Direct Determination of a Molecular Torsional Angle in the Membrane Protein Rhodopsin by Solid-State NMR

Abstract

A solid-state NMR method (double-quantum heteronuclear local field NMR) is applied to a 13C2 labeled sample of the 41 kD integral membrane protein rhodopsin. The technique operates under magic-angle-spinning conditions, with good sensitivity and resolution, and allows a direct determination of molecular torsional angles, without estimating internuclear distances. In rhodopsin, we determine the H−C10−C11−H torsional angle of the retinylidene chromophore to be 160 ± 10°, indicating a significant deviation from the planar 10-11-s-trans conformation. Double-quantum heteronuclear local field NMR is shown to be a feasible method for the accurate determination of local molecular conformation in large molecular systems which are unsuitable for crystallography.