Counting the number of magnesium ions bound to the surface-immobilized thymine oligonucleotides that comprise spherical nucleic acids.
Counting the number of magnesium ions bound to the surface-immobilized thymine oligonucleotides that comprise spherical nucleic acids.
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DOI：
10.1021/ja406551k
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发表时间：
2013-11
影响因子：
15
通讯作者：
Stephanie R. Walter;Kaylie L. Young;J. Holland;Richard L. Gieseck;C. Mirkin;F. Geiger
中科院分区：
文献类型：
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作者：
Stephanie R. Walter;Kaylie L. Young;J. Holland;Richard L. Gieseck;C. Mirkin;F. Geiger
在水相条件下进行的无标记研究定量了与表面固定的T40序列结合的Mg（2+）离子的数量、随后表面上DNA的重排以及Mg（2+）结合对DNA-DNA相互作用的影响。二次谐波产生测量表明，在误差范围内，18-20 Mg（2+）离子结合到T40链饱和，金属-DNA相互作用与链的近30%长度收缩有关。使用振动和频产生、原子力显微镜和动态光散射评估的结构重排归因于Mg（2+）离子与带负电荷的DNA结合时增加的电荷屏蔽，从而减少核苷酸之间的排斥库仑力并允许DNA单链自身塌陷或卷曲。用球形核酸（SNA）金纳米颗粒缀合物评估Mg（2+）结合对DNA杂交和双链体稳定性的影响，以确定在不存在NaCl的情况下用于DNA-DNA相互作用的Mg（2+）浓度的最佳工作范围。该发现与电荷滴定效应一致，其中，在不存在NaCl的情况下，（1）如果每条T40链结合平均17.5个或更少的Mg（2+）离子，则在室温下不发生杂交，直到本体Mg（2+）浓度接近0.5mM才达到该值;（2）如果结合平均17.5-18.0个Mg（2+）离子，则杂交继续进行，尽管具有平均Tm为31（3）°C的低双链体稳定性;和（3）如果结合18.5-19.0 Mg（2+）离子，则形成Tm为64（2）°C的高度稳定的双链体，对应于T40链的饱和。
Label-free studies carried out under aqueous phase conditions quantify the number of Mg(2+) ions binding to surface-immobilized T40 sequences, the subsequent reordering of DNA on the surface, and the consequences of Mg(2+) binding for DNA-DNA interactions. Second harmonic generation measurements indicate that, within error, 18-20 Mg(2+) ions are bound to the T40 strand at saturation and that the metal-DNA interaction is associated with a near 30% length contraction of the strand. Structural reordering, evaluated using vibrational sum frequency generation, atomic force microscopy, and dynamic light scattering, is attributed to increased charge screening as the Mg(2+) ions bind to the negatively charged DNA, reducing repulsive Coulomb forces between nucleotides and allowing the DNA single strands to collapse or coil upon themselves. The impact of Mg(2+) binding on DNA hybridization and duplex stability is assessed with spherical nucleic acid (SNA) gold nanoparticle conjugates in order to determine an optimal working range of Mg(2+) concentrations for DNA-DNA interactions in the absence of NaCl. The findings are consistent with a charge titration effect in which, in the absence of NaCl, (1) hybridization does not occur at room temperature if an average of 17.5 or less Mg(2+) ions are bound per T40 strand, which is not reached until the bulk Mg(2+) concentration approaches 0.5 mM; (2) hybridization proceeds, albeit with low duplex stability having an average Tm of 31(3)°C, if an average of 17.5-18.0 Mg(2+) ions are bound; and (3) highly stable duplexes having a Tm of 64(2)°C form if 18.5-19.0 Mg(2+) ions are bound, corresponding to saturation of the T40 strand.