Effect of Lipid Molecules on Twisting Motions of DNA Helix Studied by Fluorescence Polarization Anisotropy

Abstract

Time-resolved fluorescence polarization anisotropy (FPA) of two dyes (acridine orange and ethidium bromide) intercalated in a raw DNA and a novel DNA-lipid complex has been measured on nanosecond timescale to evaluate the effect of lipid molecules on the twisting motions of DNA helix. Steady-state fluorescence spectra show that intercalated dyes are not influenced much by solvents compared with free dyes, suggesting the similar microscopic environments of intercalated chromophores. The FPA decay times of both dyes are about twice larger in the DNA-lipid complex than in the raw DNA, which indicates that the lipid molecules around the helix make the twisting motion slower. The FPA decay profiles fit very well with double-exponential functions having time constants differing much with each other, suggesting that there exists slow and quick elements in the twisting motions.