Title : Magic Angle Spinning NMR Studies of M218--60, VDAC, and bR
In the last few years magic angle spinning (MAS) NMR has emerged as an important approach to examine the structure and function of membrane proteins. One of the primary advantages is that it enables studies of structure and function in native or quasi-native lipid environments, thus circumventing the perturbing effect of detergents which are often required for solution NMR experiments and crystallography. In addition, it has become possible to enhance the sensitivity of these experiments using dynamic nuclear polarization (DNP) by factors of ~100, thus facilitating more detailed structural studies. In this presentation we discuss the applications of MAS and DNP to three membrane proteins: M2 from influenza-A, the voltage dependent anion channel (VDAC), and bacteriorhodopsin. Studies of M218-60 indicate that this construct, which is fully functional, assembles as a dimer of dimers, rather a tetramer as seen in solution NMR and crystallographic studies. In addition, the amino-admantanyl drugs bind in the pore rather than on the surface. The structure, determined by a variety of dipole recoupling experiments shows that the His and Trp responsible for the H+ conduction are tightly packed M218-60 and that the transfer is likely an intermolecular process. We study VDAC in 2D crystals of DMPC and show that the protein perturbs the lipid gel®liquid crystalline transition, but that the protein does not change conformation dramatically in traversing this transition. We also delineate the structure of the N-terminal tail and show that it is situated in contact with the face of the β-barrel. Finally, we study the structure of photocycle intermediates of bR with DNP enhanced spectra and obtain evidence that bR could be a inward directed OH- pump rather than an outward directed H+ pump.