alpha-D-glucose residues. The IBA is consistent with the
      GH31 family assignment and with the direct experimental annotations below.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "glucose residues with release of alpha-D-glucose.; EC=3.2.1.20;"
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Belongs to the glycosyl hydrolase 31 family."
- term:
    id: GO:0005980
    label: glycogen catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetically inferred involvement in glycogen catabolism. This is the
      core biological process of GAA: lysosomal degradation of glycogen to
      glucose.
    action: ACCEPT
    reason: >-
      UniProt states GAA is essential for the degradation of glycogen in
      lysosomes, and PMID:29061980 describes GAA as involved in the lysosomal
      breakdown of glycogen. The IBA is supported by direct experimental
      annotations (PMID:29061980, PMID:9505277).
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
    - reference_id: PMID:29061980
      supporting_text: "involved in the lysosomal breakdown of glycogen"
- term:
    id: GO:0007040
    label: lysosome organization
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetically inferred role in lysosome organization. This reflects the
      downstream consequence of GAA activity (undegraded lysosomal glycogen
      distends and disrupts lysosomes when GAA is deficient) rather than a direct
      molecular role in organising the lysosome.
    action: KEEP_AS_NON_CORE
    reason: >-
      GAA does not build or organise the lysosome; the connection is that loss of
      its catalytic activity leads to lysosomal glycogen accumulation and
      secondary lysosomal/autophagic pathology. This is a valid but non-core,
      consequence-of-deficiency association, so it is retained as non-core.
    supported_by:
    - reference_id: PMID:16917947
      supporting_text: "glycogen degradation and its accumulation in the lysosomes"
- term:
    id: GO:0004553
    label: hydrolase activity, hydrolyzing O-glycosyl compounds
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro-based mapping to the broad O-glycosyl hydrolase parent term. This
      is correct but less informative than the specific alpha-1,4-glucosidase
      activity.
    action: KEEP_AS_NON_CORE
    reason: >-
      GAA is an O-glycosyl-hydrolase (GH31), so this parent term is not wrong,
      but the specific and informative molecular function is
      alpha-1,4-glucosidase activity (GO:0004558). Retained as a correct broader
      classification.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Belongs to the glycosyl hydrolase 31 family."
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Electronic (UniProt combined-methods / EC 3.2.1.20) assignment of the core
      alpha-1,4-glucosidase activity.
    action: ACCEPT
    reason: >-
      The IEA maps EC:3.2.1.20 to GO:0004558, matching the experimentally
      established catalytic activity of GAA. Correct and at the right level of
      specificity.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "glucose residues with release of alpha-D-glucose.; EC=3.2.1.20;"
- term:
    id: GO:0005764
    label: lysosome
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: >-
      Electronic subcellular-location assignment to lysosome, the primary site of
      action of GAA.
    action: ACCEPT
    reason: >-
      GAA is the lysosomal acid alpha-glucosidase; UniProt records Lysosome as
      the subcellular location and it is directly demonstrated (PMID:9505277,
      PMID:29061980). Correct core localization.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0005765
    label: lysosomal membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Subcellular-location-vocabulary mapping to lysosomal membrane. GAA is a
      soluble lumenal enzyme that co-purifies with / is associated with the
      lysosomal membrane fraction.
    action: KEEP_AS_NON_CORE
    reason: >-
      The mature enzyme is a soluble lumenal glucosidase, not an integral
      membrane protein, but UniProt lists Lysosome membrane as a location
      (detected in lysosomal membrane proteomics, PMID:17897319). This peripheral
      membrane association is retained as non-core; the core localization is the
      lysosomal lumen.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
    - reference_id: PMID:17897319
      supporting_text: "In membranes purified from placental lysosomes, we identified 58"
- term:
    id: GO:0005975
    label: carbohydrate metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      InterPro-based mapping to the broad carbohydrate metabolic process parent.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct but very general; the specific and informative process is glycogen
      catabolic process (GO:0005980). Retained as a correct broader
      classification.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0005980
    label: glycogen catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      ARBA electronic assignment of the core glycogen catabolic process.
    action: ACCEPT
    reason: >-
      Matches the experimentally and phylogenetically supported core biological
      process of GAA (lysosomal glycogen degradation).
