id: Q96C23
gene_symbol: GALM
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  GALM is the cytosolic aldose 1-epimerase (galactose mutarotase; EC 5.1.3.3) that
  catalyzes the first step of the Leloir pathway of galactose metabolism. It interconverts
  the beta- and alpha-anomers of D-galactose (beta-D-galactose <=> alpha-D-galactose),
  maintaining the anomeric equilibrium and ensuring a sufficient supply of the alpha-anomer,
  which galactokinase (GALK1) requires as its substrate; the downstream Leloir enzymes GALK1,
  GALT, and GALE then convert galactose into glucose 1-phosphate. GALM also mutarotates
  D-glucose (alpha-D-glucose <=> beta-D-glucose), though it prefers galactose over glucose.
  The enzyme is a monomer with a single-domain beta-sandwich fold typical of the aldose
  epimerase family; catalysis uses His-176 as the proton donor and Glu-307 as the proton
  acceptor, with His-107 also contributing. Biallelic loss-of-function GALM variants cause
  galactose mutarotase deficiency (galactosemia type IV, GALAC4), an autosomal recessive
  inborn error of galactose metabolism.
existing_annotations:
- term:
    id: GO:0033499
    label: beta-D-galactose catabolic process via UDP-galactose, Leloir pathway
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic (IBA) inference that GALM participates in the Leloir pathway of galactose
      catabolism. This is the core biological process of GALM: it catalyzes the first (mutarotase)
      step supplying alpha-D-galactose to GALK1.
    action: ACCEPT
    reason: >-
      Consistent with the experimentally established Leloir-pathway role and the PANTHER
      aldose-1-epimerase family. Represents a core function.
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic (IBA) inference of aldose 1-epimerase activity, the core molecular function
      of GALM, matching the family-level assignment for PTN000009552.
    action: ACCEPT
    reason: >-
      The defining catalytic activity of GALM, independently supported by direct experimental
      characterization (PMID:12753898). Core molecular function.
- term:
    id: GO:0006006
    label: glucose metabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic inference that GALM participates in glucose metabolism, reflecting the
      family's ability to mutarotate glucose in addition to galactose.
    action: KEEP_AS_NON_CORE
    reason: >-
      GALM does mutarotate D-glucose in vitro, but with lower affinity/turnover than galactose
      (KM 54 mM vs 37 mM; kcat 4900 vs 12000 s-1), and the enzyme "exhibits a preference for
      galactose over glucose" (PMID:12753898). Glucose mutarotation is a genuine but secondary
      activity, not the core physiological role.
    supported_by:
    - reference_id: PMID:12753898
      supporting_text: "the protein has aldose 1-epimerase activity and exhibits a preference for galactose over glucose"
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Automated (RHEA/EC 5.1.3.3) assignment of aldose 1-epimerase activity, the core molecular
      function.
    action: ACCEPT
    reason: >-
      Correctly mapped from EC 5.1.3.3 / RHEA:10264,RHEA:28675 to the specific MF term; matches
      experimental evidence.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Subcellular-location mapping (UniProt SL-0086) placing GALM in the cytoplasm.
    action: ACCEPT
    reason: >-
      Consistent with the UniProt subcellular location (Cytoplasm) and the Reactome cytosol
      annotation. Broader than cytosol but not incorrect.
- term:
    id: GO:0005975
    label: carbohydrate metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      InterPro2GO mapping to the high-level carbohydrate metabolic process, from the aldose
      epimerase domains.
    action: KEEP_AS_NON_CORE
    reason: >-
      True but a very general grouping term. The specific galactose/hexose processes below are
      more informative; retained as a non-core parent.
- term:
    id: GO:0016853
    label: isomerase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro2GO mapping to the generic parent term isomerase activity.
    action: MODIFY
    reason: >-
      Correct but overly general: GALM's activity is specifically aldose 1-epimerase activity
      (GO:0004034), which is a descendant of isomerase activity and is already annotated with
      strong experimental support. Replace the generic parent with the specific MF.
    proposed_replacement_terms:
    - id: GO:0004034
      label: aldose 1-epimerase activity
- term:
    id: GO:0019318
    label: hexose metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      Automated mapping (UniPathway/InterPro) to hexose metabolic process, consistent with GALM
      acting on the hexoses galactose and glucose.
    action: KEEP_AS_NON_CORE
    reason: >-
      Accurate parent term encompassing galactose and glucose metabolism, but less specific than
      the galactose process terms. Retained as a non-core grouping term.
