Glycogen synthase sensitivity to glucose-6-P is important for controlling glycogen accumulation in Saccharomyces cerevisiae.
Glycogen is a storage form of glucose utilized as an energy reserve by many organisms. Glycogen synthase, which is essential for synthesizing this glucose polymer, is regulated by both covalent phosphorylation and the concentration of glucose-6-P. With the yeast glycogen synthase Gsy2p, we recently identified two mutants, R579A/R580A/R582A [corrected] and R586A/R588A/R591A, in which multiple arginine residues were mutated to alanine that were completely insensitive to activation by glucose-6-P in vitro (Pederson, B. A., Cheng, C., Wilson, W. A., and Roach, P. J. (2000) J. Biol. Chem. 275, 27753-27761). We report here the expression of these mutants in Saccharomyces cerevisiae and, as expected from our findings in vitro, they were not activated by glucose-6-P. The R579A/R580A/R582A [corrected] mutant, which is also resistant to inhibition by phosphorylation, caused hyperaccumulation of glycogen. In contrast, the mutant R586A/R588A/R591A, which retains the ability to be inactivated by phosphorylation, resulted in lower glycogen accumulation when compared with wild-type cells. When intracellular glucose-6-P levels were increased by mutating the PFK2 gene, glycogen storage due to the wild-type enzyme was increased, whereas that associated with R579A/R580A/R582A [corrected] was not greatly changed. This is the first direct demonstration that activation of glycogen synthase by glucose-6-P in vivo is necessary for normal glycogen accumulation.
Pederson
Bartholomew A
BA
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine and the Indiana University Center for Diabetes Research, Indianapolis, Indiana 46202, USA.
Wilson
Wayne A
WA
Roach
Peter J
PJ
D019298:Glucose-6-Phosphate / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D010766:Phosphorylation; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics
D019298:Glucose-6-Phosphate; D006003:Glycogen; D006006:Glycogen Synthase