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)]4 complex) has been characterized using 1H NMR spectroscopy, and the obtained results were compared with those for the heme-[d(TTAGGG)]4 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. This finding provides novel insights as to the design of the molecular architecture of a heme-DNA complex. This article is part of a Special Issue entitled "G-quadruplex" Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors.

We introduced trifluoromethyl (CF3) group(s) as heme side chain(s) of sperm whale myoglobin (Mb) in order to characterize the electronic nature of heme Fe(II) in deoxy Mb using 19F NMR spectroscopy. On the basis of the anti-Curie behavior of CF3 signals, we found that the deoxy Mb is in thermal equilibrium between the 5B2, (dxy)2(dxz)(dyz)(dz2)(dx2-y2), and 5E, (dxy)(dxz)2(dyz)(dz2)(dx2-y2), states of the heme Fe(II), i.e., 5B2 ⇆ 5E. Analysis of the curvature in Curie plots has yielded for the first time ΔH and ΔS values of ∼-20 kJ mol-1 and ∼-60 J K-1 mol-1, respectively, for the thermal equilibrium. Thus, the 5E state is slightly dominant over the 5B2 one at 25 °C. These findings provide not only valuable information about the ground state electronic structure of the high-spin heme Fe(II) in deoxy native Mb but also an important clue for elucidating the mechanism responsible for acceleration of the spin-forbidden oxygenation of the protein.