Dresden 2011 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 6: Charged Soft Matter
CPP 6.7: Topical Talk
Monday, March 14, 2011, 15:45–16:15, ZEU 160
Charge-Controlled Protein Crystallization — •Fajun Zhang1, Georg Zocher2, Andrea Sauter1, Marcell Wolf1, Felix Roosen-Runge1, Thilo Stehle2,3, and Frank Schreiber1 — 1Institut für Angewandte Physik, Universität Tübingen, Germany — 2Institute for Biochemistry, University of Tübingen, Germany — 3Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
We have studied the phase behavior of model globular proteins in solution in the presence of multivalent counterions. Under these conditions, it has been shown that negatively charged globular proteins undergo a reentrant condensation (RC) phase behavior [1], i.e. a phase-separated regime occurs in between two critical salt concentrations, c* < c**, giving a meta-stable liquid-liquid phase separation (LLPS). This RC phase behavior corresponds to an effective charge inversion of proteins as confirmed by zeta-potential measurements and supported by Monte Carlo simulations [2]. Crystallization near phase boundaries follows different mechanisms. Close to c*, crystal growth follows classical nucleation and growth mechanism; close to c**, crystallization follows a meta-stable LLPS, namely a two-step mechanism. X-ray diffraction analysis of the high quality single crystals provides direct evidence of crystal structure and cation binding sites. Our discovery of RC and LLPS induced by multivalent cations provides a new way to tune protein interactions with predictable phase behavior as well as controlling protein crystallization. [1] F. Zhang, et al., Phys. Rev. Lett. 2008, 101, 148101. [2] F. Zhang, et al., Proteins, 2010, 78, 3450