Rational design of enantio selective enzymes requires considerations of entropy

Entropy was shown to play an equally important role as enthalpy for how enantioselectivity changes when redesigning an enzyme. By studying the temperature dependence of the enantiomeric ratio E of an enantioselective enzyme, its differential activation enthalpy (Delta (R-S)DeltaH(double dagger)) and entropy (Delta (R-S)DeltaS(double dagger)) components can be determined. This was done for the resolution of 3-methyl-2-butanol catalyzed by Candida antarctica lipase B and five variants with one or two point mutations. Delta (R-S)DeltaS(double dagger) was in all cases equally significant as Delta (R-S)DeltaH(double dagger) to E. One variant, T103G, displayed an increase in E, the others a decrease. The altered enantioselectivities of the variants were all related to simultaneous changes in Delta (R-S)DeltaH(double dagger) and Delta (R-S)DeltaS(double dagger). Although the changes in Delta (R-S)DeltaH(double dagger) and Delta (R-S)DeltaS(double dagger) were of a compensatory nature the compensation was not perfect, thereby allowing modifications of E. Both the W104H and the T103G variants displayed larger Delta (R-S)DeltaH(double dagger). than wild type but exhibited a decrease or increase, respectively, in E due to their different relative increase in Delta (R-S)DeltaS(double dagger).