Deuterium-MAS NMR spectroscopy on oriented membrane proteins: Applicationsto photointermediates of bacteriorhodopsin

We present the first application of MAOSS (magic angle oriented sample spin ning) NMR spectroscopy to a large membrane protein. This new solid-state NM R approach is used to study the orientation of the deuterated methyl group in [18-CD3]-retinal in oriented bacteriorhodopsin in both the photocycle gr ound state (bR(568)) and in the photo intermediate stare M-412 Deuterium MA S spectra consist of a set of narrow spinning sidebands if the sample spinn ing rare does not exceed the anisotropy of the quadrupole interaction. In o rdered systems, such as proteins in oriented membranes, each sideband inten sity is orientationally dependent. The observed MAS sideband pattern is mod ulated in a highly sensitive way by changes in the molecular orientation of the CD3 group during the transition from all-trans- to 13-cis-retinal upon photoactivation. The significant improvement in spectral sensitivity and r esolution, compared to static NMR on oriented samples, allows a reliable an d precise data analysis even from lower spin concentrations and has more ge neral consequences for studying oriented membrane proteins by NMR. MAOSS NM R is shown to be a feasible method for the accurate determination of local molecular orientations in large molecular systems which are currently a cha llenge for crystallography.