Antimicrobial peptides are short peptides secreted by the innate immune system to protect the host from pathogens. We have investigated the influence of the amino terminal copper and nickel binding (ATCUN) motif on derivatives of ovispirin-3 (OV-3), an α-helical peptide from the cathelicidin family, demonstrating an increased antimicrobial activity toward a broad range of bacteria, relative to OV-3, with MICs as low as 1.3 ± 0.6 μM. Each peptide was able to bind DNA and RNA with micromolar affinity, but did not display nuclease activity in vivo. The ATCUN OV-3 derivatives also displayed an increased membrane leakage and lipid peroxidation relative to Cu-GGH and OV-3 alone. These data suggest that the Cu-ATCUN derivatives inhibit bacteria by binding to the membrane, promoting oxidative damage of the lipids, which then disrupts the bilayer, resulting in cell death. This stands in contrast to the mode of action of OV-3 alone, which permeabilizes the membrane without lipid oxidation.