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Otte M, Schweinitz A, Lelle M, Thon S, Enke U, Yüksel S, Schmauder R, Bonus M, Gohlke H, Benndorf K. Novel Fluorescent Cyclic Nucleotide Derivatives to Study CNG and HCN Channel Function. Biophys J 2019; 116:2411-2422. [PMID: 31130235 DOI: 10.1016/j.bpj.2019.05.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 04/19/2019] [Accepted: 05/01/2019] [Indexed: 12/29/2022] Open
Abstract
A highly specific molecular interaction of diffusible ligands with their receptors belongs to the key processes in cellular signaling. Because an appropriate method to monitor the unitary binding events is still missing, most of our present knowledge is based on ensemble signals recorded from a big number of receptors, such as ion currents or fluorescence changes of suitably labeled receptors, and reasoning from these data to the ligand binding. To study the binding process itself, appropriately tagged ligands are required that fully activate the receptors and report the binding at the same time. Herein, we tailored a series of 18 novel fluorescent cyclic nucleotide derivatives by attaching 6 different dyes via different alkyl linkers to the 8-position of the purine ring of cGMP or cAMP. The biological activity was determined in inside-out macropatches containing either homotetrameric (CNGA2), heterotetrameric (CNGA2:CNGA4:CNGB1b), or hyperpolarization-activated cyclic nucleotide-modulated (HCN2) channels. All these novel fluorescent ligands are efficient to activate the channels, and the potency of most of them significantly exceeded that of the natural cyclic nucleotides cGMP or cAMP. Moreover, some of them showed an enhanced brightness when bound to the channels. The best of our derivatives bear great potential to systematically analyze the activation mechanism in CNG and HCN channels, at both the level of ensemble and single-molecule analyses.
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Affiliation(s)
- Maik Otte
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Andrea Schweinitz
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Marco Lelle
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Susanne Thon
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Uta Enke
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Sezin Yüksel
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Ralf Schmauder
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Michele Bonus
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
| | - Holger Gohlke
- Institut für Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany; John von Neumann Institute for Computing, Jülich Supercomputing Centre & Institute for Complex Systems Structural Biochemistry, Forschungszentrum Jülich, GmbH, Jülich, Germany
| | - Klaus Benndorf
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany.
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Hydrophobic alkyl chains substituted to the 8-position of cyclic nucleotides enhance activation of CNG and HCN channels by an intricate enthalpy - entropy compensation. Sci Rep 2018; 8:14960. [PMID: 30297855 PMCID: PMC6175941 DOI: 10.1038/s41598-018-33050-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 09/19/2018] [Indexed: 01/01/2023] Open
Abstract
Cyclic nucleotide-gated (CNG) and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are tetrameric non-specific cation channels in the plasma membrane that are activated by either cAMP or cGMP binding to specific binding domains incorporated in each subunit. Typical apparent affinities of these channels for these cyclic nucleotides range from several hundred nanomolar to tens of micromolar. Here we synthesized and characterized novel cAMP and cGMP derivatives by substituting either hydrophobic alkyl chains or similar-sized more hydrophilic heteroalkyl chains to the 8-position of the purine ring with the aim to obtain full agonists of higher potency. The compounds were tested in homotetrameric CNGA2, heterotetrameric CNGA2:CNGA4:CNGB1b and homotetrameric HCN2 channels. We show that nearly all compounds are full agonists and that longer alkyl chains systematically increase the apparent affinity, at the best more than 30 times. The effects are stronger in CNG than HCN2 channels which, however, are constitutively more sensitive to cAMP. Kinetic analyses reveal that the off-rate is significantly slowed by the hydrophobic alkyl chains. Molecular dynamics simulations and free energy calculations suggest that an intricate enthalpy - entropy compensation underlies the higher apparent affinity of the derivatives with the longer alkyl chains, which is shown to result from a reduced loss of configurational entropy upon binding.
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Schwede F, Genieser HG, Rentsch A. The Chemistry of the Noncanonical Cyclic Dinucleotide 2'3'-cGAMP and Its Analogs. Handb Exp Pharmacol 2017; 238:359-384. [PMID: 27392950 DOI: 10.1007/164_2015_43] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The cyclic dinucleotides (CDNs) cyclic diguanosine monophosphate (c-diGMP) and cyclic diadenosine monophosphate (c-diAMP) with two canonical 3'→5' internucleotide linkages are ubiquitous second messenger molecules in bacteria, regulating a multitude of physiological processes. Recently the noncanonical CDN cyclic guanosine monophosphate-adenosine monophosphate (2'3'-cGAMP) featuring a mixed linkage, which consists of a 2'→5' and a 3'→5' internucleotide bond, has been identified as a signaling molecule in metazoan species in late 2012. 2'3'-cGAMP formation is biocatalyzed by cGAMP synthase (cGAS) upon sensing of cytosolic double-stranded DNA (dsDNA) and functions as an endogenous inducer of innate immunity by directly binding to and activating the adaptor protein stimulator of interferon genes (STING). Thereby 2'3'-cGAMP can stimulate interferon-β (INF-β) secretion, a major signaling pathway of host defense, which is independent of toll-like receptor (TLR) activation. Medicinal chemistry of 2'3'-cGAMP and development of corresponding analogs are still in their infancy, and only a handful of structurally related compounds are available to the scientific community. The aim of this chapter is to summarize synthetic approaches to prepare canonical and noncanonical endogenous CDNs including 2'3'-cGAMP. Furthermore, we will describe syntheses of 2'3'-cGAMP analogs bearing modifications, which will facilitate further studies of the emerging biological functions of 2'3'-cGAMP and to identify additional receptor proteins. Finally, we will review latest developments concerning 2'3'-cGAMP analogs with improved hydrolytic stability in cell cultures and in tissues, putatively qualifying for new therapeutic options on the basis of 2'3'-cGAMP signaling.
