GLC3 and GHA1 of Saccharomyces cerevisiae are allelic and encode the glycogen branching enzyme.

Glycogen, a branched polymer of glucose, is a storage molecule whose accumulation is under rigorous nutritional control in many cells. We report the identification of two Saccharomyces cerevisiae genes, GLG1 and GLG2, whose products are implicated in the biogenesis of glycogen. These genes encode self-glucosylating proteins that in vitro can act as primers for the elongation reaction catalyzed by glycogen synthase. Over a region of 258 residues, the Glg proteins have 55% sequence identity to each other and ϳ33% identity to glycogenin, a mammalian protein postulated to have a role in the initiation of glycogen biosynthesis. Yeast cells defective in either GLG1 or GLG2 are similar to the wild type in their ability to accumulate glycogen. Disruption of both genes results in the inability of the cells to synthesize glycogen despite normal levels of glycogen synthase. These results suggest that a self-glucosylating protein is required for glycogen biosynthesis in a eukaryotic cell. The activation state of glycogen synthase in glg1 glg2 cells is suppressed, suggesting that the Glg proteins may additionally influence the phosphorylation state of glycogen synthase.

Section: Vol 15 1995 Self-glucosylating Proteins In Yeast Glycogen mentioning

confidence: 99%

“…The greatest divergence in sequence between the yeast and mammalian enzymes is at the NH 2 and COOH termini, which are implicated in the regulation by covalent phosphorylation (23). A single gene, GLC3, encodes a yeast homolog of glycogen branching enzyme (37,48).…”

mentioning

confidence: 99%

Requirement of the Self-Glucosylating Initiator Proteins Glg1p and Glg2p for Glycogen Accumulation in Saccharomyces cerevisiae

Cheng

Farkas

et al. 1995

“…Its biosynthesis requires several proteins, including the self-glucosylating initiator proteins Glg1 and Glg2 (6), the branching enzyme Glc3 (61,74), and glycogen synthase (15,16), which is generally considered to be the rate-limiting enzyme for glycogen accumulation. Yeast glycogen synthase is encoded by two closely related genes, GSY1 and GSY2, of which GSY2 appears to encode the dominant form, accounting for 90% of glycogen synthase activity at stationary phase (15,16).…”

mentioning

confidence: 99%

Cyclin Partners Determine Pho85 Protein Kinase Substrate Specificity In Vitro and In Vivo: Control of Glycogen Biosynthesis by Pcl8 and Pcl10

Huang

Moffat

Wilson

et al. 1998

118

135

In Saccharomyces cerevisiae, PHO85 encodes a cyclin-dependent protein kinase (Cdk) with multiple roles in cell cycle and metabolic controls. In association with the cyclin Pho80, Pho85 controls acid phosphatase gene expression through phosphorylation of the transcription factor Pho4. Pho85 has also been implicated as a kinase that phosphorylates and negatively regulates glycogen synthase (Gsy2), and deletion of PHO85 causes glycogen overaccumulation. We report that the Pcl8/Pcl10 subgroup of cyclins directs Pho85 to phosphorylate glycogen synthase both in vivo and in vitro. Disruption of PCL8 and PCL10 caused hyperaccumulation of glycogen, activation of glycogen synthase, and a reduction in glycogen synthase kinase activity in vivo. However, unlike pho85 mutants, pcl8 pcl10 cells had normal morphologies, grew on glycerol, and showed proper regulation of acid phosphatase gene expression. In vitro, Pho80-Pho85 complexes effectively phosphorylated Pho4 but had much lower activity toward Gsy2. In contrast, Pcl10-Pho85 complexes phosphorylated Gsy2 at Ser-654 and Thr-667, two physiologically relevant sites, but only poorly phosphorylated Pho4. Thus, both the in vitro and in vivo substrate specificity of Pho85 is determined by the cyclin partner. Mutation of PHO85 suppressed the glycogen storage deficiency of snf1 or glc7-1 mutants in which glycogen synthase is locked in an inactive state. Deletion of PCL8 and PCL10 corrected the deficit in glycogen synthase activity in both the snf1 and glc7-1 mutants, but glycogen synthesis was restored only in the glc7-1 mutant strain. This genetic result suggests an additional role for Pho85 in the negative regulation of glycogen accumulation that is independent of Pcl8 and Pcl10.

“…Its biosynthesis in yeast cells requires self-glucosylating initiator proteins, encoded by the GLG1 and GLG2 genes (8), branching enzyme encoded by GLC3/GHA1 (56,68), and glycogen synthase, which is encoded by two separate genes, GSY1 and GSY2 (14,15). GSY2 codes for the major nutritionally regulated form of the enzyme that accounts for ϳ90% of the activity in stationary phase (15).…”

mentioning

confidence: 99%

Pho85p, a Cyclin-Dependent Protein Kinase, and the Snf1p Protein Kinase Act Antagonistically To Control Glycogen Accumulation in Saccharomyces cerevisiae

Huang

Farkas

Roach

1996

118

In Saccharomyces cerevisiae, nutrient levels control multiple cellular processes. Cells lacking the SNF1 gene cannot express glucose-repressible genes and do not accumulate the storage polysaccharide glycogen. The impaired glycogen synthesis is due to maintenance of glycogen synthase in a hyperphosphorylated, inactive state. In a screen for second site suppressors of the glycogen storage defect of snf1 cells, we identified a mutant gene that restored glycogen accumulation and which was allelic with PHO85, which encodes a member of the cyclin-dependent kinase family. In cells with disrupted PHO85 genes, we observed hyperaccumulation of glycogen, activation of glycogen synthase, and impaired glycogen synthase kinase activity. In snf1 cells, glycogen synthase kinase activity was elevated. Partial purification of glycogen synthase kinase activity from yeast extracts resulted in the separation of two fractions by phenyl-Sepharose chromatography, both of which phosphorylated and inactivated glycogen synthase. The activity of one of these, GPK2, was inhibited by olomoucine, which potently inhibits cyclin-dependent protein kinases, and contained an ϳ36-kDa species that reacted with antibodies to Pho85p. Analysis of Ser-to-Ala mutations at the three potential Gsy2p phosphorylation sites in pho85 cells implicated Ser-654 and/or Thr-667 in PHO85 control of glycogen synthase. We propose that Pho85p is a physiological glycogen synthase kinase, possibly acting downstream of Snf1p.