title: Characterization of the cation and temperature dependence of DNA quadruplex hydrogen bond properties using high-resolution NMR.
abstract: Variations in the hydrogen bond network of the Oxy-1.5 DNA guanine quadruplex have been monitored by trans-H-bond scalar couplings, (h2)J(N2N7), for Na(+)-, K(+)-, and NH(4)(+)-bound forms over a temperature range from 5 to 55 degrees C. The variations in (h2)J(N2N7) couplings exhibit an overall trend of Na(+) > K(+) > NH(4)(+) and correlate with the different cation positions and N2-H2...N7 H-bond lengths in the respective structures. A global weakening of the (h2)J(N2N7) couplings with increasing temperature for the three DNA quadruplex species is accompanied by a global increase of the acceptor (15)N7 chemical shifts. Above 35 degrees C, spectral heterogeneity indicates thermal denaturation for the Na(+)-bound form, whereas spectral homogeneity persists up to 55 degrees C for the K(+)- and NH(4)(+)-coordinated forms. The average relative change of the (h2)J(N2N7) couplings amounts to approximately 0.8 x 10(-3)/K and is thus considerably smaller than respective values reported for nucleic acid duplexes. The significantly higher thermal stability of H-bond geometries in the DNA quadruplexes can be rationalized by their cation coordination of the G-quartets and the extensive H-bond network between the four strands. A detailed analysis of individual (h2)J(N2N7) couplings reveals that the 5' strand end, comprising base pairs G1-G9* and G4*-G1, is the most thermolabile region of the DNA quadruplex in all three cation-bound forms.
authors.affiliation: Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K. dingley@biochem.ucl.ac.uk
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Dingley
authors.forename: Robert D
authors.initials: RD
authors.lastname: Peterson
authors.forename: Stephan
authors.initials: S
authors.lastname: Grzesiek
authors.forename: Juli
authors.initials: J
authors.lastname: Feigon
mesh_terms: D002412:Cations / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D054856:G-Quadruplexes; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards*; D009690:Nucleic Acid Conformation; D012015:Reference Standards; D013696:Temperature
chemical_list: D002412:Cations; D006147:Guanine; D004247:DNA