Regensburg 2016 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 17: Polyelectrolytes
CPP 17.10: Vortrag
Dienstag, 8. März 2016, 12:15–12:30, H40
The influence of transition metal cation size on protein phase behaviour — •Olga Matsarskaia1, Michal Braun1, Felix Roosen-Runge2, Fajun Zhang1, and Frank Schreiber1 — 1Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen — 2Institut Laue-Langevin, Grenoble, France
Transition metal cations induce many different types of interesting phase behaviour in aqueous solutions of negatively charged proteins, including reentrant condensation and liquid-liquid phase separation (LLPS) [1] which are involved in protein condensation diseases and may be used to optimise protein crystallisation [2]. We present a systematic study of the dependence of cation size on phase transitions in bovine serum albumin (BSA) using small-angle X-ray scattering (SAXS) and isothermal titration calorimetry (ITC). SAXS reveals an increase of the reduced second virial coefficient B2/B2HS, i.e. a weaker interprotein attraction, with increasing cation size from Gd3+ to La3+. This is consistent with a weaker LLPS with increasing cation size at room temperature and its eventual disappearance in the presence of La3+. ITC shows cation-protein binding to be an entropy-driven process, presumably induced by the release of hydration water around the cations and surface residues of the protein. With decreasing cation size, the entropy-enthalpy balance of this reaction changes, as shown by both ITC and calculations [3], which has important implications for the understanding of the entropy balance of ions in solution.
[1] Zhang et al. (2014). PAC, 86, 191; [2] Sauter et al. (2015). JACS, 137, 1485; [3] Ciupka et al. (2010). PCCP, 12, 13215.