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Affiliation(s)
- Frank Schwede
- BIOLOG Life Science Institute, Forschungslabor und Biochemica-Vertrieb GmbH, Flughafendamm 9a, 28199, Bremen, Germany.
| | - Hans-Gottfried Genieser
- BIOLOG Life Science Institute, Forschungslabor und Biochemica-Vertrieb GmbH, Flughafendamm 9a, 28199, Bremen, Germany
| | - Andreas Rentsch
- BIOLOG Life Science Institute, Forschungslabor und Biochemica-Vertrieb GmbH, Flughafendamm 9a, 28199, Bremen, Germany
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Sawa T, Ihara H, Ida T, Fujii S, Nishida M, Akaike T. Formation, signaling functions, and metabolisms of nitrated cyclic nucleotide. Nitric Oxide 2013; 34:10-8. [PMID: 23632125 DOI: 10.1016/j.niox.2013.04.004] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 04/16/2013] [Indexed: 01/07/2023]
Abstract
8-Nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) is a unique derivative of guanosine 3',5'-cyclic monophosphate (cGMP) formed in mammalian and plant cells in response to production of nitric oxide and reactive oxygen species. 8-Nitro-cGMP possesses signaling activity inherited from parental cGMP, including induction of vasorelaxation through activation of cGMP-dependent protein kinase. On the other hand, 8-nitro-cGMP mediates cellular signaling that is not observed for native cGMP, e.g., it behaves as an electrophile and reacts with protein sulfhydryls, which results in cGMP adduction to protein sulfhydryls (protein S-guanylation). Several proteins have been identified as targets for endogenous protein S-guanylation, including Kelch-like ECH-associated protein 1 (Keap1), H-Ras, and mitochondrial heat shock proteins. 8-Nitro-cGMP signaling via protein S-guanylation of those proteins may have evolved to convey adaptive cellular stress responses. 8-Nitro-cGMP may not undergo conventional cGMP metabolism because of its resistance to phosphodiesterases. Hydrogen sulfide has recently been identified as a potent regulator for metabolisms of electrophiles including 8-nitro-cGMP, through sulfhydration of electrophiles, e.g., leading to the formation of 8-SH-cGMP. Better understanding of the molecular basis for the formation, signaling functions, and metabolisms of 8-nitro-cGMP would be useful for the development of new diagnostic approaches and treatment of diseases related to oxidative stress and redox metabolisms.
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Key Words
- 15-deoxy-Δ(12,14)-prostaglandin J(2)
- 15d-PGJ(2)
- 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one
- 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide
- 4-hydroxy-2-nonenal
- 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one
- 60-kDa heat-shock protein
- 8-Nitro-cGMP
- 8-bromo-cGMP
- 8-bromoguanosine 3′,5′-cyclic monophosphate
- 8-nitroguanosine 3′,5′-cyclic monophosphate
- ATP
- CBS
- CSE
- ELISA
- ETC
- Electrophile
- GSH
- GTP
- HNE
- HO-1
- HPLC-ECD
- HSP60
- Hydrogen sulfide
- IFN-γ
- IL-1β
- Keap1
- Kelch-like ECH-associated protein 1
- LC–MS/MS
- LPS
- MI
- MPO
- N(G)-nitro-l-arginine methyl ester
- N(ω)-monomethyl-l-arginine
- NADPH oxidase
- NADPH oxidase 2
- NOS
- NS 2028
- Nox
- Nox2
- Nrf2
- ODQ
- Oxidative stress
- PDEs
- PKG
- PTM
- Protein S-guanylation
- RAR
- RNOS
- ROS
- SOD
- TNFα
- adenosine 3′,5′-cyclic monophosphate
- adenosine 5′-triphosphate
- cAMP
- cGMP
- cGMP-dependent protein kinase
- cPTIO
- cystathionine β-synthase
- cystathionine γ-lyase
- eNOS
- electron transport chain
- endothelial NOS
- enzyme-linked immunosorbent assay
- glutathione
- guanosine 3′,5′-cyclic monophosphate
- guanosine 5′-triphosphate
- heme oxygenase-1
- high-performance liquid chromatography with electrochemical detector
- iNOS
- inducible NOS
- interferon-γ
- interleukin-1β
- l-NAME
- l-NMMA
- lipopolysaccharide
- liquid chromatography with tandem mass spectrometry
- mPTP
- mitochondrial permeability transition pore
- myeloperoxidase
- myocardial infarction
- nNOS
- neuronal NOS
- nitric oxide synthases
- nuclear factor erythroid 2-related factor 2
- pGC
- particulate-type guanylyl cyclase
- phosphodiesterases
- post-translational modification
- reactive nitrogen oxide species
- reactive oxygen species
- retinoic acid receptor
- sGC
- soluble-type guanylyl cyclase
- superoxide dismutase
- tumor necrosis factor α
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Affiliation(s)
- Tomohiro Sawa
- Department of Microbiology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan; PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-001, Japan
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Is the lifetime of light-stimulated cGMP phosphodiesterase regulated by recoverin through its regulation of rhodopsin phosphorylation? Behav Brain Sci 2010. [DOI: 10.1017/s0140525x00039522] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Strassmaier T, Karpen JW. Novel N7- and N1-substituted cGMP derivatives are potent activators of cyclic nucleotide-gated channels. J Med Chem 2007; 50:4186-94. [PMID: 17665892 PMCID: PMC2597524 DOI: 10.1021/jm0702581] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels, key players in olfactory and visual signal transduction, generate electrical responses to odorant- and light-induced changes in cyclic nucleotide concentration. Previous work suggests that substitutions are tolerated solely at the C8 position on the purine ring of cGMP. Our studies with C8, 2'-OH, and 2-NH2-modified cGMP derivatives support this assertion. To gain further insight into determinants important for CNG channel binding and activation, we targeted previously unexplored positions. Modifications at N7 of 8-SH-cGMP (6) are well tolerated by olfactory and retinal rod CNG channels. Toleration of a very large substituent, a 3400 molecular weight PEG, at either N7 or C8 argues for broad accommodation at these positions in the binding site. Modification at N1 of cGMP reduces the apparent affinity for the channel; however, when combined with 8-parachlorophenylthio derivatization, the resulting cGMP analogue is more potent than cGMP itself. These studies establish the N7 and N1 positions of cGMP as targets for modification in the design of novel CNG channel agonists.
