Probing the enantioselectivity of Bacillus subtilis esterase BS2 for tert. alcohols

The activity and enantioselectivity of several mutants of the esterase BS2 from Bacillus subtilis have been investigated. In the enzymatic hydrolysis of α,α-disubstituted cyanohydrin acetates, a class of tert. alcohol esters, they were active but not selective. In contrast to this result similar tert. acetylenic alcohol esters were hydrolysed with high E-values (>100). The difference in reactivity has been studied by molecular dynamics studies. The computer model suggested that the source of the observed difference in reactivity between the two very similar tert. alcohol esters lies in the ability of the cyanohydrins to form hydrogen bonds to water molecules—even when the substrate is in the active site.