An improved technique for the rapid chemical characterisation of bacterial terpene cyclases

Common Biosynthesis of Non-Canonical C16 Terpenes through a Fragmentation-Recombination Mechanism

The biosynthesis of six recently reported non-canonical C16 sesquiterpenoids named after ancient Greek philosophers, archimedene, aristotelene, eratosthenene, pythagorene, α-democritene and anaximandrene, was investigated through density functional theory (DFT) calculations and isotopic labeling experiments. The results revealed for all compounds except archimedene a unique fragmentation-recombination mechanism as previously demonstrated for sodorifen biosynthesis, in addition to a remarkable "dancing" mechanism for anaximandrene biosynthesis.

Enantioselective synthesis of all stereoisomers of geosmin and of biosynthetically related natural products

Synthetic routes to geosmin and its enantiomer are well established, but the enantioselective synthesis of stereoisomers of geosmin is unknown. Here a stereoselective synthesis of all stereoisomers of geosmin is reported, yielding all compounds in high enantiomeric purity. Furthermore, the stereoselective synthesis of a geosmin derivative isolated from a mangrove associated streptomycete was performed, establishing the absolute configuration of the natural product. Finally, a new side product of the geosmin synthase from Streptomyces ambofaciens was isolated and its structure was elucidated by NMR spectroscopy. The absolute configuration of this new compound was determined through a stereoselective synthesis.

Substrate specificity of a ketosynthase domain involved in bacillaene biosynthesis

An isotopic labelling method was developed to investigate substrate binding by ketosynthases, exemplified by the second ketosynthase of the polyketide synthase BaeJ involved in bacillaene biosynthesis (BaeJ-KS2). For this purpose, both enantiomers of a 13C-labelled N-acetylcysteamine thioester (SNAC ester) surrogate of the proposed natural intermediate of BaeJ-KS2 were synthesised, including an enzymatic step with glutamate decarboxylase, and incubated with BaeJ-KS2. Substrate binding was demonstrated through 13C NMR analysis of the products against the background of various control experiments.

The Stereochemical Course of DmdC, an Enzyme Involved in the Degradation of Dimethylsulfoniopropionate

The acyl-CoA dehydrogenase DmdC is involved in the degradation of the marine sulfur metabolite dimethylsulfonio propionate (DMSP) through the demethylation pathway. The stereochemical course of this reaction was investigated through the synthesis of four stereoselectively deuterated substrate surrogates carrying stereoselective deuterations at the α- or the β-carbon. Analysis of the products revealed a specific abstraction of the 2-pro-R proton and of the 3-pro-S hydride, establishing an anti elimination for the DmdC reaction.

A Case of Convergent Evolution: The Bacterial Sesquiterpene Synthase for 1-epi-Cubenol from Nonomuraea coxensis

A terpene synthase from Nonomuraea coxensis was identified as (+)-1-epi-cubenol synthase. The enzyme is phylogenetically unrelated to the known enzyme of the same function that is widespread in streptomycetes. Isotopic labelling experiments were performed to unambiguously assign the NMR data and to investigate hydrogen migrations during terpene cyclisations. Epoxidations of (+)-1-epi-cubenol and of the plant derived compounds (-)-cubenol and (-)-1-epi-cubenol confirmed the structure of a natural product isolated from the brown alga Dictyopteris divaricata and allowed to conclude on its absolute configuration. The crystal structures of the epoxides from (+)- and (-)-1-epi-cubenol and the acid catalysed conversion into an isomeric ketone are reported.

Mechanistic Characterisation of Collinodiene Synthase, a Diterpene Synthase from Streptomyces collinus

Two homologs of the diterpene synthase CotB2 from Streptomyces collinus (ScCotB2) and Streptomyces iakyrus (SiCotB2) were investigated for their products by in vitro incubations of the recombinant enzymes with geranylgeranyl pyrophosphate, followed by compound isolation and structure elucidation by NMR. ScCotB2 produced the new compound collinodiene, besides the canonical CotB2 product cyclooctat-9-en-7-ol, dolabella-3,7,18-triene and dolabella-3,7,12-triene, while SiCotB2 gave mainly cyclooctat-9-en-7-ol and only traces of dolabella-3,7,18-triene. The cyclisation mechanism towards the ScCotB2 products and their absolute configurations were investigated through isotopic labelling experiments.

