MAGIC ANGLE-ORIENTED SAMPLE-SPINNING (MAOSS) - A NEW APPROACH TOWARD BIOMEMBRANE STUDIES

The application of magic angle sample spinning (MAS) NMR to uniformly aligned biomembrane samples is demonstrated as a new general approach toward structural studies of membrane proteins, peptides, and lipids. The spectral linewidth from a multilamellar lipid dispersion is domina ted, in the case of protons, by the dipolar coupling. For low-gamma or dilute spins, however, the chemical shift anisotropy dominates the sp ectral linewidth, which is reduced by the two-dimensional order in a u niformly aligned lipid membrane. The remaining line broadening, which is due to orientational defects (''mosaic spread'') can be easily remo ved at low spinning speeds. This orientational order in the sample als o allows the anisotropic intermolecular motions of membrane components (such as rotational diffusion, tau(c) = 10(-10) s) for averaging dipo lar interactions to be utilized, e.g., by placing the membrane normal parallel to the rotor axis. The dramatic resolution improvement for pr otons which are achieved in a lipid sample at only 220 Hz spinning spe ed in a 9.4 T field is slightly better than any data published to date using ultra-high fields (up to 17.6 T) and highspeed spinning (14 kHz ). Additionally, the analysis of spinning sidebands provides valuable orientational information. We present the first H-1, P-31, and C-13 MA S spectra of uniformly aligned dimyristoylphosphatidylcholine (DMPC) b ilayers. Also, H-1 resolution enhancement for the aromatic region of t he M13 coat protein reconstituted into DMPC bilayers is presented. Thi s new method combines the high resolution usually achieved by MAS with the advantages of orientational constraints obtained by working with macroscopically oriented samples. We describe the general potential an d possible perspectives of this technique. (C) 1998 Academic Press.