The third extracellular loop of G-protein-coupled receptors: more than just a linker between two important transmembrane helices

2004 ◽  
Vol 32 (6) ◽  
pp. 1048-1050 ◽  
Author(s):  
Z. Lawson ◽  
M. Wheatley
Keyword(s):  
G Protein ◽  
Tertiary Structure ◽  
Large Family ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Transmembrane Helices ◽  
Ligand Selectivity ◽  
Interaction Sites ◽  
Amine Neurotransmitters ◽  
G Protein Coupled

GPCRs (G-protein-coupled receptors) are a large family of structurally related proteins, which mediate their effects by coupling with G-proteins. Despite responding to a range of very diverse stimuli, these receptors exhibit a conserved tertiary structure comprising a bundle of seven TM (transmembrane) helices linked by alternating ECLs (extracellular loops) and ICLs (intracellular loops). The hydrophobic environment formed by the cluster of TM helices is functionally important. For example, the 11-cis retinal chromophore of rhodopsin forms a protonated Schiff base linkage to a lysine in TM7, deep within the helical bundle, and small ligands, such as amine neurotransmitters and non-peptide analogues of peptide hormones, also bind within the corresponding region of their cognate receptors. In addition, activation of GPCRs involves relative movement of TM helices to present G-protein interaction sites across the intracellular face of the receptor. Consequently, it might be assumed that the ECLs of the GPCR are inert peptide linkers that merely connect important TM helices. Focusing on ECL3 (third ECL), it is becoming increasingly apparent that this extracellular domain can fulfil a range of important roles with respect to GPCR signalling, including agonist binding, ligand selectivity and receptor activation.

Extracellular loops and ligand binding to a subfamily of Family A G-protein-coupled receptors

2007 ◽  
Vol 35 (4) ◽  
pp. 717-720 ◽  
Author(s):  
M. Wheatley ◽  
J. Simms ◽  
S.R. Hawtin ◽  
V.J. Wesley ◽  
D. Wootten ◽  
...  
Keyword(s):  
Ligand Binding ◽  
G Protein ◽  
Tertiary Structure ◽  
Large Family ◽  
Peptide Hormone ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Ligand Selectivity ◽  
Extracellular Loops ◽  
G Protein Coupled

GPCRs (G-protein-coupled receptors) are a large family of structurally related proteins which mediate their effects by coupling to G-proteins. The V1aR (V1a vasopressin receptor) is a member of a family of related GPCRs that are activated by vasopressin {AVP ([Arg8]vasopressin)}, OT (oxytocin) and related peptides. These receptors are members of a subfamily of Family A GPCRs called the neurohypophysial peptide hormone receptor family. GPCRs exhibit a conserved tertiary structure comprising a bundle of seven TM (transmembrane) helices linked by alternating ECLs (extracellular loops) and ICLs (intracellular loops). The cluster of TM helices is functionally important for ligand binding, and, furthermore, activation of GPCRs involves movement of these TM helices. Consequently, it might be assumed that the extracellular face of GPCRs is composed of peptide linkers that merely connect important TM helices. However, using a systematic mutagenesis approach and focusing on the N-terminus and the second ECL of the V1aR, we have established that these extracellular domains fulfil a range of important roles with respect to GPCR signalling, including agonist binding, ligand selectivity and receptor activation.

Arrestin-dependent internalization of rhodopsin-like G protein-coupled receptors

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Lizzy Wanka ◽  
Victoria Behr ◽  
Annette G. Beck-Sickinger
Keyword(s):  
G Protein ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Emotional Behavior ◽  
Model Systems ◽  
Regulation Mechanism ◽  
Interaction Sites ◽  
Internalization Process ◽  
G Protein Coupled ◽  
Receptor Family

Abstract The internalization of G protein-coupled receptors (GPCRs) is an important mechanism regulating the signal strength and limiting the opportunity of receptor activation. Based on the importance of GPCRs, the detailed knowledge about the regulation of signal transduction is crucial. Here, current knowledge about the agonist-induced, arrestin-dependent internalization process of rhodopsin-like GPCRs is reviewed. Arrestins are conserved molecules that act as key players within the internalization process of many GPCRs. Based on highly conserved structural characteristics within the rhodopsin-like GPCRs, the identification of arrestin interaction sites in model systems can be compared and used for the investigation of internalization processes of other receptors. The increasing understanding of this essential regulation mechanism of receptors can be used for drug development targeting rhodopsin-like GPCRs. Here, we focus on the neuropeptide Y receptor family, as these receptors transmit various physiological processes such as food intake, energy homeostasis, and regulation of emotional behavior, and are further involved in pathophysiological processes like cancer, obesity and mood disorders. Hence, this receptor family represents an interesting target for the development of novel therapeutics requiring the understanding of the regulatory mechanisms influencing receptor mediated signaling.

