Structure, function and signalling in Cph1 and related phytochromes

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Phytochromes are molecular photoswitches central to plant development and known in many microorganisms. While the plant phytochrome signalling mechanism is still poorly understood, many prokaryotic phytochromes are light-regulated sensory histidine protein kinases (SHPK's) involved in "two-component" phosphorelay signalling. The cyanobacterial phytochrome Cph1 is a SHPK with many similarities to plant phytochromes, but is much more accessible for biochemical and biophysical studies – for example, allowing us to solve the 3D structure of its sensory module by X-ray crystallography. Here we propose to exploit Cph1 to study phytochrome intramolecular signalling on the basis of 3D structural information. Photoreceptor molecules will be engineered to investigate putative signal processes experimentally with the help of spectroscopic, chromatographic and enzymatic assays. We hope to obtain 3D structural information about the photoactivated Pfr state and for full-length Cph1 or a similar prokaryotic phytochrome. We also hope to obtain structural data for plant phytochromes. We expect thereby to explain the intramolecular regulatory mechanism(s) of sensory histidine protein kinases and those common to or differing between plant and cyanobacterialphytochromes.