The molecular mechanism of nitrogen-containing bisphosphonates as antiosteoporosis drugs

Osteoporosis and low bone mass are currently estimated to be a major public health risk affecting >50% of the female population over the age of 50. Because of their bone-selective pharmacokinetics, nitrogen-containing bisphosphonates (N-BPs), currently used as clinical inhibitors of bone-resorption diseases, target osteoclast farnesyl pyrophosphate synthase (FPPS) and inhibit protein prenylation. FPPS, a key branchpoint of the mevalonate pathway, catalyzes the successive condensation of isopentenyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. To understand the molecular events involved in inhibition of FPPS by N-BPs, we used protein crystallography, enzyme kinetics, and isothermal titration calorimetry. We report here high-resolution x-ray structures of the human enzyme in complexes with risedronate and zoledronate, two of the leading N-BPs in clinical use. These agents bind to the dimethylallyl/geranyl pyrophosphate ligand pocket and induce a conformational change. The interactions of the N-BP cyclic nitrogen with Thr-201 and Lys-200 suggest that these inhibitors achieve potency by positioning their nitrogen in the proposed carbocation-binding site. Kinetic analyses reveal that inhibition is competitive with geranyl pyrophosphate and is of a slow, tight binding character, indicating that isomerization of an initial enzyme-inhibitor complex occurs with inhibitor binding. Isothermal titration calorimetry indicates that binding of N-BPs to the apoenzyme is entropy-driven, presumably through desolvation entropy effects. These experiments reveal the molecular binding characteristics of an important pharmacological target and provide a route for further optimization of these important drugs.

A novel pathway for sesquiterpene biosynthesis from Z,Z-farnesyl pyrophosphate in the wild tomato Solanum habrochaites

In the wild tomato Solanum habrochaites, the Sst2 locus on chromosome 8 is responsible for the biosynthesis of several class II sesquiterpene olefins by glandular trichomes. Analysis of a trichome-specific EST collection from S. habrochaites revealed two candidate genes for the synthesis of Sst2-associated sesquiterpenes. zFPS encodes a protein with homology to Z-isoprenyl pyrophosphate synthases and SBS (for Santalene and Bergamotene Synthase) encodes a terpene synthase with homology to kaurene synthases. Both genes were found to cosegregate with the Sst2 locus. Recombinant zFPS protein catalyzed the synthesis of Z,Z-FPP from isopentenylpyrophosphate (IPP) and dimethylallylpyrophosphate (DMAPP), while coincubation of zFPS and SBS with the same substrates yielded a mixture of olefins identical to the Sst2-associated sesquiterpenes, including (+)-alpha-santalene, (+)-endo-beta-bergamotene, and (-)-endo-alpha-bergamotene. In addition, headspace analysis of tobacco (Nicotiana sylvestris) plants expressing zFPS and SBS in glandular trichomes afforded the same mix of sesquiterpenes. Each of these proteins contains a putative plastid targeting sequence that mediates transport of a fused green fluorescent protein to the chloroplasts, suggesting that the biosynthesis of these sesquiterpenes uses IPP and DMAPP from the plastidic DXP pathway. These results provide novel insights into sesquiterpene biosynthesis and have general implications concerning sesquiterpene engineering in plants.

Chimeras of Two Isoprenoid Synthases Catalyze All Four Coupling Reactions in Isoprenoid Biosynthesis

The carbon skeletons of over 55,000 naturally occurring isoprenoid compounds are constructed from four fundamental coupling reactions: chain elongation, cyclopropanation, branching, and cyclobutanation. Enzymes that catalyze chain elongation and cyclopropanation are well studied, whereas those that catalyze branching and cyclobutanation are unknown. We have catalyzed the four reactions with chimeric proteins generated by replacing segments of a chain-elongation enzyme with corresponding sequences from a cyclopropanation enzyme. Stereochemical and mechanistic considerations suggest that the four coupling enzymes could have evolved from a common ancestor through relatively small changes in the catalytic site.

