Functional Characterization of the Biosynthesis of Radicicol, an Hsp90 Inhibitor Resorcylic Acid Lactone from Chaetomium chiversii

Abstract

Fungal polyketides with the resorcylic acid lactone (RAL) scaffold are of interest for growth stimulation, the treatment of cancer, and neurodegenerative diseases. The RAL radicicol is a nanomolar inhibitor of the chaperone Hsp90, whose repression leads to a combinatorial blockade of cancer-causing pathways. Clustered genes for radicicol biosynthesis were identified and functionally characterized from the endophytic fungus Chaetomium chiversii, and compared to recently described RAL biosynthetic gene clusters. Radicicol production is abolished upon targeted inactivation of a putative cluster-specific regulator, or either of the two polyketide synthases that are predicted to collectively synthesize the radicicol polyketide core. Genomic evidence supports the existence of flavin-dependent halogenases in fungi: inactivation of such a putative halogenase from the C. chiversii radicicol locus yields dechloro-radicicol (monocillin I). Inactivation of a cytochrome P450 epoxidase furnishes pochonin D, a deepoxy-dihydro radicicol analog.

Unveiling the biosynthetic puzzle of destruxins in Metarhizium species

“…The Aspergillus parasiticus CYP65 VerB (33% identity with DtxS2) in the aflatoxin biosynthesis cluster is involved in desaturation of versicolorin B to versicolorin A (37). DtxS2 also shows an identity (35%) with the CYP65 RadP from the endophytic fungus Chaetomium chiversii that can epoxidize the antibiotic radicicol (38). These similarities suggest that DtxS2 probably functions as a multiple functional enzyme for metabolite hydroxylation, desaturation, oxidation, and/or epoxidation.…”

Rational reprogramming of fungal polyketide first-ring cyclization

“…Although the biosynthesis of most fungal polyketides requires a single iPKS enzyme, the assembly of the resorcylic acid lactones (RALs) involves a pair of collaborating hrPKSs and nrPKSs acting in sequence (12)(13)(14)(15)(16)(17). Fungal RALs are rich pharmacophores with estrogen agonist (zearalenone), mitogen-activated protein kinase inhibitory (hypothemycin), and heat shock response modulatory activities [radicicol and monocillin II (1)] ( Fig.…”

RadH: A Versatile Halogenase for Integration into Synthetic Pathways

“…Previous gene‐deletion experiments indicate that RadH is required for the production of radicicol in the fungus Chaetomium chiversii 12. Sequence similarity (Figure S1 in the Supporting Information) suggests that RadH is likely to fulfill the same function as Rdc2, which has been shown to catalyze the chlorination of monocillin II ( 1 ) to give 1 a in the biosynthesis of radicicol ( 3 ) in a different fungal strain (Figure 1).…”

“…RadH halogenates a range of natural and synthetic phenolic compounds (Figure 2 and Figure S3). Interestingly, RadH halogenates several of these compounds with higher efficiency than the proposed natural substrate 1 7, 12. Of the compounds tested, 6‐hydroxyisoquinoline ( 6 ) and the plant natural product 7‐hydroxycoumarin ( 8 ) are the best substrates for RadH (Figure 2).…”