title: Crystal structure of d(GCGCGCG) with 5'-overhang G residues.
abstract: The crystal structure of the DNA heptamer d(GCGCGCG) has been solved at 1.65 A resolution by the molecular replacement method and refined to an R-value of 0.184 for 3598 reflections. The heptamer forms a Z-DNA d(CGCGCG)2 with 5'-overhang G residues instead of an A-DNA d(GCGCGC)2 with 3'-overhang G residues. The overhang G residues from parallel strands of two adjacent duplexes form a trans reverse Hoogsteen G x G basepair that stacks on the six Z-DNA basepairs to produce a pseudocontinuous helix. The reverse Hoogsteen G x G basepair is unusual in that the displacement of one G base relative to the other allows them to participate in a bifurcated (G1)N2 . . . N7(G8) and an enhanced (G8)C8-H . . . O6(G1) hydrogen bond, in addition to the two usual hydrogen bonds. The 5'-overhang G residues are anti and C2'-endo while the 3'-terminal G residues are syn and C2'-endo. The conformations of both G residues are different from the syn/C3'-endo for the guanosine in a standard Z-DNA. The two cobalt hexammine ions bind to the phosphate groups in both GpC and CpG steps in Z(I) and Z(II) conformations. The water structure motif is similar to the other Z-DNA structures.
authors.affiliation: Biological Macromolecular Structure Center, Department of Chemistry, The Ohio State University, Columbus 43210-1002, USA.
authors.forename: B
authors.initials: B
authors.lastname: Pan
authors.forename: C
authors.initials: C
authors.lastname: Ban
authors.forename: M C
authors.initials: MC
authors.lastname: Wahl
authors.forename: M
authors.initials: M
authors.lastname: Sundaralingam
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D002942:Circular Dichroism; D003035:Cobalt; D018360:Crystallography, X-Ray / Q000379:methods; D004247:DNA / Q000737:chemistry*; D006147:Guanine; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*
chemical_list: D009838:Oligodeoxyribonucleotides; C032300:hexaamminecobalt(II); D003035:Cobalt; D006147:Guanine; D004247:DNA