title: Binding of ethidium to DNA measured using a 2D diffusion-modulated gradient COSY NMR experiment.
abstract: The binding of ethidium bromide to a DNA hairpin (dU(5)-hairpin) was investigated using a novel 2D diffusion-modulated gradient correlation spectroscopy (DMG-COSY) experiment to evaluate the applicability of this technique for studying the binding of drugs to DNA. The DMG-COSY experiment includes a preparation period during which coherent magnetization is attenuated due to molecular self-diffusion. Magnetization then evolves due to scalar coupling during an evolution delay, and is detected using gradient pulses for coherence selection. The time-domain data are processed in an analogous manner as for gradient-selected COSY experiments. The diffusion coefficient for uridine in DMSO solution was determined from the H5-H6 crosspeak intensities for a series of 2D DMG-COSY experiments that differed in the magnitude of the gradient pulses applied during the preparation period of the DMG-COSY experiment. The diffusion coefficient for uridine calculated from the DMG-COSY experiments was identical (within experimental error) to that determined from 1D diffusion experiments (5.24x10(-6) cm(2)/s at 26 degrees C). The diffusion coefficients for ethidium bromide and for the dU(5)-hairpin were first measured separately using the DMG-COSY experiment, and then measured in the putative complex. The diffusion coefficient for free ethidium bromide (4.15x10(-6) cm(2)/s at 26 degrees C) was considerably larger than for the dU(5)-hairpin (1. 60x10(-6) cm(2)/s at 26 degrees C), as expected for the smaller molecule. The diffusion coefficient for ethidium was markedly decreased upon addition of the dU(5)-hairpin, consistent with complex formation (1.22x10(-6) cm(2)/s at 26 degrees C). Complex formation of 1:1 stoichiometry between ethidium and the stem of the dU(5)-hairpin was verified independently by fluorescence spectroscopy. These results demonstrate the utility of the DMG-COSY experiment for investigating the binding of drugs to DNA in aqueous solution.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 986805 Medical Center, Omaha, NE 68198-6805, USA.
authors.forename: W H
authors.initials: WH
authors.lastname: Gmeiner
authors.forename: C J
authors.initials: CJ
authors.lastname: Hudalla
authors.forename: A M
authors.initials: AM
authors.lastname: Soto
authors.forename: L
authors.initials: L
authors.lastname: Marky
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D004058:Diffusion; D004996:Ethidium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009690:Nucleic Acid Conformation; D014529:Uridine / Q000737:chemistry
chemical_list: D004247:DNA; D004996:Ethidium; D014529:Uridine