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Asteriti S, Marino V, Avesani A, Biasi A, Dal Cortivo G, Cangiano L, Dell'Orco D. Recombinant protein delivery enables modulation of the phototransduction cascade in mouse retina. Cell Mol Life Sci 2023; 80:371. [PMID: 38001384 PMCID: PMC10673981 DOI: 10.1007/s00018-023-05022-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Revised: 10/10/2023] [Accepted: 10/27/2023] [Indexed: 11/26/2023]
Abstract
Inherited retinal dystrophies are often associated with mutations in the genes involved in the phototransduction cascade in photoreceptors, a paradigmatic signaling pathway mediated by G protein-coupled receptors. Photoreceptor viability is strictly dependent on the levels of the second messengers cGMP and Ca2+. Here we explored the possibility of modulating the phototransduction cascade in mouse rods using direct or liposome-mediated administration of a recombinant protein crucial for regulating the interplay of the second messengers in photoreceptor outer segments. The effects of administration of the free and liposome-encapsulated human guanylate cyclase-activating protein 1 (GCAP1) were compared in biological systems of increasing complexity (in cyto, ex vivo, and in vivo). The analysis of protein biodistribution and the direct measurement of functional alteration in rod photoresponses show that the exogenous GCAP1 protein is fully incorporated into the mouse retina and photoreceptor outer segments. Furthermore, only in the presence of a point mutation associated with cone-rod dystrophy in humans p.(E111V), protein delivery induces a disease-like electrophysiological phenotype, consistent with constitutive activation of the retinal guanylate cyclase. Our study demonstrates that both direct and liposome-mediated protein delivery are powerful complementary tools for targeting signaling cascades in neuronal cells, which could be particularly important for the treatment of autosomal dominant genetic diseases.
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Affiliation(s)
- Sabrina Asteriti
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134, Verona, Italy
- Department of Translational Research, University of Pisa, 56123, Pisa, Italy
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134, Verona, Italy
| | - Anna Avesani
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134, Verona, Italy
| | - Amedeo Biasi
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134, Verona, Italy
| | - Giuditta Dal Cortivo
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134, Verona, Italy
| | - Lorenzo Cangiano
- Department of Translational Research, University of Pisa, 56123, Pisa, Italy.
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134, Verona, Italy.
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2
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Barret D, Schuster D, Rodrigues M, Leitner A, Picotti P, Schertler G, Kaupp U, Korkhov V, Marino J. Structural basis of calmodulin modulation of the rod cyclic nucleotide-gated channel. Proc Natl Acad Sci U S A 2023; 120:e2300309120. [PMID: 37011209 PMCID: PMC10104587 DOI: 10.1073/pnas.2300309120] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2023] [Accepted: 03/06/2023] [Indexed: 04/05/2023] Open
Abstract
Calmodulin (CaM) regulates many ion channels to control calcium entry into cells, and mutations that alter this interaction are linked to fatal diseases. The structural basis of CaM regulation remains largely unexplored. In retinal photoreceptors, CaM binds to the CNGB subunit of cyclic nucleotide-gated (CNG) channels and, thereby, adjusts the channel's Cyclic guanosine monophosphate (cGMP) sensitivity in response to changes in ambient light conditions. Here, we provide the structural characterization for CaM regulation of a CNG channel by using a combination of single-particle cryo-electron microscopy and structural proteomics. CaM connects the CNGA and CNGB subunits, resulting in structural changes both in the cytosolic and transmembrane regions of the channel. Cross-linking and limited proteolysis-coupled mass spectrometry mapped the conformational changes induced by CaM in vitro and in the native membrane. We propose that CaM is a constitutive subunit of the rod channel to ensure high sensitivity in dim light. Our mass spectrometry-based approach is generally relevant for studying the effect of CaM on ion channels in tissues of medical interest, where only minute quantities are available.
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Affiliation(s)
- Diane C. A. Barret
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
| | - Dina Schuster
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
- Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8049Zürich, Switzerland
- Institute of Molecular Biology and Biophysics, ETH Zürich, 8049Zurich, Switzerland
| | - Matthew J. Rodrigues
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
| | - Alexander Leitner
- Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8049Zürich, Switzerland
| | - Paola Picotti
- Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8049Zürich, Switzerland
| | | | - U. Benjamin Kaupp
- Life and Medical Sciences Institute, University of Bonn, 53115Bonn, Germany
- Max Planck Institute for Multidisciplinary Sciences, 37077Göttingen, Germany
| | - Volodymyr M. Korkhov
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
- Institute of Molecular Biology and Biophysics, ETH Zürich, 8049Zurich, Switzerland
| | - Jacopo Marino
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
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3
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Ames JB. Structural basis of retinal membrane guanylate cyclase regulation by GCAP1 and RD3. Front Mol Neurosci 2022; 15:988142. [PMID: 36157073 PMCID: PMC9493048 DOI: 10.3389/fnmol.2022.988142] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 08/22/2022] [Indexed: 11/13/2022] Open
Abstract
Retinal membrane guanylate cyclases (RetGC1 and RetGC2) are expressed in photoreceptor rod and cone cells, where they promote the onset of visual recovery during phototransduction. The catalytic activity of RetGCs is regulated by their binding to regulatory proteins, guanylate cyclase activating proteins (GCAP1-5) and the retinal degeneration 3 protein (RD3). RetGC1 is activated by its binding to Ca2+-free/Mg2+-bound GCAP1 at low cytosolic Ca2+ levels in light-activated photoreceptors. By contrast, RetGC1 is inactivated by its binding to Ca2+-bound GCAP1 and/or RD3 at elevated Ca2+ levels in dark-adapted photoreceptors. The Ca2+ sensitive cyclase activation helps to replenish the cytosolic cGMP levels in photoreceptors during visual recovery. Mutations in RetGC1, GCAP1 or RD3 that disable the Ca2+-dependent regulation of cyclase activity are genetically linked to rod/cone dystrophies and other inherited forms of blindness. Here I review the structural interaction of RetGC1 with GCAP1 and RD3. I propose a two-state concerted model in which the dimeric RetGC1 allosterically switches between active and inactive conformational states with distinct quaternary structures that are oppositely stabilized by the binding of GCAP1 and RD3. The binding of Ca2+-free/Mg2+-bound GCAP1 is proposed to activate the cyclase by stabilizing RetGC1 in an active conformation (R-state), whereas Ca2+-bound GCAP1 and/or RD3 inhibit the cyclase by locking RetGC1 in an inactive conformation (T-state). Exposed hydrophobic residues in GCAP1 (residues H19, Y22, M26, F73, V77, W94) are essential for cyclase activation and could be targeted by rational drug design for the possible treatment of rod/cone dystrophies.
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Barret DC, Kaupp UB, Marino J. The structure of cyclic nucleotide-gated channels in rod and cone photoreceptors. Trends Neurosci 2022; 45:763-776. [DOI: 10.1016/j.tins.2022.07.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 07/06/2022] [Accepted: 07/19/2022] [Indexed: 10/16/2022]
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Avesani A, Bielefeld L, Weisschuh N, Marino V, Mazzola P, Stingl K, Haack TB, Koch KW, Dell’Orco D. Molecular Properties of Human Guanylate Cyclase-Activating Protein 3 (GCAP3) and Its Possible Association with Retinitis Pigmentosa. Int J Mol Sci 2022; 23:ijms23063240. [PMID: 35328663 PMCID: PMC8948881 DOI: 10.3390/ijms23063240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 03/12/2022] [Accepted: 03/15/2022] [Indexed: 11/17/2022] Open
Abstract
The cone-specific guanylate cyclase-activating protein 3 (GCAP3), encoded by the GUCA1C gene, has been shown to regulate the enzymatic activity of membrane-bound guanylate cyclases (GCs) in bovine and teleost fish photoreceptors, to an extent comparable to that of the paralog protein GCAP1. To date, the molecular mechanisms underlying GCAP3 function remain largely unexplored. In this work, we report a thorough characterization of the biochemical and biophysical properties of human GCAP3, moreover, we identified an isolated case of retinitis pigmentosa, in which a patient carried the c.301G>C mutation in GUCA1C, resulting in the substitution of a highly conserved aspartate residue by a histidine (p.(D101H)). We found that myristoylated GCAP3 can activate GC1 with a similar Ca2+-dependent profile, but significantly less efficiently than GCAP1. The non-myristoylated form did not induce appreciable regulation of GC1, nor did the p.D101H variant. GCAP3 forms dimers under physiological conditions, but at odds with its paralogs, it tends to form temperature-dependent aggregates driven by hydrophobic interactions. The peculiar properties of GCAP3 were confirmed by 2 ms molecular dynamics simulations, which for the p.D101H variant highlighted a very high structural flexibility and a clear tendency to lose the binding of a Ca2+ ion to EF3. Overall, our data show that GCAP3 has unusual biochemical properties, which make the protein significantly different from GCAP1 and GCAP2. Moreover, the newly identified point mutation resulting in a substantially unfunctional protein could trigger retinitis pigmentosa through a currently unknown mechanism.
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Affiliation(s)
- Anna Avesani
- Section of Biological Chemistry, Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, 37134 Verona, Italy; (A.A.); (V.M.)
| | - Laura Bielefeld
- Division of Biochemistry, Department of Neuroscience, University of Oldenburg, 26111 Oldenburg, Germany; (L.B.); (K.-W.K.)
| | - Nicole Weisschuh
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, 72076 Tübingen, Germany;
| | - Valerio Marino
- Section of Biological Chemistry, Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, 37134 Verona, Italy; (A.A.); (V.M.)
| | - Pascale Mazzola
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076 Tübingen, Germany; (P.M.); (T.B.H.)
| | - Katarina Stingl
- University Eye Hospital, Centre for Ophthalmology, University of Tübingen, 72076 Tübingen, Germany;
| | - Tobias B. Haack
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076 Tübingen, Germany; (P.M.); (T.B.H.)
- Centre for Rare Diseases, University of Tübingen, 72076 Tübingen, Germany
| | - Karl-Wilhelm Koch
- Division of Biochemistry, Department of Neuroscience, University of Oldenburg, 26111 Oldenburg, Germany; (L.B.); (K.-W.K.)
| | - Daniele Dell’Orco
- Section of Biological Chemistry, Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, 37134 Verona, Italy; (A.A.); (V.M.)
- Correspondence: ; Tel.: +39-045-802-7637
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6
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Kawamura S, Tachibanaki S. Molecular basis of rod and cone differences. Prog Retin Eye Res 2021; 90:101040. [PMID: 34974196 DOI: 10.1016/j.preteyeres.2021.101040] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2021] [Revised: 12/22/2021] [Accepted: 12/27/2021] [Indexed: 12/15/2022]
Abstract
In the vertebrate retina, rods and cones both detect light, but they are different in functional aspects such as light sensitivity and time resolution, for example, and in some of cell biological aspects. For functional aspects, both photoreceptors are known to share a common mechanism, phototransduction cascade, consisting of a series of enzyme reactions to convert a photon-capture signal to an electrical signal. To understand the mechanisms of the functional differences between rods and cones at the molecular level, we compared biochemically each of the reactions in the phototransduction cascade between rods and cones using the cells isolated and purified from carp retina. Although proteins in the cascade are functionally similar between rods and cones, their activities together with their expression levels are mostly different between these photoreceptors. In general, reactions to generate a response are slightly less effective, as a total, in cones than in rods, but each of the reactions for termination and recovery of a response are much more effective in cones. These findings explain lower light sensitivity and briefer light responses in cones than in rods. In addition, our considerations suggest that a Ca2+-binding protein, S-modulin or recoverin, has a currently unnoticed role in shaping light responses. With comparison of the expression levels of proteins and/or mRNAs using purified cells, several proteins were found to be specifically or predominantly expressed in cones. These proteins would be of interest for future studies on the difference between rods and cones.
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Affiliation(s)
- Satoru Kawamura
- Graduate School of Frontier Biosciences, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan.
| | - Shuji Tachibanaki
- Graduate School of Frontier Biosciences, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan.
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Biasi A, Marino V, Dal Cortivo G, Maltese PE, Modarelli AM, Bertelli M, Colombo L, Dell’Orco D. A Novel GUCA1A Variant Associated with Cone Dystrophy Alters cGMP Signaling in Photoreceptors by Strongly Interacting with and Hyperactivating Retinal Guanylate Cyclase. Int J Mol Sci 2021; 22:ijms221910809. [PMID: 34639157 PMCID: PMC8509414 DOI: 10.3390/ijms221910809] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 09/30/2021] [Accepted: 10/04/2021] [Indexed: 11/19/2022] Open
Abstract
Guanylate cyclase-activating protein 1 (GCAP1), encoded by the GUCA1A gene, is a neuronal calcium sensor protein involved in shaping the photoresponse kinetics in cones and rods. GCAP1 accelerates or slows the cGMP synthesis operated by retinal guanylate cyclase (GC) based on the light-dependent levels of intracellular Ca2+, thereby ensuring a timely regulation of the phototransduction cascade. We found a novel variant of GUCA1A in a patient affected by autosomal dominant cone dystrophy (adCOD), leading to the Asn104His (N104H) amino acid substitution at the protein level. While biochemical analysis of the recombinant protein showed impaired Ca2+ sensitivity of the variant, structural properties investigated by circular dichroism and limited proteolysis excluded major structural rearrangements induced by the mutation. Analytical gel filtration profiles and dynamic light scattering were compatible with a dimeric protein both in the presence of Mg2+ alone and Mg2+ and Ca2+. Enzymatic assays showed that N104H-GCAP1 strongly interacts with the GC, with an affinity that doubles that of the WT. The doubled IC50 value of the novel variant (520 nM for N104H vs. 260 nM for the WT) is compatible with a constitutive activity of GC at physiological levels of Ca2+. The structural region at the interface with the GC may acquire enhanced flexibility under high Ca2+ conditions, as suggested by 2 μs molecular dynamics simulations. The altered interaction with GC would cause hyper-activity of the enzyme at both low and high Ca2+ levels, which would ultimately lead to toxic accumulation of cGMP and Ca2+ in the photoreceptor outer segment, thus triggering cell death.
