Bifurcating electron-transfer pathways in DNA photolyases determine the repair quantum yield

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Science  14 Oct 2016:
Vol. 354, Issue 6309, pp. 209-213
DOI: 10.1126/science.aah6071

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Two roads diverged in a yellow photolyase

Photolyase enzymes repair DNA that has been damaged by ultraviolet sunlight. The repair process begins when blue light absorption by a cofactor drives an electron transfer step. Zhang et al. applied ultrafast absorption spectroscopy to study the dynamics of this step. A bifurcation in the electron transfer pathway favors a direct tunneling mechanism in the prokaryotic enzymes and a two-step hopping mechanism in the eukaryotic variety. This difference explains the higher repair quantum yield seen in prokaryotes.

Science, this issue p. 209


Photolyase is a blue-light–activated enzyme that repairs ultraviolet-induced DNA damage that occurs in the form of cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4) photoproducts. Previous studies on microbial photolyases have revealed an electron-tunneling pathway that is critical for the repair mechanism. In this study, we used femtosecond spectroscopy to deconvolute seven electron-transfer reactions in 10 elementary steps in all classes of CPD photolyases. We report a unified electron-transfer pathway through a conserved structural configuration that bifurcates to favor direct tunneling in prokaryotes and a two-step hopping mechanism in eukaryotes. Both bifurcation routes are operative, but their relative contributions, dictated by the reduction potentials of the flavin cofactor and the substrate, determine the overall quantum yield of repair.

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