A Key Role for Transmembrane Prolines in Calcitonin Receptor-Like Receptor Agonist Binding and Signalling: Implications for Family B G-Protein-Coupled Receptors

2004 ◽  
Vol 67 (1) ◽  
pp. 20-31 ◽  
Author(s):  
Alex C. Conner ◽  
Debbie L. Hay ◽  
John Simms ◽  
Stephen G. Howitt ◽  
Marcus Schindler ◽  
...  
Keyword(s):  
G Protein ◽  
Receptor Agonist ◽  
G Protein Coupled Receptors ◽  
Calcitonin Receptor ◽  
Agonist Binding ◽  
G Protein Coupled

scholarly journals G Protein-Coupled Receptors in Taste Physiology and Pharmacology

2020 ◽  
Vol 11 ◽  
Author(s):  
Raise Ahmad ◽  
Julie E. Dalziel
Keyword(s):  
Binding Site ◽  
G Protein ◽  
Molecular Mechanisms ◽  
Taste Receptor ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Type I ◽  
Taste Receptors ◽  
Agonist Binding ◽  
G Protein Coupled

Heterotrimeric G protein-coupled receptors (GPCRs) comprise the largest receptor family in mammals and are responsible for the regulation of most physiological functions. Besides mediating the sensory modalities of olfaction and vision, GPCRs also transduce signals for three basic taste qualities of sweet, umami (savory taste), and bitter, as well as the flavor sensation kokumi. Taste GPCRs reside in specialised taste receptor cells (TRCs) within taste buds. Type I taste GPCRs (TAS1R) form heterodimeric complexes that function as sweet (TAS1R2/TAS1R3) or umami (TAS1R1/TAS1R3) taste receptors, whereas Type II are monomeric bitter taste receptors or kokumi/calcium-sensing receptors. Sweet, umami and kokumi receptors share structural similarities in containing multiple agonist binding sites with pronounced selectivity while most bitter receptors contain a single binding site that is broadly tuned to a diverse array of bitter ligands in a non-selective manner. Tastant binding to the receptor activates downstream secondary messenger pathways leading to depolarization and increased intracellular calcium in TRCs, that in turn innervate the gustatory cortex in the brain. Despite recent advances in our understanding of the relationship between agonist binding and the conformational changes required for receptor activation, several major challenges and questions remain in taste GPCR biology that are discussed in the present review. In recent years, intensive integrative approaches combining heterologous expression, mutagenesis and homology modeling have together provided insight regarding agonist binding site locations and molecular mechanisms of orthosteric and allosteric modulation. In addition, studies based on transgenic mice, utilizing either global or conditional knock out strategies have provided insights to taste receptor signal transduction mechanisms and their roles in physiology. However, the need for more functional studies in a physiological context is apparent and would be enhanced by a crystallized structure of taste receptors for a more complete picture of their pharmacological mechanisms.

scholarly journals An allosteric role for receptor activity-modifying proteins in defining GPCR pharmacology

2016 ◽  
Vol 2 (1) ◽  
Author(s):  
Joseph J Gingell ◽  
John Simms ◽  
James Barwell ◽  
David R Poyner ◽  
Harriet A Watkins ◽  
...  
Keyword(s):  
G Protein ◽  
Protein Interaction ◽  
G Protein Coupled Receptors ◽  
Receptor Activity ◽  
Calcitonin Receptor ◽  
Related Peptide ◽  
Calcitonin Gene ◽  
Receptor Activity Modifying Proteins ◽  
G Protein Coupled ◽  
Insight Into

Abstract G protein-coupled receptors are allosteric proteins that control transmission of external signals to regulate cellular response. Although agonist binding promotes canonical G protein signalling transmitted through conformational changes, G protein-coupled receptors also interact with other proteins. These include other G protein-coupled receptors, other receptors and channels, regulatory proteins and receptor-modifying proteins, notably receptor activity-modifying proteins (RAMPs). RAMPs have at least 11 G protein-coupled receptor partners, including many class B G protein-coupled receptors. Prototypic is the calcitonin receptor, with altered ligand specificity when co-expressed with RAMPs. To gain molecular insight into the consequences of this protein–protein interaction, we combined molecular modelling with mutagenesis of the calcitonin receptor extracellular domain, assessed in ligand binding and functional assays. Although some calcitonin receptor residues are universally important for peptide interactions (calcitonin, amylin and calcitonin gene-related peptide) in calcitonin receptor alone or with receptor activity-modifying protein, others have RAMP-dependent effects, whereby mutations decreased amylin/calcitonin gene-related peptide potency substantially only when RAMP was present. Remarkably, the key residues were completely conserved between calcitonin receptor and AMY receptors, and between subtypes of AMY receptor that have different ligand preferences. Mutations at the interface between calcitonin receptor and RAMP affected ligand pharmacology in a RAMP-dependent manner, suggesting that RAMP may allosterically influence the calcitonin receptor conformation. Supporting this, molecular dynamics simulations suggested that the calcitonin receptor extracellular N-terminal domain is more flexible in the presence of receptor activity-modifying protein 1. Thus, RAMPs may act in an allosteric manner to generate a spectrum of unique calcitonin receptor conformational states, explaining the pharmacological preferences of calcitonin receptor-RAMP complexes. This provides novel insight into our understanding of G protein-coupled receptor-protein interaction that is likely broadly applicable for this receptor class.

