Review conformation, self-aggregation, and membrane interaction of peptaibols as studied by pulsed electron double resonance spectroscopy

Pulsed EPR methods, in particular pulsed electron double resonance (PELDOR) [or double electron-electron resonance (DEER)], are very sensitive to the dipole ··· dipole interaction between electron spins in a pair of free radicals. Using PELDOR, the conformations of a number of double radical-containing biomolecules have been determined. In this review article, we focused our attention on the application of this spectroscopy to nitroxide-labeled peptaibols. This is an emerging class of naturally occurring, relatively short, linear, helical peptide molecules endowed with hydrophobic character, capability to interact with and to alter the structure of membranes, and antibiotic activity. We extracted detailed information on the secondary structures of specifically site-directed, double nitroxide-labeled peptaibols under a variety of experimental conditions, including biologically relevant environments. Moreover, we examined in-depth peptaibol clustering, related to the marked propensity of these molecules to undergo self-association in model and whole-cell membrane systems, using mainly mono-nitroxide-containing synthetic analogs. Finally, based on the PELDOR data accumulated, we proposed models of supramolecular (quaternary) structures of peptaibols and their binding modes to membranes.