The crystal structure of a parallel-stranded guanine tetraplex at 0.95 angstrom resolution
The crystal structure of a parallel-stranded guanine tetraplex at 0.95 angstrom resolution
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DOI：
10.1006/jmbi.1997.1292
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发表时间：
1997-10-17
影响因子：
5.6
通讯作者：
Luisi, B
中科院分区：
文献类型：
--
作者：
Phillips, K;Dauter, Z;Luisi, B
在DNA和RNA中，在钠或钾离子存在的情况下，延伸的鸟嘌呤碱基可以形成稳定的四链螺旋。在染色体端粒、免疫球蛋白切换区和重组部位已发现有形成鸟嘌呤四链的倾向的序列。本文报道了六核苷酸d(Tg(4)T)在钠离子存在下形成的平行链四链复合体在0.95埃分辨率下的晶体结构。这四条链形成一个右旋螺旋，它由共面的鸟嘌呤碱基的氢键四元体稳定。在确定的点上，在四个平面内的和之间发现有良好分辨的钠离子，并与鸟嘌呤O6基团配位。已经确定了九个钙离子，每个离子都有一个明确的七配位水合壳。在四链体的螺旋槽中观察到氢键水模式，并聚集在磷酸基团周围。沟槽中的水分子可能与O4‘形成氢键，并可能影响鸟嘌呤的堆积行为。鸟嘌呤四分体有两种不同的堆积排列。胸腺嘧啶碱基对四链构象没有贡献，而是堆积以稳定晶格。我们提出的证据表明，糖的构象是应变的，并提出这源于优化鸟嘌呤碱基堆积的作用力。在磷酸二酯主链的几个地方观察到离散构象无序，这是由于简单的曲轴旋转不需要糖构象的净变化而引起的。(C)1997年学术出版社有限公司。
Ln both DNA and RNA, stretches of guanine bases can form stable four-stranded helices in the presence of sodium or potassium ions. Sequences with a propensity to form guanine tetraplexes have been found in chromosomal telomers, immunoglobulin switch regions, and recombination sites. We report the crystal structure at 0.95 Angstrom resolution of a parallel-stranded tetraplex formed by the hexanucleotide d(TG(4)T) in the presence of sodium ions. The four strands form a right-handed helix that is stabilized by hydrogen-bonding tetrads of co-planar guanine bases. Well-resolved sodium ions are found between and, at defined points, within tetrad planes and are coordinated with the guanine O6 groups. Nine calcium ions have been identified, each with a well-defined hepta-coordinate hydration shell. Hydrogen-bonding water patterns are observed within the tetraplex's helical grooves and clustered about the phosphate groups. Water molecules in the groove may form a hydrogen bond with the O4', and may affect the stacking behavior of guanine. Two distinct stacking arrangements are noted for the guanine tetrads. The thymine bases do not contribute to the four-stranded conformation, but instead stack to stabilize the crystal lattice. We present evidence that the sugar conformation is strained and propose that this originates from forces that optimize guanine base stacking. Discrete conformational disorder is observed at several places in the phosphodiester backbone, which results from a simple crankshaft rotation that requires no net change in the sugar conformation. (C) 1997 Academic Press Limited.