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Gromes R, Zetsche K. Evidence for a G-Protein Regulated Adenylate Cyclase and a Ca2/Calmodulin Controlled Phosphodiesterase in the PhytoflagellateChlorogonium. ACTA ACUST UNITED AC 2014. [DOI: 10.1111/j.1438-8677.1992.tb00319.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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2
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Abstract
Heterotrimeric G-proteins, which couple cell surface receptors with internal effectors, are evident in all eukaryotes. Their operation involves receptor activation, GTP/GDP exchange and modulation of effector activity; deactivation occurs by an intrinsic GTPase activity. Structurally, G-proteins comprise three dissimilar subunits; Gα, Gβ and Gγ. The Gα subunit consists of an α-helical and a GTPase domain, the latter is responsible for interaction with Gβγ, receptor and effector. Gβ and Gγ form a tightly associated heterodimer which can also modulate effector activity when released by the activated Gα. Genome sequence and other data suggest that, in plants, there are several (~8-10?) Gα, one or two Gβ and one Gγ. These proteins are expressed throughout the plant, mainly in the plasma membrane and endoplasmic reticulum. In vivo, there is strong evidence for G-protein control of ion channels, particularly K+ , in the response pathways to fungal and bacterial pathogens as well as in some aspects of gibberellin, abscisic acid and auxin signaling pathways. Finally, future prospects for understanding plant G-protein linked signaling will rely on new and emerging technologies; these include antisense suppression, gene knockouts, yeast two-hybrid and phage display molecular approaches, intracellular immunization using recombinant single chain antibodies and expression of peptide encoding minigenes.
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Affiliation(s)
- P A Millner
- School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
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3
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Seo HS, Choi CH, Lee SY, Cho MJ, Bahk JD. Biochemical characteristics of a rice (Oryza sativa L., IR36) G-protein alpha-subunit expressed in Escherichia coli. Biochem J 1997; 324 ( Pt 1):273-81. [PMID: 9164867 PMCID: PMC1218427 DOI: 10.1042/bj3240273] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A cDNA encoding the alpha-subunit of the heterotrimeric G-protein in rice (RGA1) was overexpressed in Escherichia coli and then isolated by Ni2+-nitrilotriacetic acid affinity chromatography. The molecular mass of RGA1 bearing a His tag was approx. 49 kDa. Immunoblot analysis using anti-RGA1 revealed that the RGA1 protein is most abundant in seedling leaves and least abundant in mature roots. It exists at particularly high levels in the immature embryo after pellicle extrusion. In addition, the RGA1 antiserum exhibited a difference in binding affinity for Galpha proteins from monocots (maize and rice) and dicots (Arabidopsis, pea, soya bean and tomato); whereas it cross-reacted with Galpha proteins of monocots, it did not with those of dicot plants. When bound to guanosine 5'-(gamma-thio)triphosphate (GTP[S]), the RGA1 protein was partially protected from tryptic proteolysis. In the presence of GTP[S], trypsin cleaved the RGA1 protein into four fragments 24, 14, 11 and 5 kDa in size. When RGA1 was bound to GDP, only the 5 kDa polypeptide was seen on SDS/PAGE after trypsin digestion. Photoaffinity labelling with [alpha-32P]GTP and a GTP[S]-binding assay revealed that RGA1 incorporated 32P and showed specific binding to a guanine nucleotide. Guanidine binding of RGA1 was affected by the concentration of MgCl2 (maximum at 2 mM). The rate of guanine nucleotide binding of RGA1 (kon,GTP[S]=0.0141+/-0.0014 min-1) and, at steady state, the kcat value for GTP hydrolysis (0.0075+/-0.0001 min-1) were very low even at 2 mM MgCl2. The binding affinity for the nucleotides examined was in the order GTP-S- >/= GTP > GDP > CTP > ATP >/= dTTP.
