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Kankanamge D, Tennakoon M, Karunarathne A, Gautam N. G protein gamma subunit, a hidden master regulator of GPCR signaling. J Biol Chem 2022; 298:102618. [PMID: 36272647 PMCID: PMC9678972 DOI: 10.1016/j.jbc.2022.102618] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 10/10/2022] [Accepted: 10/14/2022] [Indexed: 11/21/2022] Open
Abstract
Heterotrimeric G proteins (αβγ subunits) that are activated by G protein-coupled receptors (GPCRs) mediate the biological responses of eukaryotic cells to extracellular signals. The α subunits and the tightly bound βγ subunit complex of G proteins have been extensively studied and shown to control the activity of effector molecules. In contrast, the potential roles of the large family of γ subunits have been less studied. In this review, we focus on present knowledge about these proteins. Induced loss of individual γ subunit types in animal and plant models result in strikingly distinct phenotypes indicating that γ subtypes play important and specific roles. Consistent with these findings, downregulation or upregulation of particular γ subunit types result in various types of cancers. Clues about the mechanistic basis of γ subunit function have emerged from imaging the dynamic behavior of G protein subunits in living cells. This shows that in the basal state, G proteins are not constrained to the plasma membrane but shuttle between membranes and on receptor activation βγ complexes translocate reversibly to internal membranes. The translocation kinetics of βγ complexes varies widely and is determined by the membrane affinity of the associated γ subtype. On translocating, some βγ complexes act on effectors in internal membranes. The variation in translocation kinetics determines differential sensitivity and adaptation of cells to external signals. Membrane affinity of γ subunits is thus a parsimonious and elegant mechanism that controls information flow to internal cell membranes while modulating signaling responses.
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Affiliation(s)
- Dinesh Kankanamge
- Department of Anesthesiology, Washington University School of Medicine, St Louis, Missouri, USA
| | - Mithila Tennakoon
- Department of Chemistry, St Louis University, St Louis, Missouri, USA
| | | | - N Gautam
- Department of Anesthesiology, Washington University School of Medicine, St Louis, Missouri, USA; Department of Genetics, Washington University School of Medicine, St Louis, Missouri, USA.
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2
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McIntire WE. A model for how Gβγ couples Gα to GPCR. J Gen Physiol 2022; 154:213096. [PMID: 35333292 PMCID: PMC8961292 DOI: 10.1085/jgp.202112982] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 02/28/2022] [Indexed: 11/20/2022] Open
Abstract
Representing ∼5% of the human genome, G-protein-coupled receptors (GPCRs) are a primary target for drug discovery; however, the molecular details of how they couple to heterotrimeric G protein subunits are incompletely understood. Here, I propose a hypothetical initial docking model for the encounter between GPCR and Gβγ that is defined by transient interactions between the cytosolic surface of the GPCR and the prenyl moiety and the tripeptide motif, asparagine-proline-phenylalanine (NPF), in the C-terminus of the Gγ subunit. Analysis of class A GPCRs reveals a conserved NPF binding site formed by the interaction of the TM1 and H8. Functional studies using differentially prenylated proteins and peptides further suggest that the intracellular hydrophobic core of the GPCR is a prenyl binding site. Upon binding TM1 and H8 of GPCRs, the propensity of the C-terminal region of Gγ to convert into an α helix allows it to extend into the hydrophobic core of the GPCR, facilitating the GPCR active state. Conservation of the NPF motif in Gγ isoforms and interacting residues in TM1 and H8 suggest that this is a general mechanism of GPCR-G protein signaling. Analysis of the rhodopsin dimer also suggests that Gγ-rhodopsin interactions may facilitate GPCR dimer transactivation.
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Affiliation(s)
- William E McIntire
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA
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3
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Tennakoon M, Senarath K, Kankanamge D, Ratnayake K, Wijayaratna D, Olupothage K, Ubeysinghe S, Martins-Cannavino K, Hébert TE, Karunarathne A. Subtype-dependent regulation of Gβγ signalling. Cell Signal 2021; 82:109947. [PMID: 33582184 PMCID: PMC8026654 DOI: 10.1016/j.cellsig.2021.109947] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 02/01/2021] [Accepted: 02/02/2021] [Indexed: 01/04/2023]
Abstract
G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.
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Affiliation(s)
- Mithila Tennakoon
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA
| | - Kanishka Senarath
- Genetics and Molecular Biology Unit, University of Sri Jayewardenepura, Nugegoda, Sri Lanka
| | - Dinesh Kankanamge
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA
| | - Kasun Ratnayake
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA; Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Dhanushan Wijayaratna
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA
| | - Koshala Olupothage
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA
| | - Sithurandi Ubeysinghe
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA
| | | | - Terence E Hébert
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada.
| | - Ajith Karunarathne
- Department of Chemistry and Biochemistry, The University of Toledo, Toledo, OH 43606, USA.
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4
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Optical approaches for single-cell and subcellular analysis of GPCR-G protein signaling. Anal Bioanal Chem 2019; 411:4481-4508. [PMID: 30927013 DOI: 10.1007/s00216-019-01774-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2018] [Revised: 03/05/2019] [Accepted: 03/08/2019] [Indexed: 01/05/2023]
Abstract
G protein-coupled receptors (GPCRs), G proteins, and their signaling associates are major signal transducers that control the majority of cellular signaling and regulate key biological functions including immune, neurological, cardiovascular, and metabolic processes. These pathways are targeted by over one-third of drugs on the market; however, the current understanding of their function is limited and primarily derived from cell-destructive approaches providing an ensemble of static, multi-cell information about the status and composition of molecules. Spatiotemporal behavior of molecules involved is crucial to understanding in vivo cell behaviors both in health and disease, and the advent of genetically encoded fluorescence proteins and small fluorophore-based biosensors has facilitated the mapping of dynamic signaling in cells with subcellular acuity. Since we and others have developed optogenetic methods to regulate GPCR-G protein signaling in single cells and subcellular regions using dedicated wavelengths, the desire to develop and adopt optogenetically amenable assays to measure signaling has motivated us to take a broader look at the available optical tools and approaches compatible with measuring single-cell and subcellular GPCR-G protein signaling. Here we review such key optical approaches enabling the examination of GPCR, G protein, secondary messenger, and downstream molecules such as kinase and lipid signaling in living cells. The methods reviewed employ both fluorescence and bioluminescence detection. We not only further elaborate the underlying principles of these sensors but also discuss the experimental criteria and limitations to be considered during their use in single-cell and subcellular signal mapping.
