A grant has been awarded to explore the transmission of information through the EnvZ/OmpR two-component regulatory system in Escherichia coli. The osmo-regulation of porin expression by the sensor kinase EnvZ and response regulator OmpR is one of the simplest and best characterized two-component systems and is thus ideal for studying quantitative and mechanistic aspects of intracellular signaling. The goals of this project are oriented towards addressing the following questions: 1) Can models of EnvZ/OmpR signaling describe qualitative and quantitative aspects of porin osmoregulation in vivo? 2) What is the signal that stimulates the sensor kinase EnvZ? A quantitative model of the EnvZ/OmpR circuit has been formulated which predicts that the cycle of phosphorylation and dephosphorylation renders the system insensitive (robust) with respect to variations in a number of parameters. Fluorescent reporter strains have also been developed that permit rapid and sensitive quantitative measurements of transcriptional activity. These reporters will be used to test the predictions regarding robustness, quantify the variability in signaling behavior among single cells, characterize the kinetics of EnvZ/OmpR signal transduction, and determine whether EnvZ responds to mechanical stress. Quantitative models will be further developed and analyzed in order to explore the organization and structure of the EnvZ/OmpR circuit and to explore the extent to which variants of the models can be applied to other systems.
This project combines quantitative measurements and mathematical modeling in order to understand a relatively simple example of a biological circuit. Progress in this area will provide important steps towards developing an integrative view of the complex networks of interacting biomolecules within cells. This will ultimately make it possible to reengineer many of the adaptive signaling systems in bacteria, plants and fungi and will impact a wide range of fields such as biotechnology, drug development, and cell signaling.