Enzymatic Formation of Unnatural Novel Chalcone, Stilbene, and Benzophenone Scaffolds by Plant Type III Polyketide Synthase

A C19 hexaketide stilbene and a C21 heptaketide chalcone were synthesized by Aloe arborescens octaketide synthase (OKS), a plant-specific type III polyketide synthase (PKS). Remarkably, the C21 chalcone-forming activity was dramatically increased in a structure-guided OKS N222G mutant that produces a C20 decaketide SEK15 from 10 molecules of malonyl-CoA. The findings suggested further strategies for production of unnatural polyketides by combination of the precursor-directed biosynthesis and the structure-guided engineering of type III PKS.