Membrane-peptide interaction studied by PELDOR and CW ESR: Peptide conformations and cholesterol effect on the spatial peptide distribution in the membrane

Abstract

Pulsed electron-electron double resonance (PELDOR) combined with continuous-wave electron paramagnetic resonance was used to study inter- and intramolecular dipole-dipole interactions between spin labels for spin-labeled analogs of trichogin GA IV bound to multilamellar membranes of egg L-alpha-phosphatidylcholine (ePC) and in ePC membranes containing cholesterol. All samples were frozen to 77 K. For mono-labeled peptide concentrations in lipid over the range between 0.5 to 2.2 mol%, it is shown that in these membranes trichogin molecules are distributed homogeneously and are likely to be located on or near the inner and outer membrane surfaces. Addition of cholesterol to a final concentration of 16.5 mol% leads to an increase of the local concentration of trichogin molecules in the membranes. For the double-labeled trichogin, a distribution of the intramolecular distance between the two spin labels was observed. The distribution function is characterized by two main maxima located at distances of 1.3 and 1.8 nm. The distance of 1.3 nm is close to that expected for the alpha-helix structure of the peptide chain. The distance of 1.8 nm corresponds to a mixed structure in which a 3(10) helix is combined with a set of even more elongated conformations

Interaction of hydrophobic and amphipathic antimicrobial peptides with lipid bicelles

“…Trichogin GA IV is another hydrophobic peptaibiotic, like alamethicin. Its location in the bilayer and its mechanism of action have been studied by EPR and several other spectroscopic and theoretical methods [50,[61][62][63][64][65][66][67][68]. Although the detailed mechanism is still under debate, there is a general consensus that at low P/L ratios, the peptide is monomeric and absorbed parallel to the membrane surface below the polar headgroups.…”

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

“…As already stated earlier in the text, inspection of crystallographic data for trichogin GA IV highlights a mixed 3 10 ‐/α‐helix structure for the peptide backbone . Since the α‐ and 3 10 ‐helices exhibit different main‐chain lengths, PELDOR was used to determine the conformation for its membrane‐bound state . Thus, when two TOAC residues are concomitantly incorporated at the ends of the peptaibol, information about its conformation can be obtained from the intramolecular distance between the nitroxide labels.…”

“…On the other hand, another PELDOR study of O‐Tri in ePC vesicles showed that, over the range of peptide to lipid concentration 0.5–2.2 mol %, trichogin molecules are homogeneously distributed at the inner and outer membranes, whereas upon addition of cholesterol the distribution was found to be inhomogeneous. Therefore, the presence of cholesterol is clearly promoting formation of thermodynamically stable aggregates.…”

“…Thus, when two TOAC residues are concomitantly incorporated at the ends of the peptaibol, information about its conformation can be obtained from the intramolecular distance between the nitroxide labels. In Figure a, the distance distribution function is reported for the double spin‐labeled F‐Tri , in eggPC membranes (eggPC membranes are composed of a mixture of saturated and unsaturated lipids of different lengths). Two main maxima are shown at distances of 1.25 and 1.77 nm, which correspond to α‐ and 3 10 ‐helical conformations, respectively.…”

Pulsed electron–electron double resonance (PELDOR) distance measurements in detergent micelles

“…The distribution of spin-clusters in lipid vesicle membranes can also be assumed to be homogeneous. The dimension of this homogeneous distribution varies from two to three depending on the sample concentration [13][14][15]. This corresponds to a stretched exponential decay function describing the background [16].…”