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0005984
    label: disaccharide metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      ARBA electronic assignment reflecting GAA's in-vitro ability to hydrolyse
      disaccharides such as maltose (hence "acid maltase").
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GAA can cleave the disaccharide maltose in vitro, but its physiological
      substrate is lysosomal glycogen (a polymer), not free disaccharides;
      dietary disaccharide metabolism is the role of intestinal
      sucrase-isomaltase/maltase-glucoamylase. This is an over-annotation of the
      in-vitro substrate scope rather than the biological function.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0030246
    label: carbohydrate binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro (galactose-mutarotase-like domain) mapping to carbohydrate
      binding.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GAA necessarily binds its carbohydrate substrate (and a secondary
      carbohydrate-binding site exists in the trefoil domain, PMID:29061980), but
      "carbohydrate binding" is an uninformative molecular function that is
      subsumed by, and less useful than, the specific glucosidase catalytic
      activity. Flagged as over-annotation.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "GH31; Glycoside Hydrolase Family 31."
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Generic "membrane" location transferred electronically from the mouse
      ortholog.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      "Membrane" is an uninformative cellular-component term for a soluble
      lumenal lysosomal enzyme; the informative locations are lysosome / lysosomal
      lumen. Over-annotation.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0061723
    label: glycophagy
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Involvement in glycophagy (autophagy-mediated delivery and lysosomal
      degradation of glycogen), transferred from the mouse ortholog. GAA performs
      the terminal lysosomal glucosidase step of this pathway.
    action: KEEP_AS_NON_CORE
    reason: >-
      Glycophagy is the physiological pathway by which glycogen reaches the
      lysosome for GAA-mediated degradation, so involvement is well justified.
      Retained as non-core relative to the direct molecular-function-linked
      process glycogen catabolic process.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0120282
    label: autolysosome lumen
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: is_active_in
  review:
    summary: >-
      Activity in the autolysosome lumen, transferred from the mouse ortholog.
      The autolysosome (autophagosome-lysosome fusion product) is where
      autophagy-delivered glycogen is degraded by GAA.
    action: KEEP_AS_NON_CORE
    reason: >-
      Consistent with GAA's role in degrading autophagy-delivered glycogen; the
      autolysosome lumen is a specific compartment of the broader lysosomal
      system. Retained as non-core; the core location is the lysosomal lumen.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0005980
    label: glycogen catabolic process
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70221
  qualifier: involved_in
  review:
    summary: >-
      Reactome traceable assertion placing GAA in glycogen breakdown
      (glycogenolysis), specifically the lysosomal glycogen degradation reaction.
    action: ACCEPT
    reason: >-
      Reactome curates GAA-mediated hydrolysis of lysosomal glycogen; consistent
      with the core biological process.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: EXP
  original_reference_id: PMID:18429042
  qualifier: enables
  review:
    summary: >-
      Experimental characterization of alpha-1,4-glucosidase activity through
      enzyme-activity assays of GAA and disease-causing missense mutants.
    action: ACCEPT
    reason: >-
      Pittis et al. functionally characterized eight novel GAA mutations using
      enzyme activity and protein processing, confirming their detrimental effect
      on the protein and its (glucosidase) function; this directly supports the
      alpha-1,4-glucosidase activity of GAA.
    supported_by:
    - reference_id: PMID:18429042
      supporting_text: "detrimental effect of the eight mutations on the protein and its function"
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: EXP
  original_reference_id: PMID:1856189
  qualifier: enables
  review:
    summary: >-
      Experimental characterization of the catalytic site of human lysosomal
      alpha-glucosidase, identifying Asp-518 as the essential active-site
      carboxylate.
