Structural basis of topoisomerase targeting by delafloxacin
- Shabir Najmudin
- Xiao-Su Pan
- Beijia Wang
- Lata Govada
- Naomi E. Chayen
- Noelia Rubio
- Milo S. P. Shaffer
- Henry S. Rzepa
- L. Mark Fisher
- Mark R. Sanderson
2025-07-01
Delafloxacin is a potent anionic fluoroquinolone approved for the treatment of respiratory infections that acts by trapping the DNA cleavage complexes of bacterial topoisomerase IV and gyrase. Its N-1-pyridinyl-, C-7-azetidinyl- and C-8-chlorine substituents confer enhanced antibiotic activity against bacteria resistant to other fluoroquinolones, but its mode of action is unclear. Here we present the X-ray crystal structures of a delafloxacin-DNA cleavage complex obtained by co-crystallization with Streptococcus pneumoniae topo IV using a graphene nucleant and solved at 2.0 and 2.4 Å resolution. The two Mg 2+ -chelated delafloxacin molecules intercalated at the DNA cleavage site are bound in an unusual conformation involving interacting out-of-plane N-1-aromatic- and C-8-chlorine- substituents. The unprecedented resolution allows comprehensive imaging of water-metal ion links integrating enzyme and DNA through drug-bound and active-site Mg 2+ ions plus the discovery of enzyme-bound K + ions. Our studies on delafloxacin action suggest that intrinsic target affinity contributes to its activity against quinolone-resistant bacteria.