Simultaneous machine-directed evolution of an imine reductase for activity and stereoselectivity

Biocatalysis is an effective tool to access small quantities of chiral molecules that are otherwise hard to synthesize or purify. A time-efficient process is needed to develop an enzyme that is adequate to perform desired chemistry. We evaluated machine-directed evolution as an enzyme engineering strategy, using a stereoselective imine reductase as the model system. Within one cycle, it was found that machine-directed evolution yielded a library of high activity mutants with a dramatically shifted activity distribution, compared to traditional directed evolution. Structure-guided analysis revealed that linear additivity may provide a simple explanation for the effectiveness of machine-directed evolution. The study concludes with a cost-benefit analysis showing that machine-directed evolution gives a good return on investment in high cost per measurement regimes.