Synergistic effects of osmolytes on solvent exclusion and resulting protein stabilization: Studies with sucrose, taurine and sorbitol individually and in combination

Abstract

Osmolytes are small molecules which occur naturally and protect biomacromolecules against stress. Mixtures of small organic osmolytes occur in cells of many organisms suggesting that synergy has an important role. In this work, high sensitivity calorimetric as well as spectroscopic approach has been used to reveal individual and combined effects of three osmolytes; sucrose, taurine, and sorbitol on conformational and thermal stability of the protein hen egg-white lysozyme. Sucrose and sorbitol individually show greater extent of thermal stability on lysozyme than taurine. Intrinsic fluorescence and circular dichroism spectroscopic observations suggest absence of appreciable interaction between protein and these osmolytes. Individually taurine does not exert stabilization effect on lysozyme but in combination with sorbitol it provides higher thermal stability to the protein. The results indicate that effect of taurine and sorbitol in combination on the protein is additive at higher molality and at lower pH. In other cases, the extent of protein stability is lesser with individual osmolyte than their combined effect. The results further endorse that osmolytes modify structural properties of water leading to stabilization of the protein. The results obtained in this work provide experimental support to preferential exclusion mechanism of osmolytes in protein stabilization.