Activity of Membrane-Permeabilizing Lpt Peptides

Herein, we investigated the toxicity and membrane-permeabilizing capabilities of Lpt and Lpt-like peptides, belonging to type I toxin-antitoxin systems carried by plasmid DNA of Lacticaseibacillus strains. These 29 amino acid peptides are predicted to form α-helical structures with a conserved central hydrophobic sequence and differently charged hydrophilic termini. Like Lpt, the expression of Lpt-like in E. coli induced growth arrest, nucleoid condensation, and cell membrane damage, suggesting membrane interaction as the mode of action. The membrane permeabilization activity of both peptides was evaluated by using liposome leakage assays, dynamic light scattering, and CD spectroscopy. Lpt and Lpt-like showed liposome leakage activity, which did not lead to liposome disruption but depended on peptide concentration. Lpt was generally more effective than Lpt-like, probably due to different physical chemical properties. Leakage was significantly reduced in larger liposomes and increased with negatively charged PCPS liposomes, indicating that electrostatic interactions and membrane curvature influence peptide activity. Contrary to most membrane-active peptides, Lpt an Lpt-like progressively lost their α-helical structure upon interaction with liposomes. Our data are inconsistent with the formation of membrane-spanning peptide pores but support a mechanism relying on the transient failure of the membrane permeability barrier possibly through the formation of "lipid pores".