Fig. 1.
PISEMA spectra of single- and multiple-site-labeled samples that have been superimposed in three sequential groups: (A) sites 26–31, (B) sites 32–37, and (C) sites 38–43. Three sites in the hydrophobic transmembrane domain from residues 26–43 have not been observed: residues 31, 34, and 37. The samples are uniformly aligned DMPC bilayers containing M2-TMP in a 1:16 molar ratio oriented such that the bilayer normal is parallel to Bo. Hydration is ∼50%, pH is ∼7, and samples were observed at room temperature, above the gel to liquid-crystalline phase transition. The phase-alternated Lee-Goldberg homonuclear decoupling scales the dipolar interaction by 0.81 and, consequently, the dipolar scale has been adjusted appropriately. Only one of a symmetric pair of dipolar resonances is shown. Seven different M2-TMP preparations with the following labeled sites were used: 26–30; 26, 36, 38; 27, 28; 32, 33, 35, 39, 42; 40; 41; and 43. All spectral assignments have been confirmed by specific site labeling. Lines have been drawn between resonances from sequentially adjacent amino acids showing the presence of PISA wheels in the spectra directly reflecting helical wheels.