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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: 28] [Impact Index Per Article: 9.3] [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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2
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Aggregation and Prion-Inducing Properties of the G-Protein Gamma Subunit Ste18 are Regulated by Membrane Association. Int J Mol Sci 2020; 21:ijms21145038. [PMID: 32708832 PMCID: PMC7403958 DOI: 10.3390/ijms21145038] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 07/03/2020] [Accepted: 07/09/2020] [Indexed: 12/17/2022] Open
Abstract
Yeast prions and mnemons are respectively transmissible and non-transmissible self-perpetuating protein assemblies, frequently based on cross-β ordered detergent-resistant aggregates (amyloids). Prions cause devastating diseases in mammals and control heritable traits in yeast. It was shown that the de novo formation of the prion form [PSI+] of yeast release factor Sup35 is facilitated by aggregates of other proteins. Here we explore the mechanism of the promotion of [PSI+] formation by Ste18, an evolutionarily conserved gamma subunit of a G-protein coupled receptor, a key player in responses to extracellular stimuli. Ste18 forms detergent-resistant aggregates, some of which are colocalized with de novo generated Sup35 aggregates. Membrane association of Ste18 is required for both Ste18 aggregation and [PSI+] induction, while functional interactions involved in signal transduction are not essential for these processes. This emphasizes the significance of a specific location for the nucleation of protein aggregation. In contrast to typical prions, Ste18 aggregates do not show a pattern of heritability. Our finding that Ste18 levels are regulated by the ubiquitin-proteasome system, in conjunction with the previously reported increase in Ste18 levels upon the exposure to mating pheromone, suggests that the concentration-dependent Ste18 aggregation may mediate a mnemon-like response to physiological stimuli.
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3
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Khan SM, Sleno R, Gora S, Zylbergold P, Laverdure JP, Labbé JC, Miller GJ, Hébert TE. The expanding roles of Gβγ subunits in G protein-coupled receptor signaling and drug action. Pharmacol Rev 2013; 65:545-77. [PMID: 23406670 DOI: 10.1124/pr.111.005603] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Gβγ subunits from heterotrimeric G proteins perform a vast array of functions in cells with respect to signaling, often independently as well as in concert with Gα subunits. However, the eponymous term "Gβγ" does not do justice to the fact that 5 Gβ and 12 Gγ isoforms have evolved in mammals to serve much broader roles beyond their canonical roles in cellular signaling. We explore the phylogenetic diversity of Gβγ subunits with a view toward understanding these expanded roles in different cellular organelles. We suggest that the particular content of distinct Gβγ subunits regulates cellular activity, and that the granularity of individual Gβ and Gγ action is only beginning to be understood. Given the therapeutic potential of targeting Gβγ action, this larger view serves as a prelude to more specific development of drugs aimed at individual isoforms.
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Affiliation(s)
- Shahriar M Khan
- Department of Pharmacology and Therapeutics, McGill University, 3655 Promenade Sir-William-Osler, Room 1303, Montréal, Québec H3G 1Y6, Canada
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4
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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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5
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Navarro-Olmos R, Kawasaki L, Domínguez-Ramírez L, Ongay-Larios L, Pérez-Molina R, Coria R. The beta subunit of the heterotrimeric G protein triggers the Kluyveromyces lactis pheromone response pathway in the absence of the gamma subunit. Mol Biol Cell 2010; 21:489-98. [PMID: 20016006 PMCID: PMC2814793 DOI: 10.1091/mbc.e09-06-0472] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Revised: 11/24/2009] [Accepted: 12/02/2009] [Indexed: 11/25/2022] Open
Abstract
The Kluyveromyces lactis heterotrimeric G protein is a canonical Galphabetagamma complex; however, in contrast to Saccharomyces cerevisiae, where the Ggamma subunit is essential for mating, disruption of the KlGgamma gene yielded cells with almost intact mating capacity. Expression of a nonfarnesylated Ggamma, which behaves as a dominant-negative in S. cerevisiae, did not affect mating in wild-type and DeltaGgamma cells of K. lactis. In contrast to the moderate sterility shown by the single DeltaKlGalpha, the double DeltaKlGalpha DeltaKlGgamma mutant displayed full sterility. A partial sterile phenotype of the DeltaKlGgamma mutant was obtained in conditions where the KlGbeta subunit interacted defectively with the Galpha subunit. The addition of a CCAAX motif to the C-end of KlGbeta, partially suppressed the lack of both KlGalpha and KlGgamma subunits. In cells lacking KlGgamma, the KlGbeta subunit cofractionated with KlGalpha in the plasma membrane, but in the DeltaKlGalpha DeltaKlGgamma strain was located in the cytosol. When the KlGbeta-KlGalpha interaction was affected in the DeltaKlGgamma mutant, most KlGbeta fractionated to the cytosol. In contrast to the generic model of G-protein function, the Gbeta subunit of K. lactis has the capacity to attach to the membrane and to activate mating effectors in absence of the Ggamma subunit.
