Structural and Computational Analysis of <i>Pseudomonas aeruginosa</i> DNA Gyrase Reveals Molecular Characteristics That May Contribute to Ciprofloxacin Resistance

<i>Pseudomonas aeruginosa</i> is considered a priority pathogen by the World Health Organization due to its resistance to antibiotics. Isolates resistant to ciprofloxacin (CPFX), a bactericide commonly used against <i>P. aeruginosa</i>, usually carry the mutations T83I or D87N in the GyrA subunit of the DNA gyrase. Yet, the molecular mechanisms by which these mutations confer CPFX-resistance to <i>P. aeruginosa</i> are unknown. Here we solved the crystal structure of the <i>P. aeruginosa</i> gyrase catalytic cleavage core and used it to carry out molecular dynamic (MD) simulations of CPFX-gyrase binding in the wild-type as well as the T83I and the D87N mutant systems. Our results show that DNA plays the most prominent role in maintaining the CPFX-bound conformation, with no appreciable contributions from Thr83 or Asp87. Interestingly, we found a solvent cavity adjacent to these residues that may provide CPFX access to the active site. Interaction energy analysis using Umbrella Sampling indicates that Thr83 and Asp87 may influence CPFX trajectory during binding. In the mutant systems, the attractive potential decreases, which may hinder CPFX accessing the binding site. These results shed light on <i>P. aeruginosa</i> resistance to CPFX and may help provide a methodology to identify new therapeutic agents to target fluoroquinolone resistant bacteria.