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Gao Y, Eskici G, Ramachandran S, Poitevin F, Seven AB, Panova O, Skiniotis G, Cerione RA. Structure of the Visual Signaling Complex between Transducin and Phosphodiesterase 6. Mol Cell 2020; 80:237-245.e4. [PMID: 33007200 DOI: 10.1016/j.molcel.2020.09.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 08/04/2020] [Accepted: 09/09/2020] [Indexed: 12/21/2022]
Abstract
Heterotrimeric G proteins communicate signals from activated G protein-coupled receptors to downstream effector proteins. In the phototransduction pathway responsible for vertebrate vision, the G protein-effector complex is composed of the GTP-bound transducin α subunit (GαT·GTP) and the cyclic GMP (cGMP) phosphodiesterase 6 (PDE6), which stimulates cGMP hydrolysis, leading to hyperpolarization of the photoreceptor cell. Here we report a cryo-electron microscopy (cryoEM) structure of PDE6 complexed to GTP-bound GαT. The structure reveals two GαT·GTP subunits engaging the PDE6 hetero-tetramer at both the PDE6 catalytic core and the PDEγ subunits, driving extensive rearrangements to relieve all inhibitory constraints on enzyme catalysis. Analysis of the conformational ensemble in the cryoEM data highlights the dynamic nature of the contacts between the two GαT·GTP subunits and PDE6 that supports an alternating-site catalytic mechanism.
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Affiliation(s)
- Yang Gao
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Gözde Eskici
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Sekar Ramachandran
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA; Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Frédéric Poitevin
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Alpay Burak Seven
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Ouliana Panova
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Georgios Skiniotis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Richard A Cerione
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA; Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA.
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2
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Qureshi BM, Behrmann E, Schöneberg J, Loerke J, Bürger J, Mielke T, Giesebrecht J, Noé F, Lamb TD, Hofmann KP, Spahn CMT, Heck M. It takes two transducins to activate the cGMP-phosphodiesterase 6 in retinal rods. Open Biol 2018; 8:180075. [PMID: 30068566 PMCID: PMC6119865 DOI: 10.1098/rsob.180075] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 07/06/2018] [Indexed: 12/21/2022] Open
Abstract
Among cyclic nucleotide phosphodiesterases (PDEs), PDE6 is unique in serving as an effector enzyme in G protein-coupled signal transduction. In retinal rods and cones, PDE6 is membrane-bound and activated to hydrolyse its substrate, cGMP, by binding of two active G protein α-subunits (Gα*). To investigate the activation mechanism of mammalian rod PDE6, we have collected functional and structural data, and analysed them by reaction-diffusion simulations. Gα* titration of membrane-bound PDE6 reveals a strong functional asymmetry of the enzyme with respect to the affinity of Gα* for its two binding sites on membrane-bound PDE6 and the enzymatic activity of the intermediary 1 : 1 Gα* · PDE6 complex. Employing cGMP and its 8-bromo analogue as substrates, we find that Gα* · PDE6 forms with high affinity but has virtually no cGMP hydrolytic activity. To fully activate PDE6, it takes a second copy of Gα* which binds with lower affinity, forming Gα* · PDE6 · Gα*. Reaction-diffusion simulations show that the functional asymmetry of membrane-bound PDE6 constitutes a coincidence switch and explains the lack of G protein-related noise in visual signal transduction. The high local concentration of Gα* generated by a light-activated rhodopsin molecule efficiently activates PDE6, whereas the low density of spontaneously activated Gα* fails to activate the effector enzyme.