Fragmentation and [4 + 3] cycloaddition in sodorifen biosynthesis

Terpenes constitute the largest class of natural products. Their skeletons are formed by terpene cyclases (TCs) from acyclic oligoprenyl diphosphates through sophisticated enzymatic conversions. These enzyme reactions start with substrate ionization through diphosphate abstraction, followed by a cascade reaction via cationic intermediates. Based on isotopic-labelling experiments in combination with a computational study, the cyclization mechanism for sodorifen, a highly methylated sesquiterpene from the soil bacterium Serratia plymuthica, was resolved. A peculiar problem in its biosynthesis lies in the formation of several methyl groups from chain methylene carbons. The underlying mechanism involves a methyltransferase-mediated cyclization and unprecedented ring contraction with carbon extrusion from the chain to form a methyl group. A terpene cyclase subsequently catalyses a fragmentation into two reactive intermediates, followed by hydrogen transfers between them and recombination of the fragments by [4 + 3] cycloaddition. This study solves the intricate mechanistic problem of extra methyl group formation in sodorifen biosynthesis.

Discovery of dimethylsulfoxonium propionate lyases - a missing enzyme relevant to the global sulfur cycle

Six dimethylsulfoniopropionate (DMSP) lyases have been shown to cleave the marine sulfur metabolite dimethylsulfoxonium propionate (DMSOP) into DMSO and acrylate. This discovery characterises a missing enzyme relevant to the global sulfur cycle.

Isotopic labelling experiments and enzymatic preparation of iso-casbenes with casbene synthase from Ricinus communis

Casbene synthase was used to convert GGPP isomers into iso-casbenes. The enzyme mechanism and absolute configurations were investigated through stereoselective deuteration. 13C-labellings gave insights into the mass spectrometric fragmentation.

Mechanistic Insights into the Formation of the 6,10-Bicyclic Eunicellane Skeleton by the Bacterial Diterpene Synthase Bnd4

The eunicellane diterpenoids are a unique family of natural products seen in marine organisms, plants, and bacteria. We used a series of biochemical, bioinformatics, and theoretical experiments to investigate the mechanism of the first diterpene synthase known to form the eunicellane skeleton. Deuterium labeling studies and quantum chemical calculations support that Bnd4, from Streptomyces sp. (CL12-4), forms the 6,10-bicyclic skeleton through a 1,10-cyclization, 1,3-hydride shift, and 1,14-cyclization cascade. Bnd4 also demonstrated sesquiterpene cyclase activity and the ability to prenylate small molecules. Bnd4 possesses a unique D94 NxxxD motif and mutation experiments confirmed an absolute requirement for D94 as well as E169.

What is the role of the nitrate reductase (euknr) gene in fungi that live in nitrate-free environments? A targeted gene knock-out study in Ampelomyces mycoparasites

Mycoparasitic fungi can be utilized as biocontrol agents (BCAs) of many plant pathogens. Deciphering the molecular mechanisms of mycoparasitism may improve biocontrol efficiency. This work reports the first functional genetic studies in Ampelomyces, widespread mycoparasites and BCAs of powdery mildew fungi, and a molecular genetic toolbox for future works. The nitrate reductase (euknr) gene was targeted to reveal the biological function of nitrate assimilation in Ampelomyces. These mycoparasites live in an apparently nitrate-free environment, i.e. inside the hyphae of powdery mildew fungi that lack any nitrate uptake and assimilation system. Homologous recombination-based gene knock-out (KO) was applied to eliminate the euknr gene using Agrobacterium tumefaciens-mediated transformation. Efficient KO of euknr was confirmed by PCR, and visible phenotype caused by loss of euknr was detected on media with different nitrogen sources. Mycoparasitic ability was not affected by knocking out euknr as a tested transformant readily parasitized Blumeria graminis and Podosphaera xanthii colonies on barley and cucumber, respectively, and the rate of mycoparasitism did not differ from the wild type. These results indicate that euknr is not involved in mycoparasitism. Dissimilatory processes, involvement in nitric oxide metabolism, or other, yet undiscovered processes may explain why a functional euknr is maintained in Ampelomyces.