- term:
    id: GO:0030246
    label: carbohydrate binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro2GO mapping to carbohydrate binding, derived from the sugar-binding beta-sandwich
      (GH-type carbohydrate-binding) domain signatures.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GALM binds galactose/glucose only transiently as catalytic substrates in its active site,
      not as a lectin-type carbohydrate-binding module. GO:0030246 (carbohydrate binding) implies
      a dedicated binding function distinct from catalysis; this is an over-annotation propagated
      from the structural fold signature. The catalytic substrate interaction is already captured
      by the aldose 1-epimerase activity annotation.
- term:
    id: GO:0033499
    label: beta-D-galactose catabolic process via UDP-galactose, Leloir pathway
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70370
  qualifier: involved_in
  review:
    summary: >-
      Reactome-curated (TAS) assignment of GALM to the Leloir pathway of galactose catabolism.
    action: ACCEPT
    reason: >-
      Curator-asserted pathway membership matching the established biology; core biological process.
- term:
    id: GO:0006012
    label: galactose metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000041
  qualifier: involved_in
  review:
    summary: >-
      UniPathway-based (UPA00214) mapping to galactose metabolic process.
    action: ACCEPT
    reason: >-
      Core biological process of GALM; the anomer interconversion it catalyzes initiates galactose
      metabolism. Independently supported by IDA (PMID:12753898).
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: EXP
  original_reference_id: PMID:12753898
  qualifier: enables
  review:
    summary: >-
      Experimental demonstration that recombinant human GALM has aldose 1-epimerase activity,
      with confirmed catalytic residues.
    action: ACCEPT
    reason: >-
      Core molecular function, directly demonstrated by enzyme assays on purified recombinant
      protein plus site-directed mutagenesis of catalytic residues.
    supported_by:
    - reference_id: PMID:12753898
      supporting_text: "Enzyme assays show that the protein has aldose 1-epimerase activity and exhibits a preference for galactose over glucose. Site-directed mutagenesis confirmed the involvement of three residues involved in catalysis and substrate binding."
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9931926
  qualifier: enables
  review:
    summary: >-
      Reactome-curated (TAS) assertion of aldose 1-epimerase activity (in the context of the
      defective-GALM reaction).
    action: ACCEPT
    reason: >-
      Core molecular function; consistent with all other MF evidence.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9931853
  qualifier: located_in
  review:
    summary: >-
      Reactome-curated (TAS) localization of GALM (the "GALM converts beta-D-GAL to alpha-D-GAL"
      reaction) to the cytosol.
    action: ACCEPT
    reason: >-
      Consistent with the cytoplasmic Leloir pathway; the most specific and appropriate location
      term for GALM. Core localization.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9931926
  qualifier: located_in
  review:
    summary: >-
      Reactome-curated (TAS) cytosol localization (defective-GALM reaction context). Duplicate of
      the preceding cytosol annotation from a related Reactome reaction.
    action: ACCEPT
    reason: >-
      Correct core localization; duplicate assertion of cytosol is acceptable.
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: IDA
  original_reference_id: PMID:30451973
  qualifier: enables
  review:
    summary: >-
      Direct assay (IDA) of aldose 1-epimerase activity in the study that identified GALM
      deficiency as a novel galactosemia; patient/variant proteins showed altered activity.
    action: ACCEPT
    reason: >-
      Core molecular function, independently confirmed in the disease-gene study.
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: IMP
  original_reference_id: PMID:30451973
  qualifier: enables
  review:
    summary: >-
      Mutant-phenotype (IMP) evidence that pathogenic GALM variants reduce aldose 1-epimerase
      activity, linking loss of this MF to disease.
    action: ACCEPT
    reason: >-
      Loss-of-function variants causing galactosemia type IV support the physiological relevance
      of this core molecular function.