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Affiliation(s)
- Rocío Navarro-Olmos
- *Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F. 04510, Mexico and
| | - Laura Kawasaki
- *Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F. 04510, Mexico and
| | - Lenin Domínguez-Ramírez
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California at Davis, Davis, CA 95616
| | - Laura Ongay-Larios
- *Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F. 04510, Mexico and
| | - Rosario Pérez-Molina
- *Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F. 04510, Mexico and
| | - Roberto Coria
- *Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F. 04510, Mexico and
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6
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Prenylation-deficient G protein gamma subunits disrupt GPCR signaling in the zebrafish. Cell Signal 2009; 22:221-33. [PMID: 19786091 DOI: 10.1016/j.cellsig.2009.09.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 09/02/2009] [Accepted: 09/14/2009] [Indexed: 01/01/2023]
Abstract
Prenylation of G protein gamma (gamma) subunits is necessary for the membrane localization of heterotrimeric G proteins and for functional heterotrimeric G protein coupled receptor (GPCR) signaling. To evaluate GPCR signaling pathways during development, we injected zebrafish embryos with mRNAs encoding Ggamma subunits mutated so that they can no longer be prenylated. Low-level expression of these prenylation-deficient Ggamma subunits driven either ubiquitously or specifically in the primordial germ cells (PGCs) disrupts GPCR signaling and manifests as a PGC migration defect. This disruption results in a reduction of calcium accumulation in the protrusions of migrating PGCs and a failure of PGCs to directionally migrate. When co-expressed with a prenylation-deficient Ggamma, 8 of the 17 wildtype Ggamma isoforms individually confer the ability to restore calcium accumulation and directional migration. These results suggest that while the Ggamma subunits possess the ability to interact with G Beta (beta) proteins, only a subset of wildtype Ggamma proteins are stable within PGCs and can interact with key signaling components necessary for PGC migration. This in vivo study highlights the functional redundancy of these signaling components and demonstrates that prenylation-deficient Ggamma subunits are an effective tool to investigate the roles of GPCR signaling events during vertebrate development.
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7
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Shpakov AO, Pertseva MN. Chapter 4 Signaling Systems of Lower Eukaryotes and Their Evolution. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 269:151-282. [DOI: 10.1016/s1937-6448(08)01004-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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8
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Strickfaden SC, Pryciak PM. Distinct roles for two Galpha-Gbeta interfaces in cell polarity control by a yeast heterotrimeric G protein. Mol Biol Cell 2007; 19:181-97. [PMID: 17978098 DOI: 10.1091/mbc.e07-04-0385] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Saccharomyces cerevisiae mating pheromones trigger dissociation of a heterotrimeric G protein (Galphabetagamma) into Galpha-guanosine triphosphate (GTP) and Gbetagamma. The Gbetagamma dimer regulates both mitogen-activated protein (MAP) kinase cascade signaling and cell polarization. Here, by independently activating the MAP kinase pathway, we studied the polarity role of Gbetagamma in isolation from its signaling role. MAP kinase signaling alone could induce cell asymmetry but not directional growth. Surprisingly, active Gbetagamma, either alone or with Galpha-GTP, could not organize a persistent polarization axis. Instead, following pheromone gradients (chemotropism) or directional growth without pheromone gradients (de novo polarization) required an intact receptor-Galphabetagamma module and GTP hydrolysis by Galpha. Our results indicate that chemoattractant-induced cell polarization requires continuous receptor-Galphabetagamma communication but not modulation of MAP kinase signaling. To explore regulation of Gbetagamma by Galpha, we mutated Gbeta residues in two structurally distinct Galpha-Gbeta binding interfaces. Polarity control was disrupted only by mutations in the N-terminal interface, and not the Switch interface. Incorporation of these mutations into a Gbeta-Galpha fusion protein, which enforces subunit proximity, revealed that Switch interface dissociation regulates signaling, whereas the N-terminal interface may govern receptor-Galphabetagamma coupling. These findings raise the possibility that the Galphabetagamma heterotrimer can function in a partially dissociated state, tethered by the N-terminal interface.
