Oxidatively damaged DNA Repair and Its Related Enzymes

氧化应激尤其是活性氧对DNA有氧化损伤作用。这种损伤导致突变并引起包括癌症在内的许多疾病。在氧化损伤的碱基中，8-氧代鸟嘌呤可导致G：C到T：A颠换频率增加。MutM是一种碱基切除修复酶，识别氧化损伤的鸟嘌呤，包括8-氧代鸟嘌呤。该酶催化三个反应：切除8-氧代鸟嘌呤碱基（糖基化酶活性）。以及由此产生的脱碱基位点的b-和d-消除（AP-裂解酶活性）。最近，我们还测定了MutM-DNA复合物的结构。这些结构表明许多氨基酸残基参与DNA结合和催化活性。然而，这些残留物的拟议作用尚未得到实验验证。为了建立MutM反应的详细机理，本研究考察了几个氨基酸残基在催化中的功能作用。我们根据复合物的晶体结构选择了几个保守的残基，并使用定点突变将其替换为其他残基。所得结果表明，一些残基参与MutM的催化反应。

DNA is oxidatively damaged by oxidative stress especially reactive oxygen species. Such damages result in mutations and cause a number of diseases including cancer. Among oxidatively damaged bases 8-oxoguanine can lead to increased frequency of G : C to T : A transversion. MutM is a base excision repair enzyme that recognize oxidatively damaged guanines including 8-oxoguanine. This enzyme catalyzes three reactions: excision of the 8-oxoguanine base (glycosylase activity). and b-and d-elimination of the resultant abasic site (AP-lyase activity), Recently, we also determined the structures of MutM-DNA complex. These structures suggest involvement of many amino acid residues in DNA-binding and catalytic activities. However, proposed roles of those residues have not been verified experimentally. To establish the detailed mechanism of MutM reaction, this study investigated functional roles of several amino acid residues in the catalysis. We selected several conserved residues based on the crystal structure of the complex and replaced them by other residues using site-directed mutagenesis. The obtained results demonstrate that some residues are involved in the catalytic reaction of MutM.