UVB from sunlight is an important environmental signal for plants. In Arabidopsis thaliana, the UVB signal is perceived by photoreceptor AtUVR8, which undergoes light-induced dimer dissociation. Crystallographic and mutational studies have identified two tryptophan residues at the dimer interface that are crucial for UVB responses. However, the molecular events leading up to dimer dissociation remain elusive. We applied dynamic crystallography to capture light-induced structural changes in photoactive AtUVR8 crystals. Here we report two intermediate structures at 1.67 Å resolution. At the epicentre of UVB signalling, concerted motions associated with Trp 285/Trp 233 lead to ejection of a water molecule, which weakens a network of hydrogen bonds and salt bridges at the dimer interface. Partial opening of the β-propeller structure, due to thermal relaxation of conformational strains originating in the epicentre, further disrupts the dimer interface and leads to dissociation. These dynamic crystallographic observations provide structural insights into the photo-perception and signalling mechanism of UVR8.
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We thank L.C. Peng for providing the Arabidopsis thaliana cDNA library. We thank the LS-CAT staff at Advanced Photon Source, Argonne National Laboratory for beamline support. X.Y. acknowledges support from National Institute of Health grants GM036452 and EY024363. K.H.Z. acknowledges support from National Natural Science Foundation of China (Grants 31270893 and 31110103912) and State Key Laboratory of Agricultural Microbiology of China. The TD-DFTB calculation work was supported by the Research Grants Council of Hong Kong SAR grant (project No. CityU 103812 to R.Z.) and grants from City University of Hong Kong (project No. 7200350 and 9610291 to J.F.). Use of the Advanced Photon Source was supported by the US Department of Energy (Office of Science and Office of Basic Energy Sciences) under Contract No. DE-AC02-06CH11357.
The authors declare no competing financial interests.
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Zeng, X., Ren, Z., Wu, Q. et al. Dynamic crystallography reveals early signalling events in ultraviolet photoreceptor UVR8. Nature Plants 1, 14006 (2015). https://doi.org/10.1038/nplants.2014.6
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