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Biochim Biophys Acta. 2014 Mar;1844(3):694-704. doi: 10.1016/j.bbapap.2014.01.016. Epub 2014 Jan 30.

Structural features important for differences in protein partitioning in aqueous dextran-polyethylene glycol two-phase systems of different ionic compositions.

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Analiza, Inc., 3516 Superior Ave., Suite 4407B, Cleveland, OH 44114, USA.
Department of Electrical and Computer Engineering, University of Alberta, Canada.
Laboratory of Separation and Reaction Engineering, Department de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n 4200-465 Porto, Portugal.
Department of Molecular Medicine, USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA; Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Moscow Regions, Russia. Electronic address:
Analiza, Inc., 3516 Superior Ave., Suite 4407B, Cleveland, OH 44114, USA. Electronic address:


Partitioning of 15 proteins in dextran-70-polyethylene glycol (PEG)-8000 aqueous two-phase systems (ATPSs) in the presence of 0.01M sodium phosphate buffer, pH7.4 was studied. The effect of salt additives (NaCl, CsCl, Na2SO4, NaClO4 and NaSCN) at different concentrations on the protein partition behavior was examined. The salt effects on protein partitioning were analyzed by using the Collander solvent regression relationship between the protein partition coefficients in ATPSs with and without salt additives. The results obtained show that the presence and concentration of salt additives affect the protein partition behavior. Analysis of ATPSs in terms of the differences between the relative hydrophobicity and electrostatic properties of the phases does not explain the protein partition behavior. The differences between protein partitioning could not be explained by the protein size. The structural signatures for the proteins were constructed from partition coefficient values in four ATPSs with different salt additives, and the structural distances were calculated using cytochrome c as the reference structure. The structural distances for all the examined proteins (except lysozyme) were found to be interrelated. Analysis of about 50 different descriptors of the protein structures revealed that the partition behavior of proteins is determined by the peculiarities of their surfaces (e.g., the number of water-filled cavities and the averaged hydrophobicity of the surface residues) and by the intrinsic flexibility of the protein structure measured in terms of the B-factor (or temperature factor).


Aqueous two-phase system; Protein flexibility; Protein partition; Protein structure

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