Hud N V, Schultze P, Sklenár V, Feigon J
Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles, CA, 90095-1569, USA.
J Mol Biol. 1999 Jan 8;285(1):233-43. doi: 10.1006/jmbi.1998.2327.
Guanine quartets are readily formed by guanine nucleotides and guanine-rich oligonucleotides in the presence of certain monovalent and divalent cations. The quadruplexes composed of these quartets are of interest for their potential roles in vivo, their relatively frequent appearance in oligonucleotides derived from in vitro selection, and their inhibition of template directed RNA polymerization under proposed prebiotic conditions. The requirement of cation coordination for the stabilization of G quartets makes understanding cation-quadruplex interactions an essential step towards a complete understanding of G quadruplex formation. We have used 15NH4+ as a probe of cation coordination by the four G quartets of the DNA bimolecular quadruplex [d(G4T4G4)]2, formed from oligonucleotides with the repeat sequence found in Oxytricha nova telomeres. 1H and 15N heteronuclear NMR spectroscopy has allowed the direct localization of monovalent cation binding sites in the solution state and the analysis of cation movement between the binding sites. These experiments show that [d(G4T4G4)]2 coordinates three ammonium ions, one in each of two symmetry related sites and one on the axis of symmetry of the dimeric molecule. The NH4+ move along the central axis of the quadruplex between these sites and the solution, reminiscent of an ion channel. The residence time of the central ion is determined to be 250 ms. The 15NH4+ is shown to be a valuable probe of monovalent cation binding sites and dynamics.
在某些一价和二价阳离子存在的情况下，鸟嘌呤核苷酸和富含鸟嘌呤的寡核苷酸很容易形成鸟嘌呤四联体。由这些四联体组成的四重链因其在体内的潜在作用、在体外筛选得到的寡核苷酸中相对频繁出现以及在假定的益生元条件下对模板导向的RNA聚合的抑制作用而备受关注。阳离子配位对于G四联体的稳定至关重要，这使得理解阳离子 - 四重链相互作用成为全面理解G四联体形成的关键一步。我们使用15NH4 +作为由具有在新大草履虫端粒中发现的重复序列的寡核苷酸形成的DNA双分子四重链[d(G4T4G4)]2的四个G四联体的阳离子配位探针。1H和15N异核NMR光谱使得能够在溶液状态下直接定位一价阳离子结合位点，并分析阳离子在结合位点之间的移动。这些实验表明，[d(G4T4G4)]2配位三个铵离子，其中两个对称相关位点各有一个，二聚体分子对称轴上有一个。NH4 +在这些位点与溶液之间沿着四重链的中心轴移动，这让人联想到一个离子通道。中心离子的停留时间确定为250毫秒。15NH4 +被证明是一价阳离子结合位点和动力学的有价值的探针。