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Lohse MJ, Nuber S, Hoffmann C. Fluorescence/bioluminescence resonance energy transfer techniques to study G-protein-coupled receptor activation and signaling. Pharmacol Rev 2012; 64:299-336. [PMID: 22407612 DOI: 10.1124/pr.110.004309] [Citation(s) in RCA: 251] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Fluorescence and bioluminescence resonance energy transfer (FRET and BRET) techniques allow the sensitive monitoring of distances between two labels at the nanometer scale. Depending on the placement of the labels, this permits the analysis of conformational changes within a single protein (for example of a receptor) or the monitoring of protein-protein interactions (for example, between receptors and G-protein subunits). Over the past decade, numerous such techniques have been developed to monitor the activation and signaling of G-protein-coupled receptors (GPCRs) in both the purified, reconstituted state and in intact cells. These techniques span the entire spectrum from ligand binding to the receptors down to intracellular second messengers. They allow the determination and the visualization of signaling processes with high temporal and spatial resolution. With these techniques, it has been demonstrated that GPCR signals may show spatial and temporal patterning. In particular, evidence has been provided for spatial compartmentalization of GPCRs and their signals in intact cells and for distinct physiological consequences of such spatial patterning. We review here the FRET and BRET technologies that have been developed for G-protein-coupled receptors and their signaling proteins (G-proteins, effectors) and the concepts that result from such experiments.
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Affiliation(s)
- Martin J Lohse
- Institute of Pharmacology and Toxicology, Versbacher Str. 9, 97078 Würzburg, Germany.
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Rebois RV, Hébert TE. Protein Complexes Involved in Heptahelical Receptor-Mediated Signal Transduction. ACTA ACUST UNITED AC 2011. [DOI: 10.3109/10606820308243] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Mulligan T, Farber SA. Central and C-terminal domains of heterotrimeric G protein gamma subunits differentially influence the signaling necessary for primordial germ cell migration. Cell Signal 2011; 23:1617-24. [PMID: 21699975 DOI: 10.1016/j.cellsig.2011.05.015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Accepted: 05/23/2011] [Indexed: 10/18/2022]
Abstract
Heterotrimeric G protein signaling is involved in many pathways essential to development including those controlling cell migration, proliferation, differentiation and apoptosis. One key developmental event known to rely on proper heterotrimeric G protein signaling is primordial germ cell (PGC) migration. We previously developed an in vivo PGC migration assay that identified differences in the signaling capacity of G protein gamma subunits. In this study we developed Gγ subunit chimeras to determine the regions of Gγ isoforms that are responsible for these differences. The central section of the Gγ subunit was found to be necessary for the ability of a Gγ subunit to mediate signaling involved in PGC migration. Residues found in the carboxy-terminal segment of Gγ transducin (gngt1) were found to be responsible for the ability of this subunit to disrupt PGC migration. The type of prenylation did not affect the ability of a Gγ subunit to reverse prenylation-deficient-Gγ-induced PGC migration defects. However, a version of gng2, engineered to be farnesylated instead of geranylgeranylated, still lacks the ability to reverse PGC migration defects known to result from treatment of zebrafish with geranylgeranyl transferase inhibitors (GGTI), supporting the notion that Gγ subunits are one of several protein targets that need to be geranylgeranylated to orchestrate the proper long-range migration of PGCs.
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Affiliation(s)
- Timothy Mulligan
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD 21218, USA
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8
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Heterogeneous Prenyl Processing of the Heterotrimeric G protein Gamma Subunits. PROTEIN PRENYLATION PART A 2011. [DOI: 10.1016/b978-0-12-381339-8.00006-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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9
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McIntire WE. Structural determinants involved in the formation and activation of G protein betagamma dimers. Neurosignals 2009; 17:82-99. [PMID: 19212142 DOI: 10.1159/000186692] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Accepted: 05/13/2008] [Indexed: 01/08/2023] Open
Abstract
Heterotrimeric G proteins, composed of an alpha, beta and gamma subunit, represent one of the most important and dynamic families of signaling proteins. As a testament to the significance of G protein signaling, the hundreds of seven-transmembrane-spanning receptors that interact with G proteins are estimated to occupy 1-2% of the human genome. This broad diversity of receptors is echoed in the number of potential heterotrimer combinations that can arise from the 23 alpha subunit, 7 beta subunit and 12 gamma subunit isoforms that have been identified. The potential for such vast complexity implies that the receptor G protein interface is the site of much regulation. The historical model for the activation of a G protein holds that activated receptor catalyzes the exchange of GDP for GTP on the alpha subunit, inducing a conformational change that substantially lowers the affinity of alpha for betagamma. This decreased affinity enables dissociation of betagamma from alpha and receptor. The free form of betagamma is thought to activate effectors, until the hydrolysis of GTP by G alpha (aided by RGS proteins) allows the subunits to re-associate, effectively deactivating the G protein until another interaction with activated receptor.
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Affiliation(s)
- William E McIntire
- Department of Pharmacology, University of Virginia Health System, Charlottesville, VA 22908, USA.
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10
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Abstract
Heterotrimeric G proteins couple the activation of heptahelical receptors at the cell surface to the intracellular signaling cascades that mediate the physiological responses to extracellular stimuli. G proteins are molecular switches that are activated by receptor-catalyzed GTP for GDP exchange on the G protein alpha subunit, which is the rate-limiting step in the activation of all downstream signaling. Despite the important biological role of the receptor-G protein interaction, relatively little is known about the structure of the complex and how it leads to nucleotide exchange. This chapter will describe what is known about receptor and G protein structure and outline a strategy for assembling the current data into improved models for the receptor-G protein complex that will hopefully answer the question as to how receptors flip the G protein switch.
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Affiliation(s)
- William M Oldham
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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11
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Heterotrimeric G protein activation by G-protein-coupled receptors. Nat Rev Mol Cell Biol 2008; 9:60-71. [PMID: 18043707 DOI: 10.1038/nrm2299] [Citation(s) in RCA: 783] [Impact Index Per Article: 48.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Heterotrimeric G proteins have a crucial role as molecular switches in signal transduction pathways mediated by G-protein-coupled receptors. Extracellular stimuli activate these receptors, which then catalyse GTP-GDP exchange on the G protein alpha-subunit. The complex series of interactions and conformational changes that connect agonist binding to G protein activation raise various interesting questions about the structure, biomechanics, kinetics and specificity of signal transduction across the plasma membrane.
