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 ten tryptophans to the tryptophan cluster in 1-2 nanoseconds 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.