A Slippery Scaffold: Synthesis and Recycling of the Bacterial Cell Wall Carrier Lipid

The biosynthesis of bacterial cell envelope polysaccharides such as peptidoglycan relies on the use of a dedicated carrier lipid both for the assembly of precursors at the cytoplasmic face of the plasma membrane and for the translocation of lipid linked oligosaccharides across the plasma membrane into the periplasmic space. This dedicated carrier lipid, undecaprenyl phosphate, results from the dephosphorylation of undecaprenyl pyrophosphate, which is generated de novo in the cytoplasm by undecaprenyl pyrophosphate synthase and released as a by-product when newly synthesized glycans are incorporated into the existing cell envelope. The de novo synthesis of undecaprenyl pyrophosphate has been thoroughly characterized from a structural and mechanistic standpoint; however, its dephosphorylation to the active carrier lipid form, both in the course of de novo synthesis and recycling, has only been begun to be studied in depth in recent years. This review provides an overview of bacterial carrier lipid synthesis and presents the current state of knowledge regarding bacterial carrier lipid recycling.

Nerylneryl diphosphate is the precursor of serrulatane, viscidane and cembrane-type diterpenoids in Eremophila species

BACKGROUND

Eremophila R.Br. (Scrophulariaceae) is a diverse genus of plants with species distributed across semi-arid and arid Australia. It is an ecologically important genus that also holds cultural significance for many Indigenous Australians who traditionally use several species as sources of medicines. Structurally unusual diterpenoids, particularly serrulatane and viscidane-types, feature prominently in the chemical profile of many species and recent studies indicate that these compounds are responsible for much of the reported bioactivity. We have investigated the biosynthesis of diterpenoids in three species: Eremophila lucida, Eremophila drummondii and Eremophila denticulata subsp. trisulcata.

RESULTS

In all studied species diterpenoids were localised to the leaf surface and associated with the occurrence of glandular trichomes. Trichome-enriched transcriptome databases were generated and mined for candidate terpene synthases (TPS). Four TPSs with diterpene biosynthesis activity were identified: ElTPS31 and ElTPS3 from E. lucida were found to produce (3Z,7Z,11Z)-cembratrien-15-ol and 5-hydroxyviscidane, respectively, and EdTPS22 and EdtTPS4, from E. drummondii and E. denticulata subsp. trisulcata, respectively, were found to produce 8,9-dihydroserrulat-14-ene which readily aromatized to serrulat-14-ene. In all cases, the identified TPSs used the cisoid substrate, nerylneryl diphosphate (NNPP), to form the observed products. Subsequently, cis-prenyl transferases (CPTs) capable of making NNPP were identified in each species.

CONCLUSIONS

We have elucidated two biosynthetic steps towards three of the major diterpene backbones found in this genus. Serrulatane and viscidane-type diterpenoids are promising candidates for new drug leads. The identification of an enzymatic route to their synthesis opens up the possibility of biotechnological production, making accessible a ready source of scaffolds for further modification and bioactivity testing.

An Unusual Skeletal Rearrangement in the Biosynthesis of the Sesquiterpene Trichobrasilenol from Trichoderma

The skeletons of some classes of terpenoids are unusual in that they contain a larger number of Me groups (or their biosynthetic equivalents such as olefinic methylene groups, hydroxymethyl groups, aldehydes, or carboxylic acids and their derivatives) than provided by their oligoprenyl diphosphate precursor. This is sometimes the result of an oxidative ring-opening reaction at a terpene-cyclase-derived molecule containing the regular number of Me group equivalents, as observed for picrotoxan sesquiterpenes. In this study a sesquiterpene cyclase from Trichoderma spp. is described that can convert farnesyl diphosphate (FPP) directly via a remarkable skeletal rearrangement into trichobrasilenol, a new brasilane sesquiterpene with one additional Me group equivalent compared to FPP. A mechanistic hypothesis for the formation of the brasilane skeleton is supported by extensive isotopic labelling studies.

