Plant UVR8 photoreceptor senses UV-B by tryptophan-mediated disruption of cross-dimer salt bridges.
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.
Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.
John M
JM
Christie
Andrew S
AS
Arvai
Katherine J
KJ
Baxter
Monika
M
Heilmann
Ashley J
AJ
Pratt
Andrew
A
O'Hara
Sharon M
SM
Kelly
Michael
M
Hothorn
Brian O
BO
Smith
Kenichi
K
Hitomi
Gareth I
GI
Jenkins
Elizabeth D
ED
Getzoff
D017360:Arabidopsis / Q000502:physiology; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001120:Arginine / Q000737:chemistry; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D055537:Light Signal Transduction; D008958:Models, Molecular; D016296:Mutagenesis; D055519:Photoreceptors, Plant / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D055503:Protein Multimerization; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D014364:Tryptophan / Q000737:chemistry; D014466:Ultraviolet Rays
D029681:Arabidopsis Proteins; D002868:Chromosomal Proteins, Non-Histone; D055519:Photoreceptors, Plant; D011993:Recombinant Fusion Proteins; C525052:Uvr8 protein, Arabidopsis; D014364:Tryptophan; D001120:Arginine