DNA binding and nucleotide flipping by the human DNA repair protein AGT
DNA binding and nucleotide flipping by the human DNA repair protein AGT
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DOI：
10.1038/nsmb791
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发表时间：
2004-08-01
影响因子：
16.8
通讯作者：
Tainer, JA
中科院分区：
文献类型：
--
作者：
Daniels, DS;Woo, TT;Tainer, JA
O-6-烷基鸟嘌呤-DNA烷基转移酶(AGT)或O-6-甲基鸟嘌呤-DNA甲基转移酶(MGMT)可防止因鸟嘌呤烷化损伤而导致的突变和细胞凋亡。AGT以化学计量比的直接损伤逆转途径将烷基损伤不可逆转地转移到活性部位半胱氨酸。因此，AGT的表达会引起肿瘤对烷化化疗的耐药性，AGT抑制剂正在进行临床试验。我们报道了人AGT与含有生物底物O-6-甲基鸟嘌呤或与机械抑制剂N-1，O-6-乙氧黄嘌呤交联的双链DNA形成的复合体的结构。典型的DNA主槽结合螺旋-转角螺旋(HTH)基序介导了前所未有的小槽DNA结合。这种结合结构具有DNA修复和核苷酸翻转的优点，并为序列无关DNA结合蛋白(如RecQ和BRCA2)中的HTH相互作用提供了一个范例。结构和生化结果进一步支持Tyr114在核苷酸翻转通过磷酸旋转中的意外作用和定位烷基化碱基的有效动力学机制。
O-6-alkylguanine-DNA alkyltransferase (AGT), or O-6-methylguanine-DNA methyltransferase (MGMT), prevents mutations and apoptosis resulting from alkylation damage to guanines. AGT irreversibly transfers the alkyl lesion to an active site cysteine in a stoichiometric, direct damage reversal pathway. AGT expression therefore elicits tumor resistance to alkylating chemotherapies, and AGT inhibitors are in clinical trials. We report here structures of human AGT in complex with double-stranded DNA containing the biological substrate O-6-methylguanine or crosslinked to the mechanistic inhibitor N-1, O-6-ethanoxanthosine. The prototypical DNA major groove - binding helix-turn-helix (HTH) motif mediates unprecedented minor groove DNA binding. This binding architecture has advantages for DNA repair and nucleotide flipping, and provides a paradigm for HTH interactions in sequence-independent DNA-binding proteins like RecQ and BRCA2. Structural and biochemical results further support an unpredicted role for Tyr114 in nucleotide flipping through phosphate rotation and an efficient kinetic mechanism for locating alkylated bases.