Computational Study on the Mechanism of the Electron-Transfer-Induced Repair of the (6-4) T-T Photoproduct of DNA by Photolyase: Possibility of a Radical Cation Pathway

The oxetane and the non-oxetane mechanisms of the electron-transfer-driven repair of the (6-4) T-T photolesion of DNA by photolyase are examined by density functional theory (B3LYP). We calculated the radical cation pathway in addition to the radical anion and the neutral pathways for both mechanisms in order to assess the possibility of the radical cation pathway, because relatively large energy barriers have been found for the radical anion pathway. As a result, the radical anion pathway showed a large energy barrier in both the oxetane and the non-oxetane mechanisms in agreement with previous calculations. However, it was found that the radical cation pathway of the oxetane mechanism has a realistic low energy barrier. This advantage of the radical cation pathway was ascribed to the position of the radical before the formation of the oxetane and the stability of the oxetane in energy.