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12
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Saini DK, Kalyanaraman V, Chisari M, Gautam N. A family of G protein βγ subunits translocate reversibly from the plasma membrane to endomembranes on receptor activation. J Biol Chem 2007; 282:24099-108. [PMID: 17581822 PMCID: PMC2238721 DOI: 10.1074/jbc.m701191200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The present model of G protein activation by G protein-coupled receptors exclusively localizes their activation and function to the plasma membrane (PM). Observation of the spatiotemporal response of G protein subunits in a living cell to receptor activation showed that 6 of the 12 members of the G protein gamma subunit family translocate specifically from the PM to endomembranes. The gamma subunits translocate as betagamma complexes, whereas the alpha subunit is retained on the PM. Depending on the gamma subunit, translocation occurs predominantly to the Golgi complex or the endoplasmic reticulum. The rate of translocation also varies with the gamma subunit type. Different gamma subunits, thus, confer distinct spatiotemporal properties to translocation. A striking relationship exists between the amino acid sequences of various gamma subunits and their translocation properties. gamma subunits with similar translocation properties are more closely related to each other. Consistent with this relationship, introducing residues conserved in translocating subunits into a non-translocating subunit results in a gain of function. Inhibitors of vesicle-mediated trafficking and palmitoylation suggest that translocation is diffusion-mediated and controlled by acylation similar to the shuttling of G protein subunits (Chisari, M., Saini, D. K., Kalyanaraman, V., and Gautam, N. (2007) J. Biol. Chem. 282, 24092-24098). These results suggest that the continual testing of cytosolic surfaces of cell membranes by G protein subunits facilitates an activated cell surface receptor to direct potentially active G protein betagamma subunits to intracellular membranes.
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Affiliation(s)
- Deepak Kumar Saini
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Vani Kalyanaraman
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Mariangela Chisari
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Narasimhan Gautam
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri 63110
- To whom correspondence should be addressed: Box 8054, Washington University School of Medicine, St. Louis, MO 63110. Tel.: 314-362 8568; Fax: 314-362-8571; E-mail:
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Chisari M, Saini DK, Kalyanaraman V, Gautam N. Shuttling of G protein subunits between the plasma membrane and intracellular membranes. J Biol Chem 2007; 282:24092-8. [PMID: 17576765 PMCID: PMC2238717 DOI: 10.1074/jbc.m704246200] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Heterotrimeric G proteins (alphabetagamma) mediate the majority of signaling pathways in mammalian cells. It is long held that G protein function is localized to the plasma membrane. Here we examined the spatiotemporal dynamics of G protein localization using fluorescence recovery after photobleaching, fluorescence loss in photobleaching, and a photoswitchable fluorescent protein, Dronpa. Unexpectedly, G protein subunits shuttle rapidly (t1/2 < 1 min) between the plasma membrane and intracellular membranes. We show that consistent with such shuttling, G proteins constitutively reside in endomembranes. Furthermore, we show that shuttling is inhibited by 2-bromopalmitate. Thus, contrary to present thought, G proteins do not reside permanently on the plasma membrane but are constantly testing the cytoplasmic surfaces of the plasma membrane and endomembranes to maintain G protein pools in intracellular membranes to establish direct communication between receptors and endomembranes.
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Affiliation(s)
- Mariangela Chisari
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Deepak Kumar Saini
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Vani Kalyanaraman
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Narasimhan Gautam
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri 63110
- To whom correspondence should be addressed: Box 8054, Washington University School of Medicine, St. Louis, MO 63110. Tel.: 314-362-8568; Fax: 314-362-8571; E-mail:
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Azpiazu I, Akgoz M, Kalyanaraman V, Gautam N. G protein betagamma11 complex translocation is induced by Gi, Gq and Gs coupling receptors and is regulated by the alpha subunit type. Cell Signal 2006; 18:1190-200. [PMID: 16242307 PMCID: PMC2238718 DOI: 10.1016/j.cellsig.2005.09.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Accepted: 09/12/2005] [Indexed: 12/01/2022]
Abstract
G protein activation by Gi/Go coupling M2 muscarinic receptors, Gq coupling M3 receptors and Gs coupling beta2 adrenergic receptors causes rapid reversible translocation of the G protein gamma11 subunit from the plasma membrane to the Golgi complex. Co-translocation of the beta1 subunit suggests that gamma11 translocates as a betagamma complex. Pertussis toxin ADP ribosylation of the alphai subunit type or substitution of the C terminal domain of alphao with the corresponding region of alphas inhibits gamma11 translocation demonstrating that alpha subunit interaction with a receptor and its activation are requirements for the translocation. The rate of gamma11 translocation is sensitive to the rate of activation of the G protein alpha subunit. alpha subunit types that show high receptor activated rates of guanine nucleotide exchange in vitro support high rates of gamma11 translocation compared to alpha subunit types that have a relatively lower rate of guanine nucleotide exchange. The results suggest that the receptor induced translocation of gamma11 is controlled by the rate of cycling of the G protein through active and inactive forms. They also demonstrate that imaging of gamma11 translocation can be used as a non-invasive tool to measure the relative activities of wild type or mutant receptor and alpha subunit types in a live cell.
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Affiliation(s)
- Inaki Azpiazu
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - Muslum Akgoz
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - Vani Kalyanaraman
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - N. Gautam
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, United States
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15
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Akgoz M, Kalyanaraman V, Gautam N. G protein betagamma complex translocation from plasma membrane to Golgi complex is influenced by receptor gamma subunit interaction. Cell Signal 2006; 18:1758-68. [PMID: 16517125 PMCID: PMC2230546 DOI: 10.1016/j.cellsig.2006.01.016] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Revised: 01/23/2006] [Accepted: 01/24/2006] [Indexed: 10/24/2022]
Abstract
On activation of a receptor the G protein betagamma complex translocates away from the receptor on the plasma membrane to the Golgi complex. The rate of translocation is influenced by the type of gamma subunit associated with the G protein. Complementary approaches--imaging living cells expressing fluorescent protein tagged G proteins and assaying reconstituted receptors and G proteins in vitro--were used to identify mechanisms at the basis of the translocation process. Translocation of Gbetagamma containing mutant gamma subunits with altered prenyl moieties showed that the differences in the prenyl moieties were not sufficient to explain the differential effects of geranylgeranylated gamma5 and farnesylated gamma11 on the translocation process. The translocation properties of Gbetagamma were altered dramatically by mutating the C terminal tail region of the gamma subunit. The translocation characteristics of these mutants suggest that after receptor activation, Gbetagamma retains contact with a receptor through the gamma subunit C terminal domain and that differential interaction of the activated receptor with this domain controls Gbetagamma translocation from the plasma membrane.
