Modifying the stereochemistry of an enzyme-catalyzed reaction by directed evolution.

Aldolases have potential as tools for the synthesis of stereochemically complex carbohydrates. Here, we show that directed evolution can be used to alter the stereochemical course of the reaction catalyzed by tagatose-1,6-bisphosphate aldolase. After three rounds of DNA shuffling and screening, the evolved aldolase showed an 80-fold improvement in k(cat)/K(m) toward the non-natural substrate fructose 1,6-bisphosphate, resulting in a 100-fold change in stereospecificity.