Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
Biochimie. 2012 Nov;94(11):2431-40. doi: 10.1016/j.biochi.2012.06.024. Epub 2012 Jul 3.
Metal ion-nucleic acid interactions have attracted considerable interest for their involvement in structure formation and catalytic activity of nucleic acids. Although interactions between metal ion and mismatched base pair duplex are important to understand mechanism of gene mutations related to heavy metal ions, they have not been well-characterized. We recently found that the Ag(+) ion stabilized a C:C mismatched base pair duplex DNA. A C-Ag-C metal-mediated base pair was supposed to be formed by the binding between the Ag(+) ion and the C:C mismatched base pair to stabilize the duplex. Here, we examined specificity, thermodynamics and structure of possible C-Ag-C metal-mediated base pair. UV melting indicated that only the duplex with the C:C mismatched base pair, and not of the duplexes with the perfectly matched and other mismatched base pairs, was specifically stabilized on adding the Ag(+) ion. Isothermal titration calorimetry demonstrated that the Ag(+) ion specifically bound with the C:C base pair at 1:1 molar ratio with a binding constant of 10(6) M(-1), which was significantly larger than those for nonspecific metal ion-DNA interactions. Electrospray ionization mass spectrometry also supported the specific 1:1 binding between the Ag(+) ion and the C:C base pair. Circular dichroism spectroscopy and NMR revealed that the Ag(+) ion may bind with the N3 positions of the C:C base pair without distorting the higher-order structure of the duplex. We conclude that the specific formation of C-Ag-C base pair with large binding affinity would provide a binding mode of metal ion-DNA interactions, similar to that of the previously reported T-Hg-T base pair. The C-Ag-C base pair may be useful not only for understanding of molecular mechanism of gene mutations related to heavy metal ions but also for wide variety of potential applications of metal-mediated base pairs in various fields, such as material, life and environmental sciences.
金属离子-核酸相互作用因其参与核酸的结构形成和催化活性而引起了相当大的兴趣。尽管金属离子与错配碱基对双链体的相互作用对于理解与重金属离子相关的基因突变机制很重要，但它们尚未得到很好的表征。我们最近发现，Ag(+)离子稳定了 C:C 错配碱基对双链体 DNA。通过 Ag(+)离子与 C:C 错配碱基对的结合，形成了 C-Ag-C 金属介导的碱基对，以稳定双链体。在这里，我们研究了可能的 C-Ag-C 金属介导碱基对的特异性、热力学和结构。紫外熔融实验表明，只有具有 C:C 错配碱基对的双链体，而不是具有完全匹配和其他错配碱基对的双链体，在加入 Ag(+)离子后才会特异性稳定。等温滴定微量热法表明，Ag(+)离子以 1:1 的摩尔比特异性结合 C:C 碱基对，结合常数为 10(6) M(-1)，明显大于非特异性金属离子-DNA 相互作用。电喷雾电离质谱也支持 Ag(+)离子与 C:C 碱基对的特异性 1:1 结合。圆二色光谱和 NMR 表明，Ag(+)离子可能与 C:C 碱基对的 N3 位置结合，而不会扭曲双链体的高级结构。我们得出结论，具有大结合亲和力的特异性 C-Ag-C 碱基对的形成将提供一种类似于先前报道的 T-Hg-T 碱基对的金属离子-DNA 相互作用的结合模式。C-Ag-C 碱基对不仅可用于理解与重金属离子相关的基因突变的分子机制，而且可用于金属介导碱基对在材料、生命和环境科学等各个领域的各种潜在应用。
