The Methylerythritol Phosphate Pathway to Isoprenoids

Targeting the IspD enzyme in the MEP pathway: identification of a novel fragment class

The enzymes of the 2‐C‐methylerythritol‐d‐erythritol 4‐phosphate (MEP) pathway (MEP pathway or non‐mevalonate pathway) are responsible for the synthesis of universal precursors of the large and structurally diverse family of isoprenoids. This pathway is absent in humans, but present in many pathogenic organisms and plants, making it an attractive source of drug targets. Here, we present a high‐throughput screening approach that led to the discovery of a novel fragment hit active against the third enzyme of the MEP pathway, PfIspD. A systematic SAR investigation afforded a novel chemical structure with a balanced activity–stability profile (16). Using a homology model of PfIspD, we proposed a putative binding mode for our newly identified inhibitors that sets the stage for structure‐guided optimization.

Plasmodium metabolite HMBPP stimulates feeding of main mosquito vectors on blood and artificial toxic sources

Recent data show that parasites manipulate the physiology of mosquitoes and human hosts to increase the probability of transmission. Here, we investigate phagostimulant activity of Plasmodium-metabolite, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), in the primary vectors of multiple human diseases, Anopheles coluzzii, An. arabiensis, An. gambiae s.s., Aedes aegypti, and Culex pipiens/Culex torrentium complex species. The addition of 10 µM HMBPP to blood meals significantly increased feeding in all the species investigated. Moreover, HMBPP also exhibited a phagostimulant property in plant-based-artificial-feeding-solution made of beetroot juice adjusted to neutral pH similar to that of blood. The addition of AlbuMAXTM as a lipid/protein source significantly improved the feeding rate of An. gambiae s.l. females providing optimised plant-based-artificial-feeding-solution for delivery toxins to control vector populations. Among natural and synthetic toxins tested, only fipronil sulfone did not reduce feeding. Overall, the toxic-plant-based-artificial-feeding-solution showed potential as an effector in environmentally friendly vector-control strategies.

Biosynthesis, evolution and ecology of microbial terpenoids

Covering: through June 2021Terpenoids are the largest class of natural products recognised to date. While mostly known to humans as bioactive plant metabolites and part of essential oils, structurally diverse terpenoids are increasingly reported to be produced by microorganisms. For many of the compounds biological functions are yet unknown, but during the past years significant insights have been obtained for the role of terpenoids in microbial chemical ecology. Their functions include stress alleviation, maintenance of cell membrane integrity, photoprotection, attraction or repulsion of organisms, host growth promotion and defense. In this review we discuss the current knowledge of the biosynthesis and evolution of microbial terpenoids, and their ecological and biological roles in aquatic and terrestrial environments. Perspectives on their biotechnological applications, knowledge gaps and questions for future studies are discussed.

Reassessing the evolution of the 1-deoxy-D-xylulose 5-phosphate synthase family suggests a possible novel function for the DXS class 3 proteins

The methylerythritol 4-phosphate (MEP) pathway is of paramount importance for generating plastidial isoprenoids. The first enzyme of the MEP pathway, 1-deoxy-D-xylulose-5-phosphate synthase (DXS), catalyzes a flux-controlling step. In plants the DXS gene family is composed of three distinct classes with non-redundant functions. Although the DXS1 and DXS2 subfamilies have been well characterized, the DXS3 subfamily has been considerably understudied. Here, we carried out in silico and functional analyses to better understand the DXS3 class. Our phylogenetic analysis showed high variation in copy number among the different DXS classes, with the apparent absence of DXS1 class in some species. We found that DXS3 subfamily emerged later than DXS1 and DXS2 and it is under less intense purifying selection. Furthermore, in the DXS3 subfamily critical amino acids positions in the thiamine pyrophosphate binding pocket are not conserved. We demonstrated that the DXS3 proteins from Arabidopsis, Maize, and Rice lack functional DXS activity. Moreover, the Arabidopsis DXS3 protein displayed distinctive sub-organellar chloroplast localization not observed in any DXS1 or DXS2 proteins. Co-expression analysis of the DXS3 from Arabidopsis showed that, unlike DXS1 and DXS2 proteins, it co-expresses with genes related to post-embryonic development and reproduction and not with primary metabolism and isoprenoid synthesis.

Structural and biophysical characterization of the Burkholderia pseudomallei IspF inhibitor L-tryptophan hydroxamate

The enzyme 2-methylerythritol 2,4-cyclodiphosphate synthase, IspF, is essential for the biosynthesis of isoprenoids in most bacteria, some eukaryotic parasites, and the plastids of plant cells. The development of inhibitors that target IspF may lead to novel classes of anti-infective agents or herbicides. Enantiomers of tryptophan hydroxamate were synthesized and evaluated for binding to Burkholderia pseudomallei (Bp) IspF. The L-isomer possessed the highest potency, binding BpIspF with a K_D of 36 µM and inhibited BpIspF activity 55% at 120 µM. The high-resolution crystal structure of the L-tryptophan hydroxamate (3)/BpIspF complex revealed a non-traditional mode of hydroxamate binding where the ligand interacts with the active site zinc ion through the primary amine. In addition, two hydrogen bonds are formed with active site groups, and the indole group is buried within the hydrophobic pocket composed of side chains from the 60 s/70 s loop. Along with the co-crystal structure, STD NMR studies suggest the methylene group and indole ring are potential positions for optimization to enhance binding potency.

Recent trends in biocatalysis

Biocatalysis has undergone revolutionary progress in the past century. Benefited by the integration of multidisciplinary technologies, natural enzymatic reactions are constantly being explored. Protein engineering gives birth to robust biocatalysts that are widely used in industrial production. These research achievements have gradually constructed a network containing natural enzymatic synthesis pathways and artificially designed enzymatic cascades. Nowadays, the development of artificial intelligence, automation, and ultra-high-throughput technology provides infinite possibilities for the discovery of novel enzymes, enzymatic mechanisms and enzymatic cascades, and gradually complements the lack of remaining key steps in the pathway design of enzymatic total synthesis. Therefore, the research of biocatalysis is gradually moving towards the era of novel technology integration, intelligent manufacturing and enzymatic total synthesis.

