Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: UMLS:C0024530 (malaria)
44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The conversion of dihydroorotate to orotate, one of the key reactions in the de novo pyrimidine biosynthetic pathway, has been studied in a number of parasitic protozoa. Enzyme activities capable of carrying out this reaction were detected in six members of the Kinetoplastida (Trypanosoma brucei, Trypanosoma congolense, Trypanosoma vivax, Trypanosoma lewisi, Trypanosoma cruzi, Leishmania enriettii) and three members of the genus Plasmodium (P. knowlesi, P. berghei, P. gallinaceum). The mechanism of the reaction in the two groups of protozoa were quite distinct. In the Kinetoplastida, the enzyme is an hydroxylase which occurs in the soluble fraction of the cell and probably requires tetrahydrobiopterin for activity. In contrast, in Plasmodium, the enzyme is a dehydrogenase which is particulate, probably mitochondrial, and intimately connected to the electron transport chain to which it passes electrons directly, probably at the ubiquinone level. Neither activity is regulated by fully formed pyrimidines. The enzyme in Plasmodium is similar in mechanism to the isofunctional mammalian enzyme. However, since malarial ubiquinones are apparently different from those in the mammal and since menoctone, which is active in vivo in experimental malaria, is a good inhibitor of the malarial enzyme, it could represent a useful target for chemotherapeutic attack. The enzyme in the Kinetoplastida is quite distinct from that in the mammal so that it too apparently falls into this category, though none of the currently used antitrypanosomal drugs appears to block it activity at physiological concentrations.
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PMID:Conversion of dihydroorotate to orotate in parasitic protozoa. 21 38

Dihydroorotate dehydrogenase (DHODase) has been purified 400-fold from the rodent malaria parasite Plasmodium berghei to apparent homogeneity by Triton X-100 solubilization followed by anion-exchange, Cibacron Blue F3GA-agarose affinity, and gel filtration chromatography. The purified enzyme has a molecular mass of 52 +/- 2 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and of 55 +/- 6 kDa by gel filtration chromatography, and it has a pI of 8.2. It is active in monomeric form, contains 2.022 mol of iron and 1.602 acid-labile sulfurs per mole of enzyme, and does not contain a flavin cofactor. The purified DHODase exhibits optimal activity at pH 8.0 in the presence of the ubiquinone coenzyme CoQ6, CoQ7, CoQ9, or CoQ10. The Km values for L-DHO and CoQ6 are 7.9 +/- 2.5 microM and 21.6 +/- 5.5 microM, respectively. The kcat values for both substrates are 11.44 min-1 and 11.70 min-1, respectively. The reaction product orotate and an orotate analogue, 5-fluoroorotate, are competitive inhibitors of the enzyme-catalyzed reaction with Ki values of 30.5 microM and 34.9 microM, respectively. The requirement of the long-chain ubiquinones for activity supports the hypothesis of the linkage of pyrimidine biosynthesis to the electron transport system and oxygen utilization in malaria by DHODase via ubiquinones [Gutteridge, W. E., Dave, D., & Richards, W. H. G. (1979) Biochim. Biophys. Acta 582, 390-401].
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PMID:Purification and characterization of dihydroorotate dehydrogenase from the rodent malaria parasite Plasmodium berghei. 184 78

Mitochondria of malaria parasites generate a membrane potential through an electron transport system that is a possible target of primaquine and a new anti-malarial drug, atovaquone. However, little information is available for conclusive understanding of the respiratory chain in Plasmodium mitochondria. In the present study, we cloned and characterized from Plasmodium falciparum the genes for the catalytic subunits, SDHA for the flavoprotein (Fp) and SDHB for iron-sulfur protein (Ip), of succinate-ubiquinone oxidoreductase (complex II), which is a marker enzyme for mitochondria and links the TCA cycle and respiratory chain directly. Each of the two genes contains a single open reading frame (ORF), which are located on different chromosomes, 1860 nucleotides on chromosome 10 for SDHA and 963 nucleotides on chromosome 12 for SDHB. The expression of these genes in asynchronous erythrocytic stage cells was confirmed by observation of 3.3 and 2.4 kb transcripts from the SDHA and SDHB genes, respectively. The SDHA and SDHB genes encode proteins of 620 (Fp) and 321 (Ip) amino acids with molecular masses of 69.2 and 37.8 kDa, respectively. A mitochondrial presequence essential for the import of mitochondrial proteins encoded by nuclear DNA, as well as almost all the conserved amino acids indispensable for substrate binding and the catalytic reaction were found in these peptides, indicating the functional importance of this enzyme in the parasite. Interestingly, a P. falciparum-specific insertion and a unicellular organism-specific deletion were found in the amino acid sequence of Fp. This is the first report of the primary structure of the protozoan succinate dehydrogenase.
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PMID:Succinate dehydrogenase in Plasmodium falciparum mitochondria: molecular characterization of the SDHA and SDHB genes for the catalytic subunits, the flavoprotein (Fp) and iron-sulfur (Ip) subunits. 1077 96

