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.

G-Quadruplexes Induce Apoptosis in Tumor Cells

“…YZ5 (ATM+) and pEBS7 (ATMÀ) cells, obtained from Dr. Gary Kuo (University of Pennsylvania, Philadelphia, PA), were derived from SV40-immortalized AT fibroblast cells by transfection with ATM cDNA (pEBS7-YZ5) and the empty vector pEBS7, respectively (20). GW33 (ATR+) and GK41 (ATRÀ) cells, obtained from Dr. Stuart Schreiber (Harvard University, Cambridge, MA), were derived from human osteosarcoma U2OS cells transfected with plasmids carrying tetracycline-inducible ataxia telangiectasia-mutated and Rad3-related (ATR) wild-type cDNA and ATR kinasedead cDNA, respectively (21 4 ; TG24M2, (TTAGAG) 4 ; TG24M3, (TTAGGA) 4 ; TG24M4, (TTGGGG) 4 ; TG24M5, (TGGGGG) 4 ; N18 and N24, completely degenerate 18-mer and 24-mer, respectively; TG48, (TTAGGG) 8 ; dsTEL18, annealed product of TG18 and CA18; dsTEL24, annealed product of TG24 and CA24; G15T3, (TGGGGG) 3 ; T15C3, (CTTTTT) 3 ; A15C3, (CAAAAA) 3 ; C15T3, (TCCCCC) 3 ; and T40214, (GGGC) 4 . Temperature-dependent absorption spectroscopy.…”

“…G-quadruplexes can be parallel or antiparallel, as well as intramolecular or intermolecular (2)(3)(4). Nucleic acid sequences with multiple stretches of guanine (G) have a tendency to form thermodynamically stable G-quadruplexes.…”

NMR spectroscopy of G-quadruplexes

“…The power of NMR spectroscopy for interrogating multiple conformations was demonstrated in the study of G-quadruplex structures formed by the Tetrahymena telomeric d(TG 4 T 2 G 4 T) sequence in Na + solution, where four different strand conformations coexist [36].…”

DNA architecture: from G to Z

“…The two-repeat Tetrahymena telomeric sequence d(TGGGGTTGGGGT), which differs from the human sequence by only one G-for-A replacement in each repeat, interconverts between two asymmetric dimeric G-quadruplex structures in Na + solution (Figure 2e,f) [15]. Both structures include a core of four stacked G-tetrads and two edgewise loops.…”