Regensburg 2013 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 14: Crystallization, Nucleation and Self Assembly I

CPP 14.2: Vortrag

Dienstag, 12. März 2013, 09:45–10:00, H39

Structural evolution of a dense liquid phase in protein solutions — •Andrea Sauter, Fajun Zhang, and Frank Schreiber — Universität Tübingen, Institut für Angewandte Physik

Liquid-liquid phase separation (LLPS), the reversible transformation from a homogeneous into a protein rich and a protein poor phase, can be regarded as the equivalent of a gas-liquid transition. Here we present a study of the structural evolution of LLPS in solutions of beta-lactoglobulin (BLG) in presence of YCl₃. This system was subject of our research before [1,2] and has turned out to be a good model system for two-step crystallization. Selected samples were prepared at 35^∘C, above their critical temperature T_c of ca 20^∘C. When quenched to 5^∘C, the solution phase separates. Using SANS and SAXS, we followed the evolution of structures at different length scales. We use protein clusters based on the crystal structure to calculate theoretical scattering curves and compare them to the measured data. The results suggest the hierarchy of protein clusters to change with temperature and time. Comparison between initial and later measurements shows an increase at low q (clusters), at 1.8 nm⁻¹ (dimer formfactor) and several intermediate q regions and a simultanous decrease in others. A decrease of the monomer-monomer correlation peak at 2.2 nm⁻¹ suggests the mobility of monomers within clusters to be changed in this process. The mobility of proteins within clusters and their relaxation are crucial for nucleation, so these findings will help the understanding of two-step crystallization. [1] F. Zhang et al., J. Appl. Cryst. 44, 2011, 755-762; [2] F. Zhang et al., Faraday Discuss. 159, 2012, 313-325.