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Affiliation(s)
- Shelly C Strickfaden
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, MA 01605, USA
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9
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Shpakov AO. Serpentine type receptors and heterotrimeric G-proteins in yeasts: Structural-functional organization and molecular mechanisms of action. J EVOL BIOCHEM PHYS+ 2007. [DOI: 10.1134/s0022093007010012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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Jansen G, Wu C, Schade B, Thomas DY, Whiteway M. Drag&Drop cloning in yeast. Gene 2004; 344:43-51. [PMID: 15656971 DOI: 10.1016/j.gene.2004.10.016] [Citation(s) in RCA: 152] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2004] [Revised: 09/13/2004] [Accepted: 10/14/2004] [Indexed: 11/29/2022]
Abstract
We have developed a set of vectors that have enhanced capabilities for efficiently constructing and expressing differentially tagged fusion proteins using Drag&Drop cloning in the yeast Saccharomyces cerevisiae. The pGREG vectors are based on the pRS series with an additional general kanR selection marker. In vivo homologous recombination is used to introduce genes of interest into galactose-inducible expression vectors (pGREGs), permitting the formation of amino-terminal fusions. The vectors all contain common regions for recombination that flank the stuffer fragment. Introduction of common recombination sequences at the end of PCR fragments will permit the cloning of genes without the need for specific restriction sites. In this process, the selectable stuffer HIS3 gene is replaced by successful gene integration, and a screen for loss of the selection marker identifies potential recombinants. Due to the modular structure of the vectors, genes introduced into one vector can be readily transferred by in vivo recombination to all other members of the vector system, thus permitting rapid and easy Drag&Drop construction of a series of tagged proteins. The pGREG series combines features for expression, tagging, integration, localization and library construction with the advantage of obtaining immediate results from sub-sequent experiments. This Drag&Drop system also allows efficient cloning and expression of heterologous genes in large-scale experiments.
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Affiliation(s)
- Gregor Jansen
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6.
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11
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Peng L, Mirshahi T, Zhang H, Hirsch JP, Logothetis DE. Critical determinants of the G protein gamma subunits in the Gbetagamma stimulation of G protein-activated inwardly rectifying potassium (GIRK) channel activity. J Biol Chem 2003; 278:50203-11. [PMID: 12975366 DOI: 10.1074/jbc.m308299200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The betagamma subunits of G proteins modulate inwardly rectifying potassium (GIRK) channels through direct interactions. Although GIRK currents are stimulated by mammalian Gbetagamma subunits, we show that they were inhibited by the yeast Gbetagamma (Ste4/Ste18) subunits. A chimera between the yeast and the mammalian Gbeta1 subunits (ymbeta) stimulated or inhibited GIRK currents, depending on whether it was co-expressed with mammalian or yeast Ggamma subunits, respectively. This result underscores the critical functional influence of the Ggamma subunits on the effectiveness of the Gbetagamma complex. A series of chimeras between Ggamma2 and the yeast Ggamma revealed that the C-terminal half of the Ggamma2 subunit is required for channel activation by the Gbetagamma complex. Point mutations of Ggamma2 to the corresponding yeast Ggamma residues identified several amino acids that reduced significantly the ability of Gbetagamma to stimulate channel activity, an effect that was not due to improper association with Gbeta. Most of the identified critical Ggamma residues clustered together, forming an intricate network of interactions with the Gbeta subunit, defining an interaction surface of the Gbetagamma complex with GIRK channels. These results show for the first time a functional role for Ggamma in the effector role of Gbetagamma.
