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

• Published in: Inorganic chemistry 2012-08, Vol.51 (15), p.8168-8176
• Main Authors: Saito, Kaori, Tai, Hulin, Hemmi, Hikaru, Kobayashi, Nagao, Yamamoto, Yasuhiko
• Format: Article
• Language: English
• Subjects: Circular Dichroism; DNA - chemistry; G-Quadruplexes; Heme - chemistry; Humans; Iron - chemistry; Ligands; Magnetic Resonance Spectroscopy; Models, Molecular; Oxygen - chemistry; Protons; Repetitive Sequences, Nucleic Acid; Static Electricity
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic3005739

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.