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Affiliation(s)
| | - Jeffrey W. Karpen
- Corresponding author: Jeffrey W. Karpen, Phone 503-494-7463. E-mail:
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Brown RL, Strassmaier T, Brady JD, Karpen JW. The pharmacology of cyclic nucleotide-gated channels: emerging from the darkness. Curr Pharm Des 2006; 12:3597-613. [PMID: 17073662 PMCID: PMC2467446 DOI: 10.2174/138161206778522100] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cyclic nucleotide-gated (CNG) ion channels play a central role in vision and olfaction, generating the electrical responses to light in photoreceptors and to odorants in olfactory receptors. These channels have been detected in many other tissues where their functions are largely unclear. The use of gene knockouts and other methods have yielded some information, but there is a pressing need for potent and specific pharmacological agents directed at CNG channels. To date there has been very little systematic effort in this direction - most of what can be termed CNG channel pharmacology arose from testing reagents known to target protein kinases or other ion channels, or by accident when researchers were investigating other intracellular pathways that may regulate the activity of CNG channels. Predictably, these studies have not produced selective agents. However, taking advantage of emerging structural information and the increasing knowledge of the biophysical properties of these channels, some promising compounds and strategies have begun to emerge. In this review we discuss progress on two fronts, cyclic nucleotide analogs as both activators and competitive inhibitors, and inhibitors that target the pore or gating machinery of the channel. We also discuss the potential of these compounds for treating certain forms of retinal degeneration.
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Affiliation(s)
- R. Lane Brown
- Neurological Sciences Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Timothy Strassmaier
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA
| | - James D. Brady
- Neurological Sciences Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Jeffrey W. Karpen
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA
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Abstract
Cyclic nucleotide-gated (CNG) channels are nonselective cation channels first identified in retinal photoreceptors and olfactory sensory neurons (OSNs). They are opened by the direct binding of cyclic nucleotides, cAMP and cGMP. Although their activity shows very little voltage dependence, CNG channels belong to the superfamily of voltage-gated ion channels. Like their cousins the voltage-gated K+ channels, CNG channels form heterotetrameric complexes consisting of two or three different types of subunits. Six different genes encoding CNG channels, four A subunits (A1 to A4) and two B subunits (B1 and B3), give rise to three different channels in rod and cone photoreceptors and in OSNs. Important functional features of these channels, i.e., ligand sensitivity and selectivity, ion permeation, and gating, are determined by the subunit composition of the respective channel complex. The function of CNG channels has been firmly established in retinal photoreceptors and in OSNs. Studies on their presence in other sensory and nonsensory cells have produced mixed results, and their purported roles in neuronal pathfinding or synaptic plasticity are not as well understood as their role in sensory neurons. Similarly, the function of invertebrate homologs found in Caenorhabditis elegans, Drosophila, and Limulus is largely unknown, except for two subunits of C. elegans that play a role in chemosensation. CNG channels are nonselective cation channels that do not discriminate well between alkali ions and even pass divalent cations, in particular Ca2+. Ca2+ entry through CNG channels is important for both excitation and adaptation of sensory cells. CNG channel activity is modulated by Ca2+/calmodulin and by phosphorylation. Other factors may also be involved in channel regulation. Mutations in CNG channel genes give rise to retinal degeneration and color blindness. In particular, mutations in the A and B subunits of the CNG channel expressed in human cones cause various forms of complete and incomplete achromatopsia.
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Affiliation(s)
- U Benjamin Kaupp
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Jülich, Germany.
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Wu X, Cooperman BS. Synthesis and biological activity of a bivalent nucleotide inhibitor of ribonucleotide reductase. Bioorg Med Chem Lett 2000; 10:2387-9. [PMID: 11055362 DOI: 10.1016/s0960-894x(00)00481-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A novel nucleotide inhibitor (ADP-S-HBES-S-dGTP) of mouse ribonucleotide reductase was designed to span the active site and the allosteric specificity site of the enzyme. The inhibitor contains ADP and dGTP moieties which are linked by 1,6-hexane-(bis-ethylenesulfone), and has a Ki value of 12 microM.