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Affiliation(s)
- Amedeo Biasi
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134 Verona, Italy; (A.B.); (V.M.); (G.D.C.)
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134 Verona, Italy; (A.B.); (V.M.); (G.D.C.)
| | - Giuditta Dal Cortivo
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134 Verona, Italy; (A.B.); (V.M.); (G.D.C.)
| | | | - Antonio Mattia Modarelli
- Department of Ophthalmology, ASST Santi Paolo e Carlo Hospital, University of Milan, 20142 Milano, Italy;
| | - Matteo Bertelli
- MAGI’S Lab s.r.l., 38068 Rovereto, Italy; (P.E.M.); (M.B.)
- MAGI Euregio, 39100 Bolzano, Italy
| | - Leonardo Colombo
- Department of Ophthalmology, ASST Santi Paolo e Carlo Hospital, University of Milan, 20142 Milano, Italy;
- Correspondence: (L.C.); (D.D.); Tel.: +39-02-81844301 (L.C.); +39-045-802-7637 (D.D.)
| | - Daniele Dell’Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37134 Verona, Italy; (A.B.); (V.M.); (G.D.C.)
- Correspondence: (L.C.); (D.D.); Tel.: +39-02-81844301 (L.C.); +39-045-802-7637 (D.D.)
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8
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Structural Insights into Retinal Guanylate Cyclase Activator Proteins (GCAPs). Int J Mol Sci 2021; 22:ijms22168731. [PMID: 34445435 PMCID: PMC8395740 DOI: 10.3390/ijms22168731] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 08/09/2021] [Accepted: 08/10/2021] [Indexed: 11/16/2022] Open
Abstract
Retinal guanylate cyclases (RetGCs) promote the Ca2+-dependent synthesis of cGMP that coordinates the recovery phase of visual phototransduction in retinal rods and cones. The Ca2+-sensitive activation of RetGCs is controlled by a family of photoreceptor Ca2+ binding proteins known as guanylate cyclase activator proteins (GCAPs). The Mg2+-bound/Ca2+-free GCAPs bind to RetGCs and activate cGMP synthesis (cyclase activity) at low cytosolic Ca2+ levels in light-activated photoreceptors. By contrast, Ca2+-bound GCAPs bind to RetGCs and inactivate cyclase activity at high cytosolic Ca2+ levels found in dark-adapted photoreceptors. Mutations in both RetGCs and GCAPs that disrupt the Ca2+-dependent cyclase activity are genetically linked to various retinal diseases known as cone-rod dystrophies. In this review, I will provide an overview of the known atomic-level structures of various GCAP proteins to understand how protein dimerization and Ca2+-dependent conformational changes in GCAPs control the cyclase activity of RetGCs. This review will also summarize recent structural studies on a GCAP homolog from zebrafish (GCAP5) that binds to Fe2+ and may serve as a Fe2+ sensor in photoreceptors. The GCAP structures reveal an exposed hydrophobic surface that controls both GCAP1 dimerization and RetGC binding. This exposed site could be targeted by therapeutics designed to inhibit the GCAP1 disease mutants, which may serve to mitigate the onset of retinal cone-rod dystrophies.
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Marino V, Dal Cortivo G, Maltese PE, Placidi G, De Siena E, Falsini B, Bertelli M, Dell’Orco D. Impaired Ca 2+ Sensitivity of a Novel GCAP1 Variant Causes Cone Dystrophy and Leads to Abnormal Synaptic Transmission Between Photoreceptors and Bipolar Cells. Int J Mol Sci 2021; 22:ijms22084030. [PMID: 33919796 PMCID: PMC8070792 DOI: 10.3390/ijms22084030] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Revised: 04/06/2021] [Accepted: 04/09/2021] [Indexed: 01/23/2023] Open
Abstract
Guanylate cyclase-activating protein 1 (GCAP1) is involved in the shutdown of the phototransduction cascade by regulating the enzymatic activity of retinal guanylate cyclase via a Ca2+/cGMP negative feedback. While the phototransduction-associated role of GCAP1 in the photoreceptor outer segment is widely established, its implication in synaptic transmission to downstream neurons remains to be clarified. Here, we present clinical and biochemical data on a novel isolate GCAP1 variant leading to a double amino acid substitution (p.N104K and p.G105R) and associated with cone dystrophy (COD) with an unusual phenotype. Severe alterations of the electroretinogram were observed under both scotopic and photopic conditions, with a negative pattern and abnormally attenuated b-wave component. The biochemical and biophysical analysis of the heterologously expressed N104K-G105R variant corroborated by molecular dynamics simulations highlighted a severely compromised Ca2+-sensitivity, accompanied by minor structural and stability alterations. Such differences reflected on the dysregulation of both guanylate cyclase isoforms (RetGC1 and RetGC2), resulting in the constitutive activation of both enzymes at physiological levels of Ca2+. As observed with other GCAP1-associated COD, perturbation of the homeostasis of Ca2+ and cGMP may lead to the toxic accumulation of second messengers, ultimately triggering cell death. However, the abnormal electroretinogram recorded in this patient also suggested that the dysregulation of the GCAP1–cyclase complex further propagates to the synaptic terminal, thereby altering the ON-pathway related to the b-wave generation. In conclusion, the pathological phenotype may rise from a combination of second messengers’ accumulation and dysfunctional synaptic communication with bipolar cells, whose molecular mechanisms remain to be clarified.
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Affiliation(s)
- Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37129 Verona, Italy; (V.M.); (G.D.C.)
| | - Giuditta Dal Cortivo
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37129 Verona, Italy; (V.M.); (G.D.C.)
| | | | - Giorgio Placidi
- Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, 00168 Rome, Italy; (G.P.); (E.D.S.)
- Università Cattolica del Sacro Cuore, 00168 Rome, Italy
| | - Elisa De Siena
- Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, 00168 Rome, Italy; (G.P.); (E.D.S.)
- Università Cattolica del Sacro Cuore, 00168 Rome, Italy
| | - Benedetto Falsini
- Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, 00168 Rome, Italy; (G.P.); (E.D.S.)
- Università Cattolica del Sacro Cuore, 00168 Rome, Italy
- Correspondence: (B.F.); (D.D.); Tel.: +39-06-3015-6344 (B.F.); +39-045-802-7637 (D.D.)
| | - Matteo Bertelli
- MAGI’S Lab S.R.L., 38068 Rovereto, Italy; (P.E.M.); (M.B.)
- MAGI Euregio, 39100 Bolzano, Italy
| | - Daniele Dell’Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37129 Verona, Italy; (V.M.); (G.D.C.)
- Correspondence: (B.F.); (D.D.); Tel.: +39-06-3015-6344 (B.F.); +39-045-802-7637 (D.D.)
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10
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Avesani A, Marino V, Zanzoni S, Koch KW, Dell'Orco D. Molecular properties of human guanylate cyclase-activating protein 2 (GCAP2) and its retinal dystrophy-associated variant G157R. J Biol Chem 2021; 296:100619. [PMID: 33812995 PMCID: PMC8113879 DOI: 10.1016/j.jbc.2021.100619] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 03/25/2021] [Accepted: 03/30/2021] [Indexed: 12/31/2022] Open
Abstract
In murine and bovine photoreceptors, guanylate cyclase-activating protein 2 (GCAP2) activates retinal guanylate cyclases (GCs) at low Ca2+ levels, thus contributing to the Ca2+/cGMP negative feedback on the cyclase together with its paralog guanylate cyclase-activating protein 1, which has the same function but different Ca2+ sensitivity. In humans, a GCAP2 missense mutation (G157R) has been associated with inherited retinal degeneration (IRD) via an unknown molecular mechanism. Here, we characterized the biochemical properties of human GCAP2 and the G157R variant, focusing on its dimerization and the Ca2+/Mg2+-binding processes in the presence or absence of N-terminal myristoylation. We found that human GCAP2 and its bovine/murine orthologs significantly differ in terms of oligomeric properties, cation binding, and GC regulation. Myristoylated GCAP2 endothermically binds up to 3 Mg2+ with high affinity and forms a compact dimer that may reversibly dissociate in the presence of Ca2+. Conversely, nonmyristoylated GCAP2 does not bind Mg2+ over the physiological range and remains as a monomer in the absence of Ca2+. Both myristoylated and nonmyristoylated GCAP2 bind Ca2+ with high affinity. At odds with guanylate cyclase-activating protein 1 and independently of myristoylation, human GCAP2 does not significantly activate retinal GC1 in a Ca2+-dependent fashion. The IRD-associated G157R variant is characterized by a partly misfolded, molten globule-like conformation with reduced affinity for cations and prone to form aggregates, likely mediated by hydrophobic interactions. Our findings suggest that GCAP2 might be mostly implicated in processes other than phototransduction in human photoreceptors and suggest a possible molecular mechanism for G157R-associated IRD.
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Affiliation(s)
- Anna Avesani
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche, University of Verona, Verona, Italy
| | - Karl-Wilhelm Koch
- Department of Neuroscience, Division of Biochemistry, University of Oldenburg, Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy.
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11
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Regulation of retinal membrane guanylyl cyclase (RetGC) by negative calcium feedback and RD3 protein. Pflugers Arch 2021; 473:1393-1410. [PMID: 33537894 PMCID: PMC8329130 DOI: 10.1007/s00424-021-02523-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 01/19/2021] [Accepted: 01/21/2021] [Indexed: 11/07/2022]
Abstract
This article presents a brief overview of the main biochemical and cellular processes involved in regulation of cyclic GMP production in photoreceptors. The main focus is on how the fluctuations of free calcium concentrations in photoreceptors between light and dark regulate the activity of retinal membrane guanylyl cyclase (RetGC) via calcium sensor proteins. The emphasis of the review is on the structure of RetGC and guanylyl cyclase activating proteins (GCAPs) in relation to their functional role in photoreceptors and congenital diseases of photoreceptors. In addition to that, the structure and function of retinal degeneration-3 protein (RD3), which regulates RetGC in a calcium-independent manner, is discussed in detail in connections with its role in photoreceptor biology and inherited retinal blindness.
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12
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Dal Cortivo G, Marino V, Bonì F, Milani M, Dell'Orco D. Missense mutations affecting Ca 2+-coordination in GCAP1 lead to cone-rod dystrophies by altering protein structural and functional properties. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1867:118794. [PMID: 32650103 DOI: 10.1016/j.bbamcr.2020.118794] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 07/01/2020] [Accepted: 07/03/2020] [Indexed: 02/06/2023]
Abstract
Guanylate cyclase activating protein 1 (GCAP1) is a neuronal calcium sensor (NCS) involved in the early biochemical steps underlying the phototransduction cascade. By switching from a Ca2+-bound form in the dark to a Mg2+-bound state following light activation of the cascade, GCAP1 triggers the activation of the retinal guanylate cyclase (GC), thus replenishing the levels of 3',5'-cyclic monophosphate (cGMP) necessary to re-open CNG channels. Here, we investigated the structural and functional effects of three missense mutations in GCAP1 associated with cone-rod dystrophy, which severely perturb the homeostasis of cGMP and Ca2+. Substitutions affect residues directly involved in Ca2+ coordination in either EF3 (D100G) or EF4 (E155A and E155G) Ca2+ binding motifs. We found that all GCAP1 variants form relatively stable dimers showing decreased apparent affinity for Ca2+ and blocking the enzyme in a constitutively active state at physiological levels of Ca2+. Interestingly, by corroborating spectroscopic experiments with molecular dynamics simulations we show that beside local structural effects, mutation of the bidentate glutamate in an EF-hand calcium binding motif can profoundly perturb the flexibility of the adjacent EF-hand as well, ultimately destabilizing the whole domain. Therefore, while Ca2+-binding to GCAP1 per se occurs sequentially, allosteric effects may connect EF hand motifs, which appear to be essential for the integrity of the structural switch mechanism in GCAP1, and perhaps in other NCS proteins.
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Affiliation(s)
- Giuditta Dal Cortivo
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, I-37134 Verona, Italy
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, I-37134 Verona, Italy
| | - Francesco Bonì
- CNR-IBF, Istituto di Biofisica, Via Celoria 26, I-20133 Milano, Italy; Dipartimento di Bioscienze, Università di Milano, Via Celoria 26, I-20133 Milano, Italy
| | - Mario Milani
- CNR-IBF, Istituto di Biofisica, Via Celoria 26, I-20133 Milano, Italy; Dipartimento di Bioscienze, Università di Milano, Via Celoria 26, I-20133 Milano, Italy
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, I-37134 Verona, Italy.
