Regulatory mechanisms controlling the catabolism of glycogen in cyanobacteria

Glycogen is a wide-spread reserve polymer important for the survival to environmental stresses of all kinds of organisms. In the cyanobacterium Synechocystis sp. PCC 6803, glycogen is necessary to overcome dark and starvation periods. Given the important role of this polysaccharide, its metabolism is subjected to a complex regulation. The activity of the enzymes involved in glycogen synthesis and degradation must be tightly controlled to ensure rapid access to the sugar stores when required. Our research focuses on how such a responsive and fine control is achieved via post-translational modifications of the glycogen catabolic enzymes. We found that modulation of the activity of glycogen phosphorylase (GlgP), phosphoglucomutase (PGM), and glucose-6-phosphate dehydrogenase (G6PDH) through phosphorylation, redox-induced modifications, allosteric interactions and metabolite-level regulation is essential for survival under fluctuating environmental conditions. Interestingly, some of these mechanisms are not specific of cyanobacteria, but evolutionary conserved from bacteria to humans.