Biosynthesis of nerol from glucose in the metabolic engineered Escherichia coli

In this study, nerol was biosynthesized in the metabolic engineered Escherichia coli from glucose for the first time. Firstly, the truncated neryl diphosphate synthase gene tNDPS1 was expressed that catalyzes isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) to form neryl diphosphate (NPP), and then the nerol synthase gene GmNES was co-expressed to synthesize the final product nerol from NPP. The engineered strain LZ001 accumulated 0.053 ± 0.015 mg/L of nerol. Secondly, the IDI1, MVD1, ERG8, ERG12, tHMG1 and ERG13 were co-expressed to increase the supply of IPP and DMAPP. Finally, the heterologous ERG10 gene was overexpressed, and the recombinant strain LZ005 produced 1.564 ± 0.102 mg/L of nerol in shaking-flask culture, which represents a 29.51-fold increase over LZ001 strain. This study shows the novel method for the biosynthesis of nerol and provides new metabolic engineering strategy for the production of terpenoids.

Significantly Enhanced Production of Patchoulol in Metabolically Engineered Saccharomyces cerevisiae

Patchoulol, a natural sesquiterpene compound, is widely used in perfumes and cosmetics. Several strategies were adopted to enhance patchoulol production in Saccharomyces cerevisiae: (i) farnesyl pyrophosphate (FPP) synthase and patchoulol synthase were fused to increase the utilization of FPP precursor; (ii) expression of the limiting genes of the mevalonate pathway was enhanced; (iii) squalene synthase was weakened by a glucose-inducible promoter of HXT1 (promoter for hexose transporter) to reduce metabolic flux from FPP to ergosterol; and (iv) farnesol biosynthesis was inhibited to decrease the consumption of FPP. Glucose was used to balance the trade-off between the competitive squalene and patchoulol pathways. The patchoulol production was 59.2 ± 0.7 mg/L in a shaken flask with a final production of 466.8 ± 12.3 mg/L (20.5 ± 0.5 mg/g dry cell weight) combined with fermentation optimization, which was 7.8-fold higher than the reported maximum production. The work significantly promoted the industrialization process of patchoulol production using biobased microbial platforms.

Promiscuous terpene synthases from Prunella vulgaris highlight the importance of substrate and compartment switching in terpene synthase evolution

The mint family (Lamiaceae) is well documented as a rich source of terpene natural products. More than 200 diterpene skeletons have been reported from mints, but biosynthetic pathways are known for just a few of these. We crossreferenced chemotaxonomic data with publicly available transcriptomes to select common selfheal (Prunella vulgaris) and its highly unusual vulgarisin diterpenoids as a case study for exploring the origins of diterpene skeletal diversity in Lamiaceae. Four terpene synthases (TPS) from the TPS-a subfamily, including two localised to the plastid, were cloned and functionally characterised. Previous examples of TPS-a enzymes from Lamiaceae were cytosolic and reported to act on the 15-carbon farnesyl diphosphate. Plastidial TPS-a enzymes using the 20-carbon geranylgeranyl diphosphate are known from other plant families, having apparently arisen independently in each family. All four new enzymes were found to be active on multiple prenyl-diphosphate substrates with different chain lengths and stereochemistries. One of the new enzymes catalysed the cyclisation of geranylgeranyl diphosphate into 11-hydroxy vulgarisane, the likely biosynthetic precursor of the vulgarisins. We uncovered the pathway to a rare diterpene skeleton. Our results support an emerging paradigm of substrate and compartment switching as important aspects of TPS evolution and diversification.

Farnesyl pyrophosphate synthase is essential for the promastigote and amastigote stages in Leishmania major

Isoprenoid synthesis provides a diverse class of biomolecules including sterols, dolichols, ubiquinones and prenyl groups. The enzyme farnesyl pyrophosphate synthase (FPPS) catalyzes the formation of farnesyl pyrophosphate, a key intermediate for the biosynthesis of all isoprenoids. In Leishmania, FPPS is considered the main target of nitrogen containing bisphosphonates, yet the essentiality of this enzyme remains untested. Using a facilitated knockout approach, we carried out the genetic analysis of FPPS in Leishmania major. Our data indicated that chromosomal null mutants for FPPS could only be generated in presence of an episomally expressed FPPS. Long-term retention of the episome by the chromosomal FPPS-null mutants in culture and in infected BALB/c mice suggests that FPPS is indispensable. In addition, applying negative selection pressure failed to induce the loss of ectopic FPPS in the chromosomal FPPS-null mutants, although it led to significant growth delay in culture and in mice. Together, our findings have confirmed the essentiality of FPPS in both promastigotes and amastigotes in L. major and thus validate its potential as a drug target for the treatment of cutaneous leishmaniasis.