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Affiliation(s)
- Muslum Akgoz
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - Vani Kalyanaraman
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - N. Gautam
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, United States
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, United States
- Corresponding author. Box 8054, Washington University School Medicine, St. Louis, MO 63110. Tel.: +1 314 362 8568; fax: +1 314 362 8571. E-mail address: (N. Gautam)
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16
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Azpiazu I, Gautam N. A G protein gamma subunit peptide stabilizes a novel muscarinic receptor state. Biochem Biophys Res Commun 2006; 341:904-10. [PMID: 16466691 PMCID: PMC2232396 DOI: 10.1016/j.bbrc.2006.01.093] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Accepted: 01/20/2006] [Indexed: 10/25/2022]
Abstract
A prenylated peptide specific to the C terminal tail of a G protein gamma subunit type, gamma5, inhibits activation of a G protein by the M2 muscarinic receptor. The gamma5 peptide was tested for direct effects on the M2 receptor's properties. The wild type gamma5 peptide reduced the affinity of M2 for the agonist, carbachol, more than 5-fold in an antagonist displacement assay. The peptide was inactive when its amino acid sequence was scrambled or when it was unprenylated. Although the wild type peptide reduced the affinity of M2 for the antagonist QNB, it had no effect on the antagonists NMS or atropine. These results suggest that in the presence of the peptide the M2 receptor adopts a novel conformational state that affects the ligand binding surface. The results also suggest that the G protein gamma5 subunit tail interacts with a receptor.
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Affiliation(s)
- I. Azpiazu
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - N. Gautam
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA
- * Corresponding author. Fax: +1 314 362 8571. E-mail address: (N. Gautam)
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17
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Myung CS, Lim WK, DeFilippo JM, Yasuda H, Neubig RR, Garrison JC. Regions in the G Protein γ Subunit Important for Interaction with Receptors and Effectors. Mol Pharmacol 2005; 69:877-87. [PMID: 16319284 DOI: 10.1124/mol.105.018994] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
G betagamma dimers containing the gamma11 or gamma1 subunits are often less potent and effective in their ability to regulate effectors compared with dimers containing the gamma2 subunit. To explore the regions of the gamma subunit that affect the activity of the betagamma dimer, we constructed eight chimeric gamma subunits from the gamma1 and gamma2 subunits. Two chimeras were made in which the N-terminal regions of gamma1 and gamma2 were exchanged and two in which the C-terminal regions were transposed. Another set of chimeras was made in which the CAAX motifs of the chimeras were altered to direct modification with different prenyl groups. All eight gamma chimeras were expressed in Sf9 cells with the beta1 subunit, G betagamma dimers were purified, and then they were assayed in vitro for their ability to bind to the G alpha(i1) subunit, to couple G alpha(i1) to the A1 adenosine receptor, to stimulate phospholipase C-beta, and to regulate type I or type II adenyl cyclases. Dimers containing the C-terminal sequence of the gamma2 subunit modified with the geranylgeranyl lipid had the highest affinity for G(i1)alpha (range, 0.5-1.2 nM) and were most effective at coupling the G(i1)alpha subunit to receptor. These dimers were most effective at stimulating the phosphatidylinositol-specific phospholipase C-beta isoform and inhibiting type I adenyl cyclase. In contrast, betagamma dimers containing the N-terminal sequence of the gamma2 subunit and a geranylgeranyl group are most effective at activating type II adenyl cyclase. The results indicate that both the N- and C-terminal regions of the gamma subunit impart specificity to receptor and effector interactions.
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Affiliation(s)
- Chang-Seon Myung
- Department of Pharmacology, College of Pharmacy, Chungnam National University Daejeon, Korea
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18
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Varga EV, Hosohata K, Borys D, Navratilova E, Nylen A, Vanderah TW, Porreca F, Roeske WR, Yamamura HI. Antinociception depends on the presence of G protein gamma2-subunits in brain. Eur J Pharmacol 2005; 508:93-8. [PMID: 15680258 DOI: 10.1016/j.ejphar.2004.11.062] [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] [Received: 11/26/2004] [Accepted: 11/30/2004] [Indexed: 10/25/2022]
Abstract
We have shown previously [Hosohata, K., Logan, J.K., Varga, E., Burkey, T.H., Vanderah, T.W., Porreca, F., Hruby, V.J., Roeske, W.R., Yamamura, H.I., 2000. The role of the G protein gamma2 subunit in opioid antinociception in mice. Eur. J. Pharmacol. 392, R9-R11] that intracerebroventricular (i.c.v.) treatment of mice with a phosphorothioate oligodeoxynucleotide antisense to the gamma2 subunit (Ggamma2) of the heterotrimeric G proteins (antisense ODN) significantly attenuates antinociception by a delta-opioid receptor agonist. In the present study, we examined the involvement of Ggamma2 in antinociception mediated by other (mu- or kappa-opioid, cannabinoid, alpha2-adrenoreceptor) analgesic agents in a warm (55 degrees C) water tail-flick test in mice. Interestingly, i.c.v. treatment with the antisense ODN attenuated antinociception by each analgesic agent. Missense phosphorothioate oligodeoxynucleotide treatment, on the other hand, had no effect on antinociception mediated by these agonists. The antinociceptive response recovered in 6 days after the last antisense ODN injection, indicating a lack of nonspecific tissue damage in the animals. These results suggest a pervasive role for the G protein gamma2 subunits in supraspinal antinociception.
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Affiliation(s)
- Eva V Varga
- Department of Pharmacology, and the Sarver Heart Center, University of Arizona, Tucson, Arizona 85724, USA
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19
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Akgoz M, Kalyanaraman V, Gautam N. Receptor-mediated reversible translocation of the G protein betagamma complex from the plasma membrane to the Golgi complex. J Biol Chem 2004; 279:51541-4. [PMID: 15448129 DOI: 10.1074/jbc.m410639200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Heterotrimeric G proteins have been thought to function on the plasma membrane after activation by transmembrane receptors. Here we show that, after activation by receptors, the G protein betagamma complex selectively translocates to the Golgi. Receptor inactivation results in Gbetagamma translocating back to the plasma membrane. Both translocation processes occur rapidly within seconds. The efficiency of translocation is influenced by the type of gamma subunit present in the G protein. Distinctly different receptor types are capable of inducing the translocation. Receptor-mediated translocation of Gbetagamma can spatially segregate G protein signaling activity.
