Prokaryotic to plant phytochrome function
In Project B8, phytochrome photoactivation in plants induces the largest environmentally-regulated developmental change known in nature, affecting expression of ~20% of all genes. We have recently made dramatic progress in generating plant phytochromes in heterologous hosts, paving the way for novel structural and mechanistic investigation at the atomic level. We thus propose to expand current work on prokaryotic phytochromes to plant phytochromes to help understand their unique physiological functions. In particular will study the connection between chromophore photoisomerization, protonation dynamics and subsequent domain movements in the photoconversion process. To this end we will apply crystallography and exploit powerful new NMR methods to obtain structural information not only for the parent Pr and Pfr states but also intermediates. We will also create mutants to attach probes to the protein surface, whereby proton release can be mapped and domain movements studied. In other cooperations state-of-the art spectroscopic methods will be exploited to probe molecular function. Functional models will be tested experimentally with the help of mutants. Parallel investigation of prokaryotic and plant phytochromes within the CRC will provide insight into common functional principles regarding the role of protonation dynamics in the first steps of the signal transduction cascade.