Cu(II) Binding to the Peptide Ala-His-His, a Chimera of the Canonical Cu(II)-Binding Motifs Xxx-His and Xxx-Zzz-His

Peptides and proteins with the N-terminal motifs NH2-Xxx-His and NH2-Xxx-Zzz-His form well-established Cu(II) complexes. The canonical peptides are Gly-His-Lys and Asp-Ala-His-Lys (from the wound healing factor and human serum albumin, respectively). Cu(II) is bound to NH2-Xxx-His via three nitrogens from the peptide and an external ligand in the equatorial plane (called 3N form here). In contrast, Cu(II) is bound to NH2-Xxx-Zzz-His via four nitrogens from the peptide in the equatorial plane (called 4N form here). These two motifs are not mutually exclusive, as the peptides with the sequence NH2-Xxx-His-His contain both of them. However, this chimera has never been fully explored. In this work, we use a multispectroscopic approach to analyze the Cu(II) binding to the chimeric peptide Ala-His-His (AHH). AHH is capable of forming the 3N- and 4N-type complexes in a pH dependent manner. The 3N form predominates at pH ∼ 4–6.5 and the 4N form at ∼ pH 6.5–10. NMR experiments showed that at pH 8.5, where Cu(II) i...