Crystal structures of 3-methyladenine DNA glycosylase MagIII and the recognition of alkylated bases
Crystal structures of 3-methyladenine DNA glycosylase MagIII and the recognition of alkylated bases
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DOI：
10.1093/emboj/cdg505
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发表时间：
2003-10-01
期刊：
影响因子：
11.4
通讯作者：
Ellenberger, T
中科院分区：
文献类型：
--
作者：
Eichman, BF;O'Rourke, EJ;Ellenberger, T
DNA糖基化酶催化从DNA切除化学修饰的碱基。虽然大多数糖基化酶对特定碱基具有特异性，但3-甲基腺嘌呤（m（3）A）DNA糖基化酶既包括作用于单个修饰碱基的高度特异性酶，也包括对烷基化损伤DNA具有更广泛特异性的酶。我们对这些不同酶特异性的结构理解目前仅限于未配体酶和无碱基DNA抑制剂复合物的晶体和NMR结构。本文提供了幽门螺杆菌（MagIII）的m（3）A DNA糖基化酶的高分辨率晶体结构，该酶以未配体形式与烷基化碱基3，9-二甲基腺嘌呤和1，N-6-乙烯基腺嘌呤结合。这些是属于螺旋-发夹-螺旋超家族的m（3）A糖基化酶活性位点中结合的核碱基的第一个结构。MagIII对带正电荷的m（3）A的特异性不是通过与嘌呤或甲基取代基原子的直接相互作用实现的，而是通过将两个芳族侧链之间的碱基堆叠在不包括7-甲基鸟嘌呤的口袋中实现的。我们报告的MagIII活性位点突变体的碱基切除和DNA结合活性，连同HHH糖基化酶的结构比较。
DNA glycosylases catalyze the excision of chemically modified bases from DNA. Although most glycosylases are specific to a particular base, the 3-methyladenine (m(3)A) DNA glycosylases include both highly specific enzymes acting on a single modified base, and enzymes with broader specificity for alkylation-damaged DNA. Our structural understanding of these different enzymatic specificities is currently limited to crystal and NMR structures of the unliganded enzymes and complexes with abasic DNA inhibitors. Presented here are high-resolution crystal structures of the m(3)A DNA glycosylase from Helicobacter pylori (MagIII) in the unliganded form and bound to alkylated bases 3,9-dimethyladenine and 1,N-6-ethenoadenine. These are the first structures of a nucleobase bound in the active site of a m(3)A glycosylase belonging to the helix-hairpin-helix superfamily. MagIII achieves its specificity for positively-charged m(3)A not by direct interactions with purine or methyl substituent atoms, but rather by stacking the base between two aromatic side chains in a pocket that excludes 7-methylguanine. We report base excision and DNA binding activities of MagIII active site mutants, together with a structural comparison of the HhH glycosylases.