- term:
    id: GO:0033499
    label: beta-D-galactose catabolic process via UDP-galactose, Leloir pathway
  evidence_type: IMP
  original_reference_id: PMID:30451973
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      Mutant-phenotype (IMP) evidence that GALM loss disrupts the Leloir pathway of galactose
      catabolism, causing galactose accumulation / galactosemia type IV.
    action: ACCEPT
    reason: >-
      Biallelic GALM variants cause a novel type of galactosemia by impairing the Leloir pathway;
      core biological process supported by human disease genetics.
- term:
    id: GO:0033499
    label: beta-D-galactose catabolic process via UDP-galactose, Leloir pathway
  evidence_type: IDA
  original_reference_id: PMID:30451973
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay (IDA) evidence supporting GALM's participation in the Leloir galactose
      catabolic pathway.
    action: ACCEPT
    reason: >-
      Core biological process, directly supported. Duplicate of the IBA/TAS Leloir-pathway
      annotations with independent experimental backing.
- term:
    id: GO:0004034
    label: aldose 1-epimerase activity
  evidence_type: IDA
  original_reference_id: PMID:12753898
  qualifier: enables
  review:
    summary: >-
      Direct assay (IDA) of aldose 1-epimerase activity on purified recombinant human GALM.
    action: ACCEPT
    reason: >-
      Core molecular function; the foundational biochemical characterization of the enzyme.
    supported_by:
    - reference_id: PMID:12753898
      supporting_text: "Enzyme assays show that the protein has aldose 1-epimerase activity and exhibits a preference for galactose over glucose."
- term:
    id: GO:0005975
    label: carbohydrate metabolic process
  evidence_type: IDA
  original_reference_id: PMID:12753898
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      Direct-assay evidence placing GALM in carbohydrate metabolism (mutarotation of hexose
      sugars), a high-level grouping process.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct but very general; the specific galactose/glucose metabolic process terms are more
      informative. Retained as a non-core parent. GALM is described as "a key enzyme of
      carbohydrate metabolism" (PMID:12753898).
    supported_by:
    - reference_id: PMID:12753898
      supporting_text: "Aldose 1-epimerase or mutarotase (EC 5.1.3.3) is a key enzyme of carbohydrate metabolism catalysing the interconversion of the alpha- and beta-anomers of hexose sugars such as glucose and galactose."
- term:
    id: GO:0042803
    label: protein homodimerization activity
  evidence_type: IDA
  original_reference_id: PMID:12753898
  qualifier: enables
  negated: true
  review:
    summary: >-
      Negated (NOT) annotation: GALM does not have protein homodimerization activity. Biochemical
      and structural characterization established that GALM is a monomer.
    action: ACCEPT
    reason: >-
      The NOT annotation correctly records that GALM does not homodimerize. UniProt reports the
      SUBUNIT as Monomer (from PMID:12753898 and PMID:15026423). Retaining the negation is
      informative and consistent with the monomeric solution and crystal state.
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  qualifier: located_in
  review:
    summary: >-
      High-throughput mass-spectrometry (HDA) detection of GALM among proteins recovered from
      human urinary exosomes.
    action: KEEP_AS_NON_CORE
    reason: >-
      Reflects broad proteomic detection in secreted exosomes rather than the enzyme's site of
      catalytic function, which is the cytosol. Kept as a non-core localization; not part of the
      core Leloir-pathway function.
    supported_by:
    - reference_id: PMID:19056867
      supporting_text: "we used LC-MS/MS to profile the proteome of human urinary exosomes. Overall, the analysis identified 1132 proteins unambiguously"
- term:
    id: GO:0006006
    label: glucose metabolic process
  evidence_type: IDA
  original_reference_id: PMID:12753898
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay evidence that GALM mutarotates D-glucose, participating in glucose metabolism.
    action: KEEP_AS_NON_CORE
    reason: >-
      GALM does interconvert glucose anomers, but with lower efficiency than galactose and a
      demonstrated preference for galactose (PMID:12753898). A real but secondary activity, not
      the core physiological role.
