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Radhakrishnan R, Leung M, Lor A, More S, Lobo GP. Loss of the systemic vitamin A transporter RBPR2 affects the quantitative balance between chromophore and opsins in visual pigment synthesis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.08.602543. [PMID: 39026765 PMCID: PMC11257425 DOI: 10.1101/2024.07.08.602543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
The distribution of dietary vitamin A/all-trans retinol (ROL) throughout the body is critical for maintaining retinoid function in peripheral tissues and for generating visual pigments for photoreceptor cell function. ROL circulates in the blood bound to the retinol binding protein 4 (RBP4) as RBP4-ROL. Two membrane receptors, RBPR2 in the liver and STRA6 in the eye are proposed to bind circulatory RBP4 and this mechanism is critical for internalizing ROL into cells. Here, we present a longitudinal investigation towards the importance of RBPR2 and influence of the diet on systemic retinoid homeostasis for visual function. Age matched Rbpr2-KO (Rbpr2 -/- ) and wild-type (WT) mice were fed either a vitamin A sufficient (VAS) or a vitamin A deficient (VAD) diet. At 3- and 6-months, we performed retinoid quantification of ocular and non-ocular tissues using HPLC analysis and complemented the data with visual physiology, rhodopsin quantification by spectrophotometry, and biochemical analysis. At 3-months and compared to WT mice, Rbpr2 -/- mice fed either vitamin A diets displayed lower scotopic and photopic electroretinogram (ERG) responses, which correlated with HPLC analysis that revealed Rbpr2 -/- mice had significantly lower hepatic and ocular retinoid content. Interestingly, with the exception of the liver, long-term feeding of Rbpr2 -/- mice with a VAS diet promoted all-trans retinol accumulation in most peripheral tissues. However, even under VAS dietary conditions significant amounts of unliganded opsins in rods, together with decreased visual responses were evident in aged mice lacking RBPR2, when compared to WT mice. Together, our analyses characterize the molecular events underlying nutritional blindness in a novel mouse model and indicate that loss of the liver specific RBP4-ROL receptor, RBPR2, influences systemic retinoid homeostasis and rhodopsin synthesis, which causes profound visual function defects under severe vitamin A deficiency conditions.
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Affiliation(s)
- Rakesh Radhakrishnan
- Department of Ophthalmology, University of Minnesota, Lions Research Building, 2001 6 Street SE, Minneapolis, MN 55455, USA
| | - Matthias Leung
- Department of Ophthalmology, University of Minnesota, Lions Research Building, 2001 6 Street SE, Minneapolis, MN 55455, USA
| | - Anjelynt Lor
- Department of Ophthalmology, University of Minnesota, Lions Research Building, 2001 6 Street SE, Minneapolis, MN 55455, USA
| | - Swati More
- Center for Drug Design, College of Pharmacy, University of Minnesota, MN 55455, USA
| | - Glenn P. Lobo
- Department of Ophthalmology, University of Minnesota, Lions Research Building, 2001 6 Street SE, Minneapolis, MN 55455, USA
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Mattheisen JM, Limberakis C, Ruggeri RB, Dowling MS, Am Ende CW, Ceraudo E, Huber T, McClendon CL, Sakmar TP. Bioorthogonal Tethering Enhances Drug Fragment Affinity for G Protein-Coupled Receptors in Live Cells. J Am Chem Soc 2023; 145:11173-11184. [PMID: 37116188 DOI: 10.1021/jacs.3c00972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
G protein-coupled receptors (GPCRs) modulate diverse cellular signaling pathways and are important drug targets. Despite the availability of high-resolution structures, the discovery of allosteric modulators remains challenging due to the dynamic nature of GPCRs in native membranes. We developed a strategy to covalently tether drug fragments adjacent to allosteric sites in GPCRs to enhance their potency and enable fragment-based drug screening in cell-based systems. We employed genetic code expansion to site-specifically introduce noncanonical amino acids with reactive groups in C-C chemokine receptor 5 (CCR5) near an allosteric binding site for the drug maraviroc. We then used molecular dynamics simulations to design heterobifunctional maraviroc analogues consisting of a drug fragment connected by a flexible linker to a reactive moiety capable of undergoing a bioorthogonal coupling reaction. We synthesized a library of these analogues and employed the bioorthogonal inverse electron demand Diels-Alder reaction to couple the analogues to the engineered CCR5 in live cells, which were then assayed using cell-based signaling assays. Tetherable low-affinity maraviroc fragments displayed an increase in potency for CCR5 engineered with reactive unnatural amino acids that were adjacent to the maraviroc binding site. The strategy we describe to tether novel drug fragments to GPCRs should prove useful to probe allosteric or cryptic binding site functionality in fragment-based GPCR-targeted drug discovery.
