A Nonheme FeII/2-Oxoglutarate-Dependent Oxygenase Catalyzes a Double Bond Migration within a Dimethylallyl Moiety Accompanied by Hydroxylation.

Prenylation of cyclodipeptides contributes largely to the structure diversification and biological activity. The prenylated products can be further metabolized by modifications like hydroxylation with cytochrome P450 enzymes or nonheme FeII/2-oxoglutarate-dependent oxygenases. Herein, we cloned and overexpressed NFIA_045530 from Neosartorya fischeri, which shares high sequence similarity with the nonheme FeII/2-oxoglutarate-dependent oxygenase FtmOx1Af from Aspergillus fumigatus on the amino acid level. FtmOx1Af is a member of the biosynthetic enzymes for fumitremorgin-type mycotoxins and catalyzes the conversion of fumitremorgin B to verruculogen by insertion of an oxygen molecule into the two prenyl moieties. The recombinant protein EAW25734 encoded by NFIA_045530 was purified to apparent homogeneity and then was used for incubation with intermediates of the fumitremorgin biosynthetic pathway. LC-MS analysis revealed no consumption of fumitremorgin B but good conversion with its biosynthetic precursor tryprostatin B in the presence of FeII and 2-oxoglutarate. Structure elucidation confirmed 22-hydroxylisotryprostatin B and 14α, 22-dihydroxylisotryprostatin B as the major enzyme products. Further detailed biochemical characterization led to the identification of a novel enzyme, which catalyzes a double bond migration within the dimethylallyl moiety of tryprostatin B with concomitant hydroxylation. Incubation with 18O2-enriched atmosphere confirmed O2 as the major origin of the hydroxyl groups. Solvent exchange was also observed for that at C22. LC-MS analysis confirmed the presence of 22-hydroxylisotryprostatin B in a Neosartorya fischeri extract, highlighting the role of this enzyme in the metabolism of intermediates of the fumitremorgin/verruculogen pathway. A plausible reaction mechanism implementing a radical rearrangement prior to accepting a hydroxyl radical from FeIII is discussed.