Dual functions of the human antimicrobial peptide LL-37-target membrane perturbation and host cell cargo delivery

Area of Science:

• Biochemistry
• Cell Biology
• Membrane Biophysics

Background:

• The human antimicrobial peptide LL-37's cell recognition mechanisms are not fully understood.
• LL-37 exhibits antimicrobial properties and potential cell-penetrating capabilities.

Purpose of the Study:

• To investigate the membrane disruption capacity of LL-37 on different membrane compositions.
• To elucidate LL-37's interaction with target (bacterial) and host (eukaryotic) cell membranes.
• To explore LL-37's role in nucleic acid delivery into host cells.

Main Methods:

• Utilized large unilamellar vesicles (LUVs) with varying lipid compositions (POPC, POPG, cholesterol).
• Assessed membrane disruption via calcein leakage assays.
• Employed linear dichroism and flow-oriented LUVs to study peptide orientation.
• Conducted confocal microscopy on eukaryotic cells for delivery studies.

Main Results:

• LL-37 induced rapid and efficient calcein leakage from POPG-containing LUVs, mimicking bacterial membranes.
• LL-37 did not induce leakage from zwitterionic POPC LUVs, mimicking host membranes.
• Cholesterol reduced LL-37-induced leakage.
• LL-37 adopted an alpha-helical structure parallel to the membrane surface and showed evidence of translocation.
• LL-37 facilitated the delivery of fluorescent oligonucleotides into eukaryotic cells.

Conclusions:

• LL-37 preferentially disrupts bacterial-like membranes over host-like membranes.
• LL-37's membrane interaction involves helical orientation and potential translocation, influencing leakage kinetics.
• LL-37 possesses dual functionality: antimicrobial activity and cell-penetrating peptide (CPP) capabilities for nucleic acid delivery.