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Rysiewicz B, Błasiak E, Dziedzicka-Wasylewska M, Polit A. The polybasic region in Gαi proteins: Relevant or not? Insights from Gαi 3 research. Cell Signal 2024; 118:111138. [PMID: 38467243 DOI: 10.1016/j.cellsig.2024.111138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 02/18/2024] [Accepted: 03/08/2024] [Indexed: 03/13/2024]
Abstract
Heterotrimeric G proteins are responsible for signal transduction from G-protein-coupled receptors (GPCRs) to intracellular effectors. This process is only possible when G proteins are located on the inner side of the cell membrane due to the specific localization of GPCR receptors. The Gα subunit is directed to the cell membrane through several signals, including modification by fatty acid moieties, interaction with the Gβγ complex, and, as observed in some Gα proteins, the presence of basic amino acid residues in the N-terminal region. In this work, we focused on investigating the influence of the polybasic region on the localization and function of a representative member of the Gαi family, Gαi3. Through the use of confocal microscopy and fluorescence lifetime microscopy, we showed that, in the case of this protein, neutralizing the positive charge does not significantly affect its abundance in the cell membrane. However, it does affect its spatial arrangement concerning the dopamine D2 receptor and influences inhibitory effect of Gαi3 on intracellular cAMP production triggered by D2 receptor stimulation. Moreover, in this work, we have shown, for the first time, that nonlipidated Gαi3 binds to negatively charged lipids through electrostatic interactions, and membrane fluidity plays a significant role in this interaction.
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Affiliation(s)
- Beata Rysiewicz
- Department of Physical Biochemistry, Faculty of Biochemistry Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
| | - Ewa Błasiak
- Department of Physical Biochemistry, Faculty of Biochemistry Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
| | - Marta Dziedzicka-Wasylewska
- Department of Physical Biochemistry, Faculty of Biochemistry Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
| | - Agnieszka Polit
- Department of Physical Biochemistry, Faculty of Biochemistry Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
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The Gαi protein subclass selectivity to the dopamine D 2 receptor is also decided by their location at the cell membrane. Cell Commun Signal 2020; 18:189. [PMID: 33308256 PMCID: PMC7731117 DOI: 10.1186/s12964-020-00685-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 11/10/2020] [Indexed: 11/10/2022] Open
Abstract
Background G protein-coupled receptor (GPCR) signaling via heterotrimeric G proteins plays an important role in the cellular regulation of responses to external stimuli. Despite intensive structural research, the mechanism underlying the receptor–G protein coupling of closely related subtypes of Gαi remains unclear. In addition to the structural changes of interacting proteins, the interactions between lipids and proteins seem to be crucial in GPCR-dependent cell signaling due to their functional organization in specific membrane domains. In previous works, we found that Gαs and Gαi3 subunits prefer distinct types of membrane-anchor lipid domains that also modulate the G protein trimer localization. In the present study, we investigated the functional selectivity of dopamine D2 long receptor isoform (D2R) toward the Gαi1, Gαi2, and Gαi3 subunits, and analyzed whether the organization of Gαi heterotrimers at the plasma membrane affects the signal transduction. Methods We characterized the lateral diffusion and the receptor–G protein spatial distribution in living cells using two assays: fluorescence recovery after photobleaching microscopy and fluorescence resonance energy transfer detected by fluorescence-lifetime imaging microscopy. Depending on distribution of data differences between Gα subunits were investigated using parametric approach–unpaired T-test or nonparametric–Mann–Whitney U test. Results Despite the similarities between the examined subunits, the experiments conducted in the study revealed a significantly faster lateral diffusion of the Gαi2 subunit and the singular distribution of the Gαi1 subunit in the plasma membrane. The cell membrane partitioning of distinct Gαi heterotrimers with dopamine receptor correlated very well with the efficiency of D2R-mediated inhibition the formation of cAMP. Conclusions This study showed that even closely related subunits of Gαi differ in their membrane-trafficking properties that impact on their signaling. The interactions between lipids and proteins seem to be crucial in GPCR-dependent cell signaling due to their functional organization in specific membrane domains, and should therefore be taken into account as one of the selectivity determinants of G protein coupling. Video abstract
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Yin J, Chen KYM, Clark MJ, Hijazi M, Kumari P, Bai XC, Sunahara RK, Barth P, Rosenbaum DM. Structure of a D2 dopamine receptor-G-protein complex in a lipid membrane. Nature 2020; 584:125-129. [PMID: 32528175 PMCID: PMC7415663 DOI: 10.1038/s41586-020-2379-5] [Citation(s) in RCA: 119] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Accepted: 04/08/2020] [Indexed: 12/28/2022]
Abstract
The D2 dopamine receptor (DRD2) is a therapeutic target for Parkinson’s disease1 and antipsychotic drugs2. DRD2 is activated by the endogenous neurotransmitter dopamine and synthetic agonist drugs such as bromocriptine3, leading to stimulation of Gi and inhibition of adenylyl cyclase. We used cryo-electron microscopy to elucidate the structure of an agonist-bound activated DRD2-Gi complex reconstituted into a phospholipid membrane. The extracellular ligand binding site of DRD2 is remodeled in response to agonist binding, with conformational changes in extracellular loop 2 (ECL2), transmembrane domain 5 (TM5), TM6, and TM7 propagating to opening of the intracellular Gi binding site. The DRD2-Gi structure represents the first experimental model of a GPCR-G protein complex embedded in a phospholipid bilayer, which serves as a benchmark to validate the interactions seen in previous detergent-bound structures. The structure also reveals interactions that are unique to the membrane-embedded complex, including helix 8 burial in the inner leaflet, ordered lysine and arginine sidechains in the membrane interfacial regions, and lipid anchoring of the G protein in the membrane. Our model of the activated DRD2 will help inform the design of subtype-selective DRD2 ligands for multiple human CNS disorders.
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Affiliation(s)
- Jie Yin
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Kuang-Yui M Chen
- Institute of Bioengineering, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Mary J Clark
- Department of Pharmacology, University of California San Diego School of Medicine, La Jolla, CA, USA
| | - Mahdi Hijazi
- Institute of Bioengineering, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Punita Kumari
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Xiao-Chen Bai
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Roger K Sunahara
- Department of Pharmacology, University of California San Diego School of Medicine, La Jolla, CA, USA.
| | - Patrick Barth
- Institute of Bioengineering, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
| | - Daniel M Rosenbaum
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
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Effects of Post-translational Modifications on Membrane Localization and Signaling of Prostanoid GPCR-G Protein Complexes and the Role of Hypoxia. J Membr Biol 2019; 252:509-526. [PMID: 31485700 DOI: 10.1007/s00232-019-00091-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 08/17/2019] [Indexed: 02/07/2023]
Abstract
G protein-coupled receptors (GPCRs) play a pivotal role in the adaptive responses to cellular stresses such as hypoxia. In addition to influencing cellular gene expression profiles, hypoxic microenvironments can perturb membrane protein localization, altering GPCR effector scaffolding and altering downstream signaling. Studies using proteomics approaches have revealed significant regulation of GPCR and G proteins by their state of post-translational modification. The aim of this review is to examine the effects of post-translational modifications on membrane localization and signaling of GPCR-G protein complexes, with an emphasis on vascular prostanoid receptors, and to highlight what is known about the effect of cellular hypoxia on these mechanisms. Understanding post-translational modifications of protein targets will help to define GPCR targets in treatment of disease, and to inform research into mechanisms of hypoxic cellular responses.
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van Keulen SC, Rothlisberger U. Effect of N-Terminal Myristoylation on the Active Conformation of Gα i1-GTP. Biochemistry 2016; 56:271-280. [PMID: 27936598 DOI: 10.1021/acs.biochem.6b00388] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
G proteins are part of the G-protein-coupled receptor (GPCR) signal transduction cascade in which they transfer a signal from the membrane-embedded GPCR to other proteins in the cell. In the case of the inhibitory G-protein heterotrimer, permanent N-terminal myristoylation can transiently localize the Gαi subunit at the membrane as well as crucially influence Gαi's function in the GTP-bound conformation. The attachment of lipids to proteins is known to be essential for membrane trafficking; however, our results suggest that lipidation is also important for protein-protein interactions during signal transduction. Here we investigate the effect of myristoylation on the structure and dynamics of soluble Gαi1 and its possible implication for signal transduction. A 2 μs classical molecular dynamics simulation of a myristoylated Gαi1-GTP complex suggests that the myristoyl-induced conformational changes of the switch II and alpha helical domains create new possibilities for protein-protein interactions and emphasize the importance of permanent lipid attachment for the conformation and functional tunability of signaling proteins.
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Affiliation(s)
- Siri C van Keulen
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
| | - Ursula Rothlisberger
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
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6
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Zheng W, Yang J, Beauchamp E, Cai R, Hussein S, Hofmann L, Li Q, Flockerzi V, Berthiaume LG, Tang J, Chen XZ. Regulation of TRPP3 Channel Function by N-terminal Domain Palmitoylation and Phosphorylation. J Biol Chem 2016; 291:25678-25691. [PMID: 27754867 DOI: 10.1074/jbc.m116.756544] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 10/16/2016] [Indexed: 01/08/2023] Open
Abstract
Transient receptor potential polycystin-3 (TRPP3) is a cation channel activated by calcium and proton and is involved in hedgehog signaling, intestinal development, and sour tasting. How TRPP3 channel function is regulated remains poorly understood. By N-terminal truncation mutations, electrophysiology, and Xenopus oocyte expression, we first identified fragment Asp-21-Ser-42 to be functionally important. We then found that deletion mutant Δ1-36 (TRPP3 missing fragment Met-1-Arg-36) has a similar function as wild-type TRPP3, whereas Δ1-38 is functionally dead, suggesting the importance of Val-37 or Cys-38. Further studies found that Cys-38, but not Val-37, is functionally critical. Cys-38 is a predicted site of palmitoylation, and indeed TRPP3 channel activity was inhibited by palmitoylation inhibitor 2-bromopalmitate and rescued by palmitoylation substrate palmitic acid. The TRPP3 N terminus (TRPP3NT, Met-1-Leu-95) localized along the plasma membrane of HEK293 cells but stayed in the cytoplasm with 2-bromopalmitate treatment or C38A mutation, indicating that TRPP3NT anchors to the surface membrane through palmitoylation at Cys-38. By acyl-biotin exchange assays, we showed that TRPP3, but not mutant C38A, is indeed palmitoylated. When putative phosphorylation sites near Cys-38 were mutated to Asp or Glu to mimic phosphorylation, only T39D and T39E reduced TRPP3 function. Furthermore, TRPP3NT displayed double bands in which the upper band was abolished by λ phosphatase treatment or T39A mutation. However, palmitoylation at Cys-38 and phosphorylation at Thr-39 independently regulated TRPP3 channel function, in contrast to previous reports about correlated palmitoylation with a proximate phosphorylation. Palmitoylation at Cys-38 represents a novel mechanism of functional regulation for TRPP3.
