Biosynthesis of the Prenylated Salicylaldehyde Flavoglaucin Requires Temporary Reduction to Salicyl Alcohol for Decoration before Reoxidation to the Final Product

Abstract

The biosynthetic pathway of the prenylated salicylaldehyde flavoglaucin and congeners in Aspergillus ruber was elucidated by genome mining, heterologous expression, precursor feeding, and biochemical characterization. The polyketide skeleton was released as alkylated salicyl alcohols, which is a prerequisite for consecutive hydroxylation and prenylation, before reoxidation to the final aldehyde products. Our results provide an excellent example for a highly programmed machinery in natural product biosynthesis.

Genome Mining and Analysis of PKS Genes in Eurotium cristatum E1 Isolated from Fuzhuan Brick Tea

“…It was discovered in the last century, but the biosynthetic pathway was only reported in 2020 [50]. In 2020, the biosynthetic gene cluster of flavoglaucin in Aspergillus ruber was proposed [40,50]. Furthermore, the comparison between the proposed BGC in E1 and the known flavoglaucin gene cluster showed that the number of genes varies enormously (16 vs. 8).…”

“…However, the similarity of PKS genes and the eight genes downstream of BGC at the amino acid level was more than 85%. In addition, A. ruber can produce six kinds of flavoglaucin and congeners, including isoaspergin, dihydroauroglaucin, aspergin, flavoglaucin, auroglaucin, and 2-(1 ,5 -heptadienyl)-3,6-dihydroxy-5-(3"-methyl-2"-butenyl) benzaldehyde [40]. However, the analysis of secondary metabolites of E. cristatum E1 found that it cannot produce the last compound, but can produce iso-dihydroauroglaucin.…”

“…Feeding experiments in 1978 confirmed that the biosynthesis of flavoglaucin is regulated by PKS and modified by isoprenylation [39]. The proposed biosynthetic pathway of flavoglaucin and its congeners was published in 2020 [40]. It has been discovered these compounds have many functions, such as antioxidant and antitumor activity [41].…”

“…The length of the A7192 gene cluster was 49.7 kb, which contains 16 genes. Then, the comparison between this cluster and the known flavoglaucin gene cluster was performed [40]. Pairwise amino acid alignments with the predicted proteins in this BGC revealed a well-conserved PKS, P450, prenyltransferase, FAD-binding oxidoreductase, a transcription factor as well as three short-chain dehydrogenases.…”

Biosynthesis of Fungal Natural Products Involving Two Separate Pathway Crosstalk

“…Interestingly, compound 41 is also an intermolecular [4 + 2] adduct that involves the coupling of epoxycyclohexenone and α-pyrone two building blocks via the Diels–Alder addition. Recently, the biosynthetic pathways of epoxycyclohexenone-derived fungal polyketides trichoxide, sordarial, and flavoglaucin have been investigated in detail, which provide new insights into the biosynthesis of the naphthalenone unit in 41 [ 55 , 56 , 57 ]. The biosynthesis of some fungal α-pyrone-linked NPs such as alternapyrones and citreoviridin have been reported.…”