Chapter 7 - New Insights into the Mechanism of the Kinase and Phosphatase Activities of Escherichia coli NRII (NtrB) and Their Regulation by the PII Protein

Abstract

The NRI/NRII two-component system controls the expression of nitrogen regulated (Ntr) genes in response to signals of carbon and nitrogen status. NRII dimers consist of three types of protein domains: N-terminal domains involved in intramolecular signal transduction; a central domain mediating dimerization involved in kinase, phosphotransfer, and phosphatase catalytic activities; and C-terminal ATP-binding domains. Data indicate that the kinase and phosphatase activities of the central domain of NRII are regulated by the binding of the PII protein to the C-terminal ATP-binding domains of NRII and the N-terminal domains of NRII are involved in stabilizing the "phosphatase" conformation of the NRII central domain. The two subunits of the NRII dimer act in a highly concerted manner during the autophosphorylation reaction. An "alternating sites" hypothesis is used to explain the autophosphorylation mechanism of NRII and the regulation of NRII activities by PII.