FIG. 2.

Helical wheel projection and two-dimensional PISEMA spectra of the uniformly ¹⁵N-labeled polypeptides in oriented lipid bilayers. A, B, and C. AChR M2. D, E, and F. Magainin II. A. Helical wheel projection of the amide N atoms of AChR M2. B. Experimental PISEMA spectrum of AChR M2, which provided most of the orientational constraints used for structure determination (10). C. Spectrum calculated for an α-helix with 3.6 residues per turn, identical dihedral angles, and a tilt of 12° relative to the membrane normal. D. Helical wheel view of the CA atoms of the magainin II helix with the N-terminus in front. The three-dimensional orientation of the peptide was determined from the angular constraints for Val17 derived from the three-dimensional solid-state NMR spectrum (24). The dashed line marks the boundary between polar (white) and hydrophobic (gray) residues in the amphipathic helix. E. Experimental PISEMA spectrum of magainin II. F. Spectrum calculated from the solution NMR structure of magainin in lipid micelles (PDB file 2MAG). Conditions for sample preparation and for solid-state NMR experiments of AChR M2 (10) and magainin (28) have been described. Spectra were calculated as described in Fig. 1.