title: Rearrangement of a polar core provides a conserved mechanism for constitutive activation of class B G protein-coupled receptors.
abstract: The glucagon receptor (GCGR) belongs to the secretin-like (class B) family of G protein-coupled receptors (GPCRs) and is activated by the peptide hormone glucagon. The structures of an activated class B GPCR have remained unsolved, preventing a mechanistic understanding of how these receptors are activated. Using a combination of structural modeling and mutagenesis studies, we present here two modes of ligand-independent activation of GCGR. First, we identified a GCGR-specific hydrophobic lock comprising Met-338 and Phe-345 within the IC3 loop and transmembrane helix 6 (TM6) and found that this lock stabilizes the TM6 helix in the inactive conformation. Disruption of this hydrophobic lock led to constitutive G protein and arrestin signaling. Second, we discovered a polar core comprising conserved residues in TM2, TM3, TM6, and TM7, and mutations that disrupt this polar core led to constitutive GCGR activity. On the basis of these results, we propose a mechanistic model of GCGR activation in which TM6 is held in an inactive conformation by the conserved polar core and the hydrophobic lock. Mutations that disrupt these inhibitory elements allow TM6 to swing outward to adopt an active TM6 conformation similar to that of the canonical β2-adrenergic receptor complexed with G protein and to that of rhodopsin complexed with arrestin. Importantly, mutations in the corresponding polar core of several other members of class B GPCRs, including PTH1R, PAC1R, VIP1R, and CRFR1, also induce constitutive G protein signaling, suggesting that the rearrangement of the polar core is a conserved mechanism for class B GPCR activation.
authors.affiliation: From the Van Andel Research Institute - Shanghai Institute of Materia Medica (VARI-SIMM) Center, Center for Structure and Function of Drug Targets, The CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai 201203, China.|the Laboratory of Structural Sciences and Laboratory of Structural Biology and Biochemistry, Van Andel Research Institute, Grand Rapids, Michigan 49503.|the University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China.
authors.forename: Yanting
authors.initials: Y
authors.lastname: Yin
authors.affiliation: the Laboratory of Structural Sciences and Laboratory of Structural Biology and Biochemistry, Van Andel Research Institute, Grand Rapids, Michigan 49503.
authors.forename: Parker W
authors.initials: PW
authors.lastname: de Waal
authors.affiliation: the Laboratory of Structural Sciences and Laboratory of Structural Biology and Biochemistry, Van Andel Research Institute, Grand Rapids, Michigan 49503.
authors.forename: Yuanzheng
authors.initials: Y
authors.lastname: He
authors.affiliation: From the Van Andel Research Institute - Shanghai Institute of Materia Medica (VARI-SIMM) Center, Center for Structure and Function of Drug Targets, The CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai 201203, China.
authors.forename: Li-Hua
authors.initials: LH
authors.lastname: Zhao
authors.affiliation: The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, and.
authors.forename: Dehua
authors.initials: D
authors.lastname: Yang
authors.affiliation: The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, and.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Cai
authors.affiliation: From the Van Andel Research Institute - Shanghai Institute of Materia Medica (VARI-SIMM) Center, Center for Structure and Function of Drug Targets, The CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai 201203, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: the Laboratory of Structural Sciences and Laboratory of Structural Biology and Biochemistry, Van Andel Research Institute, Grand Rapids, Michigan 49503.
authors.forename: Karsten
authors.initials: K
authors.lastname: Melcher
authors.affiliation: The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, and mwwang@simm.ac.cn.|the School of Pharmacy, Fudan University, 826 Zhangheng Road, Shanghai 201203, China.
authors.forename: Ming-Wei
authors.initials: MW
authors.lastname: Wang
authors.affiliation: From the Van Andel Research Institute - Shanghai Institute of Materia Medica (VARI-SIMM) Center, Center for Structure and Function of Drug Targets, The CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai 201203, China, Eric.Xu@vai.org.|the Laboratory of Structural Sciences and Laboratory of Structural Biology and Biochemistry, Van Andel Research Institute, Grand Rapids, Michigan 49503.|the University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China.
authors.forename: H Eric
authors.initials: HE
authors.lastname: Xu
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D002460:Cell Line; D017124:Conserved Sequence; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010446:Peptide Fragments / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018019:Receptors, Corticotropin-Releasing Hormone / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018027:Receptors, Glucagon / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015290:Second Messenger Systems; D040681:Structural Homology, Protein; D000099052:CRF Receptor, Type 1
chemical_list: C495503:ADCYAP1R1 protein, human; D008024:Ligands; C473449:PTH1R protein, human; D010446:Peptide Fragments; D044168:Receptor, Parathyroid Hormone, Type 1; D018019:Receptors, Corticotropin-Releasing Hormone; D018027:Receptors, Glucagon; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C495506:VIPR1 protein, human; D000099052:CRF Receptor, Type 1
keywords: 7-helix receptor; G protein-coupled receptor (GPCR); arrestin; glucagon; parathyroid hormone