Expanding the chemical space of polyketides through structure-guided mutagenesis of Vitis vinifera stilbene synthase.

Several natural polyketides (PKs) have been associated with important pharmaceutical properties. Type III polyketide synthases (PKS) that generate aromatic PK polyketides have been studied extensively for their substrate promiscuity and product diversity. Stilbene synthase-like (STS) enzymes are unique in the type III PKS class as they possess a hydrogen bonding network, furnishing them with thioesterase-like properties, resulting in aldol condensation of the polyketide intermediates formed. Chalcone synthases (CHS) in contrast, lack this hydrogen-bonding network, resulting primarily in the Claisen condensation of the polyketide intermediates formed. We have attempted to expand the chemical space of this interesting class of compounds generated by creating structure-guided mutants of Vitis vinifera STS. Further, we have utilized a previously established workflow to quickly compare the wild-type reaction products to those generated by the mutants and identify novel PKs formed by using XCMS analysis of LC-MS and LC-MS/MS data. Based on this approach, we were able to generate 15 previously unreported PK molecules by exploring the substrate promiscuity of the wild-type enzyme and all mutants using unnatural substrates. These structures were specific to STSs and cannot be formed by their closely related CHS-like counterparts.