Quenching Dynamics of Ultraviolet-Light Perception by UVR8 Photoreceptor

UVR8 is a recently discovered UV-B photoreceptor with a homodimer as the active state. UV-B perception of an interfacial tryptophan (W285) causes dissociation of the dimer into two functional monomers. Here, we investigate the molecular mechanism behind UV perception by W285 in UVR8. We observed a significant quenching dynamics in about 150 ps within the interfacial four-tryptophan cluster and an unusual resonance energy transfer from the other 10 tryptophans to the tryptophan cluster in 1–2 ns to enhance functional efficiency. With mutation of W285 to F, the quenching dynamics is highly suppressed in this intact mutant dimer, and the overall fluorescence intensity dramatically increases by a factor of 6, indicating W285 as a dominant quencher. These results reveal a unique energy transfer mechanism for efficient UV perception and the critical functional role of W285 for primary quenching dynamics for initiating dimer dissociation to trigger the function.