    action: ACCEPT
    reason: >-
      Hermans et al. used the active-site-directed inhibitor CBE and site-directed
      mutagenesis to define the catalytic residues (Trp-516, Asp-518) of GAA,
      with glycogen as the natural substrate; strong direct evidence for
      alpha-1,4-glucosidase activity.
    supported_by:
    - reference_id: PMID:1856189
      supporting_text: "Asp-518 is predicted to be the essential carboxylate in the active site"
    - reference_id: PMID:1856189
      supporting_text: "The residues Trp-516 and Asp-518 are demonstrated"
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: EXP
  original_reference_id: PMID:7717400
  qualifier: enables
  review:
    summary: >-
      GAA (acid alpha-glucosidase) catalytic activity assessed in the context of
      a leaky-splicing GSD II mutation, where residual normally-spliced mRNA
      yielded ~12% of normal active enzyme.
    action: ACCEPT
    reason: >-
      Boerkoel et al. measured residual acid alpha-glucosidase activity in
      patients, directly relating enzyme activity to phenotype; supports the
      alpha-1,4-glucosidase activity of GAA.
    supported_by:
    - reference_id: PMID:7717400
      supporting_text: "An autosomal recessive deficiency of acid alpha-glucosidase (GAA), type II"
- term:
    id: GO:0090599
    label: alpha-glucosidase activity
  evidence_type: EXP
  original_reference_id: PMID:5264799
  qualifier: enables
  review:
    summary: >-
      Demonstration that both alpha-1,4-glucosidase and alpha-1,6-glucosidase
      activities (at acidic pH 4) are absent in tissues of GSD II (Pompe)
      children, establishing GAA as the acid alpha-glucosidase.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct but this is the broad parent (alpha-glucosidase activity) of the
      specific alpha-1,4-glucosidase activity (GO:0004558) that is annotated
      elsewhere; retained as a valid, less-specific classification.
    supported_by:
    - reference_id: PMID:5264799
      supporting_text: "Simultaneous absence of alpha-1,4-glucosidase and alpha-1,6-glucosidase"
- term:
    id: GO:0090599
    label: alpha-glucosidase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9036729
  qualifier: enables
  review:
    summary: >-
      Reactome traceable assertion of alpha-glucosidase activity (in the module
      describing defective GAA that does not hydrolyse lysosomal glycogen).
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct broad molecular function; less specific than GO:0004558
      alpha-1,4-glucosidase activity. Retained as non-core.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "glucose residues with release of alpha-D-glucose.; EC=3.2.1.20;"
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: IDA
  original_reference_id: PMID:24417
  qualifier: enables
  review:
    summary: >-
      Direct assay of purified human liver lysosomal alpha-glucosidase (acid
      alpha-glucosidase) supporting alpha-1,4-glucosidase activity.
    action: ACCEPT
    reason: >-
      Murray et al. purified and characterized human liver acid alpha-glucosidase;
      direct biochemical evidence for the core catalytic activity of GAA. (Cached
      record is abstract/title only; deferring to the curator who read the full
      text.)
    supported_by:
    - reference_id: PMID:24417
      supporting_text: "The molecular heterogeneity of purified human liver lysosomal alpha-glucosidase"
- term:
    id: GO:0043896
    label: glucan 1,6-alpha-glucosidase activity
  evidence_type: IDA
  original_reference_id: PMID:24417
  qualifier: enables
  review:
    summary: >-
      Direct evidence that purified human lysosomal alpha-glucosidase also
      hydrolyses alpha-1,6-linked glucans (branch points), a genuine secondary
      activity of GAA.
    action: KEEP_AS_NON_CORE
    reason: >-
      GAA can hydrolyse alpha-1,6-linkages, which is important in the lysosome
      because no debranching enzyme is present there; however this activity is
      secondary, with a ~32-fold lower specificity constant than for
      alpha-1,4-linkages (PMID:29061980). Retained as a valid non-core secondary
      function.
