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

Abstract

The molecular structure and heme electronic structure of a complex (heme-(d(TTAGGGT)) 4 complex) between heme and a parallel G-quadruplex DNA formed from heptanucleotide d(TTAGGGT), i.e., (d(TTAGGGT)) 4, have been characterized using 1 H NMR. The study demonstrated that the heme is accommodated between G6 and T7 of the G-quadruplex DNA to form a 1:1 complex between the heme and DNA. The spin state of the heme Fe 3+ of the heme(Fe 3+)-(d(TTAGGGT)) 4 complex exhibited a characteristic pH-dependent change from a high spin (HS) state, i.e., S = 5/2, at low pH to a thermal spin equilibrium between the HS and low spin state (LS), i.e., S = 1/2, at high pH, with a midpoint at the pH value of 8.9 ± 0.2. The pH-dependent spin state change of the heme(Fe 3+)-(d(TTAGGGT)) 4 complex was similar to that of metmyoglobin (T. M. McGrath and G. N. La Mar, Biochim. Biophys. Acta, 1978, 534, 99-111), demonstrating that these two systems are highly alike in terms of the heme environment. This finding provides novel insights as to the design of the heme-DNA complexes that exhibit catalytic activities similar to those of hemoproteins.