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Affiliation(s)
- Wang Zheng
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - JungWoo Yang
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Erwan Beauchamp
- Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Ruiqi Cai
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Shaimaa Hussein
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Laura Hofmann
- the Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany, and
| | - Qiang Li
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Veit Flockerzi
- the Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany, and
| | - Luc G Berthiaume
- Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Jingfeng Tang
- the Institute of Biomedical and Pharmaceutical Sciences and Provincial Cooperative Innovation Center, College of Bioengineering, Hubei University of Technology, 430068 Wuhan, China
| | - Xing-Zhen Chen
- From the Membrane Protein Disease Research Group, Departments of Physiology and .,the Institute of Biomedical and Pharmaceutical Sciences and Provincial Cooperative Innovation Center, College of Bioengineering, Hubei University of Technology, 430068 Wuhan, China
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Abstract
Protein S-acylation, the only fully reversible posttranslational lipid modification of proteins, is emerging as a ubiquitous mechanism to control the properties and function of a diverse array of proteins and consequently physiological processes. S-acylation results from the enzymatic addition of long-chain lipids, most typically palmitate, onto intracellular cysteine residues of soluble and transmembrane proteins via a labile thioester linkage. Addition of lipid results in increases in protein hydrophobicity that can impact on protein structure, assembly, maturation, trafficking, and function. The recent explosion in global S-acylation (palmitoyl) proteomic profiling as a result of improved biochemical tools to assay S-acylation, in conjunction with the recent identification of enzymes that control protein S-acylation and de-acylation, has opened a new vista into the physiological function of S-acylation. This review introduces key features of S-acylation and tools to interrogate this process, and highlights the eclectic array of proteins regulated including membrane receptors, ion channels and transporters, enzymes and kinases, signaling adapters and chaperones, cell adhesion, and structural proteins. We highlight recent findings correlating disruption of S-acylation to pathophysiology and disease and discuss some of the major challenges and opportunities in this rapidly expanding field.
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Affiliation(s)
- Luke H Chamberlain
- Strathclyde Institute of Pharmacy and Biomedical Sciences, Strathclyde University, Glasgow, United Kingdom; and Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Michael J Shipston
- Strathclyde Institute of Pharmacy and Biomedical Sciences, Strathclyde University, Glasgow, United Kingdom; and Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, United Kingdom
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Sensoy O, Weinstein H. A mechanistic role of Helix 8 in GPCRs: Computational modeling of the dopamine D2 receptor interaction with the GIPC1-PDZ-domain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:976-83. [PMID: 25592838 DOI: 10.1016/j.bbamem.2014.12.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 11/15/2014] [Accepted: 12/02/2014] [Indexed: 01/18/2023]
Abstract
Helix-8 (Hx8) is a structurally conserved amphipathic helical motif in class-A GPCRs, adjacent to the C-terminal sequence that is responsible for PDZ-domain-recognition. The Hx8 segment in the dopamine D2 receptor (D2R) constitutes the C-terminal segment and we investigate its role in the function of D2R by studying the interaction with the PDZ-containing GIPC1 using homology models based on the X-ray structures of very closely related analogs: the D3R for the D2R model, and the PDZ domain of GIPC2 for GIPC1-PDZ. The mechanism of this interaction was investigated with all-atom unbiased molecular dynamics (MD) simulations that reveal the role of the membrane in maintaining the helical fold of Hx8, and with biased MD simulations to elucidate the energy drive for the interaction with the GIPC1-PDZ. We found that it becomes more favorable energetically for Hx8 to adopt the extended conformation observed in all PDZ-ligand complexes when it moves away from the membrane, and that C-terminus palmitoylation of D2R enhanced membrane penetration by the Hx8 backbone. De-palmitoylation enables Hx8 to move out into the aqueous environment for interaction with the PDZ domain. All-atom unbiased MD simulations of the full D2R-GIPC1-PDZ complex in sphingolipid/cholesterol membranes show that the D2R carboxyl C-terminus samples the region of the conserved GFGL motif located on the carboxylate-binding loop of the GIPC1-PDZ, and the entire complex distances itself from the membrane interface. Together, these results outline a likely mechanism of Hx8 involvement in the interaction of the GPCR with PDZ-domains in the course of signaling.
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Affiliation(s)
- Ozge Sensoy
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, NY, USA
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, NY, USA.
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9
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Blaskovic S, Blanc M, van der Goot FG. What does S-palmitoylation do to membrane proteins? FEBS J 2013; 280:2766-74. [PMID: 23551889 DOI: 10.1111/febs.12263] [Citation(s) in RCA: 182] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 03/20/2013] [Accepted: 03/25/2013] [Indexed: 12/19/2022]
Abstract
S-palmitoylation is post-translational modification, which consists in the addition of a C16 acyl chain to cytosolic cysteines and which is unique amongst lipid modifications in that it is reversible. It can thus, like phosphorylation or ubiquitination, act as a switch. While palmitoylation of soluble proteins allows them to interact with membranes, the consequences of palmitoylation for transmembrane proteins are more enigmatic. We briefly review the current knowledge regarding the enzymes responsible for palmitate addition and removal. We then describe various observed consequences of membrane protein palmitoylation. We propose that the direct effects of palmitoylation on transmembrane proteins, however, might be limited to four non-mutually exclusive mechanistic consequences: alterations in the conformation of transmembrane domains, association with specific membrane domains, controlled interactions with other proteins and controlled interplay with other post-translational modifications.
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Affiliation(s)
- Sanja Blaskovic
- Global Health Institute, Ecole Polytechnique Fédérale de Lausanne, Switzerland
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10
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Keuerleber S, Thurner P, Gruber CW, Zezula J, Freissmuth M. Reengineering the collision coupling and diffusion mode of the A2A-adenosine receptor: palmitoylation in helix 8 relieves confinement. J Biol Chem 2012; 287:42104-18. [PMID: 23071116 PMCID: PMC3516756 DOI: 10.1074/jbc.m112.393579] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The A(2A)-adenosine receptor undergoes restricted collision coupling with its cognate G protein G(s) and lacks a palmitoylation site at the end of helix 8 in its intracellular C terminus. We explored the hypothesis that there was a causal link between the absence of a palmitoyl moiety and restricted collision coupling by introducing a palmitoylation site. The resulting mutant A(2A)-R309C receptor underwent palmitoylation as verified by both mass spectrometry and metabolic labeling. In contrast to the wild type A(2A) receptor, the concentration-response curve for agonist-induced cAMP accumulation was shifted to the left with increasing expression levels of A(2A)-R309C receptor, an observation consistent with collision coupling. Single particle tracking of quantum dot-labeled receptors confirmed that wild type and mutant A(2A) receptor differed in diffusivity and diffusion mode; agonist activation resulted in a decline in mean square displacement of both receptors, but the drop was substantially more pronounced for the wild type receptor. In addition, in the agonist-bound state, the wild type receptor was frequently subject to confinement events (estimated radius 110 nm). These were rarely seen with the palmitoylated A(2A)-R309C receptor, the preferred diffusion mode of which was a random walk in both the basal and the agonist-activated state. Taken together, the observations link restricted collision coupling to diffusion limits imposed by the absence of a palmitoyl moiety in the C terminus of the A(2A) receptor. The experiments allowed for visualizing local confinement of an agonist-activated G protein-coupled receptor in an area consistent with the dimensions of a lipid raft.
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Affiliation(s)
- Simon Keuerleber
- Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Währinger Strasse 13A, 1090 Vienna, Austria
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Abstract
Hedgehog (Hh) proteins are secreted signaling proteins that contain amide-linked palmitate at the N-terminus and cholesterol at the C-terminus. Palmitoylation of Hh proteins is critical for effective long- and short-range signaling. The palmitoylation reaction occurs during transit of Hh through the secretory pathway, most likely in the lumen of the ER. Attachment of palmitate to Hh proteins is independent of cholesterol modification and autoprocessing and is catalyzed by Hhat (Hedgehog acyltransferase). Hhat is a member of the membrane bound O-acyltransferase (MBOAT) family, a subgroup of multipass membrane proteins that catalyze transfer of fatty acyl groups to lipids and proteins. Several classes of secreted proteins have recently been shown to be substrates for MBOAT acyltransferases, including Hh proteins and Spitz (palmitoylated by Hhat), Wg/Wnt proteins (modified with palmitate and/or palmitoleate by Porcupine) and ghrelin (octanoylated by ghrelin O-acyltransferase). These findings highlight protein fatty acylation as a mechanism that not only influences membrane binding of intracellular proteins but also regulates the signaling range and efficacy of secreted proteins.
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12
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Abstract
The classical view of heterotrimeric G protein signaling places G -proteins at the cytoplasmic surface of the cell's plasma membrane where they are activated by an appropriate G protein-coupled receptor. Once activated, the GTP-bound Gα and the free Gβγ are able to regulate plasma membrane-localized effectors, such as adenylyl cyclase, phospholipase C-β, RhoGEFs and ion channels. Hydrolysis of GTP by the Gα subunit returns the G protein to the inactive Gαβγ heterotrimer. Although all of these events in the G protein cycle can be restricted to the cytoplasmic surface of the plasma membrane, G protein localization is dynamic. Thus, it has become increasingly clear that G proteins are able to move to diverse subcellular locations where they perform non-canonical signaling functions. This chapter will highlight our current understanding of trafficking pathways that target newly synthesized G proteins to the plasma membrane, activation-induced and reversible translocation of G proteins from the plasma membrane to intracellular locations, and constitutive trafficking of G proteins.
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Milligan G. The Use of Receptor G-Protein Fusion Proteins for the Study of Ligand Activity. ACTA ACUST UNITED AC 2011. [DOI: 10.3109/10606820214639] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Sen N, Snyder SH. Protein modifications involved in neurotransmitter and gasotransmitter signaling. Trends Neurosci 2010; 33:493-502. [PMID: 20843563 DOI: 10.1016/j.tins.2010.07.004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Revised: 07/20/2010] [Accepted: 07/27/2010] [Indexed: 02/07/2023]
Abstract
Covalent modifications of intracellular proteins, such as phosphorylation, are generally thought to occur as secondary or tertiary responses to neurotransmitters, following the intermediation of membrane receptors and second messengers such as cyclic AMP. By contrast, the gasotransmitter nitric oxide directly S-nitrosylates cysteine residues in diverse intracellular proteins. Recently, hydrogen sulfide has been acknowledged as a gasotransmitter, which analogously sulfhydrates cysteine residues in proteins. Cysteine residues are also modified by palmitoylation in response to neurotransmitter signaling, possibly in reciprocity with S-nitrosylation. Neurotransmission also elicits sumoylation and acetylation of lysine residues within diverse proteins. This review addresses how these recently appreciated protein modifications impact our thinking about ways in which neurotransmission regulates intracellular protein disposition.
