Structures and Catalytic Activities of Complexes Between Heme and DNA

Abstract

Both heme and G-quadruplex DNA are ubiquitous in living systems and play a variety of vital roles in cellular functions. Hence elucidation of the interaction between them at the atomic level is expected to provide valuable information for revealing the molecular mechanism responsible for the regulation of diverse biological processes through their interaction. Heme binds selectively to the 3’-terminal G-quartet of a parallel G-quadruplex DNA to form a stable complex, which exhibits not only peroxidase activity, but also various spectroscopic and functional properties remarkably similar to those of hemoproteins such as myoglobin. Mechanistic studies on the peroxidation cycle of the complex indicated that its catalytic cycle involves the iron(IV)oxo porphyrin π-cation radical intermediate known as compound I formed through heterolytic O-O bond cleavage of an Fe3+-bound hydroperoxo ligand (Fe3+-OOH) in compound 0, like those of peroxidases such as horseradish peroxidase (HRP), and that the formation of compound I in the complex is promoted by mechanisms that are reminiscent of the “push” and “pull” mechanisms in the catalytic cycle of HRP. These findings allow not only a deeper understanding of the functional properties of heme bound to a G-quartet, but also an insight as to control the heme reactivity of the complex. In addition, since heme is believed to be an ancient compound, the catalytic activities of complexes between heme and G-quadruplex nucleic acids could possibly help us to conceptualize redox-catalyzing ribozymes in a primordial “RNA world.”