Computational and synthetic biology approaches for the biosynthesis of antiviral and anticancer terpenoids from Bacillus subtilis

Recent advancements in medicinal research have identified several antiviral and anticancer terpenoids that are usually deployed as a source of flavor, fragrances and pharmaceuticals. Under the current COVID-19 pandemic conditions, natural therapeutics with least side effects are the need of the hour to save the patients, especially, which are pre-affected with other medical complications. Although, plants are the major sources of terpenoids; however, for the environmental concerns, the global interest has shifted to the biocatalytic production of molecules from microbial sources. The gram-positive bacterium Bacillus subtilis is a suitable host in this regard due to its GRAS (generally regarded as safe) status, ease in genetic manipulations and wide industrial acceptability. The B. subtilis synthesizes its terpenoid molecules from 1-deoxy-d-xylulose-5-phosphate (DXP) pathway, a common route in almost all microbial strains. Here, we summarize the computational and synthetic biology approaches to improve the production of terpenoid-based therapeutics from B. subtilis by utilizing DXP pathway. We focus on the in-silico approaches for screening the functionally improved enzyme-variants of the two crucial enzymes namely, the DXP synthase (DXS) and farnesyl pyrophosphate synthase (FPPS). The approaches for engineering the active sites are subsequently explained. It will be helpful to construct the functionally improved enzymes for the high-yield production of terpenoid-based anticancer and antiviral metabolites, which would help to reduce the cost and improve the availability of such therapeutics for the humankind.

Production of C20, C30 and C40 terpenes in the engineered phototrophic bacterium Rhodobacter capsulatus

Terpenes constitute one of the largest groups of secondary metabolites that are used, for example, as food-additives, fragrances or pharmaceuticals. Due to the formation of an intracytoplasmic membrane system and an efficient intrinsic tetraterpene pathway, the phototrophic α-proteobacterium Rhodobacter capsulatus offers favorable properties for the production of hydrophobic terpenes. However, research efforts have largely focused on sesquiterpene production. Recently, we have developed modular tools allowing to engineer the biosynthesis of terpene precursors. These tools were now applied to boost the biosynthesis of the diterpene casbene, the triterpene squalene and the tetraterpene β-carotene in R. capsulatus SB1003. Selected enzymes of the intrinsic isoprenoid pathway and the heterologous mevalonate (MVA) pathway were co-expressed together with the respective terpene synthases in various combinations. Remarkably, co-expression of genes ispA, idi and dxs enhanced the synthesis of casbene and β-carotene. In contrast, co-expression of precursor biosynthetic genes with the squalene synthase from Arabidopsis thaliana reduced squalene titers. Therefore, we further employed four alternative pro- and eukaryotic squalene synthases. Here, the synthase from Methylococcus capsulatus enabled highest product levels of 90 mg/L squalene upon co-expression with ispA. In summary, we demonstrate the applicability of R. capsulatus for the heterologous production of diverse terpene classes and provide relevant insights for further development of such platforms.

Metabolic engineering for the synthesis of steviol glycosides: current status and future prospects

With the pursuit of natural non-calorie sweeteners, steviol glycosides (SGs) have become one of the most popular natural sweeteners in the market. The SGs in Stevia are a mixture of SGs synthesized from steviol (a terpenoid). SGs are diterpenoids. Different SGs depend on the number and position of sugar groups on the core steviol backbone. This diversity comes from the processing of glycoside steviol by various glycosyltransferases. Due to the differences in glycosylation, each SG has unique sensory properties. At present, it is more complicated to extract high-quality SGs from plants, so the excavation of the metabolic pathways of engineered microorganisms to synthesize SGs has been extensively studied. Specifically, the expression of different glycosyltransferases in microbes is key to the synthesis of various SGs by engineered microorganisms. To trigger more researches on the functional characterization of the enzymes encoded by these genes, this review describes the latest research progresses of the related enzymes involved in SG biosynthesis and metabolic engineering.Key points• Outlines the research progress of key enzymes in the biosynthetic pathway of SGs• Factors affecting the catalytic capacity of stevia glucosyltransferase• Provide guidance for the efficient synthesis of SGs in microbial cell factories.

Bacterial terpenome

Covering: up to mid-2020 Terpenoids, also called isoprenoids, are the largest and most structurally diverse family of natural products. Found in all domains of life, there are over 80 000 known compounds. The majority of characterized terpenoids, which include some of the most well known, pharmaceutically relevant, and commercially valuable natural products, are produced by plants and fungi. Comparatively, terpenoids of bacterial origin are rare. This is counter-intuitive to the fact that recent microbial genomics revealed that almost all bacteria have the biosynthetic potential to create the C5 building blocks necessary for terpenoid biosynthesis. In this review, we catalogue terpenoids produced by bacteria. We collected 1062 natural products, consisting of both primary and secondary metabolites, and classified them into two major families and 55 distinct subfamilies. To highlight the structural and chemical space of bacterial terpenoids, we discuss their structures, biosynthesis, and biological activities. Although the bacterial terpenome is relatively small, it presents a fascinating dichotomy for future research. Similarities between bacterial and non-bacterial terpenoids and their biosynthetic pathways provides alternative model systems for detailed characterization while the abundance of novel skeletons, biosynthetic pathways, and bioactivies presents new opportunities for drug discovery, genome mining, and enzymology.

Search for the Active Ingredients from a 2-Aminothiazole DMSO Stock Solution with Antimalarial Activity

Chemical decomposition of DMSO stock solutions is a common incident that can mislead biological screening campaigns. Here, we share our case study of 2‐aminothiazole 1, originating from an antimalarial class that undergoes chemical decomposition in DMSO at room temperature. As previously measured biological activities observed against Plasmodium falciparum NF54 and for the target enzyme PfIspE were not reproducible for a fresh batch, we tackled the challenge to understand where the activity originated from. Solvent‐ and temperature‐dependent studies using HRMS and NMR spectroscopy to monitor the decomposition led to the isolation and in vitro evaluation of several fractions against PfIspE. After four days of decomposition, we successfully isolated the oxygenated and dimerised compounds using SFC purification and correlated the observed activities to them. Due to the unstable nature of the two isolates, it is likely that they undergo further decomposition contributing to the overall instability of the compound.

Assessment of the rules related to gaining activity against Gram-negative bacteria

In the search for new antibacterial compounds, we repositioned an antimalarial compound class by derivatising it based on the so-called "eNTRy" rules for enhanced accumulation into Gram-negative bacteria. We designed, synthesised and evaluated a small library of amino acid modified compounds together with the respective Boc-protected analogues, leading to no substantial improvement in antibacterial activity against Escherichia coli wild-type K12, whereas more distinct activity differences were observed in E. coli mutant strains ΔtolC, D22, ΔacrB and BL21(DE3)omp8. A comparison of the activity results of the E. coli mutants with respect to the known rules related to enhanced activity against Gram-negative bacteria revealed that applicability of the rules is not always ensured. Out of the four amino acids used in this study, glycine derivatives showed highest antibacterial activity, although still suffering from efflux issues.