Deficiency of valencene in mandarin hybrids is associated with a deletion in the promoter region of the valencene synthase gene

BACKGROUND

Valencene is a major sesquiterpene in citrus oil and biosynthesized by valencene synthase (Cstps1; EC: 4.2.3.73) from the 15-carbon substrate farnesyl diphosphate. It is abundant in juice of some mandarins (e.g. Citrus reticulata Blanco cv. Fortune), however, it is undetectable in others (e.g. C. reticulata Blanco cv. Murcott), We have discovered that the Murcott mandarin Cstps1 gene expression is severely reduced. A previous genetic mapping study using an F1 population of Fortune × Murcott found that the segregation of valencene production in fruit exhibited a Mendelian inheritance ratio of 1:1. There was only one dominant locus associated with valencene content detected on the mandarin genetic map. The goal of this study was to understand the molecular mechanism underlying the valencene deficiency observed in some citrus hybrids.

RESULTS

There was a clear relationship between presence or absence of the valencene synthase gene (Cstps1) expression, and presence or absence of valencene among randomly selected mandarin hybrids. Cloning the coding regions of Cstps1 from Fortune and Murcott mandarin, and aligning with previous reported Valencia orange Cstps1 sequence, showed that they both exhibited extremely high similarity with the known Cstps1. By further cloning and analyzing the promoter region of Cstps1 from Valencia, Fortune and Murcott, a 12-nucleotide deletion at approximately - 270 bp from the Cstps1 coding region was only found in Murcott. Three binary vectors, designated as p1380-FortP-GUSin, p1380-MurcP-GUSin and p1380-MurcP(+ 12)-GUSin, were developed for promoter activity analysis. Transient over-expression of Fortune Cstps1 promoter in sweet orange showed notable GUS activity, but the Murcott Cstps1 promoter did not. In addition, by re-inserting the 12-nucleotide fragment, the activity of the Murcott Cstps1 promoter was mostly recovered.

CONCLUSION

The deficiency of valencene production in some mandarins is probably due to a 12-nucleotide deletion in the promoter region of the Cstps1, which could be a crucial switch of Cstps1 transcription. Our results further enhanced the understanding of valencene biosynthesis in citrus.

Enzyme Fusion Removes Competition for Geranylgeranyl Diphosphate in Carotenogenesis

Geranylgeranyl diphosphate (GGPP), a prenyl diphosphate synthesized by GGPP synthase (GGPS), represents a metabolic hub for the synthesis of key isoprenoids, such as chlorophylls, tocopherols, phylloquinone, gibberellins, and carotenoids. Protein-protein interactions and the amphipathic nature of GGPP suggest metabolite channeling and/or competition for GGPP among enzymes that function in independent branches of the isoprenoid pathway. To investigate substrate conversion efficiency between the plastid-localized GGPS isoform GGPS11 and phytoene synthase (PSY), the first enzyme of the carotenoid pathway, we used recombinant enzymes and determined their in vitro properties. Efficient phytoene biosynthesis via PSY strictly depended on simultaneous GGPP supply via GGPS11. In contrast, PSY could not access freely diffusible GGPP or time-displaced GGPP supply via GGPS11, presumably due to liposomal sequestration. To optimize phytoene biosynthesis, we applied a synthetic biology approach and constructed a chimeric GGPS11-PSY metabolon (PYGG). PYGG converted GGPP to phytoene almost quantitatively in vitro and did not show the GGPP leakage typical of the individual enzymes. PYGG expression in Arabidopsis resulted in orange-colored cotyledons, which are not observed if PSY or GGPS11 are overexpressed individually. This suggests insufficient GGPP substrate availability for chlorophyll biosynthesis achieved through GGPP flux redirection to carotenogenesis. Similarly, carotenoid levels in PYGG-expressing callus exceeded that in PSY- or GGPS11-overexpression lines. The PYGG chimeric protein may assist in provitamin A biofortification of edible plant parts. Moreover, other GGPS fusions may be used to redirect metabolic flux into the synthesis of other isoprenoids of nutritional and industrial interest.

