A Resonance Assignment Method for Oriented-Sample Solid-State NMR of Proteins

A general sequential assignment strategy for uniformly N-15-labeled uniaxially aligned membrane proteins is proposed. Mismatched Hartmann-Hahn magnetization transfer is employed to establish proton-mediated correlations among the neighboring N-15 backbone spins. Magnetically aligned Pf1 phage coat protein was used to illustrate the method. Exchanged and nonexchanged separated local field spectra were acquired and overlaid to distinguish the cross-peaks from the main peaks. Most of the original assignments from the literature were confirmed without selectively labeled samples. This method is applicable to proteins with arbitrary topology and will find use in assigning solid-state NMR spectra of oriented membrane proteins for their subsequent structure determination.