Arenicin-1-induced apoptosis-like response requires RecA activation and hydrogen peroxide against Escherichia coli.

Arenicin-1, a 21-mer antimicrobial peptide exerts significant broad-spectrum antimicrobial activity with membrane-active mechanisms. However, owing to multiple mechanisms of cell death, the antibacterial mechanism of arenicin-1 requires detailed analysis. In the present study, arenicin-1-treated bacteria underwent an apoptosis-like response, which was mechanistically and morphologically similar to eukaryotic apoptosis. Changes in the physiological status of arenicin-1-treated bacterial cells involved accumulation of reactive oxygen species, imbalance of intracellular calcium gradients, disruption of membrane potential, bacterial caspase-like protein activation, and DNA damage. In arenicin-1-induced apoptosis-like death, autocleavage of LexA was observed because of the activation of the caspase-like activity of RecA. Additionally, typical reactive oxygen species such as superoxide, hydrogen peroxide, and hydroxyl radicals, were scavenged in arenicin-1-treated cells to assess the role of specific reactive oxygen species. Scavenging of hydrogen peroxide interfered with the activity of arenicin-1 in Escherichia coli, whereas the superoxide and hydroxyl radicals level did not affect arenicin-1-induced apoptosis-like death activity. Furthermore, inhibition of Fenton reaction attenuated apoptosis-like response. In conclusion, arenicin-1-induced apoptosis like death requires SOS response proteins and is mediated by hydrogen peroxide and Fenton reaction in E. coli. Arenicin-1 may be a representative antimicrobial peptide with potent apoptotic response against E. coli.

Redesigning Arenicin-1, an Antimicrobial Peptide from the Marine Polychaeta Arenicola marina, by Strand Rearrangement or Branching, Substitution of Specific Residues, and Backbone Linearization or Cyclization.

Arenicin-1, a ß-sheet antimicrobial peptide isolated from the marine polychaeta Arenicola marina coelomocytes, has a potent, broad-spectrum microbicidal activity and also shows significant toxicity towards mammalian cells. Several variants were rationally designed to elucidate the role of structural features such as cyclization, a certain symmetry of the residue arrangement, or the presence of specific residues in the sequence, in its membranolytic activity and the consequent effect on microbicidal efficacy and toxicity. The effect of variations on the structure was probed using molecular dynamics simulations, which indicated a significant stability of the ß-hairpin scaffold and showed that modifying residue symmetry and ß-strand arrangement affected both the twist and the kink present in the native structure. In vitro assays against a panel of Gram-negative and Gram-positive bacteria, including drug-resistant clinical isolates, showed that inversion of the residue arrangement improved the activity against Gram-negative strains but decreased it towards Gram-positive ones. Variants with increased symmetry were somewhat less active, whereas both backbone-cyclized and linear versions of the peptides, as well as variants with R→K and W→F replacement, showed antimicrobial activity comparable with that of the native peptide. All these variants permeabilized both the outer and the inner membranes of Escherichia coli, suggesting that a membranolytic mechanism of action was maintained. Our results indicate that the arenicin scaffold can support a considerable degree of variation while maintaining useful biological properties and can thus serve as a template for the elaboration of novel anti-infective agents.