Formation of β-Strand Oligomers of Antimicrobial Peptide Magainin 2 Contributes to Disruption of Phospholipid Membrane

The antimicrobial peptide magainin 2 (M2) interacts with and induces structural damage in bacterial cell membranes. Although extensive biophysical studies have revealed the interaction mechanism between M2 and membranes, the mechanism of membrane-mediated oligomerization of M2 is controversial. Here, we measured the synchrotron-radiation circular dichroism and linear dichroism (LD) spectra of M2 in dipalmitoyl-phosphatidylglycerol lipid membranes in lipid-to-peptide (L/P) molar ratios from 0-26 to characterize the conformation and orientation of M2 on the membrane. The results showed that M2 changed from random coil to alpha-helix structures via an intermediate state with increasing L/P ratio. Singular value decomposition analysis supported the presence of the intermediate state, and global fitting analysis revealed that M2 monomers with an alpha-helix structure assembled and transformed into M2 oligomers with a beta-strand-rich structure in the intermediate state. In addition, LD spectra showed the presence of beta-strand structures in the intermediate state, disclosing their orientations on the membrane surface. Furthermore, fluorescence spectroscopy showed that the formation of beta-strand oligomers destabilized the membrane structure and induced the leakage of calcein molecules entrapped in the membrane. These results suggest that the formation of beta-strand oligomers of M2 plays a crucial role in the disruption of the cell membrane.

Automated summary

The antimicrobial peptide magainin 2 (M2) interacts with bacterial cell membranes and causes structural damage. This study investigates the conformation and orientation of M2 on lipid membranes, as well as the mechanism of membrane-mediated oligomerization of M2. The results suggest that the formation of beta-strand oligomers plays a crucial role in the disruption of the cell membrane.