Understanding DNA transport by topo IV and gyrase to counter antimicrobial resistance

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Antibiotic resistance is a worldwide problem and a major challenge for the treatment of infection. Bacteria are becoming resistant to our most important antibiotics jeopardising even straightforward medical procedures. One serious threat is posed by Streptococcus pneumoniae, a global pathogen that causes life-threatening pneumonia and meningitis in childern and the elderly. Increasingly, S. pneumoniae isolates are found to be resistant to penicillins and to fluoroquinolones, which are key members of our antibiotic arsenal. It is known that fluoroquinolones interfere with DNA breakage by gyrase and topoisomerase (topo) IV, two enzymes that untangle DNA and are required for bacterial DNA replication and growth. Remarkably, these enzymes make a transient break in DNA and cross another DNA through the break. By this means, gyrase can remove twists when DNA is copied in the cell, and topo IV can unlink tangled chromosomes ahead of cell division. By using X-ray crystallography to solve the structure of these enzymes bound to DNA and fluoroquinolones, we now understand in detail how quinolones bind and trap the DNA break and how resistance arises. However, almost nothing is known about the nature of the transported DNA, how it is recognised, captured and then crossed through the DNA break. To fill this gap in knowledge, and guided by our recent structure of a topo IV-transport DNA complex, we shall use a combination of techniques including X-ray crystallography, cryo-electron microscopy, fluorescence and protein biochemistry to establish the mechanism of DNA transport by topo IV and gyrase from S. pneumoniae and from Klebsiella pneumoniae, another pathogen highly resistant to quinolones. Completion of the work will be a major contribution in understanding these fascinating molecular machines and will provide new opportunites for design of new drugs that overcome resistance by targeting DNA transport. New drugs will be essential in addressing the global emergency of antimicrobial resistance.