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Affiliation(s)
- Jordan M Mattheisen
- Laboratory of Chemical Biology and Signal Transduction, The Rockefeller University, New York, New York 10065, United States
- Tri-Institutional PhD Program in Chemical Biology, New York, New York 10065, United States
| | - Chris Limberakis
- Pfizer Worldwide Research, Development, and Medical, Groton, Connecticut 06340, United States
| | - Roger B Ruggeri
- Pfizer Worldwide Research, Development, and Medical, Groton, Connecticut 06340, United States
| | - Matthew S Dowling
- Pfizer Worldwide Research, Development, and Medical, Groton, Connecticut 06340, United States
| | - Christopher W Am Ende
- Pfizer Worldwide Research, Development, and Medical, Groton, Connecticut 06340, United States
| | - Emilie Ceraudo
- Laboratory of Chemical Biology and Signal Transduction, The Rockefeller University, New York, New York 10065, United States
| | - Thomas Huber
- Laboratory of Chemical Biology and Signal Transduction, The Rockefeller University, New York, New York 10065, United States
| | - Christopher L McClendon
- Pfizer Worldwide Research, Development, and Medical, Cambridge, Massachusetts 02139, United States
| | - Thomas P Sakmar
- Laboratory of Chemical Biology and Signal Transduction, The Rockefeller University, New York, New York 10065, United States
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3
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Interdisciplinary biophysical studies of membrane proteins bacteriorhodopsin and rhodopsin. Biophys Rev 2023; 15:111-125. [PMID: 36909961 PMCID: PMC9995646 DOI: 10.1007/s12551-022-01003-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 09/28/2022] [Indexed: 10/10/2022] Open
Abstract
The centenary of the birth of H. Gobind Khorana provides an auspicious opportunity to review the origins and evolution of parallel advances in biophysical methodology and molecular genetics technology used to study membrane proteins. Interdisciplinary work in the Khorana laboratory in the late 1970s and for the next three decades led to productive collaborations and fostered three subsequent scientific generations whose biophysical work on membrane proteins has led to detailed elucidation of the molecular mechanisms of energy transduction by the light-driven proton pump bacteriorhodopsin (bR) and signal transduction by the G protein-coupled receptor (GPCR) rhodopsin. This review will highlight the origins and advances of biophysical studies of membrane proteins made possible by the application of molecular genetics approaches to engineer site-specific alterations of membrane protein structures.
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4
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Molecular Basis for Variations in the Sensitivity of Pathogenic Rhodopsin Variants to 9-cis-Retinal. J Biol Chem 2022; 298:102266. [PMID: 35850308 PMCID: PMC9399271 DOI: 10.1016/j.jbc.2022.102266] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Revised: 07/11/2022] [Accepted: 07/13/2022] [Indexed: 11/24/2022] Open
Abstract
Over 100 mutations in the rhodopsin gene have been linked to a spectrum of retinopathies that include retinitis pigmentosa and congenital stationary night blindness. Though most of these variants exhibit a loss of function, the molecular defects caused by these underlying mutations vary considerably. In this work, we utilize deep mutational scanning to quantitatively compare the plasma membrane expression of 123 known pathogenic rhodopsin variants in the presence and absence of the stabilizing cofactor 9-cis-retinal. We identify 69 retinopathy variants, including 20 previously uncharacterized variants, that exhibit diminished plasma membrane expression in HEK293T cells. Of these apparent class II variants, 67 exhibit a measurable increase in expression in the presence of 9-cis-retinal. However, the magnitude of the response to this molecule varies considerably across this spectrum of mutations. Evaluation of the observed shifts relative to thermodynamic estimates for the coupling between binding and folding suggests underlying differences in stability constrains the magnitude of their response to retinal. Nevertheless, estimates from computational modeling suggest that many of the least sensitive variants also directly compromise binding. Finally, we evaluate the functional properties of three previous uncharacterized, retinal-sensitive variants (ΔN73, S131P, and R135G) and show that two of these retain residual function in vitro. Together, our results provide a comprehensive experimental characterization of the proteostatic properties of retinopathy variants and their response to retinal.