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13
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Peshenko IV, Dizhoor AM. Two clusters of surface-exposed amino acid residues enable high-affinity binding of retinal degeneration-3 (RD3) protein to retinal guanylyl cyclase. J Biol Chem 2020; 295:10781-10793. [PMID: 32493772 PMCID: PMC7397094 DOI: 10.1074/jbc.ra120.013789] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 06/02/2020] [Indexed: 11/06/2022] Open
Abstract
Retinal degeneration-3 (RD3) protein protects photoreceptors from degeneration by preventing retinal guanylyl cyclase (RetGC) activation via calcium-sensing guanylyl cyclase-activating proteins (GCAP), and RD3 truncation causes severe congenital blindness in humans and other animals. The three-dimensional structure of RD3 has recently been established, but the molecular mechanisms of its inhibitory binding to RetGC remain unclear. Here, we report the results of probing 133 surface-exposed residues in RD3 by single substitutions and deletions to identify side chains that are critical for the inhibitory binding of RD3 to RetGC. We tested the effects of these substitutions and deletions in vitro by reconstituting purified RD3 variants with GCAP1-activated human RetGC1. Although the vast majority of the surface-exposed residues tolerated substitutions without loss of RD3's inhibitory activity, substitutions in two distinct narrow clusters located on the opposite sides of the molecule effectively suppressed RD3 binding to the cyclase. The first surface-exposed cluster included residues adjacent to Leu63 in the loop connecting helices 1 and 2. The second cluster surrounded Arg101 on a surface of helix 3. Single substitutions in those two clusters drastically, i.e. up to 245-fold, reduced the IC50 for the cyclase inhibition. Inactivation of the two binding sites completely disabled binding of RD3 to RetGC1 in living HEK293 cells. In contrast, deletion of 49 C-terminal residues did not affect the apparent affinity of RD3 for RetGC. Our findings identify the functional interface on RD3 required for its inhibitory binding to RetGC, a process essential for protecting photoreceptors from degeneration.
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Affiliation(s)
- Igor V Peshenko
- Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania, USA
| | - Alexander M Dizhoor
- Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania, USA
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14
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Constitutive Activation of Guanylate Cyclase by the G86R GCAP1 Variant Is Due to "Locking" Cation-π Interactions that Impair the Activator-to-Inhibitor Structural Transition. Int J Mol Sci 2020; 21:ijms21030752. [PMID: 31979372 PMCID: PMC7037459 DOI: 10.3390/ijms21030752] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 01/18/2020] [Accepted: 01/20/2020] [Indexed: 02/06/2023] Open
Abstract
Guanylate Cyclase activating protein 1 (GCAP1) mediates the Ca2+-dependent regulation of the retinal Guanylate Cyclase (GC) in photoreceptors, acting as a target inhibitor at high [Ca2+] and as an activator at low [Ca2+]. Recently, a novel missense mutation (G86R) was found in GUCA1A, the gene encoding for GCAP1, in patients diagnosed with cone-rod dystrophy. The G86R substitution was found to affect the flexibility of the hinge region connecting the N- and C-domains of GCAP1, resulting in decreased Ca2+-sensitivity and abnormally enhanced affinity for GC. Based on a structural model of GCAP1, here, we tested the hypothesis of a cation-π interaction between the positively charged R86 and the aromatic W94 as the main mechanism underlying the impaired activator-to-inhibitor conformational change. W94 was mutated to F or L, thus, resulting in the double mutants G86R+W94L/F. The double mutants showed minor structural and stability changes with respect to the single G86R mutant, as well as lower affinity for both Mg2+ and Ca2+, moreover, substitutions of W94 abolished "phase II" in Ca2+-titrations followed by intrinsic fluorescence. Interestingly, the presence of an aromatic residue in position 94 significantly increased the aggregation propensity of Ca2+-loaded GCAP1 variants. Finally, atomistic simulations of all GCAP1 variants in the presence of Ca2+ supported the presence of two cation-π interactions involving R86, which was found to act as a bridge between W94 and W21, thus, locking the hinge region in an activator-like conformation and resulting in the constitutive activation of the target under physiological conditions.
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15
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Normal GCAPs partly compensate for altered cGMP signaling in retinal dystrophies associated with mutations in GUCA1A. Sci Rep 2019; 9:20105. [PMID: 31882816 PMCID: PMC6934868 DOI: 10.1038/s41598-019-56606-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 12/12/2019] [Indexed: 01/20/2023] Open
Abstract
Missense mutations in the GUCA1A gene encoding guanylate cyclase-activating protein 1 (GCAP1) are associated with autosomal dominant cone/cone-rod (CORD) dystrophies. The nature of the inheritance pattern implies that a pool of normal GCAP proteins is present in photoreceptors together with the mutated variant. To assess whether human GCAP1 and GCAP2 may similarly regulate the activity of the retinal membrane guanylate cyclase GC-1 (GC-E) in the presence of the recently discovered E111V-GCAP1 CORD-variant, we combined biochemical and in silico assays. Surprisingly, human GCAP2 does not activate GC1 over the physiological range of Ca2+ whereas wild-type GCAP1 significantly attenuates the dysregulation of GC1 induced by E111V-GCAP1. Simulation of the phototransduction cascade in a well-characterized murine system, where GCAP2 is able to activate the GC1, suggests that both GCAPs can act in a synergic manner to mitigate the effects of the CORD-mutation. We propose the existence of a species-dependent compensatory mechanism. In murine photoreceptors, slight increases of wild-type GCAPs levels may significantly attenuate the increase in intracellular Ca2+ and cGMP induced by E111V-GCAP1 in heterozygous conditions. In humans, however, the excess of wild-type GCAP1 may only partly attenuate the mutant-induced dysregulation of cGMP signaling due to the lack of GC1-regulation by GCAP2.
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16
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Local, nonlinear effects of cGMP and Ca2+ reduce single photon response variability in retinal rods. PLoS One 2019; 14:e0225948. [PMID: 31805112 PMCID: PMC6894879 DOI: 10.1371/journal.pone.0225948] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 11/14/2019] [Indexed: 11/26/2022] Open
Abstract
The single photon response (SPR) in vertebrate photoreceptors is inherently variable due to several stochastic events in the phototransduction cascade, the main one being the shutoff of photoactivated rhodopsin. Deactivation is driven by a random number of steps, each of random duration with final quenching occurring after a random delay. Nevertheless, variability of the SPR is relatively low, making the signal highly reliable. Several biophysical and mathematical mechanisms contributing to variability suppression have been examined by the authors. Here we investigate the contribution of local depletion of cGMP by PDE*, the non linear dependence of the photocurrent on cGMP, Ca2+ feedback by making use of a fully space resolved (FSR) mathematical model, applied to two species (mouse and salamander), by varying the cGMP diffusion rate severalfold and rod outer segment diameter by an order of magnitude, and by introducing new, more refined, and time dependent variability functionals. Globally well stirred (GWS) models, and to a lesser extent transversally well stirred models (TWS), underestimate the role of nonlinearities and local cGMP depletion in quenching the variability of the circulating current with respect to fully space resolved models (FSR). These distortions minimize the true extent to which SPR is stabilized by locality in cGMP depletion, nonlinear effects linking cGMP to current, and Ca2+ feedback arising from the physical separation of E* from the ion channels located on the outer shell, and the diffusion of these second messengers in the cytoplasm.
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17
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Klaus C, Caruso G, Gurevich VV, DiBenedetto E. Multi-scale, numerical modeling of spatio-temporal signaling in cone phototransduction. PLoS One 2019; 14:e0219848. [PMID: 31344066 PMCID: PMC6657853 DOI: 10.1371/journal.pone.0219848] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2019] [Accepted: 07/02/2019] [Indexed: 12/20/2022] Open
Abstract
Mammals have two types of photoreceptors, rods and cones. While rods are exceptionally sensitive and mediate vision at very low illumination levels, cones operate in daylight and are responsible for the bulk of visual perception in most diurnal animals, including humans. Yet the mechanisms of phototransduction in cones is understudied, largely due to unavailability of pure cone outer segment (COS) preparations. Here we present a novel mathematical model of cone phototransduction that explicitly takes into account complex cone geometry and its multiple physical scales, faithfully reproduces features of the cone response, and is orders of magnitude more efficient than the standard 3D diffusion model. This is accomplished through the mathematical techniques of homogenization and concentrated capacity. The homogenized model is then computationally implemented by finite element method. This homogenized model permits one to analyze the effects of COS geometry on visual transduction and lends itself to performing large numbers of numerical trials, as required for parameter analysis and the stochasticity of rod and cone signal transduction. Agreement between the nonhomogenized, (i.e., standard 3D), and homogenized diffusion models is reported along with their simulation times and memory costs. Virtual expression of rod biochemistry on cone morphology is also presented for understanding some of the characteristic differences between rods and cones. These simulations evidence that 3D cone morphology and ion channel localization contribute to biphasic flash response, i.e undershoot. The 3D nonhomogenized and homogenized models are contrasted with more traditional and coarser well-stirred and 1D longitudinal diffusion models. The latter are single-scale and do not explicitly account for the multi-scale geometry of the COS, unlike the 3D homogenized model. We show that simpler models exaggerate the magnitude of the current suppression, yield accelerated time to peak, and do not predict the local concentration of cGMP at the ionic channels.
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Affiliation(s)
- Colin Klaus
- The Mathematical Biosciences Institute, The Ohio State University, Columbus, OH, United States of America
| | | | - Vsevolod V. Gurevich
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States of America
| | - Emmanuele DiBenedetto
- Department of Mathematics, Vanderbilt University, Nashville, TN, United States of America
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18
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Marino V, Dal Cortivo G, Oppici E, Maltese PE, D'Esposito F, Manara E, Ziccardi L, Falsini B, Magli A, Bertelli M, Dell'Orco D. A novel p.(Glu111Val) missense mutation in GUCA1A associated with cone-rod dystrophy leads to impaired calcium sensing and perturbed second messenger homeostasis in photoreceptors. Hum Mol Genet 2019; 27:4204-4217. [PMID: 30184081 DOI: 10.1093/hmg/ddy311] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 08/24/2018] [Indexed: 01/09/2023] Open
Abstract
Guanylate Cyclase-Activating Protein 1 (GCAP1) regulates the enzymatic activity of the photoreceptor guanylate cyclases (GC), leading to inhibition or activation of the cyclic guanosine monophosphate (cGMP) synthesis depending on its Ca2+- or Mg2+-loaded state. By genetically screening a family of patients diagnosed with cone-rod dystrophy, we identified a novel missense mutation with autosomal dominant inheritance pattern (c.332A>T; p.(Glu111Val); E111V from now on) in the GUCA1A gene coding for GCAP1. We performed a thorough biochemical and biophysical investigation of wild type (WT) and E111V human GCAP1 by heterologous expression and purification of the recombinant proteins. The E111V substitution disrupts the coordination of the Ca2+ ion in the high-affinity site (EF-hand 3, EF3), thus significantly decreasing the ability of GCAP1 to sense Ca2+ (∼80-fold higher Kdapp compared to WT). Both WT and E111V GCAP1 form dimers independently on the presence of cations, but the E111V Mg2+-bound form is prone to severe aggregation over time. Molecular dynamics simulations suggest a significantly increased flexibility of both the EF3 and EF4 cation binding loops for the Ca2+-bound form of E111V GCAP1, in line with the decreased affinity for Ca2+. In contrast, a more rigid backbone conformation is observed in the Mg2+-bound state compared to the WT, which results in higher thermal stability. Functional assays confirm that E111V GCAP1 interacts with the target GC with a similar apparent affinity (EC50); however, the mutant shifts the GC inhibition out of the physiological [Ca2+] (IC50E111V ∼10 μM), thereby leading to the aberrant constitutive synthesis of cGMP under conditions of dark-adapted photoreceptors.
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Affiliation(s)
- Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy.,Department of Translational Research and of New Surgical and Medical Technologies, University of Pisa, Pisa, Italy
| | - Giuditta Dal Cortivo
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy
| | - Elisa Oppici
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy
| | | | - Fabiana D'Esposito
- Imperial College Ophthalmic Research Unit, Western Eye Hospital, Imperial College Healthcare NHS Trust, London, UK.,MAGI Euregio, Bolzano, Italy.,Eye Clinic, Department of Neurosciences, Reproductive Sciences and Dentistry, Federico II University, Naples, Italy
| | | | | | - Benedetto Falsini
- Institute of Ophthalmology, Università Cattolica del Sacro Cuore, Rome, Italy.,Fondazione Policlinico Universitario "A. Gemelli", IRCCS, Rome, Italy
| | - Adriano Magli
- Department of Pediatric Ophthalmology, University of Salerno, Fisciano (SA), Italy
| | - Matteo Bertelli
- MAGI'S Lab s.r.l., Rovereto, Italy.,MAGI Euregio, Bolzano, Italy
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy
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19
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Peshenko IV, Yu Q, Lim S, Cudia D, Dizhoor AM, Ames JB. Retinal degeneration 3 (RD3) protein, a retinal guanylyl cyclase regulator, forms a monomeric and elongated four-helix bundle. J Biol Chem 2019; 294:2318-2328. [PMID: 30559291 PMCID: PMC6378972 DOI: 10.1074/jbc.ra118.006106] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 12/07/2018] [Indexed: 12/20/2022] Open
Abstract
Retinal degeneration 3 (RD3) protein promotes accumulation of retinal membrane guanylyl cyclase (RetGC) in the photoreceptor outer segment and suppresses RetGC activation by guanylyl cyclase-activating proteins (GCAPs). Mutations truncating RD3 cause severe congenital blindness by preventing the inhibitory binding of RD3 to the cyclase. The high propensity of RD3 to aggregate in solution has prevented structural analysis. Here, we produced a highly soluble variant of human RD3 (residues 18-160) that is monomeric and can still bind and negatively regulate RetGC. The NMR solution structure of RD3 revealed an elongated backbone structure (70 Å long and 30 Å wide) consisting of a four-helix bundle with a long unstructured loop between helices 1 and 2. The structure reveals that RD3 residues previously implicated in the RetGC binding map to a localized and contiguous area on the structure, involving a loop between helices 2 and 3 and adjacent parts of helices 3 and 4. The NMR structure of RD3 was validated by mutagenesis. Introducing Trp85 or Phe29 to replace Cys or Leu, respectively, disrupts packing in the hydrophobic core and lowers RD3's apparent affinity for RetGC1. Introducing a positive charge at the interface (Glu32 to Lys) also lowered the affinity. Conversely, introducing Val in place of Cys93 stabilized the hydrophobic core and increased the RD3 affinity for the cyclase. The NMR structure of RD3 presented here provides a structural basis for elucidating RD3-RetGC interactions relevant for normal vision or blindness.