Isoishwarane synthase from Streptomyces lincolnensis

The product of a terpene synthase from Streptomyces lincolnensis has been identified as the new natural product isoishwarane. The enzyme mechanism was studied by isotopic labelling experiments and site-directed mutagenesis.

Two Diterpene Synthases from Chryseobacterium: Chryseodiene Synthase and Wanjudiene Synthase

Two bacterial diterpene synthases (DTSs) from Chryseobacterium were characterised. The first enzyme yielded the new compound chryseodiene that closely resembles the known fusicoccane diterpenes from fungi, but its experimentally and computationally studied cyclisation mechanism is fundamentally different to the mechanism of fusicoccadiene synthase. The second enzyme produced wanjudiene, a diterpene hydrocarbon with a new skeleton, besides traces of the enantiomer of bonnadiene that was recently discovered from Allokutzneria albata.

Sesquiterpene synthases for bungoene, pentalenene and epi-isozizaene from Streptomyces bungoensis

A sesquiterpene synthase from Streptomyces bungoensis was characterised and produces the new compound bungoene. The enzyme mechanism was deeply investigated using isotopically labelled substrates. Two other enzymes from S. bungoensis made epi-isozizaene and pentalenene. Synthetic oxidative chemistry towards structurally related fusagramineol and pentalenal was explored.

Exploring novel bacterial terpene synthases

Terpenes are the largest class of natural products with extensive structural diversity and are widely used as pharmaceuticals, herbicides, flavourings, fragrances, and biofuels. While they have mostly been isolated from plants and fungi, the availability and analysis of bacterial genome sequence data indicates that bacteria also possess many putative terpene synthase genes. In this study, we further explore this potential for terpene synthase activity in bacteria. Twenty two potential class I terpene synthase genes (TSs) were selected to represent the full sequence diversity of bacterial synthase candidates and recombinantly expressed in E. coli. Terpene synthase activity was detected for 15 of these enzymes, and included mono-, sesqui- and diterpene synthase activities. A number of confirmed sesquiterpene synthases also exhibited promiscuous monoterpene synthase activity, suggesting that bacteria are potentially a richer source of monoterpene synthase activity then previously assumed. Several terpenoid products not previously detected in bacteria were identified, including aromandendrene, acora-3,7(14)-diene and longiborneol. Overall, we have identified promiscuous terpene synthases in bacteria and demonstrated that terpene synthases with substrate promiscuity are widely distributed in nature, forming a rich resource for engineering terpene biosynthetic pathways for biotechnology.

Mechanistic Studies on Trichoacorenol Synthase from Amycolatopsis benzoatilytica

Isotopic labeling experiments performed with a newly identified bacterial trichoacorenol synthase established a 1,5-hydride shift occurring in the cyclization mechanism. During EI-MS analysis, major fragments of the sesquiterpenoid were shown to arise via cryptic hydrogen movements. Therefore, the interpretation of earlier results regarding the cyclization mechanism obtained by feeding experiments in Trichoderma is revised.

