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Model of UV-B sensing by UVR8, a heme-free photoreceptor.

Model of UV-B sensing by UVR8, a heme-free photoreceptor.

Researchers from [Scripps Research Institute](http://www.scripps.edu/news/press/20120209getzoff.html) and the University of Glasgow have published a detailed molecular model of how UVR8, a unique heme-free plant photoreceptor, senses UV-B light via an intricate interacting mesh of Tryptophan residues positioned at the UVR8 dimer interface which ultimately results in the disruption of a salt bridge and dissociation of the UVR8 dimer.

>The recently identified plant photoreceptor UVR8 triggers regulatory changes in gene expression in response to ultraviolet-B (UV-B) light via an unknown mechanism. Here, crystallographic and solution structures of the UVR8 homodimer, together with mutagenesis and far-UV circular dichroism spectroscopy, reveal its mechanisms for UV-B perception and signal transduction. β-propeller subunits form a remarkable, tryptophan-dominated, dimer interface stitched together by a complex salt-bridge network. Salt-bridging arginines flank the excitonically coupled cross-dimer tryptophan “pyramid” responsible for UV-B sensing. Photoreception reversibly disrupts salt bridges, triggering dimer dissociation and signal initiation. Mutation of a single tryptophan to phenylalanine retunes the photoreceptor to detect UV-C wavelengths. Our analyses establish how UVR8 functions as a photoreceptor without a prosthetic chromophore to promote plant development and survival in sunlight.

Christie, J. M., Arvai, A. S., Baxter, K. J., Heilmann, M., Pratt, A. J., O’Hara, A., Kelly, S. M., Hothorn, M., Smith, B. O., Hitomi, K., Jenkins, G. I., Getzoff, D. G.”Plant UVR8 Photoreceptor Senses UV-B by Tryptophan-Mediated Disruption of Cross-Dimer Salt Bridges” Science. Published Online February 9 2012