Chemical diversity in angiosperms - monoterpene synthases control complex reactions that provide the precursors for ecologically and commercially important monoterpenoids

Monoterpene synthases (MTSs) catalyze the first committed step in the biosynthesis of monoterpenoids, a class of specialized metabolites with particularly high chemical diversity in angiosperms. In addition to accomplishing a rate enhancement, these enzymes manage the formation and turnover of highly reactive carbocation intermediates formed from a prenyl diphosphate substrate. At each step along the reaction path, a cationic intermediate can be subject to cyclization, migration of a proton, hydride, or alkyl group, or quenching to terminate the sequence. However, enzymatic control of ligand folding, stabilization of specific intermediates, and defined quenching chemistry can maintain the specificity for forming a signature product. This review article will discuss our current understanding of how angiosperm MTSs control the reaction environment. Such knowledge allows inferences about the origin and regulation of chemical diversity, which is pertinent for appreciating the role of monoterpenoids in plant ecology but also for aiding commercial efforts that harness the accumulation of these specialized metabolites for the food, cosmetic, and pharmaceutical industries.

Biochemical characterization of acyl activating enzymes for side chain moieties of Taxol and its analogs

Taxol (paclitaxel) is a very widely used anticancer drug, but its commercial sources mainly consist of stripped bark or suspension cultures of members of the plant genus Taxus. Taxol accumulates as part of a complex mixture of chemical analogs, termed taxoids, which complicates its production in pure form, highlighting the need for metabolic engineering approaches for high-level Taxol production in cell cultures or microbial hosts. Here, we report on the characterization of acyl-activating enzymes (AAEs) that catalyze the formation of CoA esters of different organic acids relevant for the N-substitution of the 3-phenylisoserine side chain of taxoids. On the basis of similarities to AAE genes of known function from other organisms, we identified candidate genes in publicly available transcriptome data sets obtained with Taxus × media. We cloned 17 AAE genes, expressed them heterologously in Escherichia coli, purified the corresponding recombinant enzymes, and performed in vitro assays with 27 organic acids as potential substrates. We identified TmAAE1 and TmAAE5 as the most efficient enzymes for the activation of butyric acid (Taxol D side chain), TmAAE13 as the best candidate for generating a CoA ester of tiglic acid (Taxol B side chain), TmAAE3 and TmAAE13 as suitable for the activation of 4-methylbutyric acid (N-debenzoyl-N-(2-methylbutyryl)taxol side chain), TmAAE15 as a highly efficient candidate for hexanoic acid activation (Taxol C side chain), and TmAAE4 as suitable candidate for esterification of benzoic acid with CoA (Taxol side chain). This study lays important groundwork for metabolic engineering efforts aimed at improving Taxol production in cell cultures.

Enzymology of monoterpene functionalization in glandular trichomes

The plant kingdom supports an extraordinary chemical diversity, with terpenoids representing a particularly diversified class of secondary (or specialized) metabolites. Volatile and semi-volatile terpenoids in the C10-C20 range are often formed in specialized cell types and secretory structures. In the angiosperm lineage, glandular trichomes play an important role in enabling the biosynthesis and storage (or in some cases secretion) of functionalized terpenoids. The 'decoration' of a terpenoid scaffold with functional groups changes its physical and chemical properties, and can therefore affect the perception of a specific metabolite by other organisms. Because of the ecological implications (e.g. plant-herbivore interactions) and commercial relevance (e.g. volatiles used in the flavor and fragrance industries), terpenoid functionalization has been researched extensively. Recent successes in the cloning and functional evaluation of genes as well as the structural and biochemical characterization of enzyme catalysts have laid the foundation for an improved understanding of how pathways toward functionalized monoterpenes may have evolved. In this review, we will focus on an up-to-date account of functionalization reactions present in glandular trichomes.

Coenzyme M biosynthesis in bacteria involves phosphate elimination by a functionally distinct member of the aspartase/fumarase superfamily

