Cation-Induced Hydration Effects Cause Lower Critical Solution Temperature Behavior in Protein Solutions

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• 作者：Olga Matsarskaia ; Michal K. Braun ; Felix Roosen-Runge ; Marcell Wolf ; Fajun Zhang ; Roland Roth ; Frank Schreiber
• 刊名：Journal of Physical Chemistry B
• 出版年：2016
• 出版时间：August 11, 2016
• 年：2016
• 卷：120
• 期：31
• 页码：7731-7736
• 全文大小：362K
• 年卷期：0
• ISSN：1520-5207

文摘

The phase behavior of protein solutions is important for numerous phenomena in biology and soft matter. We report a lower critical solution temperature (LCST) phase behavior of aqueous solutions of a globular protein induced by multivalent metal ions around physiological temperatures. The LCST behavior manifests itself via a liquid–liquid phase separation of the protein–salt solution upon heating. Isothermal titration calorimetry and zeta-potential measurements indicate that here cation–protein binding is an endothermic, entropy-driven process. We offer a mechanistic explanation of the LCST. First, cations bind to protein surface groups driven by entropy changes of hydration water. Second, the bound cations bridge to other protein molecules, inducing an entropy-driven attraction causing the LCST. Our findings have general implications for condensation, LCST, and hydration behavior of (bio)polymer solutions as well as the understanding of biological effects of (heavy) metal ions and their hydration.