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Koch KW, Dell'Orco D. Protein and Signaling Networks in Vertebrate Photoreceptor Cells. Front Mol Neurosci 2015; 8:67. [PMID: 26635520 PMCID: PMC4646965 DOI: 10.3389/fnmol.2015.00067] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 10/26/2015] [Indexed: 01/10/2023] Open
Abstract
Vertebrate photoreceptor cells are exquisite light detectors operating under very dim and bright illumination. The photoexcitation and adaptation machinery in photoreceptor cells consists of protein complexes that can form highly ordered supramolecular structures and control the homeostasis and mutual dependence of the secondary messengers cyclic guanosine monophosphate (cGMP) and Ca2+. The visual pigment in rod photoreceptors, the G protein-coupled receptor rhodopsin is organized in tracks of dimers thereby providing a signaling platform for the dynamic scaffolding of the G protein transducin. Illuminated rhodopsin is turned off by phosphorylation catalyzed by rhodopsin kinase (GRK1) under control of Ca2+-recoverin. The GRK1 protein complex partly assembles in lipid raft structures, where shutting off rhodopsin seems to be more effective. Re-synthesis of cGMP is another crucial step in the recovery of the photoresponse after illumination. It is catalyzed by membrane bound sensory guanylate cyclases (GCs) and is regulated by specific neuronal Ca2+-sensor proteins called guanylate cyclase-activating proteins (GCAPs). At least one GC (ROS-GC1) was shown to be part of a multiprotein complex having strong interactions with the cytoskeleton and being controlled in a multimodal Ca2+-dependent fashion. The final target of the cGMP signaling cascade is a cyclic nucleotide-gated (CNG) channel that is a hetero-oligomeric protein located in the plasma membrane and interacting with accessory proteins in highly organized microdomains. We summarize results and interpretations of findings related to the inhomogeneous organization of signaling units in photoreceptor outer segments.
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Affiliation(s)
- Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurological, Biomedical and Movement Sciences, Section of Biological Chemistry and Center for BioMedical Computing (CBMC), University of Verona Verona, Italy
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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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Wolbring G, Schnetkamp PP. Spectrophotometric determination of retinal rod guanylyl cyclase. Methods Enzymol 2000; 315:718-29. [PMID: 10736736 DOI: 10.1016/s0076-6879(00)15877-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Affiliation(s)
- G Wolbring
- Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Alberta, Canada
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Biel M, Seeliger M, Pfeifer A, Kohler K, Gerstner A, Ludwig A, Jaissle G, Fauser S, Zrenner E, Hofmann F. Selective loss of cone function in mice lacking the cyclic nucleotide-gated channel CNG3. Proc Natl Acad Sci U S A 1999; 96:7553-7. [PMID: 10377453 PMCID: PMC22124 DOI: 10.1073/pnas.96.13.7553] [Citation(s) in RCA: 206] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two types of photoreceptors, rods and cones, coexist in the vertebrate retina. An in-depth analysis of the retinal circuitry that transmits rod and cone signals has been hampered by the presence of intimate physical and functional connections between rod and cone pathways. By deleting the cyclic nucleotide-gated channel CNG3 we have generated a mouse lacking any cone-mediated photoresponse. In contrast, the rod pathway is completely intact in CNG3-deficient mice. The functional loss of cone function correlates with a progressive degeneration of cone photoreceptors but not of other retinal cell types. CNG3-deficient mice provide an animal model to dissect unequivocally the contribution of rod and cone pathways for normal retinal function.
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Affiliation(s)
- M Biel
- Institut für Pharmakologie und Toxikologie, Technische Universität München, Biedersteiner Strasse 29, 80802 Munich, Germany
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Abstract
Cyclic-nucleotide-gated (CNG) channels play key roles in photoreceptor and olfactory signal-transduction pathways. Recent studies have focused on the molecular characterization of CNG channel subunits and on the identification of the structural domains that contribute to ligand selectivity and affinity, ion gating and permeation, and regulation of channel activity. Calmodulin has been shown to bind directly to the rod and olfactory channels and to modulate their sensitivity to cyclic nucleotides. This Ca2+-dependent regulation of channel activity appears to play a role in the termination of the signal-transduction pathway in olfactory neurons and rod photoreceptor cells. It remains to be determined whether calmodulin also regulates the activity of related channels in other cells.
