Barthwal R, Mujeeb A, Kukreti S, Gupta A, Govil G
Department of Biosciences and Biotechnology, University of Roorkee, India.
J Mol Recognit. 1991 Mar-Jun;4(2-3):45-52. doi: 10.1002/jmr.300040202.
The complete sequential assignment and conformation of d-GpCpGpC in D2O has been determined from 1D NMR spectra at 285-320 K and room temperature 2D-COSY and NOESY spectra. The tetradeoxynucleotide exists primarily as a right handed double helix at 285 K, having Tm as 314 K. On binding to a tripeptide Lys-Tyr-Lys in a concentration equimolar to tetranucleotide duplex, the Tyr ring protons shift upfield by 0.14 ppm at 285 K. The increase in Tm on binding suggests stabilization of duplex. The existence of intermolecular NOEs between C4 sugar protons and Tyr alpha C and Lys alpha C protons give direct evidence of proximity of Tyr residue to the C4 base of d-GpCpGpC. The conformation of d-GpCpGpC remains unchanged on binding. The observed results are interpreted in terms of preferential stacking of aromatic ring of Tyr residue with proximal base-pair of d-GpCpGpC, stabilized by electrostatic interaction of Lysine side chains with backbone phosphates. This is in contrast to intercalculation of aromatic dyes within base-pairs resulting in a change in sugar conformation at the binding site.
通过在285 - 320 K下的一维核磁共振谱以及室温下的二维COSY和NOESY谱，已确定了d-GpCpGpC在重水中的完整序列排布和构象。该四脱氧核苷酸在285 K时主要以右手双螺旋形式存在，其熔解温度（Tm）为314 K。当与浓度与四核苷酸双链体等摩尔的三肽Lys-Tyr-Lys结合时，在285 K下，酪氨酸环质子的化学位移向上移动0.14 ppm。结合时Tm的升高表明双链体得到了稳定。C4糖质子与酪氨酸α碳和赖氨酸α碳质子之间存在分子间核Overhauser效应（NOE），这直接证明了酪氨酸残基与d-GpCpGpC的C4碱基相邻。d-GpCpGpC在结合时构象保持不变。观察到的结果可以解释为酪氨酸残基的芳香环与d-GpCpGpC的近端碱基对优先堆积，通过赖氨酸侧链与主链磷酸基团的静电相互作用得以稳定。这与芳香族染料插入碱基对之间导致结合位点糖构象发生变化的情况形成对比。
