title: Role of the Escherichia coli glgX gene in glycogen metabolism.
abstract: A role for the Escherichia coli glgX gene in bacterial glycogen synthesis and/or degradation has been inferred from the sequence homology between the glgX gene and the genes encoding isoamylase-type debranching enzymes; however, experimental evidence or definition of the role of the gene has been lacking. Construction of E. coli strains with defined deletions in the glgX gene is reported here. The results show that the GlgX gene encodes an isoamylase-type debranching enzyme with high specificity for hydrolysis of chains consisting of three or four glucose residues. This specificity ensures that GlgX does not generate an extensive futile cycle during glycogen synthesis in which chains with more than four glucose residues are transferred by the branching enzyme. Disruption of glgX leads to overproduction of glycogen containing short external chains. These results suggest that the GlgX protein is predominantly involved in glycogen catabolism by selectively debranching the polysaccharide outer chains that were previously recessed by glycogen phosphorylase.
authors.affiliation: CSIRO UMR8576, Cité Scientifique, Villeneuve d'Ascq, France.
authors.forename: David
authors.initials: D
authors.lastname: Dauvillée
authors.forename: Isabelle S
authors.initials: IS
authors.lastname: Kinderf
authors.forename: Zhongyi
authors.initials: Z
authors.lastname: Li
authors.forename: Behjat
authors.initials: B
authors.lastname: Kosar-Hashemi
authors.forename: Michael S
authors.initials: MS
authors.lastname: Samuel
authors.forename: Lynette
authors.initials: L
authors.lastname: Rampling
authors.forename: Steven
authors.initials: S
authors.lastname: Ball
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Morell
mesh_terms: D000687:Amylopectin / Q000378:metabolism; D003912:Dextrins / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D005936:Glucans / Q000378:metabolism; D006003:Glycogen / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D006004:Glycogen Debranching Enzyme System / Q000235:genetics* / Q000378:metabolism*; D017384:Sequence Deletion; D013379:Substrate Specificity
chemical_list: D003912:Dextrins; D005936:Glucans; D006004:Glycogen Debranching Enzyme System; C009109:pullulan; D006003:Glycogen; D000687:Amylopectin