Dynamics of Critical Charge Separation in UVR8 Light-induced Monomerization

Photoreceptors exist in many living organisms to fulfill critical biological functions including photoprotection, vision and regulation of life cycles. UVR8 (UV RESISTANCE LOCUS 8) is a UV-B (ultraviolet-B, 280-315 nm) photoreceptor in plants. In the absence of UV light, UVR8 is a protein homodimer, and UV absorption leads to UVR8 monomerization, triggering various UV-protective and photomorphogenesis signaling events. UVR8 does not contain any external chromophore and uses natural amino acid tryptophan (Trp) for light perception. Each UVR8 monomer has 14 tryptophan residues. At the dimer interface, flanked by critical inter-subunit salt-bridges, two symmetrical “Trp pyramid” clusters are formed by close packing of Trp residues, serving as the reaction center. Here, with extensive mutagenesis studies, femtosecond resolved spectroscopy and computational methods, we revealed the reaction dynamics of charge separation during UVR8 light-induced monomerization.