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Affiliation(s)
- Bilal M Qureshi
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Elmar Behrmann
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Johannes Schöneberg
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany
| | - Justus Loerke
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Jörg Bürger
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Thorsten Mielke
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Microscopy and Cryo Electron Microscopy Group, Max-Planck Institut für Molekulare Genetik, Berlin, Germany
| | - Jan Giesebrecht
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Frank Noé
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany
| | - Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 2600, Australia
| | - Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Zentrum für Biophysik und Bioinformatik, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Christian M T Spahn
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Martin Heck
- Institut für Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
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3
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Zeng-Elmore X, Gao XZ, Pellarin R, Schneidman-Duhovny D, Zhang XJ, Kozacka KA, Tang Y, Sali A, Chalkley RJ, Cote RH, Chu F. Molecular architecture of photoreceptor phosphodiesterase elucidated by chemical cross-linking and integrative modeling. J Mol Biol 2014; 426:3713-3728. [PMID: 25149264 DOI: 10.1016/j.jmb.2014.07.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 07/01/2014] [Accepted: 07/28/2014] [Indexed: 11/20/2022]
Abstract
Photoreceptor phosphodiesterase (PDE6) is the central effector enzyme in visual excitation pathway in rod and cone photoreceptors. Its tight regulation is essential for the speed, sensitivity, recovery and adaptation of visual detection. Although major steps in the PDE6 activation/deactivation pathway have been identified, mechanistic understanding of PDE6 regulation is limited by the lack of knowledge about the molecular organization of the PDE6 holoenzyme (αβγγ). Here, we characterize the PDE6 holoenzyme by integrative structural determination of the PDE6 catalytic dimer (αβ), based primarily on chemical cross-linking and mass spectrometric analysis. Our models built from high-density cross-linking data elucidate a parallel organization of the two catalytic subunits, with juxtaposed α-helical segments within the tandem regulatory GAF domains to provide multiple sites for dimerization. The two catalytic domains exist in an open configuration when compared to the structure of PDE2 in the apo state. Detailed structural elements for differential binding of the γ-subunit to the GAFa domains of the α- and β-subunits are revealed, providing insight into the regulation of the PDE6 activation/deactivation cycle.
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Affiliation(s)
- Xiaohui Zeng-Elmore
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA; Hubbard Center for Genome Studies, University of New Hampshire, Durham, NH 03824, USA
| | - Xiong-Zhuo Gao
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA
| | - Riccardo Pellarin
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, CA 94158, USA
| | - Dina Schneidman-Duhovny
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, CA 94158, USA
| | - Xiu-Jun Zhang
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA
| | - Katie A Kozacka
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA
| | - Yang Tang
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA; Hubbard Center for Genome Studies, University of New Hampshire, Durham, NH 03824, USA
| | - Andrej Sali
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, CA 94158, USA; Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA; California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158, USA
| | - Robert J Chalkley
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA
| | - Rick H Cote
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA
| | - Feixia Chu
- Department of Molecular, Cellular & Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA; Hubbard Center for Genome Studies, University of New Hampshire, Durham, NH 03824, USA.
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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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5
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Guo LW, Hajipour AR, Ruoho AE. Complementary interactions of the rod PDE6 inhibitory subunit with the catalytic subunits and transducin. J Biol Chem 2010; 285:15209-15219. [PMID: 20231289 DOI: 10.1074/jbc.m109.086116] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Activation of the cyclic GMP phosphodiesterase (PDE6) by transducin is the central event of visual signal transduction. How the PDE6 inhibitory gamma-subunit (Pgamma) interacts with the catalytic subunits (Palphabeta) and the transducin alpha-subunit (alpha(t)) in this process is not entirely clear. Here we have investigated this issue, taking advantage of site-specific label transfer from throughout the full-length Pgamma molecule to both alpha(t) and Palphabeta. The interaction profiling and pull-down experiments revealed that the Pgamma C- terminal domain accounted for the major interaction with alpha(t) bound with guanosine 5'-3-O-(thio)triphosphate (alpha(t)GTPgammaS) in comparison with the central region, whereas an opposite pattern was observed for the Pgamma-Palphabeta interaction. This complementary feature was further exhibited when both alpha(t)GTPgammaS and Palphabeta were present and competing for Pgamma interaction, with the Pgamma C-terminal domain favoring alpha(t), whereas the central region demonstrated a preference for Palphabeta. Furthermore, alpha(t)GTPgammaS co-immunoprecipitated with PDE6 and vice versa in a Pgamma-dependent manner. Either Palphabeta or alpha(t)GTPgammaS could be pulled down by the Btn-Pgamma molecules on streptavidin beads that were saturated by the other partner, indicating simultaneous binding of these two partners to Pgamma. These data together indicate that complementary Pgamma interactions with its two targets facilitate the alpha(t).PDE6 "transducisome" formation. Thus, our study provides new insights into the molecular mechanisms of PDE6 activation.
