Reactive oxygen generation by minimal copper binding peptide motifs

Intrinsically disordered proteins such as amyloid-β (Aβ), prion protein (PRP) and α-synuclein bind copper-ions through histidine-rich motifs. Several of these copperbinding motifs catalyze formation of reactive oxygen species (ROS), which is believed to be involved in these proteins’ role in neurodegenerative disorders. The catalytic mechanism rely on binding in an ‘in-between state’, which is energetically available to both Cu(I) and Cu(II) and thus allow redox cycling. Presently, our knowledge of ROS generation is based on a few peptides studied for their pathological role and has thus not explored the minimal requirements for this function. Here, we investigate copper coordination and ROS generation in a series of synthetic histidine-rich peptides. We found that a minimal motif of two histidine residues joined by a few glycine residues is sufficient to generate ROS at two and a half times the rate of the corresponding Aβ complex. Copper-coordination and ROS generation are flexible with regard to the spacing of these two histidine residues suggesting that physiologically relevant Cubinding motifs are degenerate. Spectroscopic studies indicate that ROS activity correlate to coordination by two imidazole nitrogen atoms in a dynamic complex. This study suggests that copper-coordination and ROS production might be more prevalent in intrinsically disordered proteins than realized.