ALG1 encodes the essential chitobiosyldiphosphodolichol beta-1,4-mannosyltransferase (EC 2.4.1.142) of S. cerevisiae. Anchored in the ER membrane by an N-terminal transmembrane segment with its GT-B catalytic domain on the cytoplasmic face, Alg1p transfers the first, beta-1,4-linked mannose from GDP-mannose to GlcNAc2-PP-dolichol, forming Man1GlcNAc2-PP-Dol, the substrate for Alg2p. Alg1p self-associates and forms two distinct hetero-oligomeric mannosyltransferase complexes, one with Alg2p and one with Alg11p, which together build the Man5GlcNAc2-PP-Dol intermediate on the cytoplasmic side of the ER before it is flipped into the lumen. alg1 mutants accumulate GlcNAc2-PP-Dol and are defective in N-linked glycosylation; human ALG1 deficiency causes ALG1-CDG.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000030 mannosyltransferase activity | IBA GO_REF:0000033 | TOO GENERAL | Summary: IBA 'mannosyltransferase activity' from PANTHER ALG1 node (yeast Alg1, human ALG1, T. brucei). Correct but a broad parent of the specific beta-1,4-mannosyltransferase activity (GO:0004578). Reason: General parent of GO:0004578. |
| GO:0000030 mannosyltransferase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: IEA from InterPro IPR026051 (ALG1-like) to mannosyltransferase activity. Correct but general. Reason: General parent of GO:0004578. |
| GO:0004578 chitobiosyldiphosphodolichol beta-mannosyltransferase activity | EXP PMID:15044395 Physical interactions between the Alg1, Alg2, and Alg11 mann... | ACCEPT | Summary: EXP (Gao et al. 2004): identification of catalytically inactive Alg1 missense alleles that still assemble with Alg2/Alg11, with dominant-negative effects, supporting Alg1 as the catalytic Man1 transferase. Supporting Evidence: PMID:15044395 Missense mutations affecting catalysis but not Alg1 protein stability or assembly with Alg2 or Alg11 were also identified. |
| GO:0004578 chitobiosyldiphosphodolichol beta-mannosyltransferase activity | IDA PMID:29939232 Structural and functional analysis of Alg1 beta-1,4 mannosyl... | ACCEPT | Summary: IDA (Xu et al. 2018): Alg1 activity measured by LC-MS in vitro and by complementation of a GALpr-ALG1 strain. Supporting Evidence: PMID:29939232 the enzymatic activities of Alg1 and its variants were monitored by a complementation assay using the GALpr-ALG1 yeast strain, and further confirmed by a liquid chromatography-mass spectrometry-based in vitro quantitative assay |
| GO:0004578 chitobiosyldiphosphodolichol beta-mannosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: IEA via EC 2.4.1.142 / RHEA:13865. Correct. Supporting Evidence: PMID:6368538 The ALG1 gene product has been shown to catalyze the transfer of a mannosyl residue from GDP-mannose to the lipid-linked acceptor GlcNAc2, yielding Man beta 1-4GlcNAc2-lipid, in lysates from Escherichia coli transformants. |
| GO:0004578 chitobiosyldiphosphodolichol beta-mannosyltransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: RCA from YeastPathways (GLUCOSE-MANNOSYL-CHITO-DOLICHOL, lipid-linked oligosaccharide biosynthesis) for the GlcNAc2-PP-Dol + GDP-Man step. Correct assignment. Supporting Evidence: PMID:6368538 The ALG1 gene product has been shown to catalyze the transfer of a mannosyl residue from GDP-mannose to the lipid-linked acceptor GlcNAc2, yielding Man beta 1-4GlcNAc2-lipid, in lysates from Escherichia coli transformants. |
| GO:0005515 protein binding | IPI PMID:15044395 Physical interactions between the Alg1, Alg2, and Alg11 mann... | REMOVE | Summary: IPI with Alg2 (P43636) from Gao et al. 2004. The interaction is real and functionally meaningful (Alg1-Alg2 mannosyltransferase complex), but 'protein binding' does not describe a molecular activity. Removal does not mean the interaction is false; the biology belongs in complex membership. Reason: Uninformative MF term; the Alg1-Alg2 association is better captured as a mannosyltransferase complex. Supporting Evidence: PMID:15044395 The two Alg1-containing complexes differ from one another in that one complex contains Alg2 and the other contains Alg11. |
| GO:0005515 protein binding | IPI PMID:15044395 Physical interactions between the Alg1, Alg2, and Alg11 mann... | REMOVE | Summary: IPI with Alg11 (P53954) from Gao et al. 2004; Alg1 forms a separate complex with Alg11. The interaction is real, but 'protein binding' is not an informative molecular function; removal does not mean the interaction is false. Reason: Uninformative MF term; the Alg1-Alg11 association is better captured as complex membership. Supporting Evidence: PMID:15044395 The two Alg1-containing complexes differ from one another in that one complex contains Alg2 and the other contains Alg11. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: IBA is_active_in ER from PANTHER ALG1 node. Correct, though ER membrane / cytoplasmic side of ER membrane are more precise. Reason: Organelle-level location kept beside ER membrane, per the localization carve-out for TOO_GENERAL. Supporting Evidence: PMID:29939232 begins on the cytoplasmic face of the endoplasmic reticulum (ER) and ends within the lumen |
