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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,
Brian O. Smith,1
Kenichi Hitomi,2,4,5
Gareth I. Jenkins,1,
Elizabeth D. Getzoff2,
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.
Present address: Structural Plant Biology Laboratory, Friedrich Miescher Laboratory of the Max Planck Society, Tuebingen, Germany.
In whose labs this research was jointly undertaken and to whom correspondence should be addressed. E-mail: gareth.jenkins{at}glasgow.ac.uk (G.I.J.); edg{at}scripps.edu (E.D.G.)
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In whose labs this research was jointly undertaken and to whom correspondence should be addressed. E-mail: 
