id: Q9H553
gene_symbol: ALG2
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  ALG2 is a bifunctional alpha-1,3/alpha-1,6-mannosyltransferase that acts in the
  early, cytoplasmic phase of dolichol-linked oligosaccharide (LLO) assembly, the
  glycan-precursor pathway for protein N-glycosylation. Using GDP-mannose as donor,
  it catalyses the addition of the second and third mannose residues onto
  Man1GlcNAc2-PP-dolichol to form the branched Man3GlcNAc2-PP-dolichol core, adding
  one mannose in an alpha-1,3 linkage (EC 2.4.1.132) and one in an alpha-1,6 linkage
  (EC 2.4.1.257); the Man3GlcNAc2-PP-dolichol product is subsequently elongated by
  ALG11. It is a member of the GT4 glycosyltransferase family and is anchored to the
  endoplasmic reticulum membrane with its catalytic domain and active site on the
  cytoplasmic face. In humans it associates with the ER via a single membrane-binding
  domain (a topology divergent from the multi-domain yeast ortholog). Loss-of-function
  variants cause the multisystem congenital disorder of glycosylation type Ii
  (ALG2-CDG) and an autosomal-recessive congenital myasthenic syndrome (CMS14).
alternative_products:
- name: '1'
  id: Q9H553-1
- name: '2'
  id: Q9H553-2
  sequence_note: VSP_013188, VSP_013189
existing_annotations:
- term:
    id: GO:0012505
    label: endomembrane system
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Broad endomembrane-system localization inferred phylogenetically. Correct but
      much less informative than the experimentally supported ER membrane / cytoplasmic
      side of ER membrane annotations for this enzyme.
    action: KEEP_AS_NON_CORE
    reason: >-
      ALG2 is an ER membrane protein, and the ER is part of the endomembrane system, so
      the term is not wrong. However it is a very general cellular component; the
      specific ER membrane (GO:0005789) and cytoplasmic side of ER membrane
      (GO:0098554) annotations, both experimentally supported, capture the localization
      precisely. Retained as non-core context.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: mostly co-localizes with the resident ER membrane protein Calnexin (CANX)
- term:
    id: GO:0000033
    label: alpha-1,3-mannosyltransferase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic (IBA) inference of alpha-1,3-mannosyltransferase activity. This is
      the generic parent of the substrate-specific dolichol-linked activity
      (GO:0004378) and is well supported for ALG2, which does add an alpha-1,3 mannose.
    action: ACCEPT
    reason: >-
      ALG2 experimentally adds an alpha-1,3-linked mannose during LLO assembly
      (PMID:12684507, PMID:35136180). The IBA term is correct; it is broader than the
      substrate-specific GO:0004378 also annotated here, but is a valid parent-level
      molecular function and consistent with the phylogenetic evidence.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic inference that ALG2 participates in dolichol-linked oligosaccharide
      (LLO) biosynthesis. This is the core biological process for ALG2.
    action: ACCEPT
    reason: >-
      ALG2 adds the second and third mannoses of the LLO precursor on the cytoplasmic
      face of the ER (PMID:35136180), and its deficiency blocks LLO elongation with
      accumulation of Man1/Man2GlcNAc2-PP-dolichol (PMID:12684507). The IBA process
      annotation is well supported and represents a core function.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0004378
    label: GDP-Man:Man(1)GlcNAc(2)-PP-Dol alpha-1,3-mannosyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Automated (RHEA/EC 2.4.1.132) assignment of the substrate-specific alpha-1,3
      mannosyltransferase activity acting on Man1GlcNAc2-PP-dolichol. This is a core
      molecular function of ALG2 and is duplicated by IDA evidence below.
    action: ACCEPT
    reason: >-
      The EC/RHEA-based IEA maps exactly onto the experimentally demonstrated
      alpha-1,3-mannosyltransferase reaction of ALG2 (PMID:12684507, PMID:35136180).
