Calculating distortions of short DNA duplexes with base pairing between an oxidatively damaged guanine and a guanine.

DNA is constantly being oxidized, and oxidized DNA is prone to mutation; moreover, guanine is highly sensitive to several oxidative stressors. Several oxidatively damaged forms of guanine-including 2,2,4-triamino-5(2H)-oxazolone (Oz), iminoallantoin (Ia), and spiroiminodihydantoin (Sp)-can be paired with guanine, and cause G:C-C:G transversions. Previous findings indicate that guanine is incorporated more efficiently opposite Oz than opposite Ia or Sp, and that these differences in efficiency cannot be explained by differences in the stabilities of G:Oz, G:Ia, and G:Sp base pairs calculated ab initio. Here, to explain previous experimental result, we used a 3-base-pair model DNA duplex to calculate the difference in the stability and the distortion of DNA containing a G:Oz, G:Ia, or G:Sp base pair. We found that the stability of the structure containing 5' and 3' base pairs adjacent to G:Oz was more stable than that containing the respective base pairs adjacent to G:Ia or G:Sp. Moreover, the distortion of the structure in the DNA model duplex that contained a G:Oz was smaller than that containing a G:Ia or G:Sp. Therefore, our discussion can explain the previous results involving translesion synthesis past an oxidatively damaged guanine.