Non-Crystallographic Methods to Study Membrane Proteins

Abstract

Conventional high resolution NMR methods cannot be applied readily to the study of macromolecular complexes. The complication arises because of the intrinsic slow motion of the whole complex with respect to the applied magnetic field causing extensive line-broadening due to the anisotropy of the magnetic interactions with the applied field. However, the anisotropy of certain nuclei (²H and ³¹P) can be exploited and put to good use when studying membrane proteins using solid state, static NMR methods on oriented membranes. In an alternative approach, NMR samples are set spinning at 54.7° (the “magic” angle) to the applied field. Here the anisotropic magnetic interactions are averaged to give high resolution-like NMR spectra, but from very large complexes. Using these approaches, specific molecular details can be obtained for large integral membrane proteins in bilayers, by studying small, labelled molecules or prosthetic groups bound in specific sites within the protein to enable deductions to be made about the protein binding or interaction site.