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Affiliation(s)
- Lian-Wang Guo
- Department of Pharmacology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706.
| | - Abdol R Hajipour
- Department of Pharmacology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706; Pharmaceutical Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
| | - Arnold E Ruoho
- Department of Pharmacology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706
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6
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Jaffé M, Bubis J. Use of 5′-[p-(Fluorosulfonyl)benzoyl] Guanosine as an Affinity Probe for the Guanine Nucleotide-Binding Site of Transducin. Protein J 2007; 26:125-33. [PMID: 17253127 DOI: 10.1007/s10930-006-9053-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Transducin (T) mediates vision in retinal rods by transmitting light signals detected by rhodopsin to a cGMP phosphodiesterase. The flow of information relies on a subunit association/dissociation cycle of T regulated by a guanine nucleotide exchange/hydrolysis reaction. 5'-[p-(Fluorosulfonyl)benzoyl] guanosine (FSBG) was synthesized and examined here as an affinity label for the guanine nucleotide binding site of T. Although the relative binding affinity of FSBG to T was much lower than for GTP and beta,gamma-imido-guanosine 5'-triphosphate (GMPPNP), the incorporation of FSBG to T inhibited its light-dependent [(3)H] GMPPNP binding activity in a concentration dependent manner. Additionally, GDP, GTP and GTP analogs hindered the binding of [(3)H] FSBG to T. These results demonstrated that FSBG could be used to specifically modify the active site of T. In addition, FSBG was not capable of dissociating T from T:photoactivated rhodopsin complexes, suggesting that in this case FSBG is acting as a GDP analog.
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Affiliation(s)
- Matthias Jaffé
- Departamento de Química, Universidad Simón Bolívar, Valle de Sartenejas, Caracas, Venezuela
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7
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Yamazaki A, Moskvin O, Yamazaki RK. Phosphorylation by cyclin-dependent protein kinase 5 of the regulatory subunit (Pgamma) of retinal cgmp phosphodiesterase (PDE6): its implications in phototransduction. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 514:131-53. [PMID: 12596920 DOI: 10.1007/978-1-4615-0121-3_9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
Abstract
Cyclic GMP phosphodiesterase (PDE6) is a key enzyme in vertebrate retinal phototransduction. After GTP/GDP exchange on the a subunit of transducin (Talpha) by illuminated rhodopsin, the GTP-bound form Talpha (GTP/Talpha) interacts with the regulatory subunit (Pgamma) of PDE6 to activate cGMP hydrolytic activity. The regulatory mechanism of PDE6 has been believed to be a typical G protein-mediated signal transduction process. We found that cyclin-dependent protein kinase 5 (Cdk5) phosphorylates Pgamma complexed with GTP/Talpha in vitro and in vivo. Phosphorylated Py dissociates from GTP/Talpha without GTP hydrolysis and interacts effectively with catalytic subunits of PDE6 to inhibit the enzyme activity. These observations provide new twists to the current model of retinal phototransduction. In this article, in addition to the details of Py phosphorylation by Cdk5, we review previous studies implying the Pgamma phosphorylation and the turnoff of PDE6 without GTP hydrolysis and indicate the direction for future studies of Py phosphorylation, including the possible involvement of Ca2+/Ca2+-binding proteins.
