Protein cleavage by transition metal complexes bearing amino acid substituents

In this report, we describe protein damage by a series of metal complexes that mediate the formation of hydroxyl radical. The protein targets used are bovine serum albumin (BSA) and carboxypeptidase A (CPA). BSA contains several electrostatic, hydrogen bonding and hydrophobic binding sites for potential interaction with the metal complexes, and CPA contains a specific phenylalanine binding site. The data presented in this study show that aromatic side chain damage and backbone cleavage occur to similar extents with all the complexes. Reasonable levels of backbone cleavage specificity can be attained with relatively few recognition elements, despite the fact that a diffusible radical mediates cleavage. Incorporation of additional recognition elements can enlarge the set of cleavage sites. We show that the chemical environment of the cleavage reaction, manipulated by using different buffers, can dramatically affect the outcome of the cleavage reaction. Our work suggests that backbone cleavage site is determined by three factors: the binding sites of the metal complexes, the role of reactive sites on the protein backbone, and the influence of the chemical environment on the reaction.