Shining a light on enzyme promiscuity.

Most, if not all, enzymes are capable of catalyzing physiologically irrelevant secondary reactions-termed 'promiscuous' reactions-in addition to the reactions that they have evolved to catalyze. Promiscuous activities can provide the starting point for evolution of new enzymes, both in nature and in the hands of protein engineers. Recent work suggests that the universe of promiscuous activities available in nature is enormous. New high-throughput approaches have significantly advanced our ability to identify promiscuous activities, setting the stage for synthetic biology efforts to construct novel pathways using catalysts derived from promiscuous enzymes via directed evolution.