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J Chromatogr A. 2015 Mar 27;1387:32-41. doi: 10.1016/j.chroma.2015.02.006. Epub 2015 Feb 11.

Responses of proteins to different ionic environment are linearly interrelated.

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AnalizaDx Inc., 3615 Superior Ave., Suite 4407B, Cleveland, OH 44114, USA.
Laboratory of Separation and Reaction Engineering, Dpt. de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n 4200-465 Porto, Portugal.
Center for Data Analytics and Biomedical Informatics, Department of Computer and Information Sciences, College of Science and Technology, Temple University, Philadelphia, PA 19122, USA.
Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33612, USA; Biology Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia; Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow Region 142290 Russia; Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia. Electronic address:
AnalizaDx Inc., 3615 Superior Ave., Suite 4407B, Cleveland, OH 44114, USA. Electronic address:


Protein partitioning in aqueous two-phase systems (ATPS) is widely used as a convenient, inexpensive, and readily scaled-up separation technique. Protein partition behavior in ATPS is known to be readily manipulated by ionic composition. However, the available data on the effects of salts and buffer concentrations on protein partitioning are very limited. To fill this gap, partitioning of 15 proteins was examined in dextran-poly(ethylene glycol) ATPSs with different salt additives (Na2SO4, NaClO4, NaSCN, CsCl) in 0.11 M sodium phosphate buffer, pH 7.4. This analysis reveals that there is a linear relationship between the logarithms of the protein partition coefficients determined in the presence of different salts. This relationship suggests that the protein response to ionic environment is determined by the protein structure and type and concentrations of the ions present. Analysis of the differences between protein structures (described in terms of proteins responses to different salts) and that of cytochrome c chosen as a reference showed that the peculiarities of the protein surface structure and B-factor used as a measure of the protein flexibility are the determining parameters. Our results provide better insight into the use of different salts in manipulating protein partitioning in aqueous two-phase systems. These data also demonstrate that the protein responses to different ionic environments are interrelated and are determined by the structural peculiarities of protein surface. It is suggested that changes in ionic microenvironment of proteins may regulate protein transport and behavior in biological systems.


Aqueous two-phase system; Partitioning; Protein structure; Salts; Solvent interaction analysis; Structural changes

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