Biochemical and Mechanistic Characterization of the Fungal Reverse N-1-Dimethylallyltryptophan Synthase DMATS1Ff

Dimethylallyltryptophan synthases catalyze the regiospecific transfer of (oligo)prenylpyrophosphates to aromatic substrates like tryptophan derivatives. These reactions are key steps in many biosynthetic pathways of fungal and bacterial secondary metabolites. In vitro investigations on recombinant DMATS1_Ff from Fusarium fujikuroi identified the enzyme as the first selective reverse tryptophan-N-1 prenyltransferase of fungal origin. The enzyme was also able to catalyze the reverse N-geranylation of tryptophan. DMATS1_Ff was shown to be phylogenetically related to fungal tyrosine O-prenyltransferases and fungal 7-DMATS. Like these enzymes, DMATS1_Ff was able to convert tyrosine into its regularly O-prenylated derivative. Investigation of the binding sites of DMATS1_Ff by homology modeling and comparison to the crystal structure of 4-DMATS FgaPT2 showed an almost identical site for DMAPP binding but different residues for tryptophan coordination. Several putative active site residues were verified by site directed mutagenesis of DMATS1_Ff. Homology models of the phylogenetically related enzymes showed similar tryptophan binding residues, pointing to a unified substrate binding orientation of tryptophan and DMAPP, which is distinct from that in FgaPT2. Isotopic labeling experiments showed the reaction catalyzed by DMATS1_Ff to be nonstereospecific. Based on these data, a detailed mechanism for DMATS1_Ff catalysis is proposed.

Bacterial Semiochemicals and Transkingdom Interactions with Insects and Plants

A peculiar feature of all living beings is their capability to communicate. With the discovery of the quorum sensing phenomenon in bioluminescent bacteria in the late 1960s, it became clear that intraspecies and interspecies communications and social behaviors also occur in simple microorganisms such as bacteria. However, at that time, it was difficult to imagine how such small organisms-invisible to the naked eye-could influence the behavior and wellbeing of the larger, more complex and visible organisms they colonize. Now that we know this information, the challenge is to identify the myriad of bacterial chemical signals and communication networks that regulate the life of what can be defined, in a whole, as a meta-organism. In this review, we described the transkingdom crosstalk between bacteria, insects, and plants from an ecological perspective, providing some paradigmatic examples. Second, we reviewed what is known about the genetic and biochemical bases of the bacterial chemical communication with other organisms and how explore the semiochemical potential of a bacterium can be explored. Finally, we illustrated how bacterial semiochemicals managing the transkingdom communication may be exploited from a biotechnological point of view.

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

Terpenoids are the largest and structurally most diverse class of natural products. They possess potent and specific biological activity in multiple assays and against diseases, including cancer and malaria as notable examples. Although the number of characterized terpenoid molecules is huge, our knowledge of how they are biosynthesized is limited, particularly when compared to the well-studied thiotemplate assembly lines. Bacteria have only recently been recognized as having the genetic potential to biosynthesize a large number of complex terpenoids, but our current ability to associate genetic potential with molecular structure is severely restricted. The canonical terpene biosynthetic pathway uses a single enzyme to form a cyclized hydrocarbon backbone followed by modifications with a suite of tailoring enzymes that can generate dozens of different products from a single backbone. This functional promiscuity of terpene biosynthetic pathways renders terpene biosynthesis susceptible to rational pathway engineering using the latest developments in the field of synthetic biology. These engineered pathways will not only facilitate the rational creation of both known and novel terpenoids, their development will deepen our understanding of a significant branch of biosynthesis. The biosynthetic insights gained will likely empower a greater degree of engineering proficiency for non-natural terpene biosynthetic pathways and pave the way towards the biotechnological production of high value terpenoids.

