Activity of Membrane-Permeabilizing Lpt Peptides.

Area of Science:

• Microbiology and Molecular Biology
• Biochemistry and Biophysics

Background:

• Type I toxin-antitoxin systems, encoded on plasmid DNA in Lacticaseibacillus strains, utilize peptides like Lpt.
• These peptides are 29 amino acids long, predicted to have an alpha-helical structure with a hydrophobic core and charged termini.

Purpose of the Study:

• To investigate the toxicity and membrane-permeabilizing capabilities of Lpt and Lpt-like peptides.
• To elucidate the mechanism of action of these peptides on bacterial cell membranes.

Main Methods:

• Expression of Lpt and Lpt-like peptides in E. coli to observe cellular effects.
• Liposome leakage assays, dynamic light scattering, and circular dichroism (CD) spectroscopy to evaluate membrane interaction.
• Analysis of peptide structural changes upon liposome interaction.

Main Results:

• Lpt and Lpt-like peptides induced growth arrest, nucleoid condensation, and cell membrane damage in E. coli.
• Peptides caused liposome leakage dependent on concentration, without complete liposome disruption.
• Peptide activity was influenced by liposome size and negative charge (PCPS), and peptides lost alpha-helical structure upon membrane interaction.

Conclusions:

• Lpt and Lpt-like peptides act by transiently disrupting the membrane permeability barrier, likely forming "lipid pores".
• The mechanism differs from typical membrane-active peptides that form stable pores.
• Peptide structural destabilization upon membrane interaction is a key feature of their activity.