MUTATIONS THAT ALTER THE KINASE AND PHOSPHATASE-ACTIVITIES OF THE 2-COMPONENT SENSOR ENVZ

EnvZ, a membrane receptor kinase-phosphatase, modulates porin expressi on in Escherichia coli in response to medium osmolarity, It shares its basic scheme of signal transduction with many other sensor-kinases, p assing information from the amino-terminal, periplasmic, sensory domai n via the transmembrane helices to the carboxy-terminal, cytoplasmic, catalytic domain. The native receptor can exist in two active but oppo sed signaling states, the OmpR kinase-dominant state (K+ P-) and the O mpR-P phosphatase-dominant state (K- P+). The balance between the two states determines the level of intracellular OmpR-P, which in turn det ermines the level of porin gene transcription. To study the structural requirements for these two states of EnvZ, mutational analysis was pe rformed, Mutations that preferentially affect either the kinase or pho sphatase have been identified and characterized both in vivo and in vi tro. Most of these mapped to previously identified structural motifs, suggesting an important function for each of these conserved regions. In addition, we identified a novel motif that is weakly conserved amon g two-component sensors. Mutations that alter this motif, which is ter med the X region, alter the confirmation of EnvZ and significantly red uce the phosphatase activity.