For nearly 30 years, coenzyme M (CoM) was assumed to be present solely in methanogenic archaea. In the late 1990s, CoM was reported to play a role in bacterial propene metabolism, but no biosynthetic pathway for CoM has yet been identified in bacteria. Here, using bioinformatics and proteomic approaches in the metabolically versatile bacterium Xanthobacter autotrophicus Py2, we identified four putative CoM biosynthetic enzymes encoded by the xcbB1, C1, D1, and E1 genes. Only XcbB1 was homologous to a known CoM biosynthetic enzyme (ComA), indicating that CoM biosynthesis in bacteria involves enzymes different from those in archaea. We verified that the ComA homolog produces phosphosulfolactate from phosphoenolpyruvate (PEP), demonstrating that bacterial CoM biosynthesis is initiated similarly as the phosphoenolpyruvate-dependent methanogenic archaeal pathway. The bioinformatics analysis revealed that XcbC1 and D1 are members of the aspartase/fumarase superfamily (AFS) and that XcbE1 is a pyridoxal 5'-phosphate-containing enzyme with homology to d-cysteine desulfhydrases. Known AFS members catalyze β-elimination reactions of succinyl-containing substrates, yielding fumarate as the common unsaturated elimination product. Unexpectedly, we found that XcbC1 catalyzes β-elimination on phosphosulfolactate, yielding inorganic phosphate and a novel metabolite, sulfoacrylic acid. Phosphate-releasing β-elimination reactions are unprecedented among the AFS, indicating that XcbC1 is an unusual phosphatase. Direct demonstration of phosphosulfolactate synthase activity for XcbB1 and phosphate β-elimination activity for XcbC1 strengthened their hypothetical assignment to a CoM biosynthetic pathway and suggested functions also for XcbD1 and E1. Our results represent a critical first step toward elucidating the CoM pathway in bacteria.

Comprehensive Assessment of Transcriptional Regulation Facilitates Metabolic Engineering of Isoprenoid Accumulation in Arabidopsis

In plants, two spatially separated pathways provide the precursors for isoprenoid biosynthesis. We generated transgenic Arabidopsis (Arabidopsis thaliana) lines with modulated levels of expression of each individual gene involved in the cytosolic/peroxisomal mevalonate and plastidial methylerythritol phosphate pathways. By assessing the correlation of transgene expression levels with isoprenoid marker metabolites (gene-to-metabolite correlation), we determined the relative importance of transcriptional control at each individual step of isoprenoid precursor biosynthesis. The accumulation patterns of metabolic intermediates (metabolite-to-gene correlation) were then used to infer flux bottlenecks in the sterol pathway. The extent of metabolic cross talk, the exchange of isoprenoid intermediates between compartmentalized pathways, was assessed by a combination of gene-to-metabolite and metabolite-to-metabolite correlation analyses. This strategy allowed the selection of genes to be modulated by metabolic engineering, and we demonstrate that the overexpression of predictable combinations of genes can be used to significantly enhance flux toward specific end products of the sterol pathway. Transgenic plants accumulating increased amounts of sterols are characterized by significantly elevated biomass, which can be a desirable trait in crop and biofuel plants.

Patterns of metabolite changes identified from large-scale gene perturbations in Arabidopsis using a genome-scale metabolic network

Metabolomics enables quantitative evaluation of metabolic changes caused by genetic or environmental perturbations. However, little is known about how perturbing a single gene changes the metabolic system as a whole and which network and functional properties are involved in this response. To answer this question, we investigated the metabolite profiles from 136 mutants with single gene perturbations of functionally diverse Arabidopsis (Arabidopsis thaliana) genes. Fewer than 10 metabolites were changed significantly relative to the wild type in most of the mutants, indicating that the metabolic network was robust to perturbations of single metabolic genes. These changed metabolites were closer to each other in a genome-scale metabolic network than expected by chance, supporting the notion that the genetic perturbations changed the network more locally than globally. Surprisingly, the changed metabolites were close to the perturbed reactions in only 30% of the mutants of the well-characterized genes. To determine the factors that contributed to the distance between the observed metabolic changes and the perturbation site in the network, we examined nine network and functional properties of the perturbed genes. Only the isozyme number affected the distance between the perturbed reactions and changed metabolites. This study revealed patterns of metabolic changes from large-scale gene perturbations and relationships between characteristics of the perturbed genes and metabolic changes.

Open-access metabolomics databases for natural product research: present capabilities and future potential

Various databases have been developed to aid in assigning structures to spectral peaks observed in metabolomics experiments. In this review article, we discuss the utility of currently available open-access spectral and chemical databases for natural products discovery. We also provide recommendations on how the research community can contribute to further improvements.