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5
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Tian H, Gunnison KM, Kazmi MA, Sakmar TP, Huber T. FRET sensors reveal the retinal entry pathway in the G protein-coupled receptor rhodopsin. iScience 2022; 25:104060. [PMID: 35355518 PMCID: PMC8958324 DOI: 10.1016/j.isci.2022.104060] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 01/11/2022] [Accepted: 03/04/2022] [Indexed: 11/26/2022] Open
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6
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McKee AG, Kuntz CP, Ortega JT, Woods H, Most V, Roushar FJ, Meiler J, Jastrzebska B, Schlebach JP. Systematic Profiling of Temperature- and Retinal-Sensitive Rhodopsin Variants by Deep Mutational Scanning. J Biol Chem 2021; 297:101359. [PMID: 34756884 PMCID: PMC8649220 DOI: 10.1016/j.jbc.2021.101359] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 10/20/2021] [Accepted: 10/26/2021] [Indexed: 01/29/2023] Open
Abstract
Membrane protein variants with diminished conformational stability often exhibit enhanced cellular expression at reduced growth temperatures. The expression of “temperature-sensitive” variants is also typically sensitive to corrector molecules that bind and stabilize the native conformation. There are many examples of temperature-sensitive rhodopsin variants, the misfolding of which is associated with the molecular basis of retinitis pigmentosa. In this work, we employ deep mutational scanning to compare the effects of reduced growth temperature and 9-cis-retinal, an investigational corrector, on the plasma membrane expression of 700 rhodopsin variants in HEK293T cells. We find that the change in expression at reduced growth temperatures correlates with the response to 9-cis-retinal among variants bearing mutations within a hydrophobic transmembrane domain (TM2). The most sensitive variants appear to disrupt a native helical kink within this transmembrane domain. By comparison, mutants that alter the structure of a polar transmembrane domain (TM7) exhibit weaker responses to temperature and retinal that are poorly correlated. Statistical analyses suggest that this observed insensitivity cannot be attributed to a single variable, but likely arises from the composite effects of mutations on the energetics of membrane integration, the stability of the native conformation, and the integrity of the retinal-binding pocket. Finally, we show that the characteristics of purified temperature- and retinal-sensitive variants suggest that the proteostatic effects of retinal may be manifested during translation and cotranslational folding. Together, our findings highlight several biophysical constraints that appear to influence the sensitivity of genetic variants to temperature and small-molecule correctors.
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Affiliation(s)
- Andrew G McKee
- Department of Chemistry, Indiana University, Bloomington, Indiana, USA
| | - Charles P Kuntz
- Department of Chemistry, Indiana University, Bloomington, Indiana, USA
| | - Joseph T Ortega
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
| | - Hope Woods
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee, USA; Chemical and Physical Biology Program, Vanderbilt University, Nashville, Tennessee, USA
| | - Victoria Most
- Institute for Drug Development, Leipzig University, Leipzig, SAC, Germany
| | - Francis J Roushar
- Department of Chemistry, Indiana University, Bloomington, Indiana, USA
| | - Jens Meiler
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee, USA; Institute for Drug Development, Leipzig University, Leipzig, SAC, Germany
| | - Beata Jastrzebska
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, USA
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7
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Penn WD, McKee AG, Kuntz CP, Woods H, Nash V, Gruenhagen TC, Roushar FJ, Chandak M, Hemmerich C, Rusch DB, Meiler J, Schlebach JP. Probing biophysical sequence constraints within the transmembrane domains of rhodopsin by deep mutational scanning. SCIENCE ADVANCES 2020; 6:eaay7505. [PMID: 32181350 PMCID: PMC7056298 DOI: 10.1126/sciadv.aay7505] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 12/11/2019] [Indexed: 05/15/2023]
Abstract
Membrane proteins must balance the sequence constraints associated with folding and function against the hydrophobicity required for solvation within the bilayer. We recently found the expression and maturation of rhodopsin are limited by the hydrophobicity of its seventh transmembrane domain (TM7), which contains polar residues that are essential for function. On the basis of these observations, we hypothesized that rhodopsin's expression should be less tolerant of mutations in TM7 relative to those within hydrophobic TM domains. To test this hypothesis, we used deep mutational scanning to compare the effects of 808 missense mutations on the plasma membrane expression of rhodopsin in HEK293T cells. Our results confirm that a higher proportion of mutations within TM7 (37%) decrease rhodopsin's plasma membrane expression relative to those within a hydrophobic TM domain (TM2, 25%). These results in conjunction with an evolutionary analysis suggest solvation energetics likely restricts the evolutionary sequence space of polar TM domains.
