Targeting Genome Integrity in Mycobacterium Tuberculosis: From Nucleotide Synthesis to DNA Replication and Repair

Abstract

Mycobacterium tuberculosis (MTB) is the causative agent of tuberculosis (TB), an ancient disease which still today causes 1.4 million deaths worldwide per year. Long-term, multi-agent anti-tubercular regimens can lead to the anticipated non-compliance of the patient and increased drug toxicity, which in turn can contribute to the emergence of drug-resistant MTB strains that are not susceptible to first- and second-line available drugs. Hence, there is an urgent need for innovative antitubercular drugs and vaccines. A number of biochemical processes are required to maintain the correct homeostasis of DNA metabolism in all organisms. Here we focused on reviewing our current knowledge and understanding of biochemical and structural aspects of relevance for drug discovery, for some such processes in MTB, and particularly DNA synthesis, synthesis of its nucleotide precursors, and processes that guarantee DNA integrity and genome stability. Overall, the area of drug discovery in DNA metabolism appears very much alive, rich of investigations and promising with respect to new antitubercular drug candidates. However, the complexity of molecular events that occur in DNA metabolic processes requires an accurate characterization of mechanistic details in order to avoid major flaws, and therefore the failure, of drug discovery approaches targeting genome integrity.

Keywords: DNA repair; DNA replication; Mycobacterium tuberculosis; antitubercular drugs; novel drug targets; nucleotide synthesis.

Figure 1

Schematic overview of purine and pyrimidine metabolism. Ribose-5-phosphate and carbamoyl-phosphate are the starting points of purine and pyrimidine biosynthetic pathways, respectively. Key intermediates, across de novo biosynthesis and salvage pathways, are highlighted in gray boxes. End-products of purine and pyrimidine catabolism (i.e., uric acid and β-alanine) are in white boxes. Enzymes discussed in the manuscript are depicted in red. PRPP, 5-phosphorybosyl-1-pyrophosphate; OPRT, orotate phosphoribosyltransfrase, PrsA, PRPP synthetase; S-AMP, adenylosuccinate; SAICAR: succinylaminoimidazole carboxamide ribotide.

Figure 2

Macromolecular complexes assembled on the DNA at the replication fork. Helicase-primase complex constitutes the so-called primosome that binds the lagging strand DNA, unwinding duplex DNA while it synthesizes RNA primers for the lagging strand polymerase. DNA synthesis on both strands is catalyzed by a holoenzyme complex formed by the polymerase and a processivity β-clamp. The clamp is loaded onto the DNA by the clamp loader complex. The leading and lagging strand holoenzymes interact to form a dimer. Single-stranded DNA resulting from helicase activity is coated with single-stranded DNA-binding protein (SSB).