GLG1 (YKR058W) encodes glycogenin-1, one of two partially redundant self-glucosylating initiator proteins (with GLG2) for glycogen synthesis in Saccharomyces cerevisiae. A GT8-family glucosyltransferase (EC 2.4.1.186), it uses UDP-glucose to attach glucose to its own tyrosine residues (Tyr232 and Tyr600 are implicated in vivo) and extends the attached chain by alpha-1,4 linkages, producing the protein-bound oligosaccharide primer that glycogen synthase (Gsy1/Gsy2) elongates. Either GLG1 or GLG2 alone supports near-normal glycogen accumulation, but the glg1 glg2 double mutant makes no glycogen despite normal glycogen synthase levels. Glg1 is cytosolic and associates with glycogen synthase; it is induced at the diauxic transition.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:18467557 An in vivo map of the yeast protein interactome. | REMOVE | Summary: Genome-wide DHFR protein-fragment complementation (Tarassov et al. 2008) detected Glg1-Gsy2 proximity in vivo. This reflects the glycogenin-glycogen synthase partnership on the nascent glycogen particle. Reason: The interaction with glycogen synthase is biologically plausible (glycogenin serves as the GS primer substrate) but 'protein binding' conveys no function; there is no more specific GO MF term for this partnership; removal does not mean the interaction is false. Supporting Evidence: PMID:8524228 These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase |
| GO:0005515 protein binding | IPI PMID:28183979 Gene duplication can impart fragility, not robustness, in th... | REMOVE | Summary: PCA re-measurement of the Glg1-Gsy2 interaction in a paralog-deletion study (Diss et al. 2017); same uninformative binding term. Reason: The interaction with glycogen synthase is biologically plausible (glycogenin serves as the GS primer substrate) but 'protein binding' conveys no function; there is no more specific GO MF term for this partnership; removal does not mean the interaction is false. Supporting Evidence: PMID:8524228 These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase |
| GO:0005515 protein binding | IPI PMID:37968396 The social and structural architecture of the yeast protein ... | REMOVE | Summary: Large-scale interactome (Michaelis et al. 2023) recovering Glg1-Gsy2; consistent with the known substrate relationship between glycogenin and glycogen synthase. Reason: The interaction with glycogen synthase is biologically plausible (glycogenin serves as the GS primer substrate) but 'protein binding' conveys no function; there is no more specific GO MF term for this partnership; removal does not mean the interaction is false. Supporting Evidence: PMID:8524228 These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT is_active_in cytoplasm for the glycogenin clade (PTN000127027); appropriate, glycogen is made in the cytosol. Supporting Evidence: PMID:38832010 glycogen is synthesized in the cytosol by glycogenins (Glg1, Glg2), glycogen synthases (Gsy1, Gsy2), and glycogen branching enzyme (Glc3) in a concerted manner |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping (cytoplasm), itself by similarity to Komagataella Glg (C4R941). Correct for a cytosolic glycogen-priming enzyme. Supporting Evidence: PMID:38832010 glycogen is synthesized in the cytosol by glycogenins (Glg1, Glg2), glycogen synthases (Gsy1, Gsy2), and glycogen branching enzyme (Glc3) in a concerted manner |
| GO:0005737 cytoplasm | ISS GO_REF:0000024 | ACCEPT | Summary: ISS is_active_in cytoplasm from Komagataella phaffii glycogenin C4R941; consistent with cytosolic glycogen synthesis in S. cerevisiae. Supporting Evidence: PMID:38832010 glycogen is synthesized in the cytosol by glycogenins (Glg1, Glg2), glycogen synthases (Gsy1, Gsy2), and glycogen branching enzyme (Glc3) in a concerted manner |
| GO:0005737 cytoplasm | ISS GO_REF:0000024 | ACCEPT | Summary: ISS located_in cytoplasm from C4R941; duplicate qualifier variant of the row above; correct. Supporting Evidence: PMID:38832010 glycogen is synthesized in the cytosol by glycogenins (Glg1, Glg2), glycogen synthases (Gsy1, Gsy2), and glycogen branching enzyme (Glc3) in a concerted manner |
| GO:0005773 vacuole | IEA GO_REF:0000044 | MARK AS OVER ANNOTATED | Summary: UniProt SubCell 'Vacuole' propagated from Komagataella C4R941, where glycogenin reaches the vacuole as cargo of nitrogen-starvation glycophagy. The vacuole is a degradation destination of the glycogen particle, not where glycogenin acts; in S. cerevisiae glycogen is a non-preferred autophagic cargo delivered only late. Reason: Location as autophagic cargo, not a functional site; transferred from another species. Supporting Evidence: file:yeast/GLG1/GLG1-uniprot.txt starvation-induced glycophagy (autophagy of glycosomes). |