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Affiliation(s)
- Luying Peng
- Department of Physiology and Biophysics, Mount Sinai School of Medicine of the New York University, New York, New York 10029, USA
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12
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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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13
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Jansen G, Leberer E, Thomas DY, Whiteway M. Use of dominant negative mutations in analysis of G protein function in Saccharomyces cerevisiae. Methods Enzymol 2002; 344:82-91. [PMID: 11771425 DOI: 10.1016/s0076-6879(02)44707-6] [Citation(s) in RCA: 3] [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)
- Gregor Jansen
- Eukaryotic Genetics Department, NRC Biotechnology Research Institute, Montreal, Québec, Canada H4P 2R2
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Abstract
All cells have the capacity to respond to chemical and sensory stimuli. Central to many such signaling pathways is the heterotrimeric G protein, which transmits a signal from cell surface receptors to intracellular effectors. Recent studies using the yeast Saccharomyces cerevisiae have produced important advances in our understanding of G protein activation and inactivation. This review focuses on the mechanisms by which G proteins transmit a signal from peptide pheromone receptors to the mating response in yeast and how mechanisms elucidated in yeast can provide insights to signaling events in more complex organisms.
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Affiliation(s)
- Henrik G Dohlman
- Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA.
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15
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Dohlman HG, Thorner JW. Regulation of G protein-initiated signal transduction in yeast: paradigms and principles. Annu Rev Biochem 2002; 70:703-54. [PMID: 11395421 DOI: 10.1146/annurev.biochem.70.1.703] [Citation(s) in RCA: 366] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
All cells have the capacity to evoke appropriate and measured responses to signal molecules (such as peptide hormones), environmental changes, and other external stimuli. Tremendous progress has been made in identifying the proteins that mediate cellular response to such signals and in elucidating how events at the cell surface are linked to subsequent biochemical changes in the cytoplasm and nucleus. An emerging area of investigation concerns how signaling components are assembled and regulated (both spatially and temporally), so as to control properly the specificity and intensity of a given signaling pathway. A related question under intensive study is how the action of an individual signaling pathway is integrated with (or insulated from) other pathways to constitute larger networks that control overall cell behavior appropriately. This review describes the signal transduction pathway used by budding yeast (Saccharomyces cerevisiae) to respond to its peptide mating pheromones. This pathway is comprised by receptors, a heterotrimeric G protein, and a protein kinase cascade all remarkably similar to counterparts in multicellular organisms. The primary focus of this review, however, is recent advances that have been made, using primarily genetic methods, in identifying molecules responsible for regulation of the action of the components of this signaling pathway. Just as many of the constituent proteins of this pathway and their interrelationships were first identified in yeast, the functions of some of these regulators have clearly been conserved in metazoans, and others will likely serve as additional models for molecules that carry out analogous roles in higher organisms.
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Affiliation(s)
- H G Dohlman
- Department of Pharmacology, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06536-0812, USA.
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16
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Abstract
Hormones, sensory stimuli, neurotransmitters and chemokines signal by activating G-protein-coupled receptors (GPCRs) [1]. Although GPCRs are thought to function as monomers, they can form SDS-resistant dimers, and coexpression of two non-functional or related GPCRs can result in rescue of activity or modification of function [2-10]. Furthermore, dimerization of peptides corresponding to the third cytoplasmic loops of GPCRs increases their potency as activators of G proteins in vitro [11], and peptide inhibitors of dimerization diminish beta(2)-adrenergic receptor signaling [3]. Nevertheless, it is not known whether GPCRs exist as monomers or oligomers in intact cells and membranes, whether agonist binding regulates monomer-oligomer equilibrium, or whether oligomerization governs GPCR function. Here, we report that the alpha-factor receptor, a GPCR that is the product of the STE2 gene in the yeast Saccharomyces cerevisiae, is oligomeric in intact cells and membranes. Coexpression of receptors tagged with the cyan or yellow fluorescent proteins (CFP or YFP) resulted in efficient fluorescence resonance energy transfer (FRET) due to stable association rather than collisional interaction. Monomer-oligomer equilibrium was unaffected by binding of agonist, antagonist, or G protein heterotrimers. Oligomerization was further demonstrated by rescuing endocytosis-defective receptors with coexpressed wild-type receptors. Dominant-interfering receptor mutants inhibited signaling by interacting with wild-type receptors rather than by sequestering G protein heterotrimers. We suggest that oligomerization is likely to govern GPCR signaling and regulation.