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Affiliation(s)
- X Wu
- Department of Chemistry, University of Pennsylvania, Philadelphia 19104-6323, USA
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Schwede F, Maronde E, Genieser H, Jastorff B. Cyclic nucleotide analogs as biochemical tools and prospective drugs. Pharmacol Ther 2000; 87:199-226. [PMID: 11008001 DOI: 10.1016/s0163-7258(00)00051-6] [Citation(s) in RCA: 191] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Cyclic AMP (cAMP) and cyclic GMP (cGMP) are key second messengers involved in a multitude of cellular events. From the wealth of synthetic analogs of cAMP and cGMP, only a few have been explored with regard to their therapeutic potential. Some of the first-generation cyclic nucleotide analogs were promising enough to be tested as drugs, for instance N(6),O(2)'-dibutyryl-cAMP and 8-chloro-cAMP (currently in clinical Phase II trials as an anticancer agent). Moreover, 8-bromo and dibutyryl analogs of cAMP and cGMP have become standard tools for investigations of biochemical and physiological signal transduction pathways. The discovery of the Rp-diastereomers of adenosine 3',5'-cyclic monophosphorothioate and guanosine 3',5'-cyclic monophosphorothioate as competitive inhibitors of cAMP- and cGMP-dependent protein kinases, as well as subsequent development of related analogs, has proven very useful for studying the molecular basis of signal transduction. These analogs exhibit a higher membrane permeability, increased resistance against degradation, and improved target specificity. Furthermore, better understanding of signaling pathways and ligand/protein interactions has led to new therapeutic strategies. For instance, Rp-8-bromo-adenosine 3',5'-cyclic monophosphorothioate is employed against diseases of the immune system. This review will focus mainly on recent developments in cyclic nucleotide-related biochemical and pharmacological research, but also highlights some historical findings in the field.
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Affiliation(s)
- F Schwede
- Center for Environmental Research and Environmental Technology, Department of Bioorganic Chemistry, University of Bremen, Leobener Strasse, D-28359, Bremen, Germany
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Karpen JW, Ruiz M, Brown RL. Covalent tethering of ligands to retinal rod cyclic nucleotide-gated channels: binding site structure and allosteric mechanism. Methods Enzymol 2000; 315:755-72. [PMID: 10736739 DOI: 10.1016/s0076-6879(00)15880-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Affiliation(s)
- J W Karpen
- Department of Physiology and Biophysics, University of Colorado School of Medicine, Denver 80262, USA
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Kramer RH, Karpen JW. Spanning binding sites on allosteric proteins with polymer-linked ligand dimers. Nature 1998; 395:710-3. [PMID: 9790193 DOI: 10.1038/27227] [Citation(s) in RCA: 224] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
One approach to drug design involves determination of the structure of binding sites on target proteins to provide templates for ligand construction. Alternatively, random combinations of chemical groups can be used to generate diverse molecules for screening in the search for effective compounds. Here we report a strategy for developing potent ligands for proteins with multiple binding sites, which combines elements of both approaches: 'polymer-linked ligand dimers', in which two ligands are joined by a polymer chain of variable length. We find that polymer-linked ligand dimers containing two cyclic GMP moieties are up to a thousand times more potent than cyclic GMP in activating cyclic-nucleotide-gated channels and cGMP-dependent protein kinase. Each target protein responds optimally to a polymer-linked ligand dimer with a different average polymer length, even though their cyclic-nucleotide-binding sites are conserved. The tuning of polymer-linked ligand dimers indicates that each protein has a unique spacing of binding sites and provides an estimate of the distance between these sites. As optimal ligands are selected empirically, the polymer-linked ligand dimer strategy enables potent and selective agents to be identified without requiring previous structural information about the target proteins.
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Affiliation(s)
- R H Kramer
- Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Florida 33101, USA.
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Wei JY, Roy DS, Leconte L, Barnstable CJ. Molecular and pharmacological analysis of cyclic nucleotide-gated channel function in the central nervous system. Prog Neurobiol 1998; 56:37-64. [PMID: 9723130 DOI: 10.1016/s0301-0082(98)00029-x] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Most functional studies of cyclic nucleotide-gated (CNG) channels have been confined to photoreceptors and olfactory epithelium, in which CNG channels are abundant and easy to study. The widespread distribution of CNG channels in tissues throughout the body has only recently been recognized and the functions of this channel family in many of these tissues remain largely unknown. The molecular biological and pharmacological properties of the CNG channel family are summarized in order to put in context studies aimed at probing CNG channel functions in these tissues using pharmacological and genetic methods. Compounds have now been identified that are useful in distinguishing CNG channel activated pathways from cAMP/cGMP dependent-protein kinases or other pathways. The ways in which these interact with CNG channels are understood and this knowledge is leading to the identification of more potent and more specific CNG channel subtype-specific agonists or antagonists. Recent molecular and genetic analyses have identified novel roles of CNG channels in neuronal development and plasticity in both invertebrates and vertebrates. Targeting CNG channels via specific drugs and genetic manipulation (such as knockout mice) will permit better understanding of the role of CNG channels in both basic and higher orders of brain function.