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Affiliation(s)
- Nilkantha Sen
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Sf9 cells: a versatile model system to investigate the pharmacological properties of G protein-coupled receptors. Pharmacol Ther 2010; 128:387-418. [PMID: 20705094 DOI: 10.1016/j.pharmthera.2010.07.005] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 07/12/2010] [Indexed: 11/23/2022]
Abstract
The Sf9 cell/baculovirus expression system is widely used for high-level protein expression, often with the purpose of purification. However, proteins may also be functionally expressed in the defined Sf9 cell environment. According to the literature, the pharmacology of G-protein-coupled receptors (GPCRs) functionally reconstituted in Sf9 cells is similar to the receptor properties in mammalian cells. Sf9 cells express both recombinant GPCRs and G-proteins at much higher levels than mammalian cells. Sf9 cells can be grown in suspension culture, providing an inexpensive way of obtaining large protein amounts. Co-infection with various baculoviruses allows free combination of GPCRs with different G-proteins. The absence of constitutively active receptors in Sf9 cells provides an excellent signal-to background ratio in functional assays, allowing the detection of agonist-independent receptor activity and of small ligand-induced signals including partial agonistic and inverse agonistic effects. Insect cell Gα(i)-like proteins mostly do not couple productively to mammalian GPCRs. Thus, unlike in mammalian cells, Sf9 cells do not require pertussis toxin treatment to obtain a Gα(i)-free environment. Co-expression of GPCRs with Gα(i1), Gα(i2), Gα(i3) or Gα(o) in Sf9 cells allows the generation of a selectivity profile for these Gα(i/o)-isoforms. Additionally, GPCR-G-protein combinations can be compared with defined 1:1 stoichiometry by expressing GPCR-Gα fusion proteins. Sf9 cells can also be employed for ligand screening in medicinal chemistry programs, using radioligand binding assays or functional assays, like the steady-state GTPase- or [(35)S]GTPγS binding assay. This review shows that Sf9 cells are a versatile model system to investigate the pharmacological properties of GPCRs.
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Vögler O, Barceló JM, Ribas C, Escribá PV. Membrane interactions of G proteins and other related proteins. BIOCHIMICA ET BIOPHYSICA ACTA 2008; 1778:1640-52. [PMID: 18402765 DOI: 10.1016/j.bbamem.2008.03.008] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2007] [Revised: 03/01/2008] [Accepted: 03/12/2008] [Indexed: 01/25/2023]
Abstract
Guanine nucleotide-binding proteins, G proteins, propagate incoming messages from receptors to effector proteins. They switch from an inactive to active state by exchanging a GDP molecule for GTP, and they return to the inactive form by hydrolyzing GTP to GDP. Small monomeric G proteins, such as Ras, are involved in controlling cell proliferation, differentiation and apoptosis, and they interact with membranes through isoprenyl moieties, fatty acyl moieties, and electrostatic interactions. This protein-lipid binding facilitates productive encounters of Ras and Raf proteins in defined membrane regions, so that signals can subsequently proceed through MEK and ERK kinases, which constitute the canonical MAP kinase signaling cassette. On the other hand, heterotrimeric G proteins undergo co/post-translational modifications in the alpha (myristic and/or palmitic acid) and the gamma (farnesol or geranylgeraniol) subunits. These modifications not only assist the G protein to localize to the membrane but they also help distribute the heterotrimer (Galphabetagamma) and the subunits generated upon activation (Galpha and Gbetagamma) to appropriate membrane microdomains. These proteins transduce messages from ubiquitous serpentine receptors, which control important functions such as taste, vision, blood pressure, body weight, cell proliferation, mood, etc. Moreover, the exchange of GDP by GTP is triggered by nucleotide exchange factors. Membrane receptors that activate G proteins can be considered as such, but other cytosolic, membranal or amphitropic proteins can accelerate the rate of G protein exchange or even activate this process in the absence of receptor-mediated activation. These and other protein-protein interactions of G proteins with other signaling proteins are regulated by their lipid preferences. Thus, G protein-lipid interactions control the features of messages and cell physiology.
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Affiliation(s)
- Oliver Vögler
- Molecular Cell Biomedicine, Department of Biology-IUNICS, Universitat de les Illes Balears, Palma de Mallorca, Spain
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17
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Abstract
G protein-coupled receptor (GPCR)-Galpha fusion proteins were first characterized more than 10 years ago as a strategy for studying receptor-G protein signaling. A large number of studies have used this approach to characterize receptor coupling to members of the Gs, Gi, and Gq families of Galpha subunits, but this strategy has not been widely used to study Galpha12 and Galpha13. As described in the article by Zhang et al. in this issue of Molecular Pharmacology (p. 1433) characterization of the signaling properties of thromboxane A2 receptor (TPalpha) -Galpha12 and -Galpha13 fusion constructs demonstrates the applicability of this strategy to members of this unique family of Galpha subunits, and how this strategy can be used to resolve otherwise difficult problems of receptor pharmacology associated with these proteins. The general strategy of making receptor-Galpha fusion constructs has wide applicability to a number of research problems, but there are perhaps also "hidden messages" in how different receptor-Galpha subunit fusion pairs behave.
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Affiliation(s)
- John D Hildebrandt
- Department of Cell and Molecular Pharmacology, Medical University of South Carolina, 173 Ashley Ave., 303BSB, Charleston, SC 29425, USA.
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18
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Mikic I, Planey S, Zhang J, Ceballos C, Seron T, von Massenbach B, Watson R, Callaway S, McDonough PM, Price JH, Hunter E, Zacharias D. A live cell, image-based approach to understanding the enzymology and pharmacology of 2-bromopalmitate and palmitoylation. Methods Enzymol 2006; 414:150-87. [PMID: 17110192 DOI: 10.1016/s0076-6879(06)14010-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The addition of a lipid moiety to a protein increases its hydrophobicity and subsequently its attraction to lipophilic environments like membranes. Indeed most lipid-modified proteins are localized to membranes where they associate with multiprotein signaling complexes. Acylation and prenylation are the two common categories of lipidation. The enzymology and pharmacology of prenylation are well understood but relatively very little is known about palmitoylation, the most common form of acylation. One distinguishing characteristic of palmitoylation is that it is a dynamic modification. To understand more about how palmitoylation is regulated, we fused palmitoylation substrates to fluorescent proteins and reported their subcellular distribution and trafficking. We used automated high-throughput fluorescence microscopy and a specialized computer algorithm to image and measure the fraction of palmitoylation reporter on the plasma membrane versus the cytoplasm. Using this system we determined the residence half-life of palmitate on the dipalmitoyl substrate peptide from GAP43 as well as the EC(50) for 2-bromopalmitate, a common inhibitor of palmitoylation.
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19
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Barclay E, O'Reilly M, Milligan G. Activation of an alpha2A-adrenoceptor-Galphao1 fusion protein dynamically regulates the palmitoylation status of the G protein but not of the receptor. Biochem J 2005; 385:197-206. [PMID: 15362975 PMCID: PMC1134688 DOI: 10.1042/bj20041432] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Post-translational thio-acylation of a fusion protein between the alpha2A-adrenoceptor and the alpha subunit of the G protein G(o1) is both dynamic and regulated by agonist binding. Incorporation of [3H]palmitate into the fusion protein was reduced substantially in the presence of the agonist adrenaline. This was dependent on the concentration of adrenaline and correlated with occupancy of the ligand binding site. Both the receptor and G-protein elements of the fusion construct incorporated [3H]palmitate but this occurred more rapidly for the G-protein element and regulation of acylation by the agonist occurred only for the G protein. The kinetics of de-palmitoylation of the alpha2A-adrenoceptor-Galpha(o1) fusion were accelerated markedly by agonist. Again, this reflected modulation of the G protein but not of the receptor. Agonist-induced regulation of the kinetics of thio-acylation of the G protein was abolished, however, in a mutant unable to bind guanosine 5'-[gamma-[35S]thio]triphosphate ([35S]GTP[S]) in response to adrenaline. Despite the dynamic nature of the post-translational acylation and its regulation by agonist, the ability of adrenaline to activate the G protein, monitored by stimulation of the binding of [35S]GTP[S] to such fusion constructs, was unaffected by the palmitoylation potential of either the receptor or G-protein element.
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Affiliation(s)
- Elaine Barclay
- *Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K
| | - Mark O'Reilly
- †Pfizer Global Research and Development, Sandwich, Kent, CT13 N9J, U.K
| | - Graeme Milligan
- *Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K
- To whom correspondence should be addressed (email )
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20
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Trester-Zedlitz M, Burlingame A, Kobilka B, von Zastrow M. Mass spectrometric analysis of agonist effects on posttranslational modifications of the beta-2 adrenoceptor in mammalian cells. Biochemistry 2005; 44:6133-43. [PMID: 15835901 DOI: 10.1021/bi0475469] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Posttranslational modifications (PTMs) of the beta-2 adrenoceptor (B2AR) play a fundamental role in receptor regulation by agonists. We have examined the effects of several agonists on net levels of B2AR palmitoylation and phosphorylation using epitope tagging in stably transfected human embryonal kidney (HEK) 293 cells, immunoaffinity purification, and mass spectrometry combined with the method of stable isotope labeling by amino acids in cell culture (SILAC). Palmitoylation of Cys341 was confirmed and did not change detectably after 30 min exposure of cells to saturating concentrations of dopamine, epinephrine, or isoproterenol. However, all of these agonists produced a marked increase in net phosphorylation. Phosphorylation of the third cytoplasmic loop was increased to a similar degree by all three agonists, whereas differences between agonists were observed in net phosphorylation of the carboxyl-terminal cytoplasmic domain (isoproterenol approximately epinephrine >> dopamine). Interestingly, agonist-induced phosphorylation of the carboxyl-terminal cytoplasmic domain was observed exclusively in a proximal portion (between residues 339-369). None of the agonists produced detectable phosphorylation in a distal portion of the cytoplasmic tail, which contains all sites of agonist-induced phosphorylation identified previously by in vitro reconstitution. These results provide insight to agonist-dependent regulation of the B2AR in intact cells, suggest the existence of significant differences in regulatory phosphorylation events occurring between in vitro and in vivo conditions, and outline a general analytical approach to investigate regulated PTM of receptors in mammalian cells.
