Regulation of glycogen metabolism in yeast and bacteria (original) (raw)
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Molecular & Cellular Proteomics, 2002
At the onset of nutrient limitation, the yeast Saccharomyces cerevisiae synthesizes glycogen to serve as a carbon and energy reserve. We undertook a systematic survey for the genes that affect glycogen accumulation by taking advantage of the strain deletion set generated by the Saccharomyces Genome Deletion Project. The strain collection analyzed contained some 4600 diploid homozygous null deletants, representing ϳ88% of all viable haploid disruptants. We identified 324 strains with low and 242 with elevated glycogen stores, accounting for 12.4% of the genes analyzed. The screen was validated by the identification of many of the genes known already to influence glycogen accumulation. Many of the mutants could be placed into coherent families. For example, 195 or 60% of the hypoaccumulators carry mutations linked to respiratory function, a class of mutants well known to be defective in glycogen storage. The second largest group consists of ϳ60 genes involved in vesicular trafficking and vacuolar function, including genes encoding 13 of 17 proteins involved in the structure or assembly of the vacuolar ATPase. These data are consistent with our recent findings that the process of autophagy has a significant impact on glycogen storage (Wang, Z., Wilson, W. A., Fujino, M. A., and Roach, P. J. (2001) Antagonistic controls of autophagy and glycogen accumulation by Snf1p, the yeast homolog of AMP-activated protein kinase, and the cyclin-dependent kinase Pho85p. Mol. Cell. Biol. 21, 5742-5752). Autophagy delivers glycogen to the vacuole, and we propose that the impaired vacuolar function associated with ATPase mutants (vma10 or vma22) results in reduced degradation and subsequent hyperaccumulation of glycogen. Molecular & Cellular Proteomics 1: 232-242, 2002.
Glycogen synthesis in the absence of glycogenin in the yeast Saccharomyces cerevisiae
FEBS Letters, 2005
In eukaryotic cells, glycogenin is a self-glucosylating protein that primes glycogen synthesis. In yeast, the loss of function of GLG1 and GLG2, which encode glycogenin, normally leads to the inability of cells to synthesize glycogen. In this report, we show that a small fraction of colonies from glg1glg2 mutants can switch on glycogen synthesis to levels comparable to wild-type strain. The occurrence of glycogen positive glg1glg2 colonies is strongly enhanced by the presence of a hyperactive glycogen synthase and increased even more upon deletion of TPS1. In all cases, this phenotype is reversible, indicating the stochastic nature of this synthesis, which is furthermore illustrated by colour-sectoring of colonies upon iodine-staining. Altogether, these data suggest that glycogen synthesis in the absence of glycogenin relies on a combination of several factors, including an activated glycogen synthase and as yet unknown alternative primers whose synthesis and/or distribution may be controlled by TPS1 or under epigenetic silencing.
Microbiology, 2000
Mutant strains of Saccharomyces cerevisiae defective in respiration have been reported to be unable to store glycogen, as revealed by the iodine-staining method. In this report, it is shown that in contrast to this claim, mitochondrial respiratory mutants accumulated even more glycogen than wild-type cells during the fermentative growth on glucose. However, as soon as glucose was exhausted in the medium, these mutants readily and completely mobilized their glycogen content, contrary to wild-type cells which only transiently degraded this polymer. The mobilization of glycogen was a specific trait resulting from a defect in mitochondrial function that could not be suppressed by mutations in the cAMP-and Pho85 protein kinase-dependent nutrientsensing pathways, and by other mutations which favour glycogen synthesis. To account for this mobilization, it was found that respiration-defective cells not only contained a less active glycogen synthase, but also a more active glycogen phosphorylase. Since glucose 6-phosphate (Glc6P) is a potent inhibitor of the phosphorylation and an activator of the dephosphorylation processes of glycogen synthase and glycogen phosphorylase, it is suggested that the drop in Glc6P observed at the onset of glucose depletion in respiration-deficient cells triggers this rapid and sustained glycogen mobilization. It is also proposed that this degradation provides the energy for the viability of respiratory mutants in glucose-starved medium.