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Affiliation(s)
- Igor V Peshenko
- From the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027 and
| | - Qinhong Yu
- the Department of Chemistry, University of California, Davis, California 95616
| | - Sunghyuk Lim
- the Department of Chemistry, University of California, Davis, California 95616
| | - Diana Cudia
- the Department of Chemistry, University of California, Davis, California 95616
| | - Alexander M Dizhoor
- From the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027 and
| | - James B Ames
- the Department of Chemistry, University of California, Davis, California 95616
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20
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Mapping Calcium-Sensitive Regions in GCAPs by Site-Specific Fluorescence Labelling. Methods Mol Biol 2019. [PMID: 30710298 DOI: 10.1007/978-1-4939-9030-6_36] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Signal transduction processes that are under control of changes in cytoplasmic Ca2+-concentration involve Ca2+-sensor proteins, which often undergo pronounced conformational transitions triggered by Ca2+. Consequences of conformational changes can be the structural rearrangement of single amino acids, exposition of small patches of several amino acids, or the movement of whole protein regions or domains. Furthermore, these conformational changes can lead to the exposure or movement of posttranslationally attached acyl groups. These processes could then control the function of target proteins, for example, by Ca2+-dependent protein-protein interaction. Fluorescence spectroscopy allows for mapping these Ca2+-sensitive regions but needs site-specific fluorescence labelling. We describe the application of a new group of diaminoterephthalate-derived fluorescence probes targeting either cysteines in guanylate cyclase-activating proteins, named GCAPs, or azide moieties in covalently attached acyl groups. By monitoring Ca2+-dependent changes in fluorescence emission, we identify Ca2+-sensitive protein regions in GCAPs and correlate conformational changes to protein function.
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21
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Peshenko IV, Cideciyan AV, Sumaroka A, Olshevskaya EV, Scholten A, Abbas S, Koch KW, Jacobson SG, Dizhoor AM. A G86R mutation in the calcium-sensor protein GCAP1 alters regulation of retinal guanylyl cyclase and causes dominant cone-rod degeneration. J Biol Chem 2019; 294:3476-3488. [PMID: 30622141 DOI: 10.1074/jbc.ra118.006180] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 01/04/2019] [Indexed: 11/06/2022] Open
Abstract
The guanylyl cyclase-activating protein, GCAP1, activates photoreceptor membrane guanylyl cyclase (RetGC) in the light, when free Ca2+ concentrations decline, and decelerates the cyclase in the dark, when Ca2+ concentrations rise. Here, we report a novel mutation, G86R, in the GCAP1 (GUCA1A) gene in a family with a dominant retinopathy. The G86R substitution in a "hinge" region connecting EF-hand domains 2 and 3 in GCAP1 strongly interfered with its Ca2+-dependent activator-to-inhibitor conformational transition. The G86R-GCAP1 variant activated RetGC at low Ca2+ concentrations with higher affinity than did the WT GCAP1, but failed to decelerate the cyclase at the Ca2+ concentrations characteristic of dark-adapted photoreceptors. Ca2+-dependent increase in Trp94 fluorescence, indicative of the GCAP1 transition to its RetGC inhibiting state, was suppressed and shifted to a higher Ca2+ range. Conformational changes in G86R GCAP1 detectable by isothermal titration calorimetry (ITC) also became less sensitive to Ca2+, and the dose dependence of the G86R GCAP1-RetGC1 complex inhibition by retinal degeneration 3 (RD3) protein was shifted toward higher than normal concentrations. Our results indicate that the flexibility of the hinge region between EF-hands 2 and 3 is required for placing GCAP1-regulated Ca2+ sensitivity of the cyclase within the physiological range of intracellular Ca2+ at the expense of reducing GCAP1 affinity for the target enzyme. The disease-linked mutation of the hinge Gly86, leading to abnormally high affinity for the target enzyme and reduced Ca2+ sensitivity of GCAP1, is predicted to abnormally elevate cGMP production and Ca2+ influx in photoreceptors in the dark.
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Affiliation(s)
- Igor V Peshenko
- From the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027
| | - Artur V Cideciyan
- the Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and
| | - Alexander Sumaroka
- the Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and
| | - Elena V Olshevskaya
- From the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027
| | - Alexander Scholten
- the Department of Neuroscience, University of Oldenburg, Oldenburg D-26129, Germany
| | - Seher Abbas
- the Department of Neuroscience, University of Oldenburg, Oldenburg D-26129, Germany
| | - Karl-Wilhelm Koch
- the Department of Neuroscience, University of Oldenburg, Oldenburg D-26129, Germany
| | - Samuel G Jacobson
- the Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and
| | - Alexander M Dizhoor
- From the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027,
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22
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Tsvetkov PO, Roman AY, Baksheeva VE, Nazipova AA, Shevelyova MP, Vladimirov VI, Buyanova MF, Zinchenko DV, Zamyatnin AA, Devred F, Golovin AV, Permyakov SE, Zernii EY. Functional Status of Neuronal Calcium Sensor-1 Is Modulated by Zinc Binding. Front Mol Neurosci 2018; 11:459. [PMID: 30618610 PMCID: PMC6302015 DOI: 10.3389/fnmol.2018.00459] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2018] [Accepted: 11/28/2018] [Indexed: 11/29/2022] Open
Abstract
Neuronal calcium sensor-1 (NCS-1) protein is abundantly expressed in the central nervous system and retinal neurons, where it regulates many vital processes such as synaptic transmission. It coordinates three calcium ions by EF-hands 2-4, thereby transducing Ca2+ signals to a wide range of protein targets, including G protein-coupled receptors and their kinases. Here, we demonstrate that NCS-1 also has Zn2+-binding sites, which affect its structural and functional properties upon filling. Fluorescence and circular dichroism experiments reveal the impact of Zn2+ binding on NCS-1 secondary and tertiary structure. According to atomic absorption spectroscopy and isothermal titration calorimetry studies, apo-NCS-1 has two high-affinity (4 × 106 M-1) and one low-affinity (2 × 105 M-1) Zn2+-binding sites, whereas Mg2+-loaded and Ca2+-loaded forms (which dominate under physiological conditions) bind two zinc ions with submicromolar affinity. Metal competition analysis and circular dichroism studies suggest that Zn2+-binding sites of apo- and Mg2+-loaded NCS-1 overlap with functional EF-hands of the protein. Consistently, high Zn2+ concentrations displace Mg2+ from the EF-hands and decrease the stoichiometry of Ca2+ binding. Meanwhile, one of the EF-hands of Zn2+-saturated NCS-1 exhibits a 14-fold higher calcium affinity, which increases the overall calcium sensitivity of the protein. Based on QM/MM molecular dynamics simulations, Zn2+ binding to Ca2+-loaded NCS-1 could occur at EF-hands 2 and 4. The high-affinity zinc binding increases the thermal stability of Ca2+-free NCS-1 and favours the interaction of its Ca2+-loaded form with target proteins, such as dopamine receptor D2R and GRK1. In contrast, low-affinity zinc binding promotes NCS-1 aggregation accompanied by the formation of twisted rope-like structures. Altogether, our findings suggest a complex interplay between magnesium, calcium and zinc binding to NCS-1, leading to the appearance of multiple conformations of the protein, in turn modulating its functional status.
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Affiliation(s)
- Philipp O Tsvetkov
- Aix-Marseille University, CNRS, INP, Institute of Neurophysiopathology, Faculty of Pharmacy, Marseille, France
| | - Andrei Yu Roman
- Institute of Physiologically Active Compounds (RAS), Chernogolovka, Russia
| | - Viktoriia E Baksheeva
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Aliya A Nazipova
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Russia
| | - Marina P Shevelyova
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Russia
| | - Vasiliy I Vladimirov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Pushchino, Russia
| | - Michelle F Buyanova
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, Russia
| | - Dmitry V Zinchenko
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Pushchino, Russia
| | - Andrey A Zamyatnin
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
| | - François Devred
- Aix-Marseille University, CNRS, INP, Institute of Neurophysiopathology, Faculty of Pharmacy, Marseille, France
| | - Andrey V Golovin
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
- Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, Russia
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
- Faculty of Computer Science, Higher School of Economics, Moscow, Russia
| | - Sergei E Permyakov
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Russia
| | - Evgeni Yu Zernii
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
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23
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Vinberg F, Peshenko IV, Chen J, Dizhoor AM, Kefalov VJ. Guanylate cyclase-activating protein 2 contributes to phototransduction and light adaptation in mouse cone photoreceptors. J Biol Chem 2018; 293:7457-7465. [PMID: 29549122 DOI: 10.1074/jbc.ra117.001574] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 03/12/2018] [Indexed: 12/14/2022] Open
Abstract
Light adaptation of photoreceptor cells is mediated by Ca2+-dependent mechanisms. In darkness, Ca2+ influx through cGMP-gated channels into the outer segment of photoreceptors is balanced by Ca2+ extrusion via Na+/Ca2+, K+ exchangers (NCKXs). Light activates a G protein signaling cascade, which closes cGMP-gated channels and decreases Ca2+ levels in photoreceptor outer segment because of continuing Ca2+ extrusion by NCKXs. Guanylate cyclase-activating proteins (GCAPs) then up-regulate cGMP synthesis by activating retinal membrane guanylate cyclases (RetGCs) in low Ca2+ This activation of RetGC accelerates photoresponse recovery and critically contributes to light adaptation of the nighttime rod and daytime cone photoreceptors. In mouse rod photoreceptors, GCAP1 and GCAP2 both contribute to the Ca2+-feedback mechanism. In contrast, only GCAP1 appears to modulate RetGC activity in mouse cones because evidence of GCAP2 expression in cones is lacking. Surprisingly, we found that GCAP2 is expressed in cones and can regulate light sensitivity and response kinetics as well as light adaptation of GCAP1-deficient mouse cones. Furthermore, we show that GCAP2 promotes cGMP synthesis and cGMP-gated channel opening in mouse cones exposed to low Ca2+ Our biochemical model and experiments indicate that GCAP2 significantly contributes to the activation of RetGC1 at low Ca2+ when GCAP1 is not present. Of note, in WT mouse cones, GCAP1 dominates the regulation of cGMP synthesis. We conclude that, under normal physiological conditions, GCAP1 dominates the regulation of cGMP synthesis in mouse cones, but if its function becomes compromised, GCAP2 contributes to the regulation of phototransduction and light adaptation of cones.
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Affiliation(s)
- Frans Vinberg
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Igor V Peshenko
- Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027
| | - Jeannie Chen
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California 90033
| | - Alexander M Dizhoor
- Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027
| | - Vladimir J Kefalov
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri 63110.
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López-Begines S, Plana-Bonamaisó A, Méndez A. Molecular determinants of Guanylate Cyclase Activating Protein subcellular distribution in photoreceptor cells of the retina. Sci Rep 2018; 8:2903. [PMID: 29440717 PMCID: PMC5811540 DOI: 10.1038/s41598-018-20893-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Accepted: 01/26/2018] [Indexed: 11/10/2022] Open
Abstract
Retinal guanylate cyclase (RetGC) and guanylate cyclase activating proteins (GCAPs) play an important role during the light response in photoreceptor cells. Mutations in these proteins are linked to distinct forms of blindness. RetGC and GCAPs exert their role at the ciliary outer segment where phototransduction takes place. We investigated the mechanisms governing GCAP1 and GCAP2 distribution to rod outer segments by expressing selected GCAP1 and GCAP2 mutants as transient transgenes in the rods of GCAP1/2 double knockout mice. We show that precluding GCAP1 direct binding to RetGC (K23D/GCAP1) prevented its distribution to rod outer segments, while preventing GCAP1 activation of RetGC post-binding (W94A/GCAP1) did not. We infer that GCAP1 translocation to the outer segment strongly depends on GCAP1 binding affinity for RetGC, which points to GCAP1 requirement to bind to RetGC to be transported. We gain further insight into the distinctive regulatory steps of GCAP2 distribution, by showing that a phosphomimic at position 201 is sufficient to retain GCAP2 at proximal compartments; and that the bovine equivalent to blindness-causative mutation G157R/GCAP2 results in enhanced phosphorylation in vitro and significant retention at the inner segment in vivo, as likely contributing factors to the pathophysiology.