Control of juvenile hormone biosynthesis in Bombyx mori: cloning of the enzymes in the mevalonate pathway and assessment of their developmental expression in the corpora allata

We have isolated the cDNAs of all enzymes involved in the mevalonate pathway portion of the juvenile hormone (JH) biosynthetic pathway in Bombyx mori, i.e., those responsible for the formation of farnesyl diphosphate from acetyl-CoA. There is a single gene encoding each enzyme of this pathway, with the exception of farnesyl diphosphate synthase (FPPS), for which we identified three homologs. All but two of these enzymes are expressed almost exclusively in the corpora allata (CA), as indicated by quantitative RT-PCR analyses. Phosphomevalonate kinase (MevPK) was expressed in many tissues, including the CA. In day 2 4th instars, FPPS1 expression was detected primarily in the Malpighian tubules, but expression of the structurally related FPPS2 and FPPS3 occurred mainly in the CA. Since FPPS3 transcripts were 55 times less abundant than those of FPPS2, the latter is expected to play a major role in JH biosynthesis at this stage. Studies on the developmental expression of these enzymes in the CA showed that the levels of all transcripts were high during the 4th instar larvae, a stage at which in vitro JH biosynthesis was high. However, the transcripts of all the mevalonate enzymes declined to low levels and JH acid O-methyltransferase (JHAMT) transcript disappeared by day 3 when CA ceased JH production after the final larval molt. The CA did not synthesize JH during the pupal stage, coincident with the limited expression of mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate kinase and isopentenyl diphosphate isomerase, and the inactivation of the JHAMT gene. Only female CA produced JH in the adult stage, a feature associated with the re-expression of JHAMT in female but little in male adult CA. Altogether, our results point to a relationship between JH biosynthesis and expression of most JH biosynthetic enzymes in the CA.

Curcumin induces changes in expression of genes involved in cholesterol homeostasis

Curcuminoids, the yellow pigments of curcuma, exhibit anticarcinogenic, antioxidative and hypocholesterolemic activities. To understand the molecular basis for the hypocholesterolemic effects, we examined the effects of curcumin on hepatic gene expression, using the human hepatoma cell line HepG2 as a model system. Curcumin treatment caused an up to sevenfold, concentration-dependent increase in LDL-receptor mRNA, whereas mRNAs of the genes encoding the sterol biosynthetic enzymes HMG CoA reductase and farnesyl diphosphate synthase were only slightly increased at high curcumin concentrations where cell viability was reduced. Expression of the regulatory SREBP genes was moderately increased, whereas mRNAs of the PPARalpha target genes CD36/fatty acid translocase and fatty acid binding protein 1 were down-regulated. LXRalpha expression and accumulation of mRNA of the LXRalpha target gene ABCg1 were increased at low curcumin concentrations. Although curcumin strongly inhibited alkaline phosphatase activity, an activation of a retinoic acid response element reporter employing secreted alkaline phosphatase was observed. These changes in gene expression are consistent with the proposed hypocholesterolemic effect of curcumin.

Monoterpenoid biosynthesis inSaccharomyces cerevisiae

Plant monoterpenoids belong to a large family of plant secondary metabolites with valuable applications in cosmetics and medicine. Their usual low levels and difficult purification justify the need for alternative fermentative processes for large-scale production. Geranyl diphosphate is the universal precursor of monoterpenoids. In yeast it occurs exclusively as an intermediate of farnesyl diphosphate synthesis. In the present study we investigated the potential use of Saccharomyces cerevisiae as an alternative engineering tool. The expression of geraniol synthase of Ocimum basilicum in yeast allowed a strong and specific excretion of geraniol to the growth medium, in contrast to mutants defective in farnesyl diphosphate synthase which excreted geraniol and linalool in similar amounts. A further increase of geraniol synthesis was obtained using yeast mutants defective in farnesyl diphosphate synthase. We also showed that geraniol synthase expression affects the general ergosterol pathway, but in a manner dependent on the genetic background of the strain.

Cytosolic monoterpene biosynthesis is supported by plastid-generated geranyl diphosphate substrate in transgenic tomato fruits

