Observation of multiple protein temperature transitions dependent upon the chemical environment

Biological macromolecules initiate their biochemical activity near their glass transition temperature, which is likely controlled via their interaction with water molecules. Aligned with this theory, it has been shown experimentally that the presence of bioprotective compounds, such as sucrose and trehalose, can increase the transition temperature of a protein. Since the molecular mechanism for this observation is not well understood, we report here the use of molecular dynamics (MD) simulations to study the transition temperatures of lysozyme in three different chemical environments: solely water, a sucrose/water mixture, and a trehalose/water mixture. Simulating over a temperature range from 20 K to 370 K in 10 K increments, we introduce a new approach combining the measurement of protein hydrogen atom mean square displacement (MSD) with principal component analysis (PCA) to predict multiple temperature-dependent transitions. This reproduces trends in equivalent experimental data better than when using a single transition approach, indicating that water coupled transitions are induced at multiple temperatures rather than a single temperature. The findings of this study may be useful for selecting additives to maintain stability of biomolecules in the biotechnological, pharmaceutical, and food sectors.