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Abstract [Objective] The purpose of this study is to examine the role of the DXR gene, encoding 1-deoxy- D-xylulose-5-phosphate reductoisomerase, in monoterpenoids synthesis in lilac (Syringa oblata), and to provide genetic resources and theoretical basis for the molecular breeding of floral fragrance of lilac. [Methods] Firstly, the SoDXR gene was cloned. Then, bioinformatics and subcellular localization analysis were performed, and qRT-PCR was used to analyze the gene expression patterns in different floral development stages and tissues. Finally, transient overexpression of SoDXR in the petals of snapdragon (Antirrhinum majus) was detected. [Results] ORF of SoDXR was 1 425 bp, encoding 474 amino acids. SoDXR protein contained the conserved domain of DXP_reductoisom, which had a similarity of up to 95% with Osmanthus fragrans and Olea europaea. Subcellular localization analysis showed that the protein was mainly located in the plastids, consistent with the software prediction. With flowering, the expression level of SoDXR was increased and then decreased, with the highest expression in the initial opening stage. SoDXR was differentially expressed in various tissues with the highest in petals and the lowest in stems. Transient overexpression revealed that the expression of SoDXR was higher than the control. Moreover, the main floral volatile components in snapdragon petals, myrcene and ocimene, were increased by 15.03 and 4.83 times, respectively. [Conclusion] The SoDXR gene positively regulates monoterpenoids synthesis in lilac, and may play an important role in the synthesis of secondary metabolites of floral fragrance.

Abstract Background Oregano (Origanum vulgare L.), one of the important medicinal plants in the world, has valuable pharmacological compounds with antimicrobial, antiviral, antioxidant, anti-inflammatory, antispasmodic, antiurolithic, antiproliferative and neuroprotective activities. Phenolic monoterpenes such as thymol and carvacrol with many medical importance are found in Oregano essential oil. The biosynthesis of these compounds is carried out through the methyl erythritol-4 phosphate (MEP) pathway. Environmental stresses such as salinity might improve the secondary metabolites in medicinal plants. The influence of salinity stress (0 (control), 25, 50 and 100 mM NaCl) on the essential oil content, composition and expression of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), γ-terpinene synthase (Ovtps2) and cytochrome P450 monooxygenases (CYP71D180) genes involved in thymol and carvacrol biosynthesis, was investigated in two oregano subspecies (vulgare and gracile). Results Essential oil content was increased at low NaCl concentration (25 mM) compared with non-stress conditions, whereas it was decreased as salinity stress intensified (50 and 100 mM). Essential oil content was significantly higher in subsp. gracile than subsp. vulgare. The highest (0.20 mL pot−1) and lowest (0.06 mL pot−1) amount of essential oil yield was obtained in subsp. gracile at 25 and 100 mM NaCl, respectively. The content of carvacrol, as the main component of essential oil, decreased with increasing salinity level in subsp. gracile, but increased in subsp. vulgare. The highest expression of DXR, Ovtps2 and CYP71D180 genes was observed at 50 mM NaCl in subsp. vulgare. While, in subsp. gracile, the expression of the mentioned genes decreased with increasing salinity levels. A positive correlation was obtained between the expression of DXR, Ovtps2 and CYP71D180 genes with carvacrol content in both subspecies. On the other hand, a negative correlation was found between the expression of CYP71D180 and carvacrol content in subsp. gracile. Conclusions The findings of this study demonstrated that both oregano subspecies can tolerate NaCl salinity up to 50 mM without significant reduction in essential oil yield. Also, moderate salinity stress (50 mM NaCl) in subsp. vulgare might increase the carvacrol content partly via increment the expression levels of DXR, Ovtps2 and CYP71D180 genes.

Due to global climate change, drought is emerging as a major threat to plant growth and agricultural productivity. Abscisic acid (ABA) has been implicated in plant drought tolerance, however, its retarding effects on plant growth cannot be ignored. The reactions catalyzed by 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) proteins are critical steps within the isoprenoid biosynthesis in plants. Here, five DXS (CtDXS1-5) and two DXR (CtDXR1-2) genes were identified from Cassia tora genome. Based on multiple assays including the phylogeny, cis-acting element, expression pattern, and subcellular localization, CtDXS1 and CtDXR1 genes might be potential candidates controlling the isoprenoid biosynthesis. Intriguingly, CtDXS1 transgenic plants resulted in drought tolerance but retardant growth, while CtDXR1 transgenic plants exhibited both enhanced drought tolerance and increased growth. By comparison of b-carotene, chlorophyll, abscisic acid (ABA) and gibberellin 3 (GA3) contents in wild-type and transgenic plants, the absolute contents and (or) altered GA3/ABA levels were suggested to be responsible for the balance between drought tolerance and plant growth. The transcriptome of CtDXR1 transgenic plants suggested that the transcript levels of key genes, such as DXS, 9-cis-epoxycarotenoid dioxygenases (NCED), ent-kaurene synthase (KS) and etc, involved with chlorophyll, b-carotene, ABA and GA3 biosynthesis were induced and their contents increased accordingly. Collectively, the trade-off effect induced by CtDXR1 was associated with redesigning architecture in phytohormone homeostasis and thus was highlighted for future breeding purposes. [ABSTRACT FROM AUTHOR]

