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Journal of Nucleic Acids
Volume 2011, Article ID 631372, 8 pages
http://dx.doi.org/10.4061/2011/631372
Research Article

The Stability of a Model Substrate for Topoisomerase 1-Mediated DNA Religation Depends on the Presence of Mismatched Base Pairs

1Department of Cancer Biology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
2Department of Physics, Wake Forest University, Winston-Salem, NC 27109, USA
3Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, NE 68198, USA

Received 9 May 2011; Revised 7 June 2011; Accepted 11 June 2011

Academic Editor: Daisuke Miyoshi

Copyright © 2011 William H. Gmeiner et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Topoisomerase 1 (Top1) enzymes regulate DNA superhelicity by forming covalent cleavage complexes that undergo controlled rotation. Substitution of nucleoside analogs at the +1 position of the DNA duplex relative to the Top1 cleavage site inhibits DNA religation. The reduced efficiency for Top1-mediated religation contributes to the anticancer activity of widely used anticancer drugs including fluoropyrimidines and gemcitabine. In the present study, we report that mismatched base pairs at the +1 position destabilize the duplex DNA components for a model Top1 cleavage complex formation even though one duplex component does not directly include a mismatched base pair. Molecular dynamics simulations reveal G-dU and G-FdU mismatched base pairs, but not a G-T mismatched base pair, increase flexibility at the Top1 cleavage site, and affect coupling between the regions required for the religation reaction to occur. These results demonstrate that substitution of dT analogs into the +1 position of the non-scissile strand alters the stability and flexibility of DNA contributing to the reduced efficiency for Top1-mediated DNA religation. These effects are inherent in the DNA duplex and do not require formation of the Top1:DNA complex. These results provide a biophysical rationale for the inhibition of Top1-mediated DNA religation by nucleotide analog substitution.