Drug resistance in malarial parasites has become a major obstacle in the control of the disease. Strategies are urgently needed to control the development of resistance and to possibly reverse existing resistance. One key element required to reverse malaria drug resistance is for the parasites to "pay" a biological "cost" or suffer a loss of fitness when acquiring resistance to antimalarial drugs. Such a situation would be a disadvantage to the resistant parasites in the absence of drug pressure. We compared here the relative fitness of atovaquone-resistant Plasmodium falciparum K1 clones with single and double base mutations in their cytochrome b genes to their parent clones during erythrocytic stages in the absence of drug pressure. We found that the double amino acid mutation (M133I and G280D) is associated with a 5 to 9% loss of fitness and that the single amino acid change of M133I did not result in any detectable loss of fitness. Molecular modeling of the interaction of P. falciparum cytochrome b with ubiquinone led to the prediction that a loss of fitness of the malaria parasites would result from the G280D mutation due to its close proximity to the putative ubiquinone-binding site. This appears to have resulted in a weakening of the cytochrome b-ubiquinone complex, thereby causing the electron transport chain to become less efficient. Our results suggest that the prevalence of resistant parasites may decrease after the drug usage is discontinued.
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PMID:Mutations in cytochrome b resulting in atovaquone resistance are associated with loss of fitness in Plasmodium falciparum. 1212 15

Pyrimidine biosynthesis presents an attractive drug target in malaria parasites due to the absence of a pyrimidine salvage pathway. A set of compounds designed to inhibit the Plasmodium falciparum pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase (PfDHODH) was synthesized. PfDHODH-specific inhibitors with low nanomolar binding affinities were identified that bind in the N-terminal hydrophobic channel of dihydroorotate dehydrogenase, the presumed site of ubiquinone binding during oxidation of dihydroorotate to orotate. These compounds also prevented growth of cultured parasites at low micromolar concentrations. Models that suggest the mode of inhibitor binding is based on shape complementarity, matching hydrophobic regions of inhibitor and enzyme, and interaction of inhibitors with amino acid residues F188, H185, and R265 are supported by mutagenesis data. These results further highlight PfDHODH as a promising new target for chemotherapeutic intervention in prevention of malaria and provide better understanding of the factors that determine specificity over human dihydroorotate dehydrogenase.
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PMID:Design and synthesis of potent inhibitors of the malaria parasite dihydroorotate dehydrogenase. 1722 60

The survival of the malaria parasite Plasmodium falciparum is dependent upon the de novo biosynthesis of pyrimidines. P. falciparum dihydroorotate dehydrogenase (PfDHODH) catalyzes the fourth step in this pathway in an FMN-dependent reaction. The full-length enzyme is associated with the inner mitochondrial membrane, where ubiquinone (CoQ) serves as the terminal electron acceptor. The lipophilic nature of the co-substrate suggests that electron transfer to CoQ occurs at the two-dimensional lipid-solution interface. Here we show that PfDHODH associates with liposomes even in the absence of the N-terminal transmembrane-spanning domain. The association of a series of ubiquinone substrates with detergent micelles was studied by isothermal titration calorimetry, and the data reveal that CoQ analogs with long decyl (CoQ(D)) or geranyl (CoQ(2)) tails partition into detergent micelles, whereas that with a short prenyl tail (CoQ(1)) remains in solution. PfDHODH-catalyzed reduction of CoQ(D) and CoQ(2), but not CoQ(1), is stimulated as detergent concentrations (Tween 80 or Triton X-100) are increased up to their critical micelle concentrations, beyond which activity declines. Steady-state kinetic data acquired for the reaction with CoQ(D) and CoQ(2) in substrate-detergent mixed micelles fit well to a surface dilution kinetic model. In contrast, the data for CoQ(1) as a substrate were well described by solution steady-state kinetics. Our results suggest that the partitioning of lipophilic ubiquinone analogues into detergent micelles needs to be an important consideration in the kinetic analysis of enzymes that utilize these substrates.
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PMID:Detergent-dependent kinetics of truncated Plasmodium falciparum dihydroorotate dehydrogenase. 1732 50

