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

• Published in: Biochimica et biophysica acta 2014-03, Vol.1844 (3), p.694-704
• Main Authors: Ferreira, Luisa, Fan, Xiao, Mikheeva, Larissa M., Madeira, Pedro P., Kurgan, Lukasz, Uversky, Vladimir N., Zaslavsky, Boris Y.
• Format: Article
• Language: English
• Subjects: Aqueous two-phase system; Crystallography, X-Ray; Dextrans - chemistry; Electrophoresis, Polyacrylamide Gel; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Polyethylene Glycols - chemistry; Protein flexibility; Protein partition; Protein structure; Proteins - chemistry; Proteins - isolation & purification; Solvents - chemistry; Static Electricity
• ISSN: 1570-9639; 0006-3002; 1878-1454
• DOI: 10.1016/j.bbapap.2014.01.016

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). •The partition of 15 globular proteins in aqueous two-phase systems (ATPSs) is analyzed.•ATPSs are formed by polyethylene glycol and dextran in 0.01M sodium phosphate.•The effect of five salt additives on the protein partition behavior is examined.•Partitioning is defined by the peculiarities of protein surfaces.•Flexibility of protein structure also contributes to its partition.