scholarly journals Structural Requirements for the Activation of the Human Growth Hormone Secretagogue Receptor by Peptide and Nonpeptide Secretagogues

1998 ◽  
Vol 12 (1) ◽  
pp. 137-145 ◽  
Author(s):  
Scott D. Feighner ◽  
Andrew D. Howard ◽  
Kristine Prendergast ◽  
Oksana C. Palyha ◽  
Donna L. Hreniuk ◽  
...  
Keyword(s):  
Ligand Binding ◽  
Binding Site ◽  
G Protein ◽  
Human Growth ◽  
G Protein Coupled Receptors ◽  
Site Directed Mutagenesis ◽  
Agonist Binding ◽  
Growth Hormone Secretagogue Receptor ◽  
Growth Hormone Secretagogue ◽  
G Protein Coupled

Abstract Antibodies raised against an intracellular and extracellular domain of the GH secretagogue receptor (GHS-R) confirmed that its topological orientation in the lipid bilayer is as predicted for G protein-coupled receptors with seven transmembrane domains. A strategy for mapping the agonist-binding site of the human GHS-R was conceived based on our understanding of ligand binding in biogenic amine and peptide hormone G protein-coupled receptors. Using site-directed mutagenesis and molecular modeling, we classified GHS peptide and nonpeptide agonist binding in the context of its receptor environment. All peptide and nonpeptide ligand classes shared a common binding domain in transmembrane (TM) region 3 of the GHS-R. This finding was based on TM-3 mutation E124Q, which eliminated the counter-ion to the shared basic N+ group of all GHSs and resulted in a nonfunctional receptor. Restoration of function for the E124Q mutant was achieved by a complementary change in the MK-0677 ligand through modification of its amine side-chain to the corresponding alcohol. Contacts in other TM domains [TM-2 (D99N), TM-5 (M213K, S117A), TM-6 (H280F), and extracellular loop 1 (C116A)] of the receptor revealed specificity for the different peptide, benzolactam, and spiroindolane GHSs. GHS-R agonism, therefore, does not require identical disposition of all agonist classes at the ligand-binding site. Our results support the hypothesis that the ligand-binding pocket in the GHS-R is spatially disposed similarly to the well characterized catechol-binding site in theβ 2-adrenergic receptor.

scholarly journals Molecular basis for high-affinity agonist binding in GPCRs

Science ◽  
2019 ◽  
Vol 364 (6442) ◽  
pp. 775-778 ◽  
Author(s):  
Tony Warne ◽  
Patricia C. Edwards ◽  
Andrew S. Doré ◽  
Andrew G. W. Leslie ◽  
Christopher G. Tate
Keyword(s):  
Hydrogen Bonds ◽  
G Protein ◽  
Molecular Basis ◽  
G Protein Coupled Receptors ◽  
Active State ◽  
Agonist Binding ◽  
Inactive State ◽  
High Affinity ◽  
Wide Range ◽  
G Protein Coupled

G protein–coupled receptors (GPCRs) in the G protein–coupled active state have higher affinity for agonists as compared with when they are in the inactive state, but the molecular basis for this is unclear. We have determined four active-state structures of the β1-adrenoceptor (β1AR) bound to conformation-specific nanobodies in the presence of agonists of varying efficacy. Comparison with inactive-state structures of β1AR bound to the identical ligands showed a 24 to 42% reduction in the volume of the orthosteric binding site. Potential hydrogen bonds were also shorter, and there was up to a 30% increase in the number of atomic contacts between the receptor and ligand. This explains the increase in agonist affinity of GPCRs in the active state for a wide range of structurally distinct agonists.

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