Transcriptomic responses to grazing reveal the metabolic pathway leading to the biosynthesis of domoic acid and highlight different defense strategies in diatoms

BACKGROUND

A major cause of phytoplankton mortality is predation by zooplankton. Strategies to avoid grazers have probably played a major role in the evolution of phytoplankton and impacted bloom dynamics and trophic energy transport. Certain species of the genus Pseudo-nitzschia produce the neurotoxin, domoic acid (DA), as a response to the presence of copepod grazers, suggesting that DA is a defense compound. The biosynthesis of DA comprises fusion of two precursors, a C10 isoprenoid geranyl pyrophosphate and L-glutamate. Geranyl pyrophosphate (GPP) may derive from the mevalonate isoprenoid (MEV) pathway in the cytosol or from the methyl-erythritol phosphate (MEP) pathway in the plastid. L-glutamate is suggested to derive from the citric acid cycle. Fragilariopsis, a phylogenetically related but nontoxic genus of diatoms, does not appear to possess a similar defense mechanism. We acquired information on genes involved in biosynthesis, precursor pathways and regulatory functions for DA production in the toxigenic Pseudo-nitzschia seriata, as well as genes involved in responses to grazers to resolve common responses for defense strategies in diatoms.

RESULTS

Several genes are expressed in cells of Pseudo-nitzschia when these are exposed to predator cues. No genes are expressed in Fragilariopsis when treated similarly, indicating that the two taxa have evolved different strategies to avoid predation. Genes involved in signal transduction indicate that Pseudo-nitzschia cells receive signals from copepods that transduce cascading molecular precursors leading to the formation of DA. Five out of seven genes in the MEP pathway for synthesis of GPP are upregulated, but none in the conventional MEV pathway. Five genes with known or suggested functions in later steps of DA formation are upregulated. We conclude that no gene regulation supports that L-glutamate derives from the citric acid cycle, and we suggest the proline metabolism to be a downstream precursor.

CONCLUSIONS

Pseudo-nitzschia cells, but not Fragilariopsis, receive and respond to copepod cues. The cellular route for the C10 isoprenoid product for biosynthesis of DA arises from the MEP metabolic pathway and we suggest proline metabolism to be a downstream precursor for L-glutamate. We suggest 13 genes with unknown function to be involved in diatom responses to grazers.

A Novel Hydrolytic Activity of Tri-Functional Geranylgeranyl Pyrophosphate Synthase in Haematococcus pluvialis

Under environmental stresses, Haematococcus pluvialis accumulates large amounts of carotenoids. Scale of carotenoid biosynthesis depends on availability of geranylgeranyl pyrophosphate (GGPP) precursor, which is supplied by GGPP synthase (GGPPS) through sequential 1'-4 condensation of three isopentenyl pyrophosphates (IPPs) into dimethylallyl pyrophosphate (DMAPP). Using IPP and DMAPP as substrates, a tri-functional HpGGPPS was identified in this study to promiscuously synthesize allylic prenyl pyrophosphates (PPPs), e.g. C10 geranyl pyrophosphate (GPP), C15 farnesyl pyrophosphate (FPP), and C20 GGPP. Intriguingly, HpGGPPS can utilize GPP or FPP as a single substrate to synthesize GGPP by hydrolyzing the allylic PPP substrate into C5 IPP. Transcription of HpGGPPS and key carotenogenesis genes, morphological transformation, and carotenoid biosynthesis were differentially induced by environmental stresses, while HpGGPPS's products were low in vivo, implying that most of PPP flux had been shunted into carotenoid biosynthesis. Hydrolyzing allylic PPP intermediates into C5 building blocks by promiscuous HpGGPPS may be a fail safe for carotenoid accumulation against environmental stress.

Puerarin prevents LPS-induced acute lung injury via inhibiting inflammatory response

