Sharma Purshotam, Manderville Richard A, Wetmore Stacey D
Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada.
Department of Chemistry and Toxicology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
Nucleic Acids Res. 2014 Oct;42(18):11831-45. doi: 10.1093/nar/gku821. Epub 2014 Sep 12.
The nephrotoxic food mutagen ochratoxin A (OTA) produces DNA adducts in rat kidneys, the major lesion being the C8-linked-2'-deoxyguanosine adduct (OTB-dG). Although research on other adducts stresses the importance of understanding the structure of the associated adducted DNA, site-specific incorporation of OTB-dG into DNA has yet to be attempted. The present work uses a robust computational approach to determine the conformational preferences of OTB-dG in three ionization states at three guanine positions in the NarI recognition sequence opposite cytosine. Representative adducted DNA helices were derived from over 2160 ns of simulation and ranked via free energies. For the first time, a close energetic separation between three distinct conformations is highlighted, which indicates OTA-adducted DNA likely adopts a mixture of conformations regardless of the sequence context. Nevertheless, the preferred conformation depends on the flanking bases and ionization state due to deviations in discrete local interactions at the lesion site. The structural characteristics of the lesion thus discerned have profound implications regarding its repair propensity and mutagenic outcomes, and support recent experiments suggesting the induction of double-strand breaks and deletion mutations upon OTA exposure. This combined structural and energetic characterization of the OTB-dG lesion in DNA will encourage future biochemical experiments on this potentially genotoxic lesion.
具有肾毒性的食品诱变剂赭曲霉毒素A（OTA）可在大鼠肾脏中产生DNA加合物，主要损伤为C8连接的2'-脱氧鸟苷加合物（OTB-dG）。尽管对其他加合物的研究强调了理解相关加合DNA结构的重要性，但尚未尝试将OTB-dG位点特异性掺入DNA中。目前的工作采用了一种强大的计算方法，以确定OTB-dG在与胞嘧啶相对的NarI识别序列中三个鸟嘌呤位置的三种电离状态下的构象偏好。代表性的加合DNA螺旋是通过超过2160纳秒的模拟得出的，并通过自由能进行排序。首次突出显示了三种不同构象之间紧密的能量分离，这表明OTA加合的DNA可能采用多种构象的混合，而与序列背景无关。然而，由于损伤位点处离散局部相互作用的偏差，优选构象取决于侧翼碱基和电离状态。由此识别出的损伤结构特征对其修复倾向和诱变结果具有深远影响，并支持最近的实验，表明OTA暴露会诱导双链断裂和缺失突变。DNA中OTB-dG损伤的这种结构和能量的综合表征将鼓励未来针对这种潜在遗传毒性损伤进行生化实验。
