Conformational Changes in the G Protein-Coupled Receptor Rhodopsin Revealed by Histidine Hydrogen-Deuterium Exchange

G protein-coupled receptors (GPCRs) are activated by ligand binding, allowing extracellular signals to be efficiently transmitted through the membrane to the G protein recognition site, 40 angstrom away. Utilizing His residues found spaced throughout the GPCR, rhodopsin, we used His hydrogen-deuterium exchange (His-HDX) to monitor long-time scale structural rearrangements previously inaccessible by other means. The half-lives of His-HDX indicate clear differences in the solvent accessibility of three His residues in rhodopsin/opsin and Zn(2+)-dependent changes in the pK(a) for His(195). These results indicate the utility of His-HDX in examining structural rearrangements in native source and membrane proteins without requiring structural modification.