Extreme Conformational Diversity in Human Telomeric DNA

DNA with tandem repeats of guanines folds into G-quadruplexes made of a stack of G-quartets. In vitro, G-quadruplex formation inhibits telomere extension, and POT1 binding to the singlestranded telomeric DNA enhances telomerase activity by disrupting the G-quadruplex structure, highlighting the pote...

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Bibliographic Details
Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 52; pp. 18938 - 18943
Main Authors:	Lee, J. Y., Burak Okumu, Kim, D. S., Ha, Taekjip
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 27-12-2005 National Acad Sciences
Subjects:	Biological Sciences Biophysics Deoxyribonucleic acid DNA DNA - chemistry Dose-Response Relationship, Drug Fluorescence Fluorescence Resonance Energy Transfer Genetic diversity Guanine - chemistry Histograms Human subjects Humans Kinetics Models, Biological Molecular Conformation Molecular structure Molecules Nucleic Acid Conformation Nucleic Acid Denaturation Potassium - chemistry Potassium - pharmacology Protein Denaturation Protein Folding Room temperature Spectrum analysis Telomere - chemistry Telomere - ultrastructure Telomeres Temperature Time Factors
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Summary:	DNA with tandem repeats of guanines folds into G-quadruplexes made of a stack of G-quartets. In vitro, G-quadruplex formation inhibits telomere extension, and POT1 binding to the singlestranded telomeric DNA enhances telomerase activity by disrupting the G-quadruplex structure, highlighting the potential importance of the G-quadruplex structure in regulating telomere length in vivo. We have used single-molecule spectroscopy to probe the dynamics of human telomeric DNA. Three conformations were observed in potassium solution, one unfolded and two folded, and each conformation could be further divided into two species, long-lived and short-lived, based on lifetimes of minutes vs. seconds. Vesicle encapsulation studies suggest that the total of six states detected here is intrinsic to the DNA. Folding was severely hindered by replacing a single guanine, showing only the shortlived species. The long-lived folded states are dominant in physiologically relevant conditions and probably correspond to the parallel and antiparallel G-quadruplexes seen in high-resolution structural studies. Although rare under these conditions, the shortlived species determine the overall dynamics because they bridge the different long-lived species. We propose that these previously unobserved transient states represent the early and late intermediates toward the formation of stable G-quadruplexes. The major compaction occurs between the early and late intermediates, and it is possible that local rearrangements are sufficient in locking the late intermediates into the stably folded forms. The extremely diverse conformations of the human telomeric DNA may have mechanistic implications for the proteins and drugs that recognize G-rich sequences.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Edited by Kiyoshi Mizuuchi, National Institutes of Health, Bethesda, MD, and approved October 28, 2005 To whom correspondence should be addressed: E-mail: tjha@uiuc.edu. Author contributions: J.Y.L. and T.H. designed research; J.Y.L. and B.O. performed research; J.Y.L., B.O., and T.H. contributed new reagents/analytic tools; J.Y.L., B.O., and D.S.K. analyzed data; and J.Y.L., B.O., and T.H. wrote the paper. J.Y.L. and B.O. contributed equally to this work. Conflict of interest statement: No conflicts declared. This paper was submitted directly (Track II) to the PNAS office. Abbreviations: LU, long-lived unfolded; LF1, long-lived folded 1; LF2, long-lived folded 2; SU, short-lived unfolded; SF1, short-lived folded 1; SF2, short-lived folded 2.
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.0506144102