title: Two-repeat Tetrahymena telomeric d(TGGGGTTGGGGT) Sequence interconverts between asymmetric dimeric G-quadruplexes in solution.
abstract: Recently, the two-repeat human telomeric d(TAGGGTTAGGGT) sequence has been shown to form interconverting parallel and antiparallel G-quadruplex structures in solution. Here, we examine the structures formed by the two-repeat Tetrahymena telomeric d(TGGGGTTGGGGT) sequence, which differs from the human sequence only by one G-for-A replacement in each repeat. We show by NMR that this sequence forms two novel G-quadruplex structures in Na+-containing solution. Both structures are asymmetric, dimeric G-quadruplexes involving a core of four stacked G-tetrads and two edgewise loops. The adjacent strands of the G-tetrad core are alternately parallel and antiparallel. All G-tetrads adopt syn.syn.anti.anti alignments, which occur with 5'-syn-anti-syn-anti-3' alternations along G-tracks. In the first structure (head-to-head), two loops are at one end of the G-tetrad core; in the second structure (head-to-tail), two loops are located on opposite ends of the G-tetrad core. In contrast to the human telomere counterpart, the proportions of the two forms here are similar for a wide range of temperatures; their unfolding rates are also similar, with an activation enthalpy of 153 kJ/mol.
authors.affiliation: Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA. phantuan@sbnmr1.mskcc.org
authors.forename: Anh Tuân
authors.initials: AT
authors.lastname: Phan
authors.forename: Yasha S
authors.initials: YS
authors.lastname: Modi
authors.forename: Dinshaw J
authors.initials: DJ
authors.lastname: Patel
mesh_terms: D000818:Animals; D004247:DNA / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D054856:G-Quadruplexes; D006147:Guanine / Q000737:chemistry*; D007700:Kinetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D012091:Repetitive Sequences, Nucleic Acid; D012996:Solutions; D016615:Telomere / Q000737:chemistry*; D013768:Tetrahymena / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D012996:Solutions; D006147:Guanine; D004247:DNA