Functional characterization of four sesquiterpene synthases from Ricinus communis (castor bean)

Expanding the structural diversity of terpenes by synthetic biology approaches

Terpenoids display chemical and structural diversities as well as important biological activities. Despite their extreme variability, the range of these structures is limited by the scope of natural products that canonically derive from interconvertible five-carbon (C5) isoprene units. New approaches have recently been developed to expand their structural diversity. This review systematically explores the combinatorial biosynthesis of noncanonical building blocks via the coexpression of the canonical mevalonate (MVA) pathway and C-methyltransferases (C-MTs), or by using the lepidopteran mevalonate (LMVA) pathway. Unnatural terpenoids can be created from farnesyl diphosphate (FPP) analogs by chemobiological synthesis and terpene cyclopropanation by artificial metalloenzymes (ArMs). Advanced technologies to accelerate terpene biosynthesis are discussed. This review provides a valuable reference for increasing the diversity of valuable terpenoids and their derivatives, as well as for expanding their potential applications.

Identification and characterization of novel sesquiterpene synthases TPS9 and TPS12 from Aquilaria sinensis

Sesquiterpenes are characteristic components and important quality criterions for agarwood. Although sesquiterpenes are well-known to be biosynthesized by sesquiterpene synthases (TPSs), to date, only a few TPS genes involved in agarwood formation have been reported. Here, two new TPS genes, namely, TPS9 and TPS12, were isolated from Aquilaria sinensis (Lour.) Gilg, and their functions were examined in Escherichia coli BL21(DE3), with farnesyl pyrophosphate (FPP) and geranyl pyrophosphate (GPP) as the substrate of the corresponding enzyme activities. They were both identified as a multiproduct enzymes. After incubation with FPP, TPS9 liberated β-farnesene and cis-sesquisabinene hydrate as main products, with cedrol and another unidentified sesquiterpene as minor products. TPS12 catalyzes the formation of β-farnesene, nerolidol, γ-eudesmol, and hinesol. After incubation with GPP, TPS9 generated citronellol and geraniol as main products, with seven minor products. TPS12 converted GPP into four monoterpenes, with citral as the main product, and three minor products. Both TPS9 and TPS12 showed much higher expression in the two major tissues emitting floral volatiles: flowers and agarwood. Further, RT-PCR analysis showed TPS9 and TPS12 are typical genes mainly expressed during later stages of stress response, which is better known than that of chromone derivatives. This study will advance our understanding of agarwood formation and provide a solid theoretical foundation for clarifying its mechanism in A. sinensis.

Characterization of sandalwood (E,E)-α-farnesene synthase whose overexpression enhances cold tolerance through jasmonic acid biosynthesis and signaling in Arabidopsis

MAIN CONCLUSION

Santalum album (E,E)-α-farnesene synthase catalyzes FPP into (E,E)-α-farnesene. Overexpression of the SaAFS gene positively improved cold stress tolerance through JA biosynthesis and signaling pathways in Arabidopsis. Volatile terpenoids are released from plants that suffer negative effects following exposure to various biotic and abiotic stresses. Recent studies revealed that (E,E)-α-farnesene synthase (AFS) plays a significant role in a plant's defence against biotic attack. However, little is known about whether AFS contributes to plant resistance to cold stress. In this study, a SaAFS gene was isolated from Indian sandalwood (Santalum album L.) and functionally characterized. The SaAFS protein mainly converts farnesyl diphosphate to (E,E)-α-farnesene. SaAFS was clustered into the AFS clade from angiosperms, suggesting a highly conserved enzyme. SaAFS displayed a significant response to cold stress and methyl jasmonate. SaAFS overexpression (OE) in Arabidopsis enhanced cold tolerance by increasing proline content, reducing malondialdehyde content, electrolyte leakage, and accumulating reactive oxygen species. Transcriptomic analysis revealed that upregulated genes related to stress response and JA biosynthesis and signaling were detected in SaAFS-OE lines compared with wild type plants that were exposed to cold stress. Endogenous JA and jasmonoyl-isoleucine content increased significantly in SaAFS-OE lines exposed to cold stress. Collectively considered, these results suggest that the SaAFS gene is a positive regulator during cold stress tolerance via JA biosynthesis and signaling pathways.

