id: Q96F25
gene_symbol: ALG14
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  ALG14 is the membrane-anchoring, non-catalytic subunit of the bipartite
  ALG14-ALG13 UDP-N-acetylglucosamine (UDP-GlcNAc) transferase. ALG14 is a
  single-pass endoplasmic reticulum membrane protein that recruits and anchors
  the otherwise-soluble catalytic subunit ALG13 to the cytoplasmic face of the ER
  membrane; the resulting heterodimer catalyses the second step of dolichol-linked
  oligosaccharide (LLO) assembly, transferring a second, beta-1,4-linked GlcNAc
  from UDP-GlcNAc onto GlcNAc-PP-dolichol to form the chitobiose core
  GlcNAc2-PP-dolichol. This activity is essential for the biosynthesis of the
  lipid-linked oligosaccharide precursor used in protein N-linked glycosylation.
  Neither ALG14 nor ALG13 is active alone: ALG13 provides catalysis but lacks a
  membrane domain, whereas ALG14 provides the membrane anchor but lacks catalytic
  residues. In humans, biallelic loss-of-function variants cause ALG14-CDG, a
  spectrum encompassing congenital myasthenic syndrome (CMS15), a
  myasthenic/myopathic neurodegeneration with progressive cerebral atrophy
  (MEPCA), and an intellectual developmental disorder with epilepsy and coarse
  facies (IDDEBF).
existing_annotations:
- term:
    id: GO:0043495
    label: protein-membrane adaptor activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetically-inferred molecular function. ALG14 is the non-catalytic
      subunit that spans the ER membrane and recruits the soluble catalytic
      subunit ALG13, i.e. it acts as a protein-membrane adaptor/anchor. This is
      the correct, informative molecular function for ALG14 (catalysis proper
      is contributed by ALG13).
    action: ACCEPT
    reason: >-
      Directly supported by experimental work in yeast and human orthologues:
      ALG14 spans the membrane, lacks catalytic residues, and functions to
      recruit/anchor ALG13 to the cytosolic face of the ER. This is a core
      molecular function of ALG14.
    supported_by:
    - reference_id: PMID:16100110
      supporting_text: "Alg14 spans the membrane but lacks any sequences"
    - reference_id: PMID:16100110
      supporting_text: "as a membrane anchor that recruits Alg13 to the cytosolic face of the"
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetically-inferred involvement in dolichol-linked oligosaccharide
      (LLO/DLO) biosynthesis. As the anchoring subunit of the ALG13/14 GnTase,
      ALG14 is required for the second step of LLO assembly.
    action: ACCEPT
    reason: >-
      Core biological process for ALG14. The ALG13/14 complex catalyses addition
      of the second GlcNAc to GlcNAc-PP-dolichol, an essential step in assembly
      of the 14-sugar dolichol-linked oligosaccharide precursor. Supported by
      experimental data in the same paper series.
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: >-
        complex catalyzes the addition of a β1,4-linked GlcNAc to Gn-PDol to
        produce Gn2-PDol in the DLO synthetic pathway
- term:
    id: GO:0043541
    label: UDP-N-acetylglucosamine transferase complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: >-
      Phylogenetically-inferred complex membership. ALG14 is part of the
      heterodimeric UDP-N-acetylglucosamine transferase complex it forms with
      ALG13.
    action: ACCEPT
    reason: >-
      Core cellular-component/complex assignment, corroborated experimentally by
      co-immunoprecipitation of the human ALG13/14 complex.
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: "Co-immunoprecipitation assays confirmed the formation of the ALG13/14 complex"
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Electronic annotation from the UniProt Swiss-Prot subcellular location
      vocabulary mapping (SL-0097). ALG14 is an ER membrane protein.
    action: ACCEPT
    reason: >-
      Consistent with the experimental EXP and TAS ER-membrane annotations and
      with the single-pass transmembrane topology in UniProt.
    supported_by:
    - reference_id: file:human/ALG14/ALG14-uniprot.txt
      supporting_text: "Single-pass membrane protein"
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      InterPro2GO electronic annotation (IPR013969, Oligosacch_biosynth_Alg14).
      Duplicate of the IBA and IDA involvement in LLO biosynthesis.
    action: ACCEPT
    reason: >-
      Correct and consistent with experimental data; the ALG14 InterPro domain
      is diagnostic of the LLO-biosynthesis subunit.
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: >-
        complex catalyzes the addition of a β1,4-linked GlcNAc to Gn-PDol to
        produce Gn2-PDol in the DLO synthetic pathway
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:36200043
  qualifier: enables
  review:
    summary: >-
      IPI annotation recording physical interaction of ALG14 with ALG13 isoform 2
      (WITH/FROM UniProtKB:Q9NP73-2). The biologically meaningful content of this
      interaction (recruiting/anchoring the catalytic ALG13 subunit) is already
      captured by the more informative protein-membrane adaptor activity
      (GO:0043495) and by complex membership (GO:0043541).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" is uninformative and per curation guidelines should
      not stand as a molecular function when a more specific term applies. The
      interaction with ALG13 is real and important, but is better represented by
      the adaptor-activity MF and the UDP-GlcNAc transferase complex CC. Retained
      but flagged as over-annotated rather than removed (it is an experimentally
      supported IPI).