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Affiliation(s)
- Santiago López-Begines
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.,Department of Physiology, University of Barcelona School of Medicine-Bellvitge Health Science Campus, Barcelona, Spain
| | - Anna Plana-Bonamaisó
- Department of Physiology, University of Barcelona School of Medicine-Bellvitge Health Science Campus, Barcelona, Spain
| | - Ana Méndez
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain. .,Department of Physiology, University of Barcelona School of Medicine-Bellvitge Health Science Campus, Barcelona, Spain.
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25
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GUCY2D Cone-Rod Dystrophy-6 Is a "Phototransduction Disease" Triggered by Abnormal Calcium Feedback on Retinal Membrane Guanylyl Cyclase 1. J Neurosci 2018; 38:2990-3000. [PMID: 29440533 DOI: 10.1523/jneurosci.2985-17.2018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 01/19/2018] [Accepted: 01/24/2018] [Indexed: 12/24/2022] Open
Abstract
The Arg838Ser mutation in retinal membrane guanylyl cyclase 1 (RetGC1) has been linked to autosomal dominant cone-rod dystrophy type 6 (CORD6). It is believed that photoreceptor degeneration is caused by the altered sensitivity of RetGC1 to calcium regulation via guanylyl cyclase activating proteins (GCAPs). To determine the mechanism by which this mutation leads to degeneration, we investigated the structure and function of rod photoreceptors in two transgenic mouse lines, 362 and 379, expressing R838S RetGC1. In both lines, rod outer segments became shorter than in their nontransgenic siblings by 3-4 weeks of age, before the eventual photoreceptor degeneration. Despite the shortening of their outer segments, the dark current of transgenic rods was 1.5-2.2-fold higher than in nontransgenic controls. Similarly, the dim flash response amplitude in R838S+ rods was larger, time to peak was delayed, and flash sensitivity was increased, all suggesting elevated dark-adapted free cGMP in transgenic rods. In rods expressing R838S RetGC1, dark-current noise increased and the exchange current, detected after a saturating flash, became more pronounced. These results suggest disrupted Ca2+ phototransduction feedback and abnormally high free-Ca2+ concentration in the outer segments. Notably, photoreceptor degeneration, which typically occurred after 3 months of age in R838S RetGC1 transgenic mice in GCAP1,2+/+ or GCAP1,2+/- backgrounds, was prevented in GCAP1,2-/- mice lacking Ca2+ feedback to guanylyl cyclase. In summary, the dysregulation of guanylyl cyclase in RetGC1-linked CORD6 is a "phototransduction disease," which means it is associated with increased free-cGMP and Ca2+ levels in photoreceptors.SIGNIFICANCE STATEMENT In a mouse model expressing human membrane guanylyl cyclase 1 (RetGC1, GUCY2D), a mutation associated with early progressing congenital blindness, cone-rod dystrophy type 6 (CORD6), deregulates calcium-sensitive feedback of phototransduction to the cyclase mediated by guanylyl cyclase activating proteins (GCAPs), which are calcium-sensor proteins. The abnormal calcium sensitivity of the cyclase increases cGMP-gated dark current in the rod outer segments, reshapes rod photoresponses, and triggers photoreceptor death. This work is the first to demonstrate a direct physiological effect of GUCY2D CORD6-linked mutation on photoreceptor physiology in vivo It also identifies the abnormal regulation of the cyclase by calcium-sensor proteins as the main trigger for the photoreceptor death.
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Marino V, Borsatto A, Vocke F, Koch KW, Dell'Orco D. CaF 2 nanoparticles as surface carriers of GCAP1, a calcium sensor protein involved in retinal dystrophies. NANOSCALE 2017; 9:11773-11784. [PMID: 28785759 DOI: 10.1039/c7nr03288a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
CaF2-based nanoparticles (NP) are promising biocompatible tools for nanomedicine applications. The structure of the NP crystal lattice allows for specific interactions with Ca2+-binding proteins through their EF-hand cation binding motifs. Here we investigated the interaction of 23 nm citrate-coated CaF2 NP with a calcium sensor protein GCAP1 that is normally expressed in photoreceptor cells and involved in the regulation of the early steps of vision. Protein-NP interactions were thoroughly investigated for the wild type (WT) GCAP1 as well as for a variant carrying the Asp 100 to Glu mutation (D100E), which prevents the binding of Ca2+ to the highest affinity site and is linked to cone dystrophy. Circular dichroism and fluorescence spectroscopy showed that protein structure and Ca2+-sensing capability are conserved for both variants upon interaction with the NP surface, although the interaction mode depends on the specific occupation of Ca2+-binding sites. NP binding stabilizes the structure of the bound GCAP1 and occurs with nanomolar affinity, as probed by isothermal titration calorimetry. Surface plasmon resonance revealed a fully reversible binding compatible with physiologically relevant kinetics of protein release whereas biochemical assays indicated a residual capability for NP-dissociated GCAP1 to regulate the target retinal guanylate cyclase. Our study constitutes a proof of concept that CaF2 NP could be optimized to serve as biologically compatible carriers of high amounts of functional GCAP1 in photoreceptors affected by retinal dystrophies.
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Affiliation(s)
- Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy.
| | - Alberto Borsatto
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy.
| | - Farina Vocke
- Department of Neuroscience, Biochemistry Group, University of Oldenburg, Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Department of Neuroscience, Biochemistry Group, University of Oldenburg, Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy.
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Marino V, Dell'Orco D. Allosteric communication pathways routed by Ca 2+/Mg 2+ exchange in GCAP1 selectively switch target regulation modes. Sci Rep 2016; 6:34277. [PMID: 27739433 PMCID: PMC5064319 DOI: 10.1038/srep34277] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 09/09/2016] [Indexed: 12/11/2022] Open
Abstract
GCAP1 is a neuronal calcium sensor protein that regulates the phototransduction cascade in vertebrates by switching between activator and inhibitor of the target guanylate cyclase (GC) in a Ca2+-dependent manner. We carried out exhaustive molecular dynamics simulations of GCAP1 and determined the intramolecular communication pathways involved in the specific GC activator/inhibitor switch. The switch was found to depend on the Mg2+/Ca2+ loading states of the three EF hands and on the way the information is transferred from each EF hand to specific residues at the GCAP1/GC interface. Post-translational myristoylation is fundamental to mediate long range allosteric interactions including the EF2-EF4 coupling and the communication between EF4 and the GC binding interface. Some hubs in the identified protein network are the target of retinal dystrophy mutations, suggesting that the lack of complete inhibition of GC observed in many cases is likely due to the perturbation of intra/intermolecular communication routes.
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Affiliation(s)
- Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, strada le Grazie 8, I-37134 Verona, Italy
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, strada le Grazie 8, I-37134 Verona, Italy.,Centre for BioMedical Computing (CBMC), University of Verona, strada le Grazie 8, I-37134 Verona, Italy
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28
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Dizhoor AM, Olshevskaya EV, Peshenko IV. The R838S Mutation in Retinal Guanylyl Cyclase 1 (RetGC1) Alters Calcium Sensitivity of cGMP Synthesis in the Retina and Causes Blindness in Transgenic Mice. J Biol Chem 2016; 291:24504-24516. [PMID: 27703005 DOI: 10.1074/jbc.m116.755553] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2016] [Revised: 10/03/2016] [Indexed: 11/06/2022] Open
Abstract
Substitutions of Arg838 in the dimerization domain of a human retinal membrane guanylyl cyclase 1 (RetGC1) linked to autosomal dominant cone-rod degeneration type 6 (CORD6) change RetGC1 regulation in vitro by Ca2+ In addition, we find that R838S substitution makes RetGC1 less sensitive to inhibition by retinal degeneration-3 protein (RD3). We selectively expressed human R838S RetGC1 in mouse rods and documented the decline in rod vision and rod survival. To verify that changes in rods were specifically caused by the CORD6 mutation, we used for comparison cones, which in the same mice did not express R838S RetGC1 from the transgenic construct. The R838S RetGC1 expression in rod outer segments reduced inhibition of cGMP production in the transgenic mouse retinas at the free calcium concentrations typical for dark-adapted rods. The transgenic mice demonstrated early-onset and rapidly progressed with age decline in visual responses from the targeted rods, in contrast to the longer lasting preservation of function in the non-targeted cones. The decline in rod function in the retina resulted from a progressive degeneration of rods between 1 and 6 months of age, with the severity and pace of the degeneration consistent with the extent to which the Ca2+ sensitivity of the retinal cGMP production was affected. Our study presents a new experimental model for exploring cellular mechanisms of the CORD6-related photoreceptor death. This mouse model provides the first direct biochemical and physiological in vivo evidence for the Arg838 substitutions in RetGC1 being the culprit behind the pathogenesis of the CORD6 congenital blindness.
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Affiliation(s)
- Alexander M Dizhoor
- From the Department of Research, Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027.
| | - Elena V Olshevskaya
- From the Department of Research, Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027
| | - Igor V Peshenko
- From the Department of Research, Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027
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29
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Vinberg F, Turunen TT, Heikkinen H, Pitkänen M, Koskelainen A. A novel Ca2+-feedback mechanism extends the operating range of mammalian rods to brighter light. ACTA ACUST UNITED AC 2016; 146:307-21. [PMID: 26415569 PMCID: PMC4586592 DOI: 10.1085/jgp.201511412] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A previously unidentified calcium-dependent mechanism contributes to light adaptation in mammalian rods. Sensory cells adjust their sensitivity to incoming signals, such as odor or light, in response to changes in background stimulation, thereby extending the range over which they operate. For instance, rod photoreceptors are extremely sensitive in darkness, so that they are able to detect individual photons, but remain responsive to visual stimuli under conditions of bright ambient light, which would be expected to saturate their response given the high gain of the rod transduction cascade in darkness. These photoreceptors regulate their sensitivity to light rapidly and reversibly in response to changes in ambient illumination, thereby avoiding saturation. Calcium ions (Ca2+) play a major role in mediating the rapid, subsecond adaptation to light, and the Ca2+-binding proteins GCAP1 and GCAP2 (or guanylyl cyclase–activating proteins [GCAPs]) have been identified as important mediators of the photoreceptor response to changes in intracellular Ca2+. However, mouse rods lacking both GCAP1 and GCAP2 (GCAP−/−) still show substantial light adaptation. Here, we determined the Ca2+ dependency of this residual light adaptation and, by combining pharmacological, genetic, and electrophysiological tools, showed that an unknown Ca2+-dependent mechanism contributes to light adaptation in GCAP−/− mouse rods. We found that mimicking the light-induced decrease in intracellular [Ca2+] accelerated recovery of the response to visual stimuli and caused a fourfold decrease of sensitivity in GCAP−/− rods. About half of this Ca2+-dependent regulation of sensitivity could be attributed to the recoverin-mediated pathway, whereas half of it was caused by the unknown mechanism. Furthermore, our data demonstrate that the feedback mechanisms regulating the sensitivity of mammalian rods on the second and subsecond time scales are all Ca2+ dependent and that, unlike salamander rods, Ca2+-independent background-induced acceleration of flash response kinetics is rather weak in mouse rods.
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Affiliation(s)
- Frans Vinberg
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110
| | - Teemu T Turunen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Hanna Heikkinen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Marja Pitkänen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
| | - Ari Koskelainen
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076 Aalto, Finland
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30
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Sulmann S, Wallisch M, Scholten A, Christoffers J, Koch KW. Mapping Calcium-Sensitive Regions in the Neuronal Calcium Sensor GCAP2 by Site-Specific Fluorescence Labeling. Biochemistry 2016; 55:2567-77. [DOI: 10.1021/acs.biochem.6b00005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Stefan Sulmann
- Biochemistry
Group, Department of Neurosciences, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Melanie Wallisch
- Institut
für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Alexander Scholten
- Biochemistry
Group, Department of Neurosciences, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Jens Christoffers
- Institut
für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Biochemistry
Group, Department of Neurosciences, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
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31
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Viviano J, Krishnan A, Scully J, Wu H, Venkataraman V. Datasets depicting mobility retardation of NCS proteins observed upon incubation with calcium, but not with magnesium, barium or strontium. Data Brief 2016; 7:1606-8. [PMID: 27222862 PMCID: PMC4865663 DOI: 10.1016/j.dib.2016.04.035] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Revised: 03/30/2016] [Accepted: 04/13/2016] [Indexed: 11/26/2022] Open
Abstract
In this data article we show the specificity of the Ca(2+)-induced mobility shift in three proteins that belong to the neuronal calcium sensor (NCS) protein family: Hippocalcin, GCAP1 and GCAP2. These proteins did not display a shift in mobility in native gels when incubated with divalent cations other than Ca(2+) - such as Mg(2+), Ba(2+), and Sr(2+), even at 10× concentrations. The data is similar to that obtained with another NCS protein, neurocalcin delta (Viviano et al., 2016, "Electrophoretic Mobility Shift in Native Gels Indicates Calcium-dependent Structural Changes of Neuronal Calcium Sensor Proteins", [1]).
