An Antimicrobial Peptide, Magainin 2, Induced Rapid Flip-Flop of Phospholipids Coupled with Pore Formation and Peptide Translocation

TLDR

The study examined how the antimicrobial peptide magainin 2 alters phospholipid flip‑flop rates using fluorescent lipid probes. A model was proposed in which lipids move laterally along the walls of peptide‑lipid pores to cross the membrane. Magainin 2 reduced flip‑flop half‑lives to minutes, coupled this rapid translocation with membrane permeabilization and peptide entry, and the rate was independent of initial leaflet labeling.

Abstract

The effect of an antimicrobial peptide, magainin 2, on the flip-flop rates of phospholipids was investigated by use of fluorescent lipids, i.e., anionic N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)dipalmitoyl-l-α-phosphatidylethanolamine (NBD-PE), 1-oleoyl-2-[12-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl]-l-α-phosphatidic acid (C12-NBD-PA), 1-oleoyl-2-[12-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl]-l-α-phosphatidyl-l-serine (C12-NBD-PS), and zwitterionic 1-palmitoyl-2-[6-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)caproyl]-l-α-phosphatidylcholine (C6-NBD-PC). Their intrinsic flip-flop half-lives at 30 °C in the absence of the peptide were 1.1 h, ca. 7 h, ca. 8 days, and >2 days, respectively. The peptide accelerated the flip-flop half-lives of the fluorescent lipids to an order of minutes. Furthermore, the flip-flop was coupled with the membrane permeabilization and the peptide translocation [Matsuzaki, K., Murase, O., Fujii, N., & Miyajima, K. (1995) Biochemistry 34, 6521−6526], suggesting pore-mediated flip-flop. The flip-flop rate was independent of the initial labeling conditions (outer leaflet label or inner leaflet label). From these results, a model was proposed, in which the lipids translocate across the membrane by lateral diffusion along the wall of the pores composed of the peptides and the lipids. A simple theoretical calculation could explain the coupling of the flip-flop with the permeabilization.