A enzima hidrolase de nucleosídeos purínicos de Mycobacterium tuberculosis H37RV : caracterização bioquímica, termodinâmica e estudos de nocaute gênico

Abstract

Human tuberculosis (TB) is a major global health threat. The disease s increasing prevalence, coupled with the emergence of drug-resistant strains and the devastating effects of co-infection with human immunodeficiency virus (HIV) indicate an urgent need for the development of new and more efficient drugs to combat the disease's causative agent, Mycobacterium tuberculosis. Global health authorities have also begun to recognize the need for drugs that can kill the mycobacteria in its different physiological states including but not limited to latent TB infection. A more comprehensive understanding of the bacilli's nucleotide metabolic pathways, in particular purine and pyrimidine salvage pathways, could aid in the development of new therapeutic strategies to reduce the incidence of TB worldwide. Nucleoside hydrolase catalyzes the irreversible hydrolysis of N-glycosidic bond of ribonucleosides, forming α-D-ribose and the corresponding base. This work describes the amplification, cloning, expression and purification of the iunH-encoding purine nucleoside hydrolase from M. tuberculosis (MtIAGU-NH). Results from steadystate kinetic experiments indicate that MtIAGU-NH has broad substrate specificity, accepting inosine, adenosine, guanosine, and uridine as substrates. Kinetics analysis utilizing fluorescence spectroscopy of ribose binding to MtIAGU-NH suggests that prior to ligand association there are two pre-existing forms of the enzyme. We determined the intracellular concentrations of inosine, uridine, hypoxanthine, and uracil as well as the reaction s thermodynamic parameters. Thermodynamic activation parameters (Ea, ΔG#, ΔS#, ΔH#) for the MtIAGU-NH-catalyzed chemical reaction, along with results from mass spectrometry, isothermal titration calorimetry (ITC), pH-rate profile experiments, multiple sequence alignment, and molecular docking experiments are also presented. Knockout experiments of the iunH gene indicate that this gene is not essential for the growth of M. tuberculosis H37Rv underutilized experimental conditions. The data presented here contribute to our understanding of MtIAGU-NH, providing a solid basis for the development of efficient prophylactic and therapeutic strategies to reduce the global incidence of TB.