Quinolone binding to DNA is mediated by magnesium ions.

Abstract

The binding of plasmid DNA to norfloxacin, a quinolone antibacterial agent, was investigated by fluorescence, electrophoretic DNA unwinding, and affinity chromatography techniques. The amount of quinolone bound to DNA was modulated by the concentration of Mg2+. No interaction was evident in the absence of Mg2+ or in the presence of an excess of Mg2+, whereas maximum binding was observed at a Mg2+ concentration of 1-2 mM. The experimental data can be fitted to the formation of three types of Mg adducts: a binary adduct with norfloxacin and Mg2+, a binary adduct with DNA and Mg2+, and a ternary adduct with quinolone, plasmid, and Mg2+. We propose a model for the ternary complex, in which Mg acts as a bridge between the phosphate groups of the nucleic acid and the carbonyl and carboxyl moieties of norfloxacin. Additional stabilization may arise from stacking interactions between the condensed rings of the drug and DNA bases (especially guanine and adenine), which may account for the preference exhibited by quinolones for single-stranded and purine-rich regions ofnucleic acids. Other possible biochemical pathways of drug action are suggested by the observation that norfloxacin binds Mg2+ under conditions that are close to physiological.Conflicting literature reports have been accumulating on the role played by DNA in the mechanism of action of quinolone compounds. Although a large amount of biological data has indicated that DNA gyrase was the target for quinolone compounds (1-4), recent reports dismissed DNA gyrase as the target and pointed to DNA as the direct binding species (5). In fact, a cooperative interaction was proposed to occur between quinolones and supercoiled DNA. Subsequent publications by the same laboratory have modified this view extensively (6-8). In particular, Shen et al. (7) have proposed that in the presence of ATP bound gyrase induces a specific quinolone binding site in the relaxed DNA substrate. Gelelectrophoresis experiments by Tornaletti and Pedrini (9) showed that norfloxacin (Nor) is able to unwind the DNA double helix in the presence of Mg2+. On the other hand 19F NMR measurements failed to show any direct DNAquinolone interaction (10). We were also unable to detect binding using fluorescence spectroscopy techniques (11).Even if reconsidered in terms of affinity, the interaction with DNA is still of great concern because of the possible long-term genotoxicity of quinolone compounds, which are increasingly adopted as first-choice antibiotics for the treatment of many infections, and because it addresses the real mechanism of action of this class of molecules. To shed some light on this cumbersome problem, we have focused our attention on the role of Mg2+ in the binding of the model quinolone drug Nor to plasmid DNA. Our approach includes fluorescence and affinity chromatography measurements and electrophoretic DNA-unwinding assays. MATERIALS AND METHODSChemicals. Nor and [14C]Nor (specific activity, 46.5 ,uCi/ mg; 1 Ci = 37 GBq) were a kind gift of Merck Sharp & Dohme. Magnesium...

Magnesium deficiency induces joint cartilage lesions in juvenile rats which are identical to quinolone-induced arthropathy

“…Detailed studies on the molecular mechanism of the action of these antimicrobial agents on bacterial DNA have shown that they bind to the gyrase-associated nucleic acid via a magnesium ion (22). This finding suggests that, in general, quinolones must have a pronounced affinity for magnesium ions to exhibit antibacterial activity.…”

Molecular Basis for the Differential Quinolone Susceptibility of Mycobacterial DNA Gyrase

“…In addition, the drug was shown to preferentially bind to the single-stranded DNA. Next, the DNA binding was shown to be dependent on the concentration of Mg 2ϩ (46). Subsequent surface plasmon resonance studies on FQ-DNA interaction using single-stranded DNA showed a sequence-dependent binding with high affinity, whereas double-stranded DNA binding seemed to be sequence independent (40).…”

Cooperative Behavior of Fluoroquinolone Combinations against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>

“…[14][15][16][17][18] None of the models described is completely satisfactory, so new experimental and theoretical contributions will be of value to explain their molecular mechanism of action. Some of the existing theories propose the formation of dimers and tetramers of FQ molecules, that of Shen et al being the first and still one of the most widely accepted theories.…”