The origin of all mitochondria can be traced to the symbiotic arrangement that resulted in the emergence of eukaryotes in a world that was exclusively populated by prokaryotes. This arrangement, however, has been in continuous genetic flux: the varying degrees of gene loss and transfer from the mitochondrial genome in different eukaryotic lineages seem to signify an ongoing 'conflict' between the host and the symbiont. Eukaryotic parasites belonging to the phylum Apicomplexa provide an excellent example to support this view. These organisms contain the smallest mitochondrial genomes known, with an organization that differs among various genera; one genus, Cryptosporidium, seems to have lost the entire mitochondrial genome. Here we show that erythrocytic stages of the human malaria parasite Plasmodium falciparum seem to maintain an active mitochondrial electron transport chain to serve just one metabolic function: regeneration of ubiquinone required as the electron acceptor for dihydroorotate dehydrogenase, an essential enzyme for pyrimidine biosynthesis. Transgenic P. falciparum parasites expressing Saccharomyces cerevisiae dihydroorotate dehydrogenase, which does not require ubiquinone as an electron acceptor, were completely resistant to inhibitors of mitochondrial electron transport. Maintenance of mitochondrial membrane potential, however, was essential in these parasites, as indicated by their hypersensitivity to proguanil, a drug that collapsed the membrane potential in the presence of electron transport inhibitors. Thus, acquisition of just one enzyme can render mitochondrial electron transport nonessential in erythrocytic stages of P. falciparum.
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PMID:Specific role of mitochondrial electron transport in blood-stage Plasmodium falciparum. 1733 44

Pyrimidine biosynthesis is an attractive drug target in a variety of organisms, including humans and the malaria parasite Plasmodium falciparum. Dihydroorotate dehydrogenase, an enzyme catalyzing the only redox reaction of the pyrimidine biosynthesis pathway, is a well-characterized target for chemotherapeutical intervention. In this study, we have applied SPROUT-LeadOpt, a software package for structure-based drug discovery and lead optimization, to improve the binding of the active metabolite of the anti-inflammatory drug leflunomide to the target cavities of the P. falciparum and human dihydroorotate dehydrogenases. Following synthesis of a library of compounds based upon the SPROUT-optimized molecular scaffolds, a series of inhibitors generally showing good inhibitory activity was obtained, in keeping with the SPROUT-LeadOpt predictions. Furthermore, cocrystal structures of five of these SPROUT-designed inhibitors bound in the ubiquinone binding cavity of the human dihydroorotate dehydrogenase are also analyzed.
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PMID:Structure-based design, synthesis, and characterization of inhibitors of human and Plasmodium falciparum dihydroorotate dehydrogenases. 1935 Nov 52

Dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme that catalyzes fourth reaction of pyrimidine de-novo synthesis. Pyrimidine bases are essential for cellular metabolism and cell growth, and are considered as important precursors used in DNA (thymine and cytosine), RNA (uracil and cytosine), glycoproteins and phospholipids biosynthesis. The significance of pyrimidines biosynthesis in DNA and RNA makes them ideal targets for pharmacological intervention. Inhibitors of DHODH have proven efficacy for the treatment of malaria, autoimmune diseases, cancer, rheumatoid arthritis and psoriasis. Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) represents an important target for the treatment of malaria. Many of the clinically relevant anti-tumor and immunosuppressive drugs target human dihydroorotate dehydrogenase (hDHODH), and the two most promising drugs of such kinds are brequinar (antitumor and immunosuppressive) and leflunomide (immunosuppressive). X-ray crystal structures of DHODH in complex with inhibitors reveal common binding region shared by each inhibitor. A number of compounds are identified by high-throughput screening (HTS) of chemical libraries and structure-based computational approaches as selective DHODH inhibitors. Based upon the understanding of molecular interaction of DHODH inhibitors with binding site, some of the common structural features are identified like ability of compounds to interact with ubiquinone (CoQ) binding site and substituents linked to a variety of heterocyclic and heteroaromatic rings responsible for H-bonding with binding site. These findings provide new approaches to design DHODH inhibitors and highlights DHODH as a target for chemotherapeutics. This review is mainly focused on the recent developments in the medicinal chemistry and therapeutic potential of DHODH inhibitors as a target for drug discovery.
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PMID:Recent developments in the medicinal chemistry and therapeutic potential of dihydroorotate dehydrogenase (DHODH) inhibitors. 2186 7

The development of new drugs is one strategy for malaria control. Biochemical pathways localised in the apicoplast of the parasite, such as the synthesis of isoprenic precursors, are excellent targets because they are different or absent in the human host. Isoprenoids are a large and highly diverse group of natural products with many functions and their synthesis is essential for the parasite's survival. During the last few years, the genes, enzymes, intermediates and mechanisms of this biosynthetic route have been elucidated. In this review, we comment on some aspects of the methylerythritol phosphate pathway and discuss the presence of diverse isoprenic products such as dolichol, ubiquinone, carotenoids, menaquinone and isoprenylated proteins, which are biosynthesised during the intraerythrocytic stages of Plasmodium falciparum.
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PMID:Isoprenoid biosynthesis in the erythrocytic stages of Plasmodium falciparum. 2188 68


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