Superior removal of hydantoin lesions relative to other oxidized bases by the human DNA glycosylase hNEIL1
Superior removal of hydantoin lesions relative to other oxidized bases by the human DNA glycosylase hNEIL1
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DOI：
10.1021/bi800160s
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发表时间：
2008-07-08
期刊：
影响因子：
2.9
通讯作者：
David, Sheila S.
中科院分区：
文献类型：
--
作者：
Krishnamurthy, Nirmala;Zhao, Xiaobei;David, Sheila S.
DNA糖基酶hNEIL1启动了一系列不同病变的碱基切除修复(BER)，包括开环的嘌呤和饱和的嘧啶。其中，海因损伤--海因(Gh)和螺亚氨基二海因的两个非对映异构体(Sp1和Sp2)，由于其特殊的结构、高的诱变潜力和在细胞中的检测，最近引起了人们的极大关注。为了深入了解修复的作用，我们确定了hNEIL1对这些海因损伤相对于其他已知底物的切除效率。最值得注意的是，用hNEIL1对底物特异性的定量检测显示，与已报道的标准底物胸腺嘧啶二醇(TG)和5-羟基胞嘧啶(5-OHC)相比，海因病变的切除效率要高得多(>；快100倍)。重要的是，糖基酶和β，β-裂解酶反应是紧密耦合的，因此裂解酶的活性速率不会影响观察到的底物专一性。HNEIL1的活性也受到病变的碱基对的影响，当与T、G或C配对时，Gh和Sp的去除都比与A配对时更有效。值得注意的是，在不太可能的生理环境中，与T配对的Gh或Sp的去除最有效；实际上，这可能是与T的碱基对不稳定的结果。然而，在复制后合理形成的致突变碱基对(如Gh中心点G)中，通过BER容易去除可能是调节这些病变的突变谱的一个因素。此外，hNEIL1比Sp2更快地去除Sp1，表明该酶可以区分这两个非对映异构体。这是BER糖基酶首次被证明能够优先切除Sp的一个非对映异构体。这可能是hNEIL1活性部位的结构和Sp损伤的结构独特性的结果。这些结果表明，到目前为止，海因损伤是hNEIL1最好的底物，提示这些损伤的修复可能是hNEIL1酶在体内的关键功能。
The DNA glycosylase hNEIL1 initiates the base excision repair (BER) of a diverse array of lesions, including ring-opened purines and saturated pyrimidines. Of these, the hydantoin lesions, guanidinohydantoin (Gh) and the two diastereomers of spiroiminodihydantoin (Sp1 and Sp2), have garnered much recent attention due to their unusual structures, high mutagenic potential, and detection in cells. In order to provide insight into the role of repair, the excision efficiency by hNEIL1 of these hydantoin lesions relative to other known substrates was determined. Most notably, quantitative examination of the substrate specificity with hNEIL1 revealed that the hydantoin lesions are excised much more efficiently (> 100-fold faster) than the reported standard substrates thymine glycol (Tg) and 5-hydroxycytosine (5-OHC). Importantly, the glycosylase and beta,delta-lyase reactions are tightly coupled such that the rate of the lyase activity does not influence the observed substrate specificity. The activity of hNEIL1 is also influenced by the base pair partner of the lesion, with both Gh and Sp removal being more efficient when paired with T, G, or C than when paired with A. Notably, the most efficient removal is observed with the Gh or Sp paired in the unlikely physiological context with T; indeed, this may be a consequence of the unstable nature of base pairs with T. However, the facile removal via BER in promutagenic base pairs that are reasonably formed after replication (such as Gh center dot G) may be a factor that modulates the mutagenic profile of these lesions. In addition, hNEIL1 excises Sp1 faster than Sp2, indicating the enzyme can discriminate between the two diastereomers. This is the first time that a BER glycosylase has been shown to be able to preferentially excise one diastereomer of Sp. This may be a consequence of the architecture of the active site of hNEIL1 and the structural uniqueness of the Sp lesion. These results indicate that the hydantoin lesions are the best substrates identified thus far for hNEIL1 and suggest that repair of these lesions may be a critical function of the hNEIL1 enzyme in vivo.