1
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Ayub H, Murray RJ, Kuyler GC, Napier-Khwaja F, Gunner J, Dafforn TR, Klumperman B, Poyner DR, Wheatley M. GPCRs in the round: SMA-like copolymers and SMALPs as a platform for investigating GPCRs. Arch Biochem Biophys 2024; 754:109946. [PMID: 38395122 DOI: 10.1016/j.abb.2024.109946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2023] [Revised: 01/21/2024] [Accepted: 02/20/2024] [Indexed: 02/25/2024]
Abstract
G-protein-coupled receptors (GPCRs) are the largest family of membrane proteins, regulate a plethora of physiological responses and are the therapeutic target for 30-40% of clinically-prescribed drugs. They are integral membrane proteins deeply embedded in the plasma membrane where they activate intracellular signalling via coupling to G-proteins and β-arrestin. GPCRs are in intimate association with the bilayer lipids and that lipid environment regulates the signalling functions of GPCRs. This complex lipid 'landscape' is both heterogeneous and dynamic. GPCR function is modulated by bulk membrane properties including membrane fluidity, microdomains, curvature, thickness and asymmetry but GPCRs are also regulated by specific lipid:GPCR binding, including cholesterol and anionic lipids. Understanding the molecular mechanisms whereby GPCR signalling is regulated by lipids is a very active area of research currently. A major advance in membrane protein research in recent years was the application of poly(styrene-co-maleic acid) (SMA) copolymers. These spontaneously generate SMA lipid particles (SMALPs) encapsulating membrane protein in a nano-scale disc of cell membrane, thereby removing the historical need for detergent and preserving lipid:GPCR interaction. The focus of this review is how GPCR-SMALPs are increasing our understanding of GPCR structure and function at the molecular level. Furthermore, an increasing number of 'second generation' SMA-like copolymers have been reported recently. These are reviewed from the context of increasing our understanding of GPCR molecular mechanisms. Moreover, their potential as a novel platform for downstream biophysical and structural analyses is assessed and looking ahead, the translational application of SMA-like copolymers to GPCR drug discovery programmes in the future is considered.
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Affiliation(s)
- Hoor Ayub
- Centre for Health and Life Sciences, Coventry University, Coventry, CV1 2DS, UK.
| | - Rebecca J Murray
- Centre for Health and Life Sciences, Coventry University, Coventry, CV1 2DS, UK; Department of Chemistry and Polymer Sciences, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
| | - Gestél C Kuyler
- Centre for Health and Life Sciences, Coventry University, Coventry, CV1 2DS, UK; Department of Chemistry and Polymer Sciences, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
| | | | - Joseph Gunner
- School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK
| | - Tim R Dafforn
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
| | - Bert Klumperman
- Department of Chemistry and Polymer Sciences, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
| | - David R Poyner
- School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK
| | - Mark Wheatley
- Centre for Health and Life Sciences, Coventry University, Coventry, CV1 2DS, UK; Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
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2
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Thakur N, Ray AP, Sharp L, Jin B, Duong A, Pour NG, Obeng S, Wijesekara AV, Gao ZG, McCurdy CR, Jacobson KA, Lyman E, Eddy MT. Anionic phospholipids control mechanisms of GPCR-G protein recognition. Nat Commun 2023; 14:794. [PMID: 36781870 PMCID: PMC9925817 DOI: 10.1038/s41467-023-36425-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Accepted: 01/31/2023] [Indexed: 02/15/2023] Open
Abstract
G protein-coupled receptors (GPCRs) are embedded in phospholipids that strongly influence drug-stimulated signaling. Anionic lipids are particularly important for GPCR signaling complex formation, but a mechanism for this role is not understood. Using NMR spectroscopy, we explore the impact of anionic lipids on the function-related conformational equilibria of the human A2A adenosine receptor (A2AAR) in bilayers containing defined mixtures of zwitterionic and anionic phospholipids. Anionic lipids prime the receptor to form complexes with G proteins through a conformational selection process. Without anionic lipids, signaling complex formation proceeds through a less favorable induced fit mechanism. In computational models, anionic lipids mimic interactions between a G protein and positively charged residues in A2AAR at the receptor intracellular surface, stabilizing a pre-activated receptor conformation. Replacing these residues strikingly alters the receptor response to anionic lipids in experiments. High sequence conservation of the same residues among all GPCRs supports a general role for lipid-receptor charge complementarity in signaling.
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Affiliation(s)
- Naveen Thakur
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA
| | - Arka P Ray
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA
| | - Liam Sharp
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware, USA
| | - Beining Jin
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA
| | - Alexander Duong
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA
| | - Niloofar Gopal Pour
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA
| | - Samuel Obeng
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, USA
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL, USA
| | - Anuradha V Wijesekara
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA
| | - Zhan-Guo Gao
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, 20892, USA
| | - Christopher R McCurdy
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL, USA
- Translational Drug Development Core, Clinical and Translational Sciences Institute, University of Florida, Gainesville, Florida, USA
| | - Kenneth A Jacobson
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, 20892, USA
| | - Edward Lyman
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware, USA
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
| | - Matthew T Eddy
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL, USA.
