Genome mining of cryptic bisabolenes that were biosynthesized by intramembrane terpene synthases from Antrodia cinnamomea

Terpenoids represent the largest structural family of natural products (NPs) and have various applications in the pharmaceutical, food and fragrance industries. Their diverse scaffolds are generated via a multi-step cyclization cascade of linear isoprene substrates catalysed by terpene synthases (TPSs). Bisabolene NPs, which are sesquiterpenes (C15), have wide applications in medicines and biofuels and serve as bioactive substances in ecology. Despite the discovery of some canonical class I TPSs that synthesize bisabolenes from plants, bacteria and insects, it remained unknown whether any bisabolene synthases from fungi could produce bisabolenes as a main product. Antrodia cinnamomea, a Basidiomycota fungus, is a medicinal mushroom indigenous to Taiwan and a known prolific producer of bioactive terpenoids, but little is known regarding the enzymes involved in the biosynthetic pathways. Here, we applied a genome mining approach against A. cinnamomea and discovered two non-canonical UbiA-type TPSs that both synthesize (+)-(S,Z)-α-bisabolene (1). It was determined that two tailoring enzymes, a P450 monooxygenase and a methyltransferase, install a C14-methyl ester on the bisabolene scaffold. In addition, four new bisabolene derivatives, 2 and 4-6, were characterized from heterologous reconstitution in Saccharomyces cerevisiae. Our study uncovered enzymatic tools to generate structurally diverse bisabolene NPs. This article is part of the theme issue 'Reactivity and mechanism in chemical and synthetic biology'.

The Suzuki-Miyaura Cross-Coupling-Claisen Rearrangement-Cross-Metathesis Approach to Prenylated Isoflavones

Isoflavones were synthesized via Suzuki-Miyaura coupling of 3-iodochromones and para-methoxybenzene- and para-phenolboronic acid. In our hands, conditions commonly used for similar cross couplings turned out to be unsuccessful or difficult to reproduce, for example, due to the unplanned partial cleavage of MOM-protecting groups. Using Pd(dba)₂ as a precatalyst and tricyclohexylphosphine as an activating ligand, reliable cross-coupling conditions were identified. In all cases, notably higher yields of isoflavones were obtained with para-phenolboronic acid than with para-methoxybenzene boronic acid. This observation and the commercial availability of para-phenolboronic acid suggest that for the synthesis of the important 3'-prenyl- or 3',5'-diprenylisoflavone substitution pattern a synthetic route that introduces the prenyl substituents after the Pd-catalyzed cross-coupling step, thereby avoiding laborious and protecting-group-intensive multistep syntheses of C-prenylated arene boronic acids, is advantageous.

Challenges in the Heterologous Production of Furanocoumarins in Escherichia coli

Coumarins and furanocoumarins are plant secondary metabolites with known biological activities. As they are present in low amounts in plants, their heterologous production emerged as a more sustainable and efficient approach to plant extraction. Although coumarins biosynthesis has been positively established, furanocoumarin biosynthesis has been far more challenging. This study aims to evaluate if Escherichia coli could be a suitable host for furanocoumarin biosynthesis. The biosynthetic pathway for coumarins biosynthesis in E. coli was effectively constructed, leading to the production of umbelliferone, esculetin and scopoletin (128.7, 17.6, and 15.7 µM, respectively, from tyrosine). However, it was not possible to complete the pathway with the enzymes that ultimately lead to furanocoumarins production. Prenyltransferase, psoralen synthase, and marmesin synthase did not show any activity when expressed in E. coli. Several strategies were tested to improve the enzymes solubility and activity with no success, including removing potential N-terminal transit peptides and expression of cytochrome P450 reductases, chaperones and/or enzymes to increase dimethylallylpyrophosphate availability. Considering the results herein obtained, E. coli does not seem to be an appropriate host to express these enzymes. However, new alternative microbial enzymes may be a suitable option for reconstituting the furanocoumarins pathway in E. coli. Nevertheless, until further microbial enzymes are identified, Saccharomyces cerevisiae may be considered a preferred host as it has already been proven to successfully express some of these plant enzymes.

Biosynthesis and heterologous production of furanocoumarins: perspectives and current challenges

Covering: up to October 2020 Furanocoumarins are plant secondary metabolites used to treat several skin disorders, such as psoriasis and vitiligo, and also with other potential therapeutic activities. Furanocoumarins are extracted from plants where they accumulate in low amounts over long growth periods. In addition, their extraction and purification are difficult in an environmentally unfriendly and expensive process. Hence, new sustainable and greener production schemes able to overcome such limitations ought to be developed. While the heterologous production of simple coumarins has been demonstrated, the biosynthesis of more complex furanocoumarins remains greatly unexplored. Although several important steps of the pathway have been elucidated in the last decade, the complete pathway has not been completely unravelled. In this paper, we review the natural conversion of amino acids into furanocoumarins, as well as the heterologous expression of each enzyme of the pathway. We also explore the challenges that need to be addressed so that their heterologous production can become a viable alternative.