Lead is unusually effective in sequence-specific folding of DNA.
Lead is unusually effective in sequence-specific folding of DNA.
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DOI：
10.1006/jmbi.1999.3441
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发表时间：
2000-02
影响因子：
5.6
通讯作者：
I. Smirnov;R. Shafer
中科院分区：
文献类型：
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作者：
I. Smirnov;R. Shafer
基于鸟嘌呤四联体的DNA四链体结构通常被单价阳离子如K（+）、Na（+）或NH（+）稳定（3）。某些二价阳离子也可以诱导四链体形成，如Sr（2+）。在这里，我们表明，Pb（2+）结合异常高的亲和力凝血酶结合适体，d（GGTTGGTGTGGTTGG），诱导单分子折叠结构。在微摩尔浓度下，结合是化学计量的，并且单个铅阳离子足以折叠适体。铅诱导的UV和CD光谱的变化是折叠四链体的特征，虽然长波长CD最大值发生在312 nm，而不是典型的值293 nm。一维可交换质子NMR谱显示参与鸟嘌呤四重碱基配对的亚氨基质子的预期共振。此外，二维NMR实验揭示了NOE接触通常见于鸟嘌呤四联体形成的折叠结构中，例如凝血酶适体的K（+）形式。只有能够形成鸟嘌呤四联体的序列似乎与Pb（+2）紧密结合并改变构象。这种序列特异性的紧密DNA结合可能与环境中铅可能的遗传毒性效应有关。
DNA quadruplex structures based on the guanine quartet are typically stabilized by monovalent cations such as K(+), Na(+), or NH(+)(3). Certain divalent cations can also induce quadruplex formation, such as Sr(2+). Here we show that Pb(2+) binds with unusually high affinity to the thrombin binding aptamer, d(GGTTGGTGTGGTTGG), inducing a unimolecular folded structure. At micromolar concentrations the binding is stoichiometric, and a single lead cation suffices to fold the aptamer. The lead-induced changes in UV and CD spectra are characteristic of folded quadruplexes, although the long wavelength CD maximum occurs at 312 nm rather than the typical value of 293 nm. The one-dimensional exchangeable proton NMR spectrum shows resonances expected for imino protons involved in guanine quartet base-pairing. Furthermore, two-dimensional NMR experiments reveal NOE contacts typically seen in folded structures formed by guanine quartets, such as the K(+) form of the thrombin aptamer. Only sequences capable of forming guanine quartets appear to bind Pb(+2) tightly and change conformation. This sequence-specific, tight DNA binding may be relevant to possible genotoxic effects of lead in the environment.