    supported_by:
    - reference_id: PMID:12753898
      supporting_text: "catalysing the interconversion of the alpha- and beta-anomers of hexose sugars such as glucose and galactose"
- term:
    id: GO:0006012
    label: galactose metabolic process
  evidence_type: IDA
  original_reference_id: PMID:12753898
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay evidence that GALM participates in galactose metabolism via mutarotation of
      galactose anomers.
    action: ACCEPT
    reason: >-
      Core biological process; directly demonstrated and consistent with the enzyme's preference
      for galactose. Foundational to the Leloir pathway.
    supported_by:
    - reference_id: PMID:12753898
      supporting_text: "catalysing the interconversion of the alpha- and beta-anomers of hexose sugars such as glucose and galactose"
core_functions:
- description: >-
    Aldose 1-epimerase (galactose mutarotase) activity: GALM interconverts the beta- and
    alpha-anomers of D-galactose in the cytosol, catalyzing the first step of the Leloir pathway
    and supplying the alpha-D-galactose required by galactokinase (GALK1).
  molecular_function:
    id: GO:0004034
    label: aldose 1-epimerase activity
  directly_involved_in:
  - id: GO:0033499
    label: galactose catabolic process via UDP-galactose, Leloir pathway
  - id: GO:0006012
    label: galactose metabolic process
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: PMID:12753898
    supporting_text: "Aldose 1-epimerase or mutarotase (EC 5.1.3.3) is a key enzyme of carbohydrate metabolism catalysing the interconversion of the alpha- and beta-anomers of hexose sugars such as glucose and galactose."
  - reference_id: PMID:30451973
    supporting_text: "Biallelic GALM pathogenic variants cause a novel type of galactosemia."
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:0000041
  title: Gene Ontology annotation based on UniPathway vocabulary mapping
  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:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:12753898
  title: Identification and characterisation of human aldose 1-epimerase.
  findings:
  - statement: >-
      Recombinant human GALM has aldose 1-epimerase (mutarotase) activity (EC 5.1.3.3) and
      interconverts the alpha- and beta-anomers of hexose sugars, with a preference for galactose
      over glucose; site-directed mutagenesis confirmed catalytic/substrate-binding residues.
    supporting_text: "Enzyme assays show that the protein has aldose 1-epimerase activity and exhibits a preference for galactose over glucose. Site-directed mutagenesis confirmed the involvement of three residues involved in catalysis and substrate binding."
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Abstract-only in cache (full_text_available: false), but the abstract directly establishes
      GALM's core aldose 1-epimerase activity and galactose preference; PMID matches title.
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings:
  - statement: >-
      Large-scale LC-MS/MS proteomics of human urinary exosomes; GALM is among the many proteins
      detected in this exosome fraction.
    supporting_text: "we used LC-MS/MS to profile the proteome of human urinary exosomes. Overall, the analysis identified 1132 proteins unambiguously"
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput proteomics survey supporting only the extracellular-exosome detection
      (non-core); does not inform GALM's catalytic function.
- id: PMID:30451973
  title: Biallelic GALM pathogenic variants cause a novel type of galactosemia.
  findings:
  - statement: >-
      Biallelic loss-of-function GALM variants impair aldose 1-epimerase activity and the Leloir
      pathway, causing a novel (type IV) galactosemia (galactose mutarotase deficiency, GALAC4).
    supporting_text: "Biallelic GALM pathogenic variants cause a novel type of galactosemia."
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Abstract-only in cache; establishes the disease relevance (galactosemia type IV) and, via
      variant characterization, supports GALM's role in the Leloir galactose catabolic pathway.
- id: Reactome:R-HSA-70370
  title: Galactose catabolism
  findings: []
- id: Reactome:R-HSA-9931853
  title: GALM converts beta-D-GAL to alpha-D-GAL
  findings: []
- id: Reactome:R-HSA-9931926
  title: Defective GALM doesn't convert beta-D-GAL to alpha-D-GAL
  findings: []