Self-Aggregation of Spin-Labeled Alamethicin in ePC Vesicles Studied by Pulsed Electron-Electron Double Resonance

摘要

In this communication we demonstrate the use of the pulsed electron-electron double resonance (PELDOR) technique to determine long-range distances among transmembrane helical peptide molecules. To shed light on the mechanism of channel formation, we studied the fundamental process of self-aggregation generated by a spin-labeled synthetic alamethicin analogue in phospholipid bilayers. Alamethicin is a membrane active peptaibol antibiotic of fungal origin that is able to change the permeability of biological membranes by forming conductive ion channels. It is generally believed that these channels are formed by self-assembling of a variable number of amphipathic molecules upon insertion into the phospholipid bilayer. In ref 4 the advantages offered by the PELDOR technique were highlighted in the investigation of the aggregation of a spin mono-labeled alamethicin F50/5 analogue in a membrane mimicking environment, that is, a frozen glass formed by a mixture of chloroform and toluene. In this medium the aggregation of the amphiphatic molecules was examined at 77 K and a 3D-structure for the supramolecular aggregate was proposed. More specifically, the experimental data on-the magnetic dipole-dipole interactions of the spin labels allowed us to estimate the number of peptide molecules forming the aggregate and to derive a function for the distance distribution between labels. The goal of the present work is to elucidate the self-aggregation phenomenon of the alamethicin in egg phosphocholine (ePC) large multilamellar vesicles (LMV).