Functional Crosstalk between Discrete Indole Terpenoid Gene Clusters in Tolypocladium album

An overlooked cyclase plays a central role in the biosynthesis of indole diterpenes

Indole diterpenes (IDTs) are a large class of highly complex fungal natural products that possess a wide array of intriguing bioactivities. While IDTs are structurally diverse, the first four steps of IDT biosynthesis are highly conserved and result typically in the formation of a tetrahydropyran (THP)-ring containing structure, most commonly paspaline. The biosynthetic genes responsible for these steps are the most extensively studied of all IDT genes and collectively define the core biosynthetic pathway. Here we show that the fourth fundamental step, formation of the THP ring, is catalysed by a terpene cyclase encoded by an overlooked and uncharacterised fifth gene, idtA. All previously delineated biosynthetic routes have incorrectly attributed this step to the terpene cyclase IdtB, leading to imprecise pathway reconstructions and ignoring the fully evolved biosynthetic solution for core IDT generation. Moreover, while IdtA terpene cyclases are found in Eurotiomycetes fungi, in Sordariomycetes fungi this step is catalysed by the unrelated protein IdtS, demonstrating that two distinct solutions to this chemistry exist. All biosynthetic gene clusters known to specify production of THP-containing IDTs include an idtA or idtS gene. These findings reset the paradigm for core IDT biosynthesis and support accurate heterologous biosynthesis of these complex natural products.

Synthetic Biology in Natural Product Biosynthesis

Synthetic biology has played an important role in the renaissance of natural products research during the post-genomics era. The development and integration of new tools have transformed the workflow of natural product discovery and engineering, generating multidisciplinary interest in the field. In this review, we summarize recent developments in natural product biosynthesis from three different aspects. First, advances in bioinformatics, experimental, and analytical tools to identify natural products associated with predicted biosynthetic gene clusters (BGCs) will be covered. This will be followed by an extensive review on the heterologous expression of natural products in bacterial, fungal and plant organisms. The native host-independent paradigm to natural product identification, pathway characterization, and enzyme discovery is where synthetic biology has played the most prominent role. Lastly, strategies to engineer biosynthetic pathways for structural diversification and complexity generation will be discussed, including recent advances in assembly-line megasynthase engineering, precursor-directed structural modification, and combinatorial biosynthesis.

Biochemical characterization of a multiple prenyltransferase from Tolypocladium inflatum

Prenylation plays a pivotal role in the diversification and biological activities of natural products. This study presents the functional characterization of TolF, a multiple prenyltransferase from Tolypocladium inflatum. The heterologous expression of tolF in Aspergillus oryzae, coupled with feeding the transformed strain with paxilline, resulted in the production of 20- and 22-prenylpaxilline. Additionally, TolF demonstrated the ability to prenylated the reduced form of paxilline, β-paxitriol. A related prenyltransferase TerF from Chaunopycnis alba, exhibited similar substrate tolerance and regioselectivity. In vitro enzyme assays using purified recombinant enzymes TolF and TerF confirmed their capacity to catalyze prenylation of paxilline, β-paxitriol, and terpendole I. Based on previous reports, terpendole I should be considered a native substrate. This work not only enhances our understanding of the molecular basis and product diversity of prenylation reactions in indole diterpene biosynthesis, but also provides insights into the potential of fungal indole diterpene prenyltransferase to alter their position specificities for prenylation. This could be applicable for the synthesis of industrially useful compounds, including bioactive compounds, thereby opening up new avenues for the development of novel biosynthetic strategies and pharmaceuticals. KEY POINTS: • The study characterizes TolF as a multiple prenyltransferase from Tolypocladium inflatum. • TerF from Chaunopycnis alba shows similar substrate tolerance and regioselectivity compared to TolF. • The research offers insights into the potential applications of fungal indole diterpene prenyltransferases.

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A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as alscholarine A from Alstonia scholaris.