The stabilization of proteins by sucrose.

TLDR

Protein–solvent interactions in the sucrose/water system have been studied to understand how sucrose affects protein behavior. The study measured thermal unfolding thermodynamics and kinetics of three proteins across sucrose concentrations, complemented by density measurements interpreted with multicomponent thermodynamic theory. Sucrose preferentially excludes from protein domains, raising the free energy of unfolding and increasing activation energy, thereby stabilizing the proteins without altering their native conformation, a effect linked to the higher cohesive force and surface tension of the sucrose–water solvent.

Abstract

The interactions between proteins and solvent components have been investigated for the sucrose/water system. Thermodynamic and kinetic measurements of the thermal unfolding of alpha-chymotrypsin, chymotrypsinogen, and ribonuclease were performed as a function of sucrose concentration. The alteration in protein-solvent interactions in the presence of sucrose was also studied by density measurements and analyzed by multicomponent thermodynamic theory. Sucrose does not induce a conformational change in three proteins studied, although it does induce a small change in the circular dichroism spectrum of ribonuclease. The enthalpy of thermal unfolding shows little dependence on the concentration of sucrose, while the apparent activation energy of the unfolding process is increased by the addition of sucrose. The results from the protein-solvent interaction study indicate that sucrose is preferentially excluded from the protein domain, increasing the free energy of the system. Thermodynamically this leads to protein stabilization since the unfolded state of the protein becomes thermodynamically even less favorable in the presence of sucrose. The exclusion of sucrose from the protein domain seems to be related to the higher cohesive force of the sucrose water solvent system since all the experimental observations can be correlated with the effect of sucrose on the surface tension of water.