Abstract

In addition to effecting the catalysis of sugar uptake, the bacterial phosphoenolpyruvate:sugar phosphotransferase system regulates a variety of physiological processes. In a previous paper [Seok et al., (1997) J. Biol. Chem. 272, 26511-26521], we reported the interaction with and allosteric regulation of Escherichia coli glycogen phosphorylase activity by the histidine-containing phosphocarrier protein HPr in vitro. Here, we show that the specific interaction between HPr and glycogen phosphorylase occurs in vivo. To address the physiological role of the HPr-glycogen phosphorylase complex, intracellular glycogen levels were measured in E. coli strains transformed with various plasmids. While glycogen accumulated during the transition between exponential and stationary growth phases in wildtype cells, it did not accumulate in cells overproducing HPr or its inactive mutant regardless of the growth stage. From these results, we conclude that HPr mediates crosstalk between sugar uptake through the phosphoenolpyruvate:sugar phosphotransferase system and glycogen breakdown. The evolutionary significance of the HPr-glycogen phosphorylase complex is suggested.

• Keywords: allosteric regulation; Escherichia coli PTS; HPr; glycogen phosphorylase; protein-protein interaction