Helix Conformations in 7TM Membrane Proteins Determined Using Oriented-Sample Solid-State NMR with Multiple Residue-Specific 15N Labeling

Oriented solid-state NMR in combination with multiple-residue-specific 15N labeling and extensive numerical spectral analysis is proposed to determine helix conformations of large membrane proteins in native membranes. The method is demonstrated on uniaxially oriented samples of 15N-methionine, -valine, and -glycine-labeled bacteriorhopsin in native purple membranes. Experimental two-dimensional 1H-15N dipole-dipole coupling versus 15N chemical shift spectra for all samples are analyzed numerically to establish combined constraints on the orientation of the seven transmembrane helices relative to the membrane bilayer normal. Since the method does not depend on specific resonance assignments and proves robust toward nonidealities in the sample alignment, it may be generally feasible for the study of conformational arrangement and function-induced conformation changes of large integral membrane proteins.