Directed evolution and the creation of enantioselective biocatalysts

Directed evolution has emerged as a key technology to generate enzymes with new or improved properties that are of major importance to the biotechnolo gy industry. A directed evolution approach starts with the identification o f a target enzyme to be optimized and the cloning of the corresponding gene . An efficient expression system is needed before the target gene is subjec ted to random mutagenesis and/or in vitro recombination, thereby creating m olecular diversity. Subsequently, improved enzyme variants are identified, preferably after being secreted into culture medium, by screening or select ion for the desired property. The genes encoding the improved enzymes are t hen used to parent the next round of directed evolution. Enantioselectivity is a biocatalyst property of major biotechnological importance that is, ho wever, difficult to deal with. We discuss recent examples of creating enant ioselective biocatalysts by directed evolution.