Selective DNA cleavage by cobalt metallopeptides

The focus of the present study was the complexation of cobalt to Xaa-Gly-His tripeptides to generate cobalt metallopeptides capable of inducing DNA damage. Two different activation protocols were developed to initiate DNA strand scission by the Co·Xaa-Gly-His complexes. Both the preformed (NH3) 2Co(III)·Gly-Gly-His complex and the admixture of Co(II) + Xaa-Gly-His + O2 can be photoactivated to cause alkali-labile lesions on DNA. Photoexcitation produces a C/N-based radical on the imidazole of histidine that reacts with solvent water to produce the hydroxyl radicals responsible for the DNA damage. The photoactivated DNA cleavage by the cobalt metallopeptides is largely nonselective but shows a slight preference for 5' -TGPu sites. The admixture of Co(II) + Lys-Gly-His + O2 was also found to cleave DNA in a light-independent manner. The light-independent admixture of Co(II) + Lys-Gly-His + O2 cleaves DNA in a highly selective fashion by attacking the thymine nucleobase of 5 '-AGGTGG sites. The admixture of Co(II) + Lys-Gly-His in an aerobic environment causes formation of a mu-peroxo dimer which appears to be the active Co·peptide species responsible for DNA damage. The binding constant of the reactive species formed upon admixture of Co(II) + Lys-Gly His was found to be 6.3 x 103 M -1. The selectivity of the admixture Co(II) + Lys-Gly His reaction for 5'-AGGTGG makes it unique among known low molecular weight molecules and restriction enzymes.