Structure, Topology, and Dynamics of Membrane Peptides and Proteins from Solid-State NMR Spectroscopy

Mei Hong, John D. Corbett Professor of Chemistry at Iowa State University, received her B.A. in 1992 from Mount Holyoke College and her Ph.D. in chemistry in 1996 from the University of California at Berkeley. She then spent one year as a NIH postdoctoral fellow at the Massachusetts Institute of Technology and two years at the University of Massachusetts Amherst as a research professor. Since joining the faculty of Iowa State University in 1999, she has focused her research on the development and application of solid-state NMR techniques to the determination of the structure and dynamics of membrane proteins, with a special emphasis on membrane protein topology. She also investigates the conformation of structural proteins such as elastin and collagen.

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 Å) 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 β-sheet membrane protein orientation are described. The quaternary structure of membrane peptide assemblies can now be elucidated using a ¹⁹F spin diffusion technique that simultaneously yields the oligomeric number and intermolecular distances up to 15 Å. Finally, long-range distances up to 10 Å can now be measured using ¹H spins with an accuracy of better than 1 Å. These methods are demonstrated on several β-sheet membrane peptides with antimicrobial activities and on two α-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.