Background: Oregano (Origanum vulgare L.), one of the important medicinal plants in the world, has valuable pharmacological compounds with antimicrobial, antiviral, antioxidant, anti-inflammatory, antispasmodic, antiurolithic, antiproliferative and neuroprotective activities. Phenolic monoterpenes such as thymol and carvacrol with many medical importance are found in Oregano essential oil. The biosynthesis of these compounds is carried out through the methyl erythritol-4 phosphate (MEP) pathway. Environmental stresses such as salinity might improve the secondary metabolites in medicinal plants. The influence of salinity stress (0 (control), 25, 50 and 100 mM NaCl) on the essential oil content, composition and expression of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), γ-terpinene synthase (Ovtps2) and cytochrome P450 monooxygenases (CYP71D180) genes involved in thymol and carvacrol biosynthesis, was investigated in two oregano subspecies (vulgare and gracile). Results: Essential oil content was increased at low NaCl concentration (25 mM) compared with non-stress conditions, whereas it was decreased as salinity stress intensified (50 and 100 mM). Essential oil content was significantly higher in subsp. gracile than subsp. vulgare. The highest (0.20 mL pot−1) and lowest (0.06 mL pot−1) amount of essential oil yield was obtained in subsp. gracile at 25 and 100 mM NaCl, respectively. The content of carvacrol, as the main component of essential oil, decreased with increasing salinity level in subsp. gracile, but increased in subsp. vulgare. The highest expression of DXR, Ovtps2 and CYP71D180 genes was observed at 50 mM NaCl in subsp. vulgare. While, in subsp. gracile, the expression of the mentioned genes decreased with increasing salinity levels. A positive correlation was obtained between the expression of DXR, Ovtps2 and CYP71D180 genes with carvacrol content in both subspecies. On the other hand, a negative correlation was found between the expression of CYP71D180 and carvacrol content in subsp. gracile. Conclusions: The findings of this study demonstrated that both oregano subspecies can tolerate NaCl salinity up to 50 mM without significant reduction in essential oil yield. Also, moderate salinity stress (50 mM NaCl) in subsp. vulgare might increase the carvacrol content partly via increment the expression levels of DXR, Ovtps2 and CYP71D180 genes. [ABSTRACT FROM AUTHOR]

The methyl erythritol phosphate (MEP) pathway of isoprenoid biosynthesis is essential for malaria parasites and also for several human pathogenic bacteria, thus representing an interesting target for future antimalarials and antibiotics and for diagnostic strategies. We have developed a DNA aptamer (D10) against Plasmodium falciparum 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), the second enzyme of this metabolic route. D10 binds in vitro to recombinant DXR from P. falciparum and Escherichia coli, showing at 10 µM a ca. 50% inhibition of the bacterial enzyme. In silico docking analysis indicates that D10 associates with DXR in solvent-exposed regions outside the active center pocket. According to fluorescence confocal microscopy data, this aptamer specifically targets in P. falciparum in vitro cultures the apicoplast organelle where the MEP pathway is localized and is, therefore, a highly specific marker of red blood cells parasitized by Plasmodium vs. naïve erythrocytes. D10 is also selective for the detection of MEP+ bacteria (e.g., E. coli and Pseudomonas aeruginosa) vs. those lacking DXR (e.g., Enterococcus faecalis). Based on these results, we discuss the potential of DNA aptamers in the development of ligands that can outcompete the performance of the well-established antibody technology for future therapeutic and diagnostic approaches.