The evolution of plant secretory structures and emergence of terpenoid chemical diversity

Secretory structures in terrestrial plants appear to have first emerged as intracellular oil bodies in liverworts. In vascular plants, internal secretory structures, such as resin ducts and laticifers, are usually found in conjunction with vascular bundles, whereas subepidermal secretory cavities and epidermal glandular trichomes generally have more complex tissue distribution patterns. The primary function of plant secretory structures is related to defense responses, both constitutive and induced, against herbivores and pathogens. The ability to sequester secondary (or specialized) metabolites and defense proteins in secretory structures was a critical adaptation that shaped plant-herbivore and plant-pathogen interactions. Although this review places particular emphasis on describing the evolution of pathways leading to terpenoids, it also assesses the emergence of other metabolite classes to outline the metabolic capabilities of different plant lineages.

Biosynthesis and Biotechnology of High-Value p-Menthane Monoterpenes, Including Menthol, Carvone, and Limonene

Monoterpenes of the p-menthane group are volatile secondary (or specialized) metabolites found across the plant kingdom. They are dominant constituents of commercially important essential oils obtained from members of the genera Mentha (Lamiaceae), Carum (Apiaceae), Citrus (Rutaceae), and Eucalyptus (Myrtaceae). p-Menthane monoterpenes have also attracted interest as chiral specialty chemicals, and the harvest from natural sources is therefore supplemented by chemical synthesis. More recently, microbial and plant-based platforms for the high-level accumulation of specific target monoterpenes have been developed. In this review chapter, I discuss the properties of the genes and enzymes involved in p-menthane biosynthesis and provide a critical assessment of biotechnological production approaches.

Kinetic modeling of plant metabolism and its predictive power: peppermint essential oil biosynthesis as an example

The integration of mathematical modeling with analytical experimentation in an iterative fashion is a powerful approach to advance our understanding of the architecture and regulation of metabolic networks. Ultimately, such knowledge is highly valuable to support efforts aimed at modulating flux through target pathways by molecular breeding and/or metabolic engineering. In this article we describe a kinetic mathematical model of peppermint essential oil biosynthesis, a pathway that has been studied extensively for more than two decades. Modeling assumptions and approximations are described in detail. We provide step-by-step instructions on how to run simulations of dynamic changes in pathway metabolites concentrations.

Rapid purification of gram quantities of β-sitosterol from a commercial phytosterol mixture

Background

β-Sitosterol, a plant sterol or phytosterol, has commercial uses in the nutraceutical and pharmaceutical industries, but is also employed frequently in biological research. Phytosterols always accumulate as mixtures, and obtaining highly pure β-sitosterol in larger quantities for biological assays has been a challenge.

Findings

An improved method for the rapid purification of β-sitosterol from a commercial phytosterol extract is presented. Fractional crystallization of soybean oil yielded a soluble and an insoluble fraction. β-Sitosterol was purified by silica gel and Na-Y zeolite chromatography.

Conclusion

The rapid and cost effective three-step purification described here afforded β-sitosterol in gram quantities with high purity (>92%) and yield (>22%).

Sample preparation for single cell transcriptomics: essential oil glands in Citrus fruit peel as an example

Many plant natural products are synthesized in specialized cells and tissues. To learn more about metabolism in these cells, they have to be studied in isolation. Here, we describe a protocol for the isolation of epithelial cells that surround secretory cavities in Citrus fruit peel. Cells isolated using laser microdissection are suitable for RNA isolation and downstream transcriptome analyses.

Validation of a microscale extraction and high-throughput UHPLC-QTOF-MS analysis method for huperzine A in Huperzia

Herein we report on an improved method for the microscale extraction of huperzine A (HupA), an acetylcholinesterase-inhibiting alkaloid, from as little as 3 mg of tissue homogenate from the clubmoss Huperzia squarrosa (G. Forst.) Trevis with 99.95% recovery. We also validated a novel UHPLC-QTOF-MS method for the high-throughput analysis of H. squarrosa extracts in only 6 min, which, in combination with the very low limit of detection (20 pg on column) and the wide linear range for quantification (20-10,000 pg on column), allow for a highly efficient screening of extracts containing varying amounts of HupA. Utilization of this methodology has the potential to conserve valuable plant resources.

