Browsing by Author "Pietersen, R. D."

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    Differential inhibition of adenylylated and deadenylylated forms of M. tuberculosis glutamine synthetase as a drug discovery platform
    (Public Library of Science, 2017-03-29) Theron, A.; Roth, R. L.; Hoppe, H.; Parkinson, C.; Van Der Westhuyzen, C. W.; Stoychev, S.; Wiid, I.; Pietersen, R. D.; Baker, B.; Kenyon, C. P.
    ENGLISH ABSTRACT: Glutamine synthetase is a ubiquitous central enzyme in nitrogen metabolism that is controlled by up to four regulatory mechanisms, including adenylylation of some or all of the twelve subunits by adenylyl transferase. It is considered a potential therapeutic target for the treatment of tuberculosis, being essential for the growth of Mycobacterium tuberculosis, and is found extracellularly only in the pathogenic Mycobacterium strains. Human glutamine synthetase is not regulated by the adenylylation mechanism, so the adenylylated form of bacterial glutamine synthetase is of particular interest. Previously published reports show that, when M. tuberculosis glutamine synthetase is expressed in Escherichia coli, the E. coli adenylyl transferase does not optimally adenylylate the M. tuberculosis glutamine synthetase. Here, we demonstrate the production of soluble adenylylated M. tuberulosis glutamine synthetase in E. coli by the co-expression of M. tuberculosis glutamine synthetase and M. tuberculosis adenylyl transferase. The differential inhibition of adenylylated M. tuberulosis glutamine synthetase and deadenylylated M. tuberulosis glutamine synthetase by ATP based scaffold inhibitors are reported. Compounds selected on the basis of their enzyme inhibition were also shown to inhibit M. tuberculosis in the BACTEC 460TB™ assay as well as the intracellular inhibition of M. tuberculosis in a mouse bone-marrow derived macrophage assay.
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    Distinct host-immune response toward species related intracellular mycobacterial killing : a transcriptomic study
    (Taylor & Francis, 2020) Madhvi, Abhilasha; Mishra, Hridesh; Chegoua, Novel N.; Tromp, Gerard; Van Heerden, Carel J.; Pietersen, R. D.; Leisching, Gina; Baker, Bienyameen
    The comparison of the host immune response when challenged with pathogenic and nonpatho- genic species of mycobacteria can provide answers to the unresolved question of how pathogens subvert or inhibit an effective response. We infected human monocyte derived macrophages (hMDMs) with different species of mycobacteria, in increasing order of pathogenicity, i.e. M. smegmatis, M. bovis BCG, and M. tuberculosis R179 that had been cultured in the absence of detergents. RNA was isolated post-infection and transcriptomic analysis using amplicons (Ampliseq) revealed 274 differentially expressed genes (DEGs) across three species, out of which we selected 19 DEGs for further validation. We used qRT-PCR to confirm the differential expression of 19 DEGs. We studied biological network through Ingenuity Pathway Analysis® (IPA) which revealed up-regulated pathways of the interferon and interleukin family related to the killing of M. smegmatis. Apart from interferon and interleukin family, we found one up-regulated (EIF2AK2) and two down-regulated (MT1A and TRIB3) genes as unique potential targets found by Ampliseq and qRT-PCR which may be involved in the intracellular mycobacterial killing. The roles of these genes have not previously been described in tuberculosis. Multiplex ELISA of culture supernatants showed increased host immune response toward M. smegmatis as compared to M. bovis BCG and M.tb R179. These results enhance our understanding of host immune response against M.tb infection.