Abstract Cross-protection is a phenomenon in which infection with a mild virus strain protects host plants against subsequent infection with a closely related severe virus strain. This study showed that a mild strain mutant virus, Tobacco mosaic virus (TMV)-43A could cross protect Nicotiana benthamiana plants against wild-type TMV. Furthermore, we investigated the host responses at the proteome level to identify important host proteins involved in cross-protection. We used the isobaric tags for relative and absolute quantification (iTRAQ) technique to analyze the proteome profiles of TMV, TMV-43A and cross-protected plants at different time-points. Our results showed that TMV-43A can cross-protect N. benthamiana plants from TMV. In cross-protected plants, photosynthetic activities were augmented, as supported by the increased accumulation of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) and geranylgeranyl diphosphate synthase (GGPS) enzymes, which are crucial for chlorophyll biosynthesis. The increased abundance of ROS scavenging enzymes like thioredoxins and L-ascorbate peroxidase would prevent oxidative damage in cross-protected plants. Interestingly, the abundance of defence-related proteins (14–3-3 and NbSGT1) decreased, along with a reduction in virus accumulation during cross-protection. In conclusion, we have identified several important host proteins that are crucial in cross-protection to counter TMV infection in N. benthamiana plants. Biological significance TMV is the most studied model for host-virus interaction in plants. It can infect wide varieties of plant species, causing significant economic losses. Cross protection is one of the methods to combat virus infection. A few cross-protection mechanisms have been proposed, including replicase/coat protein-mediated resistance, RNA silencing, and exclusion/spatial separation between virus strains. However, knowledge on host responses at the proteome level during cross protection is limited. To address this knowledge gap, we have leveraged on a global proteomics analysis approach to study cross protection. We discovered that TMV-43A (protector) protects N. benthamiana plants from TMV (challenger) infection through multiple host pathways: secondary metabolite biosynthesis, photosynthesis, defence, carbon metabolism, protein translation and processing and amino acid biosynthesis. In the secondary metabolite biosynthesis pathway, enzymes 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) and geranylgeranyl diphosphate synthase (GGPS) play crucial roles in chlorophyll biosynthesis during cross protection. In addition, accumulation of ROS scavenging enzymes was also found in cross-protected plants, providing rescues from excessive oxidative damage. Reduced abundance of plant defence proteins is correlated to reduced virus accumulation in host plants. These findings have increased our knowledge in host responses during cross-protection. Graphical abstract Unlabelled Image Highlights • TMV-43A cross-protects N. benthamiana plants from TMV. • Elevated levels of DXR and GGPS enzymes support chlorophyll biosynthesis. • Thioredoxins and L-ascorbate peroxidase protect plants from oxidative damage. • Reduced accumulation of defence proteins support host survival. [ABSTRACT FROM AUTHOR]

Abstract Vibrio vulnificus , a gram-negative bacterium, is the leading cause of seafood-borne illnesses and mortality in the United States. Previous studies have identified metabolites 2- C -methylerythritol 4-phosphate (MEP) as being essential for V. vulnificus growth and function. It was shown that 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr) is a critical enzyme in the viability of V. vulnificus, and many other bacteria, as it catalyzes the rearrangement of 1-deoxy-D-xylulose-5-phosphate (Dxp) to 2- C -methylerythritol 4-phosphate (MEP) within the MEP pathway, found in plants and bacteria. The MEP pathway produces the isoprenoids, isopentenyl diphosphate and dimethylallyl pyrophosphate. In this study, we produced and structurally characterized V. vulnificus Dxr. The enzyme forms a dimeric assembly and contains a metal ion in the active site. Protein produced in Escherichia coli co-purifies with Mg2+ ions, however the Mg2+ cations may be substituted with Mn2+, as both of these metals may be utilized by Dxrs. These findings will provide a basis for the design of Dxr inhibitors that may find application as antimicrobial compounds. Graphical abstract Unlabelled Image Highlights • Drx is the key enzyme in the non-mevalonate pathway and is essential for V. vulnificus survival. • The enzyme has a dimeric structure with metal ions (Mg2+ or Mn2+) present in the active site. • Determined structures represent two out of four previously described protein conformations. • The structural studies provide insight into a drug resistance mechanism. [ABSTRACT FROM AUTHOR]