Effect of Developmental Stages on Genes Involved in Middle and Downstream Pathway of Volatile Terpene Biosynthesis in Rose Petals

Terpenoids are economically and ecologically important compounds, and they are vital constituents in rose flower fragrance and rose essential oil. The terpene synthase genes (TPSs), trans-prenyltransferases genes (TPTs), NUDX1 are involved in middle and downstream pathway of volatile terpene biosynthesis in rose flowers. We identified 7 complete RcTPTs, 49 complete RcTPSs, and 9 RcNUDX1 genes in the genome of Rosachinensis. During the flower opening process of butterfly rose (Rosachinensis ‘Mutabilis’, MU), nine RcTPSs expressed in the petals of opening MU flowers exhibited two main expression trends, namely high and low, in old and fresh petals. Five short-chain petal-expressed RcTPTs showed expression patterns corresponding to RcTPSs. Analysis of differential volatile terpenes and differential expressed genes indicated that higher emission of geraniol from old MU petals might be related to the RcGPPS expression. Comprehensive analysis of volatile emission, sequence structure, micro-synteny and gene expression suggested that RcTPS18 may encode (E,E)-α-farnesene synthase. These findings may be useful for elucidating the molecular mechanism of terpenoid metabolism in rose and are vital for future studies on terpene regulation.

Alternative metabolic pathways and strategies to high-titre terpenoid production in Escherichia coli

Covering: up to 2021Terpenoids are a diverse group of chemicals used in a wide range of industries. Microbial terpenoid production has the potential to displace traditional manufacturing of these compounds with renewable processes, but further titre improvements are needed to reach cost competitiveness. This review discusses strategies to increase terpenoid titres in Escherichia coli with a focus on alternative metabolic pathways. Alternative pathways can lead to improved titres by providing higher orthogonality to native metabolism that redirects carbon flux, by avoiding toxic intermediates, by bypassing highly-regulated or bottleneck steps, or by being shorter and thus more efficient and easier to manipulate. The canonical 2-C-methyl-D-erythritol 4-phosphate (MEP) and mevalonate (MVA) pathways are engineered to increase titres, sometimes using homologs from different species to address bottlenecks. Further, alternative terpenoid pathways, including additional entry points into the MEP and MVA pathways, archaeal MVA pathways, and new artificial pathways provide new tools to increase titres. Prenyl diphosphate synthases elongate terpenoid chains, and alternative homologs create orthogonal pathways and increase product diversity. Alternative sources of terpenoid synthases and modifying enzymes can also be better suited for E. coli expression. Mining the growing number of bacterial genomes for new bacterial terpenoid synthases and modifying enzymes identifies enzymes that outperform eukaryotic ones and expand microbial terpenoid production diversity. Terpenoid removal from cells is also crucial in production, and so terpenoid recovery and approaches to handle end-product toxicity increase titres. Combined, these strategies are contributing to current efforts to increase microbial terpenoid production towards commercial feasibility.

Functional characterization and substrate promiscuity of sesquiterpene synthases from Tripterygium wilfordii

Acyclic terpenes, commonly found in plants, are of high physiological importance and commercial value, and their diversity was controlled by different terpene synthases. During the screen of sesquiterpene synthases from Tripterygium wilfordii, we observed that Ses-TwTPS1-1 and Ses-TwTPS2 promiscuously accepted GPP, FPP, and GGPP to produce corresponding terpene alcohols (linalool/nerolidol/geranyllinalool). The Ses-TwTPS1-2, Ses-TwTPS3, and Ses-TwTPS4 also showed unusual substrate promiscuity by catalyzing GGPP or GPP in addition to FPP as substrate. Furthermore, key residues for the generation of diterpene product, (E, E)-geranyllinalool, were screened depending on mutagenesis studies. The functional analysis of Ses-TwTPS1-1:V199I and Ses-TwTPS1-2:I199V showed that Val in 199 site assisted the produce of diterpene product geranyllinalool by enzyme mutation studies, which indicated that subtle differences away from the active site could alter the product outcome. Moreover, an engineered sesquiterpene high-yielding yeast that produced 162 mg/L nerolidol in shake flask conditions was constructed to quickly identify the function of sesquiterpene synthases in vivo and develop potential applications in microbial fermentation. Our functional characterization of acyclic sesquiterpene synthases will give some insights into the substrate promiscuity of diverse acyclic terpene synthases and provide key residues for expanding the product portfolio.

