Hofmeister系列根据离子对蛋白质稳定性的影响对离子进行分类,然而微观机制仍然是个谜。在这个系列中,NaCl是中性的,Na2SO4和Na2HPO4是对称的,而GdmCl和NaSCN是离液的。本研究采用CD和NMR来研究NaCl的影响,Na2SO4和Na2HPO4的构象,稳定性,绑定,和WH4域的主链动力学(ps-ns和µs-ms时标),具有高稳定性和浓度≤200mM的可访问侧链。结果表明,三种盐都没有改变WW4的构象或显示与四个脂肪族疏水侧链的显着结合。NaCl对其热稳定性没有影响,而Na2SO4和Na2HPO4提高了~5℃的稳定性。有趣的是,NaCl仅与Arg27酰胺质子弱相互作用,而Na2SO4与Arg27和Phe31酰胺质子结合,Kd为32.7和41.6mM,分别。Na2HPO4,然而,以非饱和方式与Trp9,His24和Asn36酰胺质子结合。虽然这三种盐对ps-ns主链动力学的影响可以忽略不计,NaCl和Na2SO4没有显示效果,而Na2HPO4显着增加µs-ms主链动力学。这些发现,结合我们最近使用GdmCl和NaSCN的结果,为Hofmeister系列提供了微观机制。此外,数据显示热力学稳定性和骨架动力学之间缺乏简单的相关性,很可能是由于焓-熵补偿。我们的研究合理化选择氯化物和磷酸盐作为细胞外和细胞内空间的主要阴离子,以及聚磷酸盐作为某些单细胞生物中的原始伴侣。
The Hofmeister series categorizes ions based on their effects on protein stability, yet the microscopic mechanism remains a mystery. In this series, NaCl is neutral, Na2SO4 and Na2HPO4 are kosmotropic, while GdmCl and NaSCN are chaotropic. This study employs CD and NMR to investigate the effects of NaCl, Na2SO4, and Na2HPO4 on the conformation, stability, binding, and backbone dynamics (ps-ns and µs-ms time scales) of the WW4 domain with a high stability and accessible side chains at concentrations ≤ 200 mM. The results indicated that none of the three salts altered the conformation of WW4 or showed significant binding to the four aliphatic hydrophobic side chains. NaCl had no effect on its thermal stability, while Na2SO4 and Na2HPO4 enhanced the stability by ~5 °C. Interestingly, NaCl only weakly interacted with the Arg27 amide proton, whereas Na2SO4 bound to Arg27 and Phe31 amide protons with Kd of 32.7 and 41.6 mM, respectively. Na2HPO4, however, bound in a non-saturable manner to Trp9, His24, and Asn36 amide protons. While the three salts had negligible effects on ps-ns backbone dynamics, NaCl and Na2SO4 displayed no effect while Na2HPO4 significantly increased the µs-ms backbone dynamics. These findings, combined with our recent results with GdmCl and NaSCN, suggest a microscopic mechanism for the Hofmeister series. Additionally, the data revealed a lack of simple correlation between thermodynamic stability and backbone dynamics, most likely due to enthalpy-entropy compensation. Our study rationalizes the selection of chloride and phosphate as the primary anions in extracellular and intracellular spaces, as well as polyphosphate as a primitive chaperone in certain single-cell organisms.