Gaudin F, Paquet F, Chanteloup L, Beau J M, Nguyen T T, Lancelot G
Centre de Biophysique Moléculaire, CNRS, Orléans, France.
J Biomol NMR. 1995 Jan;5(1):49-58. doi: 10.1007/BF00227469.
In order to examine the internal dynamic processes of the dodecamer d(CGCAAATTTGCG)2, the 13C-enriched oligonucleotide has been synthesized. The three central thymines were selectively 13C-labeled at the C1' position and their spin-lattice relaxation parameters R(CZ), R(CX,Y), R(HZ-->CZ), R(2HZCZ), R(2HZCX,Y) and R(HZC) were measured. Density functions were computed for two models of internal motions. Comparisons of the experimental data were made with spin-lattice relaxation rates rather than with the density functions, whose values were altered by accumulation of the uncertainties of each relaxation rate measurement. The spin-lattice relaxation rates were computed with respect to the motions of the sugar around the C1'-N1 bond. A two-state jump model between the anti- and syn-conformations with P(anti)/P(syn) = 91/9 or a restricted rotation model with delta chi = 28 degrees and an internal diffusion coefficient of 30 x 10(7) s-1 gave a good fit with the experimental data. Twist, tilt or roll base motions have little effect on 13C1' NMR relaxation. Simulation of spin-relaxation rates with the data obtained at several temperatures between 7 and 32 degrees C, where the dodecamer is double stranded, shows that the internal motion amplitude is independent of the temperature within this range, as expected for internal motion. Using the strong correlation which exists in a B-DNA structure between the chi and delta angle, we suggest that the change in the glycosidic angle value should be indicative of a sugar puckering between the C1'-exo and C2'-endo conformations.
为了研究十二聚体d(CGCAAATTTGCG)₂的内部动态过程，合成了¹³C富集的寡核苷酸。三个中心胸腺嘧啶在C1'位置被选择性地¹³C标记，并测量了它们的自旋晶格弛豫参数R(CZ)、R(CX,Y)、R(HZ→CZ)、R(2HZCZ)、R(2HZCX,Y)和R(HZC)。针对两种内部运动模型计算了密度函数。将实验数据与自旋晶格弛豫速率进行比较，而不是与密度函数进行比较，因为密度函数的值会因每次弛豫速率测量的不确定性累积而改变。自旋晶格弛豫速率是根据糖围绕C1'-N1键的运动来计算的。反式和顺式构象之间的双态跳跃模型（P(反式)/P(顺式)=91/9）或具有δχ = 28°和内部扩散系数为30×10⁷ s⁻¹的受限旋转模型与实验数据拟合良好。扭曲、倾斜或滚动碱基运动对¹³C1' NMR弛豫影响很小。用在7至32摄氏度之间几个温度下获得的数据（此时十二聚体为双链）对自旋弛豫速率进行模拟，结果表明在此范围内内部运动幅度与温度无关，这正如内部运动所预期的那样。利用B-DNA结构中χ角和δ角之间存在的强相关性，我们认为糖苷角值的变化应表明C1'-外向和C2'-内向构象之间的糖环构象变化。
