Biosynthesis-Guided Discovery and Engineering of α-Pyrone Natural Products from Type I Polyketide Synthases.

Natural products containing the α-pyrone moiety are produced by polyketide synthases (PKSs) in bacteria, fungi, and plants. The conserved biosynthetic logic for the production of the α-pyrone moiety involves the cyclization of a triketide intermediate which also off-loads the polyketide from the activating thioester. In this study, we show that truncating a tetraketide natural product producing PKS assembly line allows for a thioesterase-independent off-loading of an α-pyrone polyketide natural product, one which we find to be natively present in the extracts of the bacterium that otherwise furnishes the tetraketide natural product. By engineering the truncated PKS , we demonstrate that a ketosynthase (KS) domain with relaxed substrate selectivity when coupled with in trans acylation of polyketide extender units can expand the chemical space of α-pyrone polyketide natural products. Findings from this study point toward heterologous intermolecular protein-protein interactions being detrimental to the efficiency of engineered PKS assembly lines.