Structure and spatial distribution of the spin-labelled lipopeptide trichogin GA IV in a phospholipid membrane studied by pulsed electron-electron double resonance (PELDOR).

The method of pulsed electron-electron double resonance (PELDOR) is exploited to study intra- and intermolecular dipole-dipole interactions between the spin labels of trichogin GA IV analogues. This lipopeptaibol antibiotic was studied in multilamellar membranes of dipalmitoylphosphatidylcholine frozen to 77 K. For mono-labelled trichogin analogues, the molecules are shown not to form aggregates in the lipid membranes studied. For the double-labelled trichogin analogues, a function of the distance distribution between the spin labels has been obtained. We determined that the distribution function has two main maxima located at distances of 1.25 nm and 1.75 nm. The value of 1.25 nm is close to the distance between labels of a alpha-helical structure. On the other hand, a distance of 1.75 nm corresponds to a mixed 3D-structure in which a 3(10)-helix is combined with a more elongated conformation.