Release of normal bases from intact DNA by a native DNA repair enzyme
Release of normal bases from intact DNA by a native DNA repair enzyme
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DOI：
10.1093/emboj/17.2.363
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发表时间：
1998-01-15
期刊：
影响因子：
11.4
通讯作者：
Seeberg, E
中科院分区：
文献类型：
--
作者：
Berdal, KG;Johansen, RF;Seeberg, E
碱基切除修复是由DNA糖基化酶从DNA中去除不适当的碱基而启动的。已经发现这些酶中的一组，包括来自大肠杆菌的3-甲基腺嘌呤DNA糖基化酶II（AlkA）和来自其他生物体的相关酶，对完全不同的碱基结构具有不寻常的广泛特异性。我们测试了这些酶是否也能够从DNA中去除正常的碱基残基，来自大肠杆菌、酿酒酵母和人细胞的天然酶以显著的频率促进完整鸟嘌呤的释放，并且对AlkA的进一步分析表明所有正常碱基都可以被去除。用表达不同水平AlkA的质粒转化大肠杆菌产生了与表达水平相关的增加的自发突变频率，表明正常碱基的切除以生物学显著的速率发生，我们提出广泛特异性3-甲基腺嘌呤DNA糖基化酶代表了一种在DNA中很大程度上随机地“拉动”碱基的一般类型的修复酶，对特定结构没有太多偏好，由于碱基结构的改变导致碱基-糖键的不稳定性，因此，一旦键活化能被酶进一步降低，受损碱基比正常碱基更容易释放。定性地，该模型与观察到的大多数（如果不是全部的话）针对AlkA和类似物描述的底物的相对切除率相当好地相关。
Base excision repair is initiated by DNA glycosylases removing inappropriate bases from DNA, One group of these enzymes, comprising 3-methyladenine DNA glycosylase II (AlkA) from Escherichia coli and related enzymes from other organisms, has been found to have an unusual broad specificity towards quite different base structures, We tested whether such enzymes might also be capable of removing normal base residues from DNA, The native enzymes from E.coli, Saccharomyces cerevisiae and human cells promoted release of intact guanines with significant frequencies, and further analysis of AlkA showed that all the normal bases can be removed, Transformation of E.coli with plasmids expressing different levels of AlkA produced an increased spontaneous mutation frequency correlated with the expression levels, indicating that excision of normal bases occurs at biologically significant rates, We propose that the broad specificity 3-methyladenine DNA glycosylases represent a general type of repair enzyme 'pulling' bases in DNA largely at random, without much preference for a specific structure, The specificity for release of damaged bases occurs because base structure alterations cause instability of the base-sugar bonds, Damaged bases are therefore released more readily than normal bases once the bond activation energy is reduced further by the enzyme. Qualitatively, the model correlates quite well with the relative rate of excision observed for most, if not all, of the substrates described for AlkA and analogues.