Acute lung injury (ALI) is a critical illness syndrome with high morbidity and mortality in patients. Inflammation has been known to be involved in the development of ALI. The purpose of this study was to investigate the effect of puerarin on lipopolysaccharide (LPS)-induced ALI in mice. The pro-inflammatory cytokines TNF-α, IL-6 and IL-1β were determined by ELISA. Western blot analysis was used for detecting the expression of NF-κB, IκBα, and LXRα. And myeloperoxidase (MPO) activity, lung wet/dry (W/D) ratio, and histopathological examination were also detected in lung tissues. The results showed that puerarin significantly inhibited LPS-stimulated MPO activity in lung tissues. Meanwhile, puerarin attenuated lung histopathological changes and lung wet/dry (W/D) ratio. We also found that the expression of pro-inflammatory cytokines, TNF-α, IL-6 and IL-1β were inhibited by puerarin. Puerarin also inhibited LPS-induced TNF-α in RAW264.7 cells and IL-8 in A549 cells. From the results of western blotting, puerarin significantly suppressed LPS-stimulated NF-κB activation. And the expression of LXRα was dose-dependently increased by treatment of puerarin. The inhibition of puerarin on TNF-α production in RAW264.7 cells and IL-8 production in A549 cells were blocked by LXRα inhibitor geranylgeranyl pyrophosphate (GGPP). These results suggested that puerarin attenuated ALI by activating LXRα, which subsequently inhibited LPS-induced inflammatory response.

Mechanistic studies of sesquiterpene cyclases based on their carbon isotope ratios at natural abundance

During the process of terpene biosynthesis, C-C bond breaking and forming steps are subjected to kinetic carbon isotope effects, leading to distinct carbon isotopic signatures of the products. Accordingly, carbon isotopic signatures could be used to reveal the 'biosynthetic history' of the produced terpenoids. Five known sesquiterpene cyclases, regulating three different pathways, representing simple to complex biosynthetic sequences, were heterologously expressed and used for in vitro assays with farnesyl diphosphate as substrate. Compound specific isotope ratio mass spectrometry measurements of the enzyme substrate farnesyl diphosphate (FDP) and the products of all the five cyclases were performed. The calculated δ¹³ C value for FDP, based on δ¹³ C values and relative amounts of the products, was identical with its measured δ¹³ C value, confirming the reliability of the approach and the precision of measurements. The different carbon isotope ratios of the products reflect the complexity of their structure and are correlated with the frequency of carbon-carbon bond forming and breaking steps on their individual biosynthetic pathways. Thus, the analysis of carbon isotopic signatures of terpenes at natural abundance can be used as a powerful tool in elucidation of associated biosynthetic mechanisms of terpene synthases and in future in vivo studies even without 'touching' the plant.

Statin-Induced Cancer Cell Death Can Be Mechanistically Uncoupled from Prenylation of RAS Family Proteins

The statin family of drugs preferentially triggers tumor cell apoptosis by depleting mevalonate pathway metabolites farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP), which are used for protein prenylation, including the oncoproteins of the RAS superfamily. However, accumulating data indicate that activation of the RAS superfamily are poor biomarkers of statin sensitivity, and the mechanism of statin-induced tumor-specific apoptosis remains unclear. Here we demonstrate that cancer cell death triggered by statins can be uncoupled from prenylation of the RAS superfamily of oncoproteins. Ectopic expression of different members of the RAS superfamily did not uniformly sensitize cells to fluvastatin, indicating that increased cellular demand for protein prenylation cannot explain increased statin sensitivity. Although ectopic expression of HRAS increased statin sensitivity, expression of myristoylated HRAS did not rescue this effect. HRAS-induced epithelial-to-mesenchymal transition (EMT) through activation of zinc finger E-box binding homeobox 1 (ZEB1) sensitized tumor cells to the antiproliferative activity of statins, and induction of EMT by ZEB1 was sufficient to phenocopy the increase in fluvastatin sensitivity; knocking out ZEB1 reversed this effect. Publicly available gene expression and statin sensitivity data indicated that enrichment of EMT features was associated with increased sensitivity to statins in a large panel of cancer cell lines across multiple cancer types. These results indicate that the anticancer effect of statins is independent from prenylation of RAS family proteins and is associated with a cancer cell EMT phenotype.Significance: The use of statins to target cancer cell EMT may be useful as a therapy to block cancer progression. Cancer Res; 78(5); 1347-57. ©2017 AACR.

