title: Conformation of guanine-8-oxoadenine base pairs in the crystal structure of d(CGCGAATT(O8A)GCG).
abstract: The structure of the synthetic deoxydodecamer d(CGCGAATT(O8A)GCG)2 (O8A = 8-oxoadenine) has been determined by single-crystal X-ray diffraction techniques. The oligonucleotide crystallizes in the orthorhombic space group P2(1)2(1)2(1) with cell dimensions of a = 25.48 A, b = 41.84 A, and c = 64.91 A. The refinement has converged with an R-factor of 0.151 for 1119 reflections in the resolution range 8.0-2.25 A. Sixty-seven solvent molecules were located during the course of the refinement. The B-DNA helix consists of ten Watson-Crick base pairs and two guanine-8-oxoadenine (G.O8A) base pairs. In order to achieve hydrogen-bonding complementarity between the two bases, an unusual G(anti).O8A-(syn) wobble conformation is adopted. It is proposed that the G.O8A mispairs are held together by a network of four interbase hydrogen bonds which are the result of the formation of two reverse three-center hydrogen-bonding systems. These involve one carbonyl oxygen lone pair interacting with two hydrogen atoms. In a departure from previous observations of the characteristics of purine-purine anti-syn base pairs, lambda 1 and lambda 2, the angles between the glycosidic bonds and the C1'-C1' vector, are symmetric. A reassessment of the other purine-purine mispairs suggests that similar three-center hydrogen bonds may occur and make a contribution to stabilizing other base pairings.
authors.affiliation: Department of Chemistry, University of Manchester, U.K.
authors.forename: G A
authors.initials: GA
authors.lastname: Leonard
authors.forename: A
authors.initials: A
authors.lastname: Guy
authors.forename: T
authors.initials: T
authors.lastname: Brown
authors.forename: R
authors.initials: R
authors.lastname: Téoule
authors.forename: W N
authors.initials: WN
authors.lastname: Hunter
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000737:chemistry; D001483:Base Sequence; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D009838:Oligodeoxyribonucleotides; C002992:8-hydroxyadenine; D006147:Guanine; D000225:Adenine