Femtosecond Dynamics of DNA Photolyase:  Energy Transfer of Antenna Initiation and Electron Transfer of Cofactor Reduction

Photolyase is an enzyme that uses light energy to repair UV-induced DNA damage. We report here our femtosecond studies of the complex dynamics of energy and electron transfer in E. coli photolyase. Under physiological conditions, the excitation energy transfer from the antenna molecule methenyltetrahydrofolate (MTHF) to the fully reduced cofactor flavin (FADH - ) occurs in 292 ps, but it takes 19 ps to the in vitro oxidized neutral cofactor (FADH). The orientation factors were found to be 0.11 for the MTHF−FADH - pair and 0.28 for MTHF−FADH, unfavorable for energy transfer, indicating the existing structural constraints probably placed by three functional binding sites. The photoreduction of the neutral FADH to the catalytically active cofactor FADH - was revealed to evolve along two electron-transfer pathways: one is along a tryptophan triad with the initial electron hop in 10 ps; the other route starts with an initial electron separation in 40 ps through the neighboring phenylalanine followed by either tunneling along an α-helix or hopping through the tryptophan triad again. Reoxidation of the fully reduced flavin cofactor was observed to occur within ∼4 ns in the presence of oxygen. These results reveal the ultrafast nature of the functional dynamics in photolyase and provide important dynamic information for further studies of mapping out the entire catalytic process of repairing damaged DNA.