A simple approach to membrane protein secondary structure and topology based on NMR spectroscopy

This paper describes a simple, qualitative approach for the determination of membrane protein secondary structure and topology in lipid bilayer membranes. The approach is based on the observation of wheel-like resonance patterns observed in the NMR H-1-N-15/N-15 polarization inversion with spin exchange at the magic angle (PISEMA) and H-1/N-15 heteronuclear correlation (HETCOR) spectra of membrane proteins in oriented lipid bilayers. These patterns, named Pisa wheels, have been previously shown to reflect helical wheel projections of residues that are characteristic of alpha -helices associated with membranes. This study extends the analysis of these patterns to beta -strands associated with membranes and demonstrates that, as for the case of alpha -helices, Pisa wheels are extremely sensitive to the tilt, rotation, and twist of beta -strands in the membrane. Therefore, the Pisa wheels provide a sensitive, visually accessible, qualitative index of membrane protein secondary structure and topology.