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Affiliation(s)
- Muslum Akgoz
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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20
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Azpiazu I, Gautam N. A fluorescence resonance energy transfer-based sensor indicates that receptor access to a G protein is unrestricted in a living mammalian cell. J Biol Chem 2004; 279:27709-18. [PMID: 15078878 DOI: 10.1074/jbc.m403712200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fluorescence recovery after photobleaching of muscarinic receptors and G protein subunits tagged with cyan or yellow fluorescent protein showed that receptors and G proteins were mobile and not immobilized on the cell membrane. The cyan fluorescent protein-tagged Galpha and yellow fluorescent protein-tagged Gbeta subunits were used to develop sensors that coupled selectively with the M2 and M3 muscarinic receptors. In living Chinese hamster ovary cells, imaging showed that sensors emitted a fluorescence resonance energy transfer signal that was abrogated on receptor activation. When sequentially activated with highly expressed muscarinic receptors and endogenous receptors expressed at low levels, sensor molecules were sensitive to the sequence of activation and the receptor numbers. The results distinguish between models proposing that receptor and G protein types interact freely with each other on the cell membrane or that they function as mutually exclusive multimolecular complexes by providing direct support for the former model in these cells.
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Affiliation(s)
- Inaki Azpiazu
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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21
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Chinault SL, Blumer KJ. The C-terminal tail preceding the CAAX box of a yeast G protein gamma subunit is dispensable for receptor-mediated G protein activation in vivo. J Biol Chem 2003; 278:20638-44. [PMID: 12665529 DOI: 10.1074/jbc.m212701200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gamma subunits of heterotrimeric G proteins are required for receptor-G protein coupling. The C-terminal domains of Ggamma subunits can contact receptors and influence the efficiency of receptor-G protein coupling in vitro. However, it is unknown whether receptor interaction with the C terminus of Ggamma is required for signaling in vivo. To address this question, we cloned Ggamma homologs with diverged C-terminal sequences from five species of budding yeast. Each Ggamma homolog functionally replaced the Ggamma subunit of the yeast Saccharomyces cerevisiae (STE18 gene product). Mutagenesis of S. cerevisiae Ste18 likewise indicated that specific C-terminal sequence motifs are not required for signaling. Strikingly, an internal in-frame deletion removing sequences preceding the C-terminal CAAX box of Ste18 did not impair signaling by either of its cognate G protein-coupled pheromone receptors. Therefore, receptor interaction with the C-terminal domain of yeast Ggamma is not required for receptor-mediated G protein activation in vivo. Because the mechanism of G protein activation by receptors is conserved from yeast to humans, mammalian receptors may not require interaction with the tail of Ggamma for G protein activation in vivo. However, receptor-Ggamma interaction may modulate the efficiency of receptor-G protein coupling or promote activation of Gbetagamma effectors that co-cluster with receptors.
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Affiliation(s)
- Sharon L Chinault
- 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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Azpiazu I, Gautam N. Role of G protein beta gamma complex in receptor-G protein interaction. Methods Enzymol 2002; 344:112-25. [PMID: 11771376 DOI: 10.1016/s0076-6879(02)44709-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Inaki Azpiazu
- Department of Anesthesiology, Washington University Medical School, St. Louis, Missouri 63110, USA
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23
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Kale TA, Turek TC, Chang V, Gautam N, Distefano MD. Preparation and application of G protein gamma subunit-derived peptides incorporating a photoactive isoprenoid. Methods Enzymol 2002; 344:245-58. [PMID: 11771387 DOI: 10.1016/s0076-6879(02)44719-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Affiliation(s)
- Tamara A Kale
- Department of Chemistry, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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24
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Abstract
This review focuses on the coupling specificity of the Galpha and Gbetagamma subunits of pertussis toxin (PTX)-sensitive G(i/o) proteins that mediate diverse signaling pathways, including regulation of ion channels and other effectors. Several lines of evidence indicate that specific combinations of G protein alpha, beta and gamma subunits are required for different receptors or receptor-effector networks, and that a higher degree of specificity for Galpha and Gbetagamma is observed in intact systems than reported in vitro. The structural determinants of receptor-G protein specificity remain incompletely understood, and involve receptor-G protein interaction domains, and perhaps other scaffolding processes. By identifying G protein specificity for individual receptor signaling pathways, ligands targeted to disrupt individual pathways of a given receptor could be developed.
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Affiliation(s)
- Paul R Albert
- Ottawa Health Research Institute, Neuroscience, University of Ottawa, 451 Smyth Road, K1H-8M5, Ottawa, ON, Canada.
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25
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Berger M, Budhu S, Lu E, Li Y, Loike D, Silverstein SC, Loike JD. Different G
i
‐coupled chemoattractant receptors signal qualitatively different functions in human neutrophils. J Leukoc Biol 2002. [DOI: 10.1189/jlb.71.5.798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Affiliation(s)
- Miles Berger
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
| | - Sadna Budhu
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
| | - Emily Lu
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
| | - Yongmei Li
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
| | - Devora Loike
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
| | - Samuel C. Silverstein
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
| | - John D. Loike
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York
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26
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Robinson DA, Wei F, Wang GD, Li P, Kim SJ, Vogt SK, Muglia LJ, Zhuo M. Oxytocin mediates stress-induced analgesia in adult mice. J Physiol 2002; 540:593-606. [PMID: 11956346 PMCID: PMC2290243 DOI: 10.1113/jphysiol.2001.013492] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2001] [Accepted: 01/23/2002] [Indexed: 11/08/2022] Open
Abstract
As a neurohormone and as a neurotransmitter, oxytocin has been implicated in the stress response. Descending oxytocin-containing fibres project to the dorsal horn of the spinal cord, an area important for processing nociceptive inputs. Here we tested the hypothesis that oxytocin plays a role in stress-induced analgesia and modulates spinal sensory transmission. Mice lacking oxytocin exhibited significantly reduced stress-induced antinociception following both cold-swim (10 degrees C, 3 min) and restraint stress (30 min). In contrast, the mice exhibited normal behavioural responses to thermal and mechanical noxious stimuli and morphine-induced antinociception. In wild-type mice, intrathecal injection of the oxytocin antagonist dOVT (200 microM in 5 microl) significantly attenuated antinociception induced by cold-swim. Immunocytochemical staining revealed that, in the mouse, oxytocin-containing neurones in the paraventricular nucleus of the hypothalamus are activated by stress. Furthermore, oxytocin-containing fibres were present in the dorsal horn of the spinal cord. To test whether descending oxytocin-containing fibres could alter nociceptive transmission, we performed intracellular recordings of dorsal horn neurones in spinal slices from adult mice. Bath application of oxytocin (1 and 10 microM) inhibited excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. This effect was reversed by the oxytocin antagonist dOVT (1 microM). Whole-cell recordings of dorsal horn neurones in postnatal rat slices revealed that the effect of oxytocin could be blocked by the addition of GTP-gamma-S to the recording pipette, suggesting activation of postsynaptic oxytocin receptors. We conclude that oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission.
