Department of Chemistry and Molecular Biophysics Program, Wesleyan University, Middletown, CT 06459, USA.
J Mol Recognit. 2013 Apr;26(4):175-80. doi: 10.1002/jmr.2262.
8-oxoguanine is a major lesion of genomic DNA that results from oxidation of guanine by reactive oxygen species. The repair of this lesion is initiated by 8-oxoguanine glycosylases, which excise the damaged base by "flipping" it outside the DNA double helix. The molecular mechanisms involved in the specific recognition of the damaged base by the enzyme are not yet fully understood. Several models have proposed that, in DNA, the base pair between 8-oxoguanine and cytosine may possess altered dynamic properties that could help the enzyme locate the lesion and could favor the selective extra-helical flipping of the damaged base. To test this proposal, we have characterized the spontaneous opening of the base pair between 8-oxoguanine and cytosine in a DNA double helix using NMR spectroscopy and proton exchange. The results show that the rate of spontaneous opening of 8-oxoguanine and the lifetime of the base in the extra-helical state are the same as those of a canonical guanine-cytosine base pair, in the same base sequence context. This finding suggests that the opening dynamics of 8-oxoguanine, when paired with cytosine in DNA, does not play a significant role in the recognition of the lesion by glycosylases.
8-氧鸟嘌呤是基因组 DNA 的主要损伤，由活性氧物种氧化鸟嘌呤引起。这种损伤的修复是由 8-氧鸟嘌呤糖苷酶启动的，它通过“翻转”将受损的碱基从 DNA 双螺旋中切除。目前，酶对损伤碱基的特异性识别的分子机制尚不完全清楚。有几个模型提出，在 DNA 中，8-氧鸟嘌呤和胞嘧啶之间的碱基对可能具有改变的动态特性，这有助于酶定位损伤部位，并有利于损伤碱基的选择性外螺旋翻转。为了验证这一假设，我们使用 NMR 光谱和质子交换技术，对 DNA 双螺旋中 8-氧鸟嘌呤和胞嘧啶之间的碱基对的自发打开进行了表征。结果表明，8-氧鸟嘌呤的自发打开速率和碱基在非螺旋状态下的寿命与同一碱基序列背景下的典型鸟嘌呤-胞嘧啶碱基对相同。这一发现表明，在 DNA 中与胞嘧啶配对时，8-氧鸟嘌呤的打开动力学在糖苷酶识别损伤方面没有发挥重要作用。