New aspects of microbial vitamin K2 production by expanding the product spectrum

Vitamin K2 (menaquinone, MK) is an essential lipid-soluble vitamin with critical roles in blood coagulation and bone metabolism. Chemically, the term vitamin K2 encompasses a group of small molecules that contain a common naphthoquinone head group and a polyisoprenyl side chain of variable length. Among them, menaquinone-7 (MK-7) is the most potent form. Here, the biosynthetic pathways of vitamin K2 and different types of MK produced by microorganisms are briefly introduced. Further, we provide a new aspect of MK-7 production, which shares a common naphthoquinone ring and polyisoprene biosynthesis pathway, by analyzing strategies for expanding the product spectrum. We review the findings of metabolic engineering strategies targeting the shikimate pathway, polyisoprene pathway, and menaquinone pathway, as well as membrane engineering, which provide comprehensive insights for enhancing the yield of MK-7. Finally, the current limitations and perspectives of microbial menaquinone production are also discussed. This article provides in-depth information on metabolic engineering strategies for vitamin K2 production by expanding the product spectrum.

Carotenoids produced by the deep-sea bacterium Erythrobacter citreus LAMA 915: detection and proposal of their biosynthetic pathway

Technologies based on synthetic biology to produce bacterial natural carotenoids depend on information regarding their biosynthesis. Although the biosynthetic pathway of common carotenoids is known, there are carotenoids whose pathways are not completely described. This work aimed to mine the genome of the deep-sea bacterium Erythrobacter citreus LAMA 915, an uncommon bacterium that forms yellow colonies under cultivation. This work further explores the potential application of the carotenoids found and low-cost substrates for bacterial growth. A combined approach of genome mining and untargeted metabolomics analysis was applied. The carotenoid erythroxanthin sulfate was detected in E. citreus LAMA 915 cell extract. A proposal for carotenoid biosynthesis by this bacterium is provided, involving the genes crtBIYZWG. These are responsible for the biosynthesis of carotenoids from the zeaxanthin pathway and their 2,2'-hydroxylated derivatives. E. citreus LAMA 915 extracts showed antioxidant and sun protection effects. Based on the high content of proteases and lipases, it was possible to rationally select substrates for bacterial growth, with residual oil from fish processing the best low-cost substrate selected. This work advances in the understanding of carotenoid biosynthesis and provides a genetic basis that can be further explored as a biotechnological route for carotenoid production.

Heterologous Production of β-Caryophyllene and Evaluation of Its Activity against Plant Pathogenic Fungi

Terpenoids constitute one of the largest and most diverse groups within the class of secondary metabolites, comprising over 80,000 compounds. They not only exhibit important functions in plant physiology but also have commercial potential in the biotechnological, pharmaceutical, and agricultural sectors due to their promising properties, including various bioactivities against pathogens, inflammations, and cancer. In this work, we therefore aimed to implement the plant sesquiterpenoid pathway leading to β-caryophyllene in the heterologous host Rhodobacter capsulatus and achieved a maximum production of 139 ± 31 mg L^-1 culture. As this sesquiterpene offers various beneficial anti-phytopathogenic activities, we evaluated the bioactivity of β-caryophyllene and its oxygenated derivative β-caryophyllene oxide against different phytopathogenic fungi. Here, both compounds significantly inhibited the growth of Sclerotinia sclerotiorum and Fusarium oxysporum by up to 40%, while growth of Alternaria brassicicola was only slightly affected, and Phoma lingam and Rhizoctonia solani were unaffected. At the same time, the compounds showed a promising low inhibitory profile for a variety of plant growth-promoting bacteria at suitable compound concentrations. Our observations thus give a first indication that β-caryophyllene and β-caryophyllene oxide are promising natural agents, which might be applicable for the management of certain plant pathogenic fungi in agricultural crop production.

Development of Potential Antitumor Agents from the Scaffolds of Plant-Derived Terpenoid Lactones

Naturally occurring terpenoid lactones and their synthetic derivatives have attracted increasing interest for their promising antitumor activity and potential utilization in the discovery and design of new antitumor agents. In the present perspective article, selected plant-derived five-membered γ-lactones and six-membered δ-lactones that occur with terpenoid scaffolds are reviewed, with their structures, cancer cell line cytotoxicity and in vivo antitumor activity, structure-activity relationships, mechanism of action, and the potential for developing cancer chemotherapeutic agents discussed in each case. The compounds presented include artemisinin (ART, 1), parthenolide (PTL, 2), thapsigargin (TPG, 3), andrographolide (AGL, 4), ginkgolide B (GKL B, 5), jolkinolide B (JKL B, 6), nagilactone E (NGL E, 7), triptolide (TPL, 8), bruceantin (BRC, 9), dichapetalin A (DCT A, 10), and limonin (LMN, 11), and their naturally occurring analogues and synthetic derivatives. It is hoped that this contribution will be supportive of the future development of additional efficacious anticancer agents derived from natural products.

Whole-Cell Production of Patchouli Oil Sesquiterpenes in Escherichia coli: Metabolic Engineering and Fermentation Optimization in Solid-Liquid Phase Partitioning Cultivation

Patchouli oil is a major ingredient in perfumery, granting a dark-woody scent due to its main constituent (-)-patchoulol. The growing demand for patchouli oil has raised interest in the development of a biotechnological process to assure a reliable supply. Herein, we report the production of patchouli oil sesquiterpenes by metabolically engineered Escherichia coli strains, using solid-liquid phase partitioning cultivation. The (-)-patchoulol production was possible using the endogenous methylerythritol phosphate pathway and overexpressing a (-)-patchoulol synthase isoform from Pogostemon cablin but at low titers. To improve the (-)-patchoulol production, the exogenous mevalonate pathway was overexpressed in the multi-plasmid PTS + Mev strain, which increased the (-)-patchoulol titer 5-fold. Fermentation was improved further by evaluating several defined media, and optimizing the pH and temperature of culture broth, enhancing the (-)-patchoulol titer 3-fold. To augment the (-)-patchoulol recovery from fermentation, the solid-liquid phase partitioning cultivation was analyzed by screening polymeric adsorbers, where the Diaion HP20 adsorber demonstrated the highest (-)-patchoulol recovery from all tests. Fermentation was scaled-up to fed-batch bioreactors, reaching a (-)-patchoulol titer of 40.2 mg L-1 and productivity of 20.1 mg L-1 d-1. The terpene profile and aroma produced from the PTS + Mev strain were similar to the patchouli oil, comprising (-)-patchoulol as the main product, and α-bulnesene, trans-β-caryophyllene, β-patchoulene, and guaia-5,11-diene as side products. This investigation represents the first study of (-)-patchoulol production in E. coli by solid-liquid phase partitioning cultivation, which provides new insights for the development of sustainable bioprocesses for the microbial production of fragrant terpenes.