Biosynthetic Machinery of Diterpene Pleuromutilin Isolated from Basidiomycete Fungi

The diterpene pleuromutilin is a ribosome-targeting antibiotic isolated from basidiomycete fungi, such as Clitopilus pseudo-pinsitus. The functional characterization of all biosynthetic enzymes involved in pleuromutilin biosynthesis is reported and a biosynthetic pathway proposed. In vitro enzymatic reactions and mutational analysis revealed that a labdane-related diterpene synthase, Ple3, catalyzed two rounds of cyclization from geranylgeranyl diphosphate to premutilin possessing a characteristic 5-6-8-tricyclic carbon skeleton. Biotransformation experiments utilizing Aspergillus oryzae transformants possessing modification enzyme genes allowed the biosynthetic pathway from premutilin to pleuromutilin to be proposed. The present study sets the stage for the enzymatic synthesis of natural products isolated from basidiomycete fungi, which are a prolific source of structurally diverse and biologically active terpenoids.

Polyprenols Are Synthesized by a Plastidial cis-Prenyltransferase and Influence Photosynthetic Performance

Plants accumulate a family of hydrophobic polymers known as polyprenols, yet how they are synthesized, where they reside in the cell, and what role they serve is largely unknown. Using Arabidopsis thaliana as a model, we present evidence for the involvement of a plastidial cis-prenyltransferase (AtCPT7) in polyprenol synthesis. Gene inactivation and RNAi-mediated knockdown of AtCPT7 eliminated leaf polyprenols, while its overexpression increased their content. Complementation tests in the polyprenol-deficient yeast ∆rer2 mutant and enzyme assays with recombinant AtCPT7 confirmed that the enzyme synthesizes polyprenols of ∼55 carbons in length using geranylgeranyl diphosphate (GGPP) and isopentenyl diphosphate as substrates. Immunodetection and in vivo localization of AtCPT7 fluorescent protein fusions showed that AtCPT7 resides in the stroma of mesophyll chloroplasts. The enzymatic products of AtCPT7 accumulate in thylakoid membranes, and in their absence, thylakoids adopt an increasingly "fluid membrane" state. Chlorophyll fluorescence measurements from the leaves of polyprenol-deficient plants revealed impaired photosystem II operating efficiency, and their thylakoids exhibited a decreased rate of electron transport. These results establish that (1) plastidial AtCPT7 extends the length of GGPP to ∼55 carbons, which then accumulate in thylakoid membranes; and (2) these polyprenols influence photosynthetic performance through their modulation of thylakoid membrane dynamics.

Transcriptome profiling of the Australian arid-land plant Eremophila serrulata (A.DC.) Druce (Scrophulariaceae) for the identification of monoterpene synthases

Plant terpenoids are a large and highly diverse class of metabolites with an important role in the immune defense. They find wide industrial application as active pharmaceutical ingredients, aroma and fragrance compounds. Several Eremophila sp. derived terpenoids have been documented. To elucidate the terpenoid metabolism, the transcriptome of juvenile and mature Eremophila serrulata (A.DC.) Druce (Scrophulariaceae) leaves was sequenced and a transcript library was generated. We report on the first transcriptomic dataset of an Eremophila plant. IlluminaMiSeq sequencing (2 × 300 bp) revealed 7,093,266 paired reads, which could be assembled to 34,505 isogroups. To enable detection of terpene biosynthetic genes, leaves were separately treated with methyl jasmonate, a well-documented inducer of plant secondary metabolites. In total, 21 putative terpene synthase genes were detected in the transcriptome data. Two terpene synthase isoenzymatic genes, termed ES01 and ES02, were successfully expressed in E. coli. The resulting proteins catalyzed the conversion of geranyl pyrophosphate, the universal substrate of monoterpene synthases to myrcene and Z-(b)-ocimene, respectively. The transcriptomic data and the discovery of the first terpene synthases from Eremophila serrulata are the initial step for the understanding of the terpene metabolism in this medicinally important plant genus.

Molecular cloning and functional analysis of a 10-epi-junenol synthase from Inula hupehensis

Junenol based-eudesmanolides have been detected in many compositae plant species and were reported to exhibit various pharmacological activities. So far, the gene encoding junenol synthase has never been isolated. Here we report the molecular cloning and functional analysis of a 10-epi-junenol synthase from Inula hupehensis (designated IhsTPS1). IhsTPS1 converts the substrate farnesyl diphosphate into multiple sesquiterpenes with the product 10-epi-junenol being predominant. The transcript levels of IhsTPS1 correlate well with the accumulation pattern of 10-epi-junenol in I. hupehensis organs, supporting its biochemical roles in vivo.