      Correct and precise; core function.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
- term:
    id: GO:0102704
    label: GDP-Man:Man(2)GlcNAc(2)-PP-Dol alpha-1,6-mannosyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Automated (RHEA/EC 2.4.1.257) assignment of the substrate-specific alpha-1,6
      mannosyltransferase activity acting on Man2GlcNAc2-PP-dolichol. This is a core
      molecular function of ALG2 and is duplicated by IDA evidence below.
    action: ACCEPT
    reason: >-
      The EC/RHEA-based IEA maps exactly onto the experimentally demonstrated
      alpha-1,6-mannosyltransferase reaction of ALG2 (PMID:12684507, PMID:35136180).
      Correct and precise; core function.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Subcellular-location keyword mapping to ER membrane. Consistent with the
      experimental EXP/IDA localization of ALG2.
    action: ACCEPT
    reason: >-
      ALG2 localization to the ER membrane is experimentally established by
      immunofluorescence co-localization with the ER marker Calnexin and by membrane
      fractionation (PMID:35136180). The IEA CC term is correct and core.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: mostly co-localizes with the resident ER membrane protein Calnexin (CANX)
- term:
    id: GO:0009101
    label: glycoprotein biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      InterPro-to-GO mapping to the broad glycoprotein biosynthetic process. Correct in
      that ALG2 supplies the N-glycan precursor, but this is a general parent of the
      more specific LLO biosynthesis / N-linked glycosylation processes.
    action: KEEP_AS_NON_CORE
    reason: >-
      ALG2 contributes to glycoprotein biosynthesis via LLO assembly, so the term is
      not wrong. It is, however, a broad parent term; the specific processes
      dolichol-linked oligosaccharide biosynthesis (GO:0006488) and protein N-linked
      glycosylation (GO:0006487), both experimentally supported, better describe the
      function. Retained as non-core.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: N-glycosylation starts with the biosynthesis of lipid-linked oligosaccharide
- term:
    id: GO:0016757
    label: glycosyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro-based assignment of the top-level glycosyltransferase activity. Correct
      but very general; ALG2 is a GT4-family mannosyltransferase.
    action: KEEP_AS_NON_CORE
    reason: >-
      ALG2 is a glycosyltransferase (CAZy GT4), so this parent term is accurate but far
      broader than the substrate-specific mannosyltransferase activities annotated
      elsewhere (GO:0004378, GO:0102704). Retained as a correct broad parent, non-core.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32814053
  qualifier: enables
  review:
    summary: >-
      IntAct IPI capturing a yeast two-hybrid interaction between ALG2 and the
      neurodegeneration protein huntingtin (HTT, P42858) from a neurodegenerative
      disease interactome screen. Bare "protein binding" is uninformative about ALG2's
      molecular function.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The interaction derives from a large-scale Y2H interactome focused on
      neurodegenerative disease proteins, not from a study of ALG2 function. Per
      curation guidance, bare "protein binding" is not an informative molecular
      function and there is no evidence this interaction underlies ALG2's
      mannosyltransferase role; it is not removed (experimental IPI) but flagged as an
      over-annotation for the purpose of describing ALG2's core function.
    supported_by:
    - reference_id: PMID:32814053
      supporting_text: systematic yeast two-hybrid
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-446193
  qualifier: involved_in
  review:
    summary: >-
      Reactome-asserted involvement in LLO (dolichol lipid-linked oligosaccharide)
      biosynthesis and transfer to nascent protein. Core biological process for ALG2.
    action: ACCEPT
    reason: >-
      Consistent with the experimental role of ALG2 in adding the second and third
      mannoses of the LLO precursor (PMID:35136180). Duplicate of the IDA/IBA
      GO:0006488 annotations; core function.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: EXP
  original_reference_id: PMID:35136180
  qualifier: located_in
  review:
    summary: >-
      Experimental (EXP) ER membrane localization from the topological study of human
      ALG2, based on immunofluorescence co-localization with Calnexin and membrane
      fractionation.
