The nitrogen-related phosphotransferase system in Escherichia coli

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The nitrogen-related phosphotransferase system PTSNtr works in parallel to the canonical PTS that catalyzes uptake of carbohydrates in bacteria. PTSNtr is highly conserved in Proteobacteria and affects important processes such as nitrogen and carbon assimilation and virulence. The underlying mechanisms, however, are largely unknown. PTSNtr consists of three proteins: Enzyme INtr (EINtr) autophosphorylates and transfers phosphoryl-groups via protein NPr to enzyme IIANtr (EIIANtr). Recently, a direct role of PTSNtr in regulation of K+ uptake was revealed in Escherichia coli. In particular, EIIANtr binds and stimulates kinase activity of histidine kinase KdpD, which in turn activates synthesis of the high affinity K+ transporter KdpFABC in response to limiting K+ concentrations. Initial data suggest that dephosphorylated EIIANtr interacts with KdpD. In the proposed project, the molecular mechanism and the physiological meaning of this regulation shall be explored. In particular, the surfaces involved in interaction shall be characterized to learn how a histidine kinase can be activated by interaction with an accessory protein. Second, the role of the phosphorylation state of EIIANtr for interaction shall be clarified and the signals triggering phosphorylation shall be identified. Third, EINtr contains a GAF signaling domain and initial data suggest that this domain controls the regulatory output of EIIANtr. Hence, the ligand that binds to GAF and presumably controls EINtr autophosphorylation shall be identified. Finally, it shall be explored whether PTSNtr exerts its pleiotropic roles through modulation of the intracellular K+ concentration, which may in turn affect activities of numerous genes and enzymes.