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Following Protein Dynamics in Real Time during Crystallization

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journal contribution
posted on 14.11.2019 by Christian Beck, Marco Grimaldo, Felix Roosen-Runge, Ralph Maier, Olga Matsarskaia, Michal Braun, Benedikt Sohmen, Orsolya Czakkel, Ralf Schweins, Fajun Zhang, Tilo Seydel, Frank Schreiber
The process of protein crystallization from aqueous protein solutions is still insufficiently understood. During macroscopic crystal formation, occurring often on time scales from a few hours to several days, protein dynamics evolves on the molecular level. Here, we present a proof of concept and a framework to observe this evolving diffusive dynamics on the pico- to nanosecond time scale, associated with cluster or precursor formation that ultimately results in emerging crystals. We investigated the model system of the protein β-lactoglobulin in D2O in the presence of ZnCl2, which induces crystallization by electrostatic bridges. First, the structural changes occurring during crystallization were followed by small-angle neutron scattering. Furthermore, we employed neutron backscattering and spin–echo spectroscopy to measure the ensemble-averaged self- and collective diffusion on nanosecond time scales of protein solutions with a kinetic time resolution on the order of 15 min. The experiments provide information on the increasing number fraction of immobilized proteins as well as on the diffusive motion of unbound proteins in an increasingly depleted phase. Simultaneously, information on the internal dynamics of the proteins is obtained.

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