AN ANTIMICROBIAL PEPTIDE, MAGAININ-2, INDUCED RAPID FLIP-FLOP OF PHOSPHOLIPIDS COUPLED WITH PORE FORMATION AND PEPTIDE TRANSLOCATION

The effect of an antimicrobial peptide, magainin 2, on the flip-flop r ates of phospholipids was investigated by use of fluorescent lipids, i .e., anionic -4-yl)dipalmitoyl-L-alpha-phosphatidylethanolamine (NBD-P E), iazol-4-yl)-amino)dodecanoyl]-L-alpha-phosphatidic acid (C-12-NBD- PA), l)-amino)dodecanoyl]-L-alpha-phosphatidyl-L-serine (C-12-NBD-PS), and zwitterionic ol-4-yl)amino)caproyl]-L-alpha-phosphatidylcholine ( C-6-NBD-PC). Their intrinsic flip-flop half-lives at 30 degrees C in t he 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 th e fluorescent lipids to an order of minutes. Furthermore, the flip-flo p was coupled with the membrane permeabilization and the peptide trans location [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 (out er leaflet label or inner leaflet label). From these results, a model was proposed, in which the lipids translocate across the membrane by l ateral diffusion along the wall of the pores composed of the peptides and the lipids. A simple theoretical calculation could explain the cou pling of the flip-flop with the permeabilization.