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Affiliation(s)
- R S Molday
- Department of Biochemistry and Molecular Biology, 2146 Health Sciences Mall, University of British Columbia, Vancouver, V6T 1Z3, Canada.
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Bauer PJ. Cyclic GMP-gated channels of bovine rod photoreceptors: affinity, density and stoichiometry of Ca(2+)-calmodulin binding sites. J Physiol 1996; 494 ( Pt 3):675-85. [PMID: 8865065 PMCID: PMC1160668 DOI: 10.1113/jphysiol.1996.sp021523] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. Ca(2+)-loaded vesicles of bovine rod outer segment (ROS) membranes were used to examine the influence of Ca(2+)-calmodulin (Ca(2+)-CaM) on the activity of cGMP-gated channels. 2. In vesicles prepared from ROS membranes which were washed at zero free Ca2+, Ca(2+)-CaM reduced the Ca2+ flux to maximally 40%. The dose-response curve for activation of the cGMP-gated channel had a half-maximal value of 36.8 +/- 2 microM in the CaM-free state, and of 55.6 +/- 5.2 microM in the Ca(2+)-CaM-bound state. In both cases the Hill coefficients were 2.2 +/- 0.2. 3. In vesicles prepared from ROS membranes which were washed at 100 microM Ca2+, the dose-response curve was identical to the Ca(2+)-CaM-bound state. 4. Titration of the Ca(2+)-CaM-dependent decrease of the channel activity upon addition of 40 microM cGMP yielded half-maximal Ca(2+)-CaM concentrations (EC50CaM) which were linearly correlated with the concentration of membrane vesicles. Extrapolation of EC50CaM to infinite dilution of vesicles yielded a Ca(2+)-CaM affinity constant for the cGMP-gated channel of 1.01 +/- 0.20 nM. Hill analysis of the Ca(2+)-CaM titrations resulted in a Hill coefficient of 1.36 +/- 0.15. 5. From the slope of the linear regression of EC50CaM plotted vs. the rhodopsin concentration, the molar ratio of rhodopsin to externally accessible Ca(2+)-CaM binding sites of fused ROS membranes was determined to be 1439 +/- 109. Therefore, there are about 720 molecules of rhodopsin per Ca(2+)-CaM binding site present in ROS. 6. Based on these data, a density of 560 Ca(2+)-CaM binding sites micron-2 is estimated for the plasma membrane of bovine ROS, suggesting that there are two Ca(2+)-CaM binding sites per channel. 7. The Ca(2+)-CaM effect did not become noticeable until the ROS membranes were hypotonically washed at free [Ca2+] below 100 nM, suggesting that an endogenous Ca(2+)-binding protein was washed off in the absence of Ca2+. 8. If the endogenous Ca(2+)-binding protein of bovine ROS membranes was washed off at zero Ca2+ and then Ca(2+)-CaM added, Ca(2+)-CaM could only be washed off again at free [Ca2+] below 100 nM. 9. These findings strongly suggest that the endogenous Ca(2+)-binding protein of the bovine cGMP-gated channel is CaM.
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Affiliation(s)
- P J Bauer
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany.
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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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Abstract
A decrease of cytoplasmic Ca(2+)-concentration in vertebrate photoreceptor cells after illumination is necessary for light adaptation. Although the mechanisms of adaptation is not completely understood, several Ca(2+)-dependent cellular processes have been discovered. Some involve calcium-binding proteins like recoverin, guanylyl cyclase-activating protein and calmodulin, and their target proteins rhodopsin kinase, guanylyl cyclase, the cGMP-gated channel, and NO synthase. The activity of several enzymes or channels is directly controlled by Ca2+ and does not involve calcium-binding proteins. These proteins are pyrophosphatase, protein kinase C and the cGMP-gated channel.