Improving peppermint essential oil yield and composition by metabolic engineering

Peppermint (Mentha × piperita L.) was transformed with various gene constructs to evaluate the utility of metabolic engineering for improving essential oil yield and composition. Oil yield increases were achieved by overexpressing genes involved in the supply of precursors through the 2C-methyl-D-erythritol 4-phosphate (MEP) pathway. Two-gene combinations to enhance both oil yield and composition in a single transgenic line were assessed as well. The most promising results were obtained by transforming plants expressing an antisense version of (+)-menthofuran synthase, which is critical for adjusting the levels of specific undesirable oil constituents, with a construct for the overexpression of the MEP pathway gene 1-deoxy-D-xylulose 5-phosphate reductoisomerase (up to 61% oil yield increase over wild-type controls with low levels of the undesirable side-product (+)-menthofuran and its intermediate (+)-pulegone). Elite transgenic lines were advanced to multiyear field trials, which demonstrated consistent oil yield increases of up to 78% over wild-type controls and desirable effects on oil composition under commercial growth conditions. The transgenic expression of a gene encoding (+)-limonene synthase was used to accumulate elevated levels of (+)-limonene, which allows oil derived from transgenic plants to be recognized during the processing of commercial formulations containing peppermint oil. Our study illustrates the utility of metabolic engineering for the sustainable agricultural production of high quality essential oils at a competitive cost.

Experimental and mathematical approaches to modeling plant metabolic networks

To support their sessile and autotrophic lifestyle higher plants have evolved elaborate networks of metabolic pathways. Dynamic changes in these metabolic networks are among the developmental forces underlying the functional differentiation of organs, tissues and specialized cell types. They are also important in the various interactions of a plant with its environment. Further complexity is added by the extensive compartmentation of the various interconnected metabolic pathways in plants. Thus, although being used widely for assessing the control of metabolic flux in microbes, mathematical modeling approaches that require steady-state approximations are of limited utility for understanding complex plant metabolic networks. However, considerable progress has been made when manageable metabolic subsystems were studied. In this article, we will explain in general terms and using simple examples the concepts underlying stoichiometric modeling (metabolic flux analysis and metabolic pathway analysis) and kinetic approaches to modeling (including metabolic control analysis as a special case). Selected studies demonstrating the prospects of these approaches, or combinations of them, for understanding the control of flux through particular plant pathways are discussed. We argue that iterative cycles of (dry) mathematical modeling and (wet) laboratory testing will become increasingly important for simulating the distribution of flux in plant metabolic networks and deriving rational experimental designs for metabolic engineering efforts.

Structure and function of the centriole in animal cells: progress and questions

The centriole is a well-recognized, yet poorly understood, organelle present in many eukaryotic cells. Despite excellent electron-microscopic descriptions of its basic triplet microtubule structure, almost nothing is known of its specific molecular components. Here, Bodo Lange and Keith Gull survey centriole structure, duplication and maturation within the cell cycle and focus attention on the possible roles and function of centrioles as components of the centrosome in animal cells.

Isoprenoid biosynthesis. Metabolite profiling of peppermint oil gland secretory cells and application to herbicide target analysis

Two independent pathways operate in plants for the synthesis of isopentenyl diphosphate and dimethylallyl diphosphate, the central intermediates in the biosynthesis of all isoprenoids. The mevalonate pathway is present in the cytosol, whereas the recently discovered mevalonate-independent pathway is localized to plastids. We have used isolated peppermint (Mentha piperita) oil gland secretory cells as an experimental model system to study the effects of the herbicides fosmidomycin, phosphonothrixin, methyl viologen, benzyl viologen, clomazone, 2-(dimethylamino)ethyl diphosphate, alendronate, and pamidronate on the pools of metabolites related to monoterpene biosynthesis via the mevalonate-independent pathway. A newly developed isolation protocol for polar metabolites together with an improved separation and detection method based on liquid chromatography-mass spectrometry have allowed assessment of the enzyme targets for a number of these herbicides.

Isoprenoid biosynthesis: the evolution of two ancient and distinct pathways across genomes

Isopentenyl diphosphate (IPP) is the central intermediate in the biosynthesis of isoprenoids, the most ancient and diverse class of natural products. Two distinct routes of IPP biosynthesis occur in nature: the mevalonate pathway and the recently discovered deoxyxylulose 5-phosphate (DXP) pathway. The evolutionary history of the enzymes involved in both routes and the phylogenetic distribution of their genes across genomes suggest that the mevalonate pathway is germane to archaebacteria, that the DXP pathway is germane to eubacteria, and that eukaryotes have inherited their genes for IPP biosynthesis from prokaryotes. The occurrence of genes specific to the DXP pathway is restricted to plastid-bearing eukaryotes, indicating that these genes were acquired from the cyanobacterial ancestor of plastids. However, the individual phylogenies of these genes, with only one exception, do not provide evidence for a specific affinity between the plant genes and their cyanobacterial homologues. The results suggest that lateral gene transfer between eubacteria subsequent to the origin of plastids has played a major role in the evolution of this pathway.

