CHAPTER 26: Large Protein Complexes Revealed by Solution-State NMR: G Proteins and G Protein-Activated Inwardly Rectifying Potassium Ion Channel

In contrast to solid-state NMR, which allows analyses of proteins with a theoretically unlimited molecular size, solution-state NMR techniques are limited by the molecular mass of proteins. However, recent progress, especially in the development of transverse relaxation-optimized spectroscopy (TROSY), has expanded the upper limit of the molecular mass to higher than 100 kDa. Furthermore, the binding interfaces of larger protein complexes can be identified by transferred cross-saturation (TCS), paramagnetic relaxation enhancement (PRE), etc. These solution-state NMR techniques for larger protein complexes were applied to GTP-binding proteins (G proteins) and the G protein-gated inwardly rectifying potassium channel (GIRK). The residues at the complex interface and those undergoing structural changes upon binding revealed the mechanism of GIRK channel regulation by G proteins.