Structural insight into glucose repression of the mannitol operon

Abstract

Carbon catabolite repression is a regulatory mechanism to ensure sequential utilization of carbohydrates and is usually accomplished by repression of genes for the transport and metabolism of less preferred carbon compounds by a more preferred one. Although glucose and mannitol share the general components, enzyme I and HPr, of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) for their transport, glucose represses the transport and metabolism of mannitol in a manner dependent on the mannitol operon repressor MtIR in Escherichia coli. In a recent study, we identified the dephosphorylated form of HPr as a regulator determining the glucose preference over mannitol by interacting with and augmenting the repressor activity of MtIR in E. coli. Here, we determined the X-ray structure of the MtIR-HPr complex at 3.5 angstrom resolution to understand how phosphorylation of HPr impedes its interaction with MtIR. The phosphorylation site (His15) of HPr is located close to Glu108 and Glu140 of MtIR and phosphorylation at His15 causes electrostatic repulsion between the two proteins. Based on this structural insight and comparative sequence analyses, we suggest that the determination of the glucose preference over mannitol solely by the MtIR-HPr interaction is conserved within the Enterobacteriaceae family.