    action: ACCEPT
    reason: >-
      Directly demonstrated: FLAG-hAlg2 co-localizes with the ER marker Calnexin and
      partitions into the ER membrane fraction (PMID:35136180). Core localization.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: mostly co-localizes with the resident ER membrane protein Calnexin (CANX)
- term:
    id: GO:0102704
    label: GDP-Man:Man(2)GlcNAc(2)-PP-Dol alpha-1,6-mannosyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:12684507
  qualifier: enables
  review:
    summary: >-
      Direct assay evidence for the alpha-1,6-mannosyltransferase activity (addition of
      the third mannose, EC 2.4.1.257). One of the two core catalytic activities of
      bifunctional ALG2.
    action: ACCEPT
    reason: >-
      Thiel et al. showed that in ALG2 deficiency both Man1GlcNAc2-PP-dolichol and
      Man2GlcNAc2-PP-dolichol accumulate, and WT hALG2 restores elongation, implicating
      ALG2 in the full second-plus-third mannose addition; the bifunctional alpha-1,6
      activity is directly confirmed with purified enzyme in PMID:35136180. Core
      molecular function.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: An accumulation of Man1GlcNAc2-PP-dolichol and
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0004378
    label: GDP-Man:Man(1)GlcNAc(2)-PP-Dol alpha-1,3-mannosyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:12684507
  qualifier: enables
  review:
    summary: >-
      Direct assay evidence that hALG2 adds the alpha-1,3-linked mannose onto
      Man1GlcNAc2-PP-dolichol (the second mannose of the LLO, EC 2.4.1.132). One of the
      two core catalytic activities.
    action: ACCEPT
    reason: >-
      hALG2 was directly shown to act as an alpha-1,3-mannosyltransferase, producing
      Manalpha1,3-ManGlcNAc2-PP-dolichol (PMID:12684507), and this substrate-specific
      activity was confirmed with purified enzyme in PMID:35136180. Core molecular
      function.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
- term:
    id: GO:0000033
    label: alpha-1,3-mannosyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:35136180
  qualifier: enables
  review:
    summary: >-
      Direct assay evidence (parent-level term) for alpha-1,3-mannosyltransferase
      activity from the purified-enzyme kinetic study of human ALG2.
    action: ACCEPT
    reason: >-
      Purified recombinant hAlg2 transfers an alpha-1,3 mannose onto Man1GlcNAc2-linked
      substrate (PMID:35136180). Correct; a valid parent of the substrate-specific
      GO:0004378. Core function (redundant with the more specific term).
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0006487
    label: protein N-linked glycosylation
  evidence_type: IDA
  original_reference_id: PMID:35136180
  qualifier: acts_upstream_of_positive_effect
  review:
    summary: >-
      ALG2 acts upstream of and positively affects protein N-linked glycosylation by
      producing the branched Man3GlcNAc2-PP-dolichol precursor required for building the
      mature N-glycan that is transferred to protein.
    action: ACCEPT
    reason: >-
      N-glycosylation begins with LLO biosynthesis, and ALG2 supplies the second and
      third mannoses of that precursor (PMID:35136180); loss of ALG2 causes CDG with
      hypoglycosylation, consistent with an upstream positive-regulatory relationship
      to N-linked glycosylation. Appropriate use of acts_upstream_of_positive_effect.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: N-glycosylation starts with the biosynthesis of lipid-linked oligosaccharide
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:35136180
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental evidence for participation in dolichol-linked oligosaccharide
      biosynthesis. Core biological process.
    action: ACCEPT
    reason: >-
      Purified hAlg2 converts Man1GlcNAc2 to the branched Man3GlcNAc2 LLO intermediate
      (PMID:35136180); this is the defining biological process for ALG2. Core function.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0098554
    label: cytoplasmic side of endoplasmic reticulum membrane
  evidence_type: IDA
  original_reference_id: PMID:35136180
  qualifier: is_active_in
  review:
    summary: >-
      Direct topological evidence that ALG2's active site faces the cytoplasm: both the
      N- and C-termini (and the catalytic C-terminal domain) are on the cytoplasmic
      side of the ER membrane.
