Substrate specificity of human thymine-DNA glycosylase on exocyclic cytosine adducts
Substrate specificity of human thymine-DNA glycosylase on exocyclic cytosine adducts
复制标题
DOI：
10.1016/j.cbi.2006.12.013
复制
发表时间：
2007-02-20
影响因子：
5.1
通讯作者：
Guhaev, Anton B.
中科院分区：
文献类型：
--
作者：
Hang, Bo;Guhaev, Anton B.
环境致癌物甘油醛（GDA）和治疗性氯乙基亚硝基源（CNUs）分别可形成羟甲基乙烯和环饱和乙醇碱。这些加合物的致突变潜力取决于它们的错误编码特性和修复效率。在这项工作中，研究了人胸腺嘧啶- dna糖基酶（TDG）去除8-（羟甲基）- 3，n -4-乙基胞嘧啶（8- ham -epsilon C）和3，n -4-乙基胞嘧啶（EC）的能力，并与已知的TDG底物epsilon C进行了比较。当使用含有单个加合物的确定寡核苷酸进行测试时，TDG能够去除8-hm-eC，但不能去除EC。8-hm-epsilon C活性主要取决于鸟嘌呤与加合物的配对。TDG去除8-hm-epsilon C的效率低于epsilon C，但它的活性可以被人类AP内切酶I （APEI）显著增强，APEI是碱基切除修复的下游酶。当将TDG放置在包括5'-CpG位点在内的各种邻近序列中时，对EC没有任何可检测到的活性。分子模型显示，在TDG活性位点内，非平面EC外环与残基Asn 191之间可能存在空间冲突，这可能是TDG对EC缺乏活性的原因。TDG对体积较大的外环加合物n -4-苯并胞嘧啶没有活性，也对与胞嘧啶衍生物相同修饰的两种腺嘌呤衍生物7-h -epsilon A和EA没有活性。这些发现扩大了TDG底物的范围，有助于了解TDG底物特异性的结构要求。2007爱思唯尔爱尔兰有限公司版权所有。
The environmental carcinogen glycidaldehyde (GDA) and therapeutic chloroethylnitrosoureas (CNUs) can form hydroxymethyl etheno and ring-saturated ethano bases, respectively. The mutagenic potential of these adducts relies on their miscoding properties and repair efficiency. In this work, the ability of human thymine-DNA glycosylase (TDG) to excise 8-(hydroxymethyl)-3,N-4-ethenocytosine (8-hm-epsilon C) and 3,N-4-ethanocytosine (EC) was investigated and compared with epsilon C, a known substrate for TDG. When tested using defined oligonucleotides containing a single adduct, TDG is able to excise 8-hm-eC but not EC. The 8-hm-epsilon C activity mainly depends on guanine pairing with the adduct. TDG removes 8-hm-epsilon C less efficiently than epsilon C but its activity can be significantly enhanced by human AP endonuclease I (APEI), a downstream enzyme in the base excision repair. TDG did not show any detectable activity toward EC when placed in various neighboring sequences, including the 5'-CpG site. Molecular modeling revealed a possible steric clash between the non-planar EC exocyclic ring and residue Asn 191 within the TDG active site, which could account for the lack of TDG activity toward EC. TDG was not active against the bulkier exocyclic adduct 3,N-4-benzethenocytosine, nor the two adenine derivatives with same modifications as the cytosine derivatives, 7-hm-epsilon A and EA. These findings expand the TDG substrate range and aid in understanding the structural requirements for TDG substrate specificity. (c) 2007 Elsevier Ireland Ltd. All rights reserved.