European Journal of Biochemistry, 1988
The addition of glucose to a suspension of yeast initiated glycogen synthesis and ethanol formation. Other effects of the glucose addition were a transient rise in the concentration of cyclic AMP and a more prolonged increase in the concentration of hexose 6-monophosphate and of fructose 2,6-bisphosphate. The activity of glycogen synthase increased about 4-fold and that of glycogen phosphorylase decreased 3 -5-fold. These changes could be reversed by the removal of glucose from the medium and induced again by a new addition of the sugar. These effects of glucose were also obtained with glucose derivatives known to form the corresponding 6phosphoester. Similar changes in glycogen synthase and glycogen phosphorylase activity were induced by glucose in a thermosensitive mutant deficient in adenylate cyclase (cdc35) when incubated at the permissive temperature of 26"C, but were much more pronounced at the nonpermissive temperature of 35°C. Under the latter condition, glycogen synthase was nearly fully activated and glycogen phosphorylase fully inactivated. Such large effects of glucose were, however, not seen in another adenylate-cyclase-deficient mutant (cyrl), able to incorporate exogenous cyclic AMP.
The subcellular localization of yeast glycogen synthase is dependent upon glycogen content
Canadian Journal of Microbiology, 2010
The budding yeast, Saccharomyces cerevisiae , accumulates the storage polysaccharide glycogen in response to nutrient limitation. Glycogen synthase, the major form of which is encoded by the GSY2 gene, catalyzes the key regulated step in glycogen storage. Here, we utilized Gsy2p fusions to green fluorescent protein (GFP) to determine where glycogen synthase was located within cells. We demonstrated that the localization pattern of Gsy2-GFP depended upon the glycogen content of the cell. When glycogen was abundant, Gsy2-GFP was found uniformly throughout the cytoplasm, but under low glycogen conditions, Gsy2-GFP localized to discrete spots within cells. Gsy2p is known to bind to glycogen, and we propose that the subcellular distribution of Gsy2-GFP reflects the distribution of glycogen particles. In the absence of glycogen, Gsy2p translocates into the nucleus. We hypothesize that Gsy2p is normally retained in the cytoplasm through its interaction with glycogen particles. When glycoge...
1995
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.
Molecular analysis of GPH1, the gene encoding glycogen phosphorylase in Saccharomyces cerevisiae
Molecular and cellular biology, 1989
In yeast cells, the activity of glycogen phosphorylase is regulated by cyclic AMP-mediated phosphorylation of the enzyme. We have previously cloned the gene for glycogen phosphorylase (GPH1) in Saccharomyces cerevisiae. To assess the role of glycogen and phosphorylase-catalyzed glycogenolysis in the yeast life cycle, yeast strains lacking a functional GPH1 gene or containing multiple copies of the gene were constructed. GPH1 was found not to be an essential gene in yeast cells. Haploid cells disrupted in GPH1 lacked phosphorylase activity and attained higher levels of intracellular glycogen but otherwise were similar to wild-type cells. Diploid cells homozygous for the disruption were able to sporulate and give rise to viable ascospores. Absence of functional GPH1 did not impair cells from synthesizing and storing trehalose. Increases in phosphorylase activity of 10- to 40-fold were detected in cells carrying multiple copies of GPH1-containing 2 microns plasmid. Northern (RNA) analy...
Glycerol Metabolism in Yeasts. Pathways of Utilization and Production
European Journal of Biochemistry, 1968
The utilization of glycerol by Candida utilis has been studied. It has been found that this yeast has a permeability for glycerol and other three carbon compounds much greater than that of baker's yeast. This permeability allows the entrance of glycerol in Candida cells rapidly enough to permit its efficient utilization even at low concentrations. The inducibility of glycerol kinase has been established. An increase in the concentration of the mitochondria1 L-a-glycerophosphate oxidase when the yeast is grown on glycerol has also been observed. A model is presented for the substrate specificity pattern of glycerol kinase of C. mycoderma. It postulates the involvement of three hydroxyl groups in the spatial distribution corresponding to the formation of L-a-glycerophosphate from glycerol. This requirement can be met by aldoand ketotrioses in their respective hydrated forms. The pathway of glycerol formation in S. cerevisim-has also been studied. Evidence is shown of the existence of a NADH dependent enzymatic activity reducing triose phosphate to oc-glycerophosphate which can roughly account for the glycerol production. A low ionic strength seems to be required for the activity of this enzyme. The a-glycerophosphatase is specific for the L form, the efficiency of a-glycerophosphatase on D-a-glycerophosphate being 1/30 of that on L-a-glycerophosphate. The concentration of the a-glycerophosphatase in yeasts is higher when grown on hexoses than when grown on non-sugar carbon sources.