Efficient Biosynthesis of Fungal Polyketides Containing the Dioxabicyclo-octane Ring System

Abstract

Aurovertins are fungal polyketides that exhibit potent inhibition of ATP synthase. Aurovertins contain a 2,6-dioxabicyclo[3.2.1]-octane ring that is proposed to be derived from a polyene precursor through regioselective oxidations and epoxide openings. In this study, we identified only four enzymes are required to produce aurovertin E 4. The core polyketide synthase produces a polyene α-pyrone 10. Following pyrone O-methylation by a methyltransferase, a flavin-dependent monooxygenase (FMO) and an epoxide hydrolase can iteratively transform the terminal triene portion of the precursor into the dioxabicyclo[3.2.1]-octane scaffold. We demonstrate that a tetrahydrofuranyl polyene 12 is the first stable intermediate in the transformation, which can undergo epoxidation and anti-Baldwin 6-endo-tet ring opening to yield the cyclic ether product. Our results further demonstrate the highly concise and efficient ways in which fungal biosynthetic pathways can generate complex natural product scaffolds.

Secondary metabolite gene clusters in the entomopathogen fungus Metarhizium anisopliae: genome identification and patterns of expression in a cuticle infection model

“…cultures [63] but lack a characterized BGC. MaPKS2 exhibited 42–77 % identity with the BGC responsible for aurovertin biosynthesis in C. arbuscula (Additional file 12) [64]. MaTERP2 (MANI_002110) was assigned as a lanosterol cyclase, exhibiting 79 % identity with the partially characterized lanosterol cyclase from Trichoderma harzianum [65].…”

“…Such is the case for the putative BGCs for aurovertin (MaPKS2; MANI_004781), elymoclavine/ergovaline-related compound (MaIND-NRPS1; MANI_029655) and terpendole E/lolitrem-related compound (MaIND-TERP1; MANI_011022). Aurovertin metabolites have been isolated from M. anisopliae , P. chlamydosporia , and C. arbuscula [63, 64, 93]. These compounds exhibit potent inhibition of adenosine triphosphate synthase [64], and aurovertin D, which was isolated from P. chlamydosporia , induced the death of the free-living nematode Panagrellus redivivus [93].…”

“…Aurovertin metabolites have been isolated from M. anisopliae , P. chlamydosporia , and C. arbuscula [63, 64, 93]. These compounds exhibit potent inhibition of adenosine triphosphate synthase [64], and aurovertin D, which was isolated from P. chlamydosporia , induced the death of the free-living nematode Panagrellus redivivus [93]. The non-expression (RPKM < 2, under the three conditions) of this cluster is intriguing, particularly in light of the reports regarding P. chlamydosporia , a species closely related to the Metarhizium genus.…”

Oxidative trans to cis Isomerization of Olefins in Polyketide Biosynthesis

“…The flavin-containing monooxygenase domain of PsoF can oxidize the sulfur atom of 8a with its flavin hydroperoxide to generate 9 , setting up the molecule for a subsequent pericyclic syn -elimination that leads to the release of the oxidized GSH and the formation of the 12,13 Z -configured stereoisomer of 5 . Lastly, the isomerized product remaining in the PsoF active site undergoes a subsequent epoxidation [15] of the C10–C11 olefin to form 1 . For PsoF to be able to perform the trans -to- cis isomerization of 8a , its active site needs to have sufficient room to allow binding of the relatively bulky GSH moiety in the vicinity of the C12–C13 olefin.…”

Saccharomyces cerevisiae as a tool for mining, studying and engineering fungal polyketide synthases

“…The two 5′ and 3′ pieces also contained overlapping regions with the 2μ yeast vector pXW55, which led to placement of the entire aurA gene in the vector under control of the ADH2 promoter. The resulting yeast strain containing the desired plasmid was then used directly to elucidate the product of the iPKSs through expression of the encoded enzymes and analysis of the resulting products (Mao et al, 2015). Other examples of TAR-based assembly of iPKSs include cazF and cazM from the chaetoviridin biosynthetic gene cluster in Chaetomium globosum (Winter et al, 2015; Winter et al, 2012a); bref-PKS from the biosynthetic gene cluster of brefeldin A in Eupenicillium brefeldianum (Zabala et al, 2014); and fma-PKS from the biosynthetic gene cluster of fumagillin in Aspergillus fumigatus (Lin et al, 2013).…”