Lipid membrane translocation mechanism of the antimicrobial peptide buforin 2

The antimicrobial peptide magainin 2 isolated from Xenopus skin crosses lipid bilayers by transiently forming a peptide-lipid supramolecular complex pore inducing membrane permeabilization and flip-flop of membrane lipids. In contrast, buforin 2 discovered in Bufo Bufo stomach efficiently translocates across lipid bilayers without inducing severe membrane permeabilization or lipid flip-flop, and the Pro(11) residue plays a key role for this unique property. The translocation efficiencies of F10W-buforin 2 (BF2), P11A-BF2, and F5W-magainin 2 (MG2) across egg yolk phosphatidylglycerol (PG)/egg yolk phosphatidylcholine (PC) (1/1) bilayers were dependent supralinearly on the peptide concentration, suggesting that several peptide molecules are involved in the translocation processes. The incorporation of the negative curvature-inducing egg. yolk phosphatidylethanolamine (PE) completely suppressed the translocation of BF2, indicating the induction of positive curvature by BF2 on the membrane is related to the translocation process, similarly to MG2. In pure PG, membrane permeabilization and coupling lipid flip-flop were clearly observed. Structural studies by use of Fourier transform infrared- polarized attenuated total reflection spectroscopy indicated that BF2 assumed distorted helical structures in PG/PC bilayers. These data indicate that BF2 translocates across lipid bilayers by a mechanism similar to that of MG2. The presence of Pro(11) distorts the helix, concentrating basic amino acid residues in a limited amphipathic region thus destabilizing the pore by enhanced electrostatic repulsion, enabling efficient translocation.