Elke Zameitat

Philipps-Universität Marburg, Marburg an der Lahn, Hesse, Germany

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Publications (6)26.7 Total impact

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    ABSTRACT: In all organisms the fourth catalytic step of the pyrimidine biosynthesis is driven by the flavoenzyme dihydroorotate dehydrogenase (DHODH, EC 1.3.99.11). Cytosolic DHODH of the established model organism Saccharomyces cerevisiae catalyses the oxidation of dihydroorotate to orotate and the reduction of fumarate to succinate. Here, we investigate the structure and mechanism of DHODH from S. cerevisiae and show that the recombinant ScDHODH exists as a homodimeric enzyme in vitro. Inhibition of ScDHODH by the reaction product was observed and kinetic studies disclosed affinity for orotate (K(ic)=7.7 microM; K(ic) is the competitive inhibition constant). The binding constant for orotate was measured through comparison of UV-visible spectra of the bound and unbound recombinant enzyme. The midpoint reduction potential of DHODH-bound flavine mononucleotide determined from analysis of spectral changes was -242 mV (vs. NHE) under anaerobic conditions. A search for alternative electron acceptors revealed that homologues such as mesaconate can be used as electron acceptors.
    FEMS Yeast Research 10/2007; 7(6):897-904. · 2.46 Impact Factor
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    ABSTRACT: Dihydroorotate dehydrogenase (DHODH; EC 1.3.99.11) is a central enzyme of pyrimidine biosynthesis and catalyzes the oxidation of dihydroorotate to orotate. DHODH is an important target for antiparasitic and cytostatic drugs since rapid cell proliferation often depends on the de novo synthesis of pyrimidine nucleotides. We have cloned the pyr4 gene encoding mitochondrial DHODH from the basidiomycetous plant pathogen Ustilago maydis. We were able to show that pyr4 contains a functional mitochondrial targeting signal. The deletion of pyr4 resulted in uracil auxotrophy, enhanced sensitivity to UV irradiation, and a loss of pathogenicity on corn plants. The biochemical characterization of purified U. maydis DHODH overproduced in Escherichia coli revealed that the U. maydis enzyme uses quinone electron acceptor Q6 and is resistant to several commonly used DHODH inhibitors. Here we show that the expression of the human DHODH gene fused to the U. maydis mitochondrial targeting signal is able to complement the auxotrophic phenotype of pyr4 mutants. While U. maydis wild-type cells were resistant to the DHODH inhibitor brequinar, strains expressing the human DHODH gene became sensitive to this cytostatic drug. Such engineered U. maydis strains can be used in sensitive in vivo assays for the development of novel drugs specifically targeted at either human or fungal DHODH.
    Applied and Environmental Microbiology 06/2007; 73(10):3371-9. · 3.95 Impact Factor
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    ABSTRACT: Candida albicans is the most prevalent yeast pathogen in humans, and recently it has become increasingly resistant to the current antifungal agents. In this study we investigated C. albicans dihydroorotate dehydrogenase (DHODH, EC 1.3.99.11), which catalyzes the fourth step of de novo pyrimidine synthesis, as a new target for controlling infection. We propose that the enzyme is a member of the DHODH family 2, which comprises mitochondrially bound enzymes, with quinone as the direct electron acceptor and oxygen as the final electron acceptor. Full-length DHODH and N-terminally truncated DHODH, which lacks the targeting sequence and the transmembrane domain, were subcloned from C. albicans, recombinantly expressed in Escherichia coli, purified, and characterized for their kinetics and substrate specificity. An inhibitor screening with 28 selected compounds was performed. Only the dianisidine derivative, redoxal, and the biphenyl quinoline-carboxylic acid derivative, brequinar sodium, which are known to be potent inhibitors of mammalian DHODH, markedly reduced C. albicans DHODH activity. This study provides a background for the development of antipyrimidines with high efficacy for decreasing in situ pyrimidine nucleotide pools in C. albicans.
    FEBS Journal 08/2006; 273(14):3183-91. · 4.25 Impact Factor
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    ABSTRACT: Genetic defects involving enzymes essential for pyrimidine nucleotide metabolism have provided new insights into the vital physiological functions of these molecules in addition to nucleic acid synthesis. Such aberrations disrupt the haematological, nervous or mitochondrial systems and can cause adverse reactions to analogue therapy. Regulation of pyrimidine pathways is also known to be disrupted in malignancies. Nine genetic defects have now been identified but only one is currently treatable. Diagnosis is aided by the accumulation of specific metabolites. Recently, progress has been made in understanding the molecular mechanisms underlying inborn errors of pyrimidine metabolism, together with the key clinical issues and the implications for the future development of novel drugs and therapeutic strategies.
    Trends in Molecular Medicine 10/2005; 11(9):430-7. · 9.57 Impact Factor
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    ABSTRACT: Genes for two structurally and functionally different dihydroorotate dehydrogenases (DHODHs, EC 1.3.99.11), catalyzing the fourth step of pyrimidine biosynthesis, have been previously found in yeast Saccharomyces kluyveri. One is closely related to the Schizosaccharomyces pombe mitochondrial family 2 enzymes, which use quinones as direct and oxygen as the final electron acceptor. The other one resembles the Saccharomyces cerevisiae cytosolic family 1A fumarate-utilizing DHODH. The DHODHs from S. kluyveri, Sch. pombe and S. cerevisiae, were expressed in Escherichia coli and compared for their biochemical properties and interaction with inhibitors. Benzoates as pyrimidine ring analogs were shown to be selective inhibitors of cytosolic DHODs. This unique property of Saccharomyces DHODHs could appoint DHODH as a species-specific target for novel anti-fungal therapeutics.
    FEBS Letters 07/2004; 568(1-3):129-34. · 3.58 Impact Factor
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    ABSTRACT: The ability to propagate under anaerobic conditions is an essential and unique trait of brewer's or baker's yeast ( Saccharomyces cervisiae). To understand the evolution of facultative anaerobiosis we studied the dependence of de novo pyrimidine biosynthesis, more precisely the fourth enzymic activity catalysed by dihydroorotate dehydrogenase (DHODase), on the enzymes of the respiratory chain in several yeast species. While the majority of yeasts possess a mitochondrial DHODase, Saccharomyces cerevisiae has a cytoplasmatic enzyme, whose activity is independent of the presence of oxygen. From the phylogenetic point of view, this enzyme is closely related to a bacterial DHODase from Lactococcus lactis. Here we show that S. kluyveri, which separated from the S. cerevisiae lineage more than 100 million years ago, represents an evolutionary intermediate, having both cytoplasmic and mitochondrial DHODases. We show that these two S. kluyveri enzymes, and their coding genes, differ in their dependence on the presence of oxygen. Only the cytoplasmic DHODase promotes growth in the absence of oxygen. Apparently a Saccharomyces yeast progenitor which had a eukaryotic-like mitochondrial DHODase acquired a bacterial gene for DHODase, which subsequently allowed cell growth gradually to become independent of oxygen.
    Molecular Genetics and Genomics 06/2004; 271(4):387-93. · 2.88 Impact Factor