Abstract
Melleolides and armillyl orsellinates are protoilludene-type aryl esters that are synthesized exclusively by parasitic fungi of the globally distributed genus Armillaria (Agaricomycetes, Physalacriaceae). Several of these compounds show potent antimicrobial and cytotoxic activities, making them promising leads for the development of new antibiotics or drugs for the treatment of cancer. We recently cloned and characterized the Armillaria gallica gene Pro1 encoding protoilludene synthase, a sesquiterpene cyclase catalyzing the pathway-committing step to all protoilludene-type aryl esters. Fungal enzymes representing secondary metabolic pathways are sometimes encoded by gene clusters, so we hypothesized that the missing steps in the pathway to melleolides and armillyl orsellinates might be identified by cloning the genes surrounding Pro1. Here we report the isolation of an A. gallica gene cluster encoding protoilludene synthase and four cytochrome P450 monooxygenases. Heterologous expression and functional analysis resulted in the identification of protoilludene-8α-hydroxylase, which catalyzes the first committed step in the armillyl orsellinate pathway. This confirms that ∆-6-protoilludene is a precursor for the synthesis of both melleolides and armillyl orsellinates, but the two pathways already branch at the level of the first oxygenation step. Our results provide insight into the synthesis of these valuable natural products and pave the way for their production by metabolic engineering.Key points• Protoilludene-type aryl esters are bioactive metabolites produced by Armillaria spp.• The pathway-committing step to these compounds is catalyzed by protoilludene synthase.• We characterized CYP-type enzymes in the cluster and identified novel intermediates.
Highlights
Natural products provide a vast array of diverse chemical structures that can be exploited in the agricultural, food/feed, cosmetics, biofuels, textiles, and healthcare industries (Hyde et al 2019)
Terpenoids are by far the largest class of natural products, but only four are currently approved as antimicrobial drugs, and these are all semisynthetic derivatives of the fungal antibiotic pleuromutilin (Mendes et al 2016; Hunt 2019; Lin et al 2019)
Having recently discovered the single-copy A. gallica Pro1 gene encoding protoilludene synthase (Engels et al 2011), we hypothesized that other genes required for the synthesis of protoilludene-type aryl esters might be clustered with this gene
Summary
Natural products provide a vast array of diverse chemical structures that can be exploited in the agricultural, food/feed, cosmetics, biofuels, textiles, and healthcare industries (Hyde et al 2019). Basidiomycetes provide a rich source of complex, structurally diverse, and bioactive sesquiterpenoids, and certain protoilludene-type sesquiterpene aryl esters produced by the genus Armillaria (class Agaricomycetes, family Physalacriaceae) are promising leads for the development of new drugs. Most Armillaria species are facultative necrotrophs, with parasitic and saprotrophic phases (Rishbeth 1985). They colonize the cambium and kill the root tissue, which provides nutrition during the saprotrophic phase. Armillaria mycelia can persist for months to years in residual root tissue and serve as an inoculum for further infections. The synthesis of protoilludene-type sesquiterpene aryl esters may help to prevent colonization by other saprotrophic fungi, avoiding competition for resources
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
