ALG5 is an endoplasmic reticulum membrane glycosyltransferase of the GT2 family (dolichyl-phosphate beta-glucosyltransferase, Dol-P-Glc synthase, EC 2.4.1.117). Anchored in the ER membrane by an N-terminal hydrophobic segment, with its catalytic domain facing the cytosol, it transfers glucose from cytosolic UDP-glucose to dolichyl phosphate to form dolichyl beta-D-glucosyl phosphate (Dol-P-Glc). After translocation to the lumenal leaflet, Dol-P-Glc is the glucose donor used by ALG6, ALG8 and ALG10 to add the three terminal glucoses that complete the Glc3Man9GlcNAc2-PP-dolichol precursor of asparagine-linked glycans. Human ALG5 partially complements the hypoglycosylation of yeast alg5 mutants. Monoallelic loss-of-function ALG5 variants cause an autosomal dominant polycystic kidney disease with interstitial fibrosis (PKD7); ALG5 haploinsufficiency alters N-glycan synthesis in renal epithelial cells and impairs maturation and ciliary delivery of polycystin-1.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004581 dolichyl-phosphate beta-glucosyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference from node PTN001653583 of PTHR10859, seeded by experimental annotations of S. cerevisiae ALG5, S. pombe alg5, Drosophila, several Trichomonas members and human ALG5 itself. Human ALG5 belongs to subfamily PTHR10859:SF91 (dolichyl-phosphate beta-glucosyltransferase), the same subfamily as yeast ALG5 (P40350) and fission yeast alg5 (O60061), so it lies inside the clade that inherited Dol-P-Glc synthase activity. Reason: Core catalytic activity. The IBA node placement is sound (the target is in the ALG5 subfamily, separate from the DPM1-type mannosyltransferase subfamilies of PTHR10859), and the activity is independently supported for the human protein by complementation of yeast alg5 and by curated UniProt catalytic activity. Human ALG5 appearing among the seeds reflects its own experimental grounding. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt Dolichyl-phosphate beta-glucosyltransferase produces dolichyl beta-D-glucosyl phosphate/Dol-P-Glc, PMID:10359825 Expression of the humanALG5andALG6cDNA partially complemented the respective yeast mutations, as shown by the improved glycosylation of CPY |
| GO:0005789 endoplasmic reticulum membrane | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference from the eukaryote-level node PTN000092356 that members act in the ER membrane. Reason: ALG5 is an ER-resident membrane enzyme; ER membrane is its core location. Correct and conserved across the dolichol-phosphate glycosyltransferase clade. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:35896117 ALG5 encodes an endoplasmic-reticulum-resident enzyme required for addition of glucose molecules to the assembling N-glycan precursors. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference (node PTN001653583) that ALG5-subfamily members participate in dolichol-linked oligosaccharide (LLO) biosynthesis. ALG5 catalyses formation of Dol-P-Glc, the lipid-linked donor for the three terminal glucosylation steps of the LLO. Reason: Core process. ALG5 does catalytic work within the LLO pathway (synthesis of the Dol-P-Glc donor consumed by ALG6/ALG8/ALG10), which Reactome places inside N-glycan precursor biosynthesis; this is participation, not mere necessity. GO:0006488 is the most specific process term available and is a descendant of protein N-linked glycosylation. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt donor substrate used sequentially by ALG6, ALG8 and ALG10 to add Reactome:R-HSA-480985 Dolichyl-phosphate-glucose functions as a donor of glucose groups in reactions including three steps of N-glycan precursor biosynthesis. |
| GO:0004581 dolichyl-phosphate beta-glucosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated assignment from EC 2.4.1.117 / RHEA:15401, matching the curated catalytic activity of human ALG5. Reason: The EC/Rhea-to-GO mapping is correct for this protein and agrees with the IBA, TAS and IGI rows for the same term. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt a di-trans,poly-cis-dolichyl phosphate + UDP-alpha-D-glucose = |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Automated assignment from the UniProt subcellular location vocabulary (SL-0097). Reason: Correct core location, consistent with the other ER membrane rows. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005515 protein binding | IPI PMID:32353859 A SARS-CoV-2 protein interaction map reveals targets for dru... | REMOVE | Summary: IntAct record of an interaction with SARS-CoV-2 ORF3a (P0DTC3) from an affinity-purification mass-spectrometry virus-host interactome. Reason: Bare protein binding carries no functional information (repo protein-binding policy). The interaction is with a viral protein in an overexpression screen and says nothing about ALG5's endogenous activity; no more informative MF term is supported by the paper. Removal does not mean the interaction is false. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt Q9Y673; P0DTC3: 3a; Xeno; NbExp=4 |