    action: ACCEPT
    reason: >-
      Protease-protection (FPP) and Suc2A glycosylation-reporter assays showed both
      termini of hAlg2 are cytosolic, placing the catalytic domain and its LLO-elongation
      reaction on the cytoplasmic face of the ER, consistent with the cytosolic phase of
      LLO assembly (PMID:35136180). Core, precise localization.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: both the N- and C-termini of hAlg2 are oriented toward cytoplasmic side of the ER
- term:
    id: GO:0004378
    label: GDP-Man:Man(1)GlcNAc(2)-PP-Dol alpha-1,3-mannosyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:35136180
  qualifier: enables
  review:
    summary: >-
      Direct assay evidence (substrate-specific, EC 2.4.1.132) for the alpha-1,3
      mannosyltransferase activity from the purified-enzyme kinetic study. Core function
      (duplicate of the PMID:12684507 IDA).
    action: ACCEPT
    reason: >-
      Kinetic analysis of purified recombinant hAlg2 quantified the alpha-1,3 mannose
      addition onto Man1GlcNAc2-PP-dolichol (PMID:35136180). Correct and precise; core
      molecular function.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0102704
    label: GDP-Man:Man(2)GlcNAc(2)-PP-Dol alpha-1,6-mannosyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:35136180
  qualifier: enables
  review:
    summary: >-
      Direct assay evidence (substrate-specific, EC 2.4.1.257) for the alpha-1,6
      mannosyltransferase activity from the purified-enzyme kinetic study. Core function
      (duplicate of the PMID:12684507 IDA).
    action: ACCEPT
    reason: >-
      Purified recombinant hAlg2 catalyzes the alpha-1,6 mannose addition producing the
      branched Man3GlcNAc2-PP-dolichol, with distinct kinetics resolved by an MGAT1-based
      assay (PMID:35136180). Correct and precise; core molecular function.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-4549368
  qualifier: located_in
  review:
    summary: >-
      Reactome-asserted ER membrane localization. Consistent with the experimental
      localization of ALG2.
    action: ACCEPT
    reason: >-
      Duplicate of the experimentally supported ER membrane localization
      (PMID:35136180). Core localization.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: mostly co-localizes with the resident ER membrane protein Calnexin (CANX)
- term:
    id: GO:0006488
    label: dolichol-linked oligosaccharide biosynthetic process
  evidence_type: IGI
  original_reference_id: PMID:12684507
  qualifier: involved_in
  review:
    summary: >-
      Genetic-interaction evidence (with the yeast ALG2 ortholog, P43636) for
      involvement in LLO biosynthesis: human ALG2 cDNA complements the yeast alg2-1
      mutant, restoring dolichol-linked oligosaccharide biosynthesis.
    action: ACCEPT
    reason: >-
      Cross-species complementation of the yeast alg2-1 mutant by wild-type hALG2 (and
      failure of mutant hALG2) demonstrated the functional orthology and role in LLO
      biosynthesis (PMID:12684507). Core process, supported by genetic interaction with
      P43636.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: the yeast ALG2 sequence was used to identify
- term:
    id: GO:0000033
    label: alpha-1,3-mannosyltransferase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-446208
  qualifier: enables
  review:
    summary: >-
      Reactome-asserted alpha-1,3-mannosyltransferase activity (addition of a second
      mannose to the N-glycan precursor by ALG2). Correct parent-level molecular
      function.
    action: ACCEPT
    reason: >-
      Consistent with the experimentally demonstrated alpha-1,3-mannosyltransferase
      activity of ALG2 (PMID:12684507, PMID:35136180). Duplicate of the IDA/IBA
      GO:0000033 annotations.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
- term:
    id: GO:0000033
    label: alpha-1,3-mannosyltransferase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-4549368
  qualifier: enables
  review:
    summary: >-
      Reactome-asserted alpha-1,3-mannosyltransferase activity (from the defective-ALG2
      / CDG-1i pathway). Correct parent-level molecular function.
    action: ACCEPT
    reason: >-
      Consistent with the experimentally demonstrated alpha-1,3-mannosyltransferase
      activity of ALG2 (PMID:12684507, PMID:35136180). Duplicate of the other GO:0000033
      annotations.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
- term:
    id: GO:0009101
    label: glycoprotein biosynthetic process
  evidence_type: IGI
  original_reference_id: PMID:12684507
  qualifier: involved_in
  review:
    summary: >-
      Genetic-interaction (yeast alg2 complementation) evidence mapped to the broad
      glycoprotein biosynthetic process. Correct but general.