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: "Co-immunoprecipitation assays confirmed the formation of the ALG13/14 complex"
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: EXP
  original_reference_id: PMID:16100110
  qualifier: located_in
  review:
    summary: >-
      Experimental localization of ALG14 to the ER membrane. ALG14 spans the ER
      membrane and, together with ALG13, is associated with the ER membrane.
    action: ACCEPT
    reason: >-
      Core cellular-component annotation with direct experimental support; ALG14
      is a single-pass ER membrane protein.
    supported_by:
    - reference_id: PMID:16100110
      supporting_text: "Alg13 and Alg14 physically interact and"
    - reference_id: file:human/ALG14/ALG14-uniprot.txt
      supporting_text: "Single-pass membrane protein"
- term:
    id: GO:0043495
    label: protein-membrane adaptor activity
  evidence_type: IGI
  original_reference_id: PMID:16100110
  qualifier: enables
  review:
    summary: >-
      Experimental (genetic-interaction) support that ALG14 functions as a
      protein-membrane adaptor/anchor recruiting ALG13 to the cytosolic face of
      the ER. WITH/FROM the yeast ALG14 (P38242) genetic system.
    action: ACCEPT
    reason: >-
      This is the core molecular function of ALG14 and is directly demonstrated:
      ALG14 is necessary and sufficient for ER localization of the catalytic
      ALG13 subunit.
    supported_by:
    - reference_id: PMID:16100110
      supporting_text: "as a membrane anchor that recruits Alg13 to the cytosolic face of the"
    - reference_id: PMID:16100110
      supporting_text: "Alg14 is both necessary and sufficient for the ER"
- term:
    id: GO:0098554
    label: cytoplasmic side of endoplasmic reticulum membrane
  evidence_type: IGI
  original_reference_id: PMID:16100110
  qualifier: is_active_in
  review:
    summary: >-
      ALG14 acts at the cytoplasmic (cytosolic) face of the ER membrane, where it
      recruits ALG13 and the complex catalyses formation of GlcNAc2-PP-dolichol.
    action: ACCEPT
    reason: >-
      More precise cellular-component location than "endoplasmic reticulum
      membrane" and consistent with the cytoplasmic topology of the large ALG14
      domain and the site of second-GlcNAc addition.
    supported_by:
    - reference_id: PMID:16100110
      supporting_text: "recruits Alg13 to the cytosolic face of the"
- term:
    id: GO:0006487
    label: protein N-linked glycosylation
  evidence_type: IDA
  original_reference_id: PMID:36200043
  qualifier: acts_upstream_of_positive_effect
  review:
    summary: >-
      ALG14 acts upstream of and positively affects protein N-linked
      glycosylation: by supporting synthesis of the LLO precursor, ALG14 activity
      is required for downstream transfer of the N-glycan to nascent proteins.
      Loss-of-function ALG14-CDG variants reduce GnTase activity.
    action: ACCEPT
    reason: >-
      Appropriate acts_upstream_of_positive_effect relation between LLO assembly
      (ALG14 function) and the N-glycosylation process. Experimentally supported
      by demonstration that ALG14-CDG variants have reduced GnTase activity.
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: >-
        Notably, all of the ALG13/ALG14-CDG mutants that were tested displayed
        reduced GnTase activity
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:36200043
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental support for ALG14 involvement in dolichol-linked
      oligosaccharide biosynthesis: the purified human ALG13/14 complex catalyses
      addition of the second, beta-1,4-linked GlcNAc to GlcNAc-PP-dolichol to
      form GlcNAc2-PP-dolichol.
    action: ACCEPT
    reason: >-
      Core biological process, directly demonstrated in vitro with purified human
      enzyme. Duplicate term to the IBA/IEA involvement annotations.
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: >-
        complex catalyzes the addition of a β1,4-linked GlcNAc to Gn-PDol to
        produce Gn2-PDol in the DLO synthetic pathway
- term:
    id: GO:0043541
    label: UDP-N-acetylglucosamine transferase complex
  evidence_type: IDA
  original_reference_id: PMID:36200043
  qualifier: part_of
  review:
    summary: >-
      Direct experimental demonstration that ALG14 is part of the heterodimeric
      ALG13/14 UDP-N-acetylglucosamine transferase complex (confirmed by
      co-immunoprecipitation and by reconstitution of the active complex).
    action: ACCEPT
    reason: >-
      Core complex-membership annotation, experimentally verified for the human
      protein.
    supported_by:
    - reference_id: PMID:36200043
      supporting_text: "Co-immunoprecipitation assays confirmed the formation of the ALG13/14 complex"
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-5633241
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable-author annotation placing ALG14 at the ER membrane
      (reaction: defective ALG14 does not transfer GlcNAc from UDP-GlcNAc to
      GlcNAcDOLP). Consistent with all other localization evidence.
    action: ACCEPT
    reason: >-
      Correct ER-membrane location; duplicate of the EXP and IEA annotations.
    supported_by:
    - reference_id: file:human/ALG14/ALG14-uniprot.txt
      supporting_text: "Single-pass membrane protein"
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-446207
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable-author annotation placing ALG14 at the ER membrane
      (reaction: ALG13:ALG14 transfers GlcNAc from UDP-GlcNAc to GlcNAcDOLP).
