Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 29: Crystallisation, Nucleation and Self assembly
CPP 29.11: Vortrag
Mittwoch, 28. März 2012, 18:15–18:30, C 243
Two-step nucleation in protein crystallization — •Fajun Zhang1, Andrea Sauter1, Marcell Wolf1, Felix Roosen-Runge1, Baohu Wu1, Michael Sztucki2, Roland Roth3, Maximilian W.A. Skoda4, Robert M.J. Jacobs5, and Frank Schreiber1 — 1Institut für Angewandte Physik, Universität Tübingen — 2ESRF, France — 3Universität Erlangen-Nürnberg — 4ISIS, RAL, UK — 5CRL, University of Oxford, UK
The attractive forces between proteins in solution are often short-ranged when compared to the size of protein, which can lead to a metastable liquid-liquid phase separation (LLPS) before crystallization. Under these conditions, the order parameters (density and structure) during protein crystal growth can be separately developed leading to a so-called 'two-step' nucleation mechanism. Here we present the results of protein crystallization in solution in the presence of multivalent counterions. It has been shown that negatively charged globular proteins undergo a reentrant condensation phase behavior [1], i.e. a phase-separated regime occurs in between two critical salt concentrations, c* < c**, resulting in a metastable LLPS region. Crystallization near the phase boundaries follows different mechanisms. Close to c*, crystal growth follows the classical nucleation and growth mechanism; close to c**, crystallization follows the two-step mechanism [2]. SAXS measurements demonstrate that protein clusters act as precursors for both the dense liquid phase and nucleation with a reduced energy barrier. [1] F. Zhang, et al., PRL 2008, 101, 148101; Proteins, 2010, 78, 3450. [2] F. Zhang, et al., J. Appl. Cryst. 2011, 44, 755.