ABSTRACT:The tetrahydrocortisol-apolipoprotein A-I complex specifically interacts with eukaryotic DNA isolated from rat liver. This interaction is highly cooperative and of a saturating nature. One DNA molecule binds about 54 molecules of the complex. Smallangle X-ray scattering has shown that hydrogen bonds between nitrous bases are destroyed and that single-stranded structures are formed at the interaction of the tetrahydrocortisolapolipoprotein A-I complex with eukaryotic DNA. The most probable site of binding the tetrahydrocortisol-apolipoprotein A-I complex with DNA is the sequence of the CC(GCC) n type entering the structure of many genes, among them the structure of the human apolipoprotein A-I gene. Oligonucleotide of this type has been synthesized. The association constant (K ass ) of its complexation was shown to be 1.66 ⅐ 10 6 M Ϫ1. Substitution of tetrahydrocortisol for cortisol in the complex results in a considerable decrease of K ass . IRspectroscopy study has shown that the interaction of tetrahydrocortisol with oligonucleotide CC(GCC) 3-5 is accompanied by the formation of hydrogen bonds via the CO-NH, PO 2 , and OH groups of desoxycytidinephosphate. The tetrahydrocortisol-apolipoprotein A-I complex alters the DNA secondary structure formed at the interaction with the hormone, causing the structural transition "order 3 tangle." It is assumed that in the GC-pairs of the given DNA sequence, tetrahydrocortisol initiates the rupture of hydrogen bonds, while the hydrophobic interactions between nitrous bases and apoA-I intensify this process.

The use of various nanoparticles is a promising way to solve the current problem of drug delivery in medicine and biology. Nanocomposites consisting of titanium dioxide and oligonucleotides noncovalently attached to nanoparticles through the polylysine linker (TiO2 x PL-DNA) have been designed to deliver of DNA fragments into cells. Three forms of TiO2 nanoparticles (amorphous, anatase, and brookite) were used for construction of nanocomposites. The size, morphology, and chemical composition of TiO2 nanoparticles and TiO2 x PL-DNA nanocomposites were characterized. DNA fragments in the proposed nanocomposites were shown to retain their ability to form complementary complexes. TiO2 x PL-DNA nanocomposites independently on the form of nanoparticles were shown by confocal microscopy to penetrate into HeLa cells without any transfection agents and physical impact. The presented type of nanocomposites can be applied in the thriving technology of drug delivery to achieve high therapeutic and biological efficacy.