Geranyl diphosphate (GPP), the precursor of most monoterpenes, is synthesized in plastids from dimethylallyl diphosphate and isopentenyl diphosphate by GPP synthases (GPPSs). In heterodimeric GPPSs, a non-catalytic small subunit (GPPS-SSU) interacts with a catalytic large subunit, such as geranylgeranyl diphosphate synthase, and determines its product specificity. Here, snapdragon (Antirrhinum majus) GPPS-SSU was over-expressed in tomato fruits under the control of the fruit ripening-specific polygalacturonase promoter to divert the metabolic flux from carotenoid formation towards GPP and monoterpene biosynthesis. Transgenic tomato fruits produced monoterpenes, including geraniol, geranial, neral, citronellol and citronellal, while exhibiting reduced carotenoid content. Co-expression of the Ocimum basilicum geraniol synthase (GES) gene with snapdragon GPPS-SSU led to a more than threefold increase in monoterpene formation in tomato fruits relative to the parental GES line, indicating that the produced GPP can be used by plastidic monoterpene synthases. Co-expression of snapdragon GPPS-SSU with the O. basilicum α-zingiberene synthase (ZIS) gene encoding a cytosolic terpene synthase that has been shown to possess both sesqui- and monoterpene synthase activities resulted in increased levels of ZIS-derived monoterpene products compared to fruits expressing ZIS alone. These results suggest that re-direction of the metabolic flux towards GPP in plastids also increases the cytosolic pool of GPP available for monoterpene synthesis in this compartment via GPP export from plastids.

Spearmint R2R3-MYB transcription factor MsMYB negatively regulates monoterpene production and suppresses the expression of geranyl diphosphate synthase large subunit (MsGPPS.LSU)

Many aromatic plants, such as spearmint, produce valuable essential oils in specialized structures called peltate glandular trichomes (PGTs). Understanding the regulatory mechanisms behind the production of these important secondary metabolites will help design new approaches to engineer them. Here, we identified a PGT-specific R2R3-MYB gene, MsMYB, from comparative RNA-Seq data of spearmint and functionally characterized it. Analysis of MsMYB-RNAi transgenic lines showed increased levels of monoterpenes, and MsMYB-overexpressing lines exhibited decreased levels of monoterpenes. These results suggest that MsMYB is a novel negative regulator of monoterpene biosynthesis. Ectopic expression of MsMYB, in sweet basil and tobacco, perturbed sesquiterpene- and diterpene-derived metabolite production. In addition, we found that MsMYB binds to cis-elements of MsGPPS.LSU and suppresses its expression. Phylogenetic analysis placed MsMYB in subgroup 7 of R2R3-MYBs whose members govern phenylpropanoid pathway and are regulated by miR858. Analysis of transgenic lines showed that MsMYB is more specific to terpene biosynthesis as it did not affect metabolites derived from phenylpropanoid pathway. Further, our results indicate that MsMYB is probably not regulated by miR858, like other members of subgroup 7.

Salicylic acid activates artemisinin biosynthesis in Artemisia annua L

This paper provides evidence that salicylic acid (SA) can activate artemisinin biosynthesis in Artemisia annua L. Exogenous application of SA to A. annua leaves was followed by a burst of reactive oxygen species (ROS) and the conversion of dihydroartemisinic acid into artemisinin. In the 24 h after application, SA application led to a gradual increase in the expression of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) gene and a temporary peak in the expression of the amorpha-4,11-diene synthase (ADS) gene. However, the expression of the farnesyl diphosphate synthase (FDS) gene and the cytochrome P450 monooxygenase (CYP71AV1) gene showed little change. At 96 h after SA (1.0 mM) treatment, the concentration of artemisinin, artemisinic acid and dihydroartemisinic acid were 54, 127 and 72% higher than that of the control, respectively. Taken together, these results suggest that SA induces artemisinin biosynthesis in at least two ways: by increasing the conversion of dihydroartemisinic acid into artemisinin caused by the burst of ROS, and by up-regulating the expression of genes involved in artemisinin biosynthesis.

The farnesyl-diphosphate/geranylgeranyl-diphosphate synthase of Toxoplasma gondii is a bifunctional enzyme and a molecular target of bisphosphonates

Farnesyl-diphosphate synthase (FPPS) catalyzes the synthesis of farnesyl diphosphate, an important precursor of sterols, dolichols, ubiquinones, and prenylated proteins. We report the cloning and characterization of two Toxoplasma gondii farnesyl-diphosphate synthase (TgFPPS) homologs. A single genetic locus produces two transcripts, TgFPPS and TgFPPSi, by alternative splicing. Both isoforms were heterologously expressed in Escherichia coli, but only TgFPPS was active. The protein products predicted from the nucleotide sequences have 646 and 605 amino acids and apparent molecular masses of 69.5 and 64.5 kDa, respectively. Several conserved sequence motifs found in other prenyl-diphosphate synthases are present in both TgFPPSs. TgFPPS was also expressed in the baculovirus system and was biochemically characterized. In contrast to the FPPS of other eukaryotic organisms, TgFPPS is bifunctional, catalyzing the formation of both farnesyl diphosphate and geranylgeranyl diphosphate. TgFPPS localizes to the mitochondria, as determined by the co-localisation of the affinity-purified antibodies against the protein with MitoTracker, and in accord with the presence of an N-terminal mitochondria-targeting signal in the protein. This enzyme is an attractive target for drug development, because the order of inhibition of the enzyme by a number of bisphosphonates is the same as that for inhibition of parasite growth. In summary, we report the first bifunctional farnesyl-diphosphate/geranylgeranyl-diphosphate synthase identified in eukaryotes, which, together with previous results, establishes this enzyme as a valid target for the chemotherapy of toxoplasmosis.