Isolation and functional characterization of four microbial type terpene synthases from ferns

Typical plant terpene synthases (TPSs) are responsible for the production of terpenes, a major class of plant secondary metabolites. However, various nonseed plants also harbor genes encoding microbial terpene synthase-like (MTPSL) enzymes. Here, a scan of 31 ferns transcriptomes revealed 40 sequences putatively encoding MTPSLs. Two groups of sequences were recognized based on the key conserved motifs. Four representative genes were isolated from each of the four species Adiantum capillus-veneris, Cyclosorus parasiticus, Drynaria bonii and Microlepia platyphylla. Following their heterologous expression in E. coli, the recombinant proteins were tested for monoterpene synthase and sesquiterpene synthase activity. These enzymatic products were typical monoterpenes and sesquiterpenes that have been previous shown to be generated by classical plant TPSs when provided with GPP and FPP as substrates. Subcellular localization experiments in the leaf epidermis of Nicotiana benthamiana and onion (Allium cepa) inner epidermal cells indicated that AcMTPSL1 and DbMTPSL were deposited in both the cytoplasm and nucleus, whereas CpMTPSL1 and MpMTPSL were localized in the cytoplasm, chloroplasts and nucleus. AcMTPSL1 was up-regulated in plants exposed to methyl jasmonate treatment, suggesting a role for this gene in host defense. This study provides more information about the catalytic function of MTPSLs in nonseed plants and for the first time, the subcellular localization of MTPSLs was experimentally characterized.

Biosynthetic pathways and metabolic engineering of spice flavors

Historically, spices have played an important economic role, due to their large applications and unique flavor. The supply and cost of spice materials and their corresponding natural products are often affected by environmental, geopolitical and climatic conditions. Secondary metabolite composition, including certain flavor compounds in spice plants, is recognized and considered closely related to plant classification. Both genes and enzymes involved in the biosynthesis of spice flavors are constantly identified, which provides insight into metabolic engineering of flavor compounds (i.e. aroma and pungent compounds) from spice plants. In this review, a systematic meta-analysis was carried out based on a comprehensive literature survey of the flavor profiles of 36 spice plants from nine families. We also reviewed typical biosynthetic pathways and metabolic engineering of most representative aroma and pungent compounds that may assist in the future study of spice plants as biosynthetic factories facing a new challenge in creating spice products.

Adaptation of hydroxymethylbutenyl diphosphate reductase enables volatile isoprenoid production

Volatile isoprenoids produced by plants are emitted in vast quantities into the atmosphere, with substantial effects on global carbon cycling. Yet, the molecular mechanisms regulating the balance between volatile and non-volatile isoprenoid production remain unknown. Isoprenoids are synthesised via sequential condensation of isopentenyl pyrophosphate (IPP) to dimethylallyl pyrophosphate (DMAPP), with volatile isoprenoids containing fewer isopentenyl subunits. The DMAPP:IPP ratio could affect the balance between volatile and non-volatile isoprenoids, but the plastidic DMAPP:IPP ratio is generally believed to be similar across different species. Here we demonstrate that the ratio of DMAPP:IPP produced by hydroxymethylbutenyl diphosphate reductase (HDR/IspH), the final step of the plastidic isoprenoid production pathway, is not fixed. Instead, this ratio varies greatly across HDRs from phylogenetically distinct plants, correlating with isoprenoid production patterns. Our findings suggest that adaptation of HDR plays a previously unrecognised role in determining in vivo carbon availability for isoprenoid emissions, directly shaping global biosphere-atmosphere interactions.