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MESH Headings
- Adrenergic beta-Agonists/pharmacology
- Amino Acid Sequence
- Binding Sites
- Cell Line
- Deuterium
- Humans
- In Vitro Techniques
- Molecular Sequence Data
- Palmitic Acids/chemistry
- Phosphorylation
- Protein Processing, Post-Translational/drug effects
- Protein Structure, Tertiary
- Receptors, Adrenergic, beta-2/chemistry
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Recombinant Proteins/chemistry
- Recombinant Proteins/genetics
- Recombinant Proteins/metabolism
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
- Transfection
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Affiliation(s)
- Michelle Trester-Zedlitz
- Department of Psychiatry and Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, California 94143, USA
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21
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Smotrys JE, Linder ME. Palmitoylation of intracellular signaling proteins: regulation and function. Annu Rev Biochem 2004; 73:559-87. [PMID: 15189153 DOI: 10.1146/annurev.biochem.73.011303.073954] [Citation(s) in RCA: 452] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Protein S-palmitoylation is the thioester linkage of long-chain fatty acids to cysteine residues in proteins. Addition of palmitate to proteins facilitates their membrane interactions and trafficking, and it modulates protein-protein interactions and enzyme activity. The reversibility of palmitoylation makes it an attractive mechanism for regulating protein activity, and this feature has generated intensive investigation of this modification. The regulation of palmitoylation occurs through the actions of protein acyltransferases and protein acylthioesterases. Identification of the protein acyltransferases Erf2/Erf4 and Akr1 in yeast has provided new insight into the palmitoylation reaction. These molecules work in concert with thioesterases, such as acyl-protein thioesterase 1, to regulate the palmitoylation status of numerous signaling molecules, ultimately influencing their function. This review discusses the function and regulation of protein palmitoylation, focusing on intracellular proteins that participate in cell signaling or protein trafficking.
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Affiliation(s)
- Jessica E Smotrys
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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22
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Abstract
Neurobiological actions of ethanol have been linked to perturbations in cyclic AMP (cAMP)-dependent signaling processes. Chronic ethanol exposure leads to desensitization of cAMP production in response to physiological ligands (heterologous desensitization). Ethanol-induced alterations in neuronal expression of G proteins G(s) and G(i) have been invoked as a cause of heterologous desensitization. However, effects of ethanol on G protein expression vary considerably among different experimental protocols, various brain regions and diverse neuronal cell types. Dynamic palmitoylation of G protein alpha subunits is critical for membrane localization and protein-protein interactions, and represents a regulatory feature of G protein function. We studied the effect of ethanol on G alpha(s) palmitoylation. In NG108-15 rat neuroblastoma x glioma hybrid cells, acute exposure to pharmacologically relevant concentrations of ethanol (25-100 mm) inhibited basal and prostaglandin E1-stimulated incorporation of palmitate into G alpha(s). Exposure of NG108-15 cells to ethanol for 72 h induced a shift in G alpha(s) to its non-palmitoylated state, coincident with an inhibition of prostaglandin E1-induced cAMP production. Both parameters were restored following 24 h of ethanol withdrawal. Chronic ethanol exposure also induced the depalmitoylation of G alpha(s) in human embryonic kidney (HEK)293 cells that overexpress wild-type G alpha(s) and caused heterologous desensitization of adenylyl cyclase. By contrast, HEK293 cells that express a non-palmitoylated mutant of G alpha(s) were insensitive to heterologous desensitization after chronic ethanol exposure. In summary, the findings identify a novel effect of ethanol on post-translational lipid modification of G alpha(s), and represent a mechanism by which ethanol might affect adenylyl cyclase activity.
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Affiliation(s)
- Hazem Hallak
- Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107-5541, USA.
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23
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Morris R, Cox H, Mombelli E, Quinn PJ. Rafts, little caves and large potholes: how lipid structure interacts with membrane proteins to create functionally diverse membrane environments. Subcell Biochem 2004; 37:35-118. [PMID: 15376618 DOI: 10.1007/978-1-4757-5806-1_2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
This chapter reviews how diverse lipid microdomains form in the membrane and partition proteins into different functional units that regulate cell trafficking, signalling and movement. We will concentrate upon five major issues: 1. the diversity of lipid structure that produces diverse microenvironments into which different subsets of proteins partition; 2. why ordered lipid domains exclude proteins, and the conditions required for select subsets of proteins to enter these domains; 3. the coupling of the inner and outer leaflets within ordered microdomains; 4. the effect of ordered lipid domains upon membrane properties including curvature and hydrophobicity that affect membrane fission, fusion and extension of filopodia; 5. the biological effects of these structural constraints; in particular how the properties of these domains combine to provide a very different signalling, trafficking and membrane fusion environment to that found in disordered (fluid mosaic) membrane. In addressing these problems, the review draws upon studies ranging from molecular dynamic modelling of lipid interactions, through physical studies of model membrane systems to structural and biological studies of whole cells, examining in the process problems inherent in visualising and purifying these microdomains. While the diversity of structure and function of ordered lipid microdomains is emphasised, some general roles emerge. In particular, the basis for having quite different, non-interacting ordered lipid domains on the same membrane is evident in the diversity of lipid structure and plays a key role in sorting signalling systems. The exclusion of ordered membrane from coated pits, and hence rapid endocytosis, is suggested to underlie the ability of highly ordered domains to establish stable secondary signalling systems required, for instance, in T cell receptor, insulin and neurotrophin signalling.
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Affiliation(s)
- Roger Morris
- Molecular Neurobiology Group, MRC Centre for Developmental Neurobiology, King's College, London, UK
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24
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Pawson AJ, Maudsley SR, Lopes J, Katz AA, Sun YM, Davidson JS, Millar RP. Multiple determinants for rapid agonist-induced internalization of a nonmammalian gonadotropin-releasing hormone receptor: a putative palmitoylation site and threonine doublet within the carboxyl-terminal tail Are critical. Endocrinology 2003; 144:3860-71. [PMID: 12933659 DOI: 10.1210/en.2003-0028] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The chicken GnRH receptor (cGnRH-R) differs from all mammalian GnRH-Rs in possessing a cytoplasmic carboxyl-terminal tail. We have previously demonstrated that the cGnRH-R undergoes more rapid agonist-induced internalization than the mammalian GnRH-Rs and requires the carboxyl-terminal tail for this process. To investigate the structural determinants mediating this rapid internalization, a series of mutant receptors was generated, including progressive truncations of the tail and substitution of serine and threonine residues with alanine. Truncation of the carboxyl-terminal tail to position 366 and then to position 356 resulted in a progressive attenuation of the rate and total extent of receptor internalization. However, truncation between positions 356 and 346 did not alter the kinetics of internalization further, whereas a further truncation to position 337 resulted in an additional marked reduction of internalization. We show that the membrane-proximal Cys(328) and the Thr(369)Thr(370) doublet located in the distal carboxyl terminus play a critical role in mediating rapid internalization. We demonstrate that the cGnRH-R, when expressed in both COS-7 and HEK 293 cells, preferentially undergoes rapid agonist-induced internalization in a caveolae-like, dynamin-dependent manner. These conclusions are based on our observation that pretreatments with filipin and methyl-beta-cyclodextrin, agents that disrupt lipid rafts such as caveolae, and coexpression of dominant-negative dynamin-1 (K44A) and caveolin-1 (Delta 1-81) mutants, effectively inhibited rapid agonist-induced internalization. Furthermore, cGnRH-Rs appeared to be mobilized to the beta-arrestin- and clathrin-coated, vesicle-mediated endocytic pathway upon beta-arrestin overexpression.
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Affiliation(s)
- Adam J Pawson
- Human Reproductive Sciences Unit, Medical Research Council, Edinburgh, United Kingdom EH16 4SB
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25
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Maack C, Böhm M, Vlaskin L, Dabew E, Lorenz K, Schäfers HJ, Lohse MJ, Engelhardt S. Partial agonist activity of bucindolol is dependent on the activation state of the human beta1-adrenergic receptor. Circulation 2003; 108:348-53. [PMID: 12847069 DOI: 10.1161/01.cir.0000080325.94345.8b] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND In contrast to other beta-blockers, bucindolol has failed to reduce mortality in patients with chronic heart failure. It is currently debated whether this is due to partial agonist activity of this agent. We investigated whether conflicting results previously reported concerning the intrinsic activity of bucindolol can be explained by species differences or by different activation states of beta-adrenergic receptors (beta-ARs) in the respective tissues. METHODS AND RESULTS On isolated right atria from transgenic mice with cardiac overexpression of human beta1-ARs, bucindolol led to a greater increase in beating frequency (P<0.05) compared with wild-type mice. The increase amounted to 47% of the effect of xamoterol and was blocked by propranolol. On isolated, electrically stimulated, left ventricular muscle-strip preparations from failing human myocardium, bucindolol did not change the force of contraction under control conditions. In myocardial preparations pretreated with metoprolol (30 micromol/L, 90 minutes, subsequent washout), bucindolol significantly increased the force of contraction (P<0.001 vs control). In nonfailing atrial myocardium, isoproterenol pretreatment (1 micromol/L, 60 minutes) abolished the positive inotropic effect of xamoterol that was present under control conditions (P<0.05 vs control). The inotropic effects of bucindolol or xamoterol were inversely correlated to the inotropic response to forskolin in the respective specimens (r=-0.75 and -0.74, respectively; P<0.005). CONCLUSIONS We conclude that bucindolol is a partial agonist at the human beta1-AR. In human failing myocardium, its partial agonist activity is masked by increased activation states of beta-ARs and is unmasked after in vitro pretreatment with metoprolol. Thus, the partial agonist activity of bucindolol is dependent on the activation state of the human beta1-AR.
