Extrinsic protein stabilization by the naturally occurring osmolytes beta-hydroxyectoine and betaine

Thermodynamic aspects of protein stabilization by two widespread naturally occurring osmolytes, beta-hydroxyectoine and betaine, were studied using differential scanning calorimetry (DSC) and bovine ribonuclease A (RNase A) as a model protein. The osmolyte beta-hydroxyectoine purified from Marinococcus was found to be a very efficient stabilizer. At a concentration of 3M it increased the melting temperature of RNase A (Tm) by more than 12K and gave rise to a stability increase of 10.6kJ/mol at room temperature. The heat capacity difference between the folded and unfolded state (deltaC(p)) was found to be significantly increased. Betaine stabilized RNase A only at concentrations less than 3M. Also, here deltaCp was found to be increased. Calculation of the number of water molecules that additionally bind to unfolded RNase A resulted in surprisingly low numbers for both osmolytes. The significant stabilization of RNase A by beta-hydroxyectoine makes this osmolyte an interesting stabilizer in biotechnological processes in which enzymes are applied in the presence of denaturants or at high temperature.