Mevalonate Pathway Promiscuity Enables Noncanonical Terpene Production

Lepidoptera (butterflies and moths) make the six-carbon compounds homoisopentenyl pyrophosphate (HIPP) and homodimethylallyl pyrophosphate (HDMAPP) that are incorporated into 16, 17, and 18 carbon farnesyl pyrophosphate (FPP) analogues. In this work we heterologously expressed the lepidopteran modified mevalonate pathway, a propionyl-CoA ligase, and terpene cyclases in E. coli to produce several novel terpenes containing 16 carbons. Changing the terpene cyclase generated different novel terpene product profiles. To further validate the new compounds we confirmed ¹³C propionate was incorporated, and that the masses and fragmentation patterns were consistent with novel 16 carbon terpenes by GC-QTOF. On the basis of the available farnesyl pyrophosphate analogues lepidoptera produce, this approach should greatly expand the reachable biochemical space with applications in areas where terpenes have traditionally found uses.

Identification of sesquiterpene synthases from the Basidiomycota Coniophora puteana for the efficient and highly selective β-copaene and cubebol production in E. coli

Background

Terpenes are an important and extremely versatile class of secondary metabolites that are commercially used in the pharmaceutical, food and cosmetics sectors. Genome mining of different fungal collections has revealed the genetic basis for a steadily increasing number of putative terpene synthases without any detailed knowledge about their biochemical properties. The analysis and research of this rich genetic source provides a precious basis for the advancing biotechnological production of an almost endless number of valuable natural metabolites.

Results

Three annotated terpene synthases from the little investigated Basidiomycota Coniophora puteana were studied in this work. For biochemical characterization, the heterologous expression in E. coli was conducted leading to the identification of two sesquiterpene synthases capable of the highly selective generation of β-copaene and cubebol. These compounds are commercially used as food and flavor additives. The new enzymes show the highest reported product selectivity for their main compounds and therefore represent the first exclusive synthases for β-copaene (62% product selectivity) and cubebol (75% product selectivity) generation. In combination with an optimized heterologous microbial production system, we obtained product titers of 215 mg/L β-copaene and 497 mg/L cubebol.

Conclusion

The reported product selectivity and our generated terpene titers exceed all published biotechnological data regarding the production of β-copaene and cubebol. This represents a promising and economic alternative to extraction from natural plant sources and the associated complex product purification.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-1010-z) contains supplementary material, which is available to authorized users.

Functional Characterisation of New Sesquiterpene Synthase from the Malaysian Herbal Plant, Polygonum Minus

Polygonum minus (syn. Persicaria minor) is a herbal plant that is well known for producing sesquiterpenes, which contribute to its flavour and fragrance. This study describes the cloning and functional characterisation of PmSTPS1 and PmSTPS2, two sesquiterpene synthase genes that were identified from P. minus transcriptome data mining. The full-length sequences of the PmSTPS1 and PmSTPS2 genes were expressed in the E. coli pQE-2 expression vector. The sizes of PmSTPS1 and PmSTPS2 were 1098 bp and 1967 bp, respectively, with open reading frames (ORF) of 1047 and 1695 bp and encoding polypeptides of 348 and 564 amino acids, respectively. The proteins consist of three conserved motifs, namely, Asp-rich substrate binding (DDxxD), metal binding residues (NSE/DTE), and cytoplasmic ER retention (RxR), as well as the terpene synthase family N-terminal domain and C-terminal metal-binding domain. From the in vitro enzyme assays, using the farnesyl pyrophosphate (FPP) substrate, the PmSTPS1 enzyme produced multiple acyclic sesquiterpenes of β-farnesene, α-farnesene, and farnesol, while the PmSTPS2 enzyme produced an additional nerolidol as a final product. The results confirmed the roles of PmSTPS1 and PmSTPS2 in the biosynthesis pathway of P. minus, to produce aromatic sesquiterpenes.

PHYTOCHEMICAL, ELEMENTAL AND BIOTECHNOLOGICAL STUDY OF CRYPTOCARYA LATIFOLIA

Background:

Existing populations of Cryptocarya latifolia (Lauraceae) are rapidly declining as a consequence of their substitutive use for Ocotea bullata. The uncontrolled and excessive removal of the bark and roots of this species has led to the death of many of these plants and may eventually result in its depletion in the natural habitat.

Materials and Methods:

The secondary metabolites from the leaves and fruits of C. latifolia were extracted using solvents of various polarities, isolated using column chromatography and identified using spectroscopic techniques. The in vitro free radical scavenging activity (antioxidant capacity) of selected phytocompounds at varied concentrations was determined by the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay. A propagation study of the species was also conducted.