Management of patients needing antibiotic prophylaxis in a dental education setting

The management of antibiotic prophylaxed (ABX) patients at an educational institution was evaluated to identify areas for improvement. Management criteria, reflecting guidelines to prevent oral-induced hematogenous microbial seeding, were pretested and applied to 1,225 record entries of eighty-five patients needing ABX for dental treatment between 1991 and 1996. Seven hundred twenty-two of the visits had 857 management or documentation problems, including no documentation indicating whether or not patients premedicated (n = 281); incomplete, insufficient, or repeated treatment (n = 214); and preventive concerns (n = 172), among others. The proportion of providers' patient visits with one or more management problems differed significantly (p < 0.001) by provider type, as did the distribution of problem categories (documentation, treatment, preventive, and scheduling concerns p < 0.001; compliance issues p < 0.005). Fifty-one percent of postgraduates' and 39 percent of faculty's record entries omitted patients' ABX status. Improved documentation, outcome measures, and patient, faculty and student education are indicated.

Hsp90 is a core centrosomal component and is required at different stages of the centrosome cycle in Drosophila and vertebrates

To determine the molecular composition of the centrosome of a higher eukaryote, we carried out a systematic nano-electrospray tandem or MALDI mass spectrometry analysis of the polypeptides present in highly enriched preparations of immunoisolated Drosophila centrosomes. One of the proteins identified is Hsp83, a member of the highly conserved Hsp90 family including chaperones known to maintain the activity of many proteins but suspected to have other essential, unidentified functions. We have found that a fraction of the total Hsp90 pool is localized at the centrosome throughout the cell cycle at different stages of development in Drosophila and vertebrates. This association between Hsp90 and the centrosome can be observed in purified centrosomes and after treatment with microtubule depolymerizing drugs, two criteria normally used to define core centrosomal components. Disruption of Hsp90 function by mutations in the Drosophila gene or treatment of mammalian cells with the Hsp90 inhibitor geldanamycin, results in abnormal centrosome separation and maturation, aberrant spindles and impaired chromosome segregation. This suggests that another role of Hsp90 might be to ensure proper centrosome function.

Probing essential oil biosynthesis and secretion by functional evaluation of expressed sequence tags from mint glandular trichomes

Functional genomics approaches, which use combined computational and expression-based analyses of large amounts of sequence information, are emerging as powerful tools to accelerate the comprehensive understanding of cellular metabolism in specialized tissues and whole organisms. As part of an ongoing effort to identify genes of essential oil (monoterpene) biosynthesis, we have obtained sequence information from 1,316 randomly selected cDNA clones, or expressed sequence tags (ESTs), from a peppermint (Mentha x piperita) oil gland secretory cell cDNA library. After bioinformatic selection, candidate genes putatively involved in essential oil biosynthesis and secretion have been subcloned into suitable expression vectors for functional evaluation in Escherichia coli. On the basis of published and preliminary data on the functional properties of these clones, it is estimated that the ESTs involved in essential oil metabolism represent about 25% of the described sequences. An additional 7% of the recognized genes code for proteins involved in transport processes, and a subset of these is likely involved in the secretion of essential oil terpenes from the site of synthesis to the storage cavity of the oil glands. The integrated approaches reported here represent an essential step toward the development of a metabolic map of oil glands and provide a valuable resource for defining molecular targets for the genetic engineering of essential oil formation.

Isopentenyl diphosphate biosynthesis via a mevalonate-independent pathway: isopentenyl monophosphate kinase catalyzes the terminal enzymatic step

