Micaelo_2005_Biophys.J_89_999

The catalytic properties of enzymes in nonaqueous solvents are known to be dependent on the nature of the solvent. Here we present a molecular modeling study of the enantioselective properties of the enzyme cutinase in hexane under varying hydration conditions. Previous simulation studies have shown that for this model enzyme in hexane, the structural and dynamical properties are affected by the amount of water associated with the protein, being more similar to the aqueous simulation at 5-10% of water content. The implications of the hydration levels on the enzyme resolution of (R,S)-1-phenylethanol and (R,S)-2-phenyl-1-propanol are investigated using free energy calculations of the tetrahedral intermediate (TI) model. With this model system we show that the enzyme enantioselective properties are under the control of the amount of water present in the organic media. Maximum enantioselectivity is achieved at 10% water content. The stabilizing effects of the catalytic histidine on the TI are evaluated at different water contents and shown to be correlated. The correlation between the amount of water present in the media and the structural, dynamical, and thermodynamic properties of the enzyme are examined as well as the active site discriminative power.