POLYNUCLEOTIDES .18. SINGLE-STRANDED NUCLEIC-ACID HELICAL SECONDARY STRUCTURE STABILIZED BY IONIC BONDS - D(A+-G)10
POLYNUCLEOTIDES .18. SINGLE-STRANDED NUCLEIC-ACID HELICAL SECONDARY STRUCTURE STABILIZED BY IONIC BONDS - D(A+-G)10
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DOI：
10.1073/pnas.89.19.9242
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发表时间：
1992-10-01
影响因子：
11.1
通讯作者：
FRESCO, JR
中科院分区：
文献类型：
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作者：
DOLINNAYA, NG;FRESCO, JR
我们已经确定了一种类型的高嘌呤低聚物d（A-G）10低于pH 6的0.01 M Na+，其特征在于强烈的CD，但只有轻微的hypochromicity的二级结构。该螺旋的稳定性，命名为d（A+-G）10，不依赖于低聚物浓度，并随着离子强度或pH值的下降而急剧增加，在4.0（熔融温度，37 ℃）时达到最大值。转变的pK（a）在25 ℃时为5.3，随着温度和[Na+]的降低甚至更高，远高于dA或dG残基的固有pK（a）值。当在280 nm处观察时，由于螺旋外的dG残基与相邻的dA残基的堆叠，螺旋的熔化首先导致减色性。的CD光谱的成分二核苷单磷酸的字符和温度依赖性表明最小的手性和碱基重叠的A+PG序列在d（A+-G）10，但左手扭曲与一些碱基重叠的GpA+序列。所观察到的性能是最好的满足有限的碱基重叠的分子内螺旋的模型，稳定的离子键之间的DA残基质子化在N-1和下游带负电荷的磷酸盐带来接近由于骨干螺旋扭曲，而G（顺）残基位于外部的螺旋。这种结构可以提供额外的稳定能量的生物相关的质子化的非B-DNA结构所采用的高嘌呤。高嘧啶序列由于拓扑应力或特异性蛋白质结合。
We have identified a type of secondary structure for the homopurine oligomer d(A-G)10 below pH 6 in 0.01 M Na+ that is characterized by intense CD but only minor hypochromicity. The stability of this helix, designated d(A+-G)10, does not depend on oligomer concentration and increases sharply as ionic strength or pH drops, reaching a maximum at 4.0 (melting temperature, 37-degrees-C). The pK(a) for the transition, 5.3 at 25-degrees-C and even higher with decreasing temperature and [Na+], is much higher than the intrinsic pK(a) values for dA or dG residues. While the dA residues are protonated in the helix, further protonation of the dG residues disrupts it. When observed at 280 nm, melting of the helix first results in hypochromicity due to stacking of extrahelical dG residues with neighboring dA residues. The character and temperature dependence of the CD spectra of the constituent dinucleoside monophosphates indicate minimal chirality and base overlap for the A+pG sequences in d(A+-G)10 but left-handed twist with some base overlap for the GpA+ sequences. The observed properties are best satisfied by a model for an intramolecular helix with limited base overlap, stabilized by ionic bonds between dA residues protonated at N-1 and downstream negatively charged phosphates brought close due to the backbone helical twist, while G(syn) residues lie external to the helix. This structure could provide additional stabilizing energy for biologically relevant protonated non-B-DNA structures adopted by homopurine.homopyrimidine sequences due to topological stress or specific protein binding.