| GO:0005515 protein binding | IPI PMID:32838362 Virus-Host Interactome and Proteomic Survey Reveal Potential... | REMOVE | Summary: IntAct record of the ALG5-SARS-CoV-2 ORF3a (P0DTC3) interaction from a virus-host interactome and proteomic survey. ALG5 is not named in the cached main text (presumably in supplementary data). Reason: Bare protein binding with a viral protein from a high-throughput screen; uninformative about ALG5 function (repo protein-binding policy). Removal does not dispute the interaction. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt Q9Y673; P0DTC3: 3a; Xeno; NbExp=4 |
| GO:0005515 protein binding | IPI PMID:33060197 Comparative host-coronavirus protein interaction networks re... | REMOVE | Summary: IntAct record of the ALG5-SARS-CoV-2 ORF3a (P0DTC3) interaction from a comparative host-coronavirus interactome. Reason: Bare protein binding with a viral protein from a high-throughput screen; uninformative about ALG5 function (repo protein-binding policy). Removal does not dispute the interaction. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt Q9Y673; P0DTC3: 3a; Xeno; NbExp=4 |
| GO:0005515 protein binding | IPI PMID:36217030 A comprehensive SARS-CoV-2-human protein-protein interactome... | REMOVE | Summary: IntAct record of the ALG5-SARS-CoV-2 ORF3a (P0DTC3) interaction from a SARS-CoV-2-human interactome. Reason: Bare protein binding with a viral protein from a high-throughput screen; uninformative about ALG5 function (repo protein-binding policy). Removal does not dispute the interaction. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt Q9Y673; P0DTC3: 3a; Xeno; NbExp=4 |
| GO:0006487 protein N-linked glycosylation | TAS Reactome:R-HSA-480985 | MODIFY | Summary: Reactome assertion that ALG5 participates in protein N-linked glycosylation, through synthesis of the Dol-P-Glc donor used in N-glycan precursor biosynthesis. Reason: True but less specific than the evidence supports. ALG5's catalytic contribution is to assembly of the lipid-linked precursor, captured by GO:0006488 dolichol-linked oligosaccharide biosynthetic process (an is_a/part_of descendant of GO:0006487 that the gene already carries by IBA and IMP). ALG5 does not act on protein; oligosaccharyltransferase performs the transfer to asparagine. Proposed replacements: dolichol-linked oligosaccharide biosynthetic process Supporting Evidence: Reactome:R-HSA-480985 Dolichyl-phosphate-glucose functions as a donor of glucose groups in reactions including three steps of N-glycan precursor biosynthesis. |
| GO:0004581 dolichyl-phosphate beta-glucosyltransferase activity | TAS Reactome:R-HSA-446214 | ACCEPT | Summary: Reactome reaction in which ALG5 converts cytosolic UDP-glucose and dolichyl phosphate to Dol-P-Glc on the cytosolic face of the ER membrane. Reason: Core catalytic activity, consistent with all other rows for this term. Supporting Evidence: Reactome:R-HSA-446214 catalyzes the reaction of cytosolic UDP-glucose with dolichyl phosphate exposed on the cytosolic face of the ER membrane to form Dolichyl-P-glucose |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:10359825 A mutation in the human ortholog of the Saccharomyces cerevi... | ACCEPT | Summary: Experimental ER-membrane localization attributed to Imbach et al. 1999, which cloned human ALG5 and showed it complements yeast alg5. The cached full text contains no direct localization experiment for ALG5 (the paper reports cloning, Northern blots, patient sequencing and yeast complementation), so the localization is inferred from the yeast complementation context rather than imaged. Reason: The location is correct and core; independent support comes from Lemoine et al. 2022 (ER-resident enzyme) and the conserved ER-membrane location of the ALG5 subfamily. The claim, not the evidence code, is what is judged here. Supporting Evidence: PMID:35896117 ALG5 encodes an endoplasmic-reticulum-resident enzyme Reactome:R-HSA-446214 Dolichyl-phosphate beta-glucosyltransferase (ALG5) associated with the endoplasmic reticulum (ER) membrane |
| GO:0098554 cytoplasmic side of endoplasmic reticulum membrane | IGI PMID:10359825 A mutation in the human ortholog of the Saccharomyces cerevi... | ACCEPT | Summary: ALG5 acts on the cytoplasmic face of the ER membrane, where it uses cytosolic UDP-glucose. The cited paper does not itself test topology; the orientation follows from the cytosolic catalytic domain predicted by UniProt (residues 29-324 cytoplasmic), the Reactome reaction, and yeast Alg5 topology work summarized in the deep research. Reason: Correct and more informative than bare ER membrane; the side of catalysis is well supported by the reaction chemistry (cytosolic nucleotide-sugar donor) and topology. Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt most probably active on the cytoplasmic side of the endoplasmic Reactome:R-HSA-446214 dolichyl phosphate exposed on the cytosolic face of the ER membrane file:human/ALG5/ALG5-deep-research-falcon.md Its use of cytosolic UDP-glucose and synthesis of dolichyl-phosphate glucose place the catalytic reaction on the |
