title: Crystal structure of glycogen debranching enzyme and insights into its catalysis and disease-causing mutations.
abstract: Glycogen is a branched glucose polymer and serves as an important energy store. Its debranching is a critical step in its mobilization. In animals and fungi, the 170 kDa glycogen debranching enzyme (GDE) catalyses this reaction. GDE deficiencies in humans are associated with severe diseases collectively termed glycogen storage disease type III (GSDIII). We report crystal structures of GDE and its complex with oligosaccharides, and structure-guided mutagenesis and biochemical studies to assess the structural observations. These studies reveal that distinct domains in GDE catalyse sequential reactions in glycogen debranching, the mechanism of their catalysis and highly specific substrate recognition. The unique tertiary structure of GDE provides additional contacts to glycogen besides its active sites, and our biochemical experiments indicate that they mediate its recruitment to glycogen and regulate its activity. Combining the understanding of the GDE catalysis and functional characterizations of its disease-causing mutations provides molecular insights into GSDIII.
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Liting
authors.initials: L
authors.lastname: Zhai
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Lingling
authors.initials: L
authors.lastname: Feng
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Xia
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Huiyong
authors.initials: H
authors.lastname: Yin
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Song
authors.identifier: http://orcid.org/0000-0001-9314-4684
authors.initials: S
authors.lastname: Xiang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D055162:Biocatalysis; D041221:Candida glabrata / Q000201:enzymology* / Q000235:genetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry / Q000378:metabolism; D006004:Glycogen Debranching Enzyme System / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006010:Glycogen Storage Disease Type III / Q000201:enzymology / Q000235:genetics; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D005656:Fungal Proteins; D006004:Glycogen Debranching Enzyme System; D009844:Oligosaccharides; D006003:Glycogen