Spassky A, Angelov D
Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, Paris, France.
Biochemistry. 1997 Jun 3;36(22):6571-6. doi: 10.1021/bi962761d.
Two major products, 2,2-diamino-4-[(2-deoxy-beta-D-erythro-pentafuranosyl)amino]-5-(2H )-oxazolone and its imidazole derivative have been generated from one-electron oxidation of the free 2'-deoxyguanosine. The formation of 7,8-dihydro-8-oxoguanine (8-oxodG), not detected in this case, has been observed from DNA exposed to oxidizing agents. Since these compounds are thought to reflect, respectively, either deprotonation or hydration of the transient guanyl radical cation, these findings suggested that the helical structure could influence the chemical decomposition pathway of the guanine moiety. In the present study, we have photoionized DNA sequences by exposure to high-intensity UV (266 nm) laser pulses. Homo- or heteroduplexes, including guanines in various environments as well as Gn runs, were used as templates. Lesions were analyzed, at the nucleotide level, by taking advantage of the specific removal of 8-oxodG from DNA by the formamidopyrimidine DNA glycosylase (Fpg protein) and of the differential sensitivity of 8-oxodG and oxazolone to piperidine. Variations were observed in the relative yield of each type of lesion at individual guanines of the DNA sequences. We found that the Fpg lesions predominate in regions of stable double helix but are decreased in favor of the piperidine ones in regions of destabilization of the helix. Results are discussed in terms of a relationship between intramolecular rearrangements of the guanyl radical cation and the DNA helical conformation and dynamics.
两种主要产物，2,2 - 二氨基 - 4 - [(2 - 脱氧 - β - D - 赤藓糖基)氨基] - 5 - (2H) - 恶唑酮及其咪唑衍生物，是由游离的2'-脱氧鸟苷经单电子氧化生成的。从暴露于氧化剂的DNA中观察到了7,8 - 二氢 - 8 - 氧代鸟嘌呤（8 - 氧代 - dG）的形成，而在这种情况下未检测到。由于这些化合物被认为分别反映了瞬时鸟嘌呤自由基阳离子的去质子化或水合作用，这些发现表明螺旋结构可能影响鸟嘌呤部分的化学分解途径。在本研究中，我们通过暴露于高强度紫外（266 nm）激光脉冲使DNA序列发生光离子化。使用了包括处于各种环境中的鸟嘌呤以及鸟嘌呤串联序列的同型或异型双链体作为模板。利用甲酰胺嘧啶DNA糖基化酶（Fpg蛋白）从DNA中特异性去除8 - 氧代 - dG以及8 - 氧代 - dG和恶唑酮对哌啶的不同敏感性，在核苷酸水平上分析损伤情况。在DNA序列中各个鸟嘌呤处每种损伤类型的相对产率存在差异。我们发现Fpg损伤在稳定双螺旋区域占主导，但在螺旋不稳定区域则减少，有利于哌啶损伤。根据鸟嘌呤自由基阳离子的分子内重排与DNA螺旋构象及动力学之间的关系对结果进行了讨论。