    supported_by:
    - reference_id: PMID:29061980
      supporting_text: "Within the lysosome, no debranching enzyme is present and GAA must assure the hydrolysis of both α-1,4- and α-1,6-glycosidic linkages"
    - reference_id: PMID:29061980
      supporting_text: "rhGAA shows clear preference for the former linkage, as the specificity constant on maltose is 32-fold higher when compared to the specificity constant on isomaltose"
- term:
    id: GO:0061723
    label: glycophagy
  evidence_type: IMP
  original_reference_id: PMID:5264799
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      Involvement in glycophagy inferred from the loss of acid glucosidase
      activities and consequent lysosomal glycogen storage in GSD II patients.
    action: KEEP_AS_NON_CORE
    reason: >-
      The GSD II phenotype (absent acid alpha-1,4/1,6-glucosidase activities,
      lysosomal glycogen accumulation) places GAA in the glycophagy pathway.
      Retained as non-core relative to the direct process glycogen catabolic
      process. (Cached record is title-only; deferring to the curator.)
    supported_by:
    - reference_id: PMID:5264799
      supporting_text: "Simultaneous absence of alpha-1,4-glucosidase and alpha-1,6-glucosidase"
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: IDA
  original_reference_id: PMID:29061980
  qualifier: enables
  review:
    summary: >-
      Structural and biochemical characterization of recombinant human GAA
      confirming alpha-1,4-glucosidase activity, catalytic residues, and
      substrate recognition.
    action: ACCEPT
    reason: >-
      Roig-Zamboni et al. solved the rhGAA structure with substrate analogues and
      assigned the catalytic nucleophile/acid-base (D518/D616), directly
      supporting alpha-1,4-glucosidase activity with preference for alpha-1,4 over
      alpha-1,6 linkages.
    supported_by:
    - reference_id: PMID:29061980
      supporting_text: "the catalytic nucleophile and acid/base can be assigned to D518 and D616, respectively"
    - reference_id: PMID:29061980
      supporting_text: "rhGAA shows clear preference for the former linkage, as the specificity constant on maltose is 32-fold higher when compared to the specificity constant on isomaltose"
- term:
    id: GO:0005980
    label: glycogen catabolic process
  evidence_type: IDA
  original_reference_id: PMID:29061980
  qualifier: involved_in
  review:
    summary: >-
      Direct evidence that GAA is involved in the lysosomal breakdown of glycogen.
    action: ACCEPT
    reason: >-
      PMID:29061980 explicitly describes GAA as involved in the lysosomal
      breakdown of glycogen and characterizes its activity on glycogen-derived
      substrates; core biological process.
    supported_by:
    - reference_id: PMID:29061980
      supporting_text: "involved in the lysosomal breakdown of glycogen"
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6798739
  qualifier: located_in
  review:
    summary: >-
      Plasma-membrane localization asserted via Reactome neutrophil-degranulation
      (azurophil granule exocytosis) pathway.
    action: KEEP_AS_NON_CORE
    reason: >-
      GAA is detected in neutrophil secretory granules (lysosome-related
      organelles) and appears at the plasma membrane upon degranulation/exocytosis;
      this is a specialized secretory context, not GAA's core lysosomal
      localization. Retained as non-core.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6798747
  qualifier: located_in
  review:
    summary: >-
      Plasma-membrane localization asserted via Reactome neutrophil-degranulation
      (tertiary granule exocytosis) pathway.
    action: KEEP_AS_NON_CORE
    reason: >-
      Duplicate of the plasma-membrane assignment from a related neutrophil
      degranulation module; specialized secretory context, non-core.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6800426
  qualifier: located_in
  review:
    summary: >-
      Plasma-membrane localization asserted via Reactome neutrophil-degranulation
      (ficolin-rich granule exocytosis) pathway.
    action: KEEP_AS_NON_CORE
    reason: >-
      Duplicate of the plasma-membrane assignment from a related neutrophil
      degranulation module; specialized secretory context, non-core.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0035577
    label: azurophil granule membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6798739
  qualifier: located_in
  review:
    summary: >-
      Localization to azurophil (primary) granule membrane via Reactome
      neutrophil-degranulation curation.