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Affiliation(s)
- J Y Wei
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06520, USA
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Brown RL, Snow SD, Haley TL. Movement of gating machinery during the activation of rod cyclic nucleotide-gated channels. Biophys J 1998; 75:825-33. [PMID: 9675183 PMCID: PMC1299756 DOI: 10.1016/s0006-3495(98)77571-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
In the visual and olfactory systems, cyclic nucleotide-gated (CNG) ion channels convert stimulus-induced changes in the internal concentrations of cGMP and cAMP into changes in membrane potential. Although it is known that significant activation of these channels requires the binding of three or more molecules of ligand, the detailed molecular mechanism remains obscure. We have probed the structural changes that occur during channel activation by using sulfhydryl-reactive methanethiosulfonate (MTS) reagents and N-ethylmaleimide (NEM). When expressed in Xenopus oocytes, the alpha-subunit of the bovine retinal channel forms homomultimeric channels that are activated by cGMP with a K1/2 of approximately 100 microM. Cyclic AMP, on the other hand, is a very poor activator; a saturating concentration elicits only 1% of the maximum current produced by cGMP. Treatment of excised patches with MTS-ethyltrimethylamine (MTSET) or NEM dramatically potentiated the channel's response to both cyclic nucleotides. After MTSET treatment, the dose-response relation for cGMP was shifted by over two orders of magnitude to lower concentrations. The effect on channel activation by cAMP was even more striking. After modification, the channels were fully activated by cAMP with a K1/2 of approximately 60 microM. This potentiation was abolished by conversion of Cys481 to a nonreactive alanine residue. Potentiation occurred more rapidly in the presence of saturating cGMP, indicating that this region of the channel is more accessible when the channel is open. Cys481 is located in a linker region between the transmembrane and cGMP-binding domains of the channel. These results suggest that this region of the channel undergoes significant movement during the activation process and is critical for coupling ligand binding to pore opening. Potentiation, however, is not mediated by the recently reported interaction between the amino- and carboxy-terminal regions of the alpha-subunit. Deletion of the entire amino-terminal domain had little effect on potentiation by MTSET.
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Affiliation(s)
- R L Brown
- Neurological Sciences Institute, Oregon Health Sciences University, Portland, Oregon 97209 USA.
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Kaupp UB, Dzeja C, Frings S, Bendig J, Hagen V. Applications of caged compounds of hydrolysis-resistant analogs of cAMP and cGMP. Methods Enzymol 1998; 291:415-30. [PMID: 9661162 DOI: 10.1016/s0076-6879(98)91026-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- U B Kaupp
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany
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Hebert MC, Schwede F, Jastorff B, Cote RH. Structural features of the noncatalytic cGMP binding sites of frog photoreceptor phosphodiesterase using cGMP analogs. J Biol Chem 1998; 273:5557-65. [PMID: 9488681 DOI: 10.1074/jbc.273.10.5557] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cGMP-specific phosphodiesterase (PDE) of retinal photoreceptors is a central regulatory enzyme in the visual transduction pathway of vertebrate vision. Although the mechanism of activation of PDE by transducin is well understood, the role of the noncatalytic cGMP binding sites located on the catalytic subunits of PDE remains obscure. We report here for the first time the molecular basis of the noncovalent interactions between cGMP and the high affinity, noncatalytic cGMP binding sites of frog photoreceptor PDE. None of the tested cGMP analogs were able to bind with greater affinity than cGMP itself, and the noncatalytic sites were unable to bind cAMP. The major determinant for discrimination of cGMP over cAMP is in the N-1/C-6 region of the purine ring of cGMP where hydrogen bonding probably stabilizes the selective binding of cGMP. Substitutions at the C-2 position demonstrate that this region of the molecule plays a secondary but significant role in stabilizing cGMP binding to PDE through hydrogen bond interactions. The unaltered hydrogen at the C-8 position is also important for high affinity binding. A significant interaction between the binding pocket and the ribose ring of cGMP occurs at the 2'-hydroxyl position. Steric constraints were greatest in the C-8 and possibly the C-6/N-1 regions, whereas the C-2/N-3 and C-2' regions tolerated bulky substituents better. Several lines of evidence indicate that the noncatalytic site binds cGMP in the anti-conformation. The numerous noncovalent interactions between cGMP and the noncatalytic binding pocket of the photoreceptor PDE described in this study account for both the high affinity for cGMP and the high level of discrimination of cGMP from other cyclic nucleotides at the noncatalytic site.
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Affiliation(s)
- M C Hebert
- Department of Biochemistry and Molecular Biology, University of New Hampshire, Durham, New Hampshire 03824, USA
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23
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Wei JY, Cohen ED, Genieser HG, Barnstable CJ. Substituted cGMP analogs can act as selective agonists of the rod photoreceptor cGMP-gated cation channel. J Mol Neurosci 1998; 10:53-64. [PMID: 9589370 DOI: 10.1007/bf02737085] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cyclic nucleotide-gated (CNG) channels are expressed in many cell types in both the nervous system and nonexcitable tissues. In order to understand the roles of cGMP-gated channels, and to distinguish actions of cGMP mediated through CNG channels from those through cGMP-dependent protein kinase (G-kinase), several new cGMP analogs were tested for potency as CNG channel agonists. Using Xenopus oocytes expressing the rat rod cGMP-gated ion channel alpha-subunit, we showed that an analog containing a pCPT group at the 8-position, 8-pCPT-cGMP, was 80 times more potent than cGMP and 14 times more potent than 8-Br-cGMP. 8-pCPT-cGMP is the most potent CNG channel agonist so far described and also has the advantages of much better membrane permeability as well as much higher resistance to PDE-hydrolysis, as compared with 8-Br-cGMP. Modification of both 8-Br-cGMP and 8-pCPT-cGMP by introduction of a sulphur atom into the cyclic phosphate group gave smaller changes in agonist efficiency. Both Sp-8-Br-cGMPS and Sp-8-pCPT-cGMPS acted as agonists of CNG channels and are also G-kinase activators. In contrast, Rp-8-Br-cGMPS was a channel agonist, with an EC50 of 173.5 microM, but a G-kinase antagonist with a Ki of 4 microM. Finally, Rp-8-pCPT-cGMPS was a channel agonist and showed additional noncompetitive antagonist activity at higher concentrations. The results suggest that 8-pCPT-cGMPS is a highly potent photoreceptor CNG channel agonist with high membrane permeability and PDE-resistance and furthermore Rp-8-Br-cGMPS can be used to test whether the actions of cGMP are selectively mediated by CNG channels.
