セミナー情報

Glycogen is a branched homopolysaccharide of a-1,4-linked glucose subunits with about 5% a-1,6-linked glucose at the branching points. The exact role of this reserve polyglucan in prokaryotes is still unknown, although several works have linked glycogen metabolism to environmental survival and even to colonization and virulence in the case of pathogens. Synthesized by glycogen synthase (GlgA) using ADP-glucose as the glucosyl moiety donor, glycogen accumulation in Escherichia coli occurs when cellular carbon sources are in excess under conditions of other nutrients deficiency. Regulation of glycogen biosynthesis in E. coli involves a complex and still not well defined assemblage of factors. At the level of enzyme activity for instance, the glycogen biosynthetic process is subjected to the allosteric regulation of GlgC, a protein that catalyzes the production of ADPglucose. At the level of gene expression, its is generally accepted that the process depends on the regulation of two tandemly arranged and differently regulated operons: glgBX (encompassing the genes coding for glycogen branching (GlgB) and debranching (GlgX) enzymes), and glgCAP (encoding the GlgC and GlgA anabolic enzymes as well as the catabolic glycogen phosphorylase (GlgP)). Nevertheless, recent studies carried out in our laboratory have provided strong evidence that E. coli glgBXCAP genes are organized in a single transcriptional unit controlled by promoter sequences occurring upstream of glgB, and that an alternative suboperonic promoter is located within glgC driving expression of glgA and glgP genes (Montero et al. unpublished). Using the Keio collection of gene-disrupted mutants of E. coli (1) and the ASKA gene expression library (2) we have recently carried out studies aimed to uncover mechanisms regulating glycogen metabolism and its connection with other biological processes in E. coli (3-5). These studies have revealed that bacterial glycogen metabolism is highly interconnected with a wide variety of cellular processes, being affected by proteins involved in the stringent response, general stress response, control of extra-cellular Mg2+ availability, carbon sensing, transport and metabolism, determination of intercellular communication, aggregative and social behaviour, sulfur nitrogen and iron metabolism, end-turnover of tRNA, envelope composition and integrity, energy production and cellular redox status, small RNA-mediated gene regulation, nucleotide metabolism and osmotic stress.

1. Baba T, Ara T, Hasegawa M, Takai Y, Okumura Y, Baba M, Datsenko KA, Tomita M, Wanner BL & Mori H (2006) Mol Syst Biol Doi:10.1038/msb4100050.
2. Kitagawa M, Ara T, Arifuzzaman M, Ioka-Nakamichi T, Inamoto E, Toyonaga H & Mori H (2005) DNA Res 12: 291-299
3. Eydallin G, Viale AM, Moran-Zorzano MT, Munoz FJ, Montero M, Baroja-Fernandez E & Pozueta-Romero J (2007b) FEBS Lett 581: 2947-2953.
4. Montero M, Eydallin G, Almagro G, Munoz FJ, Viale AM, Rahimpour M, Sesma MT, Baroja-Fernandez E & Pozueta-Romero J (2009) Biochem J 424: 129-141.
5. Eydallin G, Montero M, Almagro G, Sesma MT, Viale AM, Munoz FJ, Rahimpour M, Baroja-Fernandez E & Pozueta-Romero J (2010) DNA Res doi:10.1093/dnares/dsp028.