In plants, the biosynthesis of isopentenyl diphosphate, the central precursor of all isoprenoids, proceeds via two separate pathways. The cytosolic compartment harbors the mevalonate pathway, whereas the newly discovered deoxyxylulose 5-phosphate pathway, which also operates in certain eubacteria, including Escherichia coli, is localized to plastids. Only the first two steps of the plastidial pathway, which involve the condensation of pyruvate and glyceraldehyde 3-phosphate to deoxyxylulose 5-phosphate followed by intramolecular rearrangement and reduction to 2-C-methylerythritol 4-phosphate, have been established. Here we report the cloning from peppermint (Mentha x piperita) and E. coli, and expression, of a kinase that catalyzes the phosphorylation of isopentenyl monophosphate as the last step of this biosynthetic sequence to isopentenyl diphosphate. The plant gene defines an ORF of 1,218 bp that, when the proposed plastidial targeting sequence is excluded, corresponds to approximately 308 aa with a mature size of approximately 33 kDa. The E. coli gene (ychB), which is located at 27.2 min of the chromosomal map, consists of 852 nt, encoding a deduced enzyme of 283 aa with a size of 31 kDa. These enzymes represent a conserved class of the GHMP family of kinases, which includes galactokinase, homoserine kinase, mevalonate kinase, and phosphomevalonate kinase, with homologues in plants and several eubacteria. Besides the preferred substrate isopentenyl monophosphate, the recombinant peppermint and E. coli kinases also phosphorylate isopentenol, and, much less efficiently, dimethylallyl alcohol, but dimethylallyl monophosphate does not serve as a substrate. Incubation of secretory cells isolated from peppermint glandular trichomes with isopentenyl monophosphate resulted in the rapid production of monoterpenes and sesquiterpenes, confirming that isopentenyl monophosphate is the physiologically relevant, terminal intermediate of the deoxyxylulose 5-phosphate pathway.

Preferences for an influences on oral health prevention: perceptions of directors of nursing

Directors of Nursing (DONs) from 196 of 206 Nebraska long-term-care (LTC) facilities were sent a pre-tested questionnaire. The aim was to assess available on-site dental services, existing oral health education and prevention programs as well as future needs/preferences, and the influence of 10 factors in assessing and maintaining residents' oral health. Of the 196 DONs contacted, 126 (64%) participated. Only 36% of DON responders reported having on-site dental services. DONs indicated a preference for nursing staff (NS) oral health inservice training over other educational and/or programmatic proposals. When asked to select the five most influential factors in assessing and maintaining residents' oral health in their respective facilities, DONs selected resident factors (mean, 2.8) more often than NS factors (mean, 2.2). DONs most often identified residents' (R') ability to perform oral hygiene (n = 99), R' cooperation with OH assistance (n = 98), R' interest in their oral health (n = 83), NS interest in R' dental health (n = 70), and NS time constraints (n = 69).

Isoprenoid biosynthesis via a mevalonate-independent pathway in plants: cloning and heterologous expression of 1-deoxy-D-xylulose-5-phosphate reductoisomerase from peppermint

Two distinct pathways are utilized by plants for the biosynthesis of isopentenyl diphosphate, the universal precursor of isoprenoids. The classical acetate/mevalonate pathway operates in the cytosol, whereas plastidial isoprenoids originate via a novel mevalonate-independent route that involves a transketolase-catalyzed condensation of pyruvate and D-glyceraldehyde-3-phosphate to yield 1-deoxy-D-xylulose-5-phosphate as the first intermediate. Based on in vivo feeding experiments, rearrangement and reduction of deoxyxylulose phosphate have been proposed to give rise to 2-C-methyl-D-erythritol-4-phosphate as the second intermediate of this pyruvate/glyceraldehyde-3-phosphate pathway (1-3). The cloning of an Escherichia coli gene encoding an enzyme capable of converting 1-deoxy-D-xylulose-5-phosphate to 2-C-erythritol-4-phosphate was recently reported (4). A cloning strategy was developed for isolating the gene encoding a plant homolog of this enzyme from peppermint (Mentha x piperita), and the identity of the resulting cDNA was confirmed by heterologous expression in E. coli. Unlike the microbial reductoisomerase, the plant ortholog encodes a preprotein bearing an N-terminal plastidial transit peptide that directs the enzyme to plastids where the mevalonate-independent pathway operates in plants. The peppermint gene comprises an open reading frame of 1425 nucleotides which, when the plastidial targeting sequence is excluded, encodes a deduced enzyme of approximately 400 amino acid residues with a mature size of about 43.5 kDa.

Genetic engineering of essential oil production in mint

New approaches directed to unraveling monoterpene metabolism and secretion and recent progress in transformation protocols have set the stage for the systematic genetic engineering of essential oil production. This article focuses on specific strategies to improve the quality and quantity of mint essential oils.