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Affiliation(s)
- Christoph Maack
- Klinik und Poliklinik für Innere Medizin III, Universität des Saarlandes, Homburg/Saar, Germany
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26
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Ugur O, Onaran HO, Jones TLZ. Partial rescue of functional interactions of a nonpalmitoylated mutant of the G-protein G alpha s by fusion to the beta-adrenergic receptor. Biochemistry 2003; 42:2607-15. [PMID: 12614155 DOI: 10.1021/bi026470i] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Most heterotrimeric G-protein alpha subunits are posttranslationally modified by palmitoylation, a reversible process that is dynamically regulated. We analyzed the effects of Galpha(s) palmitoylation for its intracellular distribution and ability to couple to the beta-adrenergic receptor (betaAR) and stimulate adenylyl cyclase. Subcellular fractionation and immunofluorescence microscopy of stably transfected cyc(-) cells, which lack endogenous Galpha(s), showed that wild-type Galpha(s) was predominantly localized at the plasma membrane, but the mutant C3A-Galpha(s), which does not incorporate [(3)H]palmitate, was mostly associated with intracellular membranes. In agreement with this mislocalization, C3A-Galpha(s) showed neither isoproterenol- or GTPgammaS-stimulated adenylyl cyclase activation nor GTPgammaS-sensitive high-affinity agonist binding, all of which were present in the wild-type Galpha(s) expressing cells. Fusion of C3A-Galpha(s) with the betaAR [betaAR-(C3A)Galpha(s)] partially rescued its ability to induce high-affinity agonist binding and to stimulate adenylyl cyclase activity after isoproterenol or GTPgammaS treatment. In comparison to results with the WT-Galpha(s) and betaAR (betaAR-Galpha(s)) fusion protein, the betaAR-(C3A)Galpha(s) fusion protein was about half as efficient at coupling to the receptor and effector. Chemical depalmitoylation by hydroxylamine of membranes expressing betaAR-Galpha(s) reduced the high-affinity agonist binding and adenylyl cyclase activation to a similar degree as that observed in betaAR-(C3A)Galpha(s) expressing membranes. Altogether, these findings indicate that palmitoylation ensured proper localization of Galpha(s) and facilitated bimolecular interactions of Galpha(s) with the betaAR and adenylyl cyclase.
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MESH Headings
- Adenylyl Cyclases/metabolism
- Alanine/genetics
- Animals
- Cell Membrane/drug effects
- Cell Membrane/genetics
- Cell Membrane/metabolism
- Cysteine/genetics
- GTP-Binding Protein alpha Subunits, Gs/chemistry
- GTP-Binding Protein alpha Subunits, Gs/deficiency
- GTP-Binding Protein alpha Subunits, Gs/genetics
- GTP-Binding Protein alpha Subunits, Gs/metabolism
- Gene Expression Regulation/genetics
- Humans
- Hydroxylamine/pharmacology
- Intracellular Fluid/metabolism
- Mice
- Mutagenesis, Site-Directed
- Palmitic Acid/metabolism
- Protein Binding/drug effects
- Protein Binding/genetics
- Protein Subunits/chemistry
- Protein Subunits/deficiency
- Protein Subunits/genetics
- Protein Subunits/metabolism
- Protein Transport/drug effects
- Protein Transport/genetics
- Rats
- Receptors, Adrenergic, beta-2/biosynthesis
- Receptors, Adrenergic, beta-2/chemistry
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Recombinant Fusion Proteins/biosynthesis
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- Ozlem Ugur
- Department of Pharmacology and Clinical Pharmacology and Molecular Biology and Technology Research and Development Unit, Ankara University Faculty of Medicine, Sihhiye, 06100 Ankara, Turkey.
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27
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Massotte D. G protein-coupled receptor overexpression with the baculovirus-insect cell system: a tool for structural and functional studies. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1610:77-89. [PMID: 12586382 DOI: 10.1016/s0005-2736(02)00720-4] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
G protein-coupled receptors, whose topology shows seven transmembrane domains, form the largest known family of receptors involved in higher organism signal transduction. These receptors are generally of low natural abundance and overexpression is usually a prerequisite to their structural or functional characterisation. The baculovirus-insect cell system constitutes a versatile tool for the maximal production of receptors. This heterologous expression system also provides interesting alternatives for receptor functional studies in a well-controlled cellular context.
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Affiliation(s)
- Dominique Massotte
- Laboratoire de Biologie et Génomique Structurales, UMR 7104, IGBMC, 1 rue Laurent Fries, BP 10142, F-67404 Illkirch Cedex, France.
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28
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Qanbar R, Bouvier M. Role of palmitoylation/depalmitoylation reactions in G-protein-coupled receptor function. Pharmacol Ther 2003; 97:1-33. [PMID: 12493533 DOI: 10.1016/s0163-7258(02)00300-5] [Citation(s) in RCA: 189] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
G-protein-coupled receptors (GPCRs) constitute one of the largest protein families in the human genome. They are subject to numerous post-translational modifications, including palmitoylation. This review highlights the dynamic nature of palmitoylation and its role in GPCR expression and function. The palmitoylation of other proteins involved in GPCR signaling, such as G-proteins, regulators of G-protein signaling, and G-protein-coupled receptor kinases, is also discussed.
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Affiliation(s)
- Riad Qanbar
- Département de Biochimie, Université de Montréal, C.P. 6128 Succursale Centre-Ville, 2900 Edouard Montpetit, Montreál, Quebec, Canada H3C 3J7
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29
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Welsby PJ, Carr IC, Wilkinson G, Milligan G. Regulation of the avidity of ternary complexes containing the human 5-HT(1A) receptor by mutation of a receptor contact site on the interacting G protein alpha subunit. Br J Pharmacol 2002; 137:345-52. [PMID: 12237254 PMCID: PMC1573502 DOI: 10.1038/sj.bjp.0704880] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2002] [Revised: 07/10/2002] [Accepted: 07/19/2002] [Indexed: 11/08/2022] Open
Abstract
1 Fusion proteins were constructed between the human 5-HT(1A) receptor and pertussis toxin-resistant forms of both G(i1)alpha and G(o1)alpha mutated at residue(351) from cysteine to either glycine or isoleucine. Each of these was expressed stably in HEK293 cells. 2 Increasing concentrations of GDP inhibited binding of the agonist [(3)H]-8-OH-DPAT but not the antagonist [(3)H]-MPPF to each construct. 3 The IC(50) for GDP was greater for constructs containing isoleucine at residue(351) of the G proteins compared to those with glycine at this position. 4 The G protein antagonist suramin had similar effects to GDP on the binding of [(3)H]-8-OH-DPAT. 5 The proportion of 5-HT(1A) receptor binding sites detected by [(3)H]-MPPF that displayed high affinity for 8-OH-DPAT was significantly greater when the interacting G protein contained isoleucine rather than glycine at residue(351). 6 The 5-HT(1A) receptor displayed similar avidity of interaction with G(i1)alpha and G(o1)alpha. 7 These results indicate that a higher avidity ternary complex is formed between 8-OH-DPAT, the 5-HT(1A) receptor and G proteins when isoleucine rather than glycine is located at residue(351) of the interacting G protein.
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Affiliation(s)
- Philip J Welsby
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ
| | - I Craig Carr
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ
| | - Graeme Wilkinson
- Molecular Pharmacology and Biochemistry, Department of Enabling Science and Technology, Astra-Zeneca, Alderley Park, Macclesfield, Cheshire SK10 4TG
| | - Graeme Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ
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30
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Welsby PJ, Kellett E, Wilkinson G, Milligan G. Enhanced detection of receptor constitutive activity in the presence of regulators of G protein signaling: applications to the detection and analysis of inverse agonists and low-efficacy partial agonists. Mol Pharmacol 2002; 61:1211-21. [PMID: 11961140 DOI: 10.1124/mol.61.5.1211] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Fusion proteins between the human 5-hydroxytryptamine (5-HT)(1A) receptor and either wild type or certain pertussis toxin-resistant forms of G(o1)alpha and G(i1)alpha display constitutive GTPase activity that can be inhibited by the inverse agonist spiperone. Addition of recombinant regulator of G protein signaling (RGS) 1 or RGS16 to membranes expressing these fusion proteins resulted in elevation of this constitutive GTPase activity without significantly altering the binding affinity of antagonist/inverse agonist ligands. For a 5-HT(1A) receptor-(Cys(351)Ile)G(o1)alpha fusion protein the increase in basal GTPase activity was greater than 4-fold. Enzyme kinetic analysis demonstrated that the effect of RGS1 was as a GTPase-activating protein for the fusion construct. In the presence of the RGS proteins, both agonists and inverse agonists produced much more robust regulation of high-affinity GTPase activity than in their absence. This allowed detection of the partial agonist nature of WAY100635, which has been described previously as a neutral antagonist at the 5-HT(1A) receptor. Of a range of ligands studied, only haloperidol functioned as a neutral ligand in the presence of RGS1. These studies show that addition of a recombinant RGS protein provides a simple and novel means to elevate the fraction of basal membrane GTPase activity contributed by the constitutive activity of a receptor. By so doing, it also greatly enhances the ability to detect and analyze the effects of inverse agonists and to discriminate between neutral ligands and those with low levels of positive intrinsic efficacy.
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Affiliation(s)
- Philip J Welsby
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom
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31
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Milligan G. Construction and analysis of function of G protein-coupled receptor-G protein fusion proteins. Methods Enzymol 2002; 343:260-73. [PMID: 11665572 DOI: 10.1016/s0076-6879(02)43141-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Graeme Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
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32
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Ward RJ, Milligan G. Reciprocal mutations of highly conserved residues in transmembrane helices 2 and 7 of the alpha(2A)-adrenoceptor restore agonist activation of G(i1)alpha. Cell Signal 2002; 14:139-44. [PMID: 11781138 DOI: 10.1016/s0898-6568(01)00218-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Fusion proteins were constructed between the alpha(2A)-adrenoceptor and the alpha-subunit of the G-protein G(i1). Mutation of the highly conserved Asp(79) in transmembrane (TM) helix 2 of the receptor to Asn reduced the capacity of agonists to activate G(i1)alpha by 95% without altering [3H]antagonist or agonist ligand-binding affinity. A reciprocal mutation in TM helix 7 (Asn(422)Asp) was without effect on signalling effectiveness. Combination of these two mutations overcame the effect of the Asp(79)Asp mutation. By examining alterations in this helix 2-helix 7 microdomain, we further demonstrate the utility of receptor-G-protein fusion proteins to quantitate mutational effects on receptor-G-protein interactions and information transfer.
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Affiliation(s)
- Richard J Ward
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
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33
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Pizard A, Blaukat A, Michineau S, Dikic I, Müller-Esterl W, Alhenc-Gelas F, Rajerison RM. Palmitoylation of the human bradykinin B2 receptor influences ligand efficacy. Biochemistry 2001; 40:15743-51. [PMID: 11747451 DOI: 10.1021/bi011600t] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To investigate the palmitoylation of the human bradykinin B2 receptor, we have mutated individually or simultaneously into glycine two potential acylation sites (cysteines 324 and 329) located in the carboxyl terminus of the receptor and evaluated the effects of these mutations by transfection in COS-7, CHO-K1, and HEK 293T. The wild-type receptor and the single mutants, but not the double mutant, incorporated [3H]palmitate, indicating that the receptor carboxyl tail can be palmitoylated at both sites. The mutants did not differ from the wild-type receptor for the kinetics of [3H]bradykinin binding, the basal and bradykinin-stimulated coupling to phospholipases C and A2, and agonist-induced phosphorylation. The nonpalmitoylated receptor had a 30% reduced capacity to internalize [3H]bradykinin. This indicates that palmitoylation does not influence the basal activity of the receptor and its agonist-driven activation. However, the mutants triggered phospholipid metabolism and MAP kinase activation in response to B2 receptor antagonists. Pseudopeptide and nonpeptide compounds that behaved as antagonists on the wild-type receptor became agonists on the nonpalmitoylated receptor and produced phospholipases C and A2 responses of 25-50% as compared to that of bradykinin. These results suggest that palmitoylation is required for the stabilization of the receptor-ligand complex in an uncoupled conformation.
