Formation of 3-Orsellinoxypropanoic Acid in Penicillum crustosum is Catalyzed by a Bifunctional Nonreducing Polyketide Synthase.

The heterologous expression of a nonreducing polyketide synthase gene oesA from Penicillium crustosum led to the identification of orsellinoylpropanoic acid ( 1 ). Domain deletion and recombination proved that OesA catalyzes not only the formation of orsellinic acid but also its transfer to 3-hydroxypropanoic acid. Both ACP domains contribute independently and complementarily to the product formation. Feeding experiments provided evidence that only the orsellinyl residue is derived from acetate.