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Assembly of a GPCR-G Protein Complex

Du, Yang, Duc, Nguyen Minh, Rasmussen, Søren G.F., Hilger, Daniel, Kubiak, Xavier, Wang, Liwen, Bohon, Jennifer, Kim, Hee Ryung, Wegrecki, Marcin, Asuru, Awuri, Jeong, Kyung Min, Lee, Jeongmi, Chance, Mark R., Lodowski, David T., Kobilka, Brian K., Chung, Ka Young
Cell 2019 v.177 no.5 pp. 1232-1242.e11
G-protein coupled receptors, G-proteins, cryo-electron microscopy, crystallography, filters, hormones, mass spectrometry, neurotransmitters, protein isoforms
The activation of G proteins by G protein-coupled receptors (GPCRs) underlies the majority of transmembrane signaling by hormones and neurotransmitters. Recent structures of GPCR-G protein complexes obtained by crystallography and cryoelectron microscopy (cryo-EM) reveal similar interactions between GPCRs and the alpha subunit of different G protein isoforms. While some G protein subtype-specific differences are observed, there is no clear structural explanation for G protein subtype-selectivity. All of these complexes are stabilized in the nucleotide-free state, a condition that does not exist in living cells. In an effort to better understand the structural basis of coupling specificity, we used time-resolved structural mass spectrometry techniques to investigate GPCR-G protein complex formation and G-protein activation. Our results suggest that coupling specificity is determined by one or more transient intermediate states that serve as selectivity filters and precede the formation of the stable nucleotide-free GPCR-G protein complexes observed in crystal and cryo-EM structures.