Results:

The compounds isolated from the plant were the novel compound, α-pyrone (5-hexyltetrahydro-2H-pyran-2-one) and known compounds quercetin-3-O-rhamnoside, β-sitosterol, copaene and nerolidol. The radical scavenging activity of the isolated compounds indicated moderate to good anti-oxidant activity. Treatment of explants with BAP: NAA at 1.0:0.01 mg L^-1 produced the highest percentage of shoots (94%) and longest shoot length (8.06 mm).

Conclusion:

This study validates the ethno-medicinal use of the plant and supports the replacement of bark and roots by leaves and fruits for the management and conservation of this declining plant species. The benefits of consuming the fruits are two-fold as they can also contribute to the recommended dietary allowances of most essential elements for the majority of individuals.

Multi-Substrate Terpene Synthases: Their Occurrence and Physiological Significance

Terpene synthases are responsible for synthesis of a large number of terpenes in plants using substrates provided by two distinct metabolic pathways, the mevalonate-dependent pathway that is located in cytosol and has been suggested to be responsible for synthesis of sesquiterpenes (C15), and 2-C-methyl-D-erythritol-4-phosphate pathway located in plastids and suggested to be responsible for the synthesis of hemi- (C5), mono- (C10), and diterpenes (C20). Recent advances in characterization of genes and enzymes responsible for substrate and end product biosynthesis as well as efforts in metabolic engineering have demonstrated existence of a number of multi-substrate terpene synthases. This review summarizes the progress in the characterization of such multi-substrate terpene synthases and suggests that the presence of multi-substrate use might have been significantly underestimated. Multi-substrate use could lead to important changes in terpene product profiles upon substrate profile changes under perturbation of metabolism in stressed plants as well as under certain developmental stages. We therefore argue that multi-substrate use can be significant under physiological conditions and can result in complicate modifications in terpene profiles.

A single terpene synthase is responsible for a wide variety of sesquiterpenes in Sorangium cellulosum Soce56

The myxobacterium Sorangium cellulosum So ce56 is a prolific producer of volatile sesquiterpenes.

Production of farnesene and santalene by Saccharomyces cerevisiae using fed-batch cultivations with RQ-controlled feed

Terpenes have various applications as fragrances, cosmetics and fuels. One of the most prominent examples is the sesquiterpene farnesene, which can be used as diesel substitute in its hydrogenated form farnesane. Recent metabolic engineering efforts have enabled efficient production of several terpenes in Saccharomyces cerevisiae and Escherichia coli. Plant terpene synthases take on an essential function for sesquiterpene production as they catalyze the specific conversion of the universal precursor farnesyl diphosphate (FPP) to the sesquiterpene of interest and thereby impose limitations on the overall productivity. Using farnesene as a case study, we chose three terpene synthases with distinct plant origins and compared their applicability for farnesene production in the yeast S. cerevisiae. Differences regarding the efficiency of these enzymes were observed in shake flask cultivation with maximal final titers of 4 mg/L using α-farnesene synthase from Malus domestica. By employing two existing platform strains optimized for sesquiterpene production, final titers could be raised up 170 mg/L in fed-batch fermentations with RQ-controlled exponential feeding. Based on these experiments, the difference between the selected synthases was not significant. Lastly, the same fermentation setup was used to compare these results to production of the fragrance sesquiterpene santalene, and almost equivalent titers were obtained with 163 mg/L, using the highest producing strain expressing a santalene synthase from Clausena lansium. However, a reduction of the product yield on biomass by 50% could indicate a higher catalytic efficiency of the farnesene synthase.

Chronic toxicity of crude ricinine in rats assessed by1H NMR metabolomics analysis

A¹H-NMR based metabolomics approach combined with OSC-PLS-DA was applied to investigate the chronic toxicity of crude ricinine from castor bean shell in rats for the first time.

