Molecular Mechanism for the Hofmeister Effect Derived from NMR and DSC Measurements on Barnase
Molecular Mechanism for the Hofmeister Effect Derived from NMR and DSC Measurements on Barnase
复制标题
DOI：
10.1021/acsomega.6b00223
复制
发表时间：
2016-10-01
期刊：
影响因子：
4.1
通讯作者：
Williamson, Mike P.
中科院分区：
文献类型：
--
作者：
Bye, Jordan W.;Baxter, Nicola J.;Williamson, Mike P.
使用差示扫描量热法 (DSC) 和 NMR 研究了硫氰酸钠、氯化钠和硫酸钠对核糖核酸酶 Barnase 的影响。两种测量都揭示了低阴离子浓度（高达 250 mM）下的特异性和可饱和结合，这会产生与霍夫迈斯特系列无关的局部构象和能量效应。 C-13 异核单量子相干光谱中的峰展宽表明，硫酸盐的结合减慢了分子内运动。没有一个阴离子显示出与疏水基团的显着结合。高于 250 mM，DSC 结果与预期的霍夫迈斯特效应一致，因为离液阴离子硫氰酸盐会使芽酶不稳定。在这个较高的浓度范围内，阴离子对蛋白质 NMR 化学位移具有近似线性的影响，没有证据表明阴离子与蛋白质表面直接相互作用。我们得出结论，阴离子对芽孢杆菌RNA酶的影响是由溶剂相互作用介导的。结果与通常用于描述霍夫迈斯特效应的优先相互作用、优先水合和排除体积模型的预测不一致。相反，他们认为霍夫迈斯特阴离子对芽孢杆菌RNA酶的稳定性和溶解度的影响是由于蛋白质与水分子，特别是与水偶极子相互作用的方式，水偶极子在硫酸根阴离子周围有序性更高，而在硫氰酸根阴离子周围有序性较低。
The effects of sodium thiocyanate, sodium chloride, and sodium sulfate on the ribonuclease barnase were studied using differential scanning calorimetry (DSC) and NMR. Both measurements reveal specific and saturable binding at low anion concentrations (up to 250 mM), which produces localized conformational and energetic effects that are unrelated to the Hofmeister series. The binding of sulfate slows intramolecular motions, as revealed by peak broadening in C-13 heteronuclear single quantum coherence spectroscopy. None of the anions shows significant binding to hydrophobic groups. Above 250 mM, the DSC results are consistent with the expected Hofmeister effects in that the chaotropic anion thiocyanate destabilizes barnase. In this higher concentration range, the anions have approximately linear effects on protein NMR chemical shifts, with no evidence for direct interaction of the anions with the protein surface. We conclude that the effects of the anions on barnase are mediated by solvent interactions. The results are not consistent with the predictions of the preferential interaction, preferential hydration, and excluded volume models commonly used to describe Hofmeister effects. Instead, they suggest that the Hofmeister anion effects on both stability and solubility of barnase are due to the way in which the protein interacts with water molecules, and in particular with water dipoles, which are more ordered around sulfate anions and less ordered around thiocyanate anions.