Characterization of a Silent Azaphilone Gene Cluster from Aspergillus niger ATCC 1015 Reveals a Hydroxylation-Mediated Pyran-Ring Formation

Abstract

SUMMARY Azaphilones are a class of fungal metabolites characterized by a highly oxygenated pyrano-quinone bicyclic core and exhibits a broad range of bioactivities. While widespread among various fungi, their biosynthesis has not been thoroughly elucidated. By activation of a silent (aza) gene cluster in Aspergillus niger ATCC 1015, we have discovered six new azaphilone compounds, azanigerones A-F (1, 3-7). Transcriptional analysis and deletion of a key polyketide synthase (PKS) gene further confirmed the involvement of the aza gene cluster. The biosynthetic pathway was shown to involve the convergent actions of a highly-reducing and a non-reducing PKSs. Most significantly, in vitro reaction of a key flavin-dependent monooxygenase encoded in the cluster with an early benzaldehyde intermediate revealed its roles in hydroxylation and pyran-ring formation to afford the characteristic bicylic core shared by azaphilones.

Structures and biological activities of azaphilones produced by Penicillium sp. KCB11A109 from a ginseng field

“…Such bioactivities have led to synthetic efforts concerning azaphilones and construction of chemical libraries based on the azaphilone core (Achard et al, 2012;Zhu et al, 2004). More recently, a biosynthetic pathway to azaphilones has been studied for discovery of new azaphilones by genome mining and combinatorial biosynthesis to diversify this biologically interesting family (Chiang et al, 2009;Zabala et al, 2012).…”

Diversity-Oriented Combinatorial Biosynthesis of Hybrid Polyketide Scaffolds from Azaphilone and Benzenediol Lactone Biosynthons

“…6–8 Some other azaphilones use a convergent biosynthetic scheme, whereby the hrPKS product acylates a free pyranoquinone intermediate. 9–11 Chimeric BDL scaffolds were previously generated by us using iPKS subunit shuffling among noncognate BDL synthase (BDLS) hrPKS and nrPKS partners. 12 While domain replacements allowed the asperfuranone nrPKS to accept a single medium-chain fatty acid substrate offered either by the fatty acid synthase or another azaphilone hrPKS resident in Aspergillus nidulans , other attempts to force the enzyme to utilize alternative acyl substrates proved unproductive.…”

Rising temperature stimulates the biosynthesis of water-soluble fluorescent yellow pigments and gene expression in Monascus ruber CGMCC10910

“…Based on their UV–Visible spectra, fluorescence spectra and mass spectra, Y1 was the reported intermediate azanigerone E (Zabala et al 2012; Chen et al 2017), and we concluded that the other compounds ( Y2 – Y4 ) were novel and had not been previously reported (Table 1; Fig. 2).…”