title: The glgB-encoded glycogen branching enzyme is essential for glycogen accumulation in Corynebacterium glutamicum.
abstract: Corynebacterium glutamicum transiently accumulates glycogen as carbon capacitor during the early exponential growth phase in media containing carbohydrates. In some bacteria glycogen is synthesized by the consecutive action of ADP-glucose pyrophosphorylase (GlgC), glycogen synthase (GlgA) and glycogen branching enzyme (GlgB). GlgC and GlgA of C. glutamicum have been shown to be necessary for glycogen accumulation in this organism. However, although cg1381 has been annotated as the putative C. glutamicum glgB gene, cg1381 and its gene product have not been characterized and their role in transient glycogen accumulation has not yet been investigated. We show here that the cg1381 gene product of C. glutamicum catalyses the formation of α-1,6-glycosidic bonds in polysaccharides and thus represents a glycogen branching enzyme. RT-PCR experiments revealed glgB to be co-transcribed with glgE, probably encoding a maltosyltransferase. Promoter activity assays with the glgE promoter region revealed carbon-source-dependent expression of the glgEB operon. Characterization of the growth and glycogen content of glgB-deficient and glgB-overexpressing strains showed that the glycogen branching enzyme GlgB is essential for glycogen formation in C. glutamicum. Taken together these results suggest that an interplay of the enzymes GlgC, GlgA and GlgB is not essential for growth, but is required for synthesis of the transient carbon capacitor glycogen in C. glutamicum.
authors: Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany.
authors: Gerd M
authors: GM
authors: Seibold
authors: Institute of Microbiology and Biotechnology, University of Ulm, D-89069 Ulm, Germany.
authors: Katrin J
authors: KJ
authors: Breitinger
authors: Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany.
authors: Raoul
authors: R
authors: Kempkes
authors: Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany.
authors: Leonard
authors: L
authors: Both
authors: Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany.
authors: Matthias
authors: M
authors: Krämer
authors: Institute of Microbiology and Biotechnology, University of Ulm, D-89069 Ulm, Germany.
authors: Stefan
authors: S
authors: Dempf
authors: Institute of Microbiology and Biotechnology, University of Ulm, D-89069 Ulm, Germany.
authors: Bernhard J
authors: BJ
authors: Eikmanns
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D048230:Corynebacterium glutamicum / Q000201:enzymology* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis*; D009876:Operon; D011401:Promoter Regions, Genetic
chemical_list: D001426:Bacterial Proteins; D006003:Glycogen; D015061:1,4-alpha-Glucan Branching Enzyme; D005947:Glucose