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Affiliation(s)
- Jeffrey Viviano
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Anuradha Krishnan
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Jenna Scully
- School of Osteopathic Medicine, Rowan University, Stratford, NJ 08084, USA
| | - Hao Wu
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Venkat Venkataraman
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA; School of Osteopathic Medicine, Rowan University, Stratford, NJ 08084, USA
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32
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Krishnan A, Viviano J, Morozov Y, Venkataraman V. Single-column purification of the tag-free, recombinant form of the neuronal calcium sensor protein, hippocalcin expressed in Escherichia coli. Protein Expr Purif 2016; 123:35-41. [PMID: 27001424 DOI: 10.1016/j.pep.2016.03.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Revised: 03/07/2016] [Accepted: 03/16/2016] [Indexed: 01/24/2023]
Abstract
Hippocalcin is a 193 aa protein that is a member of the neuronal calcium sensor protein family, whose functions are regulated by calcium. Mice that lack the function of this protein are compromised in the long term potentiation aspect of memory generation. Recently, mutations in the gene have been linked with dystonia in human. The protein has no intrinsic enzyme activity but is known to bind to variety of target proteins. Very little information is available on how the protein executes its critical role in signaling pathways, except that it is regulated by binding of calcium. Further delineation of its function requires large amounts of pure protein. In this report, we present a single-step purification procedure that yields high quantities of the bacterially expressed, recombinant protein. The procedure may be adapted to purify the protein from inclusion bodies or cytosol in its myristoylated or non-myristoylated forms. MALDI-MS (in source decay) analyses demonstrates that the myristoylation occurs at the glycine residue. The protein is also biologically active as measured through tryptophan fluorescence, mobility shift and guanylate cyclase activity assays. Thus, further analyses of hippocalcin, both structural and functional, need no longer be limited by protein availability.
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Affiliation(s)
- Anuradha Krishnan
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Jeffrey Viviano
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Yaroslav Morozov
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Venkat Venkataraman
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA; School of Osteopathic Medicine, Rowan University, Stratford, NJ 08084, USA.
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33
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Viviano J, Wu H, Krishnan A, Ramanujachary K, Venkataraman V. Data on final calcium concentration in native gel reagents determined accurately through inductively coupled plasma measurements. Data Brief 2016; 6:820-2. [PMID: 26937454 PMCID: PMC4749937 DOI: 10.1016/j.dib.2016.01.030] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 01/09/2016] [Accepted: 01/18/2016] [Indexed: 11/20/2022] Open
Abstract
In this article we present data on the concentration of calcium as determined by Inductively Coupled Plasma (ICP) measurements. Calcium was estimated in the reagents used for native gel electrophoresis of Neuronal Calcium Sensor (NCS) proteins. NCS proteins exhibit calcium-dependent mobility shift in native gels. The sensitivity of this shift to calcium necessitated a precise determination of calcium concentrations in all reagents used. We determined the calcium concentrations in different components used along with the samples in the native gel experiments. These were: 20 mM Tris pH 7.5, loading dye and running buffer, with distilled water as reference. Calcium determinations were through ICP measurements. It was found that the running buffer contained calcium (244 nM) over the blank.
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Affiliation(s)
| | - Hao Wu
- Graduate School of Biomedical Sciences, USA
| | | | | | - Venkat Venkataraman
- Graduate School of Biomedical Sciences, USA
- School of Osteopathic Medicine, Rowan University, Stratford, NJ 08084, USA
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34
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Viviano J, Krishnan A, Wu H, Venkataraman V. Electrophoretic mobility shift in native gels indicates calcium-dependent structural changes of neuronal calcium sensor proteins. Anal Biochem 2015; 494:93-100. [PMID: 26617128 DOI: 10.1016/j.ab.2015.11.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 10/21/2015] [Accepted: 11/13/2015] [Indexed: 10/22/2022]
Abstract
In proteins of the neuronal calcium sensor (NCS) family, changes in structure as well as function are brought about by the binding of calcium. In this article, we demonstrate that these structural changes, solely due to calcium binding, can be assessed through electrophoresis in native gels. The results demonstrate that the NCS proteins undergo ligand-dependent conformational changes that are detectable in native gels as a gradual decrease in mobility with increasing calcium but not other tested divalent cations such as magnesium, strontium, and barium. Surprisingly, such a gradual change over the entire tested range is exhibited only by the NCS proteins but not by other tested calcium-binding proteins such as calmodulin and S100B, indicating that the change in mobility may be linked to a unique NCS family feature--the calcium-myristoyl switch. Even within the NCS family, the changes in mobility are characteristic of the protein, indicating that the technique is sensitive to the individual features of the protein. Thus, electrophoretic mobility on native gels provides a simple and elegant method to investigate calcium (small ligand)-induced structural changes at least in the superfamily of NCS proteins.
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Affiliation(s)
- Jeffrey Viviano
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Anuradha Krishnan
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Hao Wu
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA
| | - Venkat Venkataraman
- Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084, USA; School of Osteopathic Medicine, Rowan University, Stratford, NJ 08084, USA.
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35
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Marino V, Scholten A, Koch KW, Dell'Orco D. Two retinal dystrophy-associated missense mutations in GUCA1A with distinct molecular properties result in a similar aberrant regulation of the retinal guanylate cyclase. Hum Mol Genet 2015; 24:6653-66. [PMID: 26358777 DOI: 10.1093/hmg/ddv370] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 09/04/2015] [Indexed: 11/13/2022] Open
Abstract
Two recently identified missense mutations (p. L84F and p. I107T) in GUCA1A, the gene coding for guanylate cyclase (GC)-activating protein 1 (GCAP1), lead to a phenotype ascribable to cone, cone-rod and macular dystrophies. Here, we present a thorough biochemical and biophysical characterization of the mutant proteins and their distinct molecular features. I107T-GCAP1 has nearly wild-type-like protein secondary and tertiary structures, and binds Ca(2+) with a >10-fold lower affinity than the wild-type. On the contrary, L84F-GCAP1 displays altered tertiary structure in both GC-activating and inhibiting states, and a wild type-like apparent affinity for Ca(2+). The latter mutant also shows a significantly high affinity for Mg(2+), which might be important for stabilizing the GC-activating state and inducing a cooperative mechanism for the binding of Ca(2+), so far not been observed in other GCAP1 variants. Moreover, the thermal stability of L84F-GCAP1 is particularly high in the Ca(2+)-bound, GC-inhibiting state. Molecular dynamics simulations suggest that such enhanced stability arises from a deeper burial of the myristoyl moiety within the EF1-EF2 domain. The simulations also support an allosteric mechanism connecting the myristoyl moiety to the highest-affinity Ca(2+) binding site EF3. In spite of their remarkably distinct molecular features, both mutants cause constitutive activation of the target GC at physiological Ca(2+). We conclude that the similar aberrant regulation of the target enzyme results from a similar perturbation of the GCAP1-GC interaction, which may eventually cause dysregulation of both Ca(2+) and cyclic GMP homeostasis and result in retinal degeneration.
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Affiliation(s)
- Valerio Marino
- Department of Neurological, Biomedical and Movement Sciences, Section of Biological Chemistry
| | - Alexander Scholten
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, 26111 Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, 26111 Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurological, Biomedical and Movement Sciences, Section of Biological Chemistry, Centre for BioMedical Computing (CBMC), University of Verona, 37134 Verona, Italy and
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Peshenko IV, Olshevskaya EV, Dizhoor AM. Dimerization Domain of Retinal Membrane Guanylyl Cyclase 1 (RetGC1) Is an Essential Part of Guanylyl Cyclase-activating Protein (GCAP) Binding Interface. J Biol Chem 2015; 290:19584-96. [PMID: 26100624 DOI: 10.1074/jbc.m115.661371] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Indexed: 01/11/2023] Open
Abstract
The photoreceptor-specific proteins guanylyl cyclase-activating proteins (GCAPs) bind and regulate retinal membrane guanylyl cyclase 1 (RetGC1) but not natriuretic peptide receptor A (NPRA). Study of RetGC1 regulation in vitro and its association with fluorescently tagged GCAP in transfected cells showed that R822P substitution in the cyclase dimerization domain causing congenital early onset blindness disrupted RetGC1 ability to bind GCAP but did not eliminate its affinity for another photoreceptor-specific protein, retinal degeneration 3 (RD3). Likewise, the presence of the NPRA dimerization domain in RetGC1/NPRA chimera specifically disabled binding of GCAPs but not of RD3. In subsequent mapping using hybrid dimerization domains in RetGC1/NPRA chimera, multiple RetGC1-specific residues contributed to GCAP binding by the cyclase, but the region around Met(823) was the most crucial. Either positively or negatively charged residues in that position completely blocked GCAP1 and GCAP2 but not RD3 binding similarly to the disease-causing mutation in the neighboring Arg(822). The specificity of GCAP binding imparted by RetGC1 dimerization domain was not directly related to promoting dimerization of the cyclase. The probability of coiled coil dimer formation computed for RetGC1/NPRA chimeras, even those incapable of binding GCAP, remained high, and functional complementation tests showed that the RetGC1 active site, which requires dimerization of the cyclase, was formed even when Met(823) or Arg(822) was mutated. These results directly demonstrate that the interface for GCAP binding on RetGC1 requires not only the kinase homology region but also directly involves the dimerization domain and especially its portion containing Arg(822) and Met(823).
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Affiliation(s)
- Igor V Peshenko
- From the Department of Research, Salus University, Elkins Park, Pennsylvania 19027
| | - Elena V Olshevskaya
- From the Department of Research, Salus University, Elkins Park, Pennsylvania 19027
| | - Alexander M Dizhoor
- From the Department of Research, Salus University, Elkins Park, Pennsylvania 19027
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37
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Sulmann S, Vocke F, Scholten A, Koch KW. Retina specific GCAPs in zebrafish acquire functional selectivity in Ca2+-sensing by myristoylation and Mg2+-binding. Sci Rep 2015; 5:11228. [PMID: 26061947 PMCID: PMC4462140 DOI: 10.1038/srep11228] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 05/18/2015] [Indexed: 11/09/2022] Open
Abstract
Zebrafish photoreceptor cells express six guanylate cyclase-activating proteins (zGCAPs) that share a high degree of amino acid sequence homology, but differ in Ca(2+)-binding properties, Ca(2+)-sensitive target regulation and spatial-temporal expression profiles. We here study a general problem in cellular Ca(2+)-sensing, namely how similar Ca(2+)-binding proteins achieve functional selectivity to control finely adjusted cellular responses. We investigated two parameters of critical importance for the trigger and switch function of guanylate cyclase-activating proteins: the myristoylation status and the occupation of Ca(2+)-binding sites with Mg(2+). All zGCAPs can be myristoylated in living cells using click chemistry. Myristoylation does not facilitate membrane binding of zGCAPs, but it significantly modified the regulatory properties of zGCAP2 and zGCAP5. We further determined for all zGCAPs at least two binding sites exhibiting high affinities for Ca(2+) with KD values in the submicromolar range, whereas for other zGCAPs (except zGCAP3) the affinity of the third binding site was in the micromolar range. Mg(2+) either occupied the low affinity Ca(2+)-binding site or it shifted the affinities for Ca(2+)-binding. Hydrodynamic properties of zGCAPs are more influenced by Ca(2+) than by Mg(2+), although to a different extent for each zGCAP. Posttranslational modification and competing ion-binding can tailor the properties of similar Ca(2+)-sensors.
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Affiliation(s)
- Stefan Sulmann
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany
| | - Farina Vocke
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany
| | - Alexander Scholten
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany
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Gross OP, Pugh EN, Burns ME. cGMP in mouse rods: the spatiotemporal dynamics underlying single photon responses. Front Mol Neurosci 2015; 8:6. [PMID: 25788876 PMCID: PMC4349151 DOI: 10.3389/fnmol.2015.00006] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2014] [Accepted: 02/12/2015] [Indexed: 02/04/2023] Open
Abstract
Vertebrate vision begins when retinal photoreceptors transduce photons into electrical signals that are then relayed to other neurons in the eye, and ultimately to the brain. In rod photoreceptors, transduction of single photons is achieved by a well-understood G-protein cascade that modulates cGMP levels, and in turn, cGMP-sensitive inward current. The spatial extent and depth of the decline in cGMP during the single photon response (SPR) have been major issues in phototransduction research since the discovery that single photons elicit substantial and reproducible changes in membrane current. The spatial profile of cGMP decline during the SPR affects signal gain, and thus may contribute to reduction of trial-to-trial fluctuations in the SPR. Here we summarize the general principles of rod phototransduction, emphasizing recent advances in resolving the spatiotemporal dynamics of cGMP during the SPR.
