Abstract
Fusarielins are polyketides with a decalin core produced by various species of Aspergillus and Fusarium. Although the responsible gene cluster has been identified, the biosynthetic pathway remains to be elucidated. In the present study, members of the gene cluster were deleted individually in a Fusarium graminearum strain overexpressing the local transcription factor. The results suggest that a trans-acting enoyl reductase (FSL5) assists the polyketide synthase FSL1 in biosynthesis of a polyketide product, which is released by hydrolysis by a trans-acting thioesterase (FSL2). Deletion of the epimerase (FSL3) resulted in accumulation of an unstable compound, which could be the released product. A novel compound, named prefusarielin, accumulated in the deletion mutant of the cytochrome P450 monooxygenase FSL4. Unlike the known fusarielins from Fusarium, this compound does not contain oxygenized decalin rings, suggesting that FSL4 is responsible for the oxygenation.
Highlights
Filamentous fungi are a rich source of bioactive natural products and compounds containing a bicyclic decalin ring motif (Figure 1), such as the monacolins lovastatin and compactin
The putative fusarielin gene cluster consists of seven genes (FSL1-7, Table 1) in F. graminearum of
FSL7 aregene predicted to be involved fusarielin as they in whichAspergillus, FSL7 are predicted to be involved in fusarielin biosynthesis as they are conserved in where several strain can produce fusarielins A and B [12,13]
Summary
Filamentous fungi are a rich source of bioactive natural products and compounds containing a bicyclic decalin ring motif (Figure 1), such as the monacolins lovastatin and compactin. They are of great interest due to their diverse bioactive properties as antibiotics and immunosuppressives [1]. In the biosynthesis of solanapyrones, the Diels-Alder reaction is not catalyzed by the PKS (Sol1), which instead releases the pyrone product desmethylprosolanapyrone I [4]. Reduction of the growing polyketide chain, before the Diels-Alder reaction, can be mediated by the PKS’s using the β-ketoreductase (KR), dehydratase (DH), and enoyl reductase (ER) [4] as observed in solanapyrones biosynthesis. Fusarielins A–D were first isolated from an unidentified pathway with five methylations and a decalin core [11].
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