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Affiliation(s)
- J Y Wei
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06520-8061, USA
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24
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Abstract
Cyclic nucleotide-gated (CNG) channels are highly specialized to carry out their unique role in cell signalling. Significant progress has been made in the last several years determining the molecular mechanisms for these specializations. The activation of the channels begins with the binding of cyclic nucleotide to a domain in the carboxyl terminal region. This binding, in turn, produces an induced fit of the protein that involves a movement of the C-helix portion of the binding domain. The induced fit of the binding domain is coupled to an allosteric conformational change that opens the channel pore. The pore is formed primarily from the sequence between the S5 and S6 segments. A single glutamic acid in the pore represents the binding site for multiple monovalent cations, the blocking site for external divalent cations, and the site for the effect of protons on permeation.
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Affiliation(s)
- W N Zagotta
- Department of Physiology and Biophysics, Howard Hughes Medical Institute, University of Washington, School of Medicine, Seattle 98195-7290, USA
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25
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Karpen JW, Brown RL. Covalent activation of retinal rod cGMP-gated channels reveals a functional heterogeneity in the ligand binding sites. J Gen Physiol 1996; 107:169-81. [PMID: 8833339 PMCID: PMC2219270 DOI: 10.1085/jgp.107.2.169] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Ion channels gated by the binding of multiple ligands play a critical role in synaptic transmission and sensory transduction. It has been difficult to resolve the contribution of individual binding events to channel gating because ligands are continuously binding and unbinding at each site. In examining the allosteric mechanism of retinal rod cGMP-gated channels, we have circumvented this problem by making use of a cGMP derivative, 8-p-azidophenacylthio-cGMP (APT-cGMP), that can be covalently tethered to the binding sites in the presence of long-wavelength UV light. In excised membrane patches, a population of channels was isolated that contained covalently-attached ligands at all but one site. Activation of these channels by cGMP revealed a previously unknown heterogeneity in the ligand-binding sites. The dose-response relations were much shallower than predicted by single-site activation models, but were well described by models in which there are two populations of sites, in roughly equal proportion, that bind cGMP with apparent affinities that differ by a factor of 25. The two apparent affinities, incorporated into a four-site model of the channel, provided an accurate description of the patch's original dose-response relation. A comparison of results on native and expressed channels suggests that the heterogeneity in the native channel arises at least in part from the presence of two different cGMP-binding subunits.
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Affiliation(s)
- J W Karpen
- Department of Physiology, University of Colorado School of Medicine, Denver 80262, USA
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26
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Koutalos Y, Brown RL, Karpen JW, Yau KW. Diffusion coefficient of the cyclic GMP analog 8-(fluoresceinyl)thioguanosine 3',5' cyclic monophosphate in the salamander rod outer segment. Biophys J 1995; 69:2163-7. [PMID: 8580360 PMCID: PMC1236450 DOI: 10.1016/s0006-3495(95)80090-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Cyclic GMP (cGMP) is the intracellular messenger mediating phototransduction in retinal rods, with its longitudinal diffusion in the rod outer segment (ROS) likely to be a factor in determining light sensitivity. From the kinetics of cGMP-activated currents in the truncated ROS of the salamander (Ambystoma tigrinum), the cGMP diffusion coefficient was previously estimated to be approximately 60 x 10(-8) cm2 s-1. On the other hand, fluorescence measurements in intact salamander ROS using 8-(fluoresceinyl)thioguanosine 3',5'-cyclic monophosphate (Fl-cGMP) led to a diffusion coefficient for this compound of 1 x 10(-8) cm2 s-1; after corrections for differences in size and in binding to cellular components between cGMP and Fl-cGMP, this gave an upper limit of 11 x 10(-8) cm2 s-1 for the cGMP diffusion coefficient. To properly compare the two sets of measurements, we have examined the diffusion of Fl-cGMP in the truncated ROS. From the kinetics of Fl-cGMP-activated currents, we have obtained a diffusion coefficient of 3 x 10(-8) cm2 s-1 for this analog; the cGMP diffusion coefficient measured from the same truncated ROSs was approximately 80 x 10(-8) cm2 s-1. Thus, a factor of 27 appears appropriate for correcting differences in size and intracellular binding between cGMP and Fl-cGMP. Application of this correction factor to the Fl-cGMP diffusion coefficient measurements by Olson and Pugh (1993) gives a cGMP diffusion coefficient of approximately 30 x 10(-8) cm2 s-1, in reasonable agreement with the value measured from the truncated ROS.