The Arabidopsis thaliana FPP synthase isozymes have overlapping and specific functions in isoprenoid biosynthesis, and complete loss of FPP synthase activity causes early developmental arrest

Farnesyl diphosphate (FPP) synthase (FPS) catalyses the synthesis of FPP, the major substrate used by cytosolic and mitochondrial branches of the isoprenoid pathway. Arabidopsis contains two farnesyl diphosphate synthase genes, FPS1 and FPS2, that encode isozymes FPS1L (mitochondrial), FPS1S and FPS2 (both cytosolic). Here we show that simultaneous knockout of both FPS genes is lethal for Arabidopsis, and embryo development is arrested at the pre-globular stage, demonstrating that FPP-derived isoprenoid metabolism is essential. In addition, lack of FPS enzyme activity severely impairs male genetic transmission. In contrast, no major developmental and metabolic defects were observed in fps1 and fps2 single knockout mutants, demonstrating the redundancy of the genes. The levels of sterols and ubiquinone, the major mitochondrial isoprenoid, are only slightly reduced in the single mutants. Although one functional FPS gene is sufficient to support isoprenoid biosynthesis for normal growth and development, the functions of FPS1 and FPS2 during development are not completely redundant. FPS1 activity has a predominant role during most of the plant life cycle, and FPS2 appears to have a major role in seeds and during the early stages of seedling development. Lack of FPS2 activity in seeds, but not of FPS1 activity, is associated with a marked reduction in sitosterol content and positive feedback regulation of 3-hydroxy-3-methylglutaryl CoA reductase activity that renders seeds hypersensitive to the 3-hydroxy-3-methylglutaryl CoA reductase inhibitor mevastatin.

Upregulation of phytosterol and triterpene biosynthesis in Centella asiatica hairy roots overexpressed ginseng farnesyl diphosphate synthase

Farnesyl diphosphate synthase (FPS) plays an essential role in organ development in plants. However, FPS has not previously been identified as a key regulatory enzyme in triterpene biosynthesis. To elucidate the functions of FPS in triterpene biosynthesis, C. asiatica was transformed with a construct harboring Panax ginseng FPS (PgFPS)-encoding cDNA coupled to the cauliflower mosaic virus 35S promoter. Higher levels of CaDDS (C. asiatica dammarenediol synthase) and CaCYS (C. asiatica cycloartenol synthase) mRNA were detected in all hairy root lines overexpressing when compared with the controls. However, no differences were detected in any expression of the CaSQS (C. asiatica squalene synthase) gene. In particular, the upregulation of CaDDS transcripts suggests that FPS may result in alterations in triterpene biosynthesis capacity. Squalene contents in the T17, T24, and T27 lines were increased to 1.1-, 1.3- and 1.5-fold those in the controls, respectively. The total sterol contents in the T24 line were approximately three times higher than those of the controls. Therefore, these results indicated that FPS performs a regulatory function in phytosterol biosynthesis. To evaluate the contribution of FPS to triterpene biosynthesis, we applied methyl jasmonate as an elicitor of hairy roots expressing PgFPS. The results of HPLC analysis revealed that the content of madecassoside and asiaticoside in the T24 line was transiently increased by 1.15-fold after 14 days of MJ treatment. This result may indicate that FPS performs a role not only in phytosterol regulation, but also in triterpene biosynthesis.

