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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Cation-specific interactions of protein surface charges in dilute aqueous salt solutions: a combined study using dielectric relaxation spectroscopy and Raman spectroscopy
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Cation-specific interactions of protein surface charges in dilute aqueous salt solutions: a combined study using dielectric relaxation spectroscopy and Raman spectroscopy

机译：稀盐水溶液中蛋白质表面电荷的阳离子特异性相互作用：使用介电弛豫光谱和拉曼光谱的组合研究

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摘要

We exploited glycine as a zwitterionic model system to experimentally probe the cation specific interaction of protein surface charges in dilute (0.25 mol L-1) aqueous solutions of four biologically relevant inorganic salts, NaCl, KCl, MgCl2 and CaCl2, via dielectric relaxation spectroscopy (DRS) and Raman spectroscopy. Glycine is the simplest building block of proteins and it exposes the same charged groups (carboxylate and ammonium) to the solvent that dominate the protein-water interface. As a counter ion, we selected Cl- due to its biological importance. For all systems, we performed simultaneous fitting of the real (epsilon) and imaginary (epsilon) parts of the dielectric functions, assuming a multimodal relaxation model, obtained from concentration dependent dielectric measurements at approximate to 293 K. We observe a reduction of the dielectric amplitude for the glycine relaxation while the corresponding time constant shows only small (7%) deviations compared to aqueous glycine solutions. We propose that the observed reduction in dielectric amplitude is due to a reduction of the effective dipole moment (mu(eff)) of zwitterionic glycine caused by the interaction of glycine with the ion even at very low (0.05 M) salt concentrations. The interaction between divalent metal ions and zwitterionic glycine is increased compared to the monovalent cation-zwitterion interaction; a finding that is also supported by Raman spectroscopy. Our combined dielectric relaxation and Raman spectroscopic study indicates that ion-glycine interactions are weak and mediated by the solvent. Cation-specificity of protein surface charges is also observed in dilute salt solutions (0.25 mol L-1), where electrostatic interactions dominate.
机译：我们利用甘氨酸作为两端模型系统，通过介电弛豫光谱通过介电弛豫光谱进行通过介电弛豫光谱（： DRS）和拉曼光谱。甘氨酸是最简单的构建蛋白块，它将相同的带电基团（羧酸盐和铵）暴露于主导蛋白水界面的溶剂。作为反离子，我们选择了它的生物重要性。对于所有系统，我们同时拟合介电功能的真实（ε）和虚构（epsilon）部分，假设从浓度依赖性介电测量以近似为293k获得的多模式松弛模型。我们观察到电介质的减少与甘氨酸水溶液相比，相应的时间常数仅显示相应的时间常数仅小（＆7％）偏差的振幅。我们提出观察到的介电幅度的降低是由于甘氨酸与离子相互作用引起的两性离子甘氨酸的有效偶极矩（μ（EFF）），即使在非常低（0.05μm）盐浓度下也是如此。与单价阳离子 - 两性期相互作用相比，二价金属离子和两性离子甘氨酸之间的相互作用增加; RAMAN光谱也支持的发现。我们的介电松弛和拉曼光谱研究表明，离子甘氨酸相互作用弱，由溶剂介导。在稀盐溶液（0.25mol L-1）中，也观察到蛋白质表面电荷的阳离子特异性，其中静电相互作用占主导地位。

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