Ulijasz, Andrew T.Cornilescu, GabrielCornilescu, Claudia C.Zhang, JunruiRivera, MarioMarkley, John L.Vierstra, Richard D.2017-04-272017-04-272010-01-14Ulijasz, A. T., Cornilescu, G., Cornilescu, C. C., Zhang, J., Rivera, M., Markley, J. L., & Vierstra, R. D. (2010). STRUCTURAL BASIS FOR THE PHOTOCONVERSION OF A PHYTOCHROME TO THE ACTIVATED FAR-RED LIGHT-ABSORBING FORM. Nature, 463(7278), 250–254. http://doi.org/10.1038/nature08671https://hdl.handle.net/1808/23834Phytochromes are a collection of bilin-containing photoreceptors that regulate numerous photoresponses in plants and microorganisms through their ability to photointerconvert between a red light-absorbing, ground state Pr and a far-red light-absorbing, photoactivated state Pfr1,2. While the structures of several phytochromes as Pr have been determined3-7, little is known about the structure of Pfr and how it initiates signaling. Here, we describe the three-dimensional solution structure of the bilin-binding domain as Pfr using the cyanobacterial phytochrome from Synechococcus OSB’. Contrary to predictions, light-induced rotation of the A but not the D pyrrole ring is the primary motion of the chromophore during photoconversion. Subsequent rearrangements within the protein then affect intra- and interdomain contact sites within the phytochrome dimer. From our models, we propose that phytochromes act by propagating reversible light-driven conformational changes in the bilin to altered contacts between the adjacent output domains, which in most phytochromes direct differential phosphotransfer.Article10.1038/nature08671PMC2807988openAccess