title: Effects of low urea concentrations on protein-water interactions.
abstract: Solvent properties of aqueous media (dipolarity/polarizability, hydrogen bond donor acidity, and hydrogen bond acceptor basicity) were measured in the coexisting phases of Dextran-PEG aqueous two-phase systems (ATPSs) containing .5 and 2.0 M urea. The differences between the electrostatic and hydrophobic properties of the phases in the ATPSs were quantified by analysis of partitioning of the homologous series of sodium salts of dinitrophenylated amino acids with aliphatic alkyl side chains. Furthermore, partitioning of eleven different proteins in the ATPSs was studied. The analysis of protein partition behavior in a set of ATPSs with protective osmolytes (sorbitol, sucrose, trehalose, and TMAO) at the concentration of .5 M, in osmolyte-free ATPS, and in ATPSs with .5 or 2.0 M urea in terms of the solvent properties of the phases was performed. The results show unambiguously that even at the urea concentration of .5 M, this denaturant affects partitioning of all proteins (except concanavalin A) through direct urea-protein interactions and via its effect on the solvent properties of the media. The direct urea-protein interactions seem to prevail over the urea effects on the solvent properties of water at the concentration of .5 M urea and appear to be completely dominant at 2.0 M urea concentration.
authors.affiliation: a Cleveland Diagnostics , 3615 Superior Ave., Suite 4407B, Cleveland , Ohio 44114 , USA.
authors.forename: Luisa A
authors.initials: LA
authors.lastname: Ferreira
authors.affiliation: b Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology , Russian Academy of Sciences , St. Petersburg , Russia.
authors.forename: Olga I
authors.initials: OI
authors.lastname: Povarova
authors.affiliation: b Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology , Russian Academy of Sciences , St. Petersburg , Russia.
authors.forename: Olga V
authors.initials: OV
authors.lastname: Stepanenko
authors.affiliation: b Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology , Russian Academy of Sciences , St. Petersburg , Russia.
authors.forename: Anna I
authors.initials: AI
authors.lastname: Sulatskaya
authors.affiliation: c Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering , Faculty of Engineering of the University of Porto , Rua Dr. Roberto Frias, Porto 4200-465 , Portugal.
authors.forename: Pedro P
authors.initials: PP
authors.lastname: Madeira
authors.affiliation: b Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology , Russian Academy of Sciences , St. Petersburg , Russia.
authors.forename: Irina M
authors.initials: IM
authors.lastname: Kuznetsova
authors.affiliation: b Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology , Russian Academy of Sciences , St. Petersburg , Russia.|d Department of Biophysics , St. Petersburg State Polytechnic University , St. Petersburg 195251 , Russia.
authors.forename: Konstantin K
authors.initials: KK
authors.lastname: Turoverov
authors.affiliation: b Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology , Russian Academy of Sciences , St. Petersburg , Russia.|e Department of Molecular Medicine and Byrd Alzheimer's Research Institute , Morsani College of Medicine, University of South Florida , Tampa , FL 33612 , USA.
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Uversky
authors.affiliation: a Cleveland Diagnostics , 3615 Superior Ave., Suite 4407B, Cleveland , Ohio 44114 , USA.
authors.forename: Boris Y
authors.initials: BY
authors.lastname: Zaslavsky
mesh_terms: D003911:Dextrans / Q000737:chemistry / Q000494:pharmacology; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D011092:Polyethylene Glycols / Q000737:chemistry / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D058767:Protein Unfolding / Q000187:drug effects; D011506:Proteins / Q000737:chemistry*; D012995:Solubility; D012997:Solvents / Q000737:chemistry; D014508:Urea / Q000737:chemistry* / Q000494:pharmacology; D014867:Water / Q000737:chemistry*
chemical_list: D003911:Dextrans; D011506:Proteins; D012997:Solvents; D014867:Water; D011092:Polyethylene Glycols; D014508:Urea
keywords: aqueous two-phase system; partition; protein–water interaction; solvent properties; urea–protein interaction