Non-hydroxamate inhibitors of 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR): A critical review and future perspective

1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) catalyzes the second step of the non-mevalonate (or MEP) pathway that functions in several organisms and plants for the synthesis of isoprenoids. DXR is essential for the survival of multiple pathogenic bacteria/parasites, including those that cause tuberculosis and malaria in humans. DXR function is inhibited by fosmidomycin (1), a natural product, which forms a chelate with the active site divalent metal (Mg²⁺/Mn²⁺) through its hydroxamate metal-binding group (MBG). Most of the potent DXR inhibitors are structurally similar to 1 and retain hydroxamate despite the unfavourable pharmacokinetic and toxicity profile of the latter. We provide our perspective on the lack of non-hydroxamate DXR inhibitors. We also highlight the fundamental flaws in the design of MBG in these molecules, primarily responsible for their failure to inhibit DXR. We also suggest that for designing next-generation non-hydroxamate DXR inhibitors, approaches followed for other metalloenzymes targets may be exploited.

Excavating the functionally crucial active-site residues of the DXS protein of Bacillus subtilis by exploring its closest homologues

Background

To achieve a high yield of terpenoid-based therapeutics, 1-deoxy-d-xylulose-5-phosphate (DXP) pathway has been significantly exploited for the production of downstream enzymes. The DXP synthase (DXS) enzyme, the initiator of this pathway, is pivotal for the convergence of carbon flux, and is computationally studied well for the industrially utilized generally regarded as safe (GRAS) bacterium Bacillus subtilis to decode its vital regions for aiding the construction of a functionally improved mutant library.

Results

For the 546 sequence dataset of DXS sequences, a representative set of 108 sequences is created, and it shows a significant evolutionary divergence across different species clubbed into 37 clades, whereas three clades are observed for the 76 sequence dataset of Bacillus subtilis. The DXS enzyme, sharing a statistically significant homology to transketolase, is shown to be evolutionarily too distant. By the mutual information-based co-evolutionary network and hotspot analysis, the most crucial loci within the active site are deciphered. The 650-residue representative structure displays a complete conservation of 114 loci, and only two co-evolving residues ASP154 and ILE371 are found to be the conserved ones. Lastly, P318D is predicted to be the top-ranked mutation causing the increase in the thermodynamic stability of 6OUW.

Conclusion

The study excavates the vital functional, phylogenetic, and conserved residues across the active site of the DXS protein, the key rate-limiting controller of the entire pathway. It would aid to computationally understand the evolutionary landscape of this industrially useful enzyme and would allow us to widen its substrate repertoire to increase the enzymatic yield of unnatural molecules for in vivo and in vitro applications.

An overview of anoxygenic phototrophic bacteria and their applications in environmental biotechnology for sustainable Resource recovery

Anoxygenic phototrophic bacteria (APB) are a phylogenetically diverse group of organisms that can harness solar energy for their growth and metabolism. These bacteria vary broadly in terms of their metabolism as well as the composition of their photosynthetic apparatus. Unlike oxygenic phototrophic bacteria such as algae and cyanobacteria, APB can use both organic and inorganic electron donors for light-dependent fixation of carbon dioxide without generating oxygen. Their versatile metabolism, ability to adapt in extreme conditions, low maintenance cost and high biomass yield make APB ideal for wastewater treatment, resource recovery and in the production of high value substances. This review highlights the advantages of APB over algae and cyanobacteria, and their applications in photo-bioelectrochemical systems, production of poly-β-hydroxyalkanoates, single-cell protein, biofertilizers and pigments. The ecology of ABP, their distinguishing factors, various physiochemical parameters governing the production of high-value substances and future directions of APB utilization are also discussed.

Molecular Cloning and Differential Gene Expression Analysis of 1-Deoxy-D-xylulose 5-Phosphate Synthase (DXS) in Andrographis paniculata (Burm. f) Nees

Andrographis paniculata 1-deoxy-D-xylulose-5-phosphate synthase (ApDXS) gene (GenBank Accession No MG271749.1) was isolated and cloned from leaves for the first time. Expression of ApDXS gene was carried out in Escherichia coli Rosetta cells. Tissue-specific ApDXS gene expression by quantitative RT-PCR (qRT-PCR) revealed maximum fold expression in the leaves followed by stem and roots. Further, the differential gene expression profile of Jasmonic acid (JA)-elicited in vitro adventitious root cultures showed enhanced ApDXS expression compared to untreated control cultures. A. paniculata 3-hydroxy-3-methylglutaryl-coenzyme A reductase (ApHMGR) gene expression was also studied where it was up-regulated by JA elicitation but showed lower expression compared to ApDXS. The highest expression of both genes was found at 25 µm JA elicitation followed by 50 µm. HPLC data indicated that the transcription levels were correlated with increased andrographolide accumulation. The peak level of andrographolide accumulation was recorded at 25 μM JA (9.38-fold) followed by 50 µM JA (7.58-fold) in elicitation treatments. The in silico generated ApDXS 3D model revealed 98% expected amino acid residues in the favored and 2% in the allowed regions of the Ramachandran plot with 92% structural reliability. Further, prediction of conserved domains and essential amino acids [Arg (249, 252, 255), Asn (307) and Ser (247)] involved in ligand/inhibitor binding was carried out by in silico docking studies. Our present findings will generate genomic information and provide a blueprint for future studies of ApDXS and its role in diterpenoid biosynthesis in A. paniculata.

Diversity in recognition and function of human γδ T cells

As interest increases in harnessing the potential power of tissue-resident cells for human health and disease, γδ T cells have been thrust into the limelight due to their prevalence in peripheral tissues, their sentinel-like phenotypes, and their unique antigen recognition capabilities. This review focuses primarily on human γδ T cells, highlighting their distinctive characteristics including antigen recognition, function, and development, with an emphasis on where they differ from their αβ T cell comparators, as well as from γδ T cell populations in the mouse. We review the antigens that have been identified thus far to regulate members of the human Vδ1 population and discuss what players are involved in transducing phosphoantigen-mediated signals to human Vγ9Vδ2 T cells. We also briefly review distinguishing features of these cells in terms of TCR signaling, use of coreceptor and costimulatory molecules and their development. These cells have great potential to be harnessed in a clinical setting, but caution must be taken to understand their unique capabilities and how they differ from the populations to which they are commonly compared.