Monoaminergic effects of high-dose corticotropin in corticotropin-responsive pediatric opsoclonus-myoclonus

Children with the opsoclonus-myoclonus syndrome (OMS) usually respond to corticotropin (adrenocorticotrophic hormone, ACTH) treatment but the mechanism of benefit is unknown. We previously showed that both cerebrospinal fluid (CSF) homovanillic acid (HVA) and 5-hydroxyindole-acetic acid (5-HIAA) concentrations are low in pediatric OMS. In this study, we measured levels of CSF Dopa, catecholamines, deaminated metabolites of catecholamines, as well as HVA and 5-HIAA in eight patients before and during treatment with ACTH. All the children were ACTH-responsive with 50-70% improvement in multiple clinical features of OMS. ACTH treatment reduced the HVA concentration in every child by a mean of 21% (p < 0.001). Treatment with ACTH was associated with significant correlations between dopaminergic markers such as HVA, dihydroxyphenylacetic acid (DOPAC), and Dopa. There were no significant changes in the CSF concentrations of the noradrenergic markers norepinephrine (NE) and dihydroxyphenylglycol (DHPG), or the serotonergic marker 5-HIAA. The only child with a marked inflammatory pattern in CSF, which was reversed by ACTH, was atypical for a large increase in NE and decrease in 5-HIAA during ACTH treatment. Beneficial effects of ACTH in OMS are not associated with normalization of HVA or 5-HIAA levels. The pattern of decreased HVA and unchanged DOPAC levels could reflect decreased extraneuronal uptake of catecholamines (which steroids inhibit) or decreased 0-methylation of catecholamines in nonneuronal cells.

A family of transketolases that directs isoprenoid biosynthesis via a mevalonate-independent pathway

Isopentenyl diphosphate, the common precursor of all isoprenoids, has been widely assumed to be synthesized by the acetate/mevalonate pathway in all organisms. However, based on in vivo feeding experiments, isopentenyl diphosphate formation in several eubacteria, a green alga, and plant chloroplasts has been demonstrated very recently to originate via a mevalonate-independent route from pyruvate and glyceraldehyde 3-phosphate as precursors. Here we describe the cloning from peppermint (Mentha x piperita) and heterologous expression in Escherichia coli of 1-deoxy-D-xylulose-5-phosphate synthase, the enzyme that catalyzes the first reaction of this pyruvate/glyceraldehyde 3-phosphate pathway. This synthase gene contains an ORF of 2,172 base pairs. When the proposed plastid targeting sequence is excluded, the deduced amino acid sequence indicates the peppermint synthase to be about 650 residues in length, corresponding to a native size of roughly 71 kDa. The enzyme appears to represent a novel class of highly conserved transketolases and likely plays a key role in the biosynthesis of plastid-derived isoprenoids essential for growth, development, and defense in plants.

Regulatory role of microsomal 3-hydroxy-3-methylglutaryl-coenzyme A reductase for shikonin biosynthesis in Lithospermum erythrorhizon cell suspension cultures

The carbon skeleton of the naphthoquinone pigment shikonin, which is produced in Lithospermum erythrorhizon Sieb. et Zucc. cell-suspension cultures, is partly derived from the isoprenoid biosynthetic pathway. The requirement of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR, EC 1.1.1.34), a key enzyme of the mevalonate route to isoprenoids, for shikonin synthesis was investigated. Conserved regions of sequences from plant HMGR genes were used to design polymerase chain reaction (PCR) primers for the cloning of a cDNA fragment from L. erythrorhizon. The resulting 443-bp clone was used as a probe for Northern analyses and hybridized to an mRNA of approx. 2.5 kb. Under shikonin-producing conditions, microsomal HMGR enzyme activity as well as mRNA level closely correlated with the accumulation of shikonin derivatives. White light, which inhibits shikonin formation, was shown to strongly suppress HMGR gene expression. The results presented here indicate that HMGR plays a significant role in the regulation of shikonin biosynthesis and that the control appears to act at the transcriptional level.

A structural study of isolated mammalian centrioles using negative staining electron microscopy

We have used a combination of centrifugation onto electron microscope grids and negative staining to study the structure of isolated mammalian centrioles. The technique relies on visualisation of structural detail by use of a goldthioglucose negative stain. The approach provides an easy structural definition of the mature and immature centriole and has revealed some novel proximal projections on the mature centriole. The rapid technique should prove of use in future analyses of centriolar structure and biochemistry.

Hereditary spastic paraplegia linked to chromosome 15q: Analysis of candidate genes

We previously reported an extended kindred with autosomal dominant uncomplicated hereditary spastic paraplegia (HSP) and found close linkage between the disorder and microsatellite polymorphisms on chromosome 15q. Multipoint linkage analysis reached a maximum LOD score (10.16) between D15S128 and D15S156, a region that includes genes encoding alpha5 and beta3 subunits of GABAA receptor. Theoretically, abnormal GABA-mediated neurotransmission could produce spasticity and possibly other changes of HSP. We used genetic linkage analysis to evaluate these two HSP candidate genes and observed obligate recombinants for polymorphisms immediately adjacent to (or within untranslated regions of) genes encoding alpha5 and beta3 GABAA receptor subunits. Although these genes are linked tightly to the HSP locus, our findings conclusively exclude these genes from being responsible for HSP in this kindred.