| GO:0098556 cytoplasmic side of rough endoplasmic reticulum membrane | IGI PMID:10359825 A mutation in the human ortholog of the Saccharomyces cerevi... | MODIFY | Summary: Asserts activity on the cytoplasmic side of the rough ER membrane specifically. Reason: Nothing in the cited paper, UniProt or Reactome distinguishes rough from smooth ER for ALG5; the rough-ER qualifier is more specific than the evidence. The supported claim is the parent GO:0098554 cytoplasmic side of endoplasmic reticulum membrane, which the gene already carries from the same reference. Proposed replacements: cytoplasmic side of endoplasmic reticulum membrane Supporting Evidence: file:human/ALG5/ALG5-uniprot.txt most probably active on the cytoplasmic side of the endoplasmic |
| GO:0006487 protein N-linked glycosylation | IMP PMID:10359825 A mutation in the human ortholog of the Saccharomyces cerevi... | MODIFY | Summary: Human ALG5 cDNA partially restored glycosylation of the reporter glycoprotein CPY in an alg5 yeast deletion strain, showing the human enzyme functions in the N-glycosylation pathway. Reason: The experiment is sound but the claim it supports is ALG5's contribution to lipid-linked oligosaccharide completion (alg5 cells lack glucosylated LLO, which lowers oligosaccharyltransferase efficiency); ALG5 does not act on protein. Replace with the more specific descendant GO:0006488, already carried by this gene from the same paper and by IBA. Consistent with the action on the Reactome TAS row for the same term. Proposed replacements: dolichol-linked oligosaccharide biosynthetic process Supporting Evidence: PMID:10359825 A deficiency in glycosylation of the lipid-linked oligosaccharide results in the incomplete glycosylation of glycoprotein because of the decreased affinity of the oligosaccharyltransferase toward the incomplete substrate. |
| GO:0004581 dolichyl-phosphate beta-glucosyltransferase activity | IGI PMID:10359825 A mutation in the human ortholog of the Saccharomyces cerevi... | ACCEPT | Summary: Complementation of the S. cerevisiae alg5 deletion (P40350) by human ALG5 cDNA, restoring CPY glycosylation, supports human ALG5 as the functional Dol-P-Glc synthase. Reason: Experimental support for the core catalytic activity of the human protein; UniProt cites this paper for the EC 2.4.1.117 catalytic activity. Supporting Evidence: PMID:10359825 Expression of the humanALG5andALG6cDNA partially complemented the respective yeast mutations, as shown by the improved glycosylation of CPY |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:10359825 A mutation in the human ortholog of the Saccharomyces cerevi... | ACCEPT | Summary: Complementation of yeast alg5 (which accumulates non-glucosylated Man9GlcNAc2-PP-Dol) by human ALG5 supports a role in completing the lipid-linked oligosaccharide. Reason: Core process, consistent with the IBA row for the same term. Supporting Evidence: PMID:10359825 An analogous accumulation of Man9GlcNAc2-PP-Dol has been described inalg5andalg6 Saccharomyces cerevisiaemutant strains file:human/ALG5/ALG5-uniprot.txt donor substrate used sequentially by ALG6, ALG8 and ALG10 to add |
| GO:0016020 membrane | HDA PMID:19946888 Defining the membrane proteome of NK cells. | MODIFY | Summary: High-throughput mass-spectrometry detection of ALG5 in a membrane-proteome preparation from NK (YTS) cells. Reason: Correct but far less specific than the supported location. Replace with GO:0005789 endoplasmic reticulum membrane, which the gene already carries from IBA, EXP, IEA and TAS rows. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:19946888 identified 1843 proteins with high confidence scores |
| GO:0005789 endoplasmic reticulum membrane | TAS Reactome:R-HSA-446214 | ACCEPT | Summary: Reactome assertion that ALG5 is associated with the ER membrane. Reason: Correct core location, consistent with the other ER membrane rows. Supporting Evidence: Reactome:R-HSA-446214 Dolichyl-phosphate beta-glucosyltransferase (ALG5) associated with the endoplasmic reticulum (ER) membrane |
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Download this section (compressed HTML)Q: Does isoform 2 (Q9Y673-2), which lacks residues 95-124 within the GT2 catalytic domain including the conserved 108-VVDDGSKD-115 stretch, retain any Dol-P-Glc synthase activity, or is it a non-catalytic product?
Q: How is Dol-P-Glc, made on the cytosolic face, translocated to the lumenal leaflet, and does ALG5 associate with the flippase or with the lumenal glucosyltransferases?
Q: Why is renal epithelium particularly sensitive to ALG5 haploinsufficiency, given that other tissues of PKD7 carriers show no overt glycosylation defect?
Experiment: Reconstitute purified recombinant human ALG5 (canonical 324-aa isoform and isoform 2) with dolichyl phosphate and UDP-glucose to measure Dol-P-Glc synthase kinetics, and test the PKD7 missense variants (R208H, R212H) and the R79W variant for loss of catalytic activity.
Hypothesis: PKD7-associated ALG5 missense variants reduce or abolish Dol-P-Glc synthase activity, and isoform 2 is catalytically inactive.
Experiment: Use protease-protection or glycosylation-reporter topology mapping of tagged human ALG5 in mammalian cells to confirm the cytosolic orientation of the catalytic domain.
Hypothesis: The human ALG5 catalytic domain faces the cytosol, as predicted and as shown for yeast Alg5.
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