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首页> 外文期刊>Chemistry: A European journal >Examination of the Effect of the Annealing Cation on Higher Order Structures Containing Guanine or Isoguanine Repeats
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Examination of the Effect of the Annealing Cation on Higher Order Structures Containing Guanine or Isoguanine Repeats

机译：检查退火阳离子对含有鸟嘌呤或异鸟嘌呤重复序列的高阶结构的影响

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摘要

Isoguanine (2-oxo-6-aminoguanine), a natural but non-standard base, exhibits unique self-association properties compared to its isomer, guanine, and results in formation of different higher order DNA structures. In this work, the higher order structures formed by oligonucleotides containing guanine repeats or isoguanine repeats after annealing in solutions containing various cations are evaluated by electrospray ionization mass spectrometry (ESI-MS) and circular dichroism (CD) spectroscopy. The guanine-containing strand (G9) consistently formed quadruplexes upon annealing, whereas the isoguanine strand (Ig9) formed both pentaplexes and quadruplexes depending on the annealing cation. Quadruplex formation with G9 showed some dependence on the identity of the cation present during annealing with high relative quadruplex formation detected with six of ten cations. Analogous annealing experiments with Ig9 resulted in complex formation with all ten cations, and the majority of the resulting complexes were pentaplexes. CD results indicated most of the original complexes survived the desalting process necessary for ESI-MS analysis. In addition, several complexes, especially the pentaplexes, were found to be capable of cation exchange with ammonium ions. Ab initio calculations were conducted for isoguanine tetrads and pentads coordinated with all ten cations to predict the most energetically stable structures of the complexes in the gas phase. The observed preference of forming quadruplexes versus pentaplexes as a function of the coordinated cation can be interpreted by the calculated reaction energies of both the tetrads and pentads in combination with the distortion energies of tetrads.
机译：异鸟嘌呤（2-氧代-6-氨基鸟嘌呤）是一种天然但非标准的碱基，与其异构体鸟嘌呤相比，具有独特的自缔合特性，并导致形成不同的高阶DNA结构。在这项工作中，通过电喷雾电离质谱（ESI-MS）和圆二色性（CD）光谱评估了包含鸟嘌呤重复序列或异鸟嘌呤重复序列的寡核苷酸在含有各种阳离子的溶液中退火后形成的高阶结构。含鸟嘌呤的链（G9）在退火时始终形成四链体，而异鸟嘌呤的链（Ig9）则取决于退火阳离子而形成五链体和四链体。用G9形成的四链体显示出一定程度的依赖于退火过程中存在的阳离子的身份，用十个阳离子中的六个检测到的相对高的四链体形成。用Ig9进行的类似退火实验导致与所有十种阳离子形成络合物，并且大多数所得络合物为五重络合物。 CD结果表明，大多数原始复合物在ESI-MS分析所需的脱盐过程中仍然存在。另外，发现几种复合物，特别是五重复合物能够与铵离子进行阳离子交换。从头算计算了与所有十个阳离子配位的异鸟嘌呤四联体和五单元组，以预测气相中复合物的能量最稳定的结构。所观察到的形成四重体与五重体相对于配位阳离子的函数的偏好可以通过计算出的四单元和五单元的反应能结合四单元的畸变能来解释。

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