EnvZOmpR

EnvZOmpR is a bacterial two-component regulatory system that coordinates responses to environmental osmolarity, primarily in Gram-negative bacteria such as Escherichia coli. It consists of the sensor histidine kinase EnvZ and the response regulator OmpR, and it controls the expression and composition of outer membrane porins to adapt to changing conditions.

EnvZ is an inner membrane sensor with periplasmic and cytoplasmic regions. It detects osmotic changes and modulates its kinase activity by autophosphorylation on a conserved histidine residue. The phosphate group is then transferred to OmpR, the response regulator, which contains a receiver domain and a C-terminal DNA-binding domain. Phosphorylation enhances OmpR’s ability to regulate target genes.

Mechanistically, EnvZOmpR shifts the balance of OmpR phosphorylation in response to osmolarity. At low osmolarity, EnvZ activity favors dephosphorylation of OmpR, resulting in lower OmpR-P levels and promoting ompF expression while reducing ompC transcription. At high osmolarity, EnvZ increases OmpR phosphorylation; OmpR-P activates ompC transcription and, via the small RNA micF, represses ompF translation. This coordinated regulation alters porin composition, affecting nutrient uptake and membrane permeability.

Functionally, EnvZOmpR helps the bacterium optimize outer membrane permeability for varying environments and stresses. It serves as a canonical model for studying two-component signaling and has been explored for synthetic biology applications as a tunable osmosensor.

See also: EnvZ, OmpR, two-component systems, porins.