    action: KEEP_AS_NON_CORE
    reason: >-
      The yeast complementation experiment (PMID:12684507) supports ALG2's role in
      glycoprotein biosynthesis, but this is a broad parent of the more specific LLO
      biosynthesis / N-linked glycosylation processes. Retained as non-core.
    supported_by:
    - reference_id: PMID:12684507
      supporting_text: the yeast ALG2 sequence was used to identify
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  qualifier: located_in
  review:
    summary: >-
      High-throughput MS detection of ALG2 in a membrane-proteome dataset of an NK-like
      cell line. Only supports generic "membrane" localization.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      This comes from a large-scale membrane-proteome survey and provides only the
      uninformative parent term "membrane"; the specific and experimentally supported ER
      membrane / cytoplasmic side of ER membrane localizations supersede it. Not removed
      (valid detection) but flagged as an over-annotation for describing ALG2's
      localization.
    supported_by:
    - reference_id: PMID:19946888
      supporting_text: identified 1843 proteins with high confidence scores
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-446208
  qualifier: located_in
  review:
    summary: >-
      Reactome-asserted ER membrane localization. Consistent with the experimental
      localization of ALG2.
    action: ACCEPT
    reason: >-
      Duplicate of the experimentally supported ER membrane localization
      (PMID:35136180). Core localization.
    supported_by:
    - reference_id: PMID:35136180
      supporting_text: mostly co-localizes with the resident ER membrane protein Calnexin (CANX)
core_functions:
- description: >-
    Adds the second mannose of the LLO precursor in an alpha-1,3 linkage: transfers
    mannose from GDP-mannose onto Man1GlcNAc2-PP-dolichol to form
    Man(alpha1,3)Man1GlcNAc2-PP-dolichol (EC 2.4.1.132), on the cytoplasmic face of the
    ER membrane during dolichol-linked oligosaccharide biosynthesis.
  molecular_function:
    id: GO:0004378
    label: GDP-Man:Man(1)GlcNAc(2)-PP-Dol alpha-1,3-mannosyltransferase 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
  supported_by:
  - reference_id: PMID:12684507
    supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
  - reference_id: PMID:35136180
    supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- description: >-
    Adds the third mannose of the LLO precursor in an alpha-1,6 linkage: transfers
    mannose from GDP-mannose onto Man2GlcNAc2-PP-dolichol to complete the branched
    Man3GlcNAc2-PP-dolichol core (EC 2.4.1.257), on the cytoplasmic face of the ER
    membrane. This branched product is the substrate for ALG11.
  molecular_function:
    id: GO:0102704
    label: GDP-Man:Man(2)GlcNAc(2)-PP-Dol alpha-1,6-mannosyltransferase 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
  supported_by:
  - reference_id: PMID:35136180
    supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
- description: >-
    Through LLO biosynthesis, ALG2 acts upstream of protein N-linked glycosylation,
    providing the mannosylated dolichol-linked oligosaccharide precursor that is
    ultimately transferred to asparagine residues of nascent glycoproteins.
  molecular_function:
    id: GO:0004378
    label: GDP-Man:Man(1)GlcNAc(2)-PP-Dol alpha-1,3-mannosyltransferase activity
  directly_involved_in:
  - id: GO:0006487
    label: protein N-linked glycosylation
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  supported_by:
  - reference_id: PMID:35136180
    supporting_text: N-glycosylation starts with the biosynthesis of lipid-linked oligosaccharide
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:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:12684507
  title: A new type of congenital disorders of glycosylation (CDG-Ii) provides new
    insights into the early steps of dolichol-linked oligosaccharide biosynthesis.
  findings:
  - statement: >-
      Identified human ALG2 as the gene deficient in CDG-Ii; patient fibroblasts
      accumulate Man1GlcNAc2-PP-dolichol and Man2GlcNAc2-PP-dolichol, and hALG2 acts as
      an alpha-1,3-mannosyltransferase in dolichol-linked oligosaccharide biosynthesis.
    supporting_text: hALG2 was shown to act as an alpha1,3-mannosyltransferase
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Abstract-only in cache; establishes ALG2 = CDG-Ii gene, the
      alpha-1,3-mannosyltransferase activity, the LLO biosynthesis process, and the
      yeast-complementation genetic interaction (IGI to P43636).
