Deng H, Braunlin W H
Department of Chemistry, University of Nebraska-Lincoln 68588-0304, USA.
J Mol Biol. 1996 Jan 26;255(3):476-83. doi: 10.1006/jmbi.1996.0039.
The binding environments of sodium ions on oligomeric DNA quadruplex structures have been examined by 23Na NMR. Competitive ion binding experiments confirm that the selectivity of univalent cations for the strong sites on the G-quadruplex d(G4T4G4) follows the order K+ > Na+ > Cs+. 23Na intensity measurements demonstrate a class of sodium ions that are not detectable by NMR, establishing that the sodium ions bind with loss of water of hydration. These measurements define the number of occupied, specific sodium ion binding sites per quadruplex as 2(+/- 1). In contrast to the rapid exchange of specifically bound sodium ions from the tetrameric G-quadruplex structure d(T2G4T), exchange from the dimeric G-quadruplex structure of d(G4T4G4) is slow on the timescale of the 23Na NMR relaxation. 23Na NMR relaxation measurements, performed as a function of temperature, allow the kinetics of sodium ion complexation to be determined. The lifetime of specifically bound sodium ions is estimated as 180 microseconds at 20 degrees C. The temperature dependence of the exchange rates suggests a fully hydrated transition state.
通过23Na核磁共振研究了钠离子在寡聚DNA四链体结构上的结合环境。竞争性离子结合实验证实，单价阳离子对G-四链体d(G4T4G4)上强位点的选择性遵循K+>Na+>Cs+的顺序。23Na强度测量表明存在一类无法通过核磁共振检测到的钠离子，这表明钠离子结合时伴随着水合水的损失。这些测量确定每个四链体上占据的特定钠离子结合位点数量为2(±1)。与四聚体G-四链体结构d(T2G4T)中特异性结合的钠离子的快速交换不同，在23Na核磁共振弛豫的时间尺度上，d(G4T4G4)二聚体G-四链体结构中的交换很慢。作为温度函数进行的23Na核磁共振弛豫测量，可以确定钠离子络合的动力学。在20℃时，特异性结合的钠离子的寿命估计为180微秒。交换速率的温度依赖性表明存在一个完全水合的过渡态。