Monoterpene biosynthesis potential of plant subcellular compartments

Subcellular monoterpene biosynthesis capacity based on local geranyl diphosphate (GDP) availability or locally boosted GDP production was determined for plastids, cytosol and mitochondria. A geraniol synthase (GES) was targeted to plastids, cytosol, or mitochondria. Transient expression in Nicotiana benthamiana indicated local GDP availability for each compartment but resulted in different product levels. A GDP synthase from Picea abies (PaGDPS1) was shown to boost GDP production. PaGDPS1 was also targeted to plastids, cytosol or mitochondria and PaGDPS1 and GES were coexpressed in all possible combinations. Geraniol and geraniol-derived products were analyzed by GC-MS and LC-MS, respectively. GES product levels were highest for plastid-targeted GES, followed by mitochondrial- and then cytosolic-targeted GES. For each compartment local boosting of GDP biosynthesis increased GES product levels. GDP exchange between compartments is not equal: while no GDP is exchanged from the cytosol to the plastids, 100% of GDP in mitochondria can be exchanged to plastids, while only 7% of GDP from plastids is available for mitochondria. This suggests a direct exchange mechanism for GDP between plastids and mitochondria. Cytosolic PaGDPS1 competes with plastidial GES activity, suggesting an effective drain of isopentenyl diphosphate from the plastids to the cytosol.

Expression of 3-hydroxy-3-methylglutaryl-CoA reductase, p-hydroxybenzoate-m-geranyltransferase and genes of phenylpropanoid pathway exhibits positive correlation with shikonins content in arnebia [Arnebia euchroma (Royle) Johnston]

BACKGROUND

Geranyl pyrophosphate (GPP) and p-hydroxybenzoate (PHB) are the basic precursors involved in shikonins biosynthesis. GPP is derived from mevalonate (MVA) and/or 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway(s), depending upon the metabolite and the plant system under consideration. PHB, however, is synthesized by only phenylpropanoid (PP) pathway. GPP and PHB are central moieties to yield shikonins through the synthesis of m-geranyl-p-hydroxybenzoate (GHB). Enzyme p-hydroxybenzoate-m-geranyltransferase (PGT) catalyses the coupling of GPP and PHB to yield GHB. The present research was carried out in shikonins yielding plant arnebia [Arnebia euchroma (Royle) Johnston], wherein no molecular work has been reported so far. The objective of the work was to identify the preferred GPP synthesizing pathway for shikonins biosynthesis, and to determine the regulatory genes involved in the biosynthesis of GPP, PHB and GHB.

RESULTS

A cell suspension culture-based, low and high shikonins production systems were developed to facilitate pathway identification and finding the regulatory gene. Studies with mevinolin and fosmidomycin, inhibitors of MVA and MEP pathway, respectively suggested MVA as a preferred route of GPP supply for shikonins biosynthesis in arnebia. Accordingly, genes of MVA pathway (eight genes), PP pathway (three genes), and GHB biosynthesis were cloned. Expression studies showed down-regulation of all the genes in response to mevinolin treatment, whereas gene expression was not influenced by fosmidomycin. Expression of all the twelve genes vis-à-vis shikonins content in low and high shikonins production system, over a period of twelve days at frequent intervals, identified critical genes of shikonins biosynthesis in arnebia.

CONCLUSION

A positive correlation between shikonins content and expression of 3-hydroxy-3-methylglutaryl-CoA reductase (AeHMGR) and AePGT suggested critical role played by these genes in shikonins biosynthesis. Higher expression of genes of PP pathway was a general feature for higher shikonins biosynthesis.

FDPS cooperates with PTEN loss to promote prostate cancer progression through modulation of small GTPases/AKT axis

Farnesyl diphosphate synthase (FDPS), a mevalonate pathway enzyme, is highly expressed in several cancers, including prostate cancer (PCa). To date, the mechanistic, functional, and clinical significance of FDPS in cancer remains unexplored. We evaluated the FDPS expression and its cancer-associated phenotypes using in vitro and in vivo methods in PTEN-deficient and sufficient human and mouse PCa cells and tumors. Interestingly, FDPS overexpression synergizes with PTEN deficiency in PTEN conditionally knockout mice (P < 0.05) and expressed significantly higher in human (P < 0.001) PCa tissues, cell lines, and murine tumoroids compared to respective controls. In silico analysis revealed that FDPS is associated with increasing Gleason score, PTEN functionally deficient status, and poor survival of PCa. Ectopic overexpression of FDPS promotes oncogenic phenotypes such as colony formation (P < 0.01) and proliferation (P < 0.01) through activation of AKT and ERK signaling by prenylating Rho A, Rho G, and CDC42 small GTPases. Of interest, knockdown of FDPS in PCa cells exhibits decreased colony growth and proliferation (P < 0.001) by modulating AKT and ERK pathways. Further, genetic and pharmacological inhibition of PI3K but not AKT reduced FDPS expression. Pharmacological targeting of FDPS by zoledronic acid (ZOL), which is already in clinics, exhibit reduced growth and clonogenicity of human and murine PCa cells (P < 0.01) and 3D tumoroids (P < 0.02) by disrupting AKT and ERK signaling through direct interference of small GTPases protein prenylation. Thus, FDPS plays an oncogenic role in PTEN-deficient PCa through GTPase/AKT axis. Identifying mevalonate pathway proteins could serve as a therapeutic target in PTEN dysregulated tumors.

