The fundamental goal of this research program is to advance understanding of the molecular mechanisms by which extracellular agents, such as hormones, regulate intracellular processes. The specific system under study is the control of glycogen metabolism by hormones such as insulin, glucagon, epinephrine (acting via alpha- or beta-adrenergic receptors) and vasopressin. The work emphasizes the role of the multiple phosphorylation of glycogen synthase in regulation of this enzyme and the functional rationale for the existence of tissue specific isozymes of glycogen synthase in liver and muscle, the two main reserves of mammalian glycogen. The immediate aims are as follows: (i) The extension of primary structural analysis, mostly of the liver isozyme, with identification of the sites phosphorylated by different protein kinases. (ii) The cloning of cDNA's encoding liver and muscle isozymes. These two aims will permit important comparisons of the amino acid sequences of the two isozymes. (iii) Enzymological definition of a class of enzymes (F-A/GSK-3) that recognize an important proline/serine rich regulatory segment of both isozymes together with mechanistic studies of that recognition process using synthetic peptide models of this pro/ser rich region. (iv) Structure/function studies aimed at improved understanding of the interactions among the catalytic site, the allosteric (glucose-6-P) site, and the phosphorylation sites of glycogen synthase. It is hoped ultimately to bring to bear the technique of site directed mutagenesis to this problem. (v) Analysis of the phosphorylation of glycogen synthase in whole cell models for both liver and muscle. The intent is to define rigorously the phosphorylation sites critical to the physiological regulation of glycogen synthase by hormones and to probe the potential control of different glycogen synthase kinases. The several aims above are quite tightly interwoven conceptually, the unifying theme being to seek an unequivocal molecular basis for the control of glycogen synthase. Success would significantly extend knowledge of the mechanisms of action of several hormones, notably insulin, of obvious relevance to better understanding of situations of impaired insulin control such as in diabetes.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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Biochemistry Study Section (BIO)
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Indiana University-Purdue University at Indianapolis
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Gentry, Matthew S; Guinovart, Joan J; Minassian, Berge A et al. (2018) Lafora disease offers a unique window into neuronal glycogen metabolism. J Biol Chem 293:7117-7125
Irimia, Jose M; Meyer, Catalina M; Segvich, Dyann M et al. (2017) Lack of liver glycogen causes hepatic insulin resistance and steatosis in mice. J Biol Chem 292:10455-10464
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DePaoli-Roach, Anna A; Contreras, Christopher J; Segvich, Dyann M et al. (2015) Glycogen phosphomonoester distribution in mouse models of the progressive myoclonic epilepsy, Lafora disease. J Biol Chem 290:841-50
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Irimia, Jose M; Tagliabracci, Vincent S; Meyer, Catalina M et al. (2015) Muscle glycogen remodeling and glycogen phosphate metabolism following exhaustive exercise of wild type and laforin knockout mice. J Biol Chem 290:22686-98

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