Is the monomeric prion octapeptide repeat PHGGGWGQ a specific ligand for Cu2+ ions?

Abstract

Ac-PHGGGWGQ-NH2, an octarepeat peptide fragment of prion, is a relatively effective ligand for Cu2+ ions. At a pH of about 7.4 the major binding sites involve the imidazole nitrogen and two amide nitrogens of 3Gly and 4Gly giving a CuH−2L species. The stability of the complex formed is similar to other peptides having a similar type of coordination. The NMR spectra indicate that in CuH−2L the complex side chain of the Trp residue is located very close to the metal ion. The geometry around the Cu2+ ion seems to be slightly distorted from the tetragonal one. In strongly basic solution the coordination involves an additional amide nitrogen. In CuH−2L, CuH−3L and CuH−4L complexes the amide nitrogens involved in the metal ion binding are those placed towards the C-terminal from the His residue. The N-terminal of the unprotected octapeptide is very effective in binding the Cu2+ ion although at high pH the imidazole nitrogen may not be involved in metal ion binding.