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Affiliation(s)
- M C Overton
- Department of Cell Biology and Physiology, Box 8228, Washington University School of Medicine, St. Louis 63110, USA
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17
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Manahan CL, Patnana M, Blumer KJ, Linder ME. Dual lipid modification motifs in G(alpha) and G(gamma) subunits are required for full activity of the pheromone response pathway in Saccharomyces cerevisiae. Mol Biol Cell 2000; 11:957-68. [PMID: 10712512 PMCID: PMC14823 DOI: 10.1091/mbc.11.3.957] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
To establish the biological function of thioacylation (palmitoylation), we have studied the heterotrimeric guanine nucleotide-binding protein (G protein) subunits of the pheromone response pathway of Saccharomyces cerevisiae. The yeast G protein gamma subunit (Ste18p) is unusual among G(gamma) subunits because it is farnesylated at cysteine 107 and has the potential to be thioacylated at cysteine 106. Substitution of either cysteine results in a strong signaling defect. In this study, we found that Ste18p is thioacylated at cysteine 106, which depended on prenylation of cysteine 107. Ste18p was targeted to the plasma membrane even in the absence of prenylation or thioacylation. However, G protein activation released prenylation- or thioacylation-defective Ste18p into the cytoplasm. Hence, lipid modifications of the G(gamma) subunit are dispensable for G protein activation by receptor, but they are required to maintain the plasma membrane association of G(betagamma) after receptor-stimulated release from G(alpha). The G protein alpha subunit (Gpa1p) is tandemly modified at its N terminus with amide- and thioester-linked fatty acids. Here we show that Gpa1p was thioacylated in vivo with a mixture of radioactive myristate and palmitate. Mutation of the thioacylation site in Gpa1p resulted in yeast cells that displayed partial activation of the pathway in the absence of pheromone. Thus, dual lipidation motifs on Gpa1p and Ste18p are required for a fully functional pheromone response pathway.
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Affiliation(s)
- C L Manahan
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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18
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Bell B, Xing H, Yan K, Gautam N, Muslin AJ. KSR-1 binds to G-protein betagamma subunits and inhibits beta gamma-induced mitogen-activated protein kinase activation. J Biol Chem 1999; 274:7982-6. [PMID: 10075696 DOI: 10.1074/jbc.274.12.7982] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The protein kinase KSR-1 is a recently identified participant in the Ras signaling pathway. The subcellular localization of KSR-1 is variable. In serum-deprived cultured cells, KSR-1 is primarily found in the cytoplasm; in serum-stimulated cells, a significant portion of KSR-1 is found at the plasma membrane. To identify the mechanism that mediates KSR-1 translocation, we performed a yeast two-hybrid screen. Three clones that interacted with KSR-1 were found to encode the full-length gamma10 subunit of heterotrimeric G-proteins. KSR-1 also interacted with gamma2 and gamma3 in a two-hybrid assay. Deletion analysis demonstrated that the isolated CA3 domain of KSR-1, which contains a cysteine-rich zinc finger-like domain, interacted with gamma subunits. Coimmunoprecipitation experiments demonstrated that KSR-1 bound to beta1 gamma3 subunits when all three were transfected into cultured cells. Lysophosphatidic acid treatment of cells induced KSR-1 translocation to the plasma membrane from the cytoplasm that was blocked by administration of pertussis toxin but not by dominant-negative Ras. Finally, transfection of wild-type KSR-1 inhibited beta1 gamma3-induced mitogen-activated protein kinase activation in cultured cells. These results demonstrate that KSR-1 translocation to the plasma membrane is mediated, at least in part, by an interaction with beta gamma and that this interaction may modulate mitogen-activated protein kinase signaling.
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Affiliation(s)
- B Bell
- Center for Cardiovascular Research, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Dowell SJ, Bishop AL, Dyos SL, Brown AJ, Whiteway MS. Mapping of a yeast G protein betagamma signaling interaction. Genetics 1998; 150:1407-17. [PMID: 9832519 PMCID: PMC1460424 DOI: 10.1093/genetics/150.4.1407] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The mating pathway of Saccharomyces cerevisiae is widely used as a model system for G protein-coupled receptor-mediated signal transduction. Following receptor activation by the binding of mating pheromones, G protein betagamma subunits transmit the signal to a MAP kinase cascade, which involves interaction of Gbeta (Ste4p) with the MAP kinase scaffold protein Ste5p. Here, we identify residues in Ste4p required for the interaction with Ste5p. These residues define a new signaling interface close to the Ste20p binding site within the Gbetagamma coiled-coil. Ste4p mutants defective in the Ste5p interaction interact efficiently with Gpa1p (Galpha) and Ste18p (Ggamma) but cannot function in signal transduction because cells expressing these mutants are sterile. Ste4 L65S is temperature-sensitive for its interaction with Ste5p, and also for signaling. We have identified a Ste5p mutant (L196A) that displays a synthetic interaction defect with Ste4 L65S, providing strong evidence that Ste4p and Ste5p interact directly in vivo through an interface that involves hydrophobic residues. The correlation between disruption of the Ste4p-Ste5p interaction and sterility confirms the importance of this interaction in signal transduction. Identification of the Gbetagamma coiled-coil in Ste5p binding may set a precedent for Gbetagamma-effector interactions in more complex organisms.
