Analyzing the effects of protecting osmolytes on solute–water interactions by solvatochromic comparison method: II. Globular proteins

Abstract

Partitioning of 11 globular proteins was examined in aqueous dextran–PEG–sodium/potassium phosphate buffer (0.01 M K/NaPB, pH 7.4) two-phase systems (ATPSs) containing 0.5 M sorbitol. The data obtained were analyzed together with those reported previously for the same proteins in osmolyte-free ATPS and ATPS containing 0.5 M sucrose, TMAO, or trehalose. It was found that all the partition coefficients for proteins determined in the presence of 0.5 M of different osmolytes and in the absence of osmolytes may be described in terms of the differences between solvent properties of the coexisting phases. Solute-specific coefficients characterizing different types of solute–solvent interactions were calculated for each protein. These solute-specific coefficients are linearly interrelated implying cooperativity of different types of protein–water interactions. The data obtained indicate the lack of any association of the aforementioned osmolytes at concentration of 0.5 M with proteins. Computational analysis of one of the solute-specific coefficient S_s-values characterizing dipole–dipole protein–water interactions shows that it is determined by the peculiarities of protein surface.