Terpene Synthase Genes Originated from Bacteria through Horizontal Gene Transfer Contribute to Terpenoid Diversity in Fungi

Fungi are successful eukaryotes of wide distribution. They are known as rich producers of secondary metabolites, especially terpenoids, which are important for fungi-environment interactions. Horizontal gene transfer (HGT) is an important mechanism contributing to genetic innovation of fungi. However, it remains unclear whether HGT has played a role in creating the enormous chemical diversity of fungal terpenoids. Here we report that fungi have acquired terpene synthase genes (TPSs), which encode pivotal enzymes for terpenoid biosynthesis, from bacteria through HGT. Phylogenetic analysis placed the majority of fungal and bacterial TPS genes from diverse taxa into two clades, indicating ancient divergence. Nested in the bacterial TPS clade is a number of fungal TPS genes that are inferred as the outcome of HGT. These include a monophyletic clade of nine fungal TPS genes, designated as BTPSL for bacterial TPS-like genes, from eight species of related entomopathogenic fungi, including seven TPSs from six species in the genus Metarhizium. In vitro enzyme assays demonstrate that all seven BTPSL genes from the genus Metarhizium encode active enzymes with sesquiterpene synthase activities of two general product profiles. By analyzing the catalytic activity of two resurrected ancestral BTPSLs and one closely related bacterial TPS, the trajectory of functional evolution of BTPSLs after HGT from bacteria to fungi and functional divergence within Metarhizium could be traced. Using M. brunneum as a model species, both BTPSLs and typical fungal TPSs were demonstrated to be involved in the in vivo production of terpenoids, illustrating the general importance of HGT of TPS genes from bacteria as a mechanism contributing to terpenoid diversity in fungi.

Diterpene Biosynthesis in Actinomycetes: Studies on Cattleyene Synthase and Phomopsene Synthase

Three diterpene synthases from actinomycetes have been studied. The first enzyme from Streptomyces cattleya produced the novel compound cattleyene. The other two enzymes from Nocardia testacea and Nocardia rhamnosiphila were identified as phomopsene synthases. The cyclisation mechanism of cattleyene synthase and the EIMS fragmentation mechanism of its product were extensively studied by incubation experiments with isotopically labelled precursors. Oxidative transformations expanded the chemical space of these unique diterpenes.

Discovery of three novel sesquiterpene synthases from Streptomyces chartreusis NRRL 3882 and crystal structure of an α-eudesmol synthase

With more than 50,000 members, terpenoids are one of the most important classes of natural products and show an enormous diversity. Due to their unique odors and specific bioactivities they already find wide application in the flavor, fragrance and pharma industries. Since most terpenoids can only be obtained by natural product extraction, the discovery of biosynthetic genes for the generation of terpene diversity becomes increasingly important. This study describes the discovery of three novel sesquiterpene synthases from Streptomyces chartreusis with preference for the formation of germacradiene-11-ol, α-eudesmol and α-amorphene respectively. The α-eudesmol synthase showed formation of 10-epi-δ-eudesmol and elemol as side products. Eudesmol-isomers are known to have repellent activity, which makes this enzyme a potential catalyst for products for the prevention of mosquito-related disease. The determination of the structure of the apo-enzyme of α-eudesmol synthase from S. chartreusis provides the first structural insights into an eudesmol-forming enzyme.

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

A bacterial terpene synthase from Cryptosporangium arvum was characterised as a multiproduct β-himachalene synthase. In vitro studies showed not only a high promiscuity with respect to its numerous sesquiterpene products, including the structurally demanding terpenes longicyclene, longifolene and α-longipinene, but also to its substrates, as additional activity was observed with geranyl- and geranylgeranyl diphosphate. In-depth mechanistic investigations using isotopically labelled precursors regarding the stereochemical course of both 1,11-cyclisation and 1,3-hydride shift furnished a detailed catalytic model suggesting the molecular basis of the observed low product selectivity. The enzyme’s synthetic potential was also exploited in the preparation of sesquiterpene isotopomers, which provided insights into their EIMS fragmentation mechanisms.

Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum

A newly identified bacterial (Z)-γ-bisabolene synthase was used for investigating the cyclisation mechanism of the sesquiterpene. Since the stereoinformation of both chiral putative intermediates, nerolidyl diphosphate (NPP) and the bisabolyl cation, is lost during formation of the achiral product, the intriguing question of their absolute configurations was addressed by incubating both enantiomers of NPP with the recombinant enzyme, which resolved in an exclusive cyclisation of (R)-NPP, while (S)-NPP that is non-natural to the (Z)-γ-bisabolene synthase was specifically converted into (E)-β-farnesene. A hypothetical enzyme mechanistic model that explains these observations is presented.

