Depending on the coordination, copper ions can have a very high activity in catalyzing the production of reactive oxygen species. Thus interest arose in increasing the activity of antimicrobial peptides (AMPs) by equipping them with a Cu-binding unit. Several examples, native and engineered, have been investigated with the motif Xxx-Zzz-His, called Amino Terminal Cu(II)-and Ni(II)-binding (ATCUN) motif. Here we investigate a short AMP that was equipped either with Xxx-Zzz-His or Xxx-His. Xxx-His is a shorter motif and yields a more redox active copper complex. The control AMP, Xxx-His-AMP and Xxx-Zzz-His-AMP were investigated toward Cu-binding, Reactive Oxygen Species (ROS) production and antimicrobial activity in E. coli. The data indicate that these Cu-binding motifs have very limited impact on antimicrobial activity and low ROS production capability.

Copper (Cu) is essential for most organisms, but it can be poisonous in excess, through mechanisms such as protein aggregation, trans-metallation and oxidative stress. Latter could implicate the formation of potentially harmful Reactive Oxygen Species (ROS: O2•–, H2O2 and HO•) via the redox cycling between Cu(II)/Cu(I) states in the presence of dioxygen and physiological reducing agents such as ascorbate (AscH), cysteine (Cys) and the tripeptide glutathione (GSH). Although the reactivity of Cu with these reductants has been previously investigated, the reactions taking place in a more physiologically-relevant mixture of these biomolecules are not known. Hence, we report here on the reactivity of Cu with binary and ternary mixtures of AscH, Cys and GSH. By measuring ascorbate and thiol oxidation, as well as HO• formation, we show that Cu reacts preferentially with GSH and Cys, halting AscH oxidation and also HO• release. This could be explained by the formation of Cu-thiolate clusters with both GSH and, as we first demonstrate here, Cys. Moreover, we observed a remarkable acceleration of Cu-catalysed GSH oxidation in the presence of Cys. We provide evidence that both thiol-disulfide exchange and the generated H2O2 contribute to this effect. Based on these findings, we speculate that Cu-induced oxidative stress may be mainly driven by GSH depletion and/or protein disulfide formation rather than by HO• and envision a synergistic effect of Cys on Cu toxicity.