title: Cation-Induced Hydration Effects Cause Lower Critical Solution Temperature Behavior in Protein Solutions.
abstract: 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.
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen , Auf der Morgenstelle 10, 72076 Tübingen, Germany.
authors.forename: Olga
authors.initials: O
authors.lastname: Matsarskaia
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen , Auf der Morgenstelle 10, 72076 Tübingen, Germany.
authors.forename: Michal K
authors.initials: MK
authors.lastname: Braun
authors.affiliation: Institut Laue-Langevin , 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Felix
authors.initials: F
authors.lastname: Roosen-Runge
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen , Auf der Morgenstelle 10, 72076 Tübingen, Germany.
authors.forename: Marcell
authors.initials: M
authors.lastname: Wolf
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen , Auf der Morgenstelle 10, 72076 Tübingen, Germany.
authors.forename: Fajun
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Institut für Theoretische Physik, Universität Tübingen , Auf der Morgenstelle 14, 72076 Tübingen, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Roth
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen , Auf der Morgenstelle 10, 72076 Tübingen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Schreiber
mesh_terms: D000818:Animals; D002412:Cations / Q000737:chemistry*; D002417:Cattle; D019277:Entropy; D057927:Hydrophobic and Hydrophilic Interactions; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D014867:Water / Q000737:chemistry*; D015019:Yttrium / Q000737:chemistry
chemical_list: D002412:Cations; D012996:Solutions; D012997:Solvents; D014867:Water; C064782:yttrium chloride; D012710:Serum Albumin, Bovine; D015019:Yttrium