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Affiliation(s)
- D A Robinson
- Department of Anesthesiology, Washington University Pain Center, Washington University, St Louis, MO 63110, USA
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27
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Li Y, Loike JD, Ember JA, Cleary PP, Lu E, Budhu S, Cao L, Silverstein SC. The bacterial peptide N-formyl-Met-Leu-Phe inhibits killing of Staphylococcus epidermidis by human neutrophils in fibrin gels. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 168:816-24. [PMID: 11777977 DOI: 10.4049/jimmunol.168.2.816] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
To study human neutrophil (polymorphonuclear leukocyte (PMN)) migration and killing of bacteria in an environment similar to that found in inflamed tissues in vivo, we have used fibrin gels. Fibrin gels (1500 microm thick) containing Staphylococcus epidermidis were formed in Boyden-type chemotaxis chambers. PMN migrated < 300 microm into these gels in 6 h and did not kill S. epidermidis when the gels contained heat-inactivated serum, C5-deficient serum, a streptococcal peptidase specific for a fragment of cleaved C5 (C5a), or anti-C5aR IgG. In contrast, in gels containing normal human serum, PMN migrated approximately 1000 microm into the gels in 4 h and into the full thickness of the gels in 6 h, and killed 90% of S. epidermidis in 6 h. fMLP reduced PMN migration into fibrin gels and allowed S. epidermidis to increase by approximately 300% in 4 h, whereas leukotriene B(4) stimulated PMN to migrate the full thickness of the gels and to kill 80% of S. epidermidis in 4 h. We conclude that both complement opsonization and C5a-stimulated chemotaxis are required for PMN bacterial killing in fibrin gels, and that fMLP inhibits PMN bactericidal activity in fibrin gels. The latter finding is surprising and suggests that in the presence of fibrin fMLP promotes bacterial virulence.
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Affiliation(s)
- Yongmei Li
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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28
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Jian X, Clark WA, Kowalak J, Markey SP, Simonds WF, Northup JK. Gbetagamma affinity for bovine rhodopsin is determined by the carboxyl-terminal sequences of the gamma subunit. J Biol Chem 2001; 276:48518-25. [PMID: 11602594 DOI: 10.1074/jbc.m107129200] [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: 11/06/2022] Open
Abstract
Two native betagamma dimers, beta(1)gamma(1) and beta(1)gamma(2), display very different affinities for receptors. Since these gamma subunits differ in both primary structure and isoprenoid modification, we examined the relative contributions of each to Gbetagamma interaction with receptors. We constructed baculoviruses encoding gamma(1) and gamma(2) subunits with altered CAAX (where A is an aliphatic amino acid) motifs to direct alternate or no prenylation of the gamma chains and a set of gamma(1) and gamma(2) chimeras with the gamma(2) CAAX motif at the carboxyl terminus. All the gamma constructs coexpressed with beta(1) in Sf9 cells yielded beta(1)gamma dimers, which were purified to near homogeneity, and their affinities for receptors and Galpha were quantitatively determined. Whereas alteration of the isoprenoid of gamma(1) from farnesyl to geranylgeranyl and of gamma(2) from geranylgeranyl to farnesyl had no impact on the affinities of beta(1)gamma dimers for Galpha(t), the non-prenylated beta(1)gamma(2) dimer had significantly diminished affinity. Altered prenylation resulted in a <2-fold decrease in affinity of the beta(1)gamma(2) dimer for rhodopsin and a <3-fold change for the beta(1)gamma(1) dimer. In each case with identical isoprenylation, the beta(1)gamma(2) dimer displayed significantly greater affinity for rhodopsin compared with the beta(1)gamma(1) dimer. Furthermore, dimers containing chimeric Ggamma chains with identical geranylgeranyl modification displayed rhodopsin affinities largely determined by the carboxyl-terminal one-third of the protein. These results indicate that isoprenoid modification of the Ggamma subunit is essential for binding to both Galpha and receptors. The isoprenoid type influences the binding affinity for receptors, but not for Galpha. Finally, the primary structure of the Ggamma subunit provides a major contribution to receptor binding of Gbetagamma, with the carboxyl-terminal sequence conferring receptor selectivity.
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Affiliation(s)
- X Jian
- Laboratory of Cellular Biology, NIDCD, National Institutes of Health, Bethesda, Maryland 20892, USA
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29
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Fogg VC, Azpiazu I, Linder ME, Smrcka A, Scarlata S, Gautam N. Role of the gamma subunit prenyl moiety in G protein beta gamma complex interaction with phospholipase Cbeta. J Biol Chem 2001; 276:41797-802. [PMID: 11546822 DOI: 10.1074/jbc.m107661200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The G protein betagamma complex regulates a wide range of effectors, including the phospholipase Cbeta isozymes (PLCbetas). Prenyl modification of the gamma subunit is necessary for this activity. Evidence presented here supports a direct interaction between the G protein gamma subunit prenyl group and PLCbeta isozymes. A geranylgeranylated peptide corresponding to the C-terminal region of the gamma subunit type, gamma2, strongly inhibits stimulation of PLCbeta2 and PLCbeta3 activity by the betagamma complex. This effect is specific because the same peptide has no effect on stimulation of PLCbeta by an alpha subunit type, alphaq. Prenylation of the gamma peptide is required for its inhibitory effect. When interaction of prenylated gamma subunit peptide to fluorophore-tagged PLCbeta2 was examined by fluorescence spectroscopy, prenylated but not unprenylated peptide increased PLCbeta2 fluorescence emission energy, indicating direct binding of the prenyl moiety to PLCbeta. In addition, fluorescence resonance energy transfer was detected between fluorophore tagged PLCbeta and wild type betagamma complex but not an unprenylated mutant betagamma complex. We conclude that a major function of the gamma subunit prenyl group is to facilitate direct protein-protein interaction between the betagamma complex and an effector, phospholipase Cbeta.
