Berlin 2015 – wissenschaftliches Programm

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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: Vortrag

Montag, 16. März 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.