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Affiliation(s)
- Akio Yamazaki
- Department of Ophthalmology, Kresge Eye Institute, Wayne State University, School of Medicine, Detroit, Michigan 48201, USA
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8
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Yamazaki M, Li N, Bondarenko VA, Yamazaki RK, Baehr W, Yamazaki A. Binding of cGMP to GAF domains in amphibian rod photoreceptor cGMP phosphodiesterase (PDE). Identification of GAF domains in PDE alphabeta subunits and distinct domains in the PDE gamma subunit involved in stimulation of cGMP binding to GAF domains. J Biol Chem 2002; 277:40675-86. [PMID: 12177054 DOI: 10.1074/jbc.m203469200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Retinal cGMP phosphodiesterase (PDE6) is a key enzyme in vertebrate phototransduction. Rod PDE contains two homologous catalytic subunits (Palphabeta) and two identical regulatory subunits (Pgamma). Biochemical studies have shown that amphibian Palphabeta has high affinity, cGMP-specific, non-catalytic binding sites and that Pgamma stimulates cGMP binding to these sites. Here we show by molecular cloning that each catalytic subunit in amphibian PDE, as in its mammalian counterpart, contains two homologous tandem GAF domains in its N-terminal region. In Pgamma-depleted membrane-bound PDE (20-40% Pgamma still present), a single type of cGMP-binding site with a relatively low affinity (K(d) approximately 100 nm) was observed, and addition of Pgamma increased both the affinity for cGMP and the level of cGMP binding. We also show that mutations of amino acid residues in four different sites in Pgamma reduced its ability to stimulate cGMP binding. Among these, the site involved in Pgamma phosphorylation by Cdk5 (positions 20-23) had the largest effect on cGMP binding. However, except for the C terminus, these sites were not involved in Pgamma inhibition of the cGMP hydrolytic activity of Palphabeta. In addition, the Pgamma concentration required for 50% stimulation of cGMP binding was much greater than that required for 50% inhibition of cGMP hydrolysis. These results suggest that the Palphabeta heterodimer contains two spatially and functionally distinct types of Pgamma-binding sites: one for inhibition of cGMP hydrolytic activity and the second for activation of cGMP binding to GAF domains. We propose a model for the Palphabeta-Pgamma interaction in which Pgamma, by binding to one of the two sites in Palphabeta, may preferentially act either as an inhibitor of catalytic activity or as an activator of cGMP binding to GAF domains in frog PDE.
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Affiliation(s)
- Matsuyo Yamazaki
- Department of Ophthalmology, Kresge Eye Institute, Wayne State University School of Medicine, 4717 Antoine Boulevard, Detroit, MI 48201, USA
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9
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Kajimura N, Yamazaki M, Morikawa K, Yamazaki A, Mayanagi K. Three-dimensional structure of non-activated cGMP phosphodiesterase 6 and comparison of its image with those of activated forms. J Struct Biol 2002; 139:27-38. [PMID: 12372317 DOI: 10.1016/s1047-8477(02)00502-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Cyclic GMP phosphodiesterase (PDE6) in rod photoreceptors, a key enzyme in vertebrate phototransduction, consists of two homologous catalytic subunits (Palpha and Pbeta) and two identical regulatory subunits (Pgammas). Pgamma regulates the PDE activity through its direct interaction with transducin. Here, using electron microscopy and image analysis of single particles, we show the three-dimensional organization of the basic form of bovine PDE, Palphabetagammagamma, and compare its average image with those of Pgamma-released PDE. The structure of Palphabetagammagamma appears to be a flattened bell-shape, with dimensions of 150 x 108 x 60A, and with a handle-like protrusion attached to the top of the structure. Except for the protrusion, the organization consists of two homologous structures arranged side by side, with each structure having three distinct regions, showing pseudo twofold symmetry. These characteristics are consistent with a model in which the overall structure of Palphabetagammagamma is determined by hetero-dimerization of Palpha and Pbeta, with each subunit consisting of one catalytic and two GAF regions. A comparison of the average image of Palphabetagammagamma with those of Pgamma-released PDE suggests that Pgamma release does not affect the overall structure of Palphabeta, and that the Palphabeta C-terminus, but not Pgamma, is a determinant for the Palphabeta orientation on carbon-coated grids. These observations suggest that the basic structure of PDE does not change during its regulation, which implies that Palphabeta is regulated by its regional interaction with Pgamma.
