Kinetics of Membrane Permeabilization by Human Antimicrobial Peptide LL-37

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The molecular mechanism of membrane permeabilization by antimicrobial peptides (AMPs) has been an active field of research. There are suggestions that different AMPs might act with different mechanisms. One example used to support this hypothesis is LL-37 which was found by two independent studies that the helical peptide adsorbs to the membrane with its helical axis parallel to the membrane. Base on this result, it was concluded that LL-37 does not form pores, unlike many well studied AMPs, such as magainin. We have recently found that this result was due to the impediment of peptide rotation in the multilayers, because LL-37 is longer than the membrane thickness. We have detected pores by LL-37 in swollen multilayers by neutron in-plane scattering and also found that the helices were oriented normal to the membrane, exactly like magainin. We would like to know if the pore formation by long helices may exhibit kinetic potential barriers. By observing individual giant unilamellar vesicles (GUVs), we found that the pores are stable and of finite size consistent with neutron measurement. However, sometimes the pores reduce their sizes in time, allowing only partial leakage of large dye molecules, while small dye molecules completely leaked out. Both the formation of the pores and change of pore size occur stochastically as if there are potential barriers for each type of event. We also used the method of aspiration to correlate the leakage with the change of aspiration protrusion length. The maximum protrusion length before pore formation depends on the peptide concentration, exhibiting yet another type of potential barrier.