Alg7 is the UDP-N-acetylglucosamine:dolichyl-phosphate N-acetylglucosamine-1-phosphate transferase (GPT; EC 2.7.8.15). It belongs to the polytopic glycosyltransferase family 4 / MraY-WecA family, and the nucleoside antibiotic tunicamycin is its target. Alg7 catalyses the first, committed step of dolichol-linked oligosaccharide assembly: it transfers GlcNAc-1-phosphate from cytosolic UDP-GlcNAc onto dolichyl phosphate to form GlcNAc-PP-dolichol in the cytoplasmic leaflet of the ER membrane. Alg7 forms a hetero-hexameric complex with the Alg13/Alg14 UDP-GlcNAc transferase, which adds the second GlcNAc, so the first two steps of LLO assembly are physically coupled, much as MraY and MurG are in bacterial peptidoglycan synthesis. ALG7 is essential. Dominant alleles that increase transferase activity alleles confer tunicamycin resistance, and hypomorphic alleles reduce LLO levels and N-glycosylation and cause secondary mitochondrial defects.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003975 UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: UDP-GlcNAc:dolichyl-phosphate GlcNAc-1-phosphotransferase activity (EC 2.7.8.15), IBA from PANTHER PTN000060284 (GPT/DPAGT1 family; human, mouse, Arabidopsis, S. pombe, trypanosome and yeast donors). This is a deep, well-supported node and Alg7 is the yeast member. Core. Supporting Evidence: PMID:15794922 N-glycans originate from a common lipid-linked oligosaccharide (LLO) precursor whose synthesis is initiated by the Dol-P-dependent GlcNAc-1-P transferase (GPT) encoded by an essential ALG7 gene. |
| GO:0003975 UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: GO:0003975, IEA from combined methods (ARBA00026931, InterPro IPR033895 GPT, RHEA:13289, EC 2.7.8.15). Correct. Supporting Evidence: file:yeast/ALG7/ALG7-uniprot.txt cytosolic UDP-GlcNAc onto the carrier lipid dolichyl phosphate (P- |
| GO:0003975 UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase activity | IMP PMID:6096695 Asparagine-linked glycosylation in Saccharomyces cerevisiae:... | ACCEPT | Summary: GO:0003975, IMP from Barnes et al. 1984. Dominant tunicamycin-resistance alleles of ALG7 increase GlcNAc-1-P transferase activity, which identifies ALG7 as the structural gene. Core. Supporting Evidence: PMID:6096695 We identified a gene, ALG7, that is probably the structural gene for UDP-N-acetylglucosamine-1-P transferase, the enzyme inhibited by tunicamycin. PMID:6096695 Dominant mutations in this gene result in increased activity of the transferase and loss of the ability of the cell to sporulate. |
| GO:0003975 UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: GO:0003975, RCA from YeastPathways (Dol-P + UDP-GlcNAc -> GlcNAc-PP-Dol, EC 2.7.8.15). Correct. Supporting Evidence: PMID:15794922 N-glycans originate from a common lipid-linked oligosaccharide (LLO) precursor whose synthesis is initiated by the Dol-P-dependent GlcNAc-1-P transferase (GPT) encoded by an essential ALG7 gene. |
| GO:0005783 endoplasmic reticulum | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | ACCEPT | Summary: endoplasmic reticulum, HDA from the SWAp-Tag GFP library (Yofe et al. 2016). Consistent with Alg7 being an ER membrane enzyme. Supporting Evidence: PMID:26928762 we found that most new localization assignments were to the ER, punctate structures and vacuole |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: ER membrane, IEA from the UniProt subcellular-location mapping (SL-0097). Correct. Supporting Evidence: file:yeast/ALG7/ALG7-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | ISS GO_REF:0000024 | ACCEPT | Summary: ER membrane, ISS from a characterised GPT orthologue (UniProtKB:P23338). GPT enzymes are conserved polytopic ER proteins, and yeast Alg7 also co-purifies with the ER Alg13/Alg14 complex. Correct. Supporting Evidence: PMID:19129246 whose synthesis is sequentially catalyzed by the Alg7p GlcNAc phosphotransferase and by the dimeric Alg13p/Alg14p UDP-GlcNAc transferase on the cytosolic face of the endoplasmic reticulum |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: is_active_in cytosol, RCA from the YeastPathways LLO pathway compartment. Alg7 uses cytosolic UDP-GlcNAc and makes GlcNAc-PP-Dol in the cytoplasmic leaflet. It is a polytopic ER membrane enzyme, so its activity is at the cytoplasmic face of the ER membrane, not in the cytosol. Reason: Make the location precise. The reaction occurs on the cytoplasmic side of the ER membrane. Proposed replacements: cytoplasmic side of endoplasmic reticulum membrane Supporting Evidence: PMID:19129246 whose synthesis is sequentially catalyzed by the Alg7p GlcNAc phosphotransferase and by the dimeric Alg13p/Alg14p UDP-GlcNAc transferase on the cytosolic face of the endoplasmic reticulum file:yeast/ALG7/ALG7-uniprot.txt leaflet of the endoplasmic reticulum membrane. |
| GO:0006487 protein N-linked glycosylation | IMP PMID:15794922 A hypomorphic allele of the first N-glycosylation gene, ALG7... | ACCEPT | Summary: protein N-linked glycosylation, IMP from Mendelsohn et al. 2005. An ALG7 hypomorph reduces LLO levels and under-glycosylates CPY. Alg7 catalyses the committed first step of the LLO donor that N-glycosylation requires, and GO:0006488 is part_of GO:0006487. Correct. Supporting Evidence: PMID:15794922 Both mutants exhibited diminished abundance of LLO and under-glycosylation of carboxypeptidase Y (CPY). |
