Structural basis of ultraviolet-B perception by UVR8

Area of Science:

• Plant molecular biology
• Photobiology
• Structural biology

Background:

• Arabidopsis thaliana UVR8 is a known photoreceptor for ultraviolet-B (UV-B) light.
• UV-B perception by UVR8 initiates a protective signaling cascade.
• The precise mechanism of UV-B sensing by UVR8 has remained elusive.

Purpose of the Study:

• To elucidate the molecular mechanism of UV-B perception by the UVR8 photoreceptor.
• To determine the crystal structure of UVR8 and identify its UV-B chromophore.

Main Methods:

• X-ray crystallography at 1.8 Å resolution.
• Biochemical analyses.
• Structural analysis of UVR8 homodimer and its interaction interfaces.

Main Results:

• The crystal structure reveals UVR8 as a symmetric homodimer composed of seven-bladed β-propellers, utilizing intrinsic tryptophan residues as the UV-B chromophore.
• Specific arginine residues (Arg286, Arg338) form stabilizing intramolecular cation-π interactions with tryptophan residues (Trp285, Trp233).
• UV-B irradiation destabilizes these cation-π interactions, disrupting hydrogen bonds and leading to homodimer dissociation.

Conclusions:

• UV-B perception by UVR8 involves the direct absorption of UV-B photons by tryptophan residues within the homodimeric structure.
• The UV-B-induced destabilization of intramolecular cation-π interactions is the key event triggering UVR8 monomerization and downstream signaling.
• This study reveals the molecular mechanism underlying UVR8's function as a direct UV-B sensor.