G-protein-coupled-receptor activation of the smooth muscle calponin gene

2001 ◽  
Vol 357 (2) ◽  
pp. 587-592 ◽  
Author(s):  
Nickolai O. DULIN ◽  
Sergei N. ORLOV ◽  
Chad M. KITCHEN ◽  
Tatyana A. VOYNO-YASENETSKAYA ◽  
Joseph M. MIANO
Keyword(s):  
Smooth Muscle ◽  
Protein Kinase ◽  
G Protein ◽  
Transcriptional Activation ◽  
Fold Increase ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Mitogen Activated Protein Kinase ◽  
G Protein Coupled

A hallmark of cultured smooth muscle cells (SMCs) is the rapid down-regulation of several lineage-restricted genes that define their in vivo differentiated phenotype. Identifying factors that maintain an SMC differentiated phenotype has important implications in understanding the molecular underpinnings governing SMC differentiation and their subversion to an altered phenotype in various disease settings. Here, we show that several G-protein coupled receptors [α-thrombin, lysophosphatidic acid and angiotensin II (AII)] increase the expression of smooth muscle calponin (SM-Calp) in rat and human SMC. The increase in SM-Calp protein appears to be selective for G-protein-coupled receptors as epidermal growth factor was without effect. Studies using AII showed a 30-fold increase in SM-Calp protein, which was dose- and time-dependent and mediated by the angiotensin receptor-1 (AT1 receptor). The increase in SM-Calp protein with AII was attributable to transcriptional activation of SM-Calp based on increases in steady-state SM-Calp mRNA, increases in SM-Calp promoter activity and complete abrogation of protein induction with actinomycin D. To examine the potential role of extracellular signal-regulated kinase (Erk1/2), protein kinase B, p38 mitogen-activated protein kinase and protein kinase C in AII-induced SM-Calp, inhibitors to each of the signalling pathways were used. None of these signalling molecules appears to be crucial for AII-induced SM-Calp expression, although Erk1/2 may be partially involved. These results identify SM-Calp as a target of AII-mediated signalling, and suggest that the SMC response to AII may incorporate a novel activity of SM-Calp.

scholarly journals Disabling Gβγ SNARE interaction in transgenic mice disrupts GPCR-mediated presynaptic inhibition leading to physiological and behavioral phenotypes

2018 ◽  
Author(s):  
Zack Zurawski ◽  
Analisa D. Thompson Gray ◽  
Lillian J. Brady ◽  
Brian Page ◽  
Emily Church ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Calcium Channels ◽  
G Protein ◽  
Presynaptic Inhibition ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Voltage Gated ◽  
Voltage Gated Calcium Channels ◽  
Crucial Component ◽  
G Protein Coupled

ABSTRACTGi/o-coupled G-protein coupled receptors modulate neurotransmission presynaptically through inhibition of exocytosis. Release of Gβγ subunits decreases the activity of voltage-gated calcium channels (VGCC), decreasing excitability. A less understood Gβγ–mediated mechanism downstream of calcium entry is the binding of Gβγ to SNARE complexes. Here, we create a mouse partially deficient in this interaction. SNAP25Δ3 homozygote animals are developmentally normalbut impaired gait and supraspinal nociception. They also have elevated stress-induced hyperthermia and impaired inhibitory postsynaptic responses to α2A-AR, but normal inhibitory postsynaptic responses to Gi/o-coupled GABAB receptor activation. SNAP25Δ3 homozygotes have deficits in inhibition of hippocampal postsynaptic responses to 5 HT1b agonists that affect hippocampal learning. These data suggest that Gi/o-coupled GPCR inhibition of exocytosis through the Gβγ-SNARE interaction is a crucial component of numerous physiological and behavioral processes.

scholarly journals Specific oxylipins enhance vertebrate hematopoiesis via the receptor GPR132

2018 ◽  
Vol 115 (37) ◽  
pp. 9252-9257 ◽  
Author(s):  
Jamie L. Lahvic ◽  
Michelle Ammerman ◽  
Pulin Li ◽  
Megan C. Blair ◽  
Emma R. Stillman ◽  
...  
Keyword(s):  
Fatty Acids ◽  
G Protein ◽  
Cell Lines ◽  
Saturated Fatty Acids ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Hydroxy Fatty Acids ◽  
High Affinity ◽  
G Protein Coupled

