Chapter 10 The use of isotopes for probing ligand-protein interactions and ligand structure: The rhodopsin g-protein coupled membrane receptor paradigm

Abstract

This chapter presents some recent applications of enrichment with stable 13 C isotopes and magic angle spinning (MAS) nuclear magnetic resonance (NMR) studies of rhodopsin. Comprehensive information about the electronic and spatial structure of the ligand can be obtained when bound to the membrane with isotope labeling and MAS NMR. The chapter provides an overview of the labeling and MAS NMR studies aiming at a characterization of ligand-protein interactions for rhodopsin via the determination of chemical shifts. To illustrate the capabilities of MAS NMR for studying photoproducts, shift data on the ligand–protein interactions in bathorhodopsin, structural data for the pre-discharge metarhodopsin I, and shift data for the discharged metarhodopsin II photointermediate is also reviewed. MAS NMR, in conjunction with selective isotope enrichment, is the method of choice for NMR investigations of membrane protein receptors when in the membrane in their natural environment. It is a technique for obtaining high-resolution NMR data from solids. In a MAS NMR experiment, the chemical shift anisotropy broadening of the NMR response in the solid state is suppressed by macroscopic sample rotation around an axis at the magic angle β m = 54°44′ with respect to the applied magnetic field.