Addressing the Chemistry of Germacrene A by Isotope Labeling Experiments

Despite the central role of germacrene A in sesquiterpene biosynthesis and its widespread occurrence in nature, its complete NMR characterization is still pending. This problem was solved through enzymatic preparation of germacrene A isotopomers that allowed for a full signal assignment to all three conformers. The obtained materials gave insights into the stereochemical course of the Cope rearrangement to β-elemene and uncovered the Cope rearrangement as a new EI-MS fragmentation reaction.

Mechanistic characterization of three sesquiterpene synthases from the termite-associated fungus Termitomyces

Three terpene synthases from the termite associated fungus Termitomyces were studied by isotopic labelling experiments and site-directed mutagenesis.

Two Bacterial Diterpene Synthases from Allokutzneria albata Produce Bonnadiene, Phomopsene, and Allokutznerene

Two diterpene synthases from Allokutzneria albata were studied for their products, resulting in the identification of the new compound bonnadiene from the first enzyme. Although phylogenetically unrelated to fungal phomopsene synthase, the second enzyme produced a mixture of phomopsene and a biosynthetically linked new compound, allokutznerene, as well as spiroviolene. Both enzymes were subjected to in-depth mechanistic studies involving isotopic labelling experiments, metal-cofactor variation, and site-directed mutagenesis. Oxidation products of phomopsene and allokutznerene are also discussed.

Chemical differentiation of three DMSP lyases from the marine Roseobacter group

Dimethylsulfoniopropionate (DMSP) catabolism of marine bacteria plays an important role in marine and global ecology. The genome of Ruegeria pomeroyi DSS-3, a model organism from the Roseobacter group, harbours no less than three genes for different DMSP lyases (DddW, DddP and DddQ) that catalyse the degradation of DMSP to dimethyl sulfide (DMS) and acrylate. Despite their apparent similar function these enzymes show no significant overall sequence identity. In this work DddQ and DddW from R. pomeroyi and the DddP homolog from Phaeobacter inhibens DSM 17395 were functionally characterised and their substrate scope was tested using several synthetic DMSP analogues. Comparative kinetic assays revealed differences in the conversion of DMSP and its analogues in terms of selectivity and overall velocity, giving additional insights into the molecular mechanisms of DMSP lyases and into their putatively different biological functions.

Characterisation of the l-Cystine β-Lyase PatB from Phaeobacter inhibens: An Enzyme Involved in the Biosynthesis of the Marine Antibiotic Tropodithietic Acid

The l-cystine β-lyase from Phaeobacter inhibens is involved in the biosynthesis of the sulfur-containing antibiotic tropodithietic acid. The recombinant enzyme was obtained by heterologous expression in Escherichia coli and biochemically characterised by unambiguous chemical identification of the products formed from the substrate l-cystine, investigation of the substrate spectrum, determination of the enzyme kinetics, sequence alignment with closely related homologues and site-directed mutagenesis to identify a highly conserved lysine residue that is critical for functionality. PatB from P. inhibens is a new member of the small group of characterised l-cystine β-lyases and the first example of an enzyme with such an activity that is required for the biosynthesis of an antibiotic. A comparison of PatB to previously reported enzymes with l-cystine β-lyase activity from bacteria and plants is given.

18-Hydroxydolabella-3,7-diene synthase - a diterpene synthase from Chitinophaga pinensis

The product obtained in vitro from a diterpene synthase encoded in the genome of the bacterium Chitinophaga pinensis, an enzyme previously reported to have germacrene A synthase activity during heterologous expression in Escherichia coli, was identified by extensive NMR-spectroscopic methods as 18-hydroxydolabella-3,7-diene. The absolute configuration of this diterpene alcohol and the stereochemical course of the terpene synthase reaction were addressed by isotopic labelling experiments. Heterologous expression of the diterpene synthase in Nicotiana benthamiana resulted in the production of 18-hydroxydolabella-3,7-diene also in planta, while the results from the heterologous expression in E. coli were shown to be reproducible, revealing that the expression of one and the same terpene synthase in different heterologous hosts may yield different terpene products.