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Affiliation(s)
- Owen P Gross
- Center for Neuroscience, University of California Davis Davis, CA, USA
| | - Edward N Pugh
- Departments of Ophthalmology and Vision Science, University of California Davis Davis, CA, USA ; Physiology and Membrane Biology, University of California Davis Davis, CA, USA ; Cell Biology and Human Anatomy, University of California Davis Davis, CA, USA
| | - Marie E Burns
- Center for Neuroscience, University of California Davis Davis, CA, USA ; Departments of Ophthalmology and Vision Science, University of California Davis Davis, CA, USA ; Cell Biology and Human Anatomy, University of California Davis Davis, CA, USA
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Marino V, Sulmann S, Koch KW, Dell'Orco D. Structural effects of Mg²⁺ on the regulatory states of three neuronal calcium sensors operating in vertebrate phototransduction. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:2055-65. [PMID: 25447547 DOI: 10.1016/j.bbamcr.2014.10.026] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Revised: 10/25/2014] [Accepted: 10/28/2014] [Indexed: 12/13/2022]
Abstract
The effects of physiological concentration of magnesium on the switch states of the neuronal calcium sensor proteins recoverin, GCAP1 and GCAP2 were investigated. Isothermal titration calorimetry was applied for binding studies. Circular dichroism spectroscopy was used to characterize protein thermal stability, secondary and tertiary structure in conditions of high and low [Ca²⁺], mimicking respectively the dark-adapted and light-exposed photoreceptor states during the phototransduction cascade. Further, molecular dynamics (MD) simulations were run to investigate the dynamical structural properties of GCAP1 in its activator, inhibitor and putative transitory states. Our results confirmed that Mg²⁺ is unable to trigger the typical Ca²⁺-induced conformational change of recoverin (myristoyl switch) while it decreases its thermal stability. Interestingly, Mg²⁺ seems to affect the conformation of GCAP2 both at high and low [Ca²⁺], however the variations are more substantial for myristoylated GCAP2 in the absence of Ca²⁺. GCAP1 is responsive to Mg²⁺ only in its low [Ca²⁺] state and Mg²⁺-GCAP1 tertiary structure slightly differs from both apo and Ca²⁺-bound states. Finally, MD simulations suggest that the GCAP1 state harboring one Mg²⁺ ion bound to EF2 acquires structural characteristics that are thought to be relevant for the activation of the guanylate cyclase. Moreover, all the putative Mg²⁺-bound states of myristoylated GCAP1 are structurally less flexible than Ca²⁺-bound states. GCAP1 acquires a more compact tertiary structure that is less accessible to the solvent, thereby inducing a different conformation to the myristoyl moiety, which might be crucial for the activation of the guanylate cyclase. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
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Affiliation(s)
- Valerio Marino
- Department of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Italy
| | - Stefan Sulmann
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Life Sciences and Reproduction, Section of Biological Chemistry, University of Verona, Italy; Center for BioMedical Computing (CBMC), University of Verona, Italy.
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Abstract
Leber congenital amaurosis (LCA) is a clinically and genetically heterogeneous group of diseases that account for the most severe form of early-onset retinal dystrophy. Mutations in retinal guanylate cyclase-1 (GUCY2D) are associated with LCA1, a prevalent form. GUCY2D encodes guanylate cyclase-1 (GC1), a protein expressed in rod and cone photoreceptors that regulates cGMP and Ca(2+) levels within these cells. LCA1 patients present with severely impaired vision, reduced, or ablated electroretinogram and nystagmus. Despite a high degree of visual disturbance, LCA1 patients retain normal photoreceptor laminar architecture, except for foveal cone outer segment abnormalities and, in some patients, foveal cone loss. This article will summarize clinical characterization of patients and proof of concept gene replacement studies in several animal models of GC1 deficiency, both of which have laid the groundwork for clinical application of a gene therapy for treatment of LCA1.
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Hoyo NLD, López-Begines S, Rosa JL, Chen J, Méndez A. Functional EF-hands in neuronal calcium sensor GCAP2 determine its phosphorylation state and subcellular distribution in vivo, and are essential for photoreceptor cell integrity. PLoS Genet 2014; 10:e1004480. [PMID: 25058152 PMCID: PMC4109901 DOI: 10.1371/journal.pgen.1004480] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 05/17/2014] [Indexed: 11/18/2022] Open
Abstract
The neuronal calcium sensor proteins GCAPs (guanylate cyclase activating proteins) switch between Ca2+-free and Ca2+-bound conformational states and confer calcium sensitivity to guanylate cyclase at retinal photoreceptor cells. They play a fundamental role in light adaptation by coupling the rate of cGMP synthesis to the intracellular concentration of calcium. Mutations in GCAPs lead to blindness. The importance of functional EF-hands in GCAP1 for photoreceptor cell integrity has been well established. Mutations in GCAP1 that diminish its Ca2+ binding affinity lead to cell damage by causing unabated cGMP synthesis and accumulation of toxic levels of free cGMP and Ca2+. We here investigate the relevance of GCAP2 functional EF-hands for photoreceptor cell integrity. By characterizing transgenic mice expressing a mutant form of GCAP2 with all EF-hands inactivated (EF−GCAP2), we show that GCAP2 locked in its Ca2+-free conformation leads to a rapid retinal degeneration that is not due to unabated cGMP synthesis. We unveil that when locked in its Ca2+-free conformation in vivo, GCAP2 is phosphorylated at Ser201 and results in phospho-dependent binding to the chaperone 14-3-3 and retention at the inner segment and proximal cell compartments. Accumulation of phosphorylated EF−GCAP2 at the inner segment results in severe toxicity. We show that in wildtype mice under physiological conditions, 50% of GCAP2 is phosphorylated correlating with the 50% of the protein being retained at the inner segment. Raising mice under constant light exposure, however, drastically increases the retention of GCAP2 in its Ca2+-free form at the inner segment. This study identifies a new mechanism governing GCAP2 subcellular distribution in vivo, closely related to disease. It also identifies a pathway by which a sustained reduction in intracellular free Ca2+ could result in photoreceptor damage, relevant for light damage and for those genetic disorders resulting in “equivalent-light” scenarios. Visual perception is initiated at retinal photoreceptor cells, where light activates an enzymatic cascade that reduces free cGMP. As cGMP drops, cGMP-channels close and reduce the inward current –including Ca2+ influx– so that photoreceptors hyperpolarize and emit a signal. As the light extinguishes, cGMP levels are restored to reestablish sensitivity. cGMP synthesis relies on guanylate cyclase/guanylate cyclase activating protein (RetGC/GCAP) complexes. GCAPs link the rate of cGMP synthesis to intracellular Ca2+ levels, by switching between a Ca2+-free state that activates cGMP synthesis during light exposure, and a Ca2+-bound state that arrests cGMP synthesis in the dark. It is established that GCAP1 mutations linked to adCORD disrupt this tight Ca2+ control of the cGMP levels. We here show that a GCAP2 functional transition from the Ca2+-free to the Ca2+-loaded form is essential for photoreceptor cell integrity, by a non-related mechanism. We show that GCAP2 locked in its Ca2+-free form is retained by phosphorylation and 14-3-3 binding to the proximal rod compartments, causing severe cell damage. This study identifies a pathway by which a sustained reduction in intracellular free Ca2+ could result in photoreceptor damage, relevant for light damage and for those genetic disorders resulting in “equivalent-light” scenarios.
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Affiliation(s)
| | | | - Jose Luis Rosa
- Department of Physiological Sciences II, University of Barcelona-Bellvitge Health Science Campus, Barcelona, Spain
| | - Jeannie Chen
- Department of Cell and Neurobiology, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
| | - Ana Méndez
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain
- Department of Pathology and Experimental Therapeutics, University of Barcelona-Bellvitge Health Science Campus, Barcelona, Spain
- * E-mail:
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42
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Wen XH, Dizhoor AM, Makino CL. Membrane guanylyl cyclase complexes shape the photoresponses of retinal rods and cones. Front Mol Neurosci 2014; 7:45. [PMID: 24917784 PMCID: PMC4040495 DOI: 10.3389/fnmol.2014.00045] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 05/01/2014] [Indexed: 12/02/2022] Open
Abstract
In vertebrate rods and cones, photon capture by rhodopsin leads to the destruction of cyclic GMP (cGMP) and the subsequent closure of cyclic nucleotide gated ion channels in the outer segment plasma membrane. Replenishment of cGMP and reopening of the channels limit the growth of the photon response and are requisite for its recovery. In different vertebrate retinas, there may be as many as four types of membrane guanylyl cyclases (GCs) for cGMP synthesis. Ten neuronal Ca2+ sensor proteins could potentially modulate their activities. The mouse is proving to be an effective model for characterizing the roles of individual components because its relative simplicity can be reduced further by genetic engineering. There are two types of GC activating proteins (GCAPs) and two types of GCs in mouse rods, whereas cones express one type of GCAP and one type of GC. Mutant mouse rods and cones bereft of both GCAPs have large, long lasting photon responses. Thus, GCAPs normally mediate negative feedback tied to the light-induced decline in intracellular Ca2+ that accelerates GC activity to curtail the growth and duration of the photon response. Rods from other mutant mice that express a single GCAP type reveal how the two GCAPs normally work together as a team. Because of its lower Ca2+ affinity, GCAP1 is the first responder that senses the initial decrease in Ca2+ following photon absorption and acts to limit response amplitude. GCAP2, with a higher Ca2+ affinity, is recruited later during the course of the photon response as Ca2+ levels continue to decline further. The main role of GCAP2 is to provide for a timely response recovery and it is particularly important after exposure to very bright light. The multiplicity of GC isozymes and GCAP homologs in the retinas of other vertebrates confers greater flexibility in shaping the photon responses in order to tune visual sensitivity, dynamic range and frequency response.
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Affiliation(s)
- Xiao-Hong Wen
- Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School Boston, MA, USA
| | - Alexander M Dizhoor
- Department of Basic Sciences Research and Pennsylvania College of Optometry, Salus University Elkins Park, PA, USA
| | - Clint L Makino
- Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School Boston, MA, USA
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43
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Boye SE. Insights gained from gene therapy in animal models of retGC1 deficiency. Front Mol Neurosci 2014; 7:43. [PMID: 24860425 PMCID: PMC4030156 DOI: 10.3389/fnmol.2014.00043] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 04/26/2014] [Indexed: 12/29/2022] Open
Abstract
Vertebrate species possess two retinal guanylate cyclases (retGC1 and retGC2) and at least two guanylate cyclase activating proteins (GCAPs), GCAP1 and GCAP2. GCAPs function as Ca2+ sensors that regulate the activity of guanylate cyclases. Together, these proteins regulate cGMP and Ca2+ levels within the outer segments of rod and cone photoreceptors. Mutations in GUCY2D, the gene that encodes retGC1, are a leading cause of the most severe form of early onset retinal dystrophy, Leber congenital amaurosis (LCA1). These mutations, which reduce or abolish the ability of retGC1 to replenish cGMP in photoreceptors, are thought to lead to the biochemical equivalent of chronic light exposure in these cells. In spite of this, the majority of LCA1 patients retain normal photoreceptor laminar architecture aside from foveal cone outer segment abnormalities, suggesting they may be good candidates for gene replacement therapy. Work began in the 1980s to characterize multiple animal models of retGC1 deficiency. 34 years later, all models have been used in proof of concept gene replacement studies toward the goal of developing a therapy to treat GUCY2D-LCA1. Here we use the results of these studies as well as those of recent clinical studies to address specific questions relating to clinical application of a gene therapy for treatment of LCA1.
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Affiliation(s)
- Shannon E Boye
- Department of Ophthalmology, University of Florida Gainesville, FL, USA
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44
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Peshenko IV, Olshevskaya EV, Lim S, Ames JB, Dizhoor AM. Identification of target binding site in photoreceptor guanylyl cyclase-activating protein 1 (GCAP1). J Biol Chem 2014; 289:10140-54. [PMID: 24567338 PMCID: PMC3974984 DOI: 10.1074/jbc.m113.540716] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 02/10/2014] [Indexed: 12/21/2022] Open
Abstract
Retinal guanylyl cyclase (RetGC)-activating proteins (GCAPs) regulate visual photoresponse and trigger congenital retinal diseases in humans, but GCAP interaction with its target enzyme remains obscure. We mapped GCAP1 residues comprising the RetGC1 binding site by mutagenizing the entire surface of GCAP1 and testing the ability of each mutant to bind RetGC1 in a cell-based assay and to activate it in vitro. Mutations that most strongly affected the activation of RetGC1 localized to a distinct patch formed by the surface of non-metal-binding EF-hand 1, the loop and the exiting helix of EF-hand 2, and the entering helix of EF-hand 3. Mutations in the binding patch completely blocked activation of the cyclase without affecting Ca(2+) binding stoichiometry of GCAP1 or its tertiary fold. Exposed residues in the C-terminal portion of GCAP1, including EF-hand 4 and the helix connecting it with the N-terminal lobe of GCAP1, are not critical for activation of the cyclase. GCAP1 mutants that failed to activate RetGC1 in vitro were GFP-tagged and co-expressed in HEK293 cells with mOrange-tagged RetGC1 to test their direct binding in cyto. Most of the GCAP1 mutations introduced into the "binding patch" prevented co-localization with RetGC1, except for Met-26, Lys-85, and Trp-94. With these residues mutated, GCAP1 completely failed to stimulate cyclase activity but still bound RetGC1 and competed with the wild type GCAP1. Thus, RetGC1 activation by GCAP1 involves establishing a tight complex through the binding patch with an additional activation step involving Met-26, Lys-85, and Trp-94.