Due to global climate change, drought is emerging as a major threat to plant growth and agricultural productivity. Abscisic acid (ABA) has been implicated in plant drought tolerance, however, its retarding effects on plant growth cannot be ignored. The reactions catalyzed by 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) proteins are critical steps within the isoprenoid biosynthesis in plants. Here, five DXS ( CtDXS1-5 ) and two DXR ( CtDXR1-2 ) genes were identified from Cassia tora genome. Based on multiple assays including the phylogeny, cis- acting element, expression pattern, and subcellular localization, CtDXS1 and CtDXR1 genes might be potential candidates controlling the isoprenoid biosynthesis. Intriguingly, CtDXS1 transgenic plants resulted in drought tolerance but retardant growth, while CtDXR1 transgenic plants exhibited both enhanced drought tolerance and increased growth. By comparison of β -carotene, chlorophyll, abscisic acid (ABA) and gibberellin 3 (GA 3 ) contents in wild-type and transgenic plants, the absolute contents and (or) altered GA 3 /ABA levels were suggested to be responsible for the balance between drought tolerance and plant growth. The transcriptome of CtDXR1 transgenic plants suggested that the transcript levels of key genes, such as DXS , 9-cis-epoxycarotenoid dioxygenases ( NCED ), ent-kaurene synthase ( KS ) and etc, involved with chlorophyll, β -carotene, ABA and GA 3 biosynthesis were induced and their contents increased accordingly. Collectively, the trade-off effect induced by CtDXR1 was associated with redesigning architecture in phytohormone homeostasis and thus was highlighted for future breeding purposes., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Tian, Quan, Jiang, Zheng, Huang, Tan, Yan, Zhou and Liao.)

The rate-limiting enzyme of the 2-methyl-d-erythritol-4-phosphate (MEP) terpenoid biosynthetic pathway, 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR), provides the perfect target for screening new antibacterial substances. In this study, we tested the DXR inhibitory effect of 35 plant essential oils (EOs), which have long been recognized for their antimicrobial properties. The results show that the EOs of Zanbthoxylum bungeanum (ZB), Schizonepetae tenuifoliae (ST), Thymus quinquecostatus (TQ), Origanum vulgare (OV), and Eugenia caryophyllata (EC) displayed weak to medium inhibitory activity against DXR, with IC50 values of 78 μg/mL, 65 μg/mL, 59 μg/mL, 48 μg/mL, and 37 μg/mL, respectively. GC-MS analyses of the above oils and further DXR inhibitory activity tests of their major components revealed that eugenol (EC) and carvacrol (TQ and OV) possess medium inhibition against the protein (68.3% and 55.6%, respectively, at a concentration of 20 μg/mL), whereas thymol (ST, TQ, and OV), carveol (ZB), and linalool (ZB, ST, and OV) only exhibited weak inhibition against DXR, at 20 μg/mL (23%−26%). The results add more details to the antimicrobial mechanisms of plant EOs, which could be very helpful in the direction of the reasonable use of EOs in the food industry and in the control of phytopathogenic microbials.

The methyl erythritol phosphate (MEP) pathway of isoprenoid biosynthesis is essential for malaria parasites and also for several human pathogenic bacteria, thus representing an interesting target for future antimalarials and antibiotics and for diagnostic strategies. We have developed a DNA aptamer (D10) against Plasmodium falciparum 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), the second enzyme of this metabolic route. D10 binds in vitro to recombinant DXR from P. falciparum and Escherichia coli , showing at 10 µM a ca. 50% inhibition of the bacterial enzyme. In silico docking analysis indicates that D10 associates with DXR in solvent-exposed regions outside the active center pocket. According to fluorescence confocal microscopy data, this aptamer specifically targets in P. falciparum in vitro cultures the apicoplast organelle where the MEP pathway is localized and is, therefore, a highly specific marker of red blood cells parasitized by Plasmodium vs. naïve erythrocytes. D10 is also selective for the detection of MEP+ bacteria (e.g., E. coli and Pseudomonas aeruginosa ) vs. those lacking DXR (e.g., Enterococcus faecalis ). Based on these results, we discuss the potential of DNA aptamers in the development of ligands that can outcompete the performance of the well-established antibody technology for future therapeutic and diagnostic approaches.

Abstract: The apicomplexan parasite Toxoplasma gondii, the causative agent of toxoplasmosis, is an important human pathogen. 1-Deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) in the non-mevalonate isoprene biosynthesis pathway is essential to the organism and therefore a target for developing anti-toxoplasmosis drugs. In order to find potent inhibitors, we expressed and purified recombinant T. gondii DXR (TgDXR). Biochemical properties of this enzyme were characterized and an enzyme activity/inhibition assay was developed. A collection of 11 compounds with a broad structural diversity were tested against TgDXR and several potent inhibitors were identified with K i values as low as 48nM. Analysis of the results as well as those of Escherichia coli and Plasmodium falciparum DXR enzymes revealed a different structure–activity relationship profile for the inhibition of TgDXR. [Copyright &y& Elsevier]

