The efficiency of hypoxanthine excision by alkyladenine DNA glycosylase is altered by changes in nearest neighbor bases
The efficiency of hypoxanthine excision by alkyladenine DNA glycosylase is altered by changes in nearest neighbor bases
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DOI：
10.1016/j.dnarep.2005.05.008
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发表时间：
2005-09-28
期刊：
影响因子：
3.8
通讯作者：
Bloom, LB
中科院分区：
文献类型：
--
作者：
Vallur, AC;Maher, RL;Bloom, LB
烷基腺嘌呤DNA糖基化酶（AAG）从DNA中切除一组结构多样的受损嘌呤，包括次黄嘌呤、1，N-6-乙烯基腺嘌呤、3-甲基腺嘌呤和7-甲基鸟嘌呤，以在这些位点启动碱基切除修复。切除发生在酶（.）一种DNA复合物，其中受损的碱基从DNA螺旋中翻转出来进入酶的活性位点。为了确定局部DNA序列是否会影响从DNA中切除次黄嘌呤的总体效率，测量了与次黄嘌呤紧邻的5 '和3 '碱基对不同的DNA底物的切除、AAG-DNA结合和解链温度的单转换动力学。当Hx侧翼为5 ' G和3 ' C时，与含有5 ' T和3 ' A的双链体相比，切除效率显著降低。切除效率的降低主要是由于AAG对DNA的结合亲和力降低。GC与TA最近邻的总体效果是将Hx从具有胸腺嘧啶和二氟甲苯的对中切除的效率的差异从5倍放大到约100倍。一般而言，如由较高解链温度所指示的更稳定的DNA底物给出降低的Hx切除效率。这些结果进行了讨论，在一个模型中，碱基翻转与未翻转复合物的相对稳定性有助于切除和底物特异性的AAG的整体效率。(c)2005 Elsevier B. V.保留所有权利。
Alkyladenine DNA glycosylase (AAG) excises a structurally diverse group of damaged purines including hypoxanthine, 1,N-6-ethenoadenine, 3-methyladenine, and 7-methylguanine from DNA to initiate base excision repair at these sites. Excision occurs in an enzyme(.)DNA complex in which the damaged base is flipped out of the DNA helix into the enzyme active site. To determine whether local DNA sequence could affect the overall efficiency of excision of hypoxanthine from DNA, single-turnover kinetics of excision, AAG-DNA binding, and melting temperatures were measured for DNA substrates that differed in the base pairs immediately 5 ' and 3 ' to hypoxanthine. When Hx was flanked by a 5 ' G and a 3 ' C, the efficiency of excision was reduced dramatically in comparison to a duplex containing a 5 ' T and 3 ' A. The reduction in excision efficiency was largely due to a decrease in binding affinity of AAG for DNA. The overall effect of GC versus TA nearest neighbors was to magnify the difference in the efficiencies of excision of Hx from pairs with thymine and difluorotoluene from a factor of 5 to a factor of about 100. In general, DNA substrates that were more stable as indicated by higher melting temperatures gave reduced efficiencies of excision of Hx. These results are discussed in terms of a model in which the relative stabilities of base-flipped versus unflipped complexes contribute the overall efficiency of excision and substrate specificity of AAG. (c) 2005 Elsevier B.V. All rights reserved.