DNA Cleaving "Tandem-Array" Metallopeptides Activated With KHSO₅: Towards the Development of Multi-Metallated...

Amino terminal peptides of the general form Gly-Gly-His have been used to introduce single sites of metal binding and redox activity into a wide range of biomolecules to create bioactive compounds and conjugates capable of substrate oxidation. We report here that Gly-Gly-His-like peptides linked in a tandem fashion can also be generated leading to multi-metal binding arrays. While metal binding by the native Gly-Gly-His motif (typically to Cu²⁺, Ni²⁺, or Co²⁺) requires a terminal peptide amine ligand, previous work has demonstrated that an ornithine (Orn) residue can be substituted for the terminal Gly residue to allow solid-phase peptide synthesis to continue via the side chain N-δ. This strategy thus frees the Orn residue N-α for metal binding and permits placement of a Gly-Gly-His-like metal binding domain at any location within a linear, synthetic peptide chain. As we show here, this strategy also permits the assembly of tandem arrays of metal binding units in linear peptides of the form: NH₂-Gly-Gly-His-[(δ)-Orn-Gly-His]_n-(δ)-Orn-Gly-His-CONH₂ (where n = 0, 1, and 2). Metal binding titrations of these tandem arrays monitored by UV-vis and ESI-MS indicated that they bind Cu²⁺, Ni²⁺, or Co²⁺ at each available metal binding site. Further, it was found that these systems retained their ability to modify DNA oxidatively and to an extent greater than their parent M(II)•Gly-Gly-His. These findings suggest that the tandem array metallopeptides described here may function with increased efficiency as "next generation" appendages in the design of bioactive compounds and conjugates.