Designed High Affinity Cu 2+ -Binding a-Helical Foldamer

The design, synthesis, and characterization of a folded high-affinity metal-binding peptide is described. Based on the previously described folded peptide NTH-18, in which an α-helix was constrained through two disulfide bonds to a C-terminal extension of noncanonical secondary structure, a peptide (1) was designed to contain two histidine residues in positions 3 and 7. Air oxidation of 1 led to the formation of peptide 2, which contained two intramolecular disulfide bonds. The presence of the two histidines significantly destabilized the α-helical structure of 2 when compared to NTH-18. However, CD spectroscopy revealed that the addition of certain transition metal ions allowed the reformation of a stable α-helix. CD, NMR, and EPR spectroscopy as well as MALDI-TOF mass spectrometry indicated that 2 bound to Cu2+ to form a 1:1 complex via the imidazoles of the two histidine side chains. A glycine displacement assay revealed a dissociation constant for this complex of 5 nM at pH 8, which is the lowest repo...