Macromolecular Crowding Enhances Thermal Stability of Rabbit Muscle Creatine Kinase

The effect of dextran on the conformation (or secondary structure) and thermal stability of creatine kinase (CK) was studied using the far-ultraviolet (UV) circular dichroism (CD) spectra. The results showed that lower concentrations of dextran (less than 60 g/L) induced formation of the secondary CK structures. However, the secondary structure content of CK decreased when the dextran concentrations exceeded 60 g/L. Thermally induced transition curves were measured for CK in the presence of different concentrations of dextran by far-UV CD. The thermal transition curves were fitted to a two-state model by a nonlinear, least-squares method to obtain the transition temperature of the unfolding transition. An increase in the transition temperature was observed with the increase of the dextran concentration. These observations qualitatively accord with predictions of a previously proposed model for the effect of intermolecular excluded volume (macromolecular crowding) on protein stability and conformation. These findings imply that the effects of macromolecular crowding can have an important influence on our understanding of how protein folding occurs in vivo.