The Alignment of Membrane-Active Peptides Depends on the Lipid Phase State as Viewed by solid state 19F-NMR

Abstract

Amphipathic membrane-active peptides (antimicrobial, hemolytic, cell-penetrating, fusogenic, etc.) achieve their functions by distinct interaction with lipid bilayers. Some typical structural modes are described in terms of models like the “barrel stave”, “toroidal pore”, “carpet” etc. These models are related to the alignment states of the peptides in the lipid bilayers (surface bound “S-state”, inserted “I-state” or tilted “T-state”), which can be readily characterized by solid state NMR. When determining such alignment, factors like peptide/lipid ratio, charge of the bilayer surface, thickness of the bilayer core, presence of cholesterol, and humidity are typically investigated. Yet, the lipid phase state as an explicit variable parameter has not received much attention so far. Here, we demonstrate that a change in the lipid phase can directly trigger the re-alignment of many peptides. Several representative examples are illustrated here: PGLa, PGLa/Magainin, gramicidin S, SAP and alamethicin. In macroscopically oriented DMPC bilayers, using highly-sensitive 19F-NMR we have monitored the changes between known alignment states of these peptides as a function of temperature, covering both the gel and liquid-crystalline states of DMPC. We show that for all peptides studied the alignment in the gel-state differs from the one in the liquid-crystalline bilayers and can be reversibly changed by passing through the lipid phase transition temperature. The relevance of these finding for the phase state of native biological membranes and interactions of membrane-active peptides with them will be discussed.