Use of nonionic surfactants for improvement of terpene production in Saccharomyces cerevisiae

To facilitate enzyme and pathway engineering, a selection was developed for improved sesquiterpene titers in Saccharomyces cerevisiae. α-Bisabolene, a candidate advanced biofuel, was found to protect yeast against the disruptive action of nonionic surfactants such as Tween 20 (T20). An experiment employing competition between two strains of yeast, one of which makes twice as much bisabolene as the other, demonstrated that growth in the presence of T20 provided sufficient selective pressure to enrich the high-titer strain to form 97% of the population. Following this, various methods were used to mutagenize the bisabolene synthase (BIS) coding sequence, coupled with selection by subculturing in the presence of T20. Mutagenesis targeting the BIS active site did not yield an improvement in bisabolene titers, although mutants were found which made a mixture of α-bisabolene and β-farnesene, another candidate biofuel. Based on evidence that the 3' end of the BIS mRNA may be unstable in yeast, we randomly recoded the last 20 amino acids of the enzyme and, following selection in T20, found a variant which increased specific production of bisabolene by more than 30%. Since T20 could enrich a mixed population, efficiently removing strains that produced little or no bisabolene, we investigated whether it could also be applied to sustain high product titers in a monoculture for an extended period. Cultures grown in the presence of T20 for 14 days produced bisabolene at titers up to 4-fold higher than cultures grown with an overlay of dodecane, used to sequester the terpene product, and 20-fold higher than cultures grown without dodecane.

2,2-Diphenyl-1-picrylhydrazyl as a screening tool for recombinant monoterpene biosynthesis

Background

Monoterpenes are a class of natural C₁₀ compounds with a range of potential applications including use as fuel additives, fragrances, and chemical feedstocks. Biosynthesis of monoterpenes in heterologous systems is yet to reach commercially-viable levels, and therefore is the subject of strain engineering and fermentation optimization studies. Detection of monoterpenes typically relies on gas chromatography/mass spectrometry; this represents a significant analytical bottleneck which limits the potential to analyse combinatorial sets of conditions. To address this, we developed a high-throughput method for pre-screening monoterpene biosynthesis.

Results

An optimised DPPH assay was developed for detecting monoterpenes from two-phase microbial cultures using dodecane as the extraction solvent. The assay was useful for reproducible qualitative ranking of monoterpene concentrations, and detected standard preparations of myrcene and γ-terpinene dissolved in dodecane at concentrations as low as 10 and 15 μM, respectively, and limonene as low as 200 μM. The assay could not be used quantitatively due to technical difficulties in capturing the initial reaction rate in a multi-well plate and the presence of minor DPPH-reactive contaminants. Initially, limonene biosynthesis in Saccharomyces cerevisiae was tested using two different limonene synthase enzymes and three medium compositions. The assay indicated that limonene biosynthesis was enhanced in a supplemented YP medium and that the Citrus limon limonene synthase (CLLS) was more effective than the Mentha spicata limonene synthase (MSLS). GC-MS analysis revealed that the DPPH assay had correctly identified the best limonene synthase (CLLS) and culture medium (supplemented YP medium). Because only traces of limonene were detected in SD medium, we subsequently identified medium components that improved limonene production and developed a defined medium based on these findings. The best limonene titres obtained were 1.48 ± 0.22 mg limonene per L in supplemented YP medium and 0.9 ± 0.15 mg limonene per L in a pH-adjusted supplemented SD medium.

Conclusions

The DPPH assay is useful for detecting biosynthesis of limonene. Although the assay cannot be used quantitatively, it proved successful in ranking limonene production conditions qualitatively and thus is suitable as a first-tier screen. The DPPH assay will likely be applicable in detecting biosynthesis of several other monoterpenes and for screening libraries of monoterpene-producing strains.

Natural sesquiterpenoids

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. The literature from January to December 2012 is reviewed, and 471 references are cited.

Developing a yeast cell factory for the production of terpenoids

Technological developments over the past century have made microbes the work-horses of large scale industrial production processes. Current efforts focus on the metabolic engineering of microbial strains to produce high levels of desirable end-products. The arsenal of the contemporary metabolic engineer contains tools that allow either targeted rational interventions or global screens that combine classical approaches with –omics technologies. Production of terpenoids in S. cerevisiae presents a characteristic example of contemporary biotechnology that integrates all the variety of novel approaches used in metabolic engineering. Terpenoids have attracted significant interest as pharmaceuticals, flavour and fragrance additives, and, more recently, biofuels. The ongoing metabolic engineering efforts, combined with the continuously increasing number of terpene biosynthetic enzymes discovered will enable the economical and environmentally friendly production of a wide range of compounds.