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Affiliation(s)
- A Pizard
- INSERM Unité 367, 17 rue du Fer à Moulin, 75005 Paris, France
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34
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Abstract
Studies of the serotonin (5-HT) receptors have illustrated several important concepts in G-protein-mediated signaling. These concepts include G-protein specificity and cellular specificity of signaling; mechanisms of transactivation; receptor states and constitutive receptor activity; and the structural basis of coupling. The 5-HT1 receptors couple via specific G(i)/G(o) proteins to inhibitory pathways [inhibition of adenylyl cyclase (AC) activity and regulation of ion channels], but also to stimulate phospholipase C, ACII, and the mitogen-activated protein kinase (MAPK) growth-signaling pathway. 5-HT1 receptors initiate novel endocytotic and Ca(2+)-dependent pathways to activate MAPK acutely, but can downregulate MAPK on chronic activation. These pathways are often mediated via distinct G(i)/G(o)-protein subtypes. Desensitization by multiple protein kinases via receptor phosphorylation is pathway selective. Structural determination of 5-HT1 receptor and G-protein domains that mediate G-protein-specific coupling and desensitization could lead to the development of highly selective ligands that directly regulate receptor-G-protein coupling.
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Affiliation(s)
- P R Albert
- Ottawa Health Research Institute, 451 Smyth Road, University of Ottawa, Ottawa, Canada K1H-8M5.
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35
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Shi L, Simpson MM, Ballesteros JA, Javitch JA. The first transmembrane segment of the dopamine D2 receptor: accessibility in the binding-site crevice and position in the transmembrane bundle. Biochemistry 2001; 40:12339-48. [PMID: 11591153 DOI: 10.1021/bi011204a] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The binding site of the dopamine D2 receptor, like that of homologous G-protein-coupled receptors (GPCRs), is contained within a water-accessible crevice formed among its seven transmembrane segments (TMs). Using the substituted-cysteine-accessibility method (SCAM), we are mapping the residues that contribute to the surface of this binding-site crevice. We have now mutated to cysteine, one at a time, 21 consecutive residues in TM1. Six of these mutants reacted with charged sulfhydryl reagents, whereas bound antagonist only protected N52(1.50)C from reaction. Except for A38(1.36)C, none of the substituted cysteine mutants in the extracellular half of TM1 appeared to be accessible. Pro(1.48) is highly conserved in opsins, but absent in catecholamine receptors, and the high-resolution rhodopsin structure showed that Pro(1.48) bends the extracellular portion of TM1 inward toward TM2 and TM7. Analysis of the conversation of residues in the extracellular portion of TM1 of opsins showed a pattern consistent with alpha-helical structure with a conserved face. In contrast, this region in catecholamine receptors is poorly conserved, suggesting a lack of critical contacts. Thus, in catecholamine receptors in the absence of Pro(1.48), TM1 may be straighter and therefore further from the helix bundle, consistent with the apparent lack of conserved contact residues. When examined in the context of a model of the D2 receptor, the accessible residues in the cytoplasmic half of TM1 are at the interface with TM7 and with helix 8 (H8). We propose the existence of critical contacts of TM1, TM7, and H8 that may stabilize the inactive state of the receptor.
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Affiliation(s)
- L Shi
- Center for Molecular Recognition, Department of Pharmacology, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, New York 10032, USA
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36
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Hawtin SR, Tobin AB, Patel S, Wheatley M. Palmitoylation of the vasopressin V1a receptor reveals different conformational requirements for signaling, agonist-induced receptor phosphorylation, and sequestration. J Biol Chem 2001; 276:38139-46. [PMID: 11466323 DOI: 10.1074/jbc.m106142200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study, we establish that the V1a vasopressin receptor (V1aR) is palmitoylated, and we show that this modification has an important functional role. Palmitoylation of the V1aR occurs within the Cys371/Cys372 couplet located in the proximal C-terminal tail domain. Substitution of these residues in a [C371G/C372G]V1aR construct effectively disrupted receptor palmitoylation. Our data also indicate an additional palmitoylation site at another locus in the receptor, as yet undefined. [3H]Palmitate incorporation was agonist-sensitive and increased following exposure to [Arg8]vasopressin (AVP). Given the hydrophobic nature of the acyl chain, palmitoylation of the C terminus of G-protein-coupled receptors has been proposed to form an additional intracellular loop. Consequently, palmitoylation/depalmitoylation will have a profound effect on the local conformation of this domain. The V1aR palmitoylation status regulated both phosphorylation and sequestration of the receptor, and furthermore, palmitoylation, phosphorylation, and sequestration were all regulated by AVP. The palmitoylation-defective construct [C371G/C372G]V1aR exhibited decreased phosphorylation compared to wild-type V1aR, under both basal and AVP-stimulated conditions, and was sequestered at a faster rate. In contrast, the binding of four different classes of ligand and intracellular signaling were not affected by palmitoylation. This study therefore establishes that there are different conformational requirements for signaling, agonist-induced phosphorylation, and sequestration of the V1aR.
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Affiliation(s)
- S R Hawtin
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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37
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Carpentier E, Lebesgue D, Kamen AA, Hogue M, Bouvier M, Durocher Y. Increased production of active human beta(2)-adrenergic/G(alphas) fusion receptor in Sf-9 cells using nutrient limiting conditions. Protein Expr Purif 2001; 23:66-74. [PMID: 11570847 DOI: 10.1006/prep.2001.1476] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Using the baculovirus/insect-cell expression vector system, we succeeded in obtaining a high yield of active human beta(2)-adrenergic receptor/G(alphas) fusion protein. This was achieved following high cell density production under nutrient-limiting conditions using a very low multiplicity of infection (MOI). This approach was found to significantly reduce inactive protein accumulation that occurred when production was done using conventional high MOI procedures. The maximum specific and volumetric yields of active receptor using this strategy increased by factors of two- and sixfold, respectively. Our results suggest that the increase in the ratio of active/total protein produced results from production under nutrient limitation. Since low multiplicity of infection offers many advantages for large-scale applications, we suggest that this simple production method should be considered when optimizing expression of G-protein-coupled receptors and other complex proteins.
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Affiliation(s)
- E Carpentier
- Bioprocess sector, Biotechnology Research Institute, 6100 Royalmount avenue, Montreal, Quebec, H4P 2R2, Canada
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38
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Cramer H, Schmenger K, Heinrich K, Horstmeyer A, Böning H, Breit A, Piiper A, Lundstrom K, Müller-Esterl W, Schroeder C. Coupling of endothelin receptors to the ERK/MAP kinase pathway. Roles of palmitoylation and G(alpha)q. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:5449-59. [PMID: 11606208 DOI: 10.1046/j.0014-2956.2001.02486.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Endothelins are potent mitogens that stimulate extracellular signal-regulated kinases (ERK/MAP kinases) through their cognate G-protein-coupled receptors, ET(A) and ET(B). To address the role of post-translational ET receptor modifications such as acylation on ERK activation and to identify relevant downstream effectors coupling the ET receptor to the ERK signaling cascades we have constructed a panel of palmitoylation-deficient ET receptor mutants with differential G(alpha) protein binding capacity. Endothelin-1 stimulation of wild-type ET(A) or ET(B) induced a fivefold to sixfold increase in ERK in COS-7 and CHO cells whereas full-length nonpalmitoylated ET(A) and ET(B) mutants failed to stimulate ERK. A truncated ET(B) lacking the C-terminal tail domain including putative phosphorylation and arrestin binding site(s) but retaining the critical palmitoylation site(s) was still able to fully stimulate ERK activation. Using mutated ET receptors with selective G-protein-coupling we found that endothelin-induced stimulation of G(alpha)q, but not of G(alpha)i or G(alpha)s, is essential for endothelin-mediated ERK activation. Inhibition of protein kinases A and C or epidermal growth factor receptor kinase failed to prevent ET(A)- and ET(B)-mediated ERK activation whereas blockage of phospholipase C-beta completely abrogated endothelin-promoted ERK activation through ET(A) and ET(B) in recombinant COS-7 and native C6 cells. Complex formation of Ca2+ or inhibition of Src family tyrosine kinases prevented ET-1-induced ERK-2 activation in C6-cells. Our results indicate that endothelin-promoted ERK/MAPK activation criticially depends on palmitoylation but not on phosphorylation of ET receptors, and that the G(alpha)q/phospholipase C-beta/Ca2+/Src signaling cascade is necessary for efficient coupling of ET receptors to the ERK/MAPK pathway.
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Affiliation(s)
- H Cramer
- Institute for Biochemistry II, Johann Wolfgang Goethe University Frankfurt, Theodor-Stern-Kai7, Germany
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39
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Stevens PA, Pediani J, Carrillo JJ, Milligan G. Coordinated agonist regulation of receptor and G protein palmitoylation and functional rescue of palmitoylation-deficient mutants of the G protein G11alpha following fusion to the alpha1b-adrenoreceptor: palmitoylation of G11alpha is not required for interaction with beta*gamma complex. J Biol Chem 2001; 276:35883-90. [PMID: 11461908 DOI: 10.1074/jbc.m103816200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transfection of either the alpha(1b)-adrenoreceptor or Galpha(11) into a fibroblast cell line derived from a Galpha(q)/Galpha(11) double knockout mouse failed to produce elevation of intracellular [Ca(2+)] upon the addition of agonist. Co-expression of these two polypeptides, however, produced a significant stimulation. Co-transfection of the alpha(1b)-adrenoreceptor with the palmitoylation-resistant C9S,C10S Galpha(11) also failed to produce a signal, and much reduced and kinetically delayed signals were obtained using either C9S Galpha(11) or C10S Galpha(11). Expression of a fusion protein between the alpha(1b)-adrenoreceptor and Galpha(11) allowed [Ca(2+)](i) elevation, and this was also true for a fusion protein between the alpha(1b)-adrenoreceptor and C9S,C10S Galpha(11), since this strategy ensures proximity of the two polypeptides at the cell membrane. For both fusion proteins, co-expression of transducin alpha, as a beta.gamma-sequestering agent, fully attenuated the Ca(2+) signal. Both of these fusion proteins and one in which an acylation-resistant form of the receptor was linked to wild type Galpha(11) were also targets for agonist-regulated [(3)H]palmitoylation and bound [(35)S]guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) in an agonist concentration-dependent manner. The potency of agonist to stimulate [(35)S]GTPgammaS binding was unaffected by the palmitoylation potential of either receptor or G protein. These studies provide clear evidence for coordinated, agonist-mediated regulation of the post-translational acylation of both a receptor and partner G protein and demonstrate the capacity of such fusions to bind and then release beta.gamma complex upon agonist stimulation whether or not the G protein can be palmitoylated. They also demonstrate that Ca(2+) signaling in EF88 cells by such fusion proteins is mediated via release of the G protein beta.gamma complex.