| GO:0005773 vacuole | ISS GO_REF:0000024 | MARK AS OVER ANNOTATED | Summary: Same Komagataella-based transfer of vacuolar (glycophagy cargo) localisation; not a site of Glg1 activity. Reason: Cargo-of-autophagy localisation transferred by similarity. Supporting Evidence: file:yeast/GLG1/GLG1-uniprot.txt starvation-induced glycophagy (autophagy of glycosomes). |
| GO:0005829 cytosol | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways glycogen biosynthesis (PWY3O-4031) is cytosolic; correct for Glg1. Supporting Evidence: PMID:38832010 glycogen is synthesized in the cytosol by glycogenins (Glg1, Glg2), glycogen synthases (Gsy1, Gsy2), and glycogen branching enzyme (Glc3) in a concerted manner |
| GO:0005978 glycogen biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA rule for glycogen biosynthetic process; correct for a glycogenin. Supporting Evidence: PMID:8524228 Disruption of both genes results in the inability of the cells to synthesize glycogen despite normal levels of glycogen synthase |
| GO:0005978 glycogen biosynthetic process | IGI PMID:8524228 Requirement of the self-glucosylating initiator proteins Glg... | ACCEPT | Summary: glg1 glg2 double mutants cannot synthesise glycogen although glycogen synthase is present; Glg1 catalyses the priming step of synthesis, redundantly with Glg2. Supporting Evidence: PMID:8524228 Disruption of both genes results in the inability of the cells to synthesize glycogen despite normal levels of glycogen synthase PMID:8524228 Yeast cells defective in either GLG1 or GLG2 are similar to the wild type in their ability to accumulate glycogen PMID:8900126 In Glg1p, two Tyr residues are implicated, Tyr232 and Tyr600, mutation of both being required to eliminate glycogen accumulation in vivo |
| GO:0005978 glycogen biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways assignment of Glg1 to glycogen biosynthesis; correct. Supporting Evidence: PMID:38832010 glycogen is synthesized in the cytosol by glycogenins (Glg1, Glg2), glycogen synthases (Gsy1, Gsy2), and glycogen branching enzyme (Glc3) in a concerted manner |
| GO:0008466 glycogenin glucosyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT propagation of glycogenin glucosyltransferase activity from human/mouse/rat glycogenins and both yeast Glg proteins. Sound. Supporting Evidence: PMID:8524228 These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase |
| GO:0008466 glycogenin glucosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA, RHEA:23360 and RHEA:56560, EC 2.4.1.186); correct. Supporting Evidence: file:yeast/GLG1/GLG1-uniprot.txt Reaction=L-tyrosyl-[glycogenin] + UDP-alpha-D-glucose = alpha-D- |
| GO:0008466 glycogenin glucosyltransferase activity | IGI PMID:8524228 Requirement of the self-glucosylating initiator proteins Glg... | ACCEPT | Summary: Cheng et al. showed the Glg proteins are self-glucosylating primers that glycogen synthase can elongate, and that loss of both genes abolishes glycogen; the activity assignment is supported. Supporting Evidence: PMID:8524228 These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase PMID:8524228 Disruption of both genes results in the inability of the cells to synthesize glycogen despite normal levels of glycogen synthase |
| GO:0008466 glycogenin glucosyltransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways assigns both EC 2.4.1.186 half-reactions (self-glucosylation of Tyr and alpha-1,4 extension of the glucosyl-glycogenin) to Glg1; consistent with the Rhea reactions in UniProt. Supporting Evidence: file:yeast/GLG1/GLG1-uniprot.txt Reaction=L-tyrosyl-[glycogenin] + UDP-alpha-D-glucose = alpha-D- |
| GO:0016757 glycosyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from IPR002495 (GT8 family) gives generic glycosyltransferase activity; correct but uninformative. Reason: Use the specific glycogenin glucosyltransferase activity. Proposed replacements: glycogenin glucosyltransferase activity Supporting Evidence: PMID:8524228 These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase |
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Download this section (compressed HTML)Q: Why does glycogen synthase activation state fall in glg1 glg2 cells: is the primer needed to retain Gsy2 on glycogen and protect it from inhibitory phosphorylation?
Q: Do Glg1 and Glg2 differ in timing, abundance or primer length such that one dominates under particular conditions?
Glycogenin glucosyltransferase; self-glucosylating initiator of glycogen synthesis, also glucosylates n-dodecyl-beta-D-maltoside; SWAT-GFP and mCherry fusion proteins localize to the cell periphery and vacuole respectively; similar to mammalian glycogenin; GLG1 has a paralog, GLG2, that arose from the whole genome duplication
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