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Affiliation(s)
- Y Koutalos
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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27
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Abstract
AbstractRecoverin is a Ca2+-binding protein found primarily in vertebrate photoreceptors. The proposed physiological function of recoverin is based on the finding that recoverin inhibits light-stimulated phosphorylation of rhodopsin. Recoverin interacts with rod outer segment membranes in a Ca2+-dependent manner. This interaction requires N-terminal acylation of recoverin. Four types of fatty acids have been detected on the N-terminus of recoverin, but the functional significance of this heterogeneous acylation is not yet clear.
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28
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Future directions for rhodopsin structure and function studies. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractNMR (nuclear magnetic resonance) may be useful for determining the structure of retinal and its environment in rhodopsin, but not for determining the complete protein structure. Aggregation and low yield of fragments of rhodopsin may make them difficult to study by NMR. A long-term multidisciplinary attack on rhodopsin structure is required.
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29
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More answers about cGMP-gated channels pose more questions. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractOur understanding of the molecular properties and cellular role of cGMP-gated channels in outer segments of vertebrate photo-receptors has come from over a decade of studies which have continuously altered and refined ideas about these channels. Further examination of this current view may lead to future surprises and further refine the understanding of cGMP-gated channels.
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30
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Cyclic nucleotides as regulators of light-adaptation in photoreceptors. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractCyclic nucleotides can regulate the sensitivity of retinal rods to light through phosducin. The phosphorylation state of phosducin determines the amount of G available for activation by Rho*. Phosducin phosphorylation is regulated by cyclic nucleotides through their activation of cAMP-dependent protein kinase. The regulation of phosphodiesterase activity by the noncatalytic cGMP binding sites as well as Ca2+/calmodulin dependent regulation of cGMP binding to the cation channel are also discussed.
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31
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Long term potentiation and CaM-sensitive adenylyl cyclase: Long-term prospects. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractThe type I CaM-sensitive adenylyl cyclase is in a position to integrate signals from multiple inputs, consistent with the requirements for mediating long term potentiation (LTP). Biochemical and genetic evidence supports the idea that this enzyme plays an important role inc LTP. However, more work is needed before we will be certain of the role that CaM-sensitive adenylyl cyclases play in LTP.
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32
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Modulation of the cGMP-gated channel by calcium. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractCalcium acting through calmodulin has been shown to regulate the affinity of cyclic nucleotide-gated channels expressed in cell lines. But is calmodulin the Ca-sensor that normally regulates these channels?
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33
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How many light adaptation mechanisms are there? Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractThe generally positive response to our target article indicates that most of the commentators accept our contention that light adaptation consists of multiple and possibly redundant mechanisms. The commentaries fall into three general categories. The first deals with putative mechanisms that we chose not to emphasize. The second is a more extended discussion of the role of calcium in adaptation. Finally, additional aspects of cGMP involvement in adaptation are considered. We discuss each of these points in turn.
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34
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Gene therapy, regulatory mechanisms, and protein function in vision. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractHereditary retinal degeneration due to mutations in visual genes may be amenable to therapeutic interventions that modulate, either positively or negatively, the amount of protein product. Some of the proteins involved in phototransduction are rapidly moved by a lightdependent mechanism between the inner segment and the outer segment in rod photoreceptor cells, and this phenomenon is important in phototransduction.
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35
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A novel protein family of neuronal modulators. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractA number of proteins homologous to recoverin have been identified in the brains of the several vertebrate species. The brainderived members originally contain four EF-hand domains, but NH2- terminal domain is aberrant. Many of these proteins inhibited light-induced rhodopsin phosphorylation at high [Ca2+], suggesting that the brain-derived members may act as a Ca2+-sensitive modulator of receptor phosphorylation, as recoverin does.
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36
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The structure of rhodopsin and mechanisms of visual adaptation. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractRapidly advancing studies on rhodopsin have focused on new strategies for crystallization of this integral membrane protein for x-ray analysis and on alternative methods for structural determination from nuclear magnetic resonance data. Functional studies of the interactions between the apoprotein and its chromophore have clarified the role of the chromophore in deactivation of opsin and in photoactivation of the pigment.
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37
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Crucial steps in photoreceptor adaptation: Regulation of phosphodiesterase and guanylate cyclase activities and Ca 2+-buffering. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractThis commentary discusses the balance of phosphodiesterase and guanylate cyclase activities in vertebrate photoreceptors at moderate light intensities. The rate of cGMP hydrolysis and synthesis seem to equal each other. Ca2+ as regulator of both enzyme activities is also effectively buffered in photoreceptor cells by cytoplasmic buffer components.
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38
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The atomic structure of visual rhodopsin: How and when? Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractStrong arguments are presented by Hargrave suggesting that the crystallization of visual rhodopsin for high resolution analysis by X-ray crystallography or electron microscopy is feasible. However, the effort needed to achieve this goal will most likely exceed the resources of a single laboratory and a concerted approach to the research is necessary.
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39
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Molecular insights gained from covalently tethering cGMP to the ligand-binding sites of retinal rod cGMP-gated channels. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractA photoaffinity analog of cGMP has been used to biochemically identify a new ligand-binding subunit of the retinal rod cGMP-activated ion channel, as well as amino acids in contact with cGMP in the original subunit. Covalent tethering of this probe to channels in excised menbrane patches has revealed a functional heteogeneity in the ligand-binding sites that may arise from the two biochemically identified subunits.