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Affiliation(s)
- Wesley D. Penn
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
| | - Andrew G. McKee
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
| | - Charles P. Kuntz
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
| | - Hope Woods
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
- Chemical and Physical Biology Program, Vanderbilt University, Nashville, TN 37235, USA
| | - Veronica Nash
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
| | | | | | - Mahesh Chandak
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
| | - Chris Hemmerich
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN 47405, USA
| | - Douglas B. Rusch
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN 47405, USA
| | - Jens Meiler
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
| | - Jonathan P. Schlebach
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
- Corresponding author.
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8
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Marinko J, Huang H, Penn WD, Capra JA, Schlebach JP, Sanders CR. Folding and Misfolding of Human Membrane Proteins in Health and Disease: From Single Molecules to Cellular Proteostasis. Chem Rev 2019; 119:5537-5606. [PMID: 30608666 PMCID: PMC6506414 DOI: 10.1021/acs.chemrev.8b00532] [Citation(s) in RCA: 162] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Indexed: 12/13/2022]
Abstract
Advances over the past 25 years have revealed much about how the structural properties of membranes and associated proteins are linked to the thermodynamics and kinetics of membrane protein (MP) folding. At the same time biochemical progress has outlined how cellular proteostasis networks mediate MP folding and manage misfolding in the cell. When combined with results from genomic sequencing, these studies have established paradigms for how MP folding and misfolding are linked to the molecular etiologies of a variety of diseases. This emerging framework has paved the way for the development of a new class of small molecule "pharmacological chaperones" that bind to and stabilize misfolded MP variants, some of which are now in clinical use. In this review, we comprehensively outline current perspectives on the folding and misfolding of integral MPs as well as the mechanisms of cellular MP quality control. Based on these perspectives, we highlight new opportunities for innovations that bridge our molecular understanding of the energetics of MP folding with the nuanced complexity of biological systems. Given the many linkages between MP misfolding and human disease, we also examine some of the exciting opportunities to leverage these advances to address emerging challenges in the development of therapeutics and precision medicine.
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Affiliation(s)
- Justin
T. Marinko
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
| | - Hui Huang
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
| | - Wesley D. Penn
- Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - John A. Capra
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
- Department
of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37245, United States
| | - Jonathan P. Schlebach
- Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Charles R. Sanders
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
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9
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Pagano K, Paolino M, Fusi S, Zanirato V, Trapella C, Giuliani G, Cappelli A, Zanzoni S, Molinari H, Ragona L, Olivucci M. Bile Acid Binding Protein Functionalization Leads to a Fully Synthetic Rhodopsin Mimic. J Phys Chem Lett 2019; 10:2235-2243. [PMID: 30995409 DOI: 10.1021/acs.jpclett.9b00210] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Rhodopsins are photoreceptive proteins using light to drive a plethora of biological functions such as vision, proton and ion pumping, cation and anion channeling, and gene and enzyme regulation. Here we combine organic synthesis, NMR structural studies, and photochemical characterization to show that it is possible to prepare a fully synthetic mimic of rhodopsin photoreceptors. More specifically, we conjugate a bile acid binding protein with a synthetic mimic of the rhodopsin protonated Schiff base chromophore to achieve a covalent complex featuring an unnatural protein host, photoswitch, and photoswitch-protein linkage with a reverse orientation. We show that, in spite of its molecular-level diversity, light irradiation of the prepared mimic fuels a photochromic cycle driven by sequential photochemical and thermal Z/E isomerizations reminiscent of the photocycles of microbial rhodopsins.