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Affiliation(s)
- P A Stevens
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
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40
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Affiliation(s)
- J B Shabb
- Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9037, USA.
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41
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Holst B, Hastrup H, Raffetseder U, Martini L, Schwartz TW. Two active molecular phenotypes of the tachykinin NK1 receptor revealed by G-protein fusions and mutagenesis. J Biol Chem 2001; 276:19793-9. [PMID: 11279104 DOI: 10.1074/jbc.m100621200] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The NK1 neurokinin receptor presents two non-ideal binding phenomena, two-component binding curves for all agonists and significant differences between agonist affinity determined by homologous versus heterologous competition binding. Whole cell binding with fusion proteins constructed between either Galpha(s) or Galpha(q) and the NK1 receptor with a truncated tail, which secured non-promiscuous G-protein interaction, demonstrated monocomponent agonist binding closely corresponding to either of the two affinity states found in the wild-type receptor. High affinity binding of both substance P and neurokinin A was observed in the tail-truncated Galpha(s) fusion construct, whereas the lower affinity component was displayed by the tail-truncated Galpha(q) fusion. The elusive difference between the affinity determined in heterologous versus homologous binding assays for substance P and especially for neurokinin A was eliminated in the G-protein fusions. An NK1 receptor mutant with a single substitution at the extracellular end of TM-III-(F111S), which totally uncoupled the receptor from Galpha(s) signaling, showed binding properties that were monocomponent and otherwise very similar to those observed in the tail-truncated Galpha(q) fusion construct. Thus, the heterogenous pharmacological phenotype displayed by the NK1 receptor is a reflection of the occurrence of two active conformations or molecular phenotypes representing complexes with the Galpha(s) and Galpha(q) species, respectively. We propose that these molecular forms do not interchange readily, conceivably because of the occurrence of microdomains or "signal-transductosomes" within the cell membrane.
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Affiliation(s)
- B Holst
- Laboratory for Molecular Pharmacology, Department of Pharmacology, The Panum Institute, University of Copenhagen DK-2200 and the 7TM Pharma A/S, DK-2100 Copenhagen, Denmark
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42
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Horikawa R, Gaylinn BD, Lyons CE, Thorner MO. Molecular cloning of ovine and bovine growth hormone-releasing hormone receptors: the ovine receptor is C-terminally truncated. Endocrinology 2001; 142:2660-8. [PMID: 11356717 DOI: 10.1210/endo.142.6.8210] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
To provide information about species differences in GH-releasing hormone (GHRH) receptors useful for studies of receptor-ligand binding properties and receptor function, we have cloned the ovine and bovine pituitary GHRH receptors (GHRHRs). The ovine receptor (oGHRHR) was cloned from a pituitary complementary DNA library and encodes a protein that is similar to that of porcine, human, rat, and mouse with, respectively, 84.3, 80.7, 75.9, and 74.0% amino acid identity. Surprisingly, oGHRHR has a 16 amino acid truncation at its carboxyl-terminal end when compared with GHRHRs from other known mammals. RT-PCR using pooled pituitary RNA from a different population of sheep could detect only truncated receptor. Bovine GHRHR (bGHRHR) was cloned by RT-PCR and shows 92.5% amino acid sequence identity with oGHRHR, but has no truncation. Genomic sequencing of the appropriate region of goat receptor intron 13 showed that the caprine receptor shares the same truncation seen in sheep. Photoaffinity cross-linking of GHRH to ovine and bovine pituitary membranes confirms that the native ovine pituitary GHRHR protein is smaller by the amount predicted by the cloned sequences. The truncation did not affect GHRH binding as oGHRHR, bGHRHR, human GHRHR, and human GHRHR, which was truncated by site-directed mutagenesis to match the oGHRHR, all showed comparable GHRH binding affinity when expressed in transfected cell lines. In contrast, the ovine and truncated human receptors demonstrated enhanced sensitivity for GHRH stimulation of cAMP (lowered ED(50)) relative to hGHRHR and bGHRHR. This suggests that this C-terminal domain acts to inhibit cAMP signaling possibly through a role in receptor down regulation.
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MESH Headings
- Amino Acid Sequence
- Animals
- Cattle/genetics
- Cloning, Molecular
- Cross-Linking Reagents
- Cyclic AMP/metabolism
- DNA, Complementary/chemistry
- DNA, Complementary/isolation & purification
- Growth Hormone-Releasing Hormone/metabolism
- Growth Hormone-Releasing Hormone/pharmacology
- Humans
- Molecular Sequence Data
- Photoaffinity Labels
- Receptors, Neuropeptide/chemistry
- Receptors, Neuropeptide/genetics
- Receptors, Neuropeptide/metabolism
- Receptors, Pituitary Hormone-Regulating Hormone/chemistry
- Receptors, Pituitary Hormone-Regulating Hormone/genetics
- Receptors, Pituitary Hormone-Regulating Hormone/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Sequence Alignment
- Sequence Analysis, DNA
- Sheep/genetics
- Signal Transduction
- Species Specificity
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Affiliation(s)
- R Horikawa
- Division of Endocrinology and Metabolism, Department of Medicine, University of Virginia Health System, Charlottesville, Virginia 22908, USA.
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43
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Abstract
Heterotrimeric G protein alpha,beta, and gamma subunits are subject to several kinds of co- and post-translational covalent modifications. Among those relevant to G protein-coupled receptor signaling in normal cell function are lipid modifications and phosphorylation. N-myristoylation is a co-translational modification occurring for members of the G(i) family of Galpha subunits, while palmitoylation is a post-translational modification that occurs for these and most other Galpha subunits. One or both modifications are required for plasma membrane targeting and contribute to regulating strength of interaction with the Gbetagamma heterodimer, effectors, and regulators of G protein signaling (RGS proteins). Galpha subunits, including those with transforming activity, are often inactive when unable to be modified with lipids. The reversible nature of palmitoylation is intriguing in this regard, as it lends itself to a regulation integrated with the activation state of the G protein. Several Galpha subunits are substrates for phosphorylation by protein kinase C and at least one is a substrate for phosphorylation by the p21-activated protein kinase. Phosphorylation in both instances inhibits the interactions of these subunits with the Gbetagamma heterodimer and RGS proteins. Several Galpha subunits are also substrates for tyrosine phosphorylation. A Ggamma subunit is phosphorylated by protein kinase C, with the consequence that it interacts more tightly with a Galpha subunit but less well with an effector.
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Affiliation(s)
- C A Chen
- Department of Pharmacology, University of Pennsylvania School of Medicine, 3620 Hamilton Walk, Philadelphia, PA 19104-6084, USA
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44
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Munshi UM, Peegel H, Menon KM. Palmitoylation of the luteinizing hormone/human chorionic gonadotropin receptor regulates receptor interaction with the arrestin-mediated internalization pathway. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:1631-9. [PMID: 11248681 DOI: 10.1046/j.1432-1327.2001.02032.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The luteinizing hormone/human chorionic gonadotropin receptor (LH/hCGR) undergoes palmitoylation at cysteine residues 621 and 622 located in the carboxyl terminal tail of the receptor. This study examined the biological function of palmitoylation with respect to its effect on receptor internalization. Coexpression of wild-type (WT) or C621/622G mutant receptors with arrestin-2 increased receptor internalization in 293T cells. Furthermore, measurements of rate enhancement upon overexpression of arrestin indicate that the palmitoylation deficient mutant receptor is more prone to utilizing the arrestin mediated internalization pathway than the WT receptor. Coexpression of G-protein-coupled receptor kinase 4 (GRK4) with wild type receptor resulted in an increase in internalization, while coexpression with the mutant receptor did not result in further enhancement of internalization. Additionally, 293T cells expressing mutant receptor were responsive to hCG with respect to production of inositol phosphates. Taken together, these results suggest that the palmitoylation state of the receptor governs internalization by regulating the accessibility of the receptor to the arrestin-mediated internalization pathway.
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Affiliation(s)
- U M Munshi
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA
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45
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Finney PA, Donnelly LE, Belvisi MG, Chuang TT, Birrell M, Harris A, Mak JCW, Scorer C, Barnes PJ, Adcock IM, Giembycz MA. Chronic systemic administration of salmeterol to rats promotes pulmonary beta(2)-adrenoceptor desensitization and down-regulation of G(s alpha). Br J Pharmacol 2001; 132:1261-70. [PMID: 11250877 PMCID: PMC1572675 DOI: 10.1038/sj.bjp.0703946] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. The aim of the present study was to examine the effects of chronic infusion of the long-acting agonist salmeterol on pulmonary beta(2)-adrenoceptor function in Sprague-Dawley rats in vivo and to elucidate the molecular basis of any altered state. 2. Systemic administration of rats with salmeterol for 7 days compromised the ability of salmeterol and prostaglandin E(2) (PGE(2)), given acutely by the intravenous route, to protect against ACh-induced bronchoconstriction when compared to rats treated identically with vehicle. 3. beta(1)- and beta(2)-adrenoceptor density was significantly reduced in lung membranes harvested from salmeterol-treated animals, which was associated with impaired salmeterol- and PGE(2)-induced cyclic AMP accumulation ex vivo. 4. Three variants of G(s alpha) that migrated as 42, 44 and 52 kDa peptides on SDS polyacrylamide gels were detected in lung membranes prepared from both groups of rats but the intensity of each isoform was markedly reduced in rats that received salmeterol. 5. The activity of cytosolic, but not membrane-associated, G-protein receptor-coupled kinase was elevated in the lung of salmeterol-treated rats when compared to vehicle-treated animals. 6. The ability of salmeterol, administered systemically, to protect the airways of untreated rats against ACh-induced bronchoconstriction was short-acting (t(off) approximately 45 min), which contrasts with its long-acting nature when given to asthmatic subjects by inhalation. 7. These results indicate that chronic treatment of rats with salmeterol results in heterologous desensitization of pulmonary G(s)-coupled receptors. In light of previous data obtained in rats treated chronically with salbutamol, we propose that a primary mechanism responsible for this effect is a reduction in membrane-associated G(s alpha). The short-acting nature of salmeterol, when administered systemically, and the reduction in beta-adrenoceptor number may be due to metabolism to a biologically-active, short-acting and non-selective beta-adrenoceptor agonist.
