A solid-state NMR index of helical membrane protein structure and topology

The secondary structure and topology of membrane proteins can be described by inspection of two-dimensional H-1-N-15 dipolar coupling/N-15 chemical sh ift-polarization inversion spin exchange at the magic angle spectra obtaine d from uniformly N-15-labeled samples in oriented bilayers. The characteris tic wheel-like patterns of resonances observed in these spectra reflect hel ical wheel projections of residues in both transmembrane and in-plane helic es and hence provide direct indices of the secondary structure and topology of membrane proteins in phospholipid bilayers. We refer to these patterns as PISA (polarity index slant angle) wheels. The transmembrane helix of the M2 peptide corresponding to the pore-lining segment of the acetylcholine r eceptor and the membrane surface helix of the antibiotic peptide magainin a re used as examples. (C) 2000 Academic Press.