title: Small change in a G-rich sequence, a dramatic change in topology: new dimeric G-quadruplex folding motif with unique loop orientations.
abstract: NMR study has shown that DNA oligonucleotide d(G(3)T(4)G(4)) adopts an asymmetric bimolecular G-quadruplex structure in solution. The structure of d(G(3)T(4)G(4))(2) is composed of three G-quartets, overhanging G11 residue and G3, which is part of the loop. Unique structural feature of d(G(3)T(4)G(4))(2) fold is the orientation of the two loops. Thymidine residues T4-T7 form a diagonal loop, whereas T15-T18 form an edge type loop. The G-quadruplex core of d(G(3)T(4)G(4))(2) consists of two stacked G-quartets with syn-anti-anti-anti alternation of dG residues and one G-quartet with syn-syn-anti-anti alternation. Another unusual structural feature of d(G(3)T(4)G(4))(2) is a leap between G19 and G20 over the middle G-quartet and chain reversal between G19 and G20 residues. The presence of one antiparallel and three parallel strands reveals the hitherto unknown G-quadruplex folding motif consisting of antiparallel/parallel strands and diagonal as well as edge type loops. Further examination of the influence of different monovalent cations on the folding of d(G(3)T(4)G(4)) showed that it forms a bimolecular G-quadruplex in the presence of K+, Na+, and NH4+ ions with the same general fold.
authors.affiliation: NMR center, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
authors.forename: Martin
authors.initials: M
authors.lastname: Crnugelj
authors.forename: Primoz
authors.initials: P
authors.lastname: Sket
authors.forename: Janez
authors.initials: J
authors.lastname: Plavec
mesh_terms: D004247:DNA / Q000737:chemistry*; D019281:Dimerization; D054856:G-Quadruplexes; D006147:Guanine / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D009841:Oligonucleotides; D006147:Guanine; D004247:DNA