Engineering Lactococcus lactis for Increased Vitamin K2 Production

Cheese produced with Lactococcus lactis is the main source of vitamin K2 in the Western diet. Subclinical vitamin K2 deficiency is common, calling for foods with enhanced vitamin K2 content. In this study we describe analyses of vitamin K2 (menaquinone) production in the lactic acid bacterium L. lactis ssp. cremoris strain MG1363. By cloning and expression from strong promoters we have identified genes and bottlenecks in the biosynthetic pathways leading to the long-chained menaquinones, MK-8 and MK-9. Key genes of the biosynthetic menaquinone pathway were overexpressed, singly or combined, to examine how vitamin K2 production can be enhanced. We observed that the production of the long menaquinone polyprenyl side chain, rather than production of the napthoate ring (1,4-dihydroxy-2-naphtoic acid), limits total menaquinone synthesis. Overexpression of genes causing increased ring formation (menF and menA) led to overproduction of short chained MK-3, while overexpression of other key genes (mvk and llmg_0196) resulted in enhanced full-length MK-9 production. Of two putatively annotated prenyl diphosphate synthases we pinpoint llmg_0196 (preA) to be important for menaquinone production in L. lactis. The genes mvk, preA, menF, and menA were found to be important contributors to menaquinone levels as single overexpression of these genes double and more than triple the total menaquinone content in culture. Combined overexpression of mvk, preA, and menA increased menaquinone levels to a higher level than obtained individually. When the overproducing strains were applied for milk fermentations vitamin K2 content was effectively increased 3-fold compared to the wild type. The results provide a foundation for development of strains to ferment foods with increased functional value i.e., higher vitamin K2 content.

Synthesis and Evaluation of Halogenated 5-(2-Hydroxyphenyl)pyrazoles as Pseudilin Analogues Targeting the Enzyme IspD in the Methylerythritol Phosphate Pathway

This work reports halogenated 5-(2-hydroxyphenyl)pyrazoles as pseudilin analogues with the potential to target the enzyme IspD in the methylerythritol phosphate (MEP) pathway. Such analogues were designed using the bioisosteric replacement of the pseudilin core structure and synthesized via an efficient three-step route. With AtIspD-based screening and pre- and post-emergence herbicidal tests, these compounds were demonstrated to have considerable activities against AtIspD, with IC₅₀ up to 3.27 μM, and against model plants rape and barnyard grass, with moderate to excellent activities. At a rate of 150 g/ha in the greenhouse test, three compounds exhibited higher or comparable herbicidal activities than pseudilin. Molecular docking of representative compounds into the allosteric site of AtIspD revealed a binding mode similar to that of pseudilin. The established bioisosterism and synthesis method in this work may serve as an important tool for the development of new herbicides and antimicrobials targeting IspD in the MEP pathway.

Recent Advances in the Metabolic Engineering of Yeasts for Ginsenoside Biosynthesis

Ginsenosides are a group of glycosylated triterpenes isolated from Panax species. Ginsenosides are promising candidates for the prevention and treatment of cancer as well as food additives. However, owing to a lack of efficient approaches for ginsenoside production from plants and chemical synthesis, ginsenosides may not yet have reached their full potential as medicinal resources. In recent years, an alternative approach for ginsenoside production has been developed using the model yeast Saccharomyces cerevisiae and non-conventional yeasts such as Yarrowia lipolytica and Pichia pastoris. In this review, various metabolic engineering strategies, including heterologous gene expression, balancing, and increasing metabolic flux, and enzyme engineering, have been described as recent advanced engineering techniques for improving ginsenoside production. Furthermore, the usefulness of a systems approach and fermentation strategy has been presented. Finally, the present challenges and future research direction for industrial cell factories have been discussed.

Can Plasmodium's tricks for enhancing its transmission be turned against the parasite? New hopes for vector control

Approximately 120 years ago the link between mosquito and the malaria transmission was discovered. However, even today it remains an open question whether the parasite is able to direct the blood-seeking and feeding behavior of its mosquito vector to maximize the probability of transmission. If the parasite has this ability, could it occur only through the alteration of the vertebrate host's volatile organic compounds (VOCs) and/or the parasite alteration of the behavior of the infected vector in a manner that favors its transmission? Although some recent empirical evidence supports the hypothesis regarding the parasite ability in alteration of the vertebrate host's VOCs, the role of parasite alteration and behavioral differences between infected and uninfected female mosquitoes toward infected and uninfected hosts has not yet been considered in the implementation of control measures. This review will discuss the current evidence, which shows 1. Plasmodium can direct uninfected mosquito blood-seeking and feeding behavior via alteration of vertebrate-host odor profiles and production of phagostimulants and 2. Plasmodium also manipulates its vector during the sporogony cycle to increase transmission. Briefly, we also consider the next generation of methods for moving the empirical laboratory evidence to potential application in future integrated malaria control programs.

Distinct metabolic pathways drive monoterpenoid biosynthesis in a natural population of Pelargonium graveolens

Pelargonium graveolens is a wild predecessor to rose-scented geranium hybrids prized for their essential oils used as fragrances and flavorings. However, little is known about their biosynthesis. Here we present metabolic evidence that at least two distinct monoterpene biosynthetic pathways contribute to their volatile profiles, namely, cyclic p-menthanes such as (-)-isomenthone and acyclic monoterpene alcohols such as geraniol and (-)-citronellol and their derivatives (referred to here as citronelloid monoterpenes). We established their common origin via the 2C-methyl-d-erythritol-4-phosphate pathway but found no indication these pathways share common intermediates beyond geranyl diphosphate. Untargeted volatile profiling of 22 seed-grown P. graveolens lines demonstrated distinct chemotypes that preferentially accumulate (-)-isomenthone, geraniol, or (-)-citronellol along with approximately 85 minor volatile products. Whole plant 13CO2 isotopic labeling performed under physiological conditions permitted us to measure the in vivo rates of monoterpenoid accumulation in these lines and quantify differences in metabolic modes between chemotypes. We further determined that p-menthane monoterpenoids in Pelargonium are likely synthesized from (+)-limonene via (+)-piperitone rather than (+)-pulegone. Exploitation of this natural population enabled a detailed dissection of the relative rates of competing p-menthane and citronelloid pathways in this species, providing real time rates of monoterpene accumulation in glandular trichomes.

