Transbilayer Transport of Ions and Lipids Coupled with Mastoparan X Translocation

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Abstract
The transbilayer movement of ions and lipids induced by mastoparan X, a peptidic toxin from Vespa xanthoptera, was investigated by use of lipid vesicles as a model membrane system. Negatively charged phosphatidylglycerol remarkably enhanced the peptide−lipid interactions. Mastoparan X induced the ion flow by forming a short-lived, multimeric pore in the lipid bilayer, as determined from the leakage of an anionic dye, calcein, from the liposomes. The pore formation was coupled with the translocation of the peptide into the inner leaflet. The latter was detected by three experiments using fluorescence techniques [Matsuzaki, K., Murase, O., Fujii, N., & Miyajima, K. (1995) Biochemistry 34, 6521−6526; Matsuzaki, K., Murase, O., & Miyajima, K. (1995) Biochemistry 34, 12553−12559]. The lipid flip flop was monitored on the basis of the chemical quenching of 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)-labeled lipids by sodium dithionite. Mastoparan X triggered the rapid flip-flop of both negatively charged and zwitterionic lipids in coupling with the pore formation and the peptide translocation. A novel model of the mastoparan−lipid interactions was proposed to explain these observations.