title: A K cation-induced conformational switch within a loop spanning segment of a DNA quadruplex containing G-G-G-C repeats.
abstract: We have identified a unique structural transition (in slow exchange on the NMR time scale) in the tertiary fold of the d(G-G-G-C-T4-G-G-G-C) quadruplex on proceeding from Na+ to K+ as counterion in aqueous solution. Both monovalent cation-dependent conformations exhibit certain common structural features, which include head-to-tail dimerization of two symmetry-related stem-hairpin loops, adjacent strands which are antiparallel to each other and adjacent stacked G(syn).G(anti). G(syn).G(anti) tetrads in the central core of the quadruplexes. The Na and K cation stabilized structures of the d(G-G-G-C-T4-G-G-G-C) quadruplexes differ in the conformations of the T-T-T-T loops, the relative alignment of G.C base-pairs positioned opposite each other through their major groove edges and potentially in the number of monovalent cation binding sites. We have identified potential K cation binding cavities within the symmetry-related T-T-T-G segments, suggesting the potential for two additional monovalent cation binding sites in the K cation-stabilized quadruplex relative to its Na cation-stabilized counterpart. Modeling studies suggest that the major groove edges of guanine residues in Watson-Crick G.C base-pairs could potentially be bridged by coordinated K cations in the d(G-G-G-C-T4-G-G-G-C) quadruplex in KCl solution in contrast to formation of G.C.G.C tetrads for the corresponding quadruplex in NaCl solution. Our results defining the molecular basis of a Na to K cation-dependent conformational switch in the loop spanning segment of the d(G-G-G-C-T4-G-G-G-C) quadruplex may have relevance to recent observations that specific K cation coordinated loop conformations within quadruplexes exhibit inhibitory activity against HIV integrase.
authors.affiliation: Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, NY, 10021, USA.
authors.forename: S
authors.initials: S
authors.lastname: Bouaziz
authors.forename: A
authors.initials: A
authors.lastname: Kettani
authors.forename: D J
authors.initials: DJ
authors.lastname: Patel
mesh_terms: D001665:Binding Sites; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019427:HIV Integrase / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D009690:Nucleic Acid Conformation / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D004247:DNA; D019427:HIV Integrase; D011188:Potassium