Secondary Metabolites of Penicillium polonicum: Isolation, Structure Elucidation, and Biosynthetic Studies
Loading...
Date
Authors
Publisher
Abstract
Fungal secondary metabolites are an important source of structurally diverse natural
products, with oxidative tailoring reactions playing a key role in generating their
complexity. This thesis investigates the secondary metabolism of Penicillium
polonicum, focusing on the α-pyrone polyketides deoxyverrucosidin and verrucosidin.
The work combines fermentation, LC-MS-based metabolite profiling, compound
isolation, structural analysis, feeding experiments, and biosynthetic interpretation.
The first part of this thesis, in cooperation with Huiling Wei, focused on
deoxyverrucosidin biosynthesis in P. polonicum NRRL 995. The corresponding BGC
was designated as the dov cluster. The combined experimental approach enabled the
functional assignment of key dov genes and provided insight into the biosynthetic
pathway leading to deoxyverrucosidin. The results supported a proposed threeenzyme
cascade encoded by the dov cluster, involving the flavin-containing
monooxygenase DovC, the epoxide expandase DovD, and the cytochrome P450
enzyme DovE. In this cascade, DovC is proposed to initiate oxidative modification,
while DovD promotes the formation of 2,5-dihydrofuran-containing intermediates and
influences the pathway's stereochemical course. DovE is then proposed to mediate a
subsequent oxidative step leading to the epoxytetrahydrofuran-containing moiety.
These findings provide chemical and metabolite-based evidence for how coordinated
oxidation, cyclization, and stereochemical control contribute to epoxyfuran ring
formation in fungal α-pyrone polyketides.
The second part of this study, also conducted in collaboration with Huiling Wei,
investigated how closely related P. polonicum strains with highly similar BGCs produce
different pathway end products. Comparative metabolite analysis showed that P.
polonicum NRRL 995 mainly produces deoxyverrucosidin, whereas P. polonicum
CGMCC 3.15272 produces verrucosidin. The verrucosidin BGC in CGMCC 3.15272
was designated as the vec cluster. Because verrucosidin differs from
deoxyverrucosidin by an additional C6–C7 epoxide, metabolite analysis and feeding
experiments were used to investigate the origin of this late-stage modification. Thesestudies supported the role of VecG, a flavin-containing monooxygenase encoded in
the vec cluster, in the late-stage conversion of deoxyverrucosidin to verrucosidin.
Although VecG is highly homologous to DovG from the deoxyverrucosidin pathway, it
showed distinct functional behavior. In addition to supporting C6–C7 epoxidation,
VecG was able to substitute for the upstream FMO VecC under the tested conditions.
This finding suggests that small sequence differences between highly similar FMO
homologs can influence substrate conversion, pathway outcome, and metabolite
diversity.
The isolation of three known quinolone alkaloids of the viridicatin type, viridicatin,
viridicatol, and 3-O-methylviridicatin, further expands the secondary metabolite profile
of P. polonicum NRRL 995 beyond verrucosidin-related α-pyrone polyketides.
Overall, this thesis highlights the secondary metabolic versatility of P. polonicum and
the role of oxidative tailoring enzymes in fungal α-pyrone polyketides. The
deoxyverrucosidin study clarifies epoxytetrahydrofuran ring formation, whereas the
verrucosidin study reveals functional divergence between the homologous FMOs
VecG and DovG. Together, these findings expand the known chemical diversity of P.
polonicum and provide insight into oxidative scaffold diversification.
Review
Metadata
License
Except where otherwise noted, this item's license is described as Attribution-NonCommercial-ShareAlike 4.0 International