title: Studies on the structure and dynamics of the human telomeric G quadruplex by single-molecule fluorescence resonance energy transfer.
abstract: We have investigated the structure and unfolding kinetics of the human telomeric intramolecular G quadruplex by using single-molecule fluorescence resonance energy transfer. An exploration of conformational heterogeneity revealed two stable folded conformations, in both sodium- and potassium-containing buffers, with small differences between their enthalpies and entropies. Both folded conformations can be opened by the addition of a 21-base complementary DNA oligonucleotide. The unfolding of both substates occurs at the same rate, which showed dependence on the monovalent metal cation present. Temperature-dependence studies in 100 mM KCl gave an apparent activation enthalpy and entropy of 6.4 +/- 0.4 kcal.mol-1 and -52.3 +/- 1.4 cal.mol-1.K-1, respectively, indicating that the unfolding is entropically driven and can occur easily. In contrast, in 100 mM NaCl the respective values are 14.9 +/- 0.2 kcal.mol-1 and -23.0 +/- 0.8 cal.mol-1.K-1, suggesting a more significant enthalpic barrier. Molecular modeling suggests that the two species are likely to be the parallel and antiparallel quadruplex structures. The unfolding free energy barrier is estimated to be between 3 and 15 kBT based on Kramers' theory. We conclude that under near-physiological conditions these structures coexist and can interconvert on a minute time scale.
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
authors.forename: Liming
authors.initials: L
authors.lastname: Ying
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Green
authors.forename: Haitao
authors.initials: H
authors.lastname: Li
authors.forename: David
authors.initials: D
authors.lastname: Klenerman
authors.forename: Shankar
authors.initials: S
authors.lastname: Balasubramanian
mesh_terms: D001482:Base Composition; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry; D018076:DNA, Complementary / Q000737:chemistry; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry; D011189:Potassium Chloride / Q000737:chemistry; D012964:Sodium / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D016615:Telomere / Q000737:chemistry / Q000648:ultrastructure*; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D018076:DNA, Complementary; D009692:Nucleic Acid Heteroduplexes; D012965:Sodium Chloride; D011189:Potassium Chloride; D004247:DNA; D012964:Sodium; D011188:Potassium