The glgX gene product of Corynebacterium glutamicum is required for glycogen degradation and for fast adaptation to hyperosmotic stress

Abstract

Corynebacterium glutamicum cells growing in medium containing sugars accumulate glycogen in the early exponential-growth phase, and start to degrade this polymer at entry into the stationary phase. In a first attempt to investigate glycogen degradation, the C. glutamicum glgX gene, which encodes a protein with 46 % identity to the isoamylase-type debranching enzyme of Escherichia coli, was analysed, expressed and inactivated. The purified C. glutamicum gene product showed debranching activity towards glycogen, amylopectin and starch. Chromosomal inactivation of glgX in C. glutamicum wild-type led to slower growth and to a higher intracellular glycogen pool throughout growth, when compared to those in the parental strain. This result suggests that glycogen synthesis and degradation occur simultaneously in C. glutamicum. When exposed to hyperosmotic shock, C. glutamicum rapidly degrades glycogen, and at the same time, synthesizes the osmoprotectant trehalose. The glgX mutant, however, synthesized only minor amounts of trehalose throughout cultivation, and its growth ceased after hyperosmotic shock. Taken together, the results indicate that the glgX gene product is essential for glycogen degradation in C. glutamicum, that glycogen is constantly recycled in C. glutamicum, and that it serves as a carbon store for trehalose synthesis via the TreYZ pathway after hyperosmotic shock.

Glycogen: A must have storage to survive stressful emergencies

“…In Corynebacterium glutamicum, the exposure to hyperosmotic shock was shown to result in glycogen degradation and the synthesis of the osmoprotectant trehalose. 23 In C. elegans, recent reports demonstrate an important role for glycogen in mediating survival to hypoosmoticanoxic stress. 19,20 Our data suggest that glycogen degradation leads to different outcomes depending on the type of stress.…”

The α-Glucan Phosphorylase MalP of Corynebacterium glutamicum Is Subject to Transcriptional Regulation and Competitive Inhibition by ADP-Glucose

“…In contrast to the situation in E. coli, the genes for glycogen and maltose metabolism are not organized in operons in C. glutamicum and are not well distributed in the genome. Physiological studies also revealed that in C. glutamicum, glycogen synthesis and degradation have to be coordinated efficiently throughout cultivation since the glycogen level is set by the concerted action of glycogen-synthesizing and -degrading enzymes (43). The finding that activity of C. glutamicum MalP is controlled by competitive inhibition by the glycogen synthesis intermediate ADP-glucose is the first mechanism for the coordination of glycogen synthesis and degradation observed in C. glutamicum.…”

“…This mode of MalP activity control causes the fast degradation of glycogen in response to limitations of the glycogen synthesis. By this means, fluctuations of the central metabolism intermediates glucose-1-phosphate and glucose-6-phosphate are probably avoided, which reflects the proposed function of glycogen as a carbon capacitor in C. glutamicum (40,43).…”

“…Standard loading buffer (4ϫ) contained 8% (wt/vol) SDS, 20% (vol/ vol) glycerol, 10 mM EDTA, 100 mM Tris-HCl (pH 6.8), 2% (vol/vol) ␤-mercaptoethanol, and 1 mg of bromphenol blue/ml. Western blot experiments for detection of the His-tagged MalP protein were performed as previously described (43).…”

“…In cultivations of C. glutamicum on glucose, large amounts of glycogen are synthesized in the early exponential growth phase from glc-6-P by the consecutive action of phosphoglucomutase (Pgm), ADP-glucose pyrophosphorylase (GlgC), glycogen synthase (GlgA), and glycogen branching enzyme (GlgB) (34,40,42,43). Degradation of glycogen takes place in C. glutamicum before the entry of the stationary phase and proceeds by the concerted action of the glycogen debranching enzyme (GlgX) and the two ␣-glucan phosphorylases designated MalP and GlgP (41,43).…”