Abstract: Natural rubber from Hevea brasiliensis is synthesized by enzymic polymerization of isopentenyl diphosphate (IDP) units. This has been proposed to occur inside the latex vessel in a thread-like tubular reticulum, connecting rubber particles to single- (lutoid) and double- (Frey-Wyssling, FW) membrane-bound organelles. We show that a membrane-free preparation from FW particles converted [14C] glucose into radio labeled prenyl products and this was more efficiently inhibited by fosmidomycin, the MEP pathway inhibitor, than mevilonin, the inhibitor used to block the MVA pathway. This implicated the alternative plastid associated MEP pathway for IDP synthesis. We then identified a cDNA clone (Hbdxr) from a Hevea rubber latex cDNA library, encoding for 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR), a key enzyme of the MEP pathway for the IDP biosynthesis. Sequence analysis and the deduced amino acid sequence had >80% homology to other plant DXR enzymes with an ORF consisting of 1413bp capable of encoding a 50.97kDa polypeptide. A highly conserved binding site for NADPH was identified and an N-terminal transit peptide with a putative conserved cleavage site. The Hbdxr-gfp gene, transformed into Arabidopsis cells was located in the chloroplasts, thus Hbdxr may be expressed and localized in the FW plastids. The levels of Hbdxr mRNA detected in young latex containing tissues, inflorescence and seedling stems, were higher than those found in the latex from the tree and were barely detectable in the mature leaves. We therefore suggest that one function of the FW particles could be to supply IDP for rubber biosynthesis through the tubular thread-like reticulum. [Copyright &y& Elsevier]

Abstract: In view of the promising antimalarial activity of fosmidomycin or its N-acetyl homologue FR900098, the objective of this work was to investigate the influence of aromatic substituents in the α-position of the phosphonate moiety. The envisaged analogues were prepared using a linear route involving a 3-aryl-3-phosphoryl propanal intermediate. The activities of all compounds were evaluated on Eschericia coli 1-deoxy-d-xylulose 5-phosphate reductoisomerase and against two Plasmodium falciparum strains. Compared with fosmidomycin, several analogues displayed enhanced activity towards the P. falciparum strains. Compound 1e with a 3,4-dichlorophenyl substitution in the α-position of fosmidomycin emerged as the most potent analogue of this series. It is approximately three times more potent in inhibiting the growth of P. falciparum than FR900098, the most potent representative of this class reported so far. [Copyright &y& Elsevier]

Abstract: In higher plants, there are two pathways leading to the formation of isoprenoids: the acetate/mevalonate (MVA) pathway and the recently discovered 2C-methyl-d-erythritol-4-phosphate (MEP) pathway. The initial step on the MEP pathway is the condensation of pyruvate and glyceraldehyde-3-phosphate yielding 1-deoxy-d-xylulose-5-phosphate (DXP). The reaction is catalyzed by 1-deoxy-d-xylulose-5-phosphate synthase (DXS), and is encoded by the dxs gene. In this study, parts of dxs have been cloned from young leaves and mesocarp of oil palm (Elaeis guineensis Jacq., Tenera) The surprising results show that there are at least two dxs genes encoding DXS in different organs of oil palm, dxs1 in leaves and dxs2 in fruits. Cloning of full-length cDNA encoding dxs1 by the RLM-RACE (RNA ligase-mediated rapid amplification of 5′ and 3′ cDNA ends) method demonstrated that the cDNA contained an open reading frame of 2301bp encoding a deduced peptide of 707 amino acid residues with a predicted molecular mass of 76.4kDa and isoelectric point of 7.0. Expression of dxs2 and dxr transcript levels in oil palm fruits from each developmental stage were analyzed by a semiquantitative RT-PCR method. The level of dxs2 transcripts increases with the time after fertilization and reaches its maximum after 18 weeks while the expression of dxr is unchanged. The pattern of dxs2 transcripts appears to correlate with β-carotene accumulation during oil palm fruit ripening thus supports the assumed role of the dxs gene in carotenoid biosynthesis by the MEP pathway. [Copyright &y& Elsevier]