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Affiliation(s)
- H S Seo
- Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Chinju 660-701, Korea
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4
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Parmryd I, Shipton CA, Andersson B, Dallner G. Protein prenylation in spinach--tissue specificity and greening-induced changes. Arch Biochem Biophys 1997; 339:73-8. [PMID: 9056235 DOI: 10.1006/abbi.1996.9816] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Etiolated spinach seedlings, as well as petioles and blades of leaves of green seedlings, were labeled with [3H]mevalonate to study protein prenylation in several plant developmental stages. The polypeptide prenylation pattern of the leaf petiole and the leaf blade differed considerably, although some prenylated proteins were present in both tissues. During greening several prenylated polypeptides in the 30- to 46-kDa molecular mass region and two at 15 kDa became more abundant, while others in the 21.5- to 30-kDa region and one at 62 kDa showed a relative decrease. However, the relative amount of several of the prenylated polypeptides did not appear to be altered during the greening process. In etiolated seedlings, more thioether-linked farnesol than geranylgeraniol was found, whereas in seedlings grown under normal light conditions the converse situation prevailed.
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Affiliation(s)
- I Parmryd
- Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, Sweden.
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5
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Sopory SK, Chandok MR. Light-induced signal transduction pathway involving inositol phosphates. Subcell Biochem 1996; 26:345-70. [PMID: 8744271 DOI: 10.1007/978-1-4613-0343-5_12] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- S K Sopory
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
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6
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Shipton CA, Parmryd I, Swiezewska E, Andersson B, Dallner G. Isoprenylation of plant proteins in vivo. Isoprenylated proteins are abundant in the mitochondria and nuclei of spinach. J Biol Chem 1995; 270:566-72. [PMID: 7822281 DOI: 10.1074/jbc.270.2.566] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Protein isoprenylation in vivo is demonstrated using spinach seedlings labeled with [3H]mevalonate. This report provides evidence for the occurrence of a large number of isoprenylated proteins in plants. Seedlings, without roots, were labeled quantitatively through the cut stem. Mevinolin treatment of the seedlings resulted in increased incorporation of radiolabel into proteins. Approximately 30 labeled bands could be detected after autoradiography of SDS-polyacrylamide gel electrophoresis-separated polypeptides, ranging in molecular mass from 6 to 200 kDa. Methyl iodide hydrolysis resulted in the release of covalently bound farnesol, geranylgeraniol, phytol, and some unidentified isoprenoid compounds from mevalonate-labeled proteins. It was found that all cellular fractions contained some isoprenylated proteins, although most were located in the mitochondria and nuclei. Subfractionation of the nucleus revealed that the majority of isoprenylated proteins in this compartment were components of the nuclear matrix. The results demonstrate that in vivo labeling of a complex organism can be performed using a plant system in order to study protein isoprenylation and distribution of modified proteins in different cellular compartments.
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Affiliation(s)
- C A Shipton
- Arrhenius Laboratories for Natural Sciences, Biochemistry Department, University of Stockholm, Sweden
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7
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Affiliation(s)
- H Ma
- Cold Spring Harbor Laboratory, New York 11724, USA
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8
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Wise A, Thomas PG, White IR, Millner PA. Isolation of a putative receptor from Zea mays microsomal membranes that interacts with the G-protein, GP alpha 1. FEBS Lett 1994; 356:233-7. [PMID: 7805845 DOI: 10.1016/s0014-5793(94)80076-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The C-terminal region of a heterotrimeric G-protein alpha-subunit is known to be one of the principal determinants governing its interaction with its cognate receptor. Use of an oligopeptide corresponding to the fifteen C-terminal residues of the Arabidopsis G alpha-subunit (GP alpha 1), as an affinity ligand, led to the resolution of a tightly binding 37 kDa membrane polypeptide from detergent solubilised Zea microsomal fraction membranes. An identical polypeptide bound tightly to an affinity matrix containing recombinant GP alpha 1 protein as ligand: binding and release of this 37 kDa protein was dependent on the activation state of GP alpha 1 which was regulated by inclusion or omission of the G-protein activator AlF-4. Finally, the isolated 37 kDa protein was labelled with the lectin concanavalin A, indicating it to be glycosylated. These data are consistent with the identity of the 37 kDa membrane polypeptide as a receptor that interacts with the Zea homologue of GP alpha 1.
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Affiliation(s)
- A Wise
- Department of Biochemistry and Molecular Biology, University of Leeds, UK
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9
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Ma H. GTP-binding proteins in plants: new members of an old family. PLANT MOLECULAR BIOLOGY 1994; 26:1611-1636. [PMID: 7858207 DOI: 10.1007/bf00016493] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Regulatory guanine nucleotide-binding proteins (G proteins) have been studied extensively in animal and microbial organisms, and they are divided into the heterotrimeric and the small (monomeric) classes. Heterotrimeric G proteins are known to mediate signal responses in a variety of pathways in animals and simple eukaryotes, while small G proteins perform diverse functions including signal transduction, secretion, and regulation of cytoskeleton. In recent years, biochemical analyses have produced a large amount of information on the presence and possible functions of G proteins in plants. Further, molecular cloning has clearly demonstrated that plants have both heterotrimeric and small G proteins. Although the functions of the plant heterotrimeric G proteins are yet to be determined, expression analysis of an Arabidopsis G alpha protein suggests that it may be involved in the regulation of cell division and differentiation. In contrast to the very few genes cloned thus far that encode heterotrimeric G proteins in plants, a large number of small G proteins have been identified by molecular cloning from various plants. In addition, several plant small G proteins have been shown to be functional homologues of their counterparts in animals and yeasts. Future studies using a number of approaches are likely to yield insights into the role plant G proteins play.
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Affiliation(s)
- H Ma
- Cold Spring Harbor Laboratory, NY 11724
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10
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de Boer AH, van Hunnik E, Korthout HA, Sedee NJ, Wang M. Affinity purification of GTPase proteins from oat root plasma membranes using biotinylated GTP. FEBS Lett 1994; 337:281-4. [PMID: 8293815 DOI: 10.1016/0014-5793(94)80209-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Biotinylated GTP was synthesized and it was demonstrated that this ligand was bi-functional: it competed with [3H]Gpp(NH)p for binding to membrane proteins and it bound to immobilized avidin. Peripheral plasma membrane proteins were solubilized in a low-salt wash, incubated with GTP-biotin and biotinylated proteins were coupled to an avidin column. Elution with excess biotin yielded 10 polypeptides as seen with a silver stained SDS-PAGE gel. Antisera raised against Ras, a small GTPase, strongly interacted with three proteins with MW of 38, 27 and 25 kDa and also with 6 other proteins. G alpha-common antibodies interacted with proteins of MW = 66 and 38 kDa. This method enables the rapid purification of GTP-binding proteins and opens the possibility to assign a role to specific GTPases in signal transduction pathways.
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Affiliation(s)
- A H de Boer
- Department of Plant Physiology and Biochemistry, Vrije Universiteit van Amsterdam, The Netherlands
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11
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Kaufman LS. New trends in photobiology. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 1994. [DOI: 10.1016/1011-1344(93)06922-p] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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12
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Muschietti JP, Martinetto HE, Coso OA, Farber MD, Torres HN, Flawia MM. G-protein from Medicago sativa: functional association to photoreceptors. Biochem J 1993; 291 ( Pt 2):383-8. [PMID: 8484719 PMCID: PMC1132536 DOI: 10.1042/bj2910383] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
G-protein subunits were characterized from Medicago sativa (alfalfa) seedlings. Crude membranes and GTP-Sepharose-purified fractions were electrophoresed on SDS/polyacrylamide gels and analysed by Western blotting with 9193 (anti-alpha common) and AS/7 (anti-alpha t, anti-alpha i1 and anti-alpha i2) polyclonal antibodies. These procedures led to the identification of a specific polypeptide band of about 43 kDa. Another polypeptide reacting with the SW/1 (anti-beta) antibody, of about 37 kDa, was also detected. The 43 kDa polypeptide bound specifically [alpha-32P]GTP by a photoaffinity reaction and was ADP-ribosylated by activated cholera toxin, but not by pertussis toxin. Irradiation of etiolated Medicago sativa protoplast preparations at 660 nm for 1 min produced a maximal increase in the guanosine 5'-[gamma-thio]triphosphate (GTP[35S])-binding rate. After this period of irradiation, the binding rate tended to decrease. The effect of a red-light (660 nm) pulse on the binding rate was reversed when it was immediately followed by a period of far-red (> 730 nm) illumination. These results may suggest that activation of GTP[S]-binding rate was a consequence of conversion of phytochrome Pr into the Ptr form.
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Affiliation(s)
- J P Muschietti
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina
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Terryn N, Van Montagu M, Inzé D. GTP-binding proteins in plants. PLANT MOLECULAR BIOLOGY 1993; 22:143-152. [PMID: 8499613 DOI: 10.1007/bf00039002] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Affiliation(s)
- N Terryn
- Laboratorium voor Genetica, Universiteit Gent, Belgium
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Li W, Assmann SM. Characterization of a G-protein-regulated outward K+ current in mesophyll cells of vicia faba L. Proc Natl Acad Sci U S A 1993; 90:262-6. [PMID: 8419932 PMCID: PMC45640 DOI: 10.1073/pnas.90.1.262] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Whole-cell voltage-dependent currents in isolated mesophyll protoplasts of Vicia faba were investigated by patch-clamp techniques. With 104 mM K+ in the cytosol and 13 mM K+ in the external solution, depolarization of the plasma membrane from -47 mV to potentials between -15 and +85 mV activated a voltage- and time-dependent outward current (Iout). The average magnitude of Iout at +85 mV was 28.5 +/- 3.3 pA.pF-1. No inward voltage-dependent current was observed upon hyperpolarization of the plasma membrane from -55 mV to potentials as negative as -175 mV. Time-activated outward current was blocked by Ba2+ (1 mM BaCl2) and was not observed when K+ was eliminated from the external and internal solutions, indicating that this outward current was carried primarily by K+ ions. The voltage dependency of outward K+ current revealed a possible mechanism for K+ efflux from mesophyll cells. A GDP analogue guanosine 5'-[beta-thio]diphosphate (500 microM) significantly enhanced outward K+ current. The outward K+ current was inhibited by the GTP analogue guanosine 5'-[gamma-thio]triphosphate (500 microM) and by an increase in cytoplasmic free Ca2+ concentrations. Cholera toxin, which ADP-ribosylates guanine nucleotide-binding regulatory proteins, also inhibited outward K+ current. These findings illustrate the presence in mesophyll cells of outward-rectifying K+ channels that are regulated by GTP-binding proteins and calcium.
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Affiliation(s)
- W Li
- Biological Laboratories, Harvard University, Cambridge, MA 02138
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15
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Affiliation(s)
- B K Drøbak
- Department of Cell Biology, John Innes Centre for Plant Science Research, Norwich, U.K
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16
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Palme K. Molecular analysis of plant signaling elements: relevance of eukaryotic signal transduction models. INTERNATIONAL REVIEW OF CYTOLOGY 1992; 132:223-83. [PMID: 1555920 DOI: 10.1016/s0074-7696(08)62457-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- K Palme
- Max-Planck-Institut für Pflanzenzüchtung, Köln, Germany
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17
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18
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Sasaki Y, Sekiguchi K, Nagano Y, Matsuno R. Detection of small GTP-binding proteins in the outer envelope membrane of pea chloroplasts. FEBS Lett 1991; 293:124-6. [PMID: 1959643 DOI: 10.1016/0014-5793(91)81166-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We found small GTP-binding proteins in the outer envelope membrane of pea chloroplasts. The proteins in this membrane were separated by SDS-PAGE, transferred to a nitrocellulose filter, and incubated with [alpha-32P]GTP. Three GTP-binding proteins with the molecular weight of 24,000 were found. Binding was prevented by 10(-8)-10(-7) M GTP or by 10(-7) M guanosine 5'-[gamma-thio]triphosphate or GDP; binding was unaffected by 10(-8)-10(-6) M ATP. Thermolysin treatment of intact chloroplasts resulted in the loss of GTP-binding activity, suggesting that these proteins were in the cytosolic side of the outer envelope membrane.
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Affiliation(s)
- Y Sasaki
- Department of Food Science and Technology, Faculty of Agriculture, Kyoto University, Japan
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19
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Ma H, Yanofsky MF, Huang H. Isolation and sequence analysis of TGA1 cDNAs encoding a tomato G protein alpha subunit. Gene 1991; 107:189-95. [PMID: 1748292 DOI: 10.1016/0378-1119(91)90318-6] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have isolated cDNAs for a gene coding for a G protein alpha subunit from tomato (Lycopersicon esculentum, cv. VF36). This gene, named TGA1, was isolated using a cDNA of the Arabidopsis thaliana G protein alpha subunit-encoding gene, GPA1, as a DNA probe. The sequences of four cDNA clones indicate that the deduced amino acid (aa) sequence of the gene product (TG alpha 1) has 384 aa (44906 Da). The predicted TG alpha 1 protein exhibits similarity to all known G protein alpha subunits. The aa are 84.6% identical and 93% similar (identical and conservative changes) to A. thaliana GP alpha 1, and 34% identical and 59% similar to mammalian transducins. Furthermore, it has all of the consensus regions for a GTP-binding protein. Finally, hybridizations of tomato genomic DNA indicate that TGA1 is a single-copy gene.
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Affiliation(s)
- H Ma
- Cold Spring Harbor Laboratory, NY 11724-2212
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20
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Bilushi SV, Shebunin AG, Babakov AV. Purification and subunit composition of a GTP-binding protein from maize root plasma membranes. FEBS Lett 1991; 291:219-21. [PMID: 1936267 DOI: 10.1016/0014-5793(91)81288-j] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
When frozen plasma membranes isolated from maize seedling roots are thawed, a significant portion of GTP-binding activity goes into solution. The GTP-binding protein was purified by ion exchange chromatography on Mono-Q and gel filtration on Superose 6. Its molecular weight was estimated at 61 kDa by gel filtration. The same molecular weight was obtained upon solubilization of the GTP-binding protein with cholic acid followed by gel filtration in the presence of this detergent. SDS-PAGE demonstrated that the isolated GTP-binding protein consists of two types of subunit of molecular weights 27 kDa and 34 kDa.
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Affiliation(s)
- S V Bilushi
- Institute of Agricultural Biotechnology, Moscow, USSR
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21
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Warpeha KM, Hamm HE, Rasenick MM, Kaufman LS. A blue-light-activated GTP-binding protein in the plasma membranes of etiolated peas. Proc Natl Acad Sci U S A 1991; 88:8925-9. [PMID: 1924352 PMCID: PMC52623 DOI: 10.1073/pnas.88.20.8925] [Citation(s) in RCA: 132] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Heterotrimeric GTP-binding regulatory proteins (G proteins) have been identified as part of signal transduction systems in a wide variety of organisms. In this paper, we establish the presence of a G protein associated with the plasma membranes of the apical bud of etiolated peas. The GTPase activity is induced by low fluences of blue light administered to plasma membrane-enriched fractions. The activity is not responsive to red-light irradiation and is specific for GTP. The threshold for the excitation of the GTPase activity in vitro is less than 10(-1) mumol.m-2 of blue light, consistent with participation in the blue low-fluence system identified in the same tissue. A 40-kDa polypeptide is recognized by polyclonal antisera directed against the alpha subunit of the G protein transducin. The polypeptide also serves as a substrate for ADP-ribosylation by cholera and pertussis toxins. The ability of the 40-kDa polypeptide to serve as substrate for the toxin-mediated ribosylation is mediated by blue-light irradiation, implying that the 40-kDa polypeptide is the alpha subunit of a blue-light-stimulated G protein. The 40-kDa polypeptide binds a nonhydrolyzable photoaffinity-labeling analog of GTP only after irradiation with blue light. The protein we have described may function as an alpha subunit of a G protein active in the process of light-mediated development in higher plants.
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Affiliation(s)
- K M Warpeha
- Department of Biological Sciences, University of Illinois, Chicago 60680
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22
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Levy J, King RJ. GTP analogues cause preferential translocation of an 18 kDa cytosolic G-protein to the membrane fraction in the ZR-75-1 human breast-cancer cell line. Biochem J 1990; 271:223-9. [PMID: 2121131 PMCID: PMC1149536 DOI: 10.1042/bj2710223] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Several G-proteins (GTP-binding proteins) were identified by SDS/PAGE in the cytosol (105,000 g supernatant) and membrane fractions of the oestrogen-dependent human mammary-tumour cell line ZR-75-1. These proteins, with molecular masses in the range 18-29 kDa, specifically bind [alpha-32P]GTP, which can be displaced by unlabelled GTP, GDP and their non-hydrolysable analogues guanosine 5'-[delta-thio]triphosphate (GTP[S]) and guanosine 5'-[beta-thio]diphosphate (GDP[S]), but not by GMP, ATP, ADP, AMP and other unrelated nucleotides. The apparent dissociation constant for GTP was approx. 2 x 10(-8)M. Homogenization of ZR-75-1 cells in high-salt buffer (1 M-KCl), and successive washing of the membrane fraction, suggested that, among the major G-proteins found, the 18 kDa protein is predominantly soluble, whereas the 27-29 kDa complex is primarily bound to the membrane fraction under the experimental conditions employed. Possible translocation of these G-proteins between membrane and cytosol was analysed. No redistribution of the 27-29 kDa complex was observed, whereas GTP[S] in the presence of Mg2+ caused apparent translocation of the 18 kDa protein to the membrane fraction. This effect was specific for GTP and stable GTP analogues, whereas GDP, GMP, ATP, ADP, AMP and other unrelated nucleotides were ineffective. GTP[S] and guanosine 5'-[beta gamma-imido]-triphosphate (p[NH]ppG) were equally potent (apparent Kd approximately 5 x 10(-6)M), whereas GTP was rather weak. The nucleotide effect is temperature-, time- and concentration-dependent. The translocation process was reversible, slow, and reached its maximum between 30 and 60 min at 37 degrees C. The apparent translocation of this small G-protein from the cytosol to the membrane fraction, and the specific effect of GTP analogues, suggest that this process may have functional significance in mammary-tumour cells.
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Affiliation(s)
- J Levy
- Hormone Biochemistry Laboratory, Imperial Cancer Research Fund, London, U.K
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23
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Ma H, Yanofsky MF, Meyerowitz EM. Molecular cloning and characterization of GPA1, a G protein alpha subunit gene from Arabidopsis thaliana. Proc Natl Acad Sci U S A 1990; 87:3821-5. [PMID: 2111018 PMCID: PMC53995 DOI: 10.1073/pnas.87.10.3821] [Citation(s) in RCA: 209] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We have isolated a gene coding for a G protein alpha subunit from the flowering plant Arabidopsis thaliana. This gene, named GPA1, was isolated by using a DNA probe generated by polymerase chain reaction based on protein sequences from mammalian and yeast G protein alpha subunits. The sequences of genomic and cDNA clones indicate that GPA1 has 14 exons, and the deduced amino acid sequence shows that the GPA1 gene product (GP alpha 1) has 383 amino acid residues (44,582 Da). The GP alpha 1 protein exhibits similarity to all known G protein alpha subunits--36% of its amino acids are identical and 73% are similar (identical and conservative changes) to mammalian inhibitory guanine nucleotide-binding regulatory factor alpha subunits and transducins. Furthermore, the GP alpha 1 protein has all of the consensus regions for a GTP-binding protein. The GPA1-encoded mRNA of 1.55 kilobases is most abundant in vegetative plant tissues, as determined by RNA blot analysis. Restriction fragment length polymorphism mapping experiments show that GPA1 is approximately 1.2 centimorgans from the visible marker er on chromosome 2.
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Affiliation(s)
- H Ma
- Division of Biology, California Institute of Technology, Pasadena 91125
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24
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Millner PA, Robinson PS. ADP-ribosylation of thylakoid membrane polypeptides by cholera toxin is correlated with inhibition of thylakoid GTPase activity and protein phosphorylation. Cell Signal 1989; 1:421-33. [PMID: 2561911 DOI: 10.1016/0898-6568(89)90028-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Incubation of pea thylakoid membranes with [32P]-NAD+ in the presence of cholera toxin resulted in the [32P]-ADP-ribosylation of a 60 kDa thylakoid membrane polypeptide. When ATP was included in the incubation mixture, a 29 kDa polypeptide was also labelled. In the absence of electron transfer cofactors or inhibitors, the extent of labelling depended on whether the membranes were preincubated in the light or dark and also on the developmental stage of the leaves used for thylakoid isolation. Irrespective of the latter, the strongest labelling was observed when DCMU was present in the light. After pretreatment of the thylakoid membranes with cholera toxin plus NAD+ under the same conditions, light-stimulated GTPase activity and protein phosphorylation were inhibited. The extent of inhibition for both processes appeared to be correlated with the amount of [32P]-ADP-ribosylation found when [32P]-NAD+ was included in the pretreatment mixture. The data presented are fully consistent with the 60 and 29 kDa polypeptides functioning as thylakoid membrane associated guanine nucleotide binding regulatory proteins.
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Affiliation(s)
- P A Millner
- Department of Biochemistry, University of Leeds, U.K
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