    action: KEEP_AS_NON_CORE
    reason: >-
      Azurophil granules are lysosome-related organelles; GAA is detected there,
      consistent with its lysosomal identity, but this is a specialized neutrophil
      context rather than the core lysosomal function. Retained as non-core.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0070821
    label: tertiary granule membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6798747
  qualifier: located_in
  review:
    summary: >-
      Localization to tertiary granule membrane via Reactome
      neutrophil-degranulation curation.
    action: KEEP_AS_NON_CORE
    reason: >-
      Neutrophil tertiary (gelatinase) granules are lysosome-related organelles
      where GAA is detected; specialized context, non-core relative to the
      lysosomal lumen.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0101003
    label: ficolin-1-rich granule membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6800426
  qualifier: located_in
  review:
    summary: >-
      Localization to ficolin-1-rich granule membrane via Reactome
      neutrophil-degranulation curation.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ficolin-1-rich (specific) granules are lysosome-related organelles where
      GAA is detected; specialized context, non-core relative to the lysosomal
      lumen.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  qualifier: located_in
  review:
    summary: >-
      High-throughput detection of GAA in exosomes purified from expressed
      prostatic secretions in urine.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Generic large-scale exosome proteomics detects many lysosomal/secreted
      proteins; this does not represent a specific functional localization of GAA
      and is uninformative relative to its lysosomal role. Flagged as
      over-annotation.
    supported_by:
    - reference_id: PMID:23533145
      supporting_text: "exosome preparations were characterized by a shotgun proteomics procedure"
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  qualifier: located_in
  review:
    summary: >-
      High-throughput detection of GAA in an NK-cell (YTS) membrane-proteome
      analysis.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Generic "membrane" from a large-scale membrane-proteome dataset;
      uninformative for a soluble lysosomal lumenal enzyme. Over-annotation.
    supported_by:
    - reference_id: PMID:19946888
      supporting_text: "predicted as plausible membrane proteins"
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9036729
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable assertion placing mature GAA in the lysosomal lumen.
    action: ACCEPT
    reason: >-
      The mature, proteolytically processed GAA is a soluble enzyme acting in the
      lysosomal lumen; this is the core, most-specific localization.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9036727
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable assertion (GAA hydrolyzes lysosomal glycogen module)
      placing GAA in the lysosomal lumen.
    action: ACCEPT
    reason: >-
      Core, most-specific localization of the mature soluble enzyme; consistent
      with the lysosomal glycogen-degradation reaction.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Lysosome {ECO:0000269|PubMed:17897319}. Lysosome"
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  qualifier: located_in
  review:
    summary: >-
      High-throughput detection of GAA in urinary exosomes.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Generic large-scale urinary-exosome proteomics; not a specific functional
      localization of GAA. Over-annotation (duplicate of the other exosome HDA).
    supported_by:
    - reference_id: PMID:19056867
      supporting_text: "we used"
- term:
    id: GO:0005765
    label: lysosomal membrane
  evidence_type: HDA
  original_reference_id: PMID:17897319
  qualifier: located_in
  review:
    summary: >-
      Detection of GAA in a placental lysosomal-membrane proteome, reflecting
      association of the lumenal enzyme with the lysosomal membrane fraction.
    action: KEEP_AS_NON_CORE
    reason: >-
      GAA co-purifies with lysosomal membranes but is a soluble lumenal enzyme,
      not an integral membrane protein; UniProt lists Lysosome membrane as a
      location based on this dataset. Retained as non-core; core location is the
      lysosomal lumen.