A molecular marker for centriole maturation in the mammalian cell cycle

The centriole pair in animals shows duplication and structural maturation at specific cell cycle points. In G1, a cell has two centrioles. One of the centrioles is mature and was generated at least two cell cycles ago. The other centriole was produced in the previous cell cycle and is immature. Both centrioles then nucleate one procentriole each which subsequently elongate to full-length centrioles, usually in S or G2 phase. However, the point in the cell cycle at which maturation of the immature centriole occurs is open to question. Furthermore, the molecular events underlying this process are entirely unknown. Here, using monoclonal and polyclonal antibody approaches, we describe for the first time a molecular marker which localizes exclusively to one centriole of the centriolar pair and provides biochemical evidence that the two centrioles are different. Moreover, this 96-kD protein, which we name Cenexin (derived from the Latin, senex for "old man," and Cenexin for centriole) defines very precisely the mature centriole of a pair and is acquired by the immature centriole at the G2/M transition in prophase. Thus the acquisition of Cenexin marks the functional maturation of the centriole and may indicate a change in centriolar potential such as its ability to act as a basal body for axoneme development or as a congregating site for microtubule-organizing material.

Staff meetings as perceived by dental assistants

CDAs generally prefer meetings with these characteristics: organization; written agendas; longer, frequent, and regularly scheduled; compensated attendance; follow-up on progress toward goals/objectives; avoidance of personal and individual-compensation issues; input from staff members, and open discussion; and encouragement and praise. These results should help dentists and staff members to make staff meetings more efficient and effective.

Autosomal dominant, familial spastic paraplegia, type I: clinical and genetic analysis of a large North American family

"Familial spastic paraplegia" (FSP) refers to clinically and genetically diverse syndromes characterized by insidiously progressive lower extremity spasticity. We evaluated 126 members of a large kindred, including 31 affected subjects, in which FSP was transmitted as a stereotyped, autosomal dominant disorder that showed complete genetic penetrance. Affected subjects developed insidiously progressive gait disturbance between ages 12 and thirty-five. Neurologic examination revealed hyperreflexia and spasticity in the lower extremities, weakness of hip flexion and ankle dorsiflexion, extensor plantar response, diminished vibratory sense in the feet, and pes cavus. Using genetic linkage analysis, we excluded the FSP1 locus on chromosome 14q11.2 as the disease locus in this family. We present the clinical and genetic features of FSP type I, including the age-adjusted risk of developing the disorder in this family.

Autosomal dominant familial spastic paraplegia: tight linkage to chromosome 15q

Autosomal dominant, uncomplicated familial spastic paraplegia (FSP) is a genetically heterogeneous disorder characterized by insidiously progressive lower-extremity spasticity. Recently, a locus on chromosome 14q was shown to be tightly linked with the disorder in one of three families. We performed linkage analysis in a kindred with autosomal dominant uncomplicated FSP. After excluding the chromosome 14q locus, we observed tight linkage of the disorder to a group of markers on chromosome 15q (maximum two-point lod score 9.70; theta = .05). Our results clearly establish the existence of a locus for autosomal dominant FSP in the centromeric region of chromosome 15q. Comparing clinical and genetic features in FSP families linked to chromosome 14q with those linked to chromosome 15q may provide insight into the pathophysiology of this disorder.

Production and characterization of monoclonal antibodies to the mammalian sperm cytoskeleton

The cytoskeleton exerts a direct effect on the function of sperm by influencing the distribution of subcellular organelles and plasma membrane molecules. We have prepared six monoclonal antibodies to Triton X-100-insoluble components of the bull sperm cytoskeleton. One of the antibodies reacts with a detachable portion of the bull sperm acrosome. The remainder include an antibody that recognizes the principal and end piece of the tail and another that is specific to the middle piece. Two of the antibodies yield dissimilar staining patterns of the neck region and the tail, and the final monoclonal antibody stains the subacrosomal region and a detachable acrosomal domain of bull sperm. The cross reactivities of the antibodies with hamster sperm and PtK2 cells are described, as is the recognition of bull sperm polypeptides on western blots. The results suggest that these antibodies will provide interesting insights concerning the role of the cytoskeleton in sperm development and function.