Dependence of RNA Tertiary Structural Stability on Mg2+ Concentration: Interpretation of the Hill Equation and Coefficient
Dependence of RNA Tertiary Structural Stability on Mg2+ Concentration: Interpretation of the Hill Equation and Coefficient
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DOI：
10.1021/bi902036j
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发表时间：
2010-03-09
期刊：
影响因子：
2.9
通讯作者：
Draper, David E.
中科院分区：
文献类型：
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作者：
Leipply, Desirae;Draper, David E.
通过用 MgCl2 滴定 RNA，可以很容易地观察到 Mg2+ 诱导的 RNA 三级结构折叠。此类滴定通常使用位点结合形式进行分析，其中包括参数 Hill 系数 n，有时将其视为特定位点处天然 RNA 结合的 Mg2+ 吨数。然而，静电相互作用的长程性质允许离子与 RNA 保持一定距离以稳定 RNA 结构。对 Mg2+ 和 RNA 之间发生的所有相互作用的完整描述使用优先相互作用系数 Gamma(2+)，它代表中和 RNA 电荷的“过量”Mg2+。天然中间未折叠 RNA 形式的 Gamma(2+) 之间的差异（Delta Gamma(2+)）是 RNA 在折叠时“吸收”的 Mg2+ 吨数。在这里，我们确定了 Hill 系数 n 等于文件离子摄取 Delta Gamma(2+) 的条件，并发现需要两个近似值：(i) Mg2+ 活度系数与滴定期间的浓度无关，以及 (ii) Delta Gamma(2-) 核糖开关依赖性被设计来测试这些近似值。加入比 MgCl2 过量 30 倍的 KCl 足以维持恒定的 Mg2+ 活度系数。我们还观察到，随着 Mg2+ 浓度增加大约 100 倍的范围，RNA 的 Mg2+ 摄取量从接近零到大约 2.6 变化。可以通过 Mg2+-RNA 滴定确定 Delta Gamma(2+)，但这些值仅适用于有限范围的溶液条件。
The Mg2+-induced folding of RNA tertiary Structures is readily observed via titrations of RNA with MgCl2. Such titrations are commonly analyzed using a site binding formalism that includes a parameter, the Hill coefficient n, which is sometimes deemed the number of Mg2+ tons bound by the native RNA at specific sites. However, the long-range nature of electrostatic interactions allows ions some distance from the RNA to stabilize an RNA structure. A complete description of all interactions taking place between Mg2+ and an RNA uses a preferential Interaction coefficient, Gamma(2+), which represents the "excess" Mg2+ neutralizing the RNA charge. The difference between Gamma(2+) for the native mid unfolded RNA Forms (Delta Gamma(2+)) is the number of Mg2+ tons "taken up" by an RNA upon folding. Here we determine the conditions Under which the Hill coefficient n call be equated to file ion Uptake Delta Gamma(2+) and find that two approximations arc necessary: (i) the Mg2+ activity coefficient is independent of concentration during a titration, and (ii) the dependence Delta Gamma(2-)riboswitch were designed to test these approximations. Inclusion of a 30-fold excess of KCl over MgCl2 was Sufficient to maintain a constant Mg2+ activity coefficient. We also observed that Mg2+ Uptake by the RNA varied from near zero to similar to 2.6 as the Mg2+ concentration increases over an similar to 100-fold range. It is possible to determine Delta Gamma(2+) from Mg2+-RNA titrations, but the Values are only applicable to a limited range of solution conditions.