Structural mechanism underlying primary and secondary coupling between GPCRs and the Gi/o family

Hee Ryung Kim,Yang Du,Nguyen Minh Duc,Donghoon Ahn,Jun Xu,Ka Young Chung,Shoji Maeda

doi:10.1038/s41467-020-16975-2

Abstract

Heterotrimeric G proteins are categorized into four main families based on their function and sequence, Gs, Gi/o, Gq/11, and G12/13. One receptor can couple to more than one G protein subtype, and the coupling efficiency varies depending on the GPCR-G protein pair. However, the precise mechanism underlying different coupling efficiencies is unknown. Here, we study the structural mechanism underlying primary and secondary Gi/o coupling, using the muscarinic acetylcholine receptor type 2 (M2R) as the primary Gi/o-coupling receptor and the β2-adrenergic receptor (β2AR, which primarily couples to Gs) as the secondary Gi/o-coupling receptor. Hydrogen/deuterium exchange mass spectrometry and mutagenesis studies reveal that the engagement of the distal C-terminus of Gαi/o with the receptor differentiates primary and secondary Gi/o couplings. This study suggests that the conserved hydrophobic residue within the intracellular loop 2 of the receptor (residue 34.51) is not critical for primary Gi/o-coupling; however, it might be important for secondary Gi/o-coupling.

Highlights

Heterotrimeric G proteins are categorized into four main families based on their function and sequence, Gs, Gi/o, Gq/11, and G12/13
Using a combination of pulsed hydrogen/deuterium exchange mass spectrometry (HDX-MS), pulsed hydroxyl radical footprinting mass spectrometry (HRF-MS), and mutational studies, we proposed a model that delineates the sequential events during β2AR-Gs coupling, the primary G protein-coupled receptors (GPCRs)-Gs pair[19]
We suggest that the interaction of residue 34.51 with the hydrophobic pocket within the Gα subunit is not critical for primary GPCR-Gi/o coupling, but it is important for secondary GPCR-Gi/o coupling

Summary

Introduction

Heterotrimeric G proteins are categorized into four main families based on their function and sequence, Gs, Gi/o, Gq/11, and G12/13. One receptor can couple to more than one G protein subtype, and the coupling efficiency varies depending on the GPCR-G protein pair. G protein-coupled receptors (GPCRs) are the largest receptor superfamily that perceive extracellular signals, including light, smell, taste, hormones, and neurotransmitters[1]. Due to their critical functions in physiology and pathology, GPCRs are good therapeutic targets, and one third of approved medicines acts on GPCRs. it is important to understand the precise signaling mechanism of GPCRs for our fundamental knowledge on the cellular signaling and for the development of better GPCR-targeting therapeutics. The known primary and secondary GPCR-G protein pairs have been summarized in the IUPHAR/BPS Guide to Pharmacology[11] and GPCRdb

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Conclusion