Molecular and macromolecular crowding-induced stabilization of proteins: Effect of dextran and its building block alone and their mixtures on stability and structure of lysozyme

Dextran 70 and its building block (glucose) has been used as macromolecular crowder and osmolyte, respectively. The difference in size and structure of both made us inquisitive to measure stability of lysozyme in the presence of their mixture. The effects of mixture of a fixed dextran 70 concentration (300 mg/ ml) containing different concentrations of glucose and vice versa, were studied. It was observed that T-m (the midpoint of denaturation curve) and Delta G(D)(o) (standard Gibbs free energy change at 25 degrees C) of lysozyme increase with the increasing concentration of dextran 70 and glucose alone and their mixture. We asked a question whether the effect of synthetic crowding agent on the stability of protein is due to the property of its monomer or due to the crowder. In this study, we observed that both dextran and its monomer stabilize the protein by same mechanism which is volume exclusion. The stabilization arises due to change in in the entropy of unfolding, while there is insignificant change in enthalpy of the protein with increasing concentration of the co-solute. Furthermore, the efficacy of stabilization by glucose increases in the crowded environment, when the concentration of dextran 70 is more than 200 mg/ml in the mixture. (C) 2019 Elsevier B.V. All rights reserved.