Modulatory effect of farnesyl pyrophosphate synthase (FDPS) rs2297480 polymorphism on the response to long-term amino-bisphosphonate treatment in postmenopausal osteoporosis

INTRODUCTION

Polymorphisms of genes encoding enzymes of the mevalonate pathway could modulate the response to amino-bisphosphonate treatment in postmenopausal osteoporosis.

RESEARCH DESIGN AND METHODS

A characterisation of 234 Danish osteoporotic postmenopausal women (as part of the Prospective Epidemiological Risk Factors study (PERF)), treated for at least 2 years with amino-bisphosphonates, with respect to the adenosine/cytosine (A/C) rs2297480 farnesyl pyrophosphate synthase (FDPS) gene polymorphism, was carried out by PCR-based enzymatic digestion and quantitative PCR allelic discrimination on genomic DNA extracted from blood leukocytes. The association between these polymorphism genotypes and the response of spine and femur bone mineral density (BMD) and of biochemical bone biomarkers to treatment with amino-bisphosphonates was statistically examined.

RESULTS

FDPS polymorphism did not show any relationship to baseline spinal and femoral BMD in Danish postmenopausal women. BMD response to treatment with amino-bisphosphonates was similar in the AA and the AC genotypes, while the CC genotype showed a lower BMD response to 2-year-treatment with amino-bisphosphonates at all examined skeletal sites (p=0.60 at the spine and p=0.59 at the femur). Interestingly, after 2 years of treatment the response of urinary Cross-laps to amino-bisphosphonates treatment was significantly (p<0.05) lower in the CC genotype when compared to both the AC and AA genotypes. Even the response of serum osteocalcin was lower in the CC genotype, but without reaching a statistical significance (p=0.65).

CONCLUSIONS

Danish postmenopausal women with osteoporosis bearing the homozygous CC genotype for rs2297480 FDPS polymorphism showed a decreased response of bone turnover markers to amino-bisphosphonate therapy, when compared to the heterozygous AC and to the homozygous AA genotypes. Further investigation on larger and different populations, together with polymorphism functional studies are required to confirm these data.

Metabolic engineering of Saccharomyces cerevisiae for production of germacrene A, a precursor of beta-elemene

Beta-elemene, a sesquiterpene and the major component of the medicinal herb Curcuma wenyujin, has antitumor activity against various types of cancer and could potentially serve as a potent antineoplastic drug. However, its current mode of production through extraction from plants has been inefficient and suffers from limited natural resources. Here, we engineered a yeast cell factory for the sustainable production of germacrene A, which can be transformed to beta-elemene by a one-step chemical reaction in vitro. Two heterologous germacrene A synthases (GASs) converting farnesyl pyrophosphate (FPP) to germacrene A were evaluated in yeast for their ability to produce germacrene A. Thereafter, several metabolic engineering strategies were used to improve the production level. Overexpression of truncated 3-hydroxyl-3-methylglutaryl-CoA reductase and fusion of FPP synthase with GAS, led to a sixfold increase in germacrene A production in shake-flask culture. Finally, 190.7 mg/l of germacrene A was achieved. The results reported in this study represent the highest titer of germacrene A reported to date. These results provide a basis for creating an efficient route for further industrial application re-placing the traditional extraction of beta-elemene from plant sources.