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MESH Headings
- Acetylcholine/pharmacology
- Adrenergic beta-Agonists/administration & dosage
- Adrenergic beta-Agonists/pharmacology
- Albuterol/administration & dosage
- Albuterol/analogs & derivatives
- Albuterol/pharmacology
- Animals
- Bronchoconstriction/drug effects
- Cyclic AMP/metabolism
- Cyclic AMP-Dependent Protein Kinases/metabolism
- Dinoprostone/pharmacology
- Down-Regulation
- Drug Interactions
- GTP-Binding Protein alpha Subunits, Gi-Go/biosynthesis
- GTP-Binding Protein alpha Subunits, Gs/biosynthesis
- Gene Expression/drug effects
- Injections, Intravenous
- Lung/drug effects
- Lung/metabolism
- Male
- Protective Agents/pharmacology
- RNA, Messenger/drug effects
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptors, Adrenergic, beta-1/genetics
- Receptors, Adrenergic, beta-1/metabolism
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Salmeterol Xinafoate
- beta-Adrenergic Receptor Kinases
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Affiliation(s)
- Paul A Finney
- Thoracic Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Louise E Donnelly
- Thoracic Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Maria G Belvisi
- Cardiothoracic Surgery, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Tsu-Tshen Chuang
- GlaxoWellcome Research and Development, Medicines Research Centre, Stevenage, Hertfordshire
| | - Mark Birrell
- Cardiothoracic Surgery, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Andrew Harris
- GlaxoWellcome Research and Development, UK Research BioMet, Ware, Hertfordshire
| | - Judith C W Mak
- Thoracic Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Carol Scorer
- GlaxoWellcome Research and Development, Medicines Research Centre, Stevenage, Hertfordshire
| | - Peter J Barnes
- Thoracic Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Ian M Adcock
- Thoracic Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London
| | - Mark A Giembycz
- Thoracic Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London
- Author for correspondence:
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46
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Chen CA, Manning DR. Regulation of galpha i palmitoylation by activation of the 5-hydroxytryptamine-1A receptor. J Biol Chem 2000; 275:23516-22. [PMID: 10818105 DOI: 10.1074/jbc.m003439200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nearly all alpha subunits of heterotrimeric GTP-binding regulatory proteins (G proteins) are palmitoylated at cysteine residues near the N terminus. A regulated cycle of palmitoylation could provide a mechanism for modulating G protein signaling by affecting protein interactions and localization of the subunit. In the present studies we utilized both [(3)H]palmitate incorporation and pulse-chase techniques to address the dynamics of alpha(i) palmitoylation in Chinese hamster ovary cells. Both techniques demonstrated a dose- and time-dependent change in [(3)H]palmitate labeling of alpha(i) upon activation of stably expressed 5-hydroxytryptamine-1A receptors by the agonist (+/-)-2-dipropylamino-8-hydroxy-1,2,3, 4-tetrahydronaphthalene hydrobromide (DPAT), with an EC(50) of approximately 10 nm. For the incorporation assay, DPAT elicited an approximate doubling in labeling at the earliest time point measured. For the pulse-chase assay, DPAT promoted a significant loss of radiolabel almost equally as fast. These data demonstrate that the exchange of palmitate on alpha(i) is increased upon stimulation of 5-hydroxytryptamine-1A receptors through the combined processes of depalmitoylation and palmitoylation. These results provide the basis for extending the concept of regulated exchange of palmitate beyond G(s) and provide a framework for exploring the specific functional attributes of the palmitoylated and depalmitoylated forms of subunit.
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Affiliation(s)
- C A Chen
- Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6084, USA
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Cavalli A, Druey KM, Milligan G. The regulator of G protein signaling RGS4 selectively enhances alpha 2A-adreoreceptor stimulation of the GTPase activity of Go1alpha and Gi2alpha. J Biol Chem 2000; 275:23693-9. [PMID: 10807934 DOI: 10.1074/jbc.m910395199] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Agonist-stimulated high affinity GTPase activity of fusion proteins between the alpha(2A)-adrenoreceptor and the alpha subunits of forms of the G proteins G(i1), G(i2), G(i3), and G(o1), modified to render them insensitive to the action of pertussis toxin, was measured following transient expression in COS-7 cells. Addition of a recombinant regulator of G protein signaling protein, RGS4, did not significantly affect basal GTPase activity nor agonist stimulation of the fusion proteins containing Galpha(i1) and Galpha(i3) but markedly enhanced agonist-stimulation of the proteins containing Galpha(i2) and Galpha(o1.) The effect of RGS4 on the alpha(2A)-adrenoreceptor-Galpha(o1) fusion protein was concentration-dependent with EC(50) of 30 +/- 3 nm and the potency of the receptor agonist UK14304 was reduced 3-fold by 100 nm RGS4. Equivalent reconstitution with Asn(88)-Ser RGS4 failed to enhance agonist function on the alpha(2A)-adrenoreceptor-Galpha(o1) or alpha(2A)-adrenoreceptor-Galpha(i2) fusion proteins. Enzyme kinetic analysis of the GTPase activity of the alpha(2A)-adrenoreceptor-Galpha(o1) and alpha(2A)-adrenoreceptor-Galpha(i2) fusion proteins demonstrated that RGS4 both substantially increased GTPase V(max) and significantly increased K(m) of the fusion proteins for GTP. The increase in K(m) for GTP was dependent upon RGS4 amount and is consistent with previously proposed mechanisms of RGS function. Agonist-stimulated GTPase turnover number in the presence of 100 nm RGS4 was substantially higher for alpha(2A)-adrenoreceptor-Galpha(o1) than for alpha(2A)-adrenoreceptor-Galpha(i2). These studies demonstrate that although RGS4 has been described as a generic stimulator of the GTPase activity of G(i)-family G proteins, selectivity of this interaction and quantitative variation in its function can be monitored in the presence of receptor activation of the G proteins.
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Affiliation(s)
- A Cavalli
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
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Unson CG, Wu CR, Sakmar TP, Merrifield RB. Selective stabilization of the high affinity binding conformation of glucagon receptor by the long splice variant of Galpha(s). J Biol Chem 2000; 275:21631-8. [PMID: 10791965 DOI: 10.1074/jbc.m002093200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To analyze functional differences in the interactions of the glucagon receptor (GR) with the two predominant splice variants of Galpha(s), GR was covalently linked to the short and the long forms Galpha(s)-S and Galpha(s)-L to produce the fusion proteins GR-Galpha(s)-S and GR-Galpha(s)-L. GR-Galpha(s)-S bound glucagon with an affinity similar to that of GR, while GR-Galpha(s)-L showed a 10-fold higher affinity for glucagon. In the presence of GTPgammaS, GR-Galpha(s)-L reverted to the low affinity glucagon binding conformation. Both GR-Galpha(s)-L and GR-Galpha(s)-S were constitutively active, causing elevated basal levels of cAMP even in the absence of glucagon. A mutant GR that failed to activate G(s) (G23D1R) was fused to Galpha(s)-L. G23D1R-Galpha(s)-L bound glucagon with high affinity, but failed to elevate cAMP levels, suggesting that the mechanisms of GR-mediated Galpha(s)-L activation and Galpha(s)-L-induced high affinity glucagon binding are independent. Both GR-Galpha(s)-S and GR-Galpha(s)-L bound the antagonist desHis(1)[Nle(9),Ala(11),Ala(16)]glucagon amide with affinities similar to GR. The antagonist displayed partial agonist activity with GR-Galpha(s)-L, but not with GR-Galpha(s)-S. Therefore, the partial agonist activity of the antagonist observed in intact cells appears to be due to GRs coupled to Galpha(s)-L. We conclude that Galpha(s)-S and Galpha(s)-L interact differently with GR and that specific coupling of GR to Galpha(s)-L may account for GTP-sensitive high affinity glucagon binding.
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Affiliation(s)
- C G Unson
- Rockefeller University and the Howard Hughes Medical Institute, Laboratory of Molecular Biology and Biochemistry, Rockefeller University, New York, New York 10021, USA.
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Finney PA, Belvisi MG, Donnelly LE, Chuang TT, Mak JC, Scorer C, Barnes PJ, Adcock IM, Giembycz MA. Albuterol-induced downregulation of Gsalpha accounts for pulmonary beta(2)-adrenoceptor desensitization in vivo. J Clin Invest 2000; 106:125-35. [PMID: 10880056 PMCID: PMC314356 DOI: 10.1172/jci8374] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The aim of the present study was to develop a chronic in vivo model of pulmonary beta(2)-adrenoceptor desensitization and to elucidate the nature and molecular basis of this state. Subcutaneous infusion of rats with albuterol for 7 days compromised the ability of albuterol, given acutely, to protect against acetylcholine-induced bronchoconstriction. The bronchoprotective effect of prostaglandin E(2), but not forskolin, was also impaired, indicating that the desensitization was heterologous and that the primary defect in signaling was upstream of adenylyl cyclase. beta(2)-Adrenoceptor density was reduced in lung membranes harvested from albuterol-treated animals, and this was associated with impaired albuterol-induced cyclic adenosine monophosphate (cAMP) accumulation and activation of cAMP-dependent protein kinase ex vivo. Gsalpha expression was reduced in the lung and tracheae of albuterol-treated rats, and cholera toxin-induced cAMP accumulation was blunted. Chronic treatment of rats with albuterol also increased cAMP phosphodiesterase activity and G protein-coupled receptor kinase-2, but the extent to which these events contributed to beta(2)-adrenoceptor desensitization was unclear given that forskolin was active in both groups of animals and that desensitization was heterologous. Collectively, these results indicate that albuterol effects heterologous desensitization of pulmonary Gs-coupled receptors in this model, with downregulation of Gsalpha representing a primary molecular etiology.
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Affiliation(s)
- P A Finney
- Department of Thoracic Medicine, Imperial College School of Medicine, National Heart and Lung Institute, London, United Kingdom
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Abstract
Production of chimeric DNAs in which the 5' end of G-protein alpha-subunits are linked directly to the 3' tail of a G-protein-coupled receptor has recently offered an unusual strategy to explore the detailed pharmacology of receptor-G-protein interactions. Expression of such fusion proteins ensures a 1:1 stoichiometry of receptor and G-protein expression and their proximity to each other. The capacity of such fusion proteins to be regarded as agonist-activated GTPases that allow simple enzyme kinetics to be applied to issues of ligand efficacy will be considered. In addition, the effects of point mutations, in both receptors and G proteins, on ligand function are particularly amenable to the types of robust quantitative analyses that can be produced using such fusion proteins.
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Affiliation(s)
- G Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK G12 8QQ.
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