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40
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Abstract
AbstractRecent findings emphasize the complexity, both genetic and functional, of the manifold genes and mutations causing inherited retinal degeneration in humans. Knowledge of the genetic bases of these diseases can contribute to design of rational therapy, as well as elucidating the function of each gene product in normal visual processes.
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41
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Channel structure and divalent cation regulation of phototransduction. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractThe identification of additional subunits of the cGMP-gated cation channel suggests exciting questions about their regulatory roles and about structure/functional relationships. How do the different subunits interact? How is the complex assembled into the plasma membrane? Divalent cations have been implicated in the regulation of adaptation. One often overlooked cation is magnesium. Could this ion play a role in phototransduction?
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42
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Structure of the cGMP-gated channel. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x0003939x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractThe subunit structure of the cGMP-gated cation channel of rod photoreceptors is rapidly being defined, and in the process the mode of regulation by Ca2+-calmodulin unraveled. Intriguingly, early results suggest that additional subunits of unknown function are associated with the channel and remain to be identified.
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43
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Linking genotypes with phenotypes in human retinal degenerations: Implications for future research and treatment. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractAlthough undoubtedly it will be incomplete by the time it is published, the target article by Daiger et al. organizes mutations in genes that produce retinal degenerations in humans into categories of clinically relevant phenotypes. Such classifications should help us understand the link between altered photoreceptor cell proteins and subsequent cell death, and they may yield insight into methods for preventing consequent blindness.
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44
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Genetic and clinical heterogeneity in tapetal retinal dystrophies. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x0003925x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractLarge scale DNA-mutation screening in patients with hereditary retinal diseases greatly enhances our knowledge about retinal function and diseases. Scientists, clinicians, patients, and families involved with retinal disorders may directly benefit from these developments. However, certain aspects of this expanding knowledge, such as the correlation between genotype and phenotype, may be much more complicated than we expect at present.
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45
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The determination of rhodopsin structure may require alternative approaches. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractThe structure of rhodopsin is a subject of intense interest. Solving the structure by traditional methods has proved exceedingly challenging. It may therefore be useful to confront the problem by a combination of alternate techniques. These include FTIR (Fourier transform infrared spectroscopy) and AFM (atomic force microscopy) on the intact protein. Furthermore, additional insights may be gained through structural investigations of discrete rhodopsin domains.
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46
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Na-Ca + K exchanger and Ca 2+ homeostasis in retinal rod outer segments: Inactivation of the Ca 2+ efflux mode and possible involvement of intracellular Ca 2+ stores in Ca 2+ homeostasis. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractInactivation of the Ca2+ extrusion mode of the retinal rod Na- Ca + K exchanger is suggested to be the mechanism that prevents lowering of cytosolic free Ca2+ to < 1 nM when rod cells are saturated for a prolonged time under bright light conditions. Under these conditions, Ca2+ fluxes across disk membranes can contribute significantly to Ca2+ homeostasis in rods.
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47
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Nuclear magnetic resonance studies on the structure and function of rhodopsin. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractMagic angle spinning (MAS) NMR methods provide a means of obtaining high resolution structural data on rhodopsin and its photoin termediates. Current work has focused on the structure of the retinal chromophore and its interactions with surrounding protein charges. The recent development of MAS NMR methods for measuring internuclear distances with a resolution of ∼0.2 will complement diffraction methods for addressing key mechanistic questions.
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48
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Glutamate accumulation in the photoreceptor-presumed final common path of photoreceptor cell death. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractGenetic abnormalities of three factors related to the photoreceptor mechanism have been reported in both animal models and humans. Apoptotic mechanism has also been suggested as a final common pathway of photoreceptor cell death. Our findings of increased level of glutamate in photoreceptor cells in rds mice suggest that amino acid might mediate between these two pathological mechanisms.
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49
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Unique lipids and unique properties of retinal proteins. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractAmino-terminal heteroacylation has been identified in retinal proteins including recoverin and α subunit of G-protein, transducin. The tissue-specific modification seems to mediate not only a proteinmembrane interaction but also a specific protein-protein interaction. The mechanism generating the heterogeneity and its physiological role are still unclear, but an interesting idea for the latter postulates a fine regulation of the signal transduction pathway by distinct N-acyl groups.
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50
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Further insight into the structural and regulatory properties of the cGMP-gated channel. Behav Brain Sci 1995. [DOI: 10.1017/s0140525x00039571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractRecent studies from several different laboratories have provided further insight into structure-function relationships of cyclic nucleotide-gated channel and in particular the cCMPgated channel of rod photoreceptors. Site-directed mutagenesis and rod-olfactory chimeria constructs have defined important amino acids and peptide segments of the channel that are important in ion blockage, ligand specificity, and gating properties. Molecular cloning studies have indicated that cyclic nucleotide-gated channels consist of two subunits that are required to reproduce the properties of the native channels. Biochemical analysis of the cGMP-gated channel of rodcells have indicated that the 240 kDa protein that co-purifies with the 63 kDa channel subunit contains both the previously cloned second subunit of the channel and a glutamic acid-rich protein. The regulatory properties of the cGMP-gated channel from rod cells has also been studied in more detail. Studies indicate that the beta subunit of the cGMP-gated channel of rod cells contains the binding site for calmodulin. Interaction of calmodulin with the channel alters the apparent affinity of the channel for cGMP in all in vitro systems that have been studied. The significance of these recent studies are discussed in relation to the commentaries on the target article.
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