Molecular evidence for adaptive radiation of Micromeria Benth. (Lamiaceae) on the Canary Islands as inferred from chloroplast and nuclear DNA sequences and ISSR fingerprint data

The Canary Islands have been a focus for phylogeographic studies on the colonization and diversification of endemic angiosperm taxa. Based on phylogeographic patterns, both inter island colonization and adaptive radiation seem to be the driving forces for speciation in most taxa. Here, we investigated the diversification of Micromeria on the Canary Islands and Madeira at the inter- and infraspecific level using inter simple sequence repeat PCR (ISSR), the trnK-Intron and the trnT-trnL-spacer of the cpDNA and a low copy nuclear gene. The genus Micromeria (Lamiaceae, Mentheae) includes 16 species and 13 subspecies in Macaronesia. Most taxa are restricted endemics, or grow in similar ecological conditions on two islands. An exception is M. varia, a widespread species inhabits the lowland scrub on each island of the archipelago and could represent an ancestral taxon from which radiation started on the different islands. Our analyses support a split between the "eastern" islands Fuerteventura, Lanzarote and Gran Canaria and the "western" islands Tenerife, La Palma and El Hierro. The colonization of Madeira started from the western Islands, probably from Tenerife as indicated by the sequence data. We identified two lineages of Micromeria on Gomera but all other islands appear to be colonized by a single lineage, supporting adaptive radiation as the major evolutionary force for the diversification of Micromeria. We also discuss the possible role of gene flow between lineages of different Micromeria species on one island after multiple colonizations.

Molecular cloning and expression of Chimonanthus praecox farnesyl pyrophosphate synthase gene and its possible involvement in the biosynthesis of floral volatile sesquiterpenoids

Farnesyl pyrophosphate (FPP) synthase catalyzes the biosynthesis of FPP, which is the precursors of sesquiterpenoids such as floral scent volatiles, from isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). cDNA encoding wintersweet (Chimonanthus praecox L.) FPP synthase was isolated by the RT-PCR and RACE methods. The deduced amino acid sequence showed a high identity to plant FPP synthases. Expression of the gene in Escherichia coli yielded FPPS activity that catalyzed the synthesis of FPP as a main product. Tissue-specific and developmental analyses of the mRNA levels of CpFPPS and volatile sesquiterpenoids levels in C. praecox flowers revealed that the FPPS may play a regulatory role in floral volatile sesquiterpenoids of wintersweet.

Maize cDNAs expressed in endosperm encode functional farnesyl diphosphate synthase with geranylgeranyl diphosphate synthase activity

Isoprenoids are the most diverse and abundant group of natural products. In plants, farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) are precursors to many isoprenoids having essential functions. Terpenoids and sterols are derived from FPP, whereas gibberellins, carotenoids, casbenes, taxenes, and others originate from GGPP. The corresponding synthases (FPP synthase [FPPS] and GGPP synthase [GGPPS]) catalyze, respectively, the addition of two and three isopentenyl diphosphate molecules to dimethylallyl diphosphate. Maize (Zea mays L. cv B73) endosperm cDNAs encoding isoprenoid synthases were isolated by functional complementation of Escherichia coli cells carrying a bacterial gene cluster encoding all pathway enzymes needed for carotenoid biosynthesis, except for GGPPS. This approach indicated that the maize gene products were functional GGPPS enzymes. Yet, the predicted enzyme sequences revealed FPPS motifs and homology with FPPS enzymes. In vitro assays demonstrated that indeed these maize enzymes produced both FPP and GGPP and that the N-terminal sequence affected the ratio of FPP to GGPP. Their functionality in E. coli demonstrated that these maize enzymes can be coupled with a metabolon to provide isoprenoid substrates for pathway use, and suggests that enzyme bifunctionality can be harnessed. The maize cDNAs are encoded by a small gene family whose transcripts are prevalent in endosperm beginning mid development. These maize cDNAs will be valuable tools for assessing the critical structural properties determining prenyl transferase specificity and in metabolic engineering of isoprenoid pathways, especially in cereal crops.

(+)-Valencene production in Nicotiana benthamiana is increased by down-regulation of competing pathways

Plant sesquiterpenes, such as (+)-valencene, artemisinin, and farnesene are valuable chemicals for use as aromatics, pharmaceuticals, and biofuels. Plant-based production systems for terpenoids critically depend on the availability of farnesyl diphosphate (FPP). Currently, these systems show insufficient yields, due to the competition for FPP of newly introduced pathways with endogenous ones. In this study, for the first time an RNAi strategy aiming at silencing of endogenous pathways for increased (+)-valencene production was employed. Firstly, a transient production system for (+)-valencene in Nicotiana benthamiana was set up using agroinfiltration. Secondly, silencing of the endogenous 5-epi-aristolochene synthase (EAS) and squalene synthase (SQS) that compete for the FPP pool was deployed. This resulted in a N. benthamiana plant that produces (+)-valencene as a prevalent volatile with a 2.8-fold increased yield. Finally, the size of the FPP pool was increased by overexpression of enzymes that are rate-limiting in FPP biosynthesis. Combined with silencing of EAS and SQS, no further increase of (+)-valencene production was observed, but emission of farnesol. Formation of farnesol, which is a breakdown product of FPP, indicates that overproducing sesquiterpenes is no longer limited by FPP availability in the cytosol. This study shows that metabolic engineering of plants can effectively be used for increased production of desired products in plants.

