Fluorescence Polarisation Assay: In a black, 384-well polystyrene assay plate, 30 microliters/well of 5 nM Escherichia coli DNA gyrase A/B tetramer and 130 micrograms/ml of topologically relaxed plasmid containing the triplex-forming sequence TTCTTCTTCTTCTTCTTCTTCTTCTTC in an assay buffer consisting of 35 mM Tris-HCl (pH 7.5), 24 mM KCl, 4 mM MgCl2, 2 mM dithiothreitol, 1.8 mM spermidine, 5% (v/v) glycerol, 200 nM bovine serum albumin, 0.8% dimethylsulfoxide, and 0.3 mM ATP may be incubated at ambient temperature for (typically 30 minutes) in the absence or presence of 5-10 different concentrations of test compound. The supercoiling reactions may be quenched by the addition of 10 microliters/well of 40 nM oligodeoxynucleotide probe in 3x triplex-forming buffer consisting of 150 mM NaCl, and 150 mM sodium acetate at pH 3.5. The oligodeoxynucleotide probe may be 5x-BODIPY-FL-labeled TTCTTCTTC. After 60 minutes, the fluorescence anisotropy of the BODIPY-FL may be measured in a Tecan Ultra plate reader, using 485 nM.
Inhibition of recombinant Escherichia coli DNA gyrase AB expressed in Escherichia coli BL21 (DE3) using relaxed pJT519 DNA as substrate preincubated for 20 mins followed by 5'-BODIPY-TMR-TTCTTCTTCT addition and measured after 1 hr by fluorescence anisotropy
Ratio of MIC for antibacterial activity against methicillin/quinolone-resistant Staphylococcus aureus ARC517 to protein binding in human plasma assessed as unbound fraction