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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: Poster: Charged Soft Matter

CPP 22.2: Poster

Mittwoch, 28. März 2012, 11:00–13:00, Poster A

Anomalous Small-Angle X-ray Scattering (ASAXS) Study of Multi-Valent Cations around Proteins in Solution — •Baohu Wu¹, Fajun Zhang¹, Maximilian W.A. Skoda², Robert M.J. Jacobs³, Michael Sztucki⁴, and Frank Schreiber¹ — ¹Institut für Angewandte Physik, Universität Tübingen — ²ISIS, RAL, UK — ³CRL, University of Oxford, UK — ⁴ESRF, France

A detailed understanding of the ion environment is essential for a full description of charged protein systems. ASAXS represents a powerful tool for studying the distribution of targeted ions [1]. We studied protein solutions (β-lactoglobulin, BLG) in the presence of Y3+ using ASAXS. Systematic measurements show clearly energy-dependent ASAXS shifts visible in the scattered intensity. The pure anomalous term which is about 0.02% to 0.2% of the total signal for Y3+ has been successfully separated using the matrix method. The number of ions around the protein, which contribute to the ASAXS signal, is between 1 to 6 per BLG dimer depending on the initial concentration of salt and protein. The number increases from 2.4 to 5 with BLG concentration at a fixed ion concentration, which is due to the cluster formed in re-entrant condensation phase regime [2]. These data are compared with our crystallographic study [3], which indicates 2 to 4 Y3+ binding per BLG dimer. The work will contribute to a comprehensive understanding of the role of the ions in protein crystal growth. [1] M. Sztucki, et al. J. Appl. Cryst. 2010, 43, 1479. [2] F. Zhang, et al. Phys. Rev. Lett. 2008, 101, 148101. [3] F. Zhang, et al. J. Appl. Cryst. 2011, 44, 755.