DEER Analysis of GPCR Conformational Heterogeneity.G protein-coupled receptors (GPCRs) represent a large class of transmembrane helical proteins which are involved in numerous physiological signaling pathways and therefore represent crucial pharmacological targets.  To this end, the combination of site-directed spin labeling and EPR spectroscopy, in particular double electron-electron resonance (DEER), is exceedingly valuable as it has access to sub-Angstrom spatial resolution and provides a detailed picture of the number and populations of conformations in equilibrium.  This review gives an overview of existing DEER studies on GPCRs with a focus on the delineation of structure/function frameworks, highlighting recent developments in data analysis and visualization.  We introduce "conformational efficacy" as a parameter to describe ligand-specific shifts in the conformational equilibrium, taking into account the loose coupling between receptor segments observed for different GPCRs using DEER.
DEER
To this end, the combination of site-directed spin labeling and EPR spectroscopy, in particular double electron-electron resonance (DEER), is exceedingly valuable as it has access to sub-Angstrom spatial resolution and provides a detailed picture of the number and populations of conformations in equilibrium. 
EPR spectroscopy
To this end, the combination of site-directed spin labeling and EPR spectroscopy, in particular double electron-electron resonance (DEER), is exceedingly valuable as it has access to sub-Angstrom spatial resolution and provides a detailed picture of the number and populations of conformations in equilibrium. 
double electron-electron resonance (DEER)
To this end, the combination of site-directed spin labeling and EPR spectroscopy, in particular double electron-electron resonance (DEER), is exceedingly valuable as it has access to sub-Angstrom spatial resolution and provides a detailed picture of the number and populations of conformations in equilibrium. 
site-directed spin labeling