    supported_by:
    - reference_id: PMID:17897319
      supporting_text: "In membranes purified from placental lysosomes, we identified 58"
- term:
    id: GO:0000023
    label: maltose metabolic process
  evidence_type: IC
  original_reference_id: PMID:9505277
  qualifier: involved_in
  review:
    summary: >-
      Curator inference (from GO:0004558) that GAA participates in maltose
      metabolism, reflecting its historical name "acid maltase" and its in-vitro
      hydrolysis of maltose.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Maltose is a convenient in-vitro substrate for GAA, but the physiological
      substrate is lysosomal glycogen (a polymer); there is no evidence GAA has a
      biological role in maltose metabolism (dietary maltose is handled by
      intestinal maltase-glucoamylase/sucrase-isomaltase). This IC extrapolation
      from the enzyme activity over-states the biological process.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  evidence_type: IDA
  original_reference_id: PMID:9505277
  qualifier: enables
  review:
    summary: >-
      Direct assay of recombinant human acid alpha-glucosidase (GAA) activity in
      enzyme-replacement experiments correcting deficient fibroblasts/myoblasts.
    action: ACCEPT
    reason: >-
      Yang et al. showed recombinant GAA normalizes intracellular GAA and
      glycogen levels in deficient cells; the enzyme is endocytosed via
      mannose-6-phosphate receptor and localizes to lysosomes. Direct evidence for
      the alpha-1,4-glucosidase activity of GAA.
    supported_by:
    - reference_id: PMID:9505277
      supporting_text: "and glycogen levels in deficient human"
- term:
    id: GO:0005764
    label: lysosome
  evidence_type: IDA
  original_reference_id: PMID:9505277
  qualifier: located_in
  review:
    summary: >-
      Immunofluorescence demonstration that endocytosed recombinant GAA localizes
      to lysosomes (mannose-6-phosphate-receptor-mediated uptake).
    action: ACCEPT
    reason: >-
      Yang et al. showed the endocytosed enzyme localized to the lysosomes on
      immunofluorescence staining, with uptake inhibited by mannose-6-phosphate.
      Direct evidence for the core lysosomal localization.
    supported_by:
    - reference_id: PMID:9505277
      supporting_text: "the endocytosed enzyme localized to the"
    - reference_id: PMID:9505277
      supporting_text: "endocytosis was inhibited by"
- term:
    id: GO:0005980
    label: glycogen catabolic process
  evidence_type: IDA
  original_reference_id: PMID:9505277
  qualifier: involved_in
  review:
    summary: >-
      Direct evidence that GAA activity reduces intracellular glycogen, correcting
      the storage defect in GAA-deficient cells.
    action: ACCEPT
    reason: >-
      Recombinant GAA normalized both intracellular GAA and glycogen levels in
      deficient human fibroblasts, directly demonstrating its role in glycogen
      catabolism.
    supported_by:
    - reference_id: PMID:9505277
      supporting_text: "and glycogen levels in deficient human"
- term:
    id: GO:0005985
    label: sucrose metabolic process
  evidence_type: IC
  original_reference_id: PMID:9505277
  qualifier: involved_in
  review:
    summary: >-
      Curator inference (from GO:0004558) that GAA participates in sucrose
      metabolism.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GAA is not a sucrase; sucrose hydrolysis is the role of intestinal
      sucrase-isomaltase. This IC extrapolation from alpha-glucosidase activity to
      sucrose metabolism is not biologically supported for GAA and is an
      over-annotation.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "Essential for the degradation of glycogen in lysosomes"
- term:
    id: GO:0006006
    label: glucose metabolic process
  evidence_type: IC
  original_reference_id: PMID:9505277
  qualifier: involved_in
  review:
    summary: >-
      Curator inference (from GO:0004558) that GAA participates in glucose
      metabolism, reflecting that its reaction releases free glucose from
      glycogen.
    action: KEEP_AS_NON_CORE
    reason: >-
      GAA does release alpha-D-glucose as its product, so glucose metabolic
      process is a valid but broad parent-type association; retained as non-core
      relative to the specific glycogen catabolic process.
    supported_by:
    - reference_id: file:human/GAA/GAA-uniprot.txt
      supporting_text: "glucose residues with release of alpha-D-glucose.; EC=3.2.1.20;"
- term:
    id: GO:0007040
    label: lysosome organization
  evidence_type: IMP
  original_reference_id: PMID:7717400
  qualifier: involved_in
  review:
    summary: >-
      Involvement in lysosome organization inferred from a GSD II patient
      phenotype (leaky-splicing mutation with reduced enzyme causing lysosomal
      glycogen storage).
    action: KEEP_AS_NON_CORE
    reason: >-
      As with the IBA lysosome-organization annotation, this reflects the
      downstream consequence of GAA deficiency (lysosomal glycogen accumulation
      and secondary lysosomal disruption) rather than a direct organizing role.
