Characterization of Catalytic Activities and Heme Coordination Structures of Heme-DNA Complexes Composed of Some Chemically Modified Hemes and an All Parallel-Stranded Tetrameric G-Quadruplex DNA Formed from d(TTAGGG).

Heme binds selectively to the 3'-terminal G-quartet (G6 G-quartet) of an all parallel-stranded tetrameric G-quadruplex DNA, [d(TTAGGG)], to form a heme-DNA complex. Complexes between [d(TTAGGG)] and a series of chemically modified hemes possessing a heme Fe atom with a variety of electron densities were characterized in terms of their peroxidase activities to evaluate the effect of a change in the electron density of the heme Fe atom (ρ) on their activities. The peroxidase activity of a complex decreased with a decreasing ρ, supporting the idea that the activity of the complex is elicited through a reaction mechanism similar to that of a peroxidase.

Characterization of the interaction between heme and a parallel G-quadruplex DNA formed from d(TTGAGG).

Structure-function relationships of complexes between heme and G-quadruplex DNAs have attracted interest from researchers in related fields. A carbon monoxide adduct of a complex between heme and a parallel G-quadruplex DNA formed from hexanucleotide d(TTGAGG) (heme-[d(TTGAGG)] complex) has been characterized using H NMR spectroscopy, and the obtained results were compared with those for the heme-[d(TTAGGG)] complex previously studied in order to elucidate the effect of the incorporation of an A-quartet into stacked G-quartets in the 3'-terminal region of the DNA on the structure of the heme-DNA complex. We found that a π-π stacking interaction between the porphyrin moiety of the heme and the 3'-terminal G-quartet of the DNA is affected by the nature of the stacked G-quartets.

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(Fe(2+)) or heme(Fe(3+)), 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(Fe(3+)) for DNA and the structures of complexes between the modified hemes(Fe(2+)) 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.