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Journal of Bacteriology, February 2005, p. 1465-1473, Vol. 187, No. 4
0021-9193/05/$08.00+0     doi:10.1128/JB.187.4.1465-1473.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Role of the Escherichia coli glgX Gene in Glycogen Metabolism

David Dauvillée,1 Isabelle S. Kinderf,1 Zhongyi Li,2 Behjat Kosar-Hashemi,2 Michael S. Samuel,2 Lynette Rampling,2 Steven Ball,1 and Matthew K. Morell2*

CNRS, UMR8576, Cité Scientifique, Villeneuve d'Ascq, France,1 CSIRO Plant Industry, Canberra, Australia2

Received 2 October 2004/ Accepted 2 November 2004

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.

* Corresponding author. Mailing address: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 1601, Australia. Phone: 61 2 6246 5074. Fax: 61 2 6246 5000. E-mail: matthew.morell{at}csiro.au.

Journal of Bacteriology, February 2005, p. 1465-1473, Vol. 187, No. 4
0021-9193/05/$08.00+0     doi:10.1128/JB.187.4.1465-1473.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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