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Book of Abstracts: Albany 2011

category image Albany 2011
Conversation 17
June 14-18 2011
©Adenine Press (2010)

G-Quadruplex, Telomere and Telomerase

Telomeres serve as protective caps at the ends of linear eukaryotic chromosomes, playing a crucial role in cell survival and proliferation. Tandem repeats of the sequence TTAGGG con-stitute the human telomeres, with pendent G-rich single strands of 100–200 nt at the 3’ ends. The propensity of these G-rich overhangs to form G-quadruplexes, and the inhibitory effects of such structures on the catalytic activity of the enzyme telomerase, have led to a growing interest in the study of telomeric G-quadruplexes and the development of specific telomeric quadruplex-stabilizing ligands as anticancer drugs. Previously, it has been reported that human telomeric DNA sequences could adopt in different experimental conditions four different intramolecular G-quadruplexes each involving three G-tetrad layers, namely, Na+ solution antiparallel-stranded basket form (1), K+ crystal parallel-stranded propeller form (2), K+ solution (3 + 1) Form 1 (3-5), and K+ solution (3 + 1) Form 2 (6). Here we report novel intramolecular G-quadruplex struc-tures adopted by canonical (TTAGGG) (7) and variant (CTAGGG, TAGGG) (8,9) four-repeat human telomeric sequences in K+ solution, which surprisingly utilize only two of the three contiguous guanines from successive G-tracts for G-tetrad core forma-tion. Structural elucidation of these oligonucleotides revealed extensive base pairing and stacking interactions in the loops, indicating that the overall G-quadruplex topology of a G-rich sequence is defined not only by maximizing the number of G-tetrads but also by maxi-mizing all possible interactions in the loops. On the other hand, promoter G-quadruplex for-mation represents an alternative approach of selective gene regulation at the transcriptional level. The promoter for the catalytic subunit of human telomerase, hTERT, contains many guanine-rich stretches on the same DNA strand suitable for targeting (10-12). We also show here that one particular G-rich sequence in this region coexists in two G-quadruplex conforma-tions (11), each of which comprises several robust structural elements. Recurrence of struc-tural motifs in the structures presented suggests a “cut-and-paste” principle for the design and prediction of G-quadruplex topologies, for which different elements could be extracted from one G-quadruplex and inserted into another.

This research was supported by grants from Singapore Biomedical Research Council, Singa-pore Ministry of Education, and Nanyang Technological University.

References

  1. Y. Wang and D. J. Patel. Structure 1, 263-282 (1993).
  2. G. N. Parkinson, M. P. Lee and S. Neidle. Nature 417, 876-880 (2002).
  3. Y. Xu, Y. Noguchi and H. Sugiyama. Bioorg Med Chem 14, 5584-5591 (2006).
  4. K. N. Luu, A. T. Phan, V. Kuryavyi, L. Lacroix and D. J. Patel. J Am Chem Soc 128, 9963-9970 (2006).
  5. A. Ambrus, D. Chen, J. Dai, T. Bialis, R. A. Jones and D. Yang. Nucleic Acids Res 34, 2723-2735 (2006).
  6. A. T. Phan, K. N. Luu and D. J. Patel. Nucleic Acids Res 34, 5715-5719 (2006).
  7. K. W. Lim, S. Amrane, S. Bouaziz, W. Xu, Y. Mu, D. J. Patel, K. N. Luu and A. T. Phan. J Am Chem Soc 131, 4301-4309 (2009).
  8. K. W. Lim, P. Alberti, A. Guedin, L. Lacroix, J. F. Riou, N. J. Royle, J. L. Mergny and A. T. Phan. Nucleic Acids Res 37, 6239-6248 (2009).
  9. L. Hu, K. W. Lim, S. Bouaziz and A. T. Phan, J Am Chem Soc, 131, 16824-16831 (2009).
  10. S. L. Palumbo, S.W. Ebbinghaus and L. H. Hurley, J Am Chem Soc, 131, 10878-10891 (2009).
  11. K. W. Lim, L. Lacroix, D. J. Yue, J. K. Lim, J. M. Lim and A. T. Phan, J Am Chem Soc, 132, 12331-12342 (2010).
  12. E. Micheli, M. Martufi, S. Cacchione, P. De Santis and M. Savino. Biophys Chem 153, 43-53 (2010).

K. W. Lim
A. T. Phan

School of Physical and Mathematical Sciences
School of Biological Sci-ences
Nanyang Technological University
Singapore

ph:(+65)65141915
fx: (+65)67957981
kwlim@ntu.edu.sg phantuan@ntu.edu.sg