Book of Abstracts: Albany 2003
June 17-21 2003
A Comparative Study of Fe(II) and Fe(III) Bindings to DNA Duplex. Molecular Modeling and Spectroscopic Analysis
The involvement of the Fe cations in autoxidation, in cells and tissues is well documented. DNA is a major target in such reaction and can chelate Fe cation in many ways. We report a comparative study of calf-thymus DNA complexation with Fe(II) and Fe(III) in aqueous solution at pH 6.5 with cation/DNA (P) (P; phosphate) molar ratios (r) of 1:160 to 1:2. Capillary electrophoresis, UV-visible, Fourier transform infrared (FTIR) difference spectroscopic methods and molecular modeling were used to determine the cation binding site, the binding constant, helix stability and DNA conformation in Fe-DNA complexes.
Structural analysis showed that at low cation concentration (r=1/80 and 1/40), Fe(II) binds DNA through guanine N-7 and the backbone PO2 group with apparent binding constants of K(G) = 5.40 x 105 M-1 and K(P) = 2.40 x104 M-1. At higher cation content, Fe(II) bindings to adenine N-7 and thymine O-2 are included (structure 1). The Fe(III) cation shows weaker interaction with DNA due to metal hydroxyl formation. At low cation concentration (r=1:80), Fe(III) binds mainly to the backbone phosphate group, while at higher metal ion content, cation binding to both guanine N-7 atom and the backbone phosphate group is prevailing. At r=1:10, Fe(II) binding causes a minor helix destabilization, whereas Fe(III) induces DNA condensation. The numbers of Fe(II) bound DNA were 3 cations per 1000 nucleotides at r=1:80, while increased to 20 cations per 1000 nucleotides at r=1:2. No major DNA conformational changes occurred upon iron complexation and DNA remains in the B-family structure.
Structure 1: Preferential binding model proposed for Fe(II) ? DNA interaction. (A) major groove, (B) minor groove.
H. A. Tajmir-Riahi*
Department of Chemistry-Biology