Femtosecond dynamics of flavin cofactor in DNA photolyase: Radical reduction, local solvation, and charge recombination

摘要

We report here our femtosecond studies of the photoreduction dynamics of the neutral radical flavin (FADH) cofactor in E coli photolyase, a process converting the inactive form to the biologically active one, a fully reduced deprotonated flavin FADH(-). The observed temporal absorption evolution revealed two initial electron-transfer reactions, occurring in I I and 42 ps with the neighboring aromatic residues of W382 and F366, respectively. The new transient absorption, observed at 550 nm previously in photolyase, was found from the excited-state neutral radical and is probably caused by strong interactions with the adenine moiety through the flavin U-shaped configuration and the highly polar/charged surrounding residues. The solvation dynamics from the locally ordered water molecules in the active site was observed to occur in similar to2 ps. These ultrafast ordered-water motions are critical to stabilizing the photoreduction product FADH- instantaneously to prevent fast charge recombination. The back electron-transfer reaction was found to occur in similar to3 ns. This slow process, consistent with ultrafast stabilization of the catalytic cofactor, favors photoreduction in photolyase.