Rational design of enantioselective 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 (Δ R‐S Δ H ‡ ) and entropy (Δ R‐S Δ S ‡ ) 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. Δ R‐S Δ S ‡ was in all cases equally significant as Δ R‐S Δ H ‡ 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 Δ R‐S Δ H ‡ and Δ R‐S Δ S ‡ . Although the changes in Δ R‐S Δ H ‡ and Δ R‐S Δ S ‡ were of a compensatory nature the compensation was not perfect, thereby allowing modifications of E. Both the W104H and the T103G variants displayed larger Δ R‐S Δ H ‡ than wild type but exhibited a decrease or increase, respectively, in E due to their different relative increase in Δ R‐S Δ S ‡ .