Glucose-6-Phosphate–Mediated Activation of Liver Glycogen Synthase Plays a Key Role in Hepatic Glycogen Synthesis

  1. Kei Sakamoto1
  1. 1Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, Scotland, U.K.
  2. 2Institute for Research in Biomedicine and Department of Biochemistry and Molecular Biology, University of Barcelona, and CIBERDEM, Barcelona, Spain
  3. 3Department of Molecular Physiology and Biophysics and Mouse Metabolic Phenotyping Center, Vanderbilt University School of Medicine, Nashville, Tennessee
  1. Corresponding author: Kei Sakamoto, kei.sakamoto{at}rd.nestle.com.
  1. R.W.H., M.G.-R., and L.K. contributed equally to this study.

Abstract

The liver responds to an increase in blood glucose levels in the postprandial state by uptake of glucose and conversion to glycogen. Liver glycogen synthase (GYS2), a key enzyme in glycogen synthesis, is controlled by a complex interplay between the allosteric activator glucose-6-phosphate (G6P) and reversible phosphorylation through glycogen synthase kinase-3 and the glycogen-associated form of protein phosphatase 1. Here, we initially performed mutagenesis analysis and identified a key residue (Arg582) required for activation of GYS2 by G6P. We then used GYS2 Arg582Ala knockin (+/R582A) mice in which G6P-mediated GYS2 activation had been profoundly impaired (60–70%), while sparing regulation through reversible phosphorylation. R582A mutant–expressing hepatocytes showed significantly reduced glycogen synthesis with glucose and insulin or glucokinase activator, which resulted in channeling glucose/G6P toward glycolysis and lipid synthesis. GYS2+/R582A mice were modestly glucose intolerant and displayed significantly reduced glycogen accumulation with feeding or glucose load in vivo. These data show that G6P-mediated activation of GYS2 plays a key role in controlling glycogen synthesis and hepatic glucose-G6P flux control and thus whole-body glucose homeostasis.

Footnotes

  • Received June 4, 2013.
  • Accepted August 27, 2013.

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