Protein–Protein Interactions in Complex Cosolvent Solutions

Abstract

The effects of various kosmotropic and chaotropic cosolvents and salts on the intermolecular interaction potential of positively charged lysozyme is evaluated at varying protein concentrations by using synchrotron small-angle X-ray scattering in combination with liquid-state theoretical approaches. The experimentally derived static structure factors S(Q) obtained without and with added cosolvents and salts are analysed with a statistical mechanical model based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) potential, which accounts for repulsive and attractive interactions between the protein molecules. Different cosolvents and salts influence the interactions between protein molecules differently as a result of changes in the hydration level or solvation, in charge screening, specific adsorption of the additives at the protein surface, or increased hydrophobic interactions. Intermolecular interaction effects are significant above protein concentrations of 1 wt %, and with increasing protein concentration, the repulsive nature of the intermolecular pair potential V(r) increases markedly. Kosmotropic cosolvents like glycerol and sucrose exhibit strong concentration-dependent effects on the interaction potential, leading to an increase of repulsive forces between the protein molecules at low to medium high osmolyte concentrations. Addition of trifluoroethanol exhibits a multiphasic effect on V(r) when changing its concentration. Salts like sodium chloride and potassium sulfate exhibit strong concentration-dependent changes of the interaction potential due to charge screening of the positively charged protein molecules. Guanidinium chloride (GdmCl) at low concentrations exhibits a similar charge-screening effect, resulting in increased attractive interactions between the protein molecules. At higher GdmCl concentrations, V(r) becomes more repulsive in nature due to the presence of high concentrations of Gdm(+) ions binding to the protein molecules. Our findings also imply that in calculations of thermodynamic properties of proteins in solution and cosolvent mixtures, activity coefficients may not generally be neglected in the concentration range above 1 wt % protein.

Effect of Osmolytes on Pressure‐Induced Unfolding of Proteins: A High‐Pressure SAXS Study

“…Non-negligible repulsive or attractive interactions would have manifested themselves in a correlation peak or in a decrease in the forward scattered intensity IA C H T U N G T R E N N U N G (Q!0), respectively. [22] The radius of gyration R G = (15.6 AE 0.2) for the native conformation of the protein calculated from the Guinier analysis of the scattering curve is in good agreement with the values reported elsewhere [35][36][37] as well as with the theoretical value R G = 16.1 yielded by CRYSOL from the 3D molecular model (see Figure 3).…”

“…This is typically the case at and below 1 wt % protein concentration. [22] In this concentration regime the intensity scattered at small angles can be approximated by Equation (2):…”

Hofmeister ion effects on the solvation and thermal stability of model proteins lysozyme and myoglobin

“…Recently, infrared spectroscopy has been shown to be a useful technique to study differences in peptide and polymer solvation [27]. Several co-solvents including trifluoroethanol (TFE), sucrose, glucose, and trehalose sugars have been used to study protein thermal stability and solvation [27][28][29][30][31][32]. The co-solvent studies suggest specific binding and solvation changes influence the amide backbone and thermal stability.…”

Light Scattering Studies of Hydration and Structural Transformations of Lysozyme

“…Among others alcohol molecules, when added to colloidal suspension, compete with water molecules for the position on the surface of a protein molecule. Presence of the alcohol molecules disturbs an equilibrium among hydrophobic chemical groups of a protein and nally leads to destruction of its native, tertiary structure [12]. The experiments based on radiation scattering together with computer simulations [13] enable determination of the size and structure of the hydration shell.…”