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Affiliation(s)
- S J Dowell
- Glaxo Wellcome Research and Development, Stevenage, SG1 2NY, United Kingdom.
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20
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Abstract
The heterotrimeric G proteins are extensively involved in the regulation of cells by extracellular signals. The receptors that control them are often the targets of drugs. There are many isoforms of each of the three subunits that make up these proteins. Thus far, genes for at least sixteen alpha subunits, five beta subunits, and eleven gamma subunits have been identified. In addition, some of these proteins have splice variants or are differentially modified. Based upon what is already known, there are well over a thousand possible G protein heterotrimer combinations. The role of subunit diversity in heterotrimer formation and its effect on signaling by G proteins are still not well understood. However, many current lines of research are leading toward an understanding of these roles. The functional significance of subunit heterogeneity is related to the mechanisms used by G proteins to transmit and integrate the many signals coming into cells through this system. Described here are the basic mechanisms by which G proteins integrate cellular responses, the possible role of subunit heterogeneity in these mechanisms, and the evidence for and against their physiological significance. Recent studies suggest the likely possibility that subunit heterogeneity plays an important role in signaling by G proteins. This role has the potential to extend substantially the flexibility of G proteins in mediating cellular responses to extracellular signals. However, the details of this are yet to be worked out, and they are the subject of many different avenues of research.
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Affiliation(s)
- J D Hildebrandt
- Department of Cell and Molecular Pharmacology, Medical University of South Carolina, Charleston 29425-2251, U.S.A.
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21
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Hirschman JE, De Zutter GS, Simonds WF, Jenness DD. The G beta gamma complex of the yeast pheromone response pathway. Subcellular fractionation and protein-protein interactions. J Biol Chem 1997; 272:240-8. [PMID: 8995254 DOI: 10.1074/jbc.272.1.240] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Genetic evidence suggests that the yeast STE4 and STE18 genes encode G beta and G gamma subunits, respectively, that the G betagamma complex plays a positive role in the pheromone response pathway, and that its activity is subject to negative regulation by the G alpha subunit (product of the GPA1 gene) and to positive regulation by cell-surface pheromone receptors. However, as yet there is no direct biochemical evidence for a G betagamma protein complex associated with the plasma membrane. We found that the products of the STE4 and STE18 genes are stably associated with plasma membrane as well as with internal membranes and that 30% of the protein pool is not tightly associated with either membrane fraction. A slower-migrating, presumably phosphorylated, form of Ste4p is enriched in the non-membrane fraction. The Ste4p and Ste18p proteins that had been extracted from plasma membranes with detergent were found to co-sediment as an 8 S particle under low salt conditions and as a 6 S particle in the presence of 0.25 M NaCl; the Ste18p in these fractions was precipitated with anti-Ste4p antiserum. Under the conditions of our assay, Gpa1p was not associated with either particle. The levels of Ste4p and Ste18p accumulation in mutant cells provided additional evidence for a G betagamma complex. Ste18p failed to accumulate in ste4 mutant cells, and Ste4p showed reduced levels of accumulation and an increased rate of turnover in ste18 mutant cells. The gpa1 mutant blocked stable association of Ste4p with the plasma membrane, and the ste18 mutant blocked stable association of Ste4p with both plasma membranes and internal membranes. The membrane distribution of Ste4p was unaffected by the ste2 mutation or by down-regulation of the cell-surface receptors. These results indicate that at least 40% of Ste4p and Ste18p are part of a G betagamma complex at the plasma membrane and that stable association of this complex with the plasma membrane requires the presence of G alpha.
