A spectroscopic and surface plasmon resonance study of oleic acid/DNA complexes

The interaction of synthetic polynucleotide double strands with a natural lipid, oleic acid, was examined in diluted aqueous solutions by circular dichroism spectra, UV-absorption measurements, and surface plasmon resonance biosensor investigations. The investigations were performed with defined double and triple stranded oligo- and polydeoxyribonucleotides. Whereas duplexes are influenced by oleic acid ligandation, which could not be removed by ethanol dialysis procedure, no binding occurs to triple stranded DNA. The spectroscopic results indicate that oleic acid shows molecular recognition to AT b.p. motifs by groove binding. GC tracts - in particular alternating d[G-C] motifs - are strongly influenced by ligand interaction up to a ratio of one molecule per two base pairs. Likewise, the spectroscopic and morphologic changes in the supramolecular association of the complexes after treatment occur even after dialysis procedure. This was monitored with scanning force microscopy (SFM) as well. Additionally, monolayers of biotinylated DNA duplexes were immobilized on a streptavidin sensor-layer for surface plasmon resonance (SPR) observations. Small portions of the ligand were injected in continuous flow. Loosely bound molecules were removed by washing procedure. Injections of sodium hydroxide denature the DNA, releasing the tightly bound effectors. The amount of tightly bound oleic acid molecules was determined at one molecule per 2-3 base pairs. As consequence, a new mechanism of regulation of gene expression at nuclear membrane or by lipids inside DNA double helix has to be discussed.