Genetic polymorphism of geranylgeranyl diphosphate synthase (GGSP1) predicts bone density response to bisphosphonate therapy in Korean women

PURPOSE

Genetic factor is an important predisposing element influencing the susceptibility to osteoporosis and related complications. The purpose of the present study is to investigate whether genetic polymorphisms of farnesyl diphosphate synthase (FDPS) or geranylgeranyl diphosphate synthase (GGPS) genes were associated with the response to bisphosphonate therapy.

MATERIALS AND METHODS

In the present study, 144 Korean women with osteoporosis were included. Among 13 genetic polymorphisms found within the FDPS and GGPS1 gene, 4 genetic polymorphisms with frequencies > 5% were selected for further study. Bone mineral density (BMD) response after 1 year treatment of bisphosphonate therapy was analyzed according to the genotypes.

RESULTS

Women with 2 deletion allele of GGPS1 -8188A ins/del (rs3840452) had significantly higher femoral neck BMD at baseline compared with those with one or no deletion allele (0.768 +/- 0.127 vs. 0.695 +/- 0.090 respectively; p = 0.041). The response rate of women with 2 deletion allele of GGPS1 -8188A ins/del (28.6%) was significantly lower than the rate of women with one (81.4%) or no deletion allele (75.0%) (p = 0.011). Women with 2 deletion allele of GGPS1 -8188A ins/del had 7-fold higher risk of non-response to bisphosphonate therapy compared with women with other genotypes in GGPS1 -8188 after adjusting for baseline BMD (OR = 7.48; 95% CI = 1.32-42.30; p = 0.023). Other polymorphisms in FDPS or GGPS1 were not associated with lumbar spine BMD or femoral neck BMD.

CONCLUSION

Our study suggested that GGPS1 -8188A ins/del polymorphism may confer susceptibility to femoral neck BMD response to bisphosphonate therapy in Korean women. However, further study should be done to confirm the results in a larger population.

Geranylgeranyl diphosphate synthase in fission yeast is a heteromer of farnesyl diphosphate synthase (FPS), Fps1, and an FPS-like protein, Spo9, essential for sporulation

Both farnesyl diphosphate synthase (FPS) and geranylgeranyl diphosphate synthase (GGPS) are key enzymes in the synthesis of various isoprenoid-containing compounds and proteins. Here, we describe two novel Schizosaccharomyces pombe genes, fps1(+) and spo9(+), whose products are similar to FPS in primary structure, but whose functions differ from one another. Fps1 is essential for vegetative growth, whereas, a spo9 null mutant exhibits temperature-sensitive growth. Expression of fps1(+), but not spo9(+), suppresses the lethality of a Saccharomyces cerevisiae FPS-deficient mutant and also restores ubiquinone synthesis in an Escherichia coli ispA mutant, which lacks FPS activity, indicating that S. pombe Fps1 in fact functions as an FPS. In contrast to a typical FPS gene, no apparent GGPS homologues have been found in the S. pombe genome. Interestingly, although neither fps1(+) nor spo9(+) expression alone in E. coli confers clear GGPS activity, coexpression of both genes induces such activity. Moreover, the GGPS activity is significantly reduced in the spo9 mutant. In addition, the spo9 mutation perturbs the membrane association of a geranylgeranylated protein, but not that of a farnesylated protein. Yeast two-hybrid and coimmunoprecipitation analyses indicate that Fps1 and Spo9 physically interact. Thus, neither Fps1 nor Spo9 alone functions as a GGPS, but the two proteins together form a complex with GGPS activity. Because spo9 was originally identified as a sporulation-deficient mutant, we show here that expansion of the forespore membrane is severely inhibited in spo9Delta cells. Electron microscopy revealed significant accumulation membrane vesicles in spo9Delta cells. We suggest that lack of GGPS activity in a spo9 mutant results in impaired protein prenylation in certain proteins responsible for secretory function, thereby inhibiting forespore membrane formation.