Bioinorganic study on bleomycin-transition metal complexes possessing DNA cleavage activity

抗肿瘤抗生素博莱霉素在依赖于某些金属离子(如铁、锰和钒)的存在的反应中裂解DNA。博莱霉素是一种双功能化合物，由DNA的结合部位和攻击部位组成。博莱霉素的&lt；beta&gt；-aminoalanine-pyrimidine-&lt；beta&gt；-hydroxyhistidine部分是金属络合和氧活化所必需的，而双噻唑部分则有助于与鸟嘌呤碱基的选择性相互作用。用多种光谱方法对博莱霉素铁与CO、NO和RCN的络合物进行了表征。特别令人感兴趣的是，博莱霉素-铁络合物和卟啉-铁络合物的性质非常相似。金属霉素对DNA的切割主要发生在鸟嘌呤-嘧啶(5‘-&gt；3’)序列上，尤其是GC位点。在用与小沟中鸟嘌呤2-氨基发生共价反应的蒽霉素修饰DNA的过程中，本实验结果表明金属霉素使DNA的序列特异性切割模式发生了剧烈的变化。相比之下，用黄曲霉毒素B1或硫酸二甲酯修饰鸟嘌呤N-7没有明显的变化。这些结果支持金属博莱霉素更倾向于结合在B-DNA螺旋的小槽中。此外，DNase I足迹结果表明：(1)金属霉素的DNA结合位点约占3个碱基对，涉及5‘-XGC序列；(2)博莱霉素-钴复合体高度阻断裂解碱基5’侧附近的G碱基。在这些观察的基础上，我们通过计算机构建的分子模型的检验，阐明了金属博莱霉素在d(ATGCCA)_2中的立体化学适合性。

The antitumor antibiotic bleomycin cleaves DNA in a reaction that is dependent on the presence of certain metal ions such as iron, manganese and vanadium. Bleomycin is a bifunctional compound consisting of the binding and attackng sites toward DNA. The <beta>-aminoalanine-pyrimidine-<beta>-hydroxyhistidine portion of bleomycin is essential for the metal chelation and dioxygen activation, and the bithiazole moiety contributes to the selective interaction with guanine base of DNA. The bleomycin-iron complexes with CO, NO and RCN were characterized by various spectroscopic methods. Of special interest is the fact that bleomycin-iron complex and porphyrin-iron complex are remarkably similar properties. The DNA cleavage by metallobleomycin occurs preferentiall at guanine-pyrimidine(5'->3') sequences, in particular GC site. In the modification of DNA by anthramycin which reacts covalently with the 2-amino group of guanine in the minor groove, the present result showed a drastic change of the sequence-specific cleavage mode by metallobleomycin. By contrast, the modification of guanine N-7 with aflatoxin B1 or dimethyl sulfate revealed no obvious alterations. These results support that metallobleomycin prefers the binding in the minor groove of B-DNA helix. In addition, the DNase I footprinting results showed that (1) the DNA binding site of metallobleomycin occupies approximately three base pairs involving 5'-XGC sequence and (2) the bleomycin-cobalt complex highly blocks the G base adjacent to 5'-side of the cleaved base. On the basis of these observations, we clarified stereochemical fit of metallobleomycin in d(ATGCCA)_2 by inspection of computerconstructed molecular model.