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Interaction between the Heme and a G‑Quartet in a Heme–DNA Complex

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journal contribution
posted on 20.02.2016, 15:28 by Kaori Saito, Hulin Tai, Hikaru Hemmi, Nagao Kobayashi, Yasuhiko Yamamoto
The structure of a complex between heme­(Fe3+) and a parallel G-quadruplex DNA formed from a single repeat sequence of the human telomere, d­(TTAGGG), has been characterized by 1H NMR. The study demonstrated that the heme­(Fe3+) is sandwiched between the 3′-terminal G-quartets of the G-quadruplex DNA. Hence, the net +1 charge of the heme­(Fe3+) in the complex is surrounded by the eight carbonyl oxygen atoms of the G-quartets. Interaction between the heme Fe3+ and G-quartets in the complex was clearly manifested in the solvent 1H/2H isotope effect on the NMR parameters of paramagnetically shifted heme methyl proton signals, and interaction of the heme Fe3+ with the eight carbonyl oxygen atoms of the two G-quartets was shown to provide a strong and axially symmetric ligand field surrounding the heme Fe3+, yielding a heme­(Fe3+) low-spin species with a highly symmetric heme electronic structure. This finding provides new insights as to the design of the molecular architecture and functional properties of various heme–DNA complexes.