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Affiliation(s)
- V C Fogg
- Departments of Anesthesiology, Genetics, and Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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30
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Azpiazu I, Gautam N. G protein gamma subunit interaction with a receptor regulates receptor-stimulated nucleotide exchange. J Biol Chem 2001; 276:41742-7. [PMID: 11546799 DOI: 10.1074/jbc.m104034200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The surfaces of heterotrimeric G proteins (alphabetagamma) in contact with receptors and the molecular events at these sites, which lead to G protein activation, are largely unknown. We show here that a peptide from the C terminus of a G protein gamma subunit blocks muscarinic receptor-stimulated G protein activation in a sequence-dependent fashion. A G protein mutated at the same site on the gamma subunit shows enhanced receptor stimulated nucleotide exchange without affecting G protein heterotrimerization. Ineffective contact between the gamma subunit and receptor increases the rate of receptor-stimulated nucleotide exchange. Specific interaction of the G protein gamma subunit with the receptor thus helps the betagamma complex to act at a distance and control guanine nucleotide exchange in the alpha subunit.
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Affiliation(s)
- I Azpiazu
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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31
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Lim WK, Myung CS, Garrison JC, Neubig RR. Receptor-G protein gamma specificity: gamma11 shows unique potency for A(1) adenosine and 5-HT(1A) receptors. Biochemistry 2001; 40:10532-41. [PMID: 11523995 DOI: 10.1021/bi010950c] [Citation(s) in RCA: 43] [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
G protein coupled receptors activate signal transducing guanine nucleotide-binding proteins (G proteins), which consist of an alpha subunit and a betagamma dimer. Whole cell studies have reported that receptors signal through specific betagamma subtypes. Membrane reconstitution studies with the adenosine A(1) and alpha(2A) adrenergic receptors have reached a similar conclusion. We aimed to test the generality of this finding by comparing the gamma subtype specificity for four G(i)-coupled receptors: alpha(2A) adrenergic; A1 adenosine (A(1)-R); 5-hydroxytryptamine(1A) (5-HT(1A)-R); mu opioid. Membranes were reconstituted with Galpha(i)(1) and five gamma subtypes (dimerized to beta1). Using a sensitive alpha-betagamma binding assay, we show that all recombinant betagamma (except beta1gamma1) had comparable affinity for alpha(i)(1). Using high affinity agonist binding as a measure of receptor-G protein coupling, betagamma-containing gamma11 was the most potent for A(1)-R and 5-HT(1A)-R (p < 0.05, one way ANOVA) while gamma7 was most potent for the other two receptors. gamma11 was 3-8-fold more potent for the A(1)-R than were the other gamma subtypes. Also, gamma11 was 2-8-fold more potent for A(1)-R than at the other receptors, suggesting a unique coupling specificity of the A(1)-R for gamma11. In contrast, the discrimination by receptors for the other betagamma subtypes (beta1 and gamma1, gamma2, gamma7, and gamma10) was limited (2-3-fold). Thus the exquisite betagamma specificity of individual receptors reported in whole cell studies may depend on in vivo mechanisms beyond direct receptor recognition of betagamma subtypes.
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MESH Headings
- Animals
- CHO Cells
- Cell Line
- Cricetinae
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Heterotrimeric GTP-Binding Proteins/agonists
- Heterotrimeric GTP-Binding Proteins/metabolism
- Receptors, Adrenergic, alpha-2/metabolism
- Receptors, Opioid, mu/metabolism
- Receptors, Purinergic P1/metabolism
- Receptors, Serotonin/metabolism
- Receptors, Serotonin, 5-HT1
- Swine
- Tumor Cells, Cultured
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Affiliation(s)
- W K Lim
- Department of Pharmacology, The University of Michigan, Ann Arbor, Michigan 48109-0632, USA
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32
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Hou Y, Chang V, Capper AB, Taussig R, Gautam N. G Protein beta subunit types differentially interact with a muscarinic receptor but not adenylyl cyclase type II or phospholipase C-beta 2/3. J Biol Chem 2001; 276:19982-8. [PMID: 11262394 DOI: 10.1074/jbc.m010424200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In comparison with the alpha subunit of G proteins, the role of the beta subunit in signaling is less well understood. During the regulation of effectors by the betagamma complex, it is known that the beta subunit contacts effectors directly, whereas the role of the beta subunit is undefined in receptor-G protein interaction. Among the five G protein beta subunits known, the beta(4) subunit type is the least studied. We compared the ability of betagamma complexes containing beta(4) and the well characterized beta(1) to stimulate three different effectors: phospholipase C-beta2, phospholipase C-beta3, and adenylyl cyclase type II. beta(4)gamma(2) and beta(1)gamma(2) activated all three of these effectors with equal efficacy. However, nucleotide exchange in a G protein constituting alpha(o)beta(4)gamma(2) was stimulated significantly more by the M2 muscarinic receptor compared with alpha(o)beta(1)gamma(2). Because alpha(o) forms heterotrimers with beta(4)gamma(2) and beta(1)gamma(2) equally well, these results show that the beta subunit type plays a direct role in the receptor activation of a G protein.
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Affiliation(s)
- Y Hou
- Departments of Anesthesiology and Genetics, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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33
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Kale TA, Raab C, Yu N, Dean DC, Distefano MD. A photoactivatable prenylated cysteine designed to study isoprenoid recognition. J Am Chem Soc 2001; 123:4373-81. [PMID: 11457220 DOI: 10.1021/ja0012016] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Protein prenylation, involving the alkylation of a specific C-terminal cysteine with a C(15) or C(20) isoprenoid unit, is an essential posttranslational modification required by most GTP-binding proteins for normal biological activity. Despite the ubiquitous nature of this modification and numerous efforts aimed at inhibiting prenylating enzymes for therapeutic purposes, the function of prenylation remains unclear. To explore the role the isoprenoid plays in mediating protein-protein recognition, we have synthesized a photoactivatable, isoprenoid-containing cysteine analogue (2) designed to act as a mimic of the C-terminus of prenylated proteins. Photolysis experiments with 2 and RhoGDI (GDI), a protein which interacts with prenylated Rho proteins, suggest that the GDI is in direct contact with the isoprenoid moiety. These results, obtained using purified GDI as well as Escherichia coli (E. coli) crude extract containing GDI, suggest that this analogue will be an effective and versatile tool for the investigation of putative isoprenoid binding sites in a variety of systems. Incorporation of this analogue into peptides or proteins should allow for even more specific interactions between the photoactivatable isoprenoid and any number of isoprenoid binding proteins.