Abstract: 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) catalyses the first committed step in the production of isopentenyl diphosphate (IPP) according to the recently identified plastidial 2C-methyl-d-erythritol 4-phosphate (MEP) pathway. Forskolin, the major active diterpenoid component in Coleus forskohlii is synthesised via the MEP pathway. Herein, we present the investigation of a cDNA encoding C. forskohlii DXR, its heterologous expression in Escherichia coli and an examination of its properties in vitro. The full-length cDNA sequence of C. forskohlii DXR contains an open reading frame (ORF) of 1407 nucleotides encoding a peptide of 469 amino acids, resulting in an estimated molecular mass of 50.8kDa. The K m and V max of C. forskohlii DXR were determined to be 147.2μM and 0.3unitsmgprotein−1, respectively. Fosmidomycin, a specific inhibitor of DXR, showed dose-dependent inhibition with an IC50 of 0.45μM. A gene expression study using a C. forskohlii plant culture showed that DXR is strongly expressed in leaves, less in stems and at the limit of detectability in roots. The presence of fosmidomycin in C. forskohlii plant culture resulted in a decrease in forskolin production in roots. Therefore, we conclude that if C. forskohlii DXR is involved in the biosynthesis of forskolin, it is primarily synthesised in the leaves, and later accumulates in stems and roots. [Copyright &y& Elsevier]

1-Deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) is the second enzyme in the non-mevalonate pathway of isoprenoid biosynthesis. The structure of the apo-form of this enzyme from Zymomonas mobilis has been solved and refined to 1.9-A˚ resolution, and that of a binary complex with the co-substrate NADPH to 2.7-A˚ resolution. The subunit of DXR consists of three domains. Residues 1–150 form the NADPH binding domain, which is a variant of the typical dinucleotide-binding fold. The second domain comprises a four-stranded mixed β-sheet, with three helices flanking the sheet. Most of the putative active site residues are located on this domain. The C-terminal domain (residues 300–386) folds into a four-helix bundle. In solution and in the crystal, the enzyme forms a homo-dimer. The interface between the two monomers is formed predominantly by extension of the sheet in the second domain. The adenosine phosphate moiety of NADPH binds to the nucleotide-binding fold in the canonical way. The adenine ring interacts with the loop after β1 and with the loops between α2 and β2 and α5 and β5. The nicotinamide ring is disordered in crystals of this binary complex. Comparisons to Escherichia coli DXR show that the two enzymes are very similar in structure, and that the active site architecture is highly conserved. However, there are differences in the recognition of the adenine ring of NADPH in the two enzymes. [Copyright &y& Elsevier]

The rate-limiting enzyme of the 2-methyl-d-erythritol-4-phosphate (MEP) terpenoid biosynthetic pathway, 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR), provides the perfect target for screening new antibacterial substances. In this study, we tested the DXR inhibitory effect of 35 plant essential oils (EOs), which have long been recognized for their antimicrobial properties. The results show that the EOs of Zanbthoxylum bungeanum (ZB), Schizonepetae tenuifoliae (ST), Thymus quinquecostatus (TQ), Origanum vulgare (OV), and Eugenia caryophyllata (EC) displayed weak to medium inhibitory activity against DXR, with IC 50 values of 78 μg/mL, 65 μg/mL, 59 μg/mL, 48 μg/mL, and 37 μg/mL, respectively. GC-MS analyses of the above oils and further DXR inhibitory activity tests of their major components revealed that eugenol (EC) and carvacrol (TQ and OV) possess medium inhibition against the protein (68.3% and 55.6%, respectively, at a concentration of 20 μg/mL), whereas thymol (ST, TQ, and OV), carveol (ZB), and linalool (ZB, ST, and OV) only exhibited weak inhibition against DXR, at 20 μg/mL (23%-26%). The results add more details to the antimicrobial mechanisms of plant EOs, which could be very helpful in the direction of the reasonable use of EOs in the food industry and in the control of phytopathogenic microbials.

1-Deoxy- D -xylulose-5-phosphate reductoisomerase (DXR) in the non-mevalonate isoprene biosynthesis pathway is a target for developing antimalarial drugs. Fosmidomycin, a potent DXR inhibitor, showed safety as well as efficacy against P. falciparum malaria in clinical trials. Based on our previous quantitative structure activity relationship (QSAR) and crystallographic studies, several novel pyridine-containing fosmidomycin derivatives were designed, synthesized and found to be highly potent inhibitors of P. falciparum DXR ( Pf DXR) having K i values of 1.9 - 13 nM, with the best one being ~11× more active than fosmidomycin. These compounds also potently block the proliferation of multi-drug resistant P. falciparum with EC 50 values as low as 170 nM. A 2.3 Å crystal structure of Pf DXR in complex with one of the inhibitors is reported, showing the flexible loop of the protein undergoes conformational changes upon ligand binding and a hydrogen bond and favorable hydrophobic interactions between the pyridine group and Pf DXR account for the enhanced activity.