      Consistent with all other localization evidence.
    action: ACCEPT
    reason: >-
      Correct ER-membrane location; duplicate of the EXP and IEA annotations.
    supported_by:
    - reference_id: file:human/ALG14/ALG14-uniprot.txt
      supporting_text: "Single-pass membrane protein"
core_functions:
- description: >-
    Serves as the membrane-anchoring, non-catalytic subunit of the ALG14-ALG13
    UDP-N-acetylglucosamine transferase, recruiting the soluble catalytic subunit
    ALG13 to the cytoplasmic face of the ER membrane so the heterodimer can add
    the second (beta-1,4-linked) GlcNAc to GlcNAc-PP-dolichol during dolichol-linked
    oligosaccharide assembly for protein N-glycosylation.
  molecular_function:
    id: GO:0043495
    label: protein-membrane adaptor activity
  directly_involved_in:
  - id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  - id: GO:0098554
    label: cytoplasmic side of endoplasmic reticulum membrane
  in_complex:
    id: GO:0043541
    label: UDP-N-acetylglucosamine transferase complex
  supported_by:
  - reference_id: PMID:16100110
    supporting_text: "as a membrane anchor that recruits Alg13 to the cytosolic face of the"
  - reference_id: PMID:36200043
    supporting_text: >-
      complex catalyzes the addition of a β1,4-linked GlcNAc to Gn-PDol to
      produce Gn2-PDol in the DLO synthetic pathway
proposed_new_terms: []
suggested_questions:
- question: >-
    Why do most ALG14-CDG patients show normal serum transferrin glycosylation
    despite reduced ALG13/14 GnTase activity in vitro, and does ALG14 have a
    tissue- or substrate-specific requirement (e.g. at the neuromuscular junction)
    that explains the myasthenic phenotype?
- question: >-
    Does ALG14 scaffold or influence the first LLO step (DPAGT1) in addition to
    anchoring ALG13, and if so how is the cytosolic-face LLO machinery organized?
suggested_experiments:
- description: >-
    Structure of the human ALG14-ALG13 heterodimer in the ER membrane (e.g. by
    cryo-EM) to define the ALG14 residues that mediate ALG13 recruitment and how
    CDG variants (P65L, D74N, R109Q, V141G) destabilize the complex.
- description: >-
    Tissue-specific / neuromuscular-junction glycoproteomics in ALG14-deficient
    models to explain why a general LLO-assembly defect manifests predominantly as
    a myasthenic/neurodegenerative phenotype.
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: PMID:16100110
  title: Alg14 recruits Alg13 to the cytoplasmic face of the endoplasmic reticulum
    to form a novel bipartite UDP-N-acetylglucosamine transferase required for the
    second step of N-linked glycosylation.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Foundational paper establishing the bipartite ALG13/14 GnTase and ALG14's
      role as the ER membrane anchor that recruits ALG13. Abstract-only in cache
      (full_text_available: false); human ALG13/ALG14 shown to complement the
      yeast genes. Supports the adaptor-activity MF, ER-membrane CC, and complex CC.
- id: PMID:36200043
  title: An in vitro assay for enzymatic studies on human ALG13/14 heterodimeric UDP-N-acetylglucosamine
    transferase.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Full-text primary paper. Reconstitutes purified human ALG13/14, confirms
      beta-1,4-GlcNAc transfer to Gn-PDol -> Gn2-PDol (LLO second step), shows only
      ALG13 isoform 2 (Q9NP73-2) forms the active complex with ALG14, and shows
      ALG14-CDG variants (P65L, D74N, R109Q, V141G) reduce GnTase activity.
      Supports the LLO-biosynthesis BP, N-glycosylation upstream BP, complex CC,
      and the ALG13-binding IPI.
- id: Reactome:R-HSA-446207
  title: ALG13:ALG14 transfers GlcNAc from UDP-GlcNAc to GlcNAcDOLP
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Reactome reaction describing the ALG13:ALG14-catalysed second GlcNAc
      addition; source of a TAS ER-membrane annotation.
- id: Reactome:R-HSA-5633241
  title: Defective ALG14 does not transfer GlcNAc from UDP-GlcNAc to GlcNAcDOLP
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Reactome reaction covering defective ALG14 and its link to ALG14-CMS;
      source of a TAS ER-membrane annotation.
- id: file:human/ALG14/ALG14-uniprot.txt
  title: UniProtKB entry Q96F25 (ALG14_HUMAN)
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      UniProt record for human ALG14; documents single-pass ER membrane topology,
      protein-membrane adapter function recruiting ALG13, and the CDG disease
      associations (CMS15, MEPCA, IDDEBF).