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Affiliation(s)
- Naoko Kajimura
- Biomolecular Engineering Research Institute, 6-2-3, Furuedai, Suita, Osaka 565-0874, Japan
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10
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Norton AW, D'Amours MR, Grazio HJ, Hebert TL, Cote RH. Mechanism of transducin activation of frog rod photoreceptor phosphodiesterase. Allosteric interactiona between the inhibitory gamma subunit and the noncatalytic cGMP-binding sites. J Biol Chem 2000; 275:38611-9. [PMID: 10993884 DOI: 10.1074/jbc.m004606200] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The rod photoreceptor phosphodiesterase (PDE) is unique among all known vertebrate PDE families for several reasons. It is a catalytic heterodimer (alphabeta); it is directly activated by a G-protein, transducin; and its active sites are regulated by inhibitory gamma subunits. Rod PDE binds cGMP at two noncatalytic sites on the alphabeta dimer, but their function is unclear. We show that transducin activation of frog rod PDE introduces functional heterogeneity to both the noncatalytic and catalytic sites. Upon PDE activation, one noncatalytic site is converted from a high affinity to low affinity state, whereas the second binding site undergoes modest decreases in binding. Addition of gamma to transducin-activated PDE can restore high affinity binding as well as reducing cGMP exchange kinetics at both sites. A strong correlation exists between cGMP binding and gamma binding to activated PDE; dissociation of bound cGMP accompanies gamma dissociation from PDE, whereas addition of either cGMP or gamma to alphabeta dimers can restore high affinity binding of the other molecule. At the active site, transducin can activate PDE to about one-half the turnover number for catalytic alphabeta dimers completely lacking bound gamma subunit. These results suggest a mechanism in which transducin interacts primarily with one PDE catalytic subunit, releasing its full catalytic activity as well as inducing rapid cGMP dissociation from one noncatalytic site. The state of occupancy of the noncatalytic sites on PDE determines whether gamma remains bound to activated PDE or dissociates from the holoenzyme, and may be relevant to light adaptation in photoreceptor cells.
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Affiliation(s)
- A W Norton
- Department of Biochemistry and Molecular Biology, University of New Hampshire, Durham, New Hampshire 03824-3544, USA
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11
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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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12
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Melia TJ, Malinski JA, He F, Wensel TG. Enhancement of phototransduction protein interactions by lipid surfaces. J Biol Chem 2000; 275:3535-42. [PMID: 10652348 DOI: 10.1074/jbc.275.5.3535] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The G protein cascade of vision depends on two peripheral membrane proteins: the G protein, transducin (G(t)), and cGMP phosphodiesterase (PDE). Each has covalently attached lipids, and interacts with transduction components on the membrane surface. We have found that their surface interactions are critically dependent on the nature of the lipid. Membranes enhance their protein-protein interactions, especially if electrostatic attraction is introduced with positively charged lipids. These interactions are less enhanced on highly curved surfaces, but are most enhanced by unsaturated or bulky acyl chains. On positively charged membranes, G(t) assembles at a high enough density to form two-dimensional arrays with short-range crystalline order. Cationic membranes also support extremely efficient activation of PDE by the GTPgammaS (guanosine 5'-O-(thiotriphosphate)) form of Galpha(t) (Galpha(t)-GTPgammaS), minimizing functional heterogeneity of transducin and allowing activation with nanomolar Galpha(t)-GTPgammaS. Quantification of PDE activation and of the amount of Galpha(t)-GTPgammaS bound to PDE indicated that G(t) activates PDE maximally when bound in a 1:1 molar ratio. No cooperativity was observed, even at nanomolar concentrations. Thus, under these conditions, the one binding site for Galpha(t)-GTPgammaS on PDE that stimulates catalysis must be of higher affinity than one or more additional sites which are silent with respect to activation of PDE.
