Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia.
Biochemistry (Mosc). 2010 Feb;75(2):173-81. doi: 10.1134/s0006297910020070.
O(6)-Methylguanine (O(6)meG) is one of the most toxic, mutagenic, and carcinogenic lesions caused by the interaction of DNA with several catabolism products as well as with environmental methylating agents. Carcinogenic impact of O(6)meG can be conditioned not only by its mutagenic properties but also by alteration in enzymatic methylation of the C5 carbon atom of cytosine residue in CpG sequences. In this study, the effect of O(6)meG on DNA methylation by the catalytic domain of murine DNA methyltransferase (MTase) Dnmt3a (Dnmt3a-CD) is assessed. Damaged DNA duplexes cooperatively bind with Dnmt3a-CD, and O(6)meG changes the stability of enzyme-substrate complexes. Kinetic analysis of the methylation reaction revealed that O(6)meG varies the ratio of productive and nonproductive enzyme-substrate complexes and, depending on localization in substrate, causes decrease or increase in DNA methylation. Dnmt3a-CD is less sensitive to the presence of O(6)meG in DNA substrate than procaryotic MTase SssI recognizing CpG.
O(6)-甲基鸟嘌呤（O(6)meG）是 DNA 与多种代谢产物以及环境甲基化剂相互作用产生的最具毒性、致突变性和致癌性的损伤之一。O(6)meG 的致癌作用不仅取决于其致突变特性，还取决于 CpG 序列中胞嘧啶残基 C5 碳原子的酶促甲基化的改变。在这项研究中，评估了 O(6)meG 对鼠源 DNA 甲基转移酶（MTase）Dnmt3a（Dnmt3a-CD）催化结构域的 DNA 甲基化的影响。受损的 DNA 双链与 Dnmt3a-CD 协同结合，并且 O(6)meG 改变酶-底物复合物的稳定性。对甲基化反应的动力学分析表明，O(6)meG 改变了产生活性和非产生活性酶-底物复合物的比例，并且根据在底物中的定位，导致 DNA 甲基化的减少或增加。与识别 CpG 的原核 MTase SssI 相比，Dnmt3a-CD 对 DNA 底物中 O(6)meG 的存在的敏感性较低。