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Affiliation(s)
- Igor V. Peshenko
- From the Department of Basic Sciences and the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027 and
| | - Elena V. Olshevskaya
- From the Department of Basic Sciences and the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027 and
| | - Sunghyuk Lim
- the Department of Chemistry, University of California, Davis, California 95616
| | - James B. Ames
- the Department of Chemistry, University of California, Davis, California 95616
| | - Alexander M. Dizhoor
- From the Department of Basic Sciences and the Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027 and
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Lim S, Dizhoor AM, Ames JB. Structural diversity of neuronal calcium sensor proteins and insights for activation of retinal guanylyl cyclase by GCAP1. Front Mol Neurosci 2014; 7:19. [PMID: 24672427 PMCID: PMC3956117 DOI: 10.3389/fnmol.2014.00019] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Accepted: 02/27/2014] [Indexed: 01/08/2023] Open
Abstract
Neuronal calcium sensor (NCS) proteins, a sub-branch of the calmodulin superfamily, are expressed in the brain and retina where they transduce calcium signals and are genetically linked to degenerative diseases. The amino acid sequences of NCS proteins are highly conserved but their physiological functions are quite different. Retinal recoverin controls Ca2+-dependent inactivation of light-excited rhodopsin during phototransduction, guanylyl cyclase activating proteins 1 and 2 (GCAP1 and GCAP2) promote Ca2+-dependent activation of retinal guanylyl cyclases, and neuronal frequenin (NCS-1) modulates synaptic activity and neuronal secretion. Here we review the molecular structures of myristoylated forms of NCS-1, recoverin, and GCAP1 that all look very different, suggesting that the attached myristoyl group helps to refold these highly homologous proteins into different three-dimensional folds. Ca2+-binding to both recoverin and NCS-1 cause large protein conformational changes that ejects the covalently attached myristoyl group into the solvent exterior and promotes membrane targeting (Ca2+-myristoyl switch). The GCAP proteins undergo much smaller Ca2+-induced conformational changes and do not possess a Ca2+-myristoyl switch. Recent structures of GCAP1 in both its activator and Ca2+-bound inhibitory states will be discussed to understand structural determinants that control their Ca2+-dependent activation of retinal guanylyl cyclases.
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Affiliation(s)
- Sunghyuk Lim
- Department of Chemistry, University of California at Davis Davis, CA, USA
| | - Alexander M Dizhoor
- Basic Sciences, Pennsylvania College of Optometry, Salus University Elkins Park, PA, USA
| | - James B Ames
- Department of Chemistry, University of California at Davis Davis, CA, USA
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Zägel P, Koch KW. Dysfunction of outer segment guanylate cyclase caused by retinal disease related mutations. Front Mol Neurosci 2014; 7:4. [PMID: 24616660 PMCID: PMC3935488 DOI: 10.3389/fnmol.2014.00004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 02/10/2014] [Indexed: 11/13/2022] Open
Abstract
Membrane bound guanylate cyclases are expressed in rod and cone cells of the vertebrate retina and mutations in several domains of rod outer segment guanylate cyclase 1 (ROS-GC1 encoded by the gene GUCY2D) correlate with different forms of retinal degenerations. In the present work we investigated the biochemical consequences of three point mutations, one is located in position P575L in the juxtamembrane domain close to the kinase homology domain and two are located in the cyclase catalytic domain at H1019P and P1069R. These mutations correlate with various retinal diseases like autosomal dominant progressive cone degeneration, e.g., Leber Congenital Amaurosis and a juvenile form of retinitis pigmentosa. Wildtype and mutant forms of ROS-GC1 were heterologously expressed in HEK cells, their cellular distribution was investigated and activity profiles in the presence and absence of guanylate cyclase-activating proteins were measured. The mutant P575L was active under all tested conditions, but it displayed a twofold shift in the Ca2+-sensitivity, whereas the mutant P1069R remained inactive despite normal expression levels. The mutation H1019P caused the cyclase to become more labile. The different biochemical consequences of these mutations seem to reflect the different clinical symptoms. The mutation P575L induces a dysregulation of the Ca2+-sensitive cyclase activation profile causing a slow progression of the disease by the distortion of the Ca2+-cGMP homeostasis. In contrast, a strong reduction in cGMP synthesis due to an inactive or structurally unstable ROS-GC1 would trigger more severe forms of retinal diseases.
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Affiliation(s)
- Patrick Zägel
- Biochemistry Group, Department of Neurosciences, Carl von Ossietzky University Oldenburg Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Biochemistry Group, Department of Neurosciences, Carl von Ossietzky University Oldenburg Oldenburg, Germany ; Research Center Neurosensory Science, Carl von Ossietzky University Oldenburg Oldenburg, Germany
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47
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Zägel P, Dell'Orco D, Koch KW. The dimerization domain in outer segment guanylate cyclase is a Ca²⁺-sensitive control switch module. Biochemistry 2013; 52:5065-74. [PMID: 23815670 DOI: 10.1021/bi400288p] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Membrane-bound guanylate cyclases harbor a region called the dimerization or linker domain, which aids the enzymes in adopting an optimal monomer-monomer arrangement for catalysis. One subgroup of these guanylate cyclases is expressed in rod and cone cells of vertebrate retina, and mutations in the dimerization domain of rod outer segment guanylate cyclase 1 (ROS-GC1, encoded by the GUCY2D gene) correlate with retinal cone-rod dystrophies. We investigate how a Q847L/K848Q double mutation, which was found in patients suffering from cone-rod dystrophy, and the Q847L and K848Q single-point mutations affect the regulatory mechanism of ROS-GC1. Both the wild type and mutants of heterologously expressed ROS-GC1 were present in membranes. However, the mutations affected the catalytic properties of ROS-GC1 in different manners. All mutants had higher basal guanylate cyclase activities but lower levels of activation by Ca²⁺-sensing guanylate cyclase-activating proteins (GCAPs). Further, incubation with wild-type GCAP1 and GCAP2 revealed for all ROS-GC1 mutants a shift in Ca²⁺ sensitivity, but activation of the K848Q mutant by GCAPs was severely impaired. Apparent affinities for GCAP1 and GCAP2 were different for the double mutant and the wild type. Circular dichroism spectra of the dimerization domain showed that the wild type and mutants adopt a prevalently α-helical structure, but mutants exhibited lower thermal stability. Our results indicate that the dimerization domain serves as a Ca²⁺-sensitive control module. Although it is per se not a Ca²⁺-sensing unit, it seems to integrate and process information regarding Ca²⁺ sensing by sensor proteins and regulator effector affinity.
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Affiliation(s)
- Patrick Zägel
- Biochemistry Group, Department of Neurosciences, Carl von Ossietzky University Oldenburg, D-26111 Oldenburg, Germany
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48
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Koch KW, Dell’Orco D. A calcium-relay mechanism in vertebrate phototransduction. ACS Chem Neurosci 2013; 4:909-17. [PMID: 23472635 DOI: 10.1021/cn400027z] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Calcium-signaling in cells requires a fine-tuned system of calcium-transport proteins involving ion channels, exchangers, and ion-pumps but also calcium-sensor proteins and their targets. Thus, control of physiological responses very often depends on incremental changes of the cytoplasmic calcium concentration, which are sensed by calcium-binding proteins and are further transmitted to specific target proteins. This Review will focus on calcium-signaling in vertebrate photoreceptor cells, where recent physiological and biochemical data indicate that a subset of neuronal calcium sensor proteins named guanylate cyclase-activating proteins (GCAPs) operate in a calcium-relay system, namely, to make gradual responses to small changes in calcium. We will further integrate this mechanism in an existing computational model of phototransduction showing that it is consistent and compatible with the dynamics that are characteristic for the precise operation of the phototransduction pathways.
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Affiliation(s)
- Karl-Wilhelm Koch
- Department of Neurosciences,
Biochemistry Group, University of Oldenburg, Carl-von-Ossietzky-Strasse 9-11, D-26129 Oldenburg, Germany
| | - Daniele Dell’Orco
- Department of Life Sciences
and Reproduction, Section of Biological Chemistry and Center for BioMedical
Computing (CBMC), University of Verona,
Strada le Grazie 8, I-37134 Verona, Italy
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49
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Makino CL, Wen XH, Olshevskaya EV, Peshenko IV, Savchenko AB, Dizhoor AM. Enzymatic relay mechanism stimulates cyclic GMP synthesis in rod photoresponse: biochemical and physiological study in guanylyl cyclase activating protein 1 knockout mice. PLoS One 2012; 7:e47637. [PMID: 23082185 PMCID: PMC3474714 DOI: 10.1371/journal.pone.0047637] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Accepted: 09/13/2012] [Indexed: 12/21/2022] Open
Abstract
Regulation of cGMP synthesis by retinal membrane guanylyl cyclase isozymes (RetGC1 and RetGC2) in rod and cone photoreceptors by calcium-sensitive guanylyl cyclase activating proteins (GCAP1 and GCAP2) is one of the key molecular mechanisms affecting the response to light and is involved in congenital retinal diseases. The objective of this study was to identify the physiological sequence of events underlying RetGC activation in vivo, by studying the electrophysiological and biochemical properties of mouse rods in a new genetic model lacking GCAP1. The GCAP1−/− retinas expressed normal levels of RetGC isozymes and other phototransduction proteins, with the exception of GCAP2, whose expression was elevated in a compensatory fashion. RetGC activity in GCAP1−/− retinas became more sensitive to Ca2+ and slightly increased. The bright flash response in electroretinogram (ERG) recordings recovered quickly in GCAP1−/−, as well as in RetGC1−/−GCAP1−/−, and RetGC2−/−GCAP1−/− hybrid rods, indicating that GCAP2 activates both RetGC isozymes in vivo. Individual GCAP1−/− rod responses varied in size and shape, likely reflecting variable endogenous GCAP2 levels between different cells, but single-photon response (SPR) amplitude and time-to-peak were typically increased, while recovery kinetics remained faster than in wild type. Recovery from bright flashes in GCAP1−/− was prominently biphasic, because rare, aberrant SPRs producing the slower tail component were magnified. These data provide strong physiological evidence that rod photoresponse recovery is shaped by the sequential recruitment of RetGC isozyme activation by GCAPs according to the different GCAP sensitivities for Ca2+ and specificities toward RetGC isozymes. GCAP1 is the ‘first-response’ sensor protein that stimulates RetGC1 early in the response and thus limits the SPR amplitude, followed by activation of GCAP2 that adds stimulation of both RetGC1 and RetGC2 to speed-up photoreceptor recovery.
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Affiliation(s)
- Clint L. Makino
- Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Xiao-Hong Wen
- Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Elena V. Olshevskaya
- Department of Basic Sciences and Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania, United States of America
| | - Igor V. Peshenko
- Department of Basic Sciences and Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania, United States of America
| | - Andrey B. Savchenko
- Department of Basic Sciences and Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania, United States of America
| | - Alexander M. Dizhoor
- Department of Basic Sciences and Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania, United States of America
- * E-mail:
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50
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López-del Hoyo N, Fazioli L, López-Begines S, Fernández-Sánchez L, Cuenca N, Llorens J, de la Villa P, Méndez A. Overexpression of guanylate cyclase activating protein 2 in rod photoreceptors in vivo leads to morphological changes at the synaptic ribbon. PLoS One 2012; 7:e42994. [PMID: 22912773 PMCID: PMC3418235 DOI: 10.1371/journal.pone.0042994] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 07/16/2012] [Indexed: 11/19/2022] Open
Abstract
Guanylate cyclase activating proteins are EF-hand containing proteins that confer calcium sensitivity to retinal guanylate cyclase at the outer segment discs of photoreceptor cells. By making the rate of cGMP synthesis dependent on the free intracellular calcium levels set by illumination, GCAPs play a fundamental role in the recovery of the light response and light adaptation. The main isoforms GCAP1 and GCAP2 also localize to the synaptic terminal, where their function is not known. Based on the reported interaction of GCAP2 with Ribeye, the major component of synaptic ribbons, it was proposed that GCAP2 could mediate the synaptic ribbon dynamic changes that happen in response to light. We here present a thorough ultrastructural analysis of rod synaptic terminals in loss-of-function (GCAP1/GCAP2 double knockout) and gain-of-function (transgenic overexpression) mouse models of GCAP2. Rod synaptic ribbons in GCAPs-/- mice did not differ from wildtype ribbons when mice were raised in constant darkness, indicating that GCAPs are not required for ribbon early assembly or maturation. Transgenic overexpression of GCAP2 in rods led to a shortening of synaptic ribbons, and to a higher than normal percentage of club-shaped and spherical ribbon morphologies. Restoration of GCAP2 expression in the GCAPs-/- background (GCAP2 expression in the absence of endogenous GCAP1) had the striking result of shortening ribbon length to a much higher degree than overexpression of GCAP2 in the wildtype background, as well as reducing the thickness of the outer plexiform layer without affecting the number of rod photoreceptor cells. These results indicate that preservation of the GCAP1 to GCAP2 relative levels is relevant for maintaining the integrity of the synaptic terminal. Our demonstration of GCAP2 immunolocalization at synaptic ribbons at the ultrastructural level would support a role of GCAPs at mediating the effect of light on morphological remodeling changes of synaptic ribbons.
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Affiliation(s)
| | - Lucrezia Fazioli
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain
| | | | - Laura Fernández-Sánchez
- Department of Physiology, Genetics and Microbiology, Universidad de Alicante, Alicante, Spain
| | - Nicolás Cuenca
- Department of Physiology, Genetics and Microbiology, Universidad de Alicante, Alicante, Spain
| | - Jordi Llorens
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain
- Department of Physiological Sciences II, University of Barcelona-Bellvitge Health Science Campus, Barcelona, Spain
| | - Pedro de la Villa
- Department of Physiology, University of Alcalá de Henares, Madrid, Spain
| | - Ana Méndez
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain
- Department of Pathology and Experimental Therapeutics, University of Barcelona-Bellvitge Health Science Campus, Barcelona, Spain
- * E-mail:
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