Abstract
Although water is an integral part of DNA structures, the effects of water molecules on various DNA structures which are formed by not only Watson-Crick but also Hoogsteen base pairs are still unclear. Here, we studied quantitatively the effects of molecular crowding on the thermodynamics of a parallel G-quadruplex formation of [d(TG 4 )2] 4 with Hoogsteen base pairs. It was demonstrated that molecular crowding conditions stabilized the parallel G-quadruplex. Moreover, the plot of stability of the parallel G-quadruplex structure versus water activity suggested that water molecules were released through the G-quadruplex formation. The stabilization of the DNA structures consisting of Hoogsteen base pairs under cell-like conditions may lead to a structural polymorphism of various DNA sequences regulated by water molecules.
Acknowledgments
The authors thank Yumi Ueda for data collection. H.K. received a Research Fellowship from the Japan Society for the Promotion of Science for Young Scientists. This work was supported in part by Grants-in-Aid for Scientific Research and for the Academic Frontier Project (2004–2009) from MEXT, Japan.