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Cph8(cph1-envZ)

The red light sensor (Cph8) is a fusion protein which is consisted of a phytochrome Cph1 and a histidine kinase domain, Envz-OmpR, that includes a response regulator.Cph1 is the first member of the plant photoreceptor family that has been identified in bacteria. The functional expression of a phytochrome domain(Cph1) in E. coli requires the biosynthesis of the respective bilin chromophore PCB. EnvZ-OmpR, a dimeric osmosensor, is a multidomain transmembrane protein and one of the best characterized two-component histidine kinases from E.coli. The light sensing unit is connected to transcription via the EnvZ-OmpR signaling pathway, phosphorylated OmpR acting as a transcription factor of PompC.

The phytochrome Cph1 from the cyanobacterium Synechocystis sp. PCC6803 is the first member of the plant photoreceptor family that has been identified in bacteria. It is a dimeric receptor protein that binds phycocyanobilin (PCB) as a red-lightabsorbing chromophore.

EnvZ, a dimeric osmosensor, is a multidomain transmembrane protein and one of the best characterized two component histidine kinases from E. coli.Besides the periplasmic receptor domain that is flanked by two transmembrane helices, it possesses a C-terminal 228-residue histidine kinase domain that is located in the cytoplasm. Upon changes of extracellular osmolarity, EnvZ specifically phosphorylates its cognate response regulator OmpR, which, in turn, regulates the Pompc .

The fusion protein Cph8 was generated to combine the light-sensing function of Cph1 with the output function of EnvZ.

Mechnism

Cph1 is only active when it binds the chromophore phycocyanobiline (PCB). Far red light(or darkness) activates the EnvZ kinase which results in the phosphorylation of OmpR and it activates as a transcription factor.On the other hand, red light deactivates the kinase and therefore the genes downstream can not be expressed. Take the image beneath as an example, in the dark, the phosphorylated OmpR will turn on P_ompC then lacZ gene is translated, signaling out black pigment.

Sequence and Features