Laboratory of Molecular Biophysics Laboratory Journal 2001 Dr. Jasper J. van Thor

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Jasper J. van Thor

Signal transduction in photoreceptor proteins

Photo-receptors have important applications for studying signal transduction mechanisms. In particular, signalling events can be synchronised by the application of light, and can be measured using spectroscopic techniques. The chromophores of photoreceptor proteins provide sensitive intrinsic probes, which report on changes between states. The characterisation of 'switching' between states by photoreceptors using X-ray diffraction can provide detailed information about the associated molecular events, in combination with spectroscopic techniques. Two classes of photoreceptor proteins are of particular interest. The first class of photoreceptor molecules are the phytochromes, which show optical switching between two distinct states. These were initially characterised in plants, but have now also been discovered in cyanobacteria (Hughes et al., 1998) and purple bacteria (Jiang et al., 1999). Although spectroscopic-, biochemical- and genetic aspects of phytochromes have been studied intensively, no crystal structure has been obtained so far. The second class consists of the Photoactive Yellow Proteins (PYP's). These are small (14 kDa), bacterial cytoplasmic light-receptor proteins, which after light-excitation cycle through short- and long-lived states before the ground state is reformed. The Green Fluorescent Protein is also studied as a simple model for light-induced spectral transitions in photoreceptors such as PYP.

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