Elucidation of Piericidin A1 Biosynthetic Locus Revealed a Thioesterase-Dependent Mechanism of α-Pyridone Ring Formation

Piericidins are a class of alpha-pyridone antibiotics that inhibit mitochondrial respiratory chain and exhibit antimicrobial, antifungal, and antitumor activities. Sequential analysis of Streptomyces piomogeues var. Hangzhouwanensis genome revealed six modular polyketide synthases, an amidotransferase, two methyltransferases, and a monooxygenase for piericidin A1 production. Gene functional analysis and deletion results provide overview of the biosynthesis pathway. Furthermore, in vitro characterization of the terminal polyketide synthase module with the thioesterase domain using beta-ketoacyl substrates was performed. That revealed a pathway where the alpha-pyridone ring formation is dependent on hydrolysis of the product beta, delta-diketo carboxylic acid by the C-terminal thioesterase followed by amidation and cyclization. These findings set the stage to investigate unusual enzymatic mechanisms in alpha-pyridone antibiotics biosynthesis, provide a foundation for genome mining of alpha-pyridone antibiotics, and produce analogs by molecular engineering.