Medically Useful Plant Terpenoids: Biosynthesis, Occurrence, and Mechanism of Action

Specialized plant terpenoids have found fortuitous uses in medicine due to their evolutionary and biochemical selection for biological activity in animals. However, these highly functionalized natural products are produced through complex biosynthetic pathways for which we have a complete understanding in only a few cases. Here we review some of the most effective and promising plant terpenoids that are currently used in medicine and medical research and provide updates on their biosynthesis, natural occurrence, and mechanism of action in the body. This includes pharmacologically useful plastidic terpenoids such as p-menthane monoterpenoids, cannabinoids, paclitaxel (taxol®), and ingenol mebutate which are derived from the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway, as well as cytosolic terpenoids such as thapsigargin and artemisinin produced through the mevalonate (MVA) pathway. We further provide a review of the MEP and MVA precursor pathways which supply the carbon skeletons for the downstream transformations yielding these medically significant natural products.

Engineered Rhodobacter capsulatus as a Phototrophic Platform Organism for the Synthesis of Plant Sesquiterpenoids

Sesquiterpenoids are a large class of natural compounds offering manifold properties valuable for food, cosmetics, agriculture, and pharma industry. Production in microorganisms is a sustainable approach to provide sesquiterpenoids for research and industrial use independent of their natural sources. This requires the functional transfer of the respective biocatalytic pathways in an adequate host microorganism offering a sufficient supply of precursors that is ideally adjusted to the individual demand of the recombinant biosynthesis route. The phototrophic purple bacterium Rhodobacter capsulatus offers unique physiological properties that are favorable for biosynthesis of hydrophobic terpenes. Under phototrophic conditions, it develops a large intracytoplasmic membrane suitable for hosting membrane-bound enzymes and metabolites of respective biosynthetic pathways. In addition, Rhodobacter harbors an intrinsic carotenoid biosynthesis that can be engineered toward the production of foreign terpenes. Here, we evaluate R. capsulatus as host for the production of plant sesquiterpenoids under phototrophic conditions using patchoulol and valencene as a proof of concept. The heterologous expression of patchoulol synthase PcPS from Pogostemon cablin as well as the valencene synthases CsVS from Citrus sinensis and CnVS from Callitropsis nootkatensis led to the production of the respective sesquiterpenoids in R. capsulatus. To analyze, if gradually adjustable formation of the key precursor farnesylpyrophosphate (FPP) is beneficial for sesquiterpene synthesis under phototrophic conditions, the intrinsic 1-deoxy-D-xylulose 5-phosphate (DXP) pathway genes as well as the heterologous mevalonate pathway genes were modularly expressed in various combinations. To this end, different plasmids and chromosomally integrated expression tools were developed harboring the strong and tightly controlled P_nif promoter for heterologous gene expression. Notably, comparative studies identified a distinct combination of precursor biosynthetic genes as best-performing setup for each of the tested sesquiterpene synthases. In summary, we could demonstrate that R. capsulatus is a promising alternative platform organism that is suited for sustainable sesquiterpenoid formation under phototrophic cultivation conditions. A modular engineering of R. capsulatus strains via tailored co-expression of FPP biosynthetic genes further allowed adaptation of sesquiterpene precursor formation to its catalytic conversion by different plant terpene synthases.

Metabolic engineering of Escherichia coli for the production of isoprenoids

Metabolic engineering is the practice of using directed genetic manipulations to rewire cellular metabolism primarily with the aim to transform the organism into a single-celled chemical factory. Using biological processes, we can produce more complex chemicals in a more sustainable way. This is particularly important for chemicals which are hard to synthesize using traditional chemistry. However, cells have evolved for growth and must be engineered to produce a single chemical at commercially viable levels. This review focuses on the strategies used to rewire cellular metabolism to produce chemicals using isoprenoid production in Escherichia coli as an example that illustrates many of the challenges faced in metabolic engineering.

Probing the Substrate Promiscuity of Isopentenyl Phosphate Kinase as a Platform for Hemiterpene Analogue Production

Isoprenoids are a large class of natural products with wide-ranging applications. Synthetic biology approaches to the manufacture of isoprenoids and their new-to-nature derivatives are limited due to the provision in nature of just two hemiterpene building blocks for isoprenoid biosynthesis. To address this limitation, artificial chemo-enzymatic pathways such as the alcohol-dependent hemiterpene (ADH) pathway serve to leverage consecutive kinases to convert exogenous alcohols into pyrophosphates that could be coupled to downstream isoprenoid biosynthesis. To be successful, each kinase in this pathway should be permissive of a broad range of substrates. For the first time, we have probed the promiscuity of the second enzyme in the ADH pathway-isopentenyl phosphate kinase from Thermoplasma acidophilum-towards a broad range of acceptor monophosphates. Subsequently, we evaluate the suitability of this enzyme to provide unnatural pyrophosphates and provide a critical first step in characterizing the rate-limiting steps in the artificial ADH pathway.

Double prodrugs of a fosmidomycin surrogate as antimalarial and antitubercular agents

A series of eleven double prodrug derivatives of a fosmidomycin surrogate were synthesized and investigated for their ability to inhibit in vitro growth of P. falciparum and M. tuberculosis. A pivaloyloxymethyl (POM) phosphonate prodrug modification was combined with various prodrug derivatisations of the hydroxamate moiety. The majority of compounds showed activity comparable with or inferior to fosmidomycin against P. falciparum. N-benzyl substituted carbamate prodrug 6f was the most active antimalarial analog with an IC₅₀ value of 0.64 µM. Contrary to fosmidomycin and parent POM-prodrug 5, 2-nitrofuran and 2-nitrothiophene prodrugs 6i and 6j displayed promising antitubercular activities.

Phosphonodiamidate prodrugs of N-alkoxy analogs of a fosmidomycin surrogate as antimalarial and antitubercular agents

A series of N-alkoxy analogs of a l-leucine ethyl ester phosphonodiamidate prodrug of a fosmidomycin surrogate were synthesized and investigated for their ability to inhibit in vitro growth of P. falciparum and M. tuberculosis. These compounds originate by merging a previously reported successful phosphonate derivatisation with favorable modifications of the hydroxamate moiety. None of the synthesized compounds showed enhanced activity against either P. falciparum or M. tuberculosis in comparison with the parent free hydroxamate analog.

Cytosolic lipid droplets as engineered organelles for production and accumulation of terpenoid biomaterials in leaves

Cytosolic lipid droplets are endoplasmic reticulum-derived organelles typically found in seeds as reservoirs for physiological energy and carbon to fuel germination. Here, we report synthetic biology approaches to co-produce high-value sesqui- or diterpenoids together with lipid droplets in plant leaves. The formation of cytosolic lipid droplets is enhanced in the transient Nicotiana benthamiana system through ectopic production of WRINKLED1, a key regulator of plastid fatty acid biosynthesis, and a microalgal lipid droplet surface protein. Engineering of the pathways providing the universal C5-building blocks for terpenoids and installation of terpenoid biosynthetic pathways through direction of the enzymes to native and non-native compartments boost the production of target terpenoids. We show that anchoring of distinct biosynthetic steps onto the surface of lipid droplets leads to efficient production of terpenoid scaffolds and functionalized terpenoids. The co-produced lipid droplets "trap" the terpenoids in the cells.