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Affiliation(s)
- T J Melia
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA
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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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14
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Duda T, Goraczniak R, Surgucheva I, Rudnicka-Nawrot M, Gorczyca WA, Palczewski K, Sitaramayya A, Baehr W, Sharma RK. Calcium modulation of bovine photoreceptor guanylate cyclase. Biochemistry 1996; 35:8478-82. [PMID: 8679607 DOI: 10.1021/bi960752z] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Bovine photoreceptor guanylate cyclase (ROS-GC) consists of a single transmembrane polypeptide chain with extracellular and intracellular domains. In contrast to non-photoreceptor guanylate cyclases (GCs) which are activated by hormone peptides, ROS-GC is modulated in low Ca2+ by calmodulin-like Ca(2+)-binding proteins termed GCAPs (guanylate cyclase-activating proteins). In this communication we show that, like the native system, ROS-GC expressed in COS cells is activated 4-6-fold by recombinant GCAP1 at 10 nM Ca2+ and that the reconstituted system is inhibited at physiological levels of Ca2+ (1 microM). A mutant ROS-GC in which the extracellular domain was deleted was stimulated by GCAP1 indistinguishable from native ROS-GC indicating that this domain is not involved in Ca2+ modulation. Deletion of the intracellular kinase-like domain diminished the stimulation by GCAP1, indicating that this domain is at least in part involved in Ca2+ modulation. Replacement of the catalytic domain in a non-photoreceptor GC by the catalytic domain of ROS-GC yielded a chimeric GC that was sensitive to ANF/ATP and to a lesser extent to GCAP1. The results establish that GCAP1 acts at an intracellular domain, suggesting a mechanism of photoreceptor GC stimulation fundamentally distinct from hormone peptide stimulation of other cyclase receptors.
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Affiliation(s)
- T Duda
- Department of Cell Biology, University of Medicine and Dentistry of New Jersey, Stratford 08084, USA
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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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16
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Justice JM, Murtagh JJ, Moss J, Vaughan M. Hydrophobicity and subunit interactions of rod outer segment proteins investigated using Triton X-114 phase partitioning. J Biol Chem 1995; 270:17970-6. [PMID: 7629104 DOI: 10.1074/jbc.270.30.17970] [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: 01/26/2023] Open
Abstract
Triton X-114 phase partitioning, a procedure used for purifying integral membrane proteins, was used to study protein components of the mammalian visual transduction cascade. An integral membrane protein, rhodopsin, and two isoprenylated protein complexes, cyclic GMP phosphodiesterase and Gt beta gamma, partitioned into the detergent-rich phase. Arrestin, a soluble protein, accumulated in the aqueous phase. Gt alpha distributed about equally between phases whether GDP (Gt alpha.GDP) or GTP (Gt alpha.GTP) was bound. Gt beta gamma increased recovery of Gt alpha.GDP but not Gt alpha.GTP in the detergent phase. Trypsin-treated Gt alpha, which lacks the fatty acylated amino-terminal 2-kDa region, accumulated to a greater extent in the aqueous phase than did intact Gt alpha. Trypsinized cGMP phosphodiesterase, which lacks the isoprenyl group, partitioned into the aqueous phase. A carboxyl-terminal truncated mutant (Val-331 stop) of Gt alpha accumulated more in the aqueous phase then did recombinant full-length Gt alpha, supporting the role of the carboxyl terminus in increasing its hydrophobicity. N-Myristoylated recombinant Go alpha was more hydrophobic than recombinant Go alpha without myristate. ADP-ribosylation of Gt alpha catalyzed by NAD:arginine ADP-ribosyltransferase, but not by pertussis toxin, increased hydrophilicity. Triton X-114 phase partitioning can thus semiquantify the hydrophobic nature of proteins and protein domains. It may aid in evaluating changes associated with post-translational protein modification and protein-protein interactions in a defined system.
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Affiliation(s)
- J M Justice
- Pulmonary-Critical Care Medicine Branch, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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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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18
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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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