Orientation determination of membrane-disruptive proteins using powder samples and rotational diffusion: A simple solid-state NMR approach

The orientation of membrane proteins undergoing fast uniaxial rotation around the bilayer normal can be determined without macroscopic alignment. We show that the motionally averaged powder spectra exhibit their 0° frequency, δ ¯ ∥ , at the same position as the peak of an aligned sample with the alignment axis parallel to the magnetic field. This equivalence is exploited to determine the orientation of a β-sheet antimicrobial peptide not amenable to macroscopic alignment, using 13CO and 15N chemical shifts from powder spectra. This powder sample approach permits orientation determination of naturally membrane-disruptive proteins in diverse environments and under magic-angle spinning.