Physicochemical Insights into the Stabilization of Stressed Lysozyme and Glycine Homopeptides by Sorbitol.

Understanding the mode of action of osmolytes on the protein with and without stressed conditions still requires experimental proof. In this direction, we have studied the interactions of a model protein hen egg white lysozyme (HEWL) and some homopeptides with sorbitol and a mixture of [dodecyltrimethylammonium bromide (DTAB) + sorbitol] by using a combination of high sensitivity calorimetry, density, sound velocity, and conductivity measurements with spectroscopic support. The physical chemistry underlying these interactions has been addressed on the basis of the energetics of interactions and other physicochemical properties. These results have highlighted that, even though the number of -CONH groups increases in higher homopeptides, the hydrophobic effect of - CH2 groups in the peptides dominates. Further, the counteraction of the deleterious effects of DTAB by sorbitol is due to the strengthened DTAB-sorbitol interactions rather than the indirect effect of the osmolyte via preferential exclusion. The results provide insights into the nature of interactions of the protein as well as some of the building blocks with the (DTAB + osmolyte) mixture which helped in understanding the mode of action of the osmolyte. Detailed physicochemical insights into the mode of action of stress counteracting agents on the protein and its destabilizer are needed to develop strategies to achieve optimum stability and activity of proteins under such conditions.