Berlin 2015 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 14: Crystallization, Nucleation and Self Assembly II (joint session CPP, DY)
CPP 14.6: Talk
Monday, March 16, 2015, 17:30–17:45, PC 203
Real-time study of multi-step nucleation in protein crystallization — •Andrea Sauter1, Felix Roosen-Runge2, Fajun Zhang1, Gudrun Lotze3, Robert M. J. Jacobs4, and Frank Schreiber1 — 1Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen — 2Institut Laue-Langevin, Grenoble, France — 3European Synchrotron Radiation Facility, Grenoble, France — 4Department of Chemistry, University of Oxford, UK
We present a real-time study of protein crystallization of bovine β-lactoglobulin in the presence of the divalent salt CdCl2 using SAXS and optical microscopy. Monitoring the crystallization kinetics, we demonstrate a multi-step crystallization mechanism particularly focusing on the role of the metastable intermediate phase (MIP). In the first step, an intermediate phase is formed, followed by the nucleation of crystals within the intermediate phase. In the next step, this intermediate phase is consumed by nucleation and slow growth and the crystals are exposed to the dilute phase. At this stage, the number of crystals stays nearly constant, whereas the crystals grow rapidly due to access to the free protein molecules in the dilute phase. The results suggest that increasing the salt concentration near the transition zone pseudo-c** reduces the energy barrier for both the MIP and crystal nucleation. The observed kinetics can be well described using a rate-equation model based on a clear physical multi-step picture. This real-time study not only provides direct evidence for a multi-step process for protein crystallization, but also elucidates the role and the structural signature of the MIP in the non-classical process of protein crystallization.