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Affiliation(s)
- K W Koch
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany
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Körschen HG, Illing M, Seifert R, Sesti F, Williams A, Gotzes S, Colville C, Müller F, Dosé A, Godde M. A 240 kDa protein represents the complete beta subunit of the cyclic nucleotide-gated channel from rod photoreceptor. Neuron 1995; 15:627-36. [PMID: 7546742 DOI: 10.1016/0896-6273(95)90151-5] [Citation(s) in RCA: 204] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The cyclic nucleotide-gated channel from rod photoreceptors is composed of two distinct subunits (alpha and beta). The properties of the alpha subunit, which can form functional channels by itself, are modified by coexpression with a homologous polypeptide, designated the beta subunit. However, the alpha subunit from rod photoreceptor membranes copurifies with a 240 kDa protein that is significantly larger than this putative beta subunit. We now demonstrate by peptide sequencing and by cloning and functional expression of cDNA that the 240 kDa protein represents the complete beta subunit with an unusual bipartite structure. The N-terminal part is essentially identical to a glutamic acid-rich protein (GARP), whereas the C-terminal part is highly homologous to the previously cloned human "beta subunit." Expression of the complete beta subunit in HEK 293 cells results in a polypeptide with the same apparent molecular weight as the 240 kDa protein of the native rod channel. Coexpression of the alpha subunit with the full-length beta subunit yields hetero-oligomeric channels with properties characteristic of the native channel.
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Affiliation(s)
- H G Körschen
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany
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Tanaka T, Ames JB, Harvey TS, Stryer L, Ikura M. Sequestration of the membrane-targeting myristoyl group of recoverin in the calcium-free state. Nature 1995; 376:444-7. [PMID: 7630423 DOI: 10.1038/376444a0] [Citation(s) in RCA: 258] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Recoverin, a retinal calcium-binding protein of relative molecular mass (M(r)) 23K, participates in the recovery phase of visual excitation and in adaptation to background light. The Ca(2+)-bound form of recoverin prolongs the photoresponse, probably by blocking phosphorylation of photoexcited rhodopsin. Retinal recoverin contains a covalently attached myristoyl group or related acyl group at its amino terminus and two Ca(2+)-binding sites. Ca2+ binding to myristoylated, but not unmyristoylated, recoverin induces its translocation to bilayer membranes, indicating that the myristoyl group is essential to the read-out of calcium signals (calcium-myristoyl switch). Here we present the solution structure of Ca(2+)-free, myristoylated recombinant recoverin obtained by heteronuclear multidimensional NMR spectroscopy. The myristoyl group is sequestered in a deep hydrophobic pocket formed by many aromatic and other hydrophobic residues from five flanking helices.
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Affiliation(s)
- T Tanaka
- Division of Molecular and Structural Biology, Ontario Cancer Institute, Toronto, Canada
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Abstract
A variety of different cyclic nucleotide gated ion channels have recently been identified using molecular cloning and electrophysiological techniques. Current research is focussed on the specific molecular determinants that endow these channels with their distinctive character of gating, selectivity and modulation. In some cases, it has been possible to identify the specific physiological roles of different cyclic nucleotide gated channels. Their interactions with Ca2+ and calmodulin are particularly important, and determine the specific functions these channels subserve in distinct cells.
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Affiliation(s)
- U B Kaupp
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany
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Frings S, Seifert R, Godde M, Kaupp UB. Profoundly different calcium permeation and blockage determine the specific function of distinct cyclic nucleotide-gated channels. Neuron 1995; 15:169-79. [PMID: 7542461 DOI: 10.1016/0896-6273(95)90074-8] [Citation(s) in RCA: 233] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Sensory transduction in vertebrate photoreceptors and olfactory sensory neurons is mediated by cyclic nucleotide-gated (CNG) channels that conduct mono- and divalent cations. Ca2+ entering the cell through CNG channels intimately controls signaling pathways by regulating several key enzymes. Cloned CNG channels from photoreceptors and olfactory sensory neurons profoundly differ in their relative Ca2+ permeability, their blockage by external divalent cations, and the fraction of current carried by Ca2+. In particular, CNG channels from cone photoreceptors conduct significantly more Ca2+ than those from rod photoreceptors. Furthermore, the current through the olfactory CNG channel is entirely carried by Ca2+ at approximately 3 mM extracellular Ca2+. These results suggest that a major function of CNG channels is to provide a pathway for Ca2+ entry.
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Affiliation(s)
- S Frings
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Federal Republic of Germany
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