Structural basis of G protein-coupled receptor-G protein interactions

The interaction of G protein-coupled receptors (GPCRs) with heterotrimeric G proteins represents one of the most fundamental biological processes. However, the molecular architecture of the GPCR-G protein complex remains poorly defined. In the present study, we applied a comprehensive GPCR-G protein a subunit (G alpha) chemical cross-linking strategy to map a receptor-G alpha interface, both before and after agonist-induced receptor activation. Using the M(3) muscarinic acetylcholine receptor (M3R)-G alpha(q) system as a model system, we examined the ability of similar to 250 combinations of cysteine-substituted M3R and G alpha(q) proteins to undergo cross-link formation. We identified many specific M3R-G alpha(q) contact sites, in both the inactive and active receptor conformations, allowing us to draw conclusions regarding the basic architecture of the M3R-G alpha(q) interface and the nature of the conformational changes following receptor activation. As heterotrimeric G proteins as well as most GPCRs share a high degree of structural homology, our findings should be of broad general relevance.