Biosynthesis of isoprenoids: characterization of a functionally active recombinant 2-C-methyl-D-erythritol 4-phosphate cytidyltransferase (IspD) from Mycobacterium tuberculosis H37Rv.
ABSTRACT Tuberculosis, caused by Mycobacterium tuberculosis, continues to be one of the leading infectious diseases to humans. It is urgent to discover novel drug targets for the development of antitubercular agents. The 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway for isoprenoid biosynthesis has been considered as an attractive target for the discovery of novel antibiotics for its essentiality in bacteria and absence in mammals. MEP cytidyltransferase (IspD), the third-step enzyme of the pathway, catalyzes MEP and CTP to form 4-diphosphocytidyl-2-C-methylerythritol (CDP-ME) and PPi. In the work, ispD gene from M. tuberculosis H37Rv (MtIspD) was cloned and expressed. With N-terminal fusion of a histidine-tagged sequence, MtIspD could be purified to homogeneity by one-step nickel affinity chromatography. MtIspD exists as a homodimer with an apparent molecular mass of 52 kDa. Enzyme property analysis revealed that MtIspD has high specificity for pyrimidine bases and narrow divalent cation requirements, with maximal activity found in the presence of CTP and Mg(2+). The turnover number of MtIspD is 3.4 s(-1). The Km for MEP and CTP are 43 and 92 muM, respectively. Furthermore, MtIspD shows thermal instable above 50 degrees C. Circular dichroism spectra revealed that the alteration of tertiary conformation is closely related with sharp loss of enzyme activity at higher temperature. This study is expected to help better understand the features of IspD and provide useful information for the development of novel antibiotics to treat M. tuberculosis.
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ABSTRACT: Streptococcus pneumoniae is a major human pathogen associated with many diseases worldwide. Capsular polysaccharides (CPSs) are the major virulence factor. The biosynthetic pathway of D-arabinitol, which is present in the CPSs of several S. pneumoniae serotypes, has never been identified. In this study, the genes abpA (previously known as abp1) and abpB (previously known as abp2), which have previously been reported to be responsible for nucleoside diphosphate (NDP)-D-arabinitol (the nucleotide-activated form of D-arabinitol) synthesis, were cloned. The enzyme products were overexpressed, purified, and analyzed for their respective activities. Novel products produced by AbpA- and AbpB-catalyzing reactions were detected by capillary electrophoresis, and the structures of the products were elucidated using electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. As a result, abpA was identified to be a D-xylulose-5-phosphate cytidylyltransferase-encoding gene, responsible for the transfer of CTP to D-xylulose-5-phosphate (D-Xlu-5-P) to form CDP-D-xylulose, and abpB was characterized to be a CDP-D-xylulose reductase-encoding gene, responsible for the conversion of CDP-D-xylulose to CDP-D-arabinitol as the final product. The kinetic parameters of AbpA for the substrates D-Xlu-5-P and CTP and those of AbpB for the substrate CDP-D-xylulose and the cofactors NADH or NADPH were measured, and the effects of temperature, pH, and cations on the two enzymes were analyzed. This study confirmed the involvement of the genes abpA and abpB and their products in the biosynthetic pathway of CDP-D-arabinitol.Journal of bacteriology 02/2012; 194(8):1868-74. · 3.94 Impact Factor
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ABSTRACT: Isoprenoid biosynthesis is essential for cell survival. Over 35 000 isoprenoid molecules have been identified to date in the three domains of life (bacteria, archaea and eukaryotes), and these molecules are involved in a wide variety of vital biological functions. Isoprenoids may be synthesized via one of two independent nonhomologous pathways, the classical mevalonate pathway or the alternative 2C-methyl-D-erythritol 4-phosphate (MEP) pathway. Given that isoprenoids are indispensable, enzymes involved in their production have been investigated as potential drug targets. It has also been observed that the MEP pathway intermediate 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (HMB-PP) can activate human Vγ9/Vδ2 T cells. Herein we review isoprenoid biosynthesis in bacterial pathogens. The role of isoprenoid biosynthesis pathways in host-pathogen interactions (virulence potential and immune stimulation) is examined. Finally, the design of antimicrobial drugs that target isoprenoid biosynthesis pathways is discussed.Microbiology 03/2012; 158(Pt 6):1389-401. · 3.06 Impact Factor
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ABSTRACT: Streptococcus pneumoniae is a major human pathogen associated with diseases worldwide. The capsular polysaccharides (CPS) are considered a major virulence factor and are targets for a vaccine. D-mannitol was found to be present in the CPS of several S. pneumoniae serotypes. Two genes, mnp1 and mnp2, which are located in the CPS gene cluster were proposed to be responsible for the synthesis of NDP-D-mannitol (the nucleotide activated form of D-mannitol). However, the pathway has never been identified by experimental methods and we aimed to characterize it in the present study. To achieve this, the two genes, mnp1 and mnp2, were cloned and the gene products were overexpressed, purified, and analyzed in vitro for their respective enzymatic activities. Products of reactions catalyzed by Mnp1 and Mnp2 were detected by capillary electrophoresis, and validated using electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. We show that Mnp1 is responsible for the transfer of CMP from CTP to D-fructose-6-phosphate to form CDP-D-fructose while Mnp2 catalyzed the conversion of CDP-D-fructose to CDP-D-mannitol. Therefore, Mnp1 (renamed as mnpA) was identified as D-fructose-6-phosphate cytidylyltransferase encoding gene, and mnp2 (renamed as mnpB) as a CDP-D-fructose reductase encoding gene. The kinetics of Mnp1 for the substrate (D-fructose-6-phosphate and CTP) and of Mnp2 for the substrate (CDP-D-fructose) and the cofactor (NADH or NADPH) fitted the Michaelis-Menten model. The effects of temperature, pH, and cations on the two enzymes were analyzed. This is the first time that the biosynthetic pathway of CDP-D-mannitol has been identified biochemically.Glycobiology 07/2012; · 3.54 Impact Factor