Gaynutdinov Timur I, Neumann Ronald D, Panyutin Igor G
Department of Nuclear Medicine, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892-1180, USA.
Nucleic Acids Res. 2008 Jul;36(12):4079-87. doi: 10.1093/nar/gkn351. Epub 2008 Jun 4.
G-quadruplex structures formed in the telomeric DNA are thought to play a role in the telomere function. Drugs that stabilize the G-quadruplexes were shown to have anticancer effects. The structures formed by the basic telomeric quadruplex-forming unit G(3)(TTAG(3))(3) were the subject of multiple studies. Here, we employ (125)I-radioprobing, a method based on analysis of the distribution of DNA breaks after decay of (125)I incorporated into one of the nucleotides, to determine the fold of the telomeric DNA in the presence of TMPyP4 and telomestatin, G-quadruplex-binding ligands and putative anticancer drugs. We show that d[G(3)(TTAG(3))(3)(125)I-CT] adopts basket conformation in the presence of NaCl and that addition of either of the drugs does not change this conformation of the quadruplex. In KCl, the d[G(3)(TTAG(3))(3)(125)I-CT] is most likely present as a mixture of two or more conformations, but addition of the drugs stabilize the basket conformation. We also show that d[G(3)(TTAG(3))(3)(125)I-CT] with a 5'-flanking sequence folds into (3+1) type 2 conformation in KCl, while in NaCl it adopts a novel (3+1) basket conformation with a diagonal central loop. The results demonstrate the structural flexibility of the human telomeric DNA; and show how cations, quadruplex-binding drugs and flanking sequences can affect the conformation of the telomeric quadruplex.
端粒DNA中形成的G-四链体结构被认为在端粒功能中发挥作用。已表明稳定G-四链体的药物具有抗癌作用。由基本的端粒四链体形成单元G(3)(TTAG(3))(3)形成的结构是多项研究的主题。在这里，我们采用(125)I放射性探测法，这是一种基于分析掺入其中一个核苷酸的(125)I衰变后DNA断裂分布的方法，来确定在TMPyP4和端粒抑素（G-四链体结合配体和假定的抗癌药物）存在下的端粒DNA折叠情况。我们表明，d[G(3)(TTAG(3))(3)(125)I-CT]在NaCl存在下呈篮状构象，并且添加任何一种药物都不会改变这种四链体的构象。在KCl中，d[G(3)(TTAG(3))(3)(125)I-CT]很可能以两种或更多种构象的混合物形式存在，但添加药物会稳定篮状构象。我们还表明，具有5'侧翼序列的d[G(3)(TTAG(3))(3)(125)I-CT]在KCl中折叠成(3+1) 2型构象，而在NaCl中它采用具有对角中心环的新型(3+1)篮状构象。结果证明了人类端粒DNA的结构灵活性；并展示了阳离子、四链体结合药物和侧翼序列如何影响端粒四链体的构象。
