title: Topoisomerase IV catalysis and the mechanism of quinolone action.
abstract: Topoisomerase IV is a bacterial type II topoisomerase that is essential for proper chromosome segregation and is a target for quinolone-based antimicrobial agents. Despite the importance of this enzyme to the survival of prokaryotic cells and to the treatment of bacterial infections, relatively little is known about the details of its catalytic mechanism or the basis by which quinolones alter its enzymatic functions. Therefore, a series of experiments that analyzed individual steps of the topoisomerase IV catalytic cycle were undertaken to address these critical mechanistic issues. The following conclusions were drawn. First, equilibrium levels of DNA cleavage mediated by the bacterial enzyme were considerably (>10-fold) higher than those observed with its eukaryotic counterparts. To a large extent, this reflected decreased rates of DNA religation. Second, the preference of topoisomerase IV for catalyzing DNA decatenation over relaxation reflects increased rates of strand passage and enzyme recycling rather than a heightened recognition of intermolecular DNA helices. Third, quinolones stimulate topoisomerase IV-mediated DNA cleavage both by increasing rates of DNA scission and by inhibiting religation of cleaved DNA. Finally, quinolones inhibit the overall catalytic activity of topoisomerase IV primarily by interfering with enzyme-ATP interactions.
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
authors.forename: V E
authors.initials: VE
authors.lastname: Anderson
authors.forename: T D
authors.initials: TD
authors.lastname: Gootz
authors.forename: N
authors.initials: N
authors.lastname: Osheroff
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D002384:Catalysis; D002939:Ciprofloxacin / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004789:Enzyme Activation; D006868:Hydrolysis; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D000890:Anti-Infective Agents; D011994:Recombinant Proteins; D002939:Ciprofloxacin; D004247:DNA; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II