[alpha]-chymotrypsin in water-acetone and water-dimethyl sulfoxide mixtures: Effect of preferential solvation and hydration

• Published in: Proteins, structure, function, and bioinformatics structure, function, and bioinformatics, 2017-10, Vol.85 (10), p.1808
• Main Authors: Sirotkin, Vladimir A, Kuchierskaya, Alexandra A
• Format: Article
• Language: English
• Subjects: Acetone; Catalysis; Catalytic activity; Chymotrypsin; Dehydration; Destabilization; Dimethyl sulfoxide; Enzymatic activity; Enzyme activity; Enzymes; Hydration; Hydrogen bonds; Intermediate water; Macromolecules; Moisture content; Organic solvents; Pancreas; Proteins; Solvation; Water content
• ISSN: 0887-3585; 1097-0134
• DOI: 10.1002/prot.25334

We investigated water/organic solvent sorption and residual enzyme activity to simultaneously monitor preferential solvation/hydration of protein macromolecules in the entire range of water content at 25°C. We applied this approach to estimate protein destabilization/stabilization due to the preferential interactions of bovine pancreatic [alpha]-chymotrypsin with water-acetone (moderate-strength H-bond acceptor) and water-DMSO (strong H-bond acceptor) mixtures. There are three concentration regimes for the dried [alpha]-chymotrypsin. [alpha]-Chymotrypsin is preferentially hydrated at high water content. The residual enzyme activity values are close to 100%. At intermediate water content, the dehydrated [alpha]-chymotrypsin has a higher affinity for acetone/DMSO than for water. Residual enzyme activity is minimal in this concentration range. The acetone/DMSO molecules are preferentially excluded from the protein surface at the lowest water content, resulting in preferential hydration. The residual catalytic activity in the water-poor acetone is 80%, compared with that observed after incubation in pure water. This effect is very small for the water-poor DMSO. Two different schemes are operative for the hydrated enzyme. At high and intermediate water content, [alpha]-chymotrypsin exhibits preferential hydration. However, at intermediate water content, in contrast to the dried enzyme, the initially hydrated [alpha]-chymotrypsin possesses increased preferential hydration parameters. At low water content, no residual enzyme activity was observed. Preferential binding of DMSO/acetone to [alpha]-chymotrypsin was detected. Our data clearly demonstrate that the hydrogen bond accepting ability of organic solvents and the protein hydration level constitute key factors in determining the stability of protein-water-organic solvent systems.