Topoisomerase I from Pseudomonas aeruginosa can act as a drug target for fluoroquinolones

Abstract

Despite the recognition of Pseudomonas aeruginosa as the most prevalent opportunistic human pathogen causing life‐threatening conditions in immunocompromised patients with neutropenic cancer and bone marrow transplant, little has been accomplished to resolve the infection due to the intrinsic resistance to a wide variety of antimicrobial agents and active efflux pumps in P. aeruginosa. P. aeruginosa encodes a topoisomerase (PAT) with sequence similarity to the eukaryotic type IB topoisomerase from vaccinia virus (VT). The human topoisomerases are effective molecular targets for many antitumor drugs. The VT is also a model system to study the much larger human topoisomerase. Binding the duplex DNA, PAT forms a covalent protein DNA complex where the active site tyrosine attacks a phosphodiester bond on one of the DNA strands. Residues in the active site are conserved, notably Tyr292 which is predicted to form the covalent bond to the DNA, and substitution of the Tyr292 renders the enzyme inactive. Fluoroquinolones are antibacterial agents in clinical use as inhibitors of type II topoisomerases. Sparfloxacin, a synthetic fluoroquinolone, inhibits PAT at high concentrations, but other drugs belonging to this family do not. We therefore hypothesize that PAT could act as a structurally optimized target for fluoroquinolones that target the covalent complex between the DNA and the PAT.