      Retained as non-core. (Cached record is abstract-only; deferring to the
      curator's full-text reading.)
    supported_by:
    - reference_id: PMID:7717400
      supporting_text: "An autosomal recessive deficiency of acid alpha-glucosidase (GAA), type II"
- term:
    id: GO:0002086
    label: diaphragm contraction
  evidence_type: IMP
  original_reference_id: PMID:16917947
  qualifier: involved_in
  review:
    summary: >-
      Involvement in diaphragm contraction inferred from the respiratory/diaphragm
      muscle failure seen in late-onset Pompe disease patients.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Diaphragm/respiratory muscle failure is a clinical consequence of glycogen
      accumulation in GAA-deficient muscle, not a molecular function of GAA in
      muscle contraction. This disease-phenotype-to-process annotation
      over-states GAA's biological role; the underlying defect is impaired
      lysosomal glycogen degradation. (Cached record is abstract-only; deferring
      to the curator on the specific evidence.)
    supported_by:
    - reference_id: PMID:16917947
      supporting_text: "deficiency of acid alpha-glucosidase (GAA) that results in impaired"
core_functions:
- description: >-
    Lysosomal acid alpha-glucosidase (acid maltase; GH31): at acidic lysosomal
    pH, hydrolyses terminal alpha-1,4-glucosidic bonds (and, more slowly,
    alpha-1,6 branch linkages) of glycogen, releasing glucose. This is the
    terminal step of lysosomal glycogen degradation (glycophagy), degrading
    glycogen delivered to the lysosome by autophagy; it is distinct from cytosolic
    glycogenolysis. Loss of this activity causes Pompe disease.
  molecular_function:
    id: GO:0004558
    label: alpha-1,4-glucosidase activity
  directly_involved_in:
  - id: GO:0005980
    label: glycogen catabolic process
  locations:
  - id: GO:0043202
    label: lysosomal lumen
  - id: GO:0005764
    label: lysosome
  supported_by:
  - reference_id: file:human/GAA/GAA-uniprot.txt
    supporting_text: "Essential for the degradation of glycogen in lysosomes"
  - reference_id: file:human/GAA/GAA-uniprot.txt
    supporting_text: "highest activity on alpha-1,4-linked glycosidic linkages, but can also"
  - reference_id: PMID:29061980
    supporting_text: "involved in the lysosomal breakdown of glycogen"
suggested_questions:
- question: >-
    Does GAA have any physiological substrate beyond lysosomal glycogen (e.g. a
    biological role for its in-vitro maltose/disaccharide-hydrolysing activity)?
- question: >-
    What is the functional significance of GAA's presence in neutrophil secretory
    granules and its detection at the plasma membrane upon degranulation?
suggested_experiments:
- description: >-
    Quantify the relative in-vivo contribution of GAA's alpha-1,6 (debranching)
    activity to complete lysosomal glycogen clearance, e.g. using structurally
    defined branched substrates or branch-specific mutants.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  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: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/GAA/GAA-uniprot.txt
  title: UniProtKB entry P10253 (LYAG_HUMAN), lysosomal alpha-glucosidase
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Primary UniProt record for GAA; source of the FUNCTION, CATALYTIC ACTIVITY,
      SUBCELLULAR LOCATION, PTM (M6P targeting, proteolytic maturation) and GH31
      family assignments used throughout this review.