An Artificial Pathway for Isoprenoid Biosynthesis Decoupled from Native Hemiterpene Metabolism

Isoprenoids are constructed in nature using hemiterpene building blocks that are biosynthesized from lengthy enzymatic pathways with little opportunity to deploy precursor-directed biosynthesis. Here, an artificial alcohol-dependent hemiterpene biosynthetic pathway was designed and coupled to several isoprenoid biosynthetic systems, affording lycopene and a prenylated tryptophan in robust yields. This approach affords a potential route to diverse non-natural hemiterpenes and by extension isoprenoids modified with non-natural chemical functionality. Accordingly, the prototype chemo-enzymatic pathway is a critical first step toward the construction of engineered microbial strains for bioconversion of simple scalable building blocks into complex isoprenoid scaffolds.

The function, biogenesis and regulation of the electron transport chains in Campylobacter jejuni: New insights into the bioenergetics of a major food-borne pathogen

Campylobacter jejuni is a zoonotic Epsilonproteobacterium that grows in the gastrointestinal tract of birds and mammals, and is the most frequent cause of food-borne bacterial gastroenteritis worldwide. As an oxygen-sensitive microaerophile, C. jejuni has to survive high environmental oxygen tensions, adapt to oxygen limitation in the host intestine and resist host oxidative attack. Despite its small genome size, C. jejuni is a versatile and metabolically active pathogen, with a complex and highly branched set of respiratory chains allowing the use of a wide range of electron donors and alternative electron acceptors in addition to oxygen, including fumarate, nitrate, nitrite, tetrathionate and N- or S-oxides. Several novel enzymes participate in these electron transport chains, including a tungsten containing formate dehydrogenase, a Complex I that uses flavodoxin and not NADH, a periplasmic facing fumarate reductase and a cytochrome c tetrathionate reductase. This review presents an updated description of the composition and bioenergetics of these various respiratory chains as they are currently understood, including recent work that gives new insights into energy conservation during electron transport to various alternative electron acceptors. The regulation of synthesis and assembly of the electron transport chains is also discussed. A deeper appreciation of the unique features of the respiratory systems of C. jejuni may be helpful in informing strategies to control this important pathogen.

Alternative Carbon Sources for Isoprene Emission

Isoprene and other plastidial isoprenoids are produced primarily from recently assimilated photosynthates via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. However, when environmental conditions limit photosynthesis, a fraction of carbon for MEP pathway can come from extrachloroplastic sources. The flow of extrachloroplastic carbon depends on the species and on leaf developmental and environmental conditions. The exchange of common phosphorylated intermediates between the MEP pathway and other metabolic pathways can occur via plastidic phosphate translocators. C1 and C2 carbon intermediates can contribute to chloroplastic metabolism, including photosynthesis and isoprenoid synthesis. Integration of these metabolic processes provide an example of metabolic flexibility, and results in the synthesis of primary metabolites for plant growth and secondary metabolites for plant defense, allowing effective use of environmental resources under multiple stresses.

Microbial Platform for Terpenoid Production: Escherichia coli and Yeast

Terpenoids, also called isoprenoids, are a large and highly diverse family of natural products with important medical and industrial properties. However, a limited production of terpenoids from natural resources constrains their use of either bulk commodity products or high valuable products. Microbial production of terpenoids from Escherichia coli and yeasts provides a promising alternative owing to available genetic tools in pathway engineering and genome editing, and a comprehensive understanding of their metabolisms. This review summarizes recent progresses in engineering of industrial model strains, E. coli and yeasts, for terpenoids production. With advances of synthetic biology and systems biology, both strains are expected to present the great potential as a platform of terpenoid synthesis.

Acyloxybenzyl and Alkoxyalkyl Prodrugs of a Fosmidomycin Surrogate as Antimalarial and Antitubercular Agents

Two classes of prodrugs of a fosmidomycin surrogate were synthesized and investigated for their ability to inhibit in vitro growth of P. falciparum and M. tuberculosis. To this end, a novel efficient synthesis route was developed involving a cross metathesis reaction as a key step. Alkoxyalkyl prodrugs show decent antimalarial activities, but acyloxybenzyl prodrugs proved to be the most interesting and show enhanced antimalarial and antitubercular activity. The most active antimalarial analogues show low nanomolar IC₅₀ values.

Aryl bis-sulfonamides bind to the active site of a homotrimeric isoprenoid biosynthesis enzyme IspF and extract the essential divalent metal cation cofactor

Characterizing the mode of action of non-covalent inhibitors in multisubunit enzymes often presents a great challenge. Most of the conventionally used methods are based on ensemble measurements of protein-ligand binding in bulk solution. They often fail to accurately describe multiple binding processes occurring in such systems. Native electrospray ionization mass spectrometry (ESI-MS) of intact protein complexes is a direct, label-free approach that can render the entire distribution of ligand-bound states in multimeric protein complexes. Here we apply native ESI-MS to comprehensively characterize the isoprenoid biosynthesis enzyme IspF from Arabidopsis thaliana, an example of a homomeric protein complex with multiple binding sites for several types of ligands, including a metal cofactor and a synthetic inhibitor. While standard biophysical techniques failed to reveal the mode of action of recently discovered aryl-sulfonamide-based inhibitors of AtIspF, direct native ESI-MS titrations of the protein with the ligands and ligand competition assays allowed us to accurately capture the solution-phase protein-ligand binding equilibria in full complexity and detail. Based on these combined with computational modeling, we propose a mechanism of AtIspF inhibition by aryl bis-sulfonamides that involves both the competition with the substrate for the ligand-binding pocket and the extraction of Zn2+ from the enzyme active site. This inhibition mode is therefore mixed competitive and non-competitive, the latter exerting a key inhibitory effect on the enzyme activity. The results of our study deliver a profound insight into the mechanisms of AtIspF action and inhibition, open new perspectives for designing inhibitors of this important drug target, and demonstrate the applicability and value of the native ESI-MS approach for deep analysis of complex biomolecular binding equilibria.