Functional Analysis of Amorpha-4,11-Diene Synthase (ADS) Homologs from Non-Artemisinin-Producing Artemisia Species: The Discovery of Novel Koidzumiol and (+)-α-Bisabolol Synthases

The production of artemisinin, the most effective antimalarial compound, is limited to Artemisia annua. Enzymes involved in artemisinin biosynthesis include amorpha-4,11-diene synthase (ADS), amorpha-4,11-diene 12-monooxygenase (CYP71AV1) and artemisinic aldehyde Δ(11)13 reductase (DBR2). Although artemisinin and its specific intermediates are not detected in other Artemisia species, we reported previously that CYP71AV1 and DBR2 homologs were expressed in some non-artemisinin-producing Artemisia plants. These homologous enzymes showed similar functions to their counterparts in A. annua and can convert fed intermediates into the following products along the artemisinin biosynthesis in planta These findings suggested a partial artemisinin-producing ability in those species. In this study, we examined genes highly homologous to ADS, the first committed gene in the pathway, in 13 Artemisia species. We detected ADS homologs in A. absinthium, A. kurramensis and A. maritima. We analyzed the enzymatic functions of all of the ADS homologs after obtaining their cDNA. We found that the ADS homolog from A. absinthium exhibited novel activity in the cyclization of farnesyl pyrophosphate (FPP) to koidzumiol, a rare natural sesquiterpenoid. Those from A. kurramensis and A. maritima showed similar, but novel, activities in the cyclization of FPP to (+)-α-bisabolol. The unique functions of the novel sesquiterpene synthases highly homologous to ADS found in this study could provide insight into the molecular basis of the exceptional artemisinin-producing ability in A. annua.

Overexpression of a synthetic insect-plant geranyl pyrophosphate synthase gene in Camelina sativa alters plant growth and terpene biosynthesis

A novel plastidial homodimeric insect-plant geranyl pyrophosphate synthase gene is synthesized from three different cDNA origins. Its overexpression in Camelina sativa effectively alters plant development and terpenoid metabolism. Geranyl pyrophosphate synthase (GPPS) converts one isopentenyl pyrophosphate and dimethylallyl pyrophosphate to GPP. Here, we report a synthetic insect-plant GPPS gene and effects of its overexpression on plant growth and terpenoid metabolism of Camelina sativa. We synthesized a 1353-bp cDNA, namely PTP-MpGPPS. This synthetic cDNA was composed of a 1086-bp cDNA fragment encoding a small GPPS isomer of the aphid Myzus persicae (Mp), 240-bp Arabidopsis thaliana cDNA fragment encoding a plastidial transit peptide (PTP), and a 27-bp short cDNA fragment encoding a human influenza hemagglutinin tag peptide. Structural modeling showed that the deduced protein was a homodimeric prenyltransferase. Confocal microscopy analysis demonstrated that the PTP-MpGPPS fused with green florescent protein was localized in the plastids. The synthetic PTP-MpGPPS cDNA driven by 2 × 35S promoters was introduced into Camelina (Camelina sativa) by Agrobacterium-mediated transformation and its overexpression in transgenic plants were demonstrated by western blot. T2 and T3 progeny of transgenic plants developed larger leaves, grew more and longer internodes, and flowered earlier than wild-type plants. Metabolic analysis showed that the levels of beta-amyrin and campesterol were higher in tissues of transgenic plants than in those of wild-type plants. Fast isoprene sensor analysis demonstrated that transgenic Camelina plants emitted significantly less isoprene than wild-type plants. In addition, transcriptional analyses revealed that the expression levels of gibberellic acid and brassinosteroids-responsive genes were higher in transgenic plants than in wild-type plants. Taken together, these data demonstrated that this novel synthetic insect-plant GPPS cDNA was effective to improve growth traits and alter terpenoid metabolism of Camelina.

Analogs of farnesyl diphosphate alter CaaX substrate specificity and reactions rates of protein farnesyltransferase

Attempts to identify the prenyl-proteome of cells or changes in prenylation following drug treatment have used 'clickable' alkyne-modified analogs of the lipid substrates farnesyl- and geranylgeranyl-diphosphate (FPP and GGPP). We characterized the reactivity of four alkyne-containing analogs of FPP with purified protein farnesyltransferase and a small library of dansylated peptides using an in vitro continuous spectrofluorimetric assay. These analogs alter prenylation specificity and reactivity suggesting that in vivo results obtained using these FPP analogs should be interpreted cautiously.

