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Science 335 (6075): 1492-1496

Copyright © 2012 by the American Association for the Advancement of Science

Plant UVR8 Photoreceptor Senses UV-B by Tryptophan-Mediated Disruption of Cross-Dimer Salt Bridges

John M. Christie,1,2 Andrew S. Arvai,2 Katherine J. Baxter,1,* Monika Heilmann,1,* Ashley J. Pratt,2 Andrew O’Hara,1 Sharon M. Kelly,1 Michael Hothorn,3,{dagger} Brian O. Smith,1 Kenichi Hitomi,2,4,5 Gareth I. Jenkins,1,{ddagger} Elizabeth D. Getzoff2,{ddagger}

Abstract: The recently identified plant photoreceptor UVR8 (UV RESISTANCE LOCUS 8) triggers regulatory changes in gene expression in response to ultraviolet-B (UV-B) light through 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.

1 Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK.
2 Department of Molecular Biology and Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
3 Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
4 Life Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
5 Section of Laboratory Equipment, National Institute of Biomedical Innovation, 7-6-8, Saito-Asagi, Ibaraki, Osaka 567-0085, Japan.

* These authors contributed equally to this work.

{dagger} Present address: Structural Plant Biology Laboratory, Friedrich Miescher Laboratory of the Max Planck Society, Tuebingen, Germany.

{ddagger} In whose labs this research was jointly undertaken and to whom correspondence should be addressed. E-mail: gareth.jenkins{at} (G.I.J.); edg{at} (E.D.G.)

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