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.

Roles of maltodextrin and glycogen phosphorylases in maltose utilization and glycogen metabolism in Corynebacterium glutamicum

“…1), two different glucan phosphorylases, i.e. GlgP and MalP (Alonso-Casajus et al, 2006;Dauvillee et al, 2005), are required for efficient glycogen degradation in C. glutamicum. Indeed, we found evidence for a glgP gene, most probably encoding a protein with GlgP activity.…”

“…1). Glycogen phosphorylase (GlgP) cleaves a-1,4-glycosidic bonds at the non-reducing ends of glycogen and forms glucose 1-phosphate and phosphorylase-limited dextrins (pl-dextrins) (Dauvillee et al, 2005;Alonso-Casajus et al, 2006). Cleavage of the a-1,6-glycosidic bonds by the debranching enzyme GlgX leads to the formation of maltodextrins, which are then further degraded by maltodextrin phosphorylase (MalP) and maltodextrin glucosidase (MalZ) (Dippel et al, 2005).…”

Glycogen production by different Salmonella enterica serotypes: contribution of functional glgC to virulence, intestinal colonization and environmental survival

“…Glycogen reserves have been reported to be important for biofilm formation and virulence of S. Enteritidis (Bonafonte et al, 2000). The production of excess glycogen can be induced by mutation in a number of regulatory genes, such as glgX, glgR, glgQ and csrA, the last, at least, of which is known to be pleiotropic (Preiss, 1996;Baker et al, 2002;Dauvillee et al, 2005) and to regulate the expression of some virulence genes (Altier et al, 2000). Glycogen is known to be of importance to sporulating bacteria such as Clostridium and Bacillus (Preiss, 1984), but its known contribution to survival in E. coli has so far been limited to a role in prolonged survival under starvation conditions (Strange, 1968).…”

Convergent Evolution of Polysaccharide Debranching Defines a Common Mechanism for Starch Accumulation in Cyanobacteria and Plants

“…In bacteria, such enzymes, generally named GlgX (by reference to the Escherichia coli glycogen metabolism locus coding it), are known to be involved in glycogen catabolism by debranching only those external chains that have been first recessed by the catabolic enzyme glycogen phosphorylase. The E. coli enzyme is thus known to be very selective for chains of 3-4 Glc residues left over by glycogen/ starch phosphorylase action on external chains and displays very little residual activity on longer chains (Jeanningros et al, 1976;Dauvillée et al, 2005). This restricted enzyme selectivity prevents futile cycles during polysaccharide synthesis since such activities are unable to debranch directly the products of branching enzyme activity that branches a minimum of six Glc residues on an acceptor chain.…”