Interaction of Cu(II)-Arg-Gly-His-Xaa metallopeptides with DNA: effect of C-terminal residues, Leu and Glu.

The interactions of Cu(II)-Arg-Gly-His-Xaa metallopeptides with DNA (where Xaa is L-Leu or L-Glu) were investigated by DNA-fiber EPR spectroscopy, ESI-MS spectrometry, and agarose gel electrophoresis. The average angle between the g// axis of Cu(II)-Arg-Gly-His-Leu and the DNA-fiber axis increased from 45 degrees at room temperature to 90 degrees at -150 degrees C. The Cu(II)-Arg-Gly-His-Glu complex partly dissociated on DNA to several species. The g//value (2.341) of the main species was smaller than that (2.377) observed for free Cu(II) ion bound to DNA. This indicated that the Cu(II) ion was transferred by the peptide to a DNA site where the free Cu(II) ion can hardly reach. ESI-MS spectra of a mixture of the Cu(II) peptide complex and the oligodeoxynucleotide, [d(CGCGTATACGCG)], suggested that the maximum binding stoichiometries of Cu(II) peptide complexes and double stranded oligodeoxynucleotides were 3:1 for Cu(II)-Arg-Gly-His-Leu and 2:1 for Cu(II)-Arg-Gly-His-Glu, respectively. Cu(II)-Arg-Gly-His-Glu completely converted the supercoiled DNA to the nicked-circular form, whereas the cleavage activity was considerably reduced when excess ligand was added. In the presence of excess peptide, nicked DNA formation ratios were 64% for Cu(II)-Arg-Gly-His-Leu and 15% for Cu(II)-Arg-Gly-His-Glu, respectively. The negative charge on Cu(II)-Arg-Gly-His-Glu reduced the affinity of the complex for DNA and enhanced the specificity of the binding.