Chapter 19. Solid-state NMR and Membrane Proteins: Key Interactions in Biomacromolecules

Membrane proteins play a crucial role in maintaining the homeostasis of living cells. The characterization of key membrane protein interactions, such as specific hydrogen bonds and electrostatic contacts in the reaction centre of membrane proteins, is a fairly straightforward approach for understanding their function at a molecular level. Solid-state nuclear magnetic resonance (NMR) spectroscopy is convenient for the structural and biophysical analysis of membrane proteins embedded in lipid bilayers. In this chapter, we introduce several recent NMR approaches for ingenious detection of key interactions on membrane proteins. Monitoring of the alterations in isotropic chemical shifts can find local structural change of sodium ion pump rhodopsin depending on pH, alkali metal ions, site-specific mutation, etc. Magic angle spinning (MAS) NMR experiments using recoupled 13C–15N heteronuclear and 13C–13C homonuclear dipolar interactions are applied to determine drug-binding site in M2 protein. To detect an initial proton transfer pathway in the light-driven proton pump protein, 1H–15N correlations assisted by dynamic nuclear polarization (DNP) with photo-irradiation can be observed for each photo-intermediate as a snapshot.