The nonribosomal peptide synthetase enzyme DdaD tethers N _β-fumaramoyl-l -2,3-diaminopropionate for Fe(II)/α- ketoglutarate-dependent epoxidation by DdaC during dapdiamide antibiotic biosynthesis

The gene cluster from Pantoea agglomerans responsible for biosynthesis of the dapdiamide antibiotics encodes an adenylation-thiolation didomain protein, DdaD, and an Fe(II)/α-ketoglutarate-dependent dioxygenase homologue, DdaC. Here we show that DdaD, a nonribosomal peptide synthetase module, activates and sequesters N_β-fumaramoyl-l-2,3-diaminopropionate as a covalently tethered thioester for subsequent oxidative modification of the fumaramoyl group. DdaC catalyzes Fe(II)- and α-ketoglutarate-dependent epoxidation of the covalently bound N_β-fumaramoyl-l-2,3- diaminopropionyl-S-DdaD species to generate N_β-epoxysuccinamoyl- DAP (DAP = 2,3-diaminopropionate) in thioester linkage to DdaD. After hydrolytic release, N_β-epoxysuccinamoyl-DAP can be ligated to l-valine by the ATP-dependent ligase DdaF to form the natural antibiotic N _β-epoxysuccinamoyl-DAP-Val.