Gessner R V, Quigley G J, Wang A H, van der Marel G A, van Boom J H, Rich A
Biochemistry. 1985 Jan 15;24(2):237-40. doi: 10.1021/bi00323a001.
In the equilibrium between B-DNA and Z-DNA in poly(dC-dG), the [Co(NH3)6]3+ ion stabilizes the Z form 4 orders of magnitude more effectively than the Mg2+ ion. The structural basis of this difference is revealed in Z-DNA crystal structures of d(CpGpCpGpCpG) stabilized by either Na+/Mg2+ or Na+/Mg2+ plus [Co(NH3)6]3+. The crystals diffract X-rays to high resolution, and the structures were refined at 1.25 A. The [Co(NH3)6]3+ ion forms five hydrogen bonds onto the surface of Z-DNA, bonding to a guanine O6 and N7 as well as to a phosphate group in the ZII conformation. The Mg2+ ion binds through its hydration shell with up to three hydrogen bonds to guanine N7 and O6. Higher charge, specific fitting of more hydrogen bonds, and a more stable complex all contribute to the great effectiveness of [Co(NH3)6]3+ in stabilizing Z-DNA.
在聚（dC-dG）中B-DNA与Z-DNA的平衡体系中，[Co(NH₃)₆]³⁺离子比Mg²⁺离子更有效地稳定Z型结构达4个数量级。这种差异的结构基础在由Na⁺/Mg²⁺或Na⁺/Mg²⁺加[Co(NH₃)₆]³⁺稳定的d（CpGpCpGpCpG）的Z-DNA晶体结构中得以揭示。这些晶体对X射线进行高分辨率衍射，结构在1.25 Å下精修。[Co(NH₃)₆]³⁺离子在Z-DNA表面形成五个氢键，与鸟嘌呤的O6和N7以及ZII构象中的一个磷酸基团结合。Mg²⁺离子通过其水合壳层与鸟嘌呤的N7和O6最多形成三个氢键。更高的电荷、更多氢键的特异性匹配以及更稳定的复合物都有助于[Co(NH₃)₆]³⁺在稳定Z-DNA方面的巨大有效性。
