Characterisation of iunH gene knockout strain from Mycobacterium tuberculosis.

BACKGROUND: Tuberculosis (TB) is an infectious disease caused mainly by the bacillus Mycobacterium tuberculosis. The better understanding of important metabolic pathways from M. tuberculosis can contribute to the development of novel therapeutic and prophylactic strategies to combat TB. Nucleoside hydrolase (MtIAGU-NH), encoded by iunH gene (Rv3393), is an enzyme from purine salvage pathway in M. tuberculosis. MtIAGU-NH accepts inosine, adenosine, guanosine, and uridine as substrates, which may point to a pivotal metabolic role. OBJECTIVES: Our aim was to construct a M. tuberculosis knockout strain for iunH gene, to evaluate in vitro growth and the effect of iunH deletion in M. tuberculosis in non-activated and activated macrophages models of infection. METHODS: A M. tuberculosis knockout strain for iunH gene was obtained by allelic replacement, using pPR27xylE plasmid. The complemented strain was constructed by the transformation of the knockout strain with pNIP40::iunH. MtIAGU-NH expression was analysed by Western blot and LC-MS/MS. In vitro growth was evaluated in Sauton's medium. Bacterial load of non-activated and interferon-γ activated RAW 264.7 cells infected with knockout strain was compared with wild-type and complemented strains. FINDINGS: Western blot and LC-MS/MS validated iunH deletion at protein level. The iunH knockout led to a delay in M. tuberculosis growth kinetics in Sauton's medium during log phase, but did not affect bases and nucleosides pool in vitro. No significant difference in bacterial load of knockout strain was observed when compared with both wild-type and complemented strains after infection of non-activated and interferon-γ activated RAW 264.7 cells. MAIN CONCLUSION: The disruption of iunH gene does not influence M. tuberculosis growth in both non-activated and activated RAW 264.7 cells, which show that iunH gene is not important for macrophage invasion and virulence. Our results indicated that MtIAGU-NH is not a target for drug development.

Biochemical characterization of recombinant nucleoside hydrolase from Mycobacterium tuberculosis H37Rv.

Tuberculosis (TB) is a major global health threat. There is a need for the development of more efficient drugs for the sterilization of the disease's causative agent, Mycobacterium tuberculosis (MTB). A more comprehensive understanding of the bacilli's nucleotide metabolic pathways could aid in the development of new anti-mycobacterial drugs. Here we describe expression and purification of recombinant iunH-encoded nucleoside hydrolase from MTB (MtIAGU-NH). Glutaraldehyde cross-linking results indicate that MtIAGU-NH predominates as a monomer, presenting varied oligomeric states depending upon binding of ligands. Steady-state kinetics results show that MtIAGU-NH has broad substrate specificity, accepting inosine, adenosine, guanosine, and uridine as substrates. Inosine and adenosine displayed positive homotropic cooperativity kinetics, whereas guanosine and uridine displayed hyperbolic saturation curves. Measurements of kinetics of ribose binding to MtIAGU-NH by fluorescence spectroscopy suggest two pre-existing forms of enzyme prior to ligand association. The intracellular concentrations of inosine, uridine, hypoxanthine, and uracil were determined and thermodynamic parameters estimated. Thermodynamic activation parameters (Ea, ΔG(#), ΔS(#), ΔH(#)) for MtIAGU-NH-catalyzed chemical reaction are presented. Results from mass spectrometry, isothermal titration calorimetry (ITC), pH-rate profile experiment, multiple sequence alignment, and molecular docking experiments are also presented. These data should contribute to our understanding of the biological role played by MtIAGU-NH.

Homogeneous recombinant Mycobacterium tuberculosis shikimate dehydrogenase production: an essential step towards target-based drug design.

Mycobacterium tuberculosis shikimate dehydrogenase (MtbSD) catalyzes the forth reaction in the shikimate pathway. Here we describe production of K69A, K69H, K69I, K69Q, D105A, and D105N mutant proteins. Screening of several conditions was performed to optimize MtbSD production yield, and an improved purification protocol to obtain homogeneous MtbSD is presented. The rational design of new antitubercular drugs hinges on the availability of M. tuberculosis proteins. Our results show that optimization of expression, disruption, and purification protocols resulted in a higher yield of functional MtbSD enzyme.