Qi Jianying, Shafer Richard H
Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, San Francisco, California 94143-0446, USA.
Biochemistry. 2007 Jun 26;46(25):7599-606. doi: 10.1021/bi602392u. Epub 2007 Jun 1.
The conformation of the guanine quadruplex formed by the human telomere (HT) repeat in solutions containing physiological concentrations of K+ ions has been a topic of intensive investigation during the past several years. Of particular interest are the directionality of the overall folding pattern, i.e., parallel, antiparallel, or a combination of these two modes, and the alternation, if any, of the glycosidic bond conformation between syn and anti. An additional issue involves resolving mixtures of conformations when more than one species is present. We approach these questions using selective substitution of riboguanosine, rG, for deoxyriboguanosine, dG. Using a combination of circular dichroism, gel electrophoresis, equilibrium ultracentrifugation, and imino proton NMR, we are able to show that these modifications can yield sequences which fold into parallel or antiparallel conformations consisting of one or two strands. We also demonstrate that chimeric editing of the HT sequence permits isolating one of two conformational isomers existing in solution in the presence of KCl. The ability to engineer and control quadruplex folding motifs illustrated here with HT may prove useful more generally for a variety of quadruplex-forming sequences.
在含有生理浓度钾离子的溶液中，由人类端粒（HT）重复序列形成的鸟嘌呤四链体的构象在过去几年一直是深入研究的课题。特别令人感兴趣的是整体折叠模式的方向性，即平行、反平行或这两种模式的组合，以及糖苷键构象在顺式和反式之间是否存在交替。另一个问题涉及当存在不止一种构象时如何解析构象混合物。我们通过用核糖鸟苷（rG）选择性取代脱氧核糖鸟苷（dG）来解决这些问题。结合使用圆二色性、凝胶电泳、平衡超速离心和亚氨基质子核磁共振，我们能够表明这些修饰可以产生折叠成由一条或两条链组成的平行或反平行构象的序列。我们还证明，HT序列的嵌合编辑允许在氯化钾存在的情况下分离溶液中存在的两种构象异构体之一。这里用HT说明的设计和控制四链体折叠基序的能力可能对各种形成四链体的序列更普遍地有用。