| GO:0006487 protein N-linked glycosylation | IMP PMID:6096695 Asparagine-linked glycosylation in Saccharomyces cerevisiae:... | ACCEPT | Summary: protein N-linked glycosylation, IMP from Barnes et al. 1984 (tunicamycin-resistance genetics of ALG7). Correct. Supporting Evidence: PMID:6096695 The synthesis of N-linked oligosaccharide is an essential function in cells. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: dolichol-linked oligosaccharide biosynthetic process, IEA from InterPro IPR033895 (GPT). Correct. Supporting Evidence: PMID:15794922 N-glycans originate from a common lipid-linked oligosaccharide (LLO) precursor whose synthesis is initiated by the Dol-P-dependent GlcNAc-1-P transferase (GPT) encoded by an essential ALG7 gene. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:6096695 Asparagine-linked glycosylation in Saccharomyces cerevisiae:... | ACCEPT | Summary: dolichol-linked oligosaccharide biosynthetic process, IMP from Barnes et al. 1984. Alg7 catalyses the first, tunicamycin-sensitive step of LLO synthesis. Core. Supporting Evidence: PMID:6096695 We identified a gene, ALG7, that is probably the structural gene for UDP-N-acetylglucosamine-1-P transferase, the enzyme inhibited by tunicamycin. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: dolichol-linked oligosaccharide biosynthetic process, RCA from YeastPathways. Correct. Supporting Evidence: PMID:15794922 N-glycans originate from a common lipid-linked oligosaccharide (LLO) precursor whose synthesis is initiated by the Dol-P-dependent GlcNAc-1-P transferase (GPT) encoded by an essential ALG7 gene. |
| GO:0009060 aerobic respiration | IMP PMID:15794922 A hypomorphic allele of the first N-glycosylation gene, ALG7... | MARK AS OVER ANNOTATED | Summary: aerobic respiration, IMP from Mendelsohn et al. 2005. The alg7 hypomorph lost mtDNA and respiratory activity, but the authors attribute this to dysregulated N-glycosylation in general, and an alg6 LLO mutant behaved the same way. This is an indirect consequence of an LLO defect. Alg7 does none of the work of respiration. Reason: Indirect, pleiotropic phenotype. Being required for mitochondrial maintenance does not make Alg7 a participant in aerobic respiration. Supporting Evidence: PMID:15794922 We show that ALG7 knockdown gave rise to an unexpected phenotype of mitochondrial dysfunction. PMID:15794922 our studies provide evidence that the dysregulation of N-glycosylation in haploid yeast cells leads to mitochondrial dysfunction |
| GO:0016020 membrane | IBA GO_REF:0000033 | MODIFY | Summary: is_active_in membrane, IBA from PANTHER PTN000060284. Correct but uninformative. The GPT family acts in the ER membrane. Reason: Make specific with ER membrane. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000060284 · PANTHER:PTN000060284 SUPPORTS TRANSFER The GPT clade node is sound. Only the location granularity is at issue. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:19129246 whose synthesis is sequentially catalyzed by the Alg7p GlcNAc phosphotransferase and by the dimeric Alg13p/Alg14p UDP-GlcNAc transferase on the cytosolic face of the endoplasmic reticulum |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: membrane, IEA from InterPro IPR000715 (glycosyl transferase family 4). Correct but uninformative. Reason: Make specific with ER membrane. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:19129246 whose synthesis is sequentially catalyzed by the Alg7p GlcNAc phosphotransferase and by the dimeric Alg13p/Alg14p UDP-GlcNAc transferase on the cytosolic face of the endoplasmic reticulum |
| GO:0016780 phosphotransferase activity, for other substituted phosphate groups | IEA GO_REF:0000002 | MODIFY | Summary: phosphotransferase activity, for other substituted phosphate groups, IEA from InterPro IPR000715 (GT4 / MraY-WecA family). This is the correct parent class but too general for Alg7, whose reaction is known. Reason: Make specific with EC 2.7.8.15 GlcNAc-1-P transferase. Proposed replacements: UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase activity Supporting Evidence: PMID:6096695 We identified a gene, ALG7, that is probably the structural gene for UDP-N-acetylglucosamine-1-P transferase, the enzyme inhibited by tunicamycin. |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IDA PMID:19129246 Hetero-oligomeric interactions between early glycosyltransfe... | ACCEPT | Summary: UDP-N-acetylglucosamine transferase complex, IDA from Noffz et al. 2009. Alg7 forms a hexameric complex (1:1:1) with Alg13 and Alg14, and this is the defining reference for the GO term. Supporting Evidence: PMID:19129246 Here, we show that the Alg7p, Alg13p, and Alg14p glycosyltransferases form a functional multienzyme complex. PMID:19129246 Alg7p:Alg13:Alg14p stoichiometry of 1:1:1 |
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Q: How is ALG7 expression or activity coupled to cell proliferation and to dolichyl-phosphate availability?
Experiment: Compare Alg7 kinetics alone and within a reconstituted Alg7/Alg13/Alg14 complex, and test whether GlcNAc-PP-Dol is channelled by measuring intermediate release.
UDP-N-acetyl-glucosamine-1-P transferase; transfers Glc-Nac-P from UDP-GlcNac to Dol-P in the ER in the first step of the dolichol pathway of protein asparagine-linked glycosylation; inhibited by tunicamycin; human homolog DPAGT1 can complement yeast ALG7 mutant
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