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Affiliation(s)
- J E Hirschman
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655-0122, USA
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22
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Kübler E, Dohlman HG, Lisanti MP. Identification of Triton X-100 insoluble membrane domains in the yeast Saccharomyces cerevisiae. Lipid requirements for targeting of heterotrimeric G-protein subunits. J Biol Chem 1996; 271:32975-80. [PMID: 8955141 DOI: 10.1074/jbc.271.51.32975] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Low density Triton X-100 insoluble (LDTI) membrane domains are found in most mammalian cell types. Previous biochemical and immunolocalization studies have revealed the presence of G-protein coupled receptors and heterotrimeric G-protein subunits (Galpha and Gbetagamma subunits) within these structures, implicating mammalian LDTI membrane domains in G-protein coupled signaling. Here, we present biochemical evidence that similar LDTI structures exist in a genetically tractable organism, the yeast Saccharomyces cerevisiae. Yeast LDTI membranes were purified based on the known biochemical properties of mammalian LDTI membranes: (i) their Triton X-100 insolubility; and (ii) their discrete buoyant density in sucrose gradients. As with purified mammalian LDTI membranes, these yeast LDTI membranes harbor the subunits of the heterotrimeric G-proteins (Galpha and Gbetagamma subunits). Other plasma membrane marker proteins (the plasma membrane H+-ATPase and a GPI-linked protein Gas1p) are preferentially excluded from these purified fractions. Mutational and genetic analyses were performed to define the requirements for the targeting of G-protein subunits to these yeast membrane domains. We find that the targeting of Galpha is independent of myristoylation, whereas targeting of Ggamma requires prenylation. Perhaps surprisingly, the targeting of Gbeta to this membrane domain did not require coexpression of Ggamma. It should now be possible to dissect the function of LDTI membrane domains using yeast as a model genetic system.
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Affiliation(s)
- E Kübler
- The Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142-1479, USA.
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23
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Abstract
Over the past year, the thrust of work in the field of heterotrimeric G proteins has been primarily in the following areas: first, resolution of their three-dimensional structures by X-ray crystallography; second, elucidation of the effect of lipid modifications on the Galpha and Ggamma subunits; third, understanding the role of the Gbetagamma dimer in stimulation of a variety of effectors following receptor activation; and fourth, identification of the points of contact among the Galpha, Gbeta, and Ggamma subunits, and between these subunits and their cognate receptor or effector molecules.
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Affiliation(s)
- H E Hamm
- University of Illinois at Chicago, Department of Physiology and Biophysics, 835 S Wolcott, Chicago, IL 60612, USA
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24
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Sondek J, Bohm A, Lambright DG, Hamm HE, Sigler PB. Crystal structure of a G-protein beta gamma dimer at 2.1A resolution. Nature 1996; 379:369-74. [PMID: 8552196 DOI: 10.1038/379369a0] [Citation(s) in RCA: 661] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Many signalling cascades use seven-helical transmembrane receptors coupled to heterotrimeric G proteins (G alpha beta gamma) to convert extracellular signals into intracellular responses. Upon nucleotide exchange catalysed by activated receptors, heterotrimers dissociate into GTP-bound G alpha subunits and G beta gamma dimers, either of which can modulate many downstream effectors. Here we use multiwavelength anomalous diffraction data to solve the crystal structure of the beta gamma dimer of the G protein transducin. The beta-subunit is primarily a seven-bladed beta-propeller that is partially encircled by an extended gamma-subunit. The beta-propeller, which contains seven structurally similar WD repeats, defines the stereochemistry of the WD repeat and the probable architecture of all WD-repeat-containing domains. The structure details interactions between G protein beta- and gamma-subunits and highlights regions implicated in effector modulation for the conserved family of G protein beta gamma dimers.
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Affiliation(s)
- J Sondek
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06510, USA
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25
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Lambright DG, Sondek J, Bohm A, Skiba NP, Hamm HE, Sigler PB. The 2.0 A crystal structure of a heterotrimeric G protein. Nature 1996; 379:311-9. [PMID: 8552184 DOI: 10.1038/379311a0] [Citation(s) in RCA: 891] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The structure of a heterotrimeric G protein reveals the mechanism of the nucleotide-dependent engagement of the alpha and beta gamma subunits that regulates their interaction with receptor and effector molecules. The interaction involves two distinct interfaces and dramatically alters the conformation of the alpha but not of the beta gamma subunits. The location of the known sites for post-translational modification and receptor coupling suggest a plausible orientation with respect to the membrane surface and an activated heptahelical receptor.
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Affiliation(s)
- D G Lambright
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06510, USA
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