title: Glycogen phosphomonoester distribution in mouse models of the progressive myoclonic epilepsy, Lafora disease.
abstract: Glycogen is a branched polymer of glucose that acts as an energy reserve in many cell types. Glycogen contains trace amounts of covalent phosphate, in the range of 1 phosphate per 500-2000 glucose residues depending on the source. The function, if any, is unknown, but in at least one genetic disease, the progressive myoclonic epilepsy Lafora disease, excessive phosphorylation of glycogen has been implicated in the pathology by disturbing glycogen structure. Some 90% of Lafora cases are attributed to mutations of the EPM2A or EPM2B genes, and mice with either gene disrupted accumulate hyperphosphorylated glycogen. It is, therefore, of importance to understand the chemistry of glycogen phosphorylation. Rabbit skeletal muscle glycogen contained covalent phosphate as monoesters of C2, C3, and C6 carbons of glucose residues based on analyses of phospho-oligosaccharides by NMR. Furthermore, using a sensitive assay for glucose 6-P in hydrolysates of glycogen coupled with measurement of total phosphate, we determined the proportion of C6 phosphorylation in rabbit muscle glycogen to be ∼20%. C6 phosphorylation also accounted for ∼20% of the covalent phosphate in wild type mouse muscle glycogen. Glycogen phosphorylation in Epm2a(-/-) and Epm2b(-/-) mice was increased 8- and 4-fold compared with wild type mice, but the proportion of C6 phosphorylation remained unchanged at ∼20%. Therefore, our results suggest that C2, C3, and/or C6 phosphate could all contribute to abnormal glycogen structure or to Lafora disease.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202 and.
authors.forename: Anna A
authors.initials: AA
authors.lastname: DePaoli-Roach
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202 and.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Contreras
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202 and.
authors.forename: Dyann M
authors.initials: DM
authors.lastname: Segvich
authors.affiliation: the Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602.
authors.forename: Christian
authors.initials: C
authors.lastname: Heiss
authors.affiliation: the Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Ishihara
authors.affiliation: the Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602.
authors.forename: Parastoo
authors.initials: P
authors.lastname: Azadi
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202 and proach@iu.edu.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Roach
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D054637:Dual-Specificity Phosphatases / Q000235:genetics; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D020192:Lafora Disease / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D010766:Phosphorylation; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011817:Rabbits; D044767:Ubiquitin-Protein Ligases / Q000235:genetics
chemical_list: D019298:Glucose-6-Phosphate; D006003:Glycogen; C572596:NHLRC1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D054637:Dual-Specificity Phosphatases; C491989:Epm2a protein, mouse; D054558:Protein Tyrosine Phosphatases, Non-Receptor
keywords: Epm2a; Epm2b; Glycobiology; Glycogen; Glycogen Storage Disease; Lafora Disease; Laforin; Malin; Phosphorylation; Polysaccharide