Arabidopsis GERANYLGERANYL DIPHOSPHATE SYNTHASE 11 is a hub isozyme required for the production of most photosynthesis-related isoprenoids

Most plastid isoprenoids, including photosynthesis-related metabolites such as carotenoids and the side chain of chlorophylls, tocopherols (vitamin E), phylloquinones (vitamin K), and plastoquinones, derive from geranylgeranyl diphosphate (GGPP) synthesized by GGPP synthase (GGPPS) enzymes. Seven out of 10 functional GGPPS isozymes in Arabidopsis thaliana reside in plastids. We aimed to address the function of different GGPPS paralogues for plastid isoprenoid biosynthesis. We constructed a gene co-expression network (GCN) using GGPPS paralogues as guide genes and genes from the upstream and downstream pathways as query genes. Furthermore, knock-out and/or knock-down ggpps mutants were generated and their growth and metabolic phenotypes were analyzed. Also, interacting protein partners of GGPPS11 were searched for. Our data showed that GGPPS11, encoding the only plastid isozyme essential for plant development, functions as a hub gene among GGPPS paralogues and is required for the production of all major groups of plastid isoprenoids. Furthermore, we showed that the GGPPS11 protein physically interacts with enzymes that use GGPP for the production of carotenoids, chlorophylls, tocopherols, phylloquinone, and plastoquinone. GGPPS11 is a hub isozyme required for the production of most photosynthesis-related isoprenoids. Both gene co-expression and protein-protein interaction likely contribute to the channeling of GGPP by GGPPS11.

Carotenoid Distribution in Nature

Carotenoids are naturally occurring red, orange and yellow pigments that are synthesized by plants and some microorganisms and fulfill many important physiological functions. This chapter describes the distribution of carotenoid in microorganisms, including bacteria, archaea, microalgae, filamentous fungi and yeasts. We will also focus on their functional aspects and applications, such as their nutritional value, their benefits for human and animal health and their potential protection against free radicals. The central metabolic pathway leading to the synthesis of carotenoids is described as the three following principal steps: (i) the synthesis of isopentenyl pyrophosphate and the formation of dimethylallyl pyrophosphate, (ii) the synthesis of geranylgeranyl pyrophosphate and (iii) the synthesis of carotenoids per se, highlighting the differences that have been found in several carotenogenic organisms and providing an evolutionary perspective. Finally, as an example, the synthesis of the xanthophyll astaxanthin is discussed.

Identification of geranylgeranyl diphosphate synthase genes from Tripterygium wilfordii

We found triptolide synthesis is correlated with the expressions of TwGGPPS1 and TwGGPPS4 . This lays the foundation for future studies of biosynthetic pathways for triptolide and other diterpenoids in T. wilfordii. Tripterygium wilfordii is a traditional Chinese medical plant commonly used to treat rheumatoid arthritis. One of its main bioactive compounds is triptolide, which is identified as an abietane-type diterpenoid natural product. Geranylgeranyl diphosphate synthase (GGPPS) catalyses the synthesis of GGPP (geranylgeranyl diphosphate), the common precursor of diterpenes, and is therefore a crucial enzyme in diterpene biosynthesis. A previous study showed that GGPP could be catalyzed by copalyl diphosphate synthase and kaurene synthase like of Salvia miltiorrhiza (SmCPS, SmKSL) to miltiradiene, a key intermediate in tanshinone biosynthesis. In this paper, five new full-length cDNAs (TwGGPPS) encoding GGPP synthases were cloned from T. wilfordii. Sequence comparisons revealed that all six TwGGPPSs (including TwGGPPS2 cloned previously) exhibit similarities to GGPPSs of other plants. Subsequent functional complement assays demonstrated that TwGGPPS1, TwGGPPS4 and TwGGPPS5 can participate in miltiradiene biosynthesis in the recombinant E. coli. Correlation analysis of gene expressions and secondary metabolite accumulation indicated that TwGGPPS1 and TwGGPPS4 are likely involved in the biosynthesis of triptolide. These findings lay the foundation for future studies of the biosynthetic pathways for triptolide and other diterpenoids in T. wilfordii.