Multi-Functional Metal Complexes with DNA Base-Sequence Selectivity

我们研究了DNA-配体相互作用的分子基础，特别是各种DNA结合蛋白和抗生素所表现出的序列识别和多功能的相互作用。我们选择了卟啉作为本研究的探针，合成了多种新型的卟啉化合物。游离碱的卟啉或它们的铜、镍配合物嵌入到DNA的碱基对之间，而轴向配体的锰配合物以非嵌入的方式与DNA结合。在DNA拓扑异构酶I存在下，通过螺旋稳定化和DNA解离研究，携带四个带电侧链的卟啉类似地结合和插入到DNA中，尽管它们的侧链不同，但这些络合物提供了基本上相同的DNaseI足迹模式。与单个带电的卟啉相比，侧链体积较小的卟啉表明，带电的侧链的存在似乎是有效插入DNA的关键，而不是它们的特性。所有以插层方式与DNA结合的卟啉都表现出对DNA的Rsa I酶切的特异性抑制。在两个识别位点中，一个含有富含GC的侧翼序列的位点被选择性地抑制。涉及这两个位点的DNA的DNase I足迹显示，紧邻被抑制的切割位点的5‘被保护，不被DNase I消化。保护区域出人意料地富含AT。我们已经将工作扩展到一系列新的化合物的合成上，这些化合物与DNA的相互作用可以通过引入到化合物中的第二结合部分来控制。在卟啉的六亚甲基侧链末端，连接了一个插入物，该嵌入物具有与博莱霉素或光裂解剂相同的序列特异性。用螺旋稳定化、可见吸收光谱研究了它们与DNA的结合。已经获得了DNA六聚体-卟啉络合物的晶体，尽管不幸的是它们太小了，无法进行X射线结构分析。

We have studied the molecular basis of DNA-ligand interactions, particularly, sequence recognitions and interplay of multi-functions displayed by various DNA-binding proteins and antibiotics. We have chosen porphyrins as a probe for this study and synthesized various novel porphyrins. Free base porphyrins or their Cu, Ni complexes intercalated between the base pairs of DNA, while Mn complexes with axial ligands bound to DNA by nonintercalative mode. Porphyrins carrying four charged sidechains bound and intercalated similarly into DNA as measured by helix stabilization and DNA unwinding studies in the presence of DNA topoisomerase I. Despite their different bulky sidechains, these complexes gave essentially identical DNase I footprinting patterns. Comparison with single charged porphyrins with less bulky sidechains has shown that the presence of charged sidechains on the porphyrin rather than their identity appears to be critical for efficient DNA intercalation. All the porphyrins which bind to DNA by intercalative mode showed site-specific inhibition of Rsa I digestion of DNA. Out of two recognition sites, a site with GC-rich flanking sequence was selectively inhibited. DNase I footprinting of DNA involving the two sites has shown that 5' immediate to the inhibited cutting-site was protected from DNase I digestion. The protected regions were unexpectedly AT-rich.We have extended the work to a synthesis of a new series of compounds whose interaction with DNA can be controlled by the second binding part introduced into the compound. At the end of hexamethylene sidechain of a porphyrin, an intercalator which is known to exhibit the same sequence specificity as bleomycin or a photocleaving agent was attached. Their binding with DNA has also been studied with helix stabilization, visible absorption spectroscopy. A crystals of a DNA hexamer-porphyrin complex have been obtained, although they are unfortunately too small for X-ray structural analysis.