The Structural Twist of His1 Residue in Cu-ATCUN Metallopeptides: A Rule Breaker on Redox Activity

The Amino-Terminal Copper and Nickel (ATCUN) motif (H2N-Xxx-Zzz-His) is renowned for forming exceptionally stable, 4N square-planar Cu(II) complexes that are typically “redox-silent” due to their inability to effectively coordinate Cu(I). This study demonstrates a “structural twist” where the characteristic redox inactivity of the canonical ATCUN motif is bypassed strategically incorporating a histidine residue at the N-terminal position (His1). Through a comparative analysis of three peptides, NH2-ADHV-Am (canonical), NH2-HDHV-Am (modified), and Ac-HDHV-Am (acetylated), we investigated the impact of the His1 residue on Cu(I/II) coordination, thermodynamic stability, and catalytic Reactive Oxygen Species (ROS) production. Spectroscopic and thermodynamic data reveal that while both NH2-ADHV-Am and NH2-HDHV-Am form stable 4N Cu(II) complexes at physiological pH, the presence of His1 in the latter sequence increases its affinity for Cu(I) by approximately 1 order of magnitude. This modification also enables the formation of transient “histamine-like” coordination intermediates involving the terminal amine and the His1 imidazole nitrogen, which could act as structural bridges to promote the Cu(II/I) transition. Consequently, NH2-HDHV-Am effectively promotes ascorbate-mediated ROS generation, exhibiting a catalytic activity halfway between the redox-silent canonical motif and the highly reactive acetylated control. These findings redefine the structural boundaries for peptide-mediated catalysis, identifying the N-terminal residue’s chemical nature as a key parameter for transforming inert copper reservoirs into tunable generators of oxidative species.