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings:
  - statement: >-
      Large-scale membrane-proteome MS study of an NK-like cell line that detected ALG2
      among membrane-associated proteins, supporting only a generic membrane
      localization.
    supporting_text: identified 1843 proteins with high confidence scores
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Abstract-only in cache. High-throughput proteomics; provides only broad "membrane"
      CC evidence, superseded by ER membrane localization.
- id: PMID:32814053
  title: Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins
    and Uncovers Widespread Protein Aggregation in Affected Brains.
  findings:
  - statement: >-
      Systematic yeast two-hybrid interactome of neurodegenerative disease proteins that
      is the source of the ALG2 IntAct protein-binding interactions (with ATXN1 and HTT);
      not a study of ALG2 enzymatic function.
    supporting_text: systematic yeast two-hybrid
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Abstract-only in cache. Source of bare "protein binding" IPIs; interactions are
      from a ND-focused Y2H screen and do not inform ALG2's mannosyltransferase function.
- id: PMID:35136180
  title: Topological and enzymatic analysis of human Alg2 mannosyltransferase reveals
    its role in lipid-linked oligosaccharide biosynthetic pathway.
  findings:
  - statement: >-
      Human ALG2 is a bifunctional alpha-1,3/alpha-1,6-mannosyltransferase that adds the
      second and third mannoses to Man1GlcNAc2-PP-dolichol to form branched
      Man3GlcNAc2-PP-dolichol.
    supporting_text: Alg2 catalyzes addition of both the second and third mannose to M1Gn2-PDol to form a branched
  - statement: >-
      ALG2 localizes to the ER membrane (co-localizes with Calnexin) and both its termini
      and catalytic domain face the cytoplasm; in human it uses a single membrane-binding
      domain.
    supporting_text: both the N- and C-termini of hAlg2 are oriented toward cytoplasmic side of the ER
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Full text available (PMC8827073). Definitive source for the bifunctional MF terms,
      ER membrane localization, and cytoplasmic-side topology of human ALG2.
- id: Reactome:R-HSA-446193
  title: Biosynthesis of the N-glycan precursor (dolichol lipid-linked oligosaccharide,
    LLO) and transfer to a nascent protein
  findings: []
- id: Reactome:R-HSA-446208
  title: Addition of a second mannose to the N-glycan precursor by ALG2
  findings: []
- id: Reactome:R-HSA-4549368
  title: Defective ALG2 does not transfer a second Man to N-glycan precursor
  findings: []
suggested_questions:
- question: >-
    Under physiological GDP-mannose and substrate concentrations in human cells, what is
    the in vivo balance between the alpha-1,3-first and alpha-1,6-first routes to
    Man3GlcNAc2-PP-dolichol, and does the M2Gn2(alpha-1,6) intermediate serve any
    regulatory function?
- question: >-
    Does ALG2 function as part of a stable ALG1-ALG2-ALG11 mannosyltransferase complex
    in human cells, and how does complex assembly affect its bifunctional activity?
suggested_experiments:
- description: >-
    Reconstitute the human ALG1-ALG2-ALG11 pathway with purified enzymes and defined
    dolichol-linked substrates to measure channeling and the order of mannose additions
    in a membrane-mimetic system.
  experiment_type: in vitro reconstitution / LC-MS kinetics
- description: >-
    Structure determination (cryo-EM or crystallography) of human ALG2 in complex with
    GDP-mannose and a Man1/Man2GlcNAc2-PP-dolichol analog to define the basis of its dual
    alpha-1,3/alpha-1,6 regioselectivity.
  experiment_type: structural biology