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Affiliation(s)
- Katiuscia Pagano
- Istituto per lo Studio delle Macromolecole, CNR , Via A. Corti 12 , 20133 Milano , Italy
| | - Marco Paolino
- Dipartimento di Biotecnologie, Chimica e Farmacia (Dipartimento di Eccellenza 2018-2022) , Università degli Studi di Siena , Via Aldo Moro 2 , 53100 Siena , Italy
| | - Stefania Fusi
- Dipartimento di Biotecnologie, Chimica e Farmacia (Dipartimento di Eccellenza 2018-2022) , Università degli Studi di Siena , Via Aldo Moro 2 , 53100 Siena , Italy
| | | | | | - Germano Giuliani
- Dipartimento di Biotecnologie, Chimica e Farmacia (Dipartimento di Eccellenza 2018-2022) , Università degli Studi di Siena , Via Aldo Moro 2 , 53100 Siena , Italy
| | - Andrea Cappelli
- Dipartimento di Biotecnologie, Chimica e Farmacia (Dipartimento di Eccellenza 2018-2022) , Università degli Studi di Siena , Via Aldo Moro 2 , 53100 Siena , Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche , Università di Verona , Strada Le Grazie , 37134 Verona , Italy
| | - Henriette Molinari
- Istituto per lo Studio delle Macromolecole, CNR , Via A. Corti 12 , 20133 Milano , Italy
| | - Laura Ragona
- Istituto per lo Studio delle Macromolecole, CNR , Via A. Corti 12 , 20133 Milano , Italy
| | - Massimo Olivucci
- Dipartimento di Biotecnologie, Chimica e Farmacia (Dipartimento di Eccellenza 2018-2022) , Università degli Studi di Siena , Via Aldo Moro 2 , 53100 Siena , Italy
- Chemistry Department , Bowling Green State University , Bowling Green , Ohio 43403 , United States
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10
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Srinivasan S, Guixà-González R, Cordomí A, Garriga P. Ligand Binding Mechanisms in Human Cone Visual Pigments. Trends Biochem Sci 2019; 44:629-639. [PMID: 30853245 DOI: 10.1016/j.tibs.2019.02.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 02/04/2019] [Accepted: 02/07/2019] [Indexed: 12/13/2022]
Abstract
Vertebrate vision starts with light absorption by visual pigments in rod and cone photoreceptor cells of the retina. Rhodopsin, in rod cells, responds to dim light, whereas three types of cone opsins (red, green, and blue) function under bright light and mediate color vision. Cone opsins regenerate with retinal much faster than rhodopsin, but the molecular mechanism of regeneration is still unclear. Recent advances in the area pinpoint transient intermediate opsin conformations, and a possible secondary retinal-binding site, as determinant factors for regeneration. In this Review, we compile previous and recent findings to discuss possible mechanisms of ligand entry in cone opsins, involving a secondary binding site, which may have relevant functional and evolutionary implications.
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Affiliation(s)
- Sundaramoorthy Srinivasan
- Grup de Biotecnologia Molecular i Industrial, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya-Barcelona Tech, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain
| | - Ramon Guixà-González
- Laboratori de Medicina Computational, Universitat Autonòma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Arnau Cordomí
- Laboratori de Medicina Computational, Universitat Autonòma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Pere Garriga
- Grup de Biotecnologia Molecular i Industrial, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya-Barcelona Tech, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain.
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11
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Roushar FJ, Gruenhagen TC, Penn WD, Li B, Meiler J, Jastrzebska B, Schlebach JP. Contribution of Cotranslational Folding Defects to Membrane Protein Homeostasis. J Am Chem Soc 2018; 141:204-215. [PMID: 30537820 DOI: 10.1021/jacs.8b08243] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Membrane proteins are prone to misfolding and degradation within the cell, yet the nature of the conformational defects involved in this process remain poorly understood. The earliest stages of membrane protein folding are mediated by the Sec61 translocon, a molecular machine that facilitates the lateral partitioning of the polypeptide into the membrane. Proper membrane integration is an essential prerequisite for folding of the nascent chain. However, the marginal energetic drivers of this reaction suggest the translocon may operate with modest fidelity. In this work, we employed biophysical modeling in conjunction with quantitative biochemical measurements in order to evaluate the extent to which cotranslational folding defects influence membrane protein homeostasis. Protein engineering was employed to selectively perturb the topological energetics of human rhodopsin, and the expression and cellular trafficking of engineered variants were quantitatively compared. Our results reveal clear relationships between topological energetics and the efficiency of rhodopsin biogenesis, which appears to be limited by the propensity of a polar transmembrane domain to achieve its correct topological orientation. Though the polarity of this segment is functionally constrained, we find that its topology can be stabilized in a manner that enhances biogenesis without compromising the functional properties of rhodopsin. Furthermore, sequence alignments reveal this topological instability has been conserved throughout the course of evolution. These results suggest that topological defects significantly contribute to the inefficiency of membrane protein folding in the cell. Additionally, our findings suggest that the marginal stability of rhodopsin may represent an evolved trait.
