Metallopeptides of the form M(II).Xaa-Xaa-His [where MU(II) is Ni(II) or Co(III) and Xaa is an a-amino acid] interact selectively with DNA as a function of their amino acid composition, chirality and overall shape. Given that metallopeptides are composed of the same chemical functionalities used by Nature to promote selective DNA binding by anti-tumor natural products and proteins, the goal of this project is to exploit the chemical diversity of metallopeptides to better understand the recognition activities of natural DNA binding agents and to generate model compounds with efficient and selective binding properties. These goals will be pursued through the synthesis of combinatorial peptide-ligand libraries, using both naturally occurring amino acids and select unnatural amino acids. These libraries will be screened in oligonucleotide binding and cleavage assays to determine the identity of amino acids that are best for a particular DNA binding site and to rank quantitatively the ability of all the amino acids included. Information gained through the above screen will be used in two ways: (1) the best amino acids for a particular DNA site will be used to synthesize discrete metallopeptides for structural studies (NMR, DNA fiber EPR, and molecular modeling) to understand the amino acid-DNA contacts that are formed and (2) the relative rank-ordering of all amino acids for a given binding site will be used to carry out a comparative molecular field analysis(CoMFA)/QSAR study to assist in the de novo design of better ligands that promote the binding of select DNA sites. In addition to the above, the oxygen activation & DNA recognition/modification activities of Co(II) + Lys-Gly-His will be explored. This metallopeptide can activate ambient dioxygen (through the formation of a u-peroxo dimer) to mediate the highly selective modification of DNA. Oxygen activation by this system will be evaluated through a quantification of 02 uptake and peroxide release. The DNA lesion(s) formed by this complex will also be identified and characterized through the use of oligonucleotide substrates. Nucleobase modifications and substitutions within the metallopeptide binding site of these same DNA substrates will be used to determine the DNA structural features that promote metallopeptide recognition and reaction. The ability of Co(II) + alternative tripeptide ligands (Lys-Xaa-His & Xaa-Lys-His) to promote aerobic DNA modification at alternative DNA sequences will also be evaluated.
