Figure 1

Classical pathway of glycogen metabolism in prokaryotes. Pgm converts glucose-6-phosphate into glucose-1-phosphate, which serves as a substrate for ADP-glucose synthesis catalyzed by glucose-1-phosphate adenylyltransferase (GlgCD) encoded by glgC and glgD genes. Then, GlgA catalyzes the transfer of glucosyl moieties from ADP-glucose to the elongating chain of linear ?-1,4-glucan; GlgB subsequently cleaves off a portion of the glucan and attaches it to existing chains via ?-1,6 linkages to form the glycogen structure. For glycogen degradation, GlgP sequentially releases glucose moieties from the non-reducing ends to form glucose-1-phosphate and ?-1,6-branched dextrins. GlgX or Amy hydrolyzes the ?-1,6 branches of the phosphorylase-limit dextrins (typically 35 glucosyl residues in length) leading to the release of maltodextrins. Glycogen biosynthetic steps are indicated in red arrows, whereas glycogen degradation pathway is indicated in dashed purple arrows.