Structure, topology, and dynamics of membrane peptides and proteins from solid-state NMR Spectroscopy

The high-resolution structure of membrane proteins is notoriously difficult to determine due to the hydrophobic nature of the protein-membrane complexes. Solid-state NMR spectroscopy is a unique and powerful atomic-resolution probe of the structure and dynamics of these important biological molecules. A number of new solid-state NMR methods for determining the depth of insertion, orientation, oligomeric structure, and long-range (10-15 angstrom) distances of membrane proteins are summarized. Membrane protein depths can now be determined using several complementary techniques with varying site-specificity, distance precision, and mobility requirement on the protein. Membrane protein orientation can now be determined with or without macroscopic alignment, the latter providing a novel alternative for orientation determination of intrinsically curvature-inducing proteins. The novel analyses of beta-sheet membrane protein orientation are described. The quaternary structure of membrane peptide assemblies can now be elucidated using a F-19 spin diffusion technique that simultaneously yields the oligomeric number and intermolecular distances up to 15 angstrom. Finally, long-range distances up to similar to 10 angstrom can now be measured using H-1 spins with an accuracy of better than 1 angstrom. These methods are demonstrated on several beta-sheet membrane peptides with antimicrobial activities and on two a-helical ion-channel proteins. Finally, we show that the nearly ubiquitous dynamics of membrane proteins can be readily examined using 2D correlation experiments. An intimate appreciation of molecular motion in these systems not only leads to important insights into the specific function of these membrane proteins but also may be exploited for other purposes such as orientation determination.