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Inter-Strand C--H$\cdots $O Hydrogen Bonds Stabilizing Four-Stranded Intercalated Molecules: Stereoelectronic Effects of O4$^{\prime}$ in Cytosine-Rich DNA

Imre Berger, Martin Egli and Alexander Rich
Proceedings of the National Academy of Sciences of the United States of America
Vol. 93, No. 22 (Oct. 29, 1996), pp. 12116-12121
Stable URL: http://www.jstor.org/stable/40578
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Inter-Strand C--H$\cdots $O Hydrogen Bonds Stabilizing Four-Stranded Intercalated Molecules: Stereoelectronic Effects of O4$^{\prime}$ in Cytosine-Rich DNA
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Abstract

DNA fragments with stretches of cytosine residues can fold into four-stranded structures in which two parallel duplexes, held together by hemiprotonated cytosine$\cdot $cytosine$^{+}$ (C$\cdot $C$^{+}$) base pairs, intercalate into each other with opposite polarity. The structural details of this intercalated DNA quadruplex have been assessed by solution NMR and single crystal x-ray diffraction studies of cytosine-rich sequences, including those present in metazoan telomeres. A conserved feature of these structures is the absence of stabilizing stacking interactions between the aromatic ring systems of adjacent C$\cdot $C$^{+}$ base pairs from intercalated duplexes. Effective stacking involves only the exocyclic keto groups and amino groups of the cytidine bases. The apparent absence of stability provided by stacking interactions between the bases in this intercalated DNA has prompted us to examine the available structures in detail, in particular with regard to unusual features that could compensate for the lack of base stacking. In addition to base-on-deoxyribose stacking and intra-cytidine C--H$\cdots $O hydrogen bonds, this analysis reveals the presence of a hitherto unobserved, systematic intermolecular C--H$\cdots $O hydrogen bonding network between the deoxyribose sugar moieties of antiparallel backbones in the four-stranded molecule.

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