Zeng Tao, Fleming Aaron M, Ding Yun, White Henry S, Burrows Cynthia J
Department of Chemistry, University of Utah , 315 South 1400 East, Salt Lake City, Utah 84112-0850, United States.
Biochemistry. 2017 Mar 21;56(11):1596-1603. doi: 10.1021/acs.biochem.6b01175. Epub 2017 Mar 9.
Spiroiminodihydantoin (Sp) is a hyperoxidized form of guanine (G) resulting from oxidation by reactive oxygen species. The lesion is highly mutagenic, and the stereocenter renders the two isomers with distinct behaviors in chemical, spectroscopic, enzymatic, and computational studies. In this work, the α-hemolysin (αHL) latch sensing zone was employed to investigate the base pairing properties of the Sp diastereomers embedded in a double-stranded DNA. Duplexes containing (S)-Sp consistently gave deeper current blockage, and a baseline resolution of ∼0.8 pA was achieved between (S)-Sp:G and (R)-Sp:G base pairs. Ion fluxes were generally more hindered when Sp was placed opposite pyrimidines. Analysis of the current noise of blockade events further provided dynamics information about the Sp-containing base pairs. In general, base pairs comprised of (S)-Sp generated current fluctuations larger than those of their (R)-Sp counterparts, suggesting enhanced base pairing dynamics. The current noise was also substantially affected by the identity of the base opposite Sp, increasing in the following order: A < G < T < C. This report provides information about the dynamic structure of Sp in the DNA duplex and therefore has implications for the enzymatic repair of the Sp diastereomers.
螺环亚氨基二氢尿嘧啶（Sp）是鸟嘌呤（G）被活性氧氧化后形成的高度氧化形式。该损伤具有高度致突变性，且其立体中心使得这两种异构体在化学、光谱、酶学和计算研究中表现出不同的行为。在这项工作中，利用α-溶血素（αHL）锁扣传感区研究了嵌入双链DNA中的Sp非对映异构体的碱基配对特性。含有（S）-Sp的双链体始终产生更深的电流阻断，并且在（S）-Sp:G和（R）-Sp:G碱基对之间实现了约0.8 pA的基线分辨率。当Sp与嘧啶相对时，离子通量通常受到更大阻碍。对阻断事件的电流噪声分析进一步提供了有关含Sp碱基对的动力学信息。一般来说，由（S）-Sp组成的碱基对产生的电流波动大于其（R）-Sp对应物，表明碱基配对动力学增强。电流噪声也受到与Sp相对的碱基身份的显著影响，按以下顺序增加：A < G < T < C。本报告提供了有关DNA双链体中Sp动态结构的信息，并因此对Sp非对映异构体的酶促修复具有启示意义。
