Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase.
Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase.
复制标题
O6-烷基鸟嘌呤-DNA 烷基转移酶修复人端粒 G-四链体 DNA 中的 O6-甲基鸟嘌呤加合物。
DOI：
10.1093/nar/gku659
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发表时间：
2014
影响因子：
14.9
通讯作者：
Fried,MichaelG
中科院分区：
文献类型：
--
作者：
Hellman,LanceM;Spear,TylerJ;Koontz,ColtonJ;Melikishvili,Manana;Fried,MichaelG
O6-烷基鸟嘌呤-DNA 烷基转移酶 (AGT) 是一种单循环 DNA 修复酶，可从 DNA 中去除促诱变的 O6-烷基鸟嘌呤加合物。它对短单链和双链体底物的功能已得到表征，但其作用于其他 DNA 结构的能力仍知之甚少。在这里，我们检查了这种酶对人端粒 G-四链体四链结构中 O6-甲基鸟嘌呤 (6mG) 加合物的功能。在折叠的 22-nt G-四链体底物上，结合在 2 AGT:DNA 处饱和，显着低于相似长度的线性单链 DNA 发现的~5 AGT:DNA 值，并且低于抑制四链体形成条件下端粒序列发现的值 (4 AGT:DNA)。尽管存在这些差异，AGT 仍修复了位于折叠 G-四链体内的 6mG 加合物，修复速度与类似条件下双链 DNA 底物的修复速度相当。修复在动力学上是双相的，快相和慢相的幅度取决于加合物在 G-四联体内的位置：一般来说，位于四联体堆叠顶部或底部四联体的加合物比位于内部四联体的加合物表现出更多的快相修复。这种区别可能反映了 G-四链体 DNA 中 6mG 残基构象动力学的差异。
O6-alkylguanine-DNA alkyltransferase (AGT) is a single-cycle DNA repair enzyme that removes pro-mutagenicO6-alkylguanine adducts from DNA. Its functions with short single-stranded and duplex substrates have been characterized, but its ability to act on other DNA structures remains poorly understood. Here, we examine the functions of this enzyme onO6-methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex. On a folded 22-nt G-quadruplex substrate, binding saturated at 2 AGT:DNA, significantly less than the ∼5 AGT:DNA found with linear single-stranded DNAs of similar length, and less than the value found with the telomere sequence under conditions that inhibit quadruplex formation (4 AGT:DNA). Despite these differences, AGT repaired 6mG adducts located within folded G-quadruplexes, at rates that were comparable to those found for a duplex DNA substrate under analogous conditions. Repair was kinetically biphasic with the amplitudes of rapid and slow phases dependent on the position of the adduct within the G-quadruplex: in general, adducts located in the top or bottom tetrads of a quadruplex stack exhibited more rapid-phase repair than did adducts located in the inner tetrad. This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs.