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Maziarz M, Broselid S, DiGiacomo V, Park JC, Luebbers A, Garcia-Navarrete L, Blanco-Canosa JB, Baillie GS, Garcia-Marcos M. A biochemical and genetic discovery pipeline identifies PLCδ4b as a nonreceptor activator of heterotrimeric G-proteins. J Biol Chem 2018; 293:16964-16983. [PMID: 30194280 DOI: 10.1074/jbc.ra118.003580] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 08/21/2018] [Indexed: 02/06/2023] Open
Abstract
Recent evidence has revealed that heterotrimeric G-proteins can be activated by cytoplasmic proteins that share an evolutionarily conserved sequence called the Gα-binding-and-activating (GBA) motif. This mechanism provides an alternative to canonical activation by G-protein-coupled receptors (GPCRs) and plays important roles in cell function, and its dysregulation is linked to diseases such as cancer. Here, we describe a discovery pipeline that uses biochemical and genetic approaches to validate GBA candidates identified by sequence similarity. First, putative GBA motifs discovered in bioinformatics searches were synthesized on peptide arrays and probed in batch for Gαi3 binding. Then, cDNAs encoding proteins with Gαi3-binding sequences were expressed in a genetically-modified yeast strain that reports mammalian G-protein activity in the absence of GPCRs. The resulting GBA motif candidates were characterized by comparison of their biochemical, structural, and signaling properties with those of all previously described GBA motifs in mammals (GIV/Girdin, DAPLE, Calnuc, and NUCB2). We found that the phospholipase Cδ4 (PLCδ4) GBA motif binds G-proteins with high affinity, has guanine nucleotide exchange factor activity in vitro, and activates G-protein signaling in cells, as indicated by bioluminescence resonance energy transfer (BRET)-based biosensors of G-protein activity. Interestingly, the PLCδ4 isoform b (PLCδ4b), which lacks the domains required for PLC activity, bound and activated G-proteins more efficiently than the full-length isoform a, suggesting that PLCδ4b functions as a G-protein regulator rather than as a PLC. In summary, we have identified PLCδ4 as a nonreceptor activator of G-proteins and established an experimental pipeline to discover and characterize GBA motif-containing proteins.
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Affiliation(s)
- Marcin Maziarz
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
| | - Stefan Broselid
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
| | - Vincent DiGiacomo
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
| | - Jong-Chan Park
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
| | - Alex Luebbers
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
| | - Lucia Garcia-Navarrete
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
| | - Juan B Blanco-Canosa
- the Department of Biological Chemistry and Molecular Modelling, Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), 08034 Barcelona, Spain, and
| | - George S Baillie
- the Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
| | - Mikel Garcia-Marcos
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, 02118
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2
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de Opakua AI, Parag-Sharma K, DiGiacomo V, Merino N, Leyme A, Marivin A, Villate M, Nguyen LT, de la Cruz-Morcillo MA, Blanco-Canosa JB, Ramachandran S, Baillie GS, Cerione RA, Blanco FJ, Garcia-Marcos M. Molecular mechanism of Gαi activation by non-GPCR proteins with a Gα-Binding and Activating motif. Nat Commun 2017; 8:15163. [PMID: 28516903 PMCID: PMC5454376 DOI: 10.1038/ncomms15163] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 03/06/2017] [Indexed: 01/03/2023] Open
Abstract
Heterotrimeric G proteins are quintessential signalling switches activated by nucleotide exchange on Gα. Although activation is predominantly carried out by G-protein-coupled receptors (GPCRs), non-receptor guanine-nucleotide exchange factors (GEFs) have emerged as critical signalling molecules and therapeutic targets. Here we characterize the molecular mechanism of G-protein activation by a family of non-receptor GEFs containing a Gα-binding and -activating (GBA) motif. We combine NMR spectroscopy, computational modelling and biochemistry to map changes in Gα caused by binding of GBA proteins with residue-level resolution. We find that the GBA motif binds to the SwitchII/α3 cleft of Gα and induces changes in the G-1/P-loop and G-2 boxes (involved in phosphate binding), but not in the G-4/G-5 boxes (guanine binding). Our findings reveal that G-protein-binding and activation mechanisms are fundamentally different between GBA proteins and GPCRs, and that GEF-mediated perturbation of nucleotide phosphate binding is sufficient for Gα activation. Nonreceptor guanine-nucleotide exchange factors (GEFs) are emerging as important regulators of heterotrimeric G proteins. Here, the authors present structural and mechanistic insights into how a class of nonreceptor GEFs containing the Ga-Binding and Activating motif interact and modulate G proteins.
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Affiliation(s)
| | - Kshitij Parag-Sharma
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
| | - Vincent DiGiacomo
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
| | | | - Anthony Leyme
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
| | - Arthur Marivin
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
| | | | - Lien T Nguyen
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
| | | | - Juan B Blanco-Canosa
- Department of Chemistry and Molecular Pharmacology, IRB Barcelona, 08028 Barcelona, Spain
| | - Sekar Ramachandran
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
| | - George S Baillie
- Institute of Cardiovascular and Medical Sciences, Department of Molecular Pharmacology, University of Glasgow, Glasgow G12 8QQ, UK
| | - Richard A Cerione
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.,Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA
| | - Francisco J Blanco
- CIC bioGUNE, 48160 Derio, Spain.,IKERBASQUE, Basque Foundation for Science, 48160 Bilbao, Spain
| | - Mikel Garcia-Marcos
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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3
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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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4
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Ramachandran S, Cerione RA. A dominant-negative Galpha mutant that traps a stable rhodopsin-Galpha-GTP-betagamma complex. J Biol Chem 2011; 286:12702-11. [PMID: 21285355 DOI: 10.1074/jbc.m110.166538] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Residues comprising the guanine nucleotide-binding sites of the α subunits of heterotrimeric (large) G-proteins (Gα subunits), as well as the Ras-related (small) G-proteins, are highly conserved. This is especially the case for the phosphate-binding loop (P-loop) where both Gα subunits and Ras-related G-proteins have a conserved serine or threonine residue. Substitutions for this residue in Ras and related (small) G-proteins yield nucleotide-depleted, dominant-negative mutants. Here we have examined the consequences of changing the conserved serine residue in the P-loop to asparagine, within a chimeric Gα subunit (designated αT*) that is mainly comprised of the α subunit of the retinal G-protein transducin and a limited region from the α subunit of Gi1. The αT*(S43N) mutant exhibits a significantly higher rate of intrinsic GDP-GTP exchange compared with wild-type αT*, with light-activated rhodopsin (R*) causing only a moderate increase in the kinetics of nucleotide exchange on αT*(S43N). The αT*(S43N) mutant, when bound to either GDP or GTP, was able to significantly slow the rate of R*-catalyzed GDP-GTP exchange on wild-type αT*. Thus, GTP-bound αT*(S43N), as well as the GDP-bound mutant, is capable of forming a stable complex with R*. αT*(S43N) activated the cGMP phosphodiesterase (PDE) with a dose-response similar to wild-type αT*. Activation of the PDE by αT*(S43N) was unaffected if either R* or β1γ1 alone was present, whereas it was inhibited when R* and the β1γ1 subunit were added together. Overall, our studies suggest that the S43N substitution on αT* stabilizes an intermediate on the G-protein activation pathway consisting of an activated G-protein-coupled receptor, a GTP-bound Gα subunit, and the β1γ1 complex.
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Affiliation(s)
- Sekar Ramachandran
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-6401, USA
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5
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Guo LW, Hajipour AR, Gavala ML, Arbabian M, Martemyanov KA, Arshavsky VY, Ruoho AE. Sulfhydryl-reactive, cleavable, and radioiodinatable benzophenone photoprobes for study of protein-protein interaction. Bioconjug Chem 2005; 16:685-93. [PMID: 15898738 DOI: 10.1021/bc050016k] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The major task in proteomics is to understand how proteins interact with their partners. The photo-cross-linking technique enables direct probing of protein-protein interaction. Here we report the development of three novel sulfhydryl-reactive benzophenone photoprobes of short "arm" length, each with a substitution of either amino, iodo, or nitro at the para-position, rendering the benzophenone moiety directly radioiodinatable. Their potential for study of protein-protein interaction was assessed using the inhibitory subunit of rod cGMP phosphodiesterase (PDEgamma) and the activated transducin alphasubunit (G alpha t-GTPgammaS) as a model system. These photoprobes proved to be stable at neutral pH and dithiothreitol-cleavable in addition. The PDEgamma constructs derivatized at the C-terminal positions with these probes could be readily purified, had unaltered PDEgamma functional activity, and were shown to photo-cross-link to G alpha t-GTPgammaS with an efficiency as high as 40%. Additionally, the amino benzophenone probe was radioiodinated, facilitating sensitive detection of label transfer. The uniquely combined features of these benzophenone photoprobes promise robust and flexible methods for characterization of protein-protein interaction, either by mass spectrometry when a nonradioactive label is available or by autoradiography when using radioiodinated derivatives.
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Affiliation(s)
- Lian-Wang Guo
- Department of Pharmacology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
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6
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Ramachandran S, Cerione RA. Stabilization of an intermediate activation state for transducin by a fluorescent GTP analogue. Biochemistry 2004; 43:8778-86. [PMID: 15236586 DOI: 10.1021/bi0362774] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The GTP-binding protein (G protein), transducin, serves as a key molecular switch in vertebrate vision through the tight regulation of its GTP-binding (activation)/GTP hydrolytic (deactivation) cycle by the photoreceptor rhodopsin. To better understand the structure-function characteristics of transducin activation, we have set out to identify spectroscopic probes that bind to the guanine nucleotide-binding site of this G protein and maintain its ability to interact with its specific cellular target/effector, the cyclic GMP phosphodiesterase (PDE). In this study, we describe the characterization of a fluorescently labeled GTP analogue, BODIPY-FL GTPgammaS (BOD-GTPgammaS), that binds to the alpha subunit of transducin (alpha(T)) in a rhodopsin- and Gbetagamma-dependent manner, similar to the binding of GTP or GTPgammaS, with an apparent dissociation constant of 100 nM. The rhodopsin-dependent binding of BOD-GTPgammaS to alpha(T) is slow, relative to the rate of binding of GTPgammaS, particularly under conditions where rhodopsin must act catalytically to stimulate the exchange of BOD-GTPgammaS for GDP on multiple alpha(T) subunits. This reflects a slower rate of dissociation of rhodopsin and Gbetagamma from alpha(T)-BOD-GTPgammaS complexes, relative to their rates of dissociation from alpha(T)-GTPgammaS. The binding of BOD-GTPgammaS occurs without a change in the intrinsic tryptophan fluorescence of alpha(T), indicating that only a subtle movement of the Switch 2 domain on alpha(T) accompanies the binding of this GTPgammaS analogue. Nevertheless, the BOD-GTPgammaS-bound alpha(T) subunit is able to bind with high affinity to the recombinant, purified gamma subunit of PDE (gamma(PDE)) labeled with 5-((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid (IAEDANS (K(d) approximately 13 nM)), as well as bind to and stimulate the activity of PDE, albeit less efficiently compared to alpha(T)-GTPgammaS. Taken together, these findings suggest that the binding of BOD-GTPgammaS to transducin causes it to adopt a distinct conformation that appears to be intermediate between the inactive and fully active states of alpha(T), and this fluorescent nucleotide analogue can be used as a reporter group to characterize the interactions of alpha(T) in this conformational state with its biological target/effector.
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Affiliation(s)
- Sekar Ramachandran
- Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA
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7
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Uversky VN, Permyakov SE, Zagranichny VE, Rodionov IL, Fink AL, Cherskaya AM, Wasserman LA, Permyakov EA. Effect of zinc and temperature on the conformation of the gamma subunit of retinal phosphodiesterase: a natively unfolded protein. J Proteome Res 2002; 1:149-59. [PMID: 12643535 DOI: 10.1021/pr0155127] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The cyclic GMP phosphodiesterase gamma-subunit (PDEgamma) was shown to belong to the family of natively unfolded proteins. Increasing temperature transforms the protein into a more ordered (but still relatively disordered) conformation. The C-terminal part of PDEgamma has a high-affinity zinc-binding site (Kd approximately 1 microM), with His75 and His79 being directly involved into the coordination of Zn2+. Zinc-loaded protein remains effectively unfolded. Possible implications of these findings to the functioning of PDEgamma are discussed.
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Affiliation(s)
- Vladimir N Uversky
- Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Russia.
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8
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Zelent B, Veklich Y, Murray J, Parkes JH, Gibson S, Liebman PA. Rapid irreversible G protein alpha subunit misfolding due to intramolecular kinetic bottleneck that precedes Mg2+ "lock" after GTP/GDP exchange. Biochemistry 2001; 40:9647-56. [PMID: 11583165 DOI: 10.1021/bi010272u] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Stoichiometric exchange of GTP for GDP on heterotrimeric G protein alpha (Galpha) subunits is essential to most hormone and neurotransmitter initiated signal transduction. Galphas are stably activated in a Mg2+ complex with GTPgammaS, a nonhydrolyzable GTP analogue that is reported to bind Galpha, with very high affinity. Yet, it is common to find that substantial amounts (30-90%) of purified G proteins cannot be activated. Inactivatable G protein has heretofore been thought to have become "denatured" during formation of the obligatory nucleotide-free or empty (MT) Galpha-state that is intermediary to GDP/GTP exchange at a single binding site. We find Galpha native secondary and tertiary structure to persist during formation of the irreversibly inactivatable state of transducin. MT Galpha is therefore irreversibly misfolded rather than denatured. Inactivation by misfolding is found to compete kinetically with protective but weak preequilibrium nucleotide binding at micromolar ambient GTPgammaS concentrations. Because of the weak preequilibrium, quantitative protection against Galpha aggregation is only achieved at free nucleotide concentrations 10-100 times higher than those commonly employed in G protein radio-nucleotide binding studies. Initial GTP protection is also poor because of the extreme slowness of an intramolecular Galpha refolding step (isomerization) necessary for GTP sequestration after its weak preequilibrium binding. Of the two slowly interconverting Galpha x GTP isomers described here, only the second can bind Mg2+, "locking" GTP in place with a large net rise in GTP binding affinity. A companion Galpha x GDP isomerization reaction is identified as the cause of the very slow spontaneous GDP dissociation that characterizes G protein nucleotide exchange and low spontaneous background activity in the absence of GPCR activation. Galpha x GDP and Galpha x GTP isomerization reactions are proposed as the dual target for GPCR catalysis of nucleotide exchange.
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Affiliation(s)
- B Zelent
- Department of Biochemistry and Biophysics, University of Pennsylvania Medical Center, Philadelphia 19104-6059, USA
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9
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Min KC, Gravina SA, Sakmar TP. Reconstitution of the vertebrate visual cascade using recombinant heterotrimeric transducin purified from Sf9 cells. Protein Expr Purif 2000; 20:514-26. [PMID: 11087692 DOI: 10.1006/prep.2000.1326] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
For reconstitution studies with rhodopsin and cGMP phosphodiesterase (PDE), all three subunits of heterotrimeric transducin (T alpha beta gamma) were simultaneously expressed in Sf9 cells at high levels using a baculovirus expression system and purified to homogeneity. Light-activated rhodopsin catalyzed the loading of purified recombinant T alpha with GTP gamma S. In vitro reconstitution of rhodopsin, recombinant transducin, and PDE in detergent solution resulted in cGMP hydrolysis upon illumination, demonstrating that recombinant transducin was able to activate PDE. The rate of cGMP hydrolysis by PDE as a function of GTP gamma S-loaded recombinant transducin (T(*)) concentration gave a Hill coefficient of approximately 2, suggesting that the activation of PDE by T(*) was cooperatively regulated. Furthermore, the kinetic rate constants for the activation of PDE by T(*) suggested that only the complex of PDE with two T(*) molecules, PDE. T(2)(*), was significantly catalytically active under the conditions of the assay. We conclude that the model of essential coactivation best describes the activation of PDE by T(*) in a reconstituted vertebrate visual cascade using recombinant heterotrimeric transducin.
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Affiliation(s)
- K C Min
- Laboratory of Molecular Biology and Biochemistry, Howard Hughes Medical Institute, Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
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10
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Gibson SK, Parkes JH, Liebman PA. Phosphorylation modulates the affinity of light-activated rhodopsin for G protein and arrestin. Biochemistry 2000; 39:5738-49. [PMID: 10801324 DOI: 10.1021/bi991857f] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Reduced effector activity and binding of arrestin are widely accepted consequences of GPCR phosphorylation. However, the effect of receptor multiphosphorylation on G protein activation and arrestin binding parameters has not previously been quantitatively examined. We have found receptor phosphorylation to alter both G protein and arrestin binding constants for light-activated rhodopsin in proportion to phosphorylation stoichiometry. Rod disk membranes containing different average receptor phosphorylation stoichiometries were combined with G protein or arrestin, and titrated with a series of brief light flashes. Binding of G(t) or arrestin to activated rhodopsin augmented the 390 nm MII optical absorption signal by stabilizing MII as MII.G or MII.Arr. The concentration of active arrestin or G(t) and the binding constant of each to MII were determined using a nonlinear least-squares (Simplex) reaction model analysis of the titration data. The binding affinity of phosphorylated MII for G(t) decreased while that for arrestin increased with each added phosphate. G(t) binds more tightly to MII at phosphorylation levels less than or equal to two phosphates per rhodopsin; at higher phosphorylation levels, arrestin binding is favored. However, arrestin was found to bind much more slowly than G(t) at all phosphorylation levels, perhaps allowing time for phosphorylation to gradually reduce receptor-G protein interaction before arrestin capping of rhodopsin. Sensitivity of the binding constants to ionic strength suggests that a strong membrane electrostatic component is involved in both the reduction of G(t) binding and the increase of arrestin binding with increasing rhodopsin phosphorylation.
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Affiliation(s)
- S K Gibson
- Department of Biochemistry and Biophysics, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104-6059, USA
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11
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Parkes JH, Gibson SK, Liebman PA. Temperature and pH dependence of the metarhodopsin I-metarhodopsin II equilibrium and the binding of metarhodopsin II to G protein in rod disk membranes. Biochemistry 1999; 38:6862-78. [PMID: 10346908 DOI: 10.1021/bi9827666] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The equilibria between metarhodopsins I and II (MI and MII) and the binding of MII to retinal G protein (G) were investigated, using the dual wavelength absorbance response of rod disk membrane (RDM) suspensions to a series of small bleaches, together with a nonlinear least-squares fitting procedure that decouples the two reactions. This method has been subjected to a variety of theoretical and experimental tests that establish its validity. The two equilibrium constants, the amount of active G protein (that can bind to and stabilize MII) and the fraction bleached by the flash, have been determined without a priori assumptions about these values, at temperatures between 0 and 15 degrees C and pHs from 6.2 to 8.2. Binding of G to MII in normal RDM exhibits 1:1 stoichiometry (not cooperative), relatively weak, 2-4 x 10(4) M-1 affinity on the membrane, with a pH dependence maximal at pH 7.6, and a low thermal coefficient. The reported amount of active G remained constant even when its binding constant was reduced more than 10-fold at low pH. The method can readily be applied to the binding of MII to other proteins or polypeptides that stabilize its conformation as MII. It appears capable of determining many of the essential physical constants of G protein coupled receptor interaction with immediate signaling partners and the effect of perturbation of environmental parameters on these constants.
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Affiliation(s)
- J H Parkes
- Department of Biochemistry and Biophysics, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104-6059, USA
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12
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Klinker JF, Seifert R. Nucleoside diphosphate kinase activity in soluble transducin preparations biochemical properties and possible role of transducin-beta as phosphorylated enzyme intermediate. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 261:72-80. [PMID: 10103035 DOI: 10.1046/j.1432-1327.1999.00209.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Known nucleoside diphosphate kinases (NDPKs) are oligomers of 17-23-kDa subunits and catalyze the reaction N1TP + N2DP --> N1DP + N2TP via formation of a histidine-phosphorylated enzyme intermediate. NDPKs are involved in the activation of heterotrimeric GTP-binding proteins (G-proteins) by catalyzing the formation of GTP from GDP, but the properties of G-protein-associated NDPKs are still incompletely known. The aim of our present study was to characterize NDPK in soluble preparations of the retinal G-protein transducin. The NDPK is operationally referred to as transducin-NDPK. Like known NDPKs, transducin-NDPK utilizes NTPs and phosphorothioate analogs of NTPs as substrates. GDP was a more effective phosphoryl group acceptor at transducin-NDPK than ADP and CDP, and guanosine 5'-[gamma-thio]triphosphate (GTP[S]) was a more effective thiophosphoryl group donor than adenosine 5'-[gamma-thio]triphosphate (ATP[S]). In contrast with their action on known NDPKs, mastoparan and mastoparan 7 had no stimulatory effect on transducin-NDPK. Guanosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppG) potentiated [3H]GTP[S] formation from [3H]GDP and ATP[S] but not [3H]GTP[S] formation from [3H]GDP and GTP[S]. Depending on the thiophosphoryl group acceptor and donor, [3H]NTP[S] formation was differentially regulated by Mg2+, Mn2+, Co2+, Ca2+ and Zn2+. [gamma-32P]ATP and [gamma-32P]GTP [32P]phosphorylated, and [35S]ATP[S] [35S]thiophosphorylated, a 36-kDa protein comigrating with transducin-beta. p[NH]ppG potentiated [35S]thiophosphorylation of the 36-kDa protein. 32P-labeling of the 36-kDa protein showed characteristics of histidine phosphorylation. There was no evidence for (thio)phosphorylation of 17-23-kDa proteins. Our data show the following: (a) soluble transducin preparations contain a GDP-prefering and guanine nucleotide-regulated NDPK; (b) transducin-beta may serve as a (thio)phosphorylated NDPK intermediate; (c) transducin-NDPK is distinct from known NDPKs and may consist of multiple kinases or a single kinase with multiple regulatory domains.
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Affiliation(s)
- J F Klinker
- Institut für Pharmakologie, Freie Universität Berlin, Germany
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13
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Berger AL, Cerione RA, Erickson JW. Delineation of two functionally distinct gammaPDE binding sites on the bovine retinal cGMP phosphodiesterase by a mutant gammaPDE subunit. Biochemistry 1999; 38:1293-9. [PMID: 9930990 DOI: 10.1021/bi981683m] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The gamma subunit of the retinal cGMP phosphodiesterase (gammaPDE) acts as an inhibitor of phosphodiesterase (PDE) catalytic activity and mediates enzyme regulation by the alpha subunit of the GTP-binding protein transducin (alphaT). In this work, we describe a full length, doubly point-mutated gamma subunit, C68S, Y84C gammaPDE, which binds to PDE with increased affinity but has a decreased ability to inhibit the enzyme. Fluorescence studies monitoring the competition between wild-type gammaPDE and the C68S, Y84C gammaPDE mutant suggest that the mutant gammaPDE binds with high affinity to only half of the total sites occupied by wild-type gammaPDE. Competition studies between wild-type gammaPDE and the mutant further suggest that the wild-type protein is able to fully inhibit PDE activity even when the mutant gammaPDE occupies its high-affinity binding site on PDE. Taken together, our findings are consistent with a model in which there are two distinguishable binding sites for gammaPDE on the PDE enzyme but that only one of the two sites mediates PDE inhibition.
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Affiliation(s)
- A L Berger
- College of Veterinary Medicine, Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA
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14
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Liu W, Clark WA, Sharma P, Northup JK. Mechanism of allosteric regulation of the rod cGMP phosphodiesterase activity by the helical domain of transducin alpha subunit. J Biol Chem 1998; 273:34284-92. [PMID: 9852093 DOI: 10.1074/jbc.273.51.34284] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The G protein alpha subunit (Galpha) is composed of two distinct folding domains: a GTP-binding Ras-like domain and an alpha helical domain (HD). We have recently reported that the helical domain (HDt) of the vertebrate visual transducin alpha subunit (Galphat) synergizes activation of retinal cyclic GMP phosphodiesterase (PDE) by activated Galphat (Liu, W., and Northup, J. K., (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 12878-12883). Here, we examine the molecular basis for this HD-based signaling regulation, and we provide a new model for the activation of the target effector. The HD proteins derived from visual transducin or taste gustducin alpha subunits, but no other Galpha HD proteins, each attenuate the PDE catalytic core (Palphabeta) and synergize Galphat stimulation of the holoPDE (Palphabetagamma2) with similar apparent affinities. The data from studies of both HDt-mediated attenuation and stimulation indicate that the HDt and the PDE inhibitory subunit (Pgamma) interact with PDE at independent sites and that Palphabeta contains the binding sites for HD. The saturation of both processes by HDt displays positive cooperativity with Hill coefficients of 1.5 for the attenuation of Palphabeta activity and 2.1 for synergism of holoPDE activation. Our data suggest the that Galphat-HDt regulates PDE by allosterically decreasing the affinity of Palphabeta for Pgamma and thus simultaneously facilitating the interaction of the activated Galphat-Ras-like domain with Pgamma. Thus, we propose a new model for the high efficiency of PDE activation as well as deactivation, and, overall, a novel mechanism for controlling fidelity, sensitivity, and efficacy of G protein signaling.
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Affiliation(s)
- W Liu
- Laboratory of Cellular Biology, NIDCD, National Institutes of Health, Rockville, Maryland 20850, USA
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15
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Liu W, Northup JK. The helical domain of a G protein alpha subunit is a regulator of its effector. Proc Natl Acad Sci U S A 1998; 95:12878-83. [PMID: 9789008 PMCID: PMC23639 DOI: 10.1073/pnas.95.22.12878] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The alpha subunit (Galpha) of heterotrimeric G proteins is a major determinant of signaling selectivity. The Galpha structure essentially comprises a GTPase "Ras-like" domain (RasD) and a unique alpha-helical domain (HD). We used the vertebrate phototransduction model to test for potential functions of HD and found that the HD of the retinal transducin Galpha (Galphat) and the closely related gustducin (Galphag), but not Galphai1, Galphas, or Galphaq synergistically enhance guanosine 5'-gamma[-thio]triphosphate bound Galphat (GalphatGTPgammaS) activation of bovine rod cGMP phosphodiesterase (PDE). In addition, both HDt and HDg, but not HDi1, HDs, or HDq attenuate the trypsin-activated PDE. GalphatGDP and HDt attenuation of trypsin-activated PDE saturate with similar affinities and to an identical 38% of initial activity. These data suggest that interaction of intact Galphat with the PDE catalytic core may be caused by the HD moiety, and they indicate an independent site(s) for the HD moiety of Galphat within the PDE catalytic core in addition to the sites for the inhibitory Pgamma subunits. The HD moiety of GalphatGDP is an attenuator of the activated catalytic core, whereas in the presence of activated GalphatGTPgammaS the independently expressed HDt is a potent synergist. Rhodopsin catalysis of Galphat activation enhances the PDE activation produced by subsaturating levels of Galphat, suggesting a HD-moiety synergism from a transient conformation of Galphat. These results establish HD-selective regulations of vertebrate retinal PDE, and they provide evidence demonstrating that the HD is a modulatory domain. We suggest that the HD works in concert with the RasD, enhancing the efficiency of G protein signaling.
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Affiliation(s)
- W Liu
- Laboratory of Cellular Biology, National Institute on Deafness and Other Communication Disorders, 5 Research Court, Rockville, MD 20850, USA
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16
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Klinker JF, Seifert R. Functionally nonequivalent interactions of guanosine 5'-triphosphate, inosine 5'-triphosphate, and xanthosine 5'-triphosphate with the retinal G-protein, transducin, and with Gi-proteins in HL-60 leukemia cell membranes. Biochem Pharmacol 1997; 54:551-62. [PMID: 9337071 DOI: 10.1016/s0006-2952(97)00205-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
G-proteins mediate signal transfer from receptors to effector systems. In their guanosine 5'-triphosphate (GTP)-bound form, G-protein alpha-subunits activate effector systems. Termination of G-protein activation is achieved by the high-affinity GTPase [E.C. 3.6.1.-] of their alpha-subunits. Like GTP, inosine 5'-triphosphate (ITP) and xanthosine 5'-triphosphate (XTP) can support effector system activation. We studied the interactions of GTP, ITP, and XTP with the retinal G-protein, transducin (TD), and with G-proteins in HL-60 leukemia cell membranes. TD hydrolyzed nucleoside 5'-triphosphates (NTPs) in the order of efficacy GTP > ITP > XTP. NTPs eluted TD from rod outer segment disk membranes in the same order of efficacy. ITP and XTP competitively inhibited TD-catalyzed GTP hydrolysis. In HL-60 membranes, the chemoattractants N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) and leukotriene B4 (LTB4) effectively activated GTP and ITP hydrolysis by Gi-proteins. fMLP and LTB4 were at least 10-fold more potent activators of ITPase than of GTPase. Complement C5a effectively activated the GTPase of Gi-proteins but was only a weak stimulator of ITPase. The potency of C5a to activate GTP and ITP hydrolysis was similar. The fMLP-stimulated GTPase had a lower Km value than the fMLP-stimulated ITPase, whereas the opposite was true for the Vmax values. fMLP, C5a, and LTB4 did not stimulate XTP hydrolysis. Collectively, our data show that GTP, ITP, and XTP bind to G-proteins with different affinities, that G-proteins hydrolyze NTPs with different efficacies, and that chemoattractants stimulate GTP and ITP hydrolysis by Gi-proteins in a receptor-specific manner. On the basis of our results and the data in the literature, we put forward the hypothesis that GTP, ITP, and XTP act as differential signal amplifiers and signal sorters at the G-protein level.
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Affiliation(s)
- J F Klinker
- Institut für Neuropsychopharmakologie, Freie Universität Berlin, Germany
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17
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Klinker JF, Seifert R, Damm H, Rommelspacher H. Activation by beta-carbolines of G-proteins in HL-60 membranes and the bovine retinal G-protein transducin in a receptor-independent manner. Biochem Pharmacol 1997; 53:1621-6. [PMID: 9264314 DOI: 10.1016/s0006-2952(97)00065-8] [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: 02/05/2023]
Abstract
Naturally occurring beta-carbolines are lipophilic compounds which show psychotropic and physiological effects in mammals. They bind to distinct high-affinity binding sites in various mammalian tissues. However, the mechanism by which the beta-carbolines affect transmembrane signal transduction processes is still unknown. Since beta-carbolines are cationic-amphiphilic substances and since such substances are known to activate heterotrimeric regulatory guanine nucleotide binding proteins (G-proteins) in a receptor-independent manner, we put forward the hypothesis that beta-carbolines act directly on G-proteins. Therefore, we investigated the ability of beta-carbolines to stimulate high-affinity GTP hydrolysis in membranes of dibutyryl-cAMP differentiated HL-60 cells and of the purified bovine G-protein, transducin (TD). The beta-carbolines norharman and harman, stimulated the GTPase in HL-60 membranes with an EC50 of 410 microM and 450 microM, respectively, and a maximum effect at 1 mM each. Norharman and harman stimulated the GTPase of TD with an EC50 of 60 microM and 300 microM, and a maximum at 1 mM for both compounds. The stimulatory effect of norharman in HL-60 membranes was pertussis toxin-sensitive. Structure/activity characteristics of the beta-carbolines showed a specificity of norharman to stimulate the GTPase of TD, because norharman activated GTP hydrolysis in HL-60 membranes approximately 7 times less potently than that of TD. Norharman was a five-fold more potent activator of TD than tetrahydronorharman. Hydroxylation of the beta-carboline molecule in position 6 led to a loss of GTPase-activating properties. Our data suggest that naturally occurring beta-carbolines are a novel class of receptor-independent G-protein activating substances. This mechanism could contribute to their diverse biological effects.
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Affiliation(s)
- J F Klinker
- Howard Hughes Medical Institute, Beckman Center for Molecular and Genetic Medicine, Stanford University Medical Center, CA 94305, USA
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18
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Berger AL, Cerione RA, Erickson JW. Real time conformational changes in the retinal phosphodiesterase gamma subunit monitored by resonance energy transfer. J Biol Chem 1997; 272:2714-21. [PMID: 9006909 DOI: 10.1074/jbc.272.5.2714] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The gamma subunit of the retinal cGMP phosphodiesterase (gammaPDE) acts as an inhibitor of phosphodiesterase (PDE) catalytic activity and mediates enzyme regulation by the alpha subunit of the GTP-binding protein transducin (alphaT). In order to characterize conformational changes in the 87-amino acid gammaPDE subunit that may accompany the activation of the holoenzyme, gammaPDE was labeled with the fluorescent probes 5-iodoacetamidofluorescein and eosin-5-isothiocyanate for use in resonance energy transfer measurements. 5-Iodoacetamidofluorescein specifically labeled a cysteine residue at position 68 and served as a resonance energy transfer donor. The site of modification of eosin-5-isothiocyanate, which served as the resonance energy transfer acceptor, was determined to be within the first seven residues of the amino terminus of gammaPDE. Energy transfer between the labeled sites on free, unbound gammaPDE indicated that they were separated by a distance of 63 A, consistent with a random conformation. Upon binding the catalytic alphabeta subunits of the PDE, the distance between the two probes on gammaPDE increased to 77 A. Binding of the labeled gammaPDE by alphaT.guanosine 5'-3-O-(thio)triphosphate did not affect the distance between the probes under conditions where the PDE was activated. These data are consistent with the view that the binding of activated alphaT to gammaPDE, which is essential for the stimulation of PDE activity, does not impart significant alterations in the tertiary structure of the gammaPDE molecule. They also support a model for PDE activation that places active alphaT in a complex with the holoenzyme.
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Affiliation(s)
- A L Berger
- Department of Pharmacology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
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19
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Helmreich EJ, Hofmann KP. Structure and function of proteins in G-protein-coupled signal transfer. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1286:285-322. [PMID: 8982287 DOI: 10.1016/s0304-4157(96)00013-5] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- E J Helmreich
- Department of Clinical Biochemistry and Pathobiochemistry, University of Würzburg, Germany
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20
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Liu Y, Arshavsky VY, Ruoho AE. Interaction sites of the COOH-terminal region of the gamma subunit of cGMP phosphodiesterase with the GTP-bound alpha subunit of transducin. J Biol Chem 1996; 271:26900-7. [PMID: 8900174 DOI: 10.1074/jbc.271.43.26900] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
In photoreceptor cells, visual transduction occurs through photoexcitation of rhodopsin, GTP activation of the alpha subunit of transducin, and interaction between GTP-bound transducin alpha subunit and the inhibitory gamma subunit of phosphodiesterase. The gamma subunit of phosphodiesterase, in turn, accelerates the hydrolysis of GTP on the alpha subunit of transducin. Within the COOH-terminal residues (46-87) of the phosphodiesterase gamma subunit, Trp-70 has been implicated in phosphodiesterase activation, transducin alpha subunit-phosphodiesterase gamma subunit interaction, and the GTP hydrolysis accelerating activity. We have derivatized the phosphodiesterase gamma subunit with a reversible photoactivatable reagent, [125I]N-[(3-iodo-4-azidophenylpropionamido-S-(2-thiopyridyl) ]cysteine ([125I]ACTP), at cysteine (Cys-68). A light-dependent, cross-linked complex of guanosine 5'-(gamma-thio)triphosphate-bound transducin alpha subunit and ACTPderivatized phosphodiesterase gamma subunit formed after photolysis of a 1:1 stoichiometic complex of the two proteins. The specificity of complex formation between the transducin alpha subunit and the phosphodiesterase gamma subunit was demonstrated by specific protection by the C68A mutant of the phosphodiesterase gamma subunit. The cross-linked complex was treated with beta-mercaptoethanol to transfer the 125I photomoiety from the phosphodiesterase gamma subunit to the transducin alpha subunit. Combined techniques involving electrophoresis, chemical and enzymatic cleavage, and chemical and radiosequencing were used to identify photoinsertion sites on the alpha3 and alpha4/beta6 regions of the transducin alpha subunit. Three photo-labeled residues, His-244 (alpha3 helix), Met-308, and Arg-310 (alpha4/beta6 interface), were specifically identified as photoinsertion sites. Utilizing the crystal structure coordinates of the GTP-bound transducin alpha subunit and molecular modeling, we conclude that Cys-68 of the phosphodiesterase gamma subunit is located at a position between the exposed face of the alpha3 and alpha4 helices of the transducin alpha subunit. We propose that the phosphodiesterase gamma subunit interacts with GTP-bound transducin alpha subunit at multiple sites in which the cysteine 68 to tryptophan 70 sequence of the phosphodiesterase gamma subunit, which is critical for GTP hydrolysis accelerating activity, interacts in the alpha3/alpha4/beta6 region of GTP-bound transducin alpha subunit.
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Affiliation(s)
- Y Liu
- Department of Pharmacology, University Wisconsin Medical School, Madison, Wisconsin 53706, USA
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21
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Tsang SH, Gouras P, Yamashita CK, Kjeldbye H, Fisher J, Farber DB, Goff SP. Retinal degeneration in mice lacking the gamma subunit of the rod cGMP phosphodiesterase. Science 1996; 272:1026-9. [PMID: 8638127 PMCID: PMC2757426 DOI: 10.1126/science.272.5264.1026] [Citation(s) in RCA: 136] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The retinal cyclic guanosine 3',5'-monophosphate (cGMP) phosphodiesterase (PDE) is a key regulator of phototransduction in the vertebrate visual system. PDE consists of a catalytic core of alpha and beta subunits associated with two inhibitory gamma subunits. A gene-targeting approach was used to disrupt the mouse PDEgamma gene. This mutation resulted in a rapid retinal degeneration resembling human retinitis pigmentosa. In homozygous mutant mice, reduced rather than increased PDE activity was apparent; the PDEalphabeta dimer was formed but lacked hydrolytic activity. Thus, the inhibitory gamma subunit appears to be necessary for integrity of the photoreceptors and expression of PDE activity in vivo.
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Affiliation(s)
- S H Tsang
- Howard Hughes Medical Institute, Department of Biochemistry and Molecular Biophysics, Columbia University, College of Physicians and Surgeons, New York 10032, USA
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22
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Burde R, Dippel E, Seifert R. Receptor-independent G protein activation may account for the stimulatory effects of first-generation H1-receptor antagonists in HL-60 cells, basophils, and mast cells. Biochem Pharmacol 1996; 51:125-31. [PMID: 8615880 DOI: 10.1016/0006-2952(95)02123-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The first-generation histamine H1-receptor antagonists, chlorpheniramine (CPHE) and diphenhydramine (DPH), may activate histamine release from basophils and mast cells. Because CPHE and DPH are cationic-amphiphilic and because several substances with such physicochemical properties activate heterotrimeric regulatory guanine nucleotide-binding proteins (G-proteins) in a receptor-independent manner, we asked the question of whether or not H1-receptor antagonists could be G-protein activators as well. In dibutyryl cAMP-differentiated HL-60 cells, CPHE and DPH increased cytosolic Ca2+ concentration and azurophilic granule release in pertussis toxin (PTX)-sensitive manners. In HL-60 membranes, PTX-sensitive stimulations of GTPase [E.C. 3.6.1.] and binding of guanosine 5'-[gamma-thio]triphosphate by H1 receptor antagonists were observed. CPHE and DPH also increased GTP hydrolysis by the purified PTX-sensitive G-protein, transducin. In all-trans-retinoic acid-differentiated HL-60 cells and rat basophilic leukemia cells (RBL 2H3 cells), H1-receptor antagonists induced, unlike in dibutyryl cAMP-differentiated HL-60 cells, Ca2+ influx without Ca2+ mobilization from intracellular stores. CPHE and DPH also induced serotonin release from RBL 2H3 cells. Our data indicate that first-generation H1-receptor antagonists are receptor-independent G-protein activators and that such a mechanism of action accounts for their stimulatory effects in HL-60 cells, basophils, and mast cells.
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Affiliation(s)
- R Burde
- Institut für Pharmakologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Germany
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23
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Peter Hofmann K, Heck M. Light-induced protein-protein interactions on the rod photoreceptor disc membrane. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1874-5342(07)80006-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
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24
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Mittal R, Cerione RA, Erickson JW. Aluminum fluoride activation of bovine transducin induces two distinct conformational changes in the alpha subunit. Biochemistry 1994; 33:10178-84. [PMID: 7520280 DOI: 10.1021/bi00199a046] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We have used resonance energy transfer to read out the interactions of the alpha subunit of transducin (alpha T) with the transducin beta gamma subunit complex (beta gamma T) and to compare the rate of aluminum fluoride-induced alpha T activation, as reflected by the enhancement of the alpha T tryptophan fluorescence, with the rate for the dissociation of holotransducin into its component subunits. Specifically, a beta gamma T complex that was labeled with 5-(iodoacetamido)fluorescein (IAF-beta gamma T) served as a donor for resonance energy transfer and an alpha T-GDP species labeled with eosin 5-isothiocyanate (EITC-alpha TGDP) served as the acceptor. The quenching of IAF-beta gamma T fluorescence emission by the addition of the EITC-alpha TGDP species, due to resonance energy transfer between the IAF and EITC moieities, ranged from 10% to 15%. The association of the transducin subunits was rapid (i.e., within the time period of mixing) and dose-dependent, yielding an apparent Kd of approximately 150 nM for the alpha TGDP/beta gamma T interaction. Unexpectedly, we find that the dissociation of IAF-beta gamma T from an aluminum fluoride-activated alpha TGDP/IAF-beta gamma T complex occurs prior to the onset of the intrinsic fluorescence changes in alpha T that accompany activation of this subunit. Thus, there are at least two structural changes in alpha T that result from the occupation of the gamma-phosphate position in the nucleotide binding cleft of alpha T by aluminum fluoride.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R Mittal
- Department of Pharmacology, Cornell University, Ithaca, New York 14853-6401
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25
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Kutuzov M, Pfister C. Activation of the retinal cGMP-specific phosphodiesterase by the GDP-loaded alpha-subunit of transducin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 220:963-71. [PMID: 8143750 DOI: 10.1111/j.1432-1033.1994.tb18700.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The interaction of the GDP-bound form of the alpha-subunit of transducin (T alpha GDP) with the cGMP-specific phosphodiesterase, the effector enzyme in the visual system, has been studied. T alpha GDP is demonstrated to be able to activate the phosphodiesterase: (a) the basal activity in suspensions of dark-adapted retinal rod outer segments, examined in the absence of GTP, was found to be inhibited by binding of transducin to activated rhodopsin (Rh*) and by the complex of the beta- and gamma-subunits of transducin (T beta gamma); (b) purified T alpha GDP is able to activate phosphodiesterase in the presence of membranes; (c) no activation is obtained either with holotransducin (T alpha GDP T beta gamma) or with T alpha GDP in the presence of excess T beta gamma to prevent dissociation of TGDP. The maximal level of phosphodiesterase activation reached with T alpha GDP (about 1500 mol cGMP/mol phosphodiesterase-1.s-1) is similar to that obtained through the 'classical' activation by T alpha GTP whereas the apparent affinity of T alpha GDP for phosphodiesterase (Kd about 50 microM) is much lower than that of T alpha GTP. Our data suggest that GTP hydrolysis itself does not inactivate T alpha. The role of T beta gamma to sequester T alpha is therefore of critical importance for phosphodiesterase inactivation. Our results support observations on the regulation of adenylyl cyclase by G-proteins, which suggested the ability of the free alpha-subunits loaded with GDP to activate their effectors.
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Affiliation(s)
- M Kutuzov
- Département de Biologie Moléculaire et Structurale, Centre d'Etudes Nucléaires, Grenoble, France
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26
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Rarick HM, Artemyev NO, Mills JS, Skiba NP, Hamm HE. Specific peptide probes for G-protein interaction with effectors. Methods Enzymol 1994; 238:13-28. [PMID: 7799779 DOI: 10.1016/0076-6879(94)38004-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- H M Rarick
- Department of Physiology and Biophysics, University of Illinois at Chicago 60612
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27
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Enhancement by phosphodiesterase subunits of the rate of GTP hydrolysis by transducin in bovine retinal rods. Essential role of the phosphodiesterase catalytic core. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)74323-3] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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28
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Pfister C, Bennett N, Bruckert F, Catty P, Clerc A, Pagès F, Deterre P. Interactions of a G-protein with its effector: transducin and cGMP phosphodiesterase in retinal rods. Cell Signal 1993; 5:235-41. [PMID: 7688544 DOI: 10.1016/0898-6568(93)90015-e] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- C Pfister
- Laboratoire de Biophysique Moléculaire et Cellulaire, Unité Associée 520 du Centre National de la Recherche Scientifique, Centre d'Etudes Nucléaires, Grenoble, France
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29
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Lipkin VM, Bondarenko VA, Zagranichny VE, Dobrynina LN, Muradov KG. Site-directed mutagenesis of the cGMP phosphodiesterase gamma subunit from bovine rod outer segments: role of separate amino acid residues in the interaction with catalytic subunits and transducin alpha subunit. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1176:250-6. [PMID: 8385997 DOI: 10.1016/0167-4889(93)90052-q] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The recombinant and 21 mutant phosphodiesterase (PDE) gamma subunit (PDE gamma) genes were expressed by sequential transcription and translation in vitro. Inhibitory properties of these mutants and their interactions with PDE catalytic and transducin alpha subunits were studied. The interaction of the PDE gamma subunit with the catalytic ones proceeds in two steps--primary binding and inhibition. The central region of the PDE gamma molecule enriched with the basic amino acid residues (particularly, Lys-29, Lys-31 and Arg-33), is involved in the primary binding, and the PDE gamma C-terminus plays the key role in inhibition. The spatial orientation of the C-terminus is of great importance here. The PDE gamma C-terminus also affects binding to catalytic moieties.
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Affiliation(s)
- V M Lipkin
- Branch of Shemyakin Institute of Bioorganic Chemistry, Russian Academy of Sciences, Pushchino, Moscow Region
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30
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31
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Erickson J, Cerione R. Regulation of the cGMP phosphodiesterase in bovine rod outer segments. Use of resonance energy transfer to distinguish between associative and dissociative activation mechanisms. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53697-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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32
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Artemyev N, Rarick H, Mills J, Skiba N, Hamm H. Sites of interaction between rod G-protein alpha-subunit and cGMP-phosphodiesterase gamma-subunit. Implications for the phosphodiesterase activation mechanism. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)74006-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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33
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Interaction between cGMP-phosphodiesterase and transducin alpha-subunit in retinal rods. A cross-linking study. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)88649-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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34
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Erickson MA, Robinson P, Lisman J. Deactivation of visual transduction without guanosine triphosphate hydrolysis by G protein. Science 1992; 257:1255-8. [PMID: 1519062 DOI: 10.1126/science.1519062] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
G proteins couple receptors to their target enzymes in many signal transduction cascades. It has generally been thought that deactivation of such cascades cannot occur without the hydrolysis of guanosine triphosphate (GTP) by G protein. This requirement has now been reexamined in both vertebrate and invertebrate phototransduction. Results indicate that GTP hydrolysis is not required for deactivation. Evidence is presented for an alternative model in which the target enzyme is deactivated by an inhibitory factor that is available even when GTP hydrolysis is blocked.
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Affiliation(s)
- M A Erickson
- Department of Biochemistry, Brandeis University, Waltham, MA 02254
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35
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Immunologic evidence that vacuolar H+ ATPases with heterogeneous forms of Mr = 31,000 subunit have different membrane distributions in mammalian kidney. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)50184-3] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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36
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Yamazaki A, Hayashi F, Tatsumi M, Bitensky MW, George JS. Interactions between the subunits of transducin and cyclic GMP phosphodiesterase in Rana catesbiana rod photoreceptors. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38431-5] [Citation(s) in RCA: 96] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Voaden MJ, Willmott NJ. Evidence for reduced binding of cyclic GMP to cyclic GMP phosphodiesterase in photoreceptors of mice heterozygous for the rd gene. Curr Eye Res 1990; 9:643-51. [PMID: 2170076 DOI: 10.3109/02713689008999579] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The binding of radiolabelled cGMP to rod outer segment proteins has been investigated in mice, heterozygous for the recessive rd gene that leads to rod dysplasia. Two binding sites were detected, by Scatchard analysis, in a crude cGMP phosphodiesterase fraction, extracted with an EDTA wash from outer segments. Affinities were normal but the capacity of both was reduced 25-35%. Photoaffinity labelling with 3H-cGMP, followed by SDS PAGE and fluorography, suggested that cGMP PDE was the principal binding component in the extracts. If the finding reflects cGMP binding in situ, it might explain the 30-40% lower than normal level of cGMP found in the +/rd retina. Visual pigment has been regenerated in isolated normal and heterozygotic retinas by the application of active isomers of cis-retinal, and the time course of cGMP recovery to 'dark-adapted' levels monitored. The increase in the concentration of cGMP was significantly delayed as compared to that of rhodopsin. No differences in time course or kinetics of recovery were discerned between the two genotypes.
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Affiliation(s)
- M J Voaden
- Department of Visual Science, University of London, UK
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Phillips WJ, Trukawinski S, Cerione RA. An Antibody-induced Enhancement of the Transducin-stimulated Cyclic GMP Phosphodiesterase Activity. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)84759-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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