The impressively high conversion rates of natural enzymes partly result from increasing the catalytic activity of a selected few amino acid side chains through precise positioning within the protein binding cavity. Scientists have now demonstrated that such fine-tuning is also possible for “designer” enzymes with unnatural catalytic amino acids. In the journal Angewandte Chemie, they report that laboratory “evolution” of a designer enzyme with an aniline side chain led to variants with significantly higher activity.