GLG2

UniProt ID: P47011
Organism: Saccharomyces cerevisiae S288C
Review Status: COMPLETE
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Gene Description

GLG2 (YJL137C) encodes glycogenin-2, the second of two partially redundant self-glucosylating initiator proteins (with GLG1) for glycogen synthesis in Saccharomyces cerevisiae. A GT8-family glucosyltransferase (EC 2.4.1.186), purified Glg2 transfers glucose from UDP-glucose onto its own Tyr230 and Tyr232 and extends the attached chain to an alpha-1,4-linked oligosaccharide; it can also glucosylate exogenous acceptors. The protein-bound primer is elongated by glycogen synthase (Gsy1/Gsy2) and Glg2 remains covalently associated with the high-molecular-weight glycogen fraction. Either GLG gene alone supports glycogen accumulation, whereas the glg1 glg2 double mutant makes no glycogen. Glg2 is cytosolic and interacts with glycogen synthase Gsy2.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0005737 cytoplasm
HDA
PMID:14562095
Global analysis of protein localization in budding yeast. 		ACCEPT
Summary: Genome-wide GFP screen scored Glg2 as cytoplasmic; consistent with cytosolic glycogen synthesis.
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
IBA
GO_REF:0000033 		ACCEPT
Summary: PAINT is_active_in cytoplasm for the glycogenin clade (PTN000127027); appropriate.
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); 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:0005737 cytoplasm
ISS
GO_REF:0000024 		ACCEPT
Summary: ISS is_active_in cytoplasm from Komagataella glycogenin C4R941; consistent with the GFP data for Glg2.
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; 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 during nitrogen-starvation glycophagy. This is a degradation destination of the glycogen particle, not where Glg2 acts.
Reason: Location as autophagic cargo, transferred from another species; not a functional site.
Supporting Evidence:
file:yeast/GLG2/GLG2-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 Glg2 activity.
Reason: Cargo-of-autophagy localisation transferred by similarity.
Supporting Evidence:
file:yeast/GLG2/GLG2-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 Glg2.
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 make glycogen despite normal glycogen synthase; Glg2 performs the priming step, redundantly with Glg1.
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
GO:0005978 glycogen biosynthetic process
RCA
GO_REF:0000123 		ACCEPT
Summary: YeastPathways assignment 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 (PTN000127027); Glg2 is one of the experimentally characterised members of the clade.
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:8900126
In Glg2p, mutation of both Tyr230 and Tyr232 is necessary to suppress self-glucosylation of purified protein in vitro
GO:0008466 glycogenin glucosyltransferase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Combined IEA (ARBA, RHEA:23360/RHEA:56560, EC 2.4.1.186); correct.
Supporting Evidence:
file:yeast/GLG2/GLG2-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: Genetic interaction data from Cheng et al. together with in vitro self-glucosylation of Glg proteins; supports the activity. Direct biochemical evidence for Glg2 (self-glucosylation on Tyr230/Tyr232, mass-spectrometric mapping) exists in later papers.
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:8900126
In Glg2p, mutation of both Tyr230 and Tyr232 is necessary to suppress self-glucosylation of purified protein in vitro
PMID:15479227
MS/MS spectra revealed that glucosyl residues were attached to both Tyr232 and Tyr230 within the same peptide
GO:0008466 glycogenin glucosyltransferase activity
RCA
GO_REF:0000123 		ACCEPT
Summary: YeastPathways assigns both EC 2.4.1.186 half-reactions (initial Tyr glucosylation and chain extension) to Glg2; matches the biochemistry.
Supporting Evidence:
PMID:15479227
MS/MS spectra revealed that glucosyl residues were attached to both Tyr232 and Tyr230 within the same peptide
GO:0016757 glycosyltransferase activity
IEA
GO_REF:0000002 		MODIFY
Summary: InterPro2GO from IPR002495 (GT8) gives generic glycosyltransferase activity; correct but uninformative.
Reason: Use the specific 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

Core Functions

Self-glucosylating glycogenin: glucosylates its own Tyr230/Tyr232 from UDP-glucose and extends an alpha-1,4 oligoglucan primer that glycogen synthase elongates (redundant with Glg1).

Molecular Function:
glycogenin glucosyltransferase activity
Directly Involved In:
glycogen biosynthetic process
Cellular Locations:
cytosol
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
  • PMID:8900126
    In Glg2p, mutation of both Tyr230 and Tyr232 is necessary to suppress self-glucosylation of purified protein in vitro
  • PMID:15479227
    MS/MS spectra revealed that glucosyl residues were attached to both Tyr232 and Tyr230 within the same peptide
  • PMID:8900126
    Glg2p was shown to be associated with carbohydrate in vivo and was released from the high molecular weight glycogen fraction by treatment with alpha-amylase

References

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Suggested Questions for Experts

Q: Glg2 needs multiple tyrosines (Tyr230, Tyr232, and the C-terminal Tyr367 region) for function unlike mammalian glycogenin; does each glycogen particle carry one or several primers?

Deep Research

SGD

(GLG2-deep-research-sgd.md)
SGD gene description for GLG2 (yeast) SGD

SGD gene description for GLG2 (yeast)

Glycogenin glucosyltransferase; self-glucosylating initiator of glycogen synthesis, also glucosylates n-dodecyl-beta-D-maltoside; similar to mammalian glycogenin; GLG2 has a paralog, GLG1, that arose from the whole genome duplication

📚 Additional Documentation

Notes

(GLG2-notes.md)

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