Epoxyeicosatrienoic acids (EETs) are lipid-derived signaling molecules with cardioprotective and vasodilatory actions. We recently showed that 11,12-EET enhances hematopoietic induction and engraftment in mice and zebrafish. EETs are known to signal via G protein-coupled receptors, with evidence supporting the existence of a specific high-affinity receptor. Identification of a hematopoietic-specific EET receptor would enable genetic interrogation of EET signaling pathways, and perhaps clinical use of this molecule. We developed a bioinformatic approach to identify an EET receptor based on the expression of G protein-coupled receptors in cell lines with differential responses to EETs. We found 10 candidate EET receptors that are expressed in three EET-responsive cell lines, but not expressed in an EET-unresponsive line. Of these, only recombinant GPR132 showed EET-responsiveness in vitro, using a luminescence-based β-arrestin recruitment assay. Knockdown of zebrafish gpr132b prevented EET-induced hematopoiesis, and marrow from GPR132 knockout mice showed decreased long-term engraftment capability. In contrast to high-affinity EET receptors, GPR132 is reported to respond to additional hydroxy-fatty acids in vitro, and we found that these same hydroxy-fatty acids enhance hematopoiesis in the zebrafish. We conducted structure–activity relationship analyses using both cell culture and zebrafish assays on diverse medium-chain fatty acids. Certain oxygenated, unsaturated free fatty acids showed high activation of GPR132, whereas unoxygenated or saturated fatty acids had lower activity. Absence of the carbon-1 position carboxylic acid prevented activity, suggesting that this moiety is required for receptor activation. GPR132 responds to a select panel of oxygenated polyunsaturated fatty acids to enhance both embryonic and adult hematopoiesis.

Molecular mechanisms of GABAB receptor activation: new insights from the mechanism of action of CGP7930, a positive allosteric modulator

2004 ◽  
Vol 32 (5) ◽  
pp. 871-872 ◽  
Author(s):  
V. Binet ◽  
C. Goudet ◽  
C. Brajon ◽  
L. Le Corre ◽  
F. Acher ◽  
...  
Keyword(s):  
G Protein ◽  
Mechanism Of Action ◽  
Molecular Mechanisms ◽  
Gabab Receptor ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Class Iii ◽  
G Protein Coupled ◽  
New Strategies

The GABAB (γ-aminobutyric acid-B) receptor is composed of two subunits, GABAB1 and GABAB2. Both subunits share structural homology with other class-III G-protein-coupled receptors. They contain two main domains, a heptahelical domain typical of all G-protein-coupled receptors and a large ECD (extracellular domain). It has not been demonstrated whether the association of these two subunits is always required for function. However, GABAB2 plays a major role in coupling with G-proteins, and GABAB1 has been shown to bind GABA. To date, only ligands interacting with GABAB1-ECD have been identified. In the present study, we explored the mechanism of action of CGP7930, a compound described as a positive allosteric regulator of the GABAB receptor. We have shown that it can weakly activate the wild-type GABAB receptor, but also the GABAB2 expressed alone, thus being the first described agonist of GABAB2. CGP7930 retains its weak agonist activity on a GABAB2 subunit deleted of its ECD. Thus the heptahelical domain of GABAB2 behaves similar to a rhodopsin-like receptor. These results open new strategies for studying the mechanism of activation of GABAB receptor and examine any possible role of GABAB2.

scholarly journals Dissecting the allosteric networks governing agonist efficacy and potency in G protein-coupled receptors

2021 ◽  
Author(s):  
Franziska Marie Heydenreich ◽  
Maria Marti-Solano ◽  
Manbir Sandhu ◽  
Brian K Kobilka ◽  
Michel Bouvier ◽  
...  
Keyword(s):  
G Protein ◽  
Conformational Changes ◽  
Structural Changes ◽  
Receptor Activation ◽  
Residue Level ◽  
G Protein Coupled Receptors ◽  
Maximal Response ◽  
Pharmacological Properties ◽  
Receptor Ligand ◽  
G Protein Coupled

G protein-coupled receptors (GPCRs) translate binding of extracellular ligands into intracellular responses through conformational changes. Ligand properties are described by the maximum response (efficacy) and the agonist concentration at half-maximal response (potency). Integrating structural changes with pharmacological properties remains challenging and has not yet been performed at the resolution of individual amino acids. We use epinephrine and β2-adrenergic receptor as a model to integrate residue-level pharmacology data with intramolecular residue contact data describing receptor activation. This unveils the allosteric networks driving ligand efficacy and potency. We provide detailed insights into how structural rearrangements are linked to fundamental pharmacological properties at single-residue level in a receptor-ligand system. Our approach can be used to determine such pharmacological networks for any receptor-ligand complex.

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