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Affiliation(s)
- Francis J Roushar
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Timothy C Gruenhagen
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Wesley D Penn
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
| | - Bian Li
- Department of Chemistry , Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Jens Meiler
- Department of Chemistry , Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Beata Jastrzebska
- Department of Pharmacology , Case Western Reserve University , Cleveland , Ohio 44106 , United States
| | - Jonathan P Schlebach
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405 , United States
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12
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Apo-Opsin Exists in Equilibrium Between a Predominant Inactive and a Rare Highly Active State. J Neurosci 2018; 39:212-223. [PMID: 30459230 DOI: 10.1523/jneurosci.1980-18.2018] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/30/2018] [Accepted: 11/04/2018] [Indexed: 12/17/2022] Open
Abstract
Bleaching adaptation in rod photoreceptors is mediated by apo-opsin, which activates phototransduction with effective activity 105- to 106-fold lower than that of photoactivated rhodopsin (meta II). However, the mechanism that produces such low opsin activity is unknown. To address this question, we sought to record single opsin responses in mouse rods. We used mutant mice lacking efficient calcium feedback to boosts rod responses and generated a small fraction of opsin by photobleaching ∼1% of rhodopsin. The bleach produced a dramatic increase in the frequency of discrete photoresponse-like events. This activity persisted for hours, was quenched by 11-cis-retinal, and was blocked by uncoupling opsin from phototransduction, all indicating opsin as its source. Opsin-driven discrete activity was also observed in rods containing non-activatable rhodopsin, ruling out transactivation of rhodopsin by opsin. We conclude that bleaching adaptation is mediated by opsin that exists in equilibrium between a predominant inactive and a rare meta II-like state.SIGNIFICANCE STATEMENT Electrophysiological analysis is used to show that the G-protein-coupled receptor opsin exists in equilibrium between a predominant inactive and a rare highly active state that mediates bleaching adaptation in photoreceptors.
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13
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Gao S, Kahremany S, Zhang J, Jastrzebska B, Querubin J, Petersen-Jones SM, Palczewski K. Retinal-chitosan Conjugates Effectively Deliver Active Chromophores to Retinal Photoreceptor Cells in Blind Mice and Dogs. Mol Pharmacol 2018; 93:438-452. [PMID: 29453250 DOI: 10.1124/mol.117.111294] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Accepted: 02/13/2018] [Indexed: 12/13/2022] Open
Abstract
The retinoid (visual) cycle consists of a series of biochemical reactions needed to regenerate the visual chromophore 11-cis-retinal and sustain vision. Genetic or environmental factors affecting chromophore production can lead to blindness. Using animal models that mimic human retinal diseases, we previously demonstrated that mechanism-based pharmacological interventions can maintain vision in otherwise incurable genetic diseases of the retina. Here, we report that after 9-cis-retinal administration to lecithin:retinol acyltransferase-deficient (Lrat-/- ) mice, the drug was rapidly absorbed and then cleared within 1 to 2 hours. However, when conjugated to form chitosan-9-cis-retinal, this prodrug was slowly absorbed from the gastrointestinal tract, resulting in sustainable plasma levels of 9-cis-retinol and recovery of visual function without causing elevated levels, as occurs with unconjugated drug treatment. Administration of chitosan-9-cis-retinal conjugate intravitreally in retinal pigment epithelium-specific 65 retinoid isomerase (RPE65)-deficient dogs improved photoreceptor function as assessed by electroretinography. Functional rescue was dose dependent and maintained for several weeks. Dosing via the gastrointestinal tract in canines was found ineffective, most likely due to peculiarities of vitamin A blood transport in canines. Use of the chitosan conjugate in combination with 11-cis-6-ring-retinal, a locked ring analog of 11-cis-retinal that selectively blocks rod opsin consumption of chromophore while largely sparing cone opsins, was found to prolong cone vision in Lrat-/- mice. Development of such combination low-dose regimens to selectively prolong useful cone vision could not only expand retinal disease treatments to include Leber congenital amaurosis but also the age-related decline in human dark adaptation from progressive retinoid cycle deficiency.
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Affiliation(s)
- Songqi Gao
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
| | - Shirin Kahremany
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
| | - Jianye Zhang
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
| | - Beata Jastrzebska
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
| | - Janice Querubin
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
| | - Simon M Petersen-Jones
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
| | - Krzysztof Palczewski
- Department of Pharmacology and Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio (S.G., S.K., J.Z., B.J., K.P.) and Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (J.Q., S.M.P.-J.)
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