Structural insights into differences in G protein activation by family A and family B GPCRs

• Published in: Science (American Association for the Advancement of Science) 2020-07, Vol.369 (6503)
• Main Authors: Hilger, Daniel, Kumar, Kaavya Krishna, Hu, Hongli, Pedersen, Mie Fabricius, O'Brien, Evan S, Giehm, Lise, Jennings, Christine, Eskici, Gözde, Inoue, Asuka, Lerch, Michael, Mathiesen, Jesper Mosolff, Skiniotis, Georgios, Kobilka, Brian K
• Format: Article
• Language: English
• Subjects: Activation; Adenosine; Adenosine monophosphate; Adrenergic receptors; Agonists; BASIC BIOLOGICAL SCIENCES; Bending; Binding sites; Carbohydrate metabolism; Carbohydrates; Cryoelectron Microscopy; Cyclic AMP; Disruption; Electron microscopy; Enzyme Activation; Exchanging; Fluorescence; G protein-coupled receptors; Glucagon; Glucose; GTP-Binding Protein alpha Subunits, Gs - chemistry; Guanine; Guanine nucleotide exchange factor; Guanine nucleotide-binding protein; Guanosine; Guanosine diphosphate; Guanosine triphosphate; Humans; Hypoglycemia; Intracellular; Kinetics; Ligands; Microscopy; Nucleotides; Protein Structure, Secondary; Proteins; Receptors; Receptors, Adrenergic, beta-2 - chemistry; Receptors, Glucagon - chemistry; Resonance; Signal transduction; Signaling; Spectroscopy; Structure-function relationships; Transducers
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aba3373

Family B heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) play important roles in carbohydrate metabolism. Recent structures of family B GPCR-G protein complexes reveal a disruption in the α-helix of transmembrane segment 6 (TM6) not observed in family A GPCRs. To investigate the functional impact of this structural difference, we compared the structure and function of the glucagon receptor (GCGR; family B) with the β adrenergic receptor (β AR; family A). We determined the structure of the GCGR-G complex by means of cryo-electron microscopy at 3.1-angstrom resolution. This structure shows the distinct break in TM6. Guanosine triphosphate (GTP) turnover, guanosine diphosphate release, GTP binding, and G protein dissociation studies revealed much slower rates for G protein activation by the GCGR compared with the β AR. Fluorescence and double electron-electron resonance studies suggest that this difference is due to the inability of agonist alone to induce a detectable outward movement of the cytoplasmic end of TM6.