Ho P S, Frederick C A, Saal D, Wang A H, Rich A
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
J Biomol Struct Dyn. 1987 Feb;4(4):521-34. doi: 10.1080/07391102.1987.10507657.
A crystal of d(CGCGCG) in the Z-DNA lattice was soaked with ruthenium(III) hexaammine and its structure refined at 1.2 A resolution. Three unique metal complexes were found absorbed to each hexamer duplex. In addition, two symmetry-related binding sites were located, yielding a total of five ruthenium complexes bound to each d(CGCGCG) duplex. One unique site and its symmetry related site are nearly identical to the binding site of cobalt(III) hexaammine on Z-DNA. At that position, the metal complex bridges the convex surfaces of two adjacent Z-DNA strands by hydrogen bonds to the N7 and O6 functional groups of the guanine bases. The remaining three ruthenium three ruthenium(III) hexaammine binding sites are not present in the cobalt(III) hexaammine Z-DNA structure. Of these, two are related by symmetry and span the gap between the convex outer surface of one Z-DNA strand and the helical groove crevice of a neighboring strand. The third ruthenium site has no symmetry mate and involves interactions with only the deep groove. In this interaction, the metal complex hydrogen bonds to both the phosphate backbone and to a set of primary shell water molecules that extend the hydrogen bonding potential of the deep groove crevice out to the surface of the molecule. Solution studies comparing the circular dichroism spectra of low salt poly(dG-dC).poly(dG-dC) samples in the presence of ruthenium(III) and cobalt(III) hexammine show that the ruthenium complex does stabilize Z-DNA in solution, but not as effectively as the cobalt analogue. This suggests that some of the interactions available for the larger ruthenium complex may not be important for stabilization of the left-handed DNA conformation.
将Z-DNA晶格中的d（CGCGCG）晶体用六氨合钌（III）浸泡，并在1.2埃分辨率下对其结构进行精修。发现每个六聚体双链体上吸附有三种独特的金属配合物。此外，还定位了两个对称相关的结合位点，每个d（CGCGCG）双链体总共结合有五个钌配合物。一个独特的位点及其对称相关位点与六氨合钴（III）在Z-DNA上的结合位点几乎相同。在该位置，金属配合物通过与鸟嘌呤碱基的N7和O6官能团形成氢键，桥接两条相邻Z-DNA链的凸面。其余三个钌（III）六氨合钌结合位点在六氨合钴（III）Z-DNA结构中不存在。其中，两个通过对称相关，跨越一条Z-DNA链的凸外表面与相邻链的螺旋槽缝隙之间的间隙。第三个钌位点没有对称配偶体，仅涉及与深沟的相互作用。在这种相互作用中，金属配合物与磷酸主链以及一组初级壳层水分子形成氢键，这些水分子将深沟缝隙的氢键潜力延伸到分子表面。比较在钌（III）和钴（III）六氨合存在下低盐聚（dG-dC）.聚（dG-dC）样品的圆二色光谱的溶液研究表明，钌配合物确实能在溶液中稳定Z-DNA，但不如钴类似物有效。这表明较大的钌配合物可用的一些相互作用对于稳定左手DNA构象可能并不重要。
