Transmembrane Signal Transduction and Osmoregulation in Escherichia coli: II. The Osmotic Sensor, EnvZ, Located in the Isolated Cytoplasmic Membrane Displays Its Phosphorylation and Dephosphorylation Abilities as to the Activator Protein, OmpR1

Abstract

The EnvZ protein is presumably a membrane-located osmotic sensor, which specifically phosphorylates the activator protein, OmpR, involved in expression of the ompF and ompC genes in Escherichia coli. In this study, we developed an in vitro system for analyzing the intact form of the EnvZ protein located in the isolated cytoplasmic membrane. This particular form of the EnvZ protein exhibited its in vitro ability not only as to OmpR-phosphorylation but also OmpR-dephosphorylation. It was found that when a high concentration of a mono-cation (K⁺, Na⁺, or Li⁺) was present during the in vitro reactions, OmpR-dephosphorylation was preferentially inhibited and consequently the phospho-rylated form of the OmpR protein was accumulated under the in vitro conditions used, although the K⁺ ion appears to be essential for the OmpR-phosphorylation reaction. Procaine, a local anesthetic, is known to affect the osmotic regulation of the ompF and ompC genes in vivo. In this study, procaine was also found to preferentially inhibit OmpR-dephosphorylation mediated by the EnvZ protein in vitro.