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3
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Thakur N, Ray AP, Sharp L, Jin B, Duong A, Pour NG, Obeng S, Wijesekara AV, Gao ZG, McCurdy CR, Jacobson KA, Lyman E, Eddy MT. Anionic Phospholipids Control Mechanisms of GPCR-G Protein Recognition. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.11.523010. [PMID: 36711594 PMCID: PMC9882065 DOI: 10.1101/2023.01.11.523010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
G protein-coupled receptors (GPCRs) are embedded in phospholipids that strongly influence drug-stimulated signaling. Anionic lipids are particularly important for GPCR signaling complex formation, but a mechanism for this role is not understood. Using NMR spectroscopy, we visualized the impact of anionic lipids on the function-related conformational equilibria of the human A 2A adenosine receptor (A 2A AR) in bilayers containing defined mixtures of zwitterionic and anionic phospholipids. Anionic lipids primed the receptor to form complexes with G proteins through a conformational selection process. Without anionic lipids, signaling complex formation proceeded through a less favorable induced fit mechanism. In computational models, anionic lipids mimicked interactions between a G protein and positively charged residues in A 2A AR at the receptor intracellular surface, stabilizing a pre-activated receptor conformation. Replacing these residues strikingly altered the receptor response to anionic lipids in experiments. High sequence conservation of the same residues among all GPCRs supports a general role for lipid-receptor charge complementarity in signaling.
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Affiliation(s)
- Naveen Thakur
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
| | - Arka P Ray
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
| | - Liam Sharp
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware
| | - Beining Jin
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
| | - Alexander Duong
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
| | - Niloofar Gopal Pour
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
| | - Samuel Obeng
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA
| | - Anuradha V Wijesekara
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
| | - Zhan-Guo Gao
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Christopher R McCurdy
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA
- Translational Drug Development Core, Clinical and Translational Sciences Institute, University of Florida, Gainesville, Florida 32610, USA
| | - Kenneth A Jacobson
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Edward Lyman
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware
| | - Matthew T Eddy
- Department of Chemistry, College of Liberal Arts & Sciences, University of Florida, 126 Sisler Hall, Gainesville, FL 32611, USA
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Sander CL, Sears AE, Pinto AF, Choi EH, Kahremany S, Gao F, Salom D, Jin H, Pardon E, Suh S, Dong Z, Steyaert J, Saghatelian A, Skowronska-Krawczyk D, Kiser PD, Palczewski K. Nano-scale resolution of native retinal rod disk membranes reveals differences in lipid composition. J Cell Biol 2021; 220:e202101063. [PMID: 34132745 PMCID: PMC8240855 DOI: 10.1083/jcb.202101063] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 04/26/2021] [Accepted: 05/18/2021] [Indexed: 02/07/2023] Open
Abstract
Photoreceptors rely on distinct membrane compartments to support their specialized function. Unlike protein localization, identification of critical differences in membrane content has not yet been expanded to lipids, due to the difficulty of isolating domain-specific samples. We have overcome this by using SMA to coimmunopurify membrane proteins and their native lipids from two regions of photoreceptor ROS disks. Each sample's copurified lipids were subjected to untargeted lipidomic and fatty acid analysis. Extensive differences between center (rhodopsin) and rim (ABCA4 and PRPH2/ROM1) samples included a lower PC to PE ratio and increased LC- and VLC-PUFAs in the center relative to the rim region, which was enriched in shorter, saturated FAs. The comparatively few differences between the two rim samples likely reflect specific protein-lipid interactions. High-resolution profiling of the ROS disk lipid composition gives new insights into how intricate membrane structure and protein activity are balanced within the ROS, and provides a model for future studies of other complex cellular structures.
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Affiliation(s)
- Christopher L. Sander
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Avery E. Sears
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Antonio F.M. Pinto
- Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, CA
| | - Elliot H. Choi
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Shirin Kahremany
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Fangyuan Gao
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - David Salom
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Hui Jin
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
| | - Els Pardon
- Vlaams Instituut voor Biotechnologie–Vrije Universiteit Brussel Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
| | - Susie Suh
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Zhiqian Dong
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
| | - Jan Steyaert
- Vlaams Instituut voor Biotechnologie–Vrije Universiteit Brussel Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
| | - Alan Saghatelian
- Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, CA
| | - Dorota Skowronska-Krawczyk
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA
| | - Philip D. Kiser
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA
- Research Service, VA Long Beach Healthcare System, Long Beach, CA
| | - Krzysztof Palczewski
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Irvine, CA
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA
- Department of Chemistry, University of California, Irvine, Irvine, CA
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5
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Szundi I, Funatogawa C, Guo Y, Yan ECY, Kliger DS. Protein Sequence and Membrane Lipid Roles in the Activation Kinetics of Bovine and Human Rhodopsins. Biophys J 2017; 113:1934-1944. [PMID: 29117518 DOI: 10.1016/j.bpj.2017.08.051