- id: PMID:16917947
  title: Mutation profile of the GAA gene in 40 Italian patients with late onset glycogen
    storage disease type II.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Late-onset Pompe mutation-profile study; establishes that GAA deficiency
      impairs glycogen degradation with lysosomal accumulation. Supports the
      disease context but the diaphragm-contraction annotation derived from it is
      a disease consequence, not a molecular function.
- id: PMID:17897319
  title: Integral and associated lysosomal membrane proteins.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Placental lysosomal-membrane proteome; basis for UniProt's lysosome and
      lysosome-membrane location. GAA co-purifies with lysosomal membranes though
      it is a soluble lumenal enzyme.
- id: PMID:18429042
  title: Molecular and functional characterization of eight novel GAA mutations in
    Italian infants with Pompe disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Functional (enzyme-activity) characterization of GAA missense mutants;
      supports the alpha-1,4-glucosidase activity annotation. Cached record is
      abstract-only.
- id: PMID:1856189
  title: Human lysosomal alpha-glucosidase. Characterization of the catalytic site.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Defines the catalytic residues (Trp-516, Asp-518) of GAA via inhibitor
      labelling and mutagenesis; strong support for the core catalytic activity.
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput urinary exosome proteomics; incidental detection of GAA, not
      a specific functional localization.
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      NK-cell (YTS) membrane-proteome dataset; incidental detection of GAA in a
      generic membrane fraction.
- 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: >-
      High-throughput prostatic-secretion exosome proteomics; incidental detection
      of GAA, not a specific functional localization.
- id: PMID:24417
  title: The molecular heterogeneity of purified human liver lysosomal alpha-glucosidase
    (acid alpha-glucosidase).
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Purification/characterization of human liver acid alpha-glucosidase; basis
      for the IDA alpha-1,4- and alpha-1,6-glucosidase activity annotations.
      Cached record is title-only.
- id: PMID:29061980
  title: Structure of human lysosomal acid α-glucosidase-a guide for the treatment
    of Pompe disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      High-resolution rhGAA crystal structures with substrate analogues; assigns
      catalytic residues D518/D616, documents preference for alpha-1,4 over
      alpha-1,6 linkages, M6P targeting and proteolytic maturation. Full text
      available; central reference for the molecular function and mechanism.
- id: PMID:5264799
  title: Simultaneous absence of alpha-1,4-glucosidase and alpha-1,6-glucosidase activities
    (pH 4) in tissues of children with type II glycogen storage disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Classic demonstration that both acid alpha-1,4- and alpha-1,6-glucosidase
      activities are absent in GSD II tissues, establishing GAA as the acid
      alpha-glucosidase. Cached record is title-only.
- id: PMID:7717400
  title: Leaky splicing mutation in the acid maltase gene is associated with delayed
    onset of glycogenosis type II.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Genotype-phenotype study relating residual GAA activity (~12% of normal) to
      delayed-onset GSD II; supports the catalytic activity annotation.
- id: PMID:9505277
  title: Recombinant human acid alpha-glucosidase corrects acid alpha-glucosidase-deficient
    human fibroblasts, quail fibroblasts, and quail myoblasts.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      ERT proof-of-concept: recombinant GAA normalizes glycogen in deficient
      cells, is taken up by M6P-receptor-mediated endocytosis, and localizes to
      lysosomes. Supports alpha-1,4-glucosidase activity, glycogen catabolism and
      lysosomal localization.
- id: Reactome:R-HSA-6798739
  title: Exocytosis of azurophil granule membrane proteins
  findings: []
- id: Reactome:R-HSA-6798747
  title: Exocytosis of tertiary granule membrane proteins
  findings: []
- id: Reactome:R-HSA-6800426
  title: Exocytosis of ficolin-rich granule membrane proteins
  findings: []
- id: Reactome:R-HSA-70221
  title: Glycogen breakdown (glycogenolysis)
  findings: []
- id: Reactome:R-HSA-9036727
  title: GAA hydrolyzes lysosomal glycogen
  findings: []
- id: Reactome:R-HSA-9036729
  title: Defective GAA does not hydrolyze lysosomal glycogen
  findings: []