| GO:0005783 endoplasmic reticulum | IPI PMID:15044395 Physical interactions between the Alg1, Alg2, and Alg11 mann... | ACCEPT | Summary: IPI-based ER location (with Alg11) from Gao et al. 2004, where Alg1 complexes were characterised in ER membranes. Location is correct. Supporting Evidence: PMID:15044395 The two Alg1-containing complexes differ from one another in that one complex contains Alg2 and the other contains Alg11. |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:29939232 Structural and functional analysis of Alg1 beta-1,4 mannosyl... | ACCEPT | Summary: EXP (Xu et al. 2018): membrane topology study showing the N-terminal TM domain anchors Alg1 in the ER membrane. Supporting Evidence: PMID:29939232 strictly coordinate the Alg1 orientation on the ER membrane |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: IEA from UniProt SubCell SL-0097 (ER membrane). Correct. Supporting Evidence: PMID:29939232 strictly coordinate the Alg1 orientation on the ER membrane |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: RCA is_active_in cytosol from the YeastPathways LLO pathway conversion, which defaults reactions to the cytosol. Alg1p is an ER membrane protein whose catalytic domain acts on GlcNAc2-PP-Dol on the cytoplasmic face of the ER membrane; this is already annotated by IDA (GO:0098554). Reason: Converter compartment default; the correct site of activity is the cytoplasmic side of the ER membrane. Proposed replacements: cytoplasmic side of endoplasmic reticulum membrane Supporting Evidence: PMID:29939232 begins on the cytoplasmic face of the endoplasmic reticulum (ER) and ends within the lumen file:yeast/ALG1/ALG1-uniprot.txt dolichol-pyrophosphate-GlcNAc(2)-Man(5) intermediate on the cytoplasmic |
| GO:0006487 protein N-linked glycosylation | IMP PMID:6369318 Yeast mutants deficient in protein glycosylation. | ACCEPT | Summary: IMP (Huffaker and Robbins 1983): alg1 mutants accumulate lipid-linked GlcNAc2 and are defective in N-glycosylation of invertase. Supporting Evidence: PMID:6369318 The alg1 mutant accumulated lipid-linked GlcNAc2 |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IDA PMID:29939232 Structural and functional analysis of Alg1 beta-1,4 mannosyl... | ACCEPT | Summary: IDA (Xu et al. 2018) for dolichol-linked oligosaccharide biosynthesis; Alg1 activity in vitro on the LLO intermediate. Supporting Evidence: PMID:29939232 the enzymatic activities of Alg1 and its variants were monitored by a complementation assay using the GALpr-ALG1 yeast strain, and further confirmed by a liquid chromatography-mass spectrometry-based in vitro quantitative assay |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:7037780 Temperature-sensitive yeast mutants deficient in asparagine-... | ACCEPT | Summary: IMP (Huffaker and Robbins 1982): alg1-1 cells cannot add the first mannose to GlcNAc2-PP-lipid. Supporting Evidence: PMID:7037780 These results indicate that the alg1-1 mutant is blocked specifically in the addition of the first mannose residue to the lipid-linked oligosaccharide precursor. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: RCA from YeastPathways LLO biosynthesis pathway. Correct. Supporting Evidence: PMID:7037780 These results indicate that the alg1-1 mutant is blocked specifically in the addition of the first mannose residue to the lipid-linked oligosaccharide precursor. |
| GO:0009101 glycoprotein biosynthetic process | IBA GO_REF:0000033 | TOO GENERAL | Summary: IBA 'glycoprotein biosynthetic process' from PANTHER ALG1 node. True but a broad ancestor of protein N-linked glycosylation; the specific process is LLO biosynthesis. Reason: General parent; GO:0006488 and GO:0006487 are precise. |
| GO:0016757 glycosyltransferase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: IEA from InterPro IPR001296 (glycosyl transferase family 1). Correct but general. Reason: General parent of GO:0004578. |
| GO:0019187 beta-1,4-mannosyltransferase activity | IDA PMID:6368538 Cloning and expression in Escherichia coli of a yeast mannos... | TOO GENERAL | Summary: IDA (Couto et al. 1984): ALG1 expressed in E. coli transfers mannose from GDP-Man to GlcNAc2-lipid forming Man beta1-4GlcNAc2-lipid. Correct; parent of the more specific GO:0004578. Supporting Evidence: PMID:6368538 The ALG1 gene product has been shown to catalyze the transfer of a mannosyl residue from GDP-mannose to the lipid-linked acceptor GlcNAc2, yielding Man beta 1-4GlcNAc2-lipid, in lysates from Escherichia coli transformants. |
| GO:0098554 cytoplasmic side of endoplasmic reticulum membrane | IDA PMID:29939232 Structural and functional analysis of Alg1 beta-1,4 mannosyl... | ACCEPT | Summary: IDA (Xu et al. 2018): topology analysis places the Alg1 catalytic domain on the cytoplasmic side of the ER membrane, where cytosolic LLO assembly occurs. This is the most precise location of activity. Supporting Evidence: PMID:29939232 strictly coordinate the Alg1 orientation on the ER membrane PMID:29939232 begins on the cytoplasmic face of the endoplasmic reticulum (ER) and ends within the lumen |
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Download this section (compressed HTML)Q: Does assembly of Alg1 with Alg2 versus Alg11 channel the LLO intermediate between successive mannosyltransferases, and what determines the partition of Alg1 between the two complexes?
Experiment: Reconstitute purified Alg1, Alg2 and Alg11 in nanodiscs at defined stoichiometries and measure Man1-Man5 intermediate kinetics to test substrate channelling within the complexes.
Mannosyltransferase; involved in asparagine-linked glycosylation in the endoplasmic reticulum (ER); essential for viability; human homolog ALG1 complements yeast null mutant
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