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Affiliation(s)
- T A Kale
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
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34
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McIntire WE, MacCleery G, Garrison JC. The G protein beta subunit is a determinant in the coupling of Gs to the beta 1-adrenergic and A2a adenosine receptors. J Biol Chem 2001; 276:15801-9. [PMID: 11278863 DOI: 10.1074/jbc.m011233200] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The signaling specificity of five purified G protein betagamma dimers, beta(1)gamma(2), beta(2)gamma(2), beta(3)gamma(2), beta(4)gamma(2), and beta(5)gamma(2), was explored by reconstituting them with G(s) alpha and receptors or effectors in the adenylyl cyclase cascade. The ability of the five betagamma dimers to support receptor-alpha-betagamma interactions was examined using membranes expressing the beta(1)-adrenergic or A2a adenosine receptors. These receptors discriminated among the defined heterotrimers based solely on the beta isoform. The beta(4)gamma(2) dimer demonstrated the highest coupling efficiency to either receptor. The beta(5)gamma(2) dimer coupled poorly to each receptor, with EC(50) values 40-200-fold higher than those observed with beta(4)gamma(2). Strikingly, whereas the EC(50) of the beta(1)gamma(2) dimer at the beta(1)-adrenergic receptor was similar to beta(4)gamma(2), its EC(50) was 20-fold higher at the A2a adenosine receptor. Inhibition of adenylyl cyclase type I (AC1) and stimulation of type II (AC2) by the betagamma dimers were measured. betagamma dimers containing Gbeta(1-4) were able to stimulate AC2 similarly, and beta(5)gamma(2) was much less potent. beta(1)gamma(2), beta(2)gamma(2), and beta(4)gamma(2) inhibited AC1 equally; beta(3)gamma(2) was 10-fold less effective, and beta(5)gamma(2) had no effect. These data argue that the beta isoform in the betagamma dimer can determine the specificity of signaling at both receptors and effectors.
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Affiliation(s)
- W E McIntire
- Department of Pharmacology, University of Virginia Health System, Charlottesville, Virginia 22908, USA
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Hou Y, Azpiazu I, Smrcka A, Gautam N. Selective role of G protein gamma subunits in receptor interaction. J Biol Chem 2000; 275:38961-4. [PMID: 11042163 DOI: 10.1074/jbc.c000604200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Receptor stimulation of nucleotide exchange in a heterotrimeric G protein (alphabetagamma) is the primary event-modulating signaling by G proteins. The molecular mechanisms at the basis of this event and the role of the G protein subunits, especially the betagamma complex, in receptor activation are unclear. In a reconstituted system, a purified muscarinic receptor, M2, activates G protein heterotrimers alphai2beta1gamma5 and alphai2beta1gamma7 with equal efficacy. However, when the alpha subunit type is substituted with alphao, alphaobeta1gamma7 shows a 100% increase in M2-stimulated GTP hydrolysis compared with alphaobeta1gamma5. Using a sensitive assay based on betagamma complex stimulation of phospholipase C activity, we show that both beta1gamma5 and beta1gamma7 form heterotrimers equally well with alphao and alphai. These results indicate that the gamma subunit interaction with a receptor is critical for modulating nucleotide exchange and is influenced by the subunit-type composition of the heterotrimer.
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Affiliation(s)
- Y Hou
- Departments of Anesthesiology and Genetics, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Robillard L, Ethier N, Lachance M, Hébert TE. Gbetagamma subunit combinations differentially modulate receptor and effector coupling in vivo. Cell Signal 2000; 12:673-82. [PMID: 11080620 DOI: 10.1016/s0898-6568(00)00118-2] [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: 11/17/2022]
Abstract
In vitro, little specificity is seen for modulation of effectors by different combinations of Gbetagamma subunits from heterotrimeric G proteins. Here, we demonstrate that the coupling of specific combinations of Gbetagamma subunits to different receptors leads to a differential ability to modulate effectors in vivo. We have shown that the beta(1)AR and beta(2)AR can activate homomultimers of the human inwardly rectifying potassium channel Kir 3.2 when coexpressed in Xenopus oocytes, and that this requires a functional mammalian Gs heterotrimer. Modulation was independent of cAMP production, suggesting a membrane-delimited mechanism. To analyze further the importance of different Gbetagamma combinations, we have tested the facilitation of Kir 3.2 activation by betaAR mediated by different Gbetagamma subunits. The subunits tested were Gbeta(1,5) and Ggamma(1,2,7,11). These experiments demonstrated significant variation between the ability of the Gbetagamma combinations to activate the channels after receptor stimulation. This was in marked contrast to the situation in vitro where little specificity for binding of a Kir 3.1 C-terminal GST fusion protein by different Gbetagamma combinations was detected. More importantly, neither receptor, although homologous both structurally and functionally, shared the same preference for Gbetagamma subunits. In the presence of beta(1)AR, Gbeta(5)gamma(1) and Gbeta(5)gamma(11) activated Kir 3.2 to the greatest extent, while for the beta(2)AR, Gbeta(1)gamma(7), Gbeta(1)gamma(11,) and Gbeta(5)gamma(2) produced the greatest responses. Interestingly, no preference was seen in the ability of different Gbetagamma subunits to facilitate receptor-stimulated GTPase activity of the Gsalpha. These results suggest that it is not the receptor/G protein alpha subunit interaction or the Gbetagamma/effector interaction that is altered by Gbetagamma, but rather that the ability of the receptor to interact productively with the Gbetagamma subunit directly and/or the G protein/effector complex is dependent on the specific G protein heterotrimer associated with the receptor.
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Affiliation(s)
- L Robillard
- Centre de recherche, Institut de cardiologie de Montréal et Département d'anésthesie-réanimation, Université de Montréal 5000 rue Bélanger est, H1T 1C8, Montréal, PQ, Canada
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