Characterization of Heme-DNA Complexes Composed of Some Chemically Modified Hemes and Parallel G-Quadruplex DNAs.

Heme {Fe(II)- or Fe(III)-protoporphyrin IX complex [heme(Fe2+) or heme(Fe3+), respectively]} binds selectively to the 3′-terminal G-quartet of a parallel G-quadruplex DNA formed from a single repeat sequence of the human telomere, d(TTAGGG), through a π–π stacking interaction between the porphyrin moiety of the heme and the G-quartet. The binding affinities of some chemically modified hemes(Fe3+) for DNA and the structures of complexes between the modified hemes(Fe2+) and DNA, with carbon monoxide (CO) coordinated to the heme Fe atom on the side of the heme opposite the G6 G-quartet, have been characterized to elucidate the interaction between the heme and G-quartet in the complexes through analysis of the effects of the heme modification on the structural properties of the complex. The study revealed that the binding affinities and structures of the complexes were barely affected by the heme modification performed in the study. Such plasticity in the binding of heme to the G-quartet is useful for the ver...