title: Changes in the secondary structure of highly polymeric DNA and CC(GCC)n-type oligonucleotides under the action of steroid hormones and their complexes with apolipoprotein A I.
abstract: A small-angle X-ray scattering study showed that the action of tetrahydrocortisol (THC) in complex with apolipoprotein A I (ApoA-I) on DNA leads to local melting of DNA. The most probable site of interaction between this complex and DNA is the (GCC)n-type sequence. Oligonucleotides (duplexes) of this type have been synthesized. It was demonstrated that the interaction of this oligonucleotide with the THC-ApoA-I complex leads to dissociation into complementary oligonucleotides. The latter ones also interact with the THC-ApoA-I complex. The kinetics of this multistep process is presented. The mechanism of interaction between hormones or their ApoA-I complexes and duplex CC(GCC)5.GG(CGG)5Li2 was studied using IR spectroscopy. It was shown that the interaction with THC or the THC-ApoA-I complex leads to the formation of hydrogen bonds between the OH group of the hormone A-ring and the C=O group of cytosine or guanine. Interaction with cortisol or the cortisol-ApoA-I complex leads to the formation of a hydrogen bond with the NH group of cytosine; in addition, THC and cortisol form hydrogen bonds with the PO2 group of the duplex and with the OH group of the monosaccharide. The interaction of ApoA-I with the duplex is accompanied by the formation of hydrogen bonds between the protein NH2 group and the C=O group of cytosine and the P=O group. The order-to-order structural transition takes place in the duplex under the action of THC or cortisol, with THC causing a higher ordering as compared to cortisol. The order-to-disorder structural transition occurs in the duplex under the action of the THC-ApoA-I, cortisol-ApoA-I, or ApoA-I complexes. Shifting the pH of the medium from 7.2 to 6.0 also leads to an order-to-disorder-type structural transition.
authors.affiliation: State Institute of Biochemistry SD RAMS, Timakov Str. 2, Novosibirsk 630117, Russia.
authors.forename: L E
authors.initials: LE
authors.lastname: Panin
authors.forename: V G
authors.initials: VG
authors.lastname: Kunitsyn
authors.forename: F V
authors.initials: FV
authors.lastname: Tuzikov
mesh_terms: D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry*; D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D006728:Hormones / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D051381:Rats; D012542:Scattering, Radiation; D013055:Spectrophotometry, Infrared; D013256:Steroids / Q000737:chemistry*
chemical_list: D016632:Apolipoprotein A-I; D006728:Hormones; D013256:Steroids; D004247:DNA