Interaction of mastoparan with membranes studied by 1H-NMR spectroscopy in detergent micelles and by solid-state 2H-NMR and 15N-NMR spectroscopy in oriented lipid bilayers

Abstract

Several complementary NMR approaches were used to study the interaction of mastoparan, a 14-residue peptide toxin from wasp venom, with lipid membranes. First, the 3D structure of mastoparan was determined using 1 H-NMR spectroscopy in perdeuterated (SDS-d 25 ) micelles. NOESY experiments and distance geometry calculations yielded a straight amphiphilic α-helix with high-order parameters, and the chemical shifts of the amide protons showed a characteristic periodicity of 3-4 residues. Secondly, solid-state 2 H-NMR spectoscopy was used to describe the binding of mastoparan to lipid bilayers, composed of headgroup-deuterated dimyristoylglycerophosphocholine (DMPC-d 4 ) and dimyristoylphosphatidylglycerol (DMPG). By correlating the deuterium quadrupole splittings of the α-segments and β-segments, it was possible to differentiate the electrostatically induced structural response of the choline headgroup from dynamic effects induced by the peptide. A partial phase separation was observed, leading to a DMPG-rich phase and a DMPG-depleted phase, each containing some mastoparan. Finally, the insertion and orientation of a specifically 15 N-labeled mastoparan (at position Ala10) in the bilayer environment was investigated by solid-state 15 N-NMR spectroscopy, using macroscopically oriented samples. Two distinct orientational states were observed for the mastoparan helix, namely an in-plane and a trans-membrane alignment. The two populations of 90% in-plane and 10% trans-membrane helices are characterized by a mosaic spread of ± 30° and ± 10°, respectively. The biological activity of mastoparan is discussed in terms of a pore-forming model, as the pept ide is known to be able to induce nonlamellar phases and facilitate a flip-flop between the monolayers.