Coactivation of MEP-biosynthetic genes and accumulation of abietane diterpenes in Salvia sclarea by heterologous expression of WRKY and MYC2 transcription factors

Plant abietane diterpenoids (e.g. aethiopinone, 1- oxoaethiopinone, salvipisone and ferruginol), synthesized in the roots of several Salvia spp, have antibacterial, antifungal, sedative and anti-proliferative properties. Recently we have reported that content of these compounds in S. sclarea hairy roots is strongly depending on transcriptional regulation of genes belonging to the plastidial MEP-dependent terpenoid pathway, from which they mostly derive. To boost the synthesis of this interesting class of compounds, heterologous AtWRKY18, AtWRKY40, and AtMYC2 TFs were overexpressed in S. sclarea hairy roots and proved to regulate in a coordinated manner the expression of several genes encoding enzymes of the MEP-dependent pathway, especially DXS, DXR, GGPPS and CPPS. The content of total abietane diterpenes was enhanced in all overexpressing lines, although in a variable manner due to a negative pleiotropic effect on HR growth. Interestingly, in the best performing HR lines overexpressing the AtWRKY40 TF induced a significant 4-fold increase in the final yield of aethiopinone, for which we have reported an interesting anti-proliferative activity against resistant melanoma cells. The present results are also informative and instrumental to enhance the synthesis of abietane diterpenes derived from the plastidial MEP-derived terpenoid pathway in other Salvia species.

Patchoulol Production with Metabolically Engineered Corynebacterium glutamicum

Patchoulol is a sesquiterpene alcohol and an important natural product for the perfume industry. Corynebacterium glutamicum is the prominent host for the fermentative production of amino acids with an average annual production volume of ~6 million tons. Due to its robustness and well established large-scale fermentation, C. glutamicum has been engineered for the production of a number of value-added compounds including terpenoids. Both C40 and C50 carotenoids, including the industrially relevant astaxanthin, and short-chain terpenes such as the sesquiterpene valencene can be produced with this organism. In this study, systematic metabolic engineering enabled construction of a patchoulol producing C. glutamicum strain by applying the following strategies: (i) construction of a farnesyl pyrophosphate-producing platform strain by combining genomic deletions with heterologous expression of ispA from Escherichia coli; (ii) prevention of carotenoid-like byproduct formation; (iii) overproduction of limiting enzymes from the 2-c-methyl-d-erythritol 4-phosphate (MEP)-pathway to increase precursor supply; and (iv) heterologous expression of the plant patchoulol synthase gene PcPS from Pogostemon cablin. Additionally, a proof of principle liter-scale fermentation with a two-phase organic overlay-culture medium system for terpenoid capture was performed. To the best of our knowledge, the patchoulol titers demonstrated here are the highest reported to date with up to 60 mg L^−1 and volumetric productivities of up to 18 mg L^−1 d^−1.

The Methylerythritol Phosphate Pathway: Promising Drug Targets in the Fight against Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a severe infectious disease in need of new chemotherapies especially for drug-resistant cases. To meet the urgent requirement of new TB drugs with novel modes of action, the TB research community has been validating numerous targets from several biosynthetic pathways. The methylerythritol phosphate (MEP) pathway is utilized by Mtb for the biosynthesis of isopentenyl pyrophosphate (IPP) and its isomer dimethylallyl pyrophosphate (DMAPP), the universal five-carbon building blocks of isoprenoids. While being a common biosynthetic pathway in pathogens, the MEP pathway is completely absent in humans. Due to its unique presence in pathogens as well as the essentiality of the MEP pathway in Mtb, the enzymes in this pathway are promising targets for the development of new drugs against tuberculosis. In this Review, we discuss three enzymes in the MEP pathway: 1-deoxy-d-xylulose-5-phosphate synthase (DXS), 1-deoxy-d-xylulose-5-phosphate reductoisomerase (IspC/DXR), and 2 C-methyl-d-erythritol 2,4-cyclodiphosphate synthase (IspF), which appear to be the most promising antitubercular drug targets. Structural and mechanistic features of these enzymes are reviewed, as well as selected inhibitors that show promise as antitubercular agents.

Biosynthesis and applications of prenylquinones

Prenylquinones are isoprenoid compounds with a characteristic quinone structure and isoprenyl tail that are ubiquitous in almost all living organisms. There are four major prenylquinone classes: ubiquinone (UQ), menaquinone (MK), plastoquinone (PQ), and rhodoquinone (RQ). The quinone structure and isoprenyl tail length differ among organisms. UQ, PQ, and RQ contain benzoquinone, while MK contains naphthoquinone. UQ, MK, and RQ are involved in oxidative phosphorylation, while PQ functions in photosynthetic electron transfer. Some organisms possess two types of prenylquinones; Escherichia coli has UQ₈ and MK₈, and Caenorhabditis elegans has UQ₉ and RQ₉. Crystal structures of most of the enzymes involved in MK synthesis have been solved. Studies on the biosynthesis and functions of quinones have advanced recently, including for phylloquinone (PhQ), which has a phytyl moiety instead of an isoprenyl tail. Herein, the synthesis and applications of prenylquinones are reviewed.

Human viperin catalyzes the modification of GPP and FPP potentially affecting cholesterol synthesis

Viperin is a radical SAM enzyme that possesses antiviral properties against a broad range of enveloped viruses. Here, we describe the activity of human viperin with two molecules of the mevalonate pathway, geranyl pyrophosphate, and farnesyl pyrophosphate, involved in cholesterol biosynthesis. We postulate that the radical modification of these two molecules by viperin might lead to defects in cholesterol synthesis, thereby affecting the composition of lipid rafts and subsequent enveloped virus budding.

A Synthetic Isoprenoid Lipoquinone, Menaquinone-2, Adopts a Folded Conformation in Solution and at a Model Membrane Interface

Menaquinones (naphthoquinones, MK) are isoprenoids that play key roles in the respiratory electron transport system of some prokaryotes by shuttling electrons between membrane-bound protein complexes acting as electron acceptors and donors. Menaquinone-2 (MK-2), a truncated MK, was synthesized, and the studies presented herein characterize the conformational and chemical properties of the hydrophobic MK-2 molecule. Using 2D NMR spectroscopy, we established for the first time that MK-2 has a folded conformation defined by the isoprenyl side-chain folding back over the napthoquinone in a U-shape, which depends on the specific environmental conditions found in different solvents. We used molecular mechanics to illustrate conformations found by the NMR experiments. The measured redox potentials of MK-2 differed in three organic solvents, where MK-2 was most easily reduced in DMSO, which may suggest a combination of solvent effect (presumably in part because of differences in dielectric constants) and/or conformational differences of MK-2 in different organic solvents. Furthermore, MK-2 was found to associate with the interface of model membranes represented by Langmuir phospholipid monolayers and Aerosol-OT (AOT) reverse micelles. MK-2 adopts a slightly different U-shaped conformation within reverse micelles compared to within solution, which is in sharp contrast to the extended conformations illustrated in literature for MKs.