The GATA-Type Transcription Factor Csm1 Regulates Conidiation and Secondary Metabolism in Fusarium fujikuroi

GATA-type transcription factors (TFs) such as the nitrogen regulators AreA and AreB, or the light-responsive TFs WC-1 and WC-2, play global roles in fungal growth and development. The conserved GATA TF NsdD is known as an activator of sexual development and key repressor of conidiation in Aspergillus nidulans, and as light-regulated repressor of macroconidia formation in Botrytis cinerea. In the present study, we functionally characterized the NsdD ortholog in Fusarium fujikuroi, named Csm1. Deletion of this gene resulted in elevated microconidia formation in the wild-type (WT) and restoration of conidiation in the non-sporulating velvet mutant Δvel1 demonstrating that Csm1 also plays a role as repressor of conidiation in F. fujikuroi. Furthermore, biosynthesis of the PKS-derived red pigments, bikaverin and fusarubins, is de-regulated under otherwise repressing conditions. Cross-species complementation of the Δcsm1 mutant with the B. cinerea ortholog LTF1 led to full restoration of WT-like growth, conidiation and pigment formation. In contrast, the F. fujikuroi CSM1 rescued only the defects in growth, the tolerance to H₂O₂ and virulence, but did not restore the light-dependent differentiation when expressed in the B. cinerea Δltf1 mutant. Microarray analysis comparing the expression profiles of the F. fujikuroi WT and the Δcsm1 mutant under different nitrogen conditions revealed a strong impact of this GATA TF on 19 of the 47 gene clusters in the genome of F. fujikuroi. One of the up-regulated silent gene clusters is the one containing the sesquiterpene cyclase-encoding key gene STC1. Heterologous expression of STC1 in Escherichia coli enabled us to identify the product as the volatile bioactive compound (-)-germacrene D.

Mechanistic Investigations of Two Bacterial Diterpene Cyclases: Spiroviolene Synthase and Tsukubadiene Synthase

The mechanisms of two diterpene cyclases from streptomycetes-one with an unknown product that was identified as the spirocyclic hydrocarbon spiroviolene and one with the known product tsukubadiene-were investigated in detail by isotope labeling experiments. Although the structures of the products were very different, the cyclization mechanisms of both enzymes proceed through the same initial cyclization reactions, before they diverge towards the individual products, which is reflected in the close phylogenetic relationship of the enzymes.

Isoafricanol synthase from Streptomyces malaysiensis

A terpene cyclases from Streptomyces malaysiensis was characterised as (+)-isoafricanol synthase and its mechanism was investigated using isotopically labelled substrates.

Terpene Cyclases from Social Amoebae

Genome sequences of social amoebae reveal the presence of terpene cyclases (TCs) in these organisms. Two TCs from Dictyostelium discoideum converted farnesyl diphosphate into (2S,3R,6S,9S)-(-)-protoillud-7-ene and (3S)-(+)-asterisca-2(9),6-diene. The enzyme mechanisms and EI-MS fragmentations of the products were studied by labeling experiments.

A detailed view on 1,8-cineol biosynthesis by Streptomyces clavuligerus

The stereochemical course of the cyclisation reaction catalysed by the bacterial 1,8-cineol synthase from Streptomyces clavuligerus was investigated using stereospecifically deuterated substrates. In contrast to the well investigated plant enzyme from Salvia officinalis, the reaction proceeds via (S)-linalyl diphosphate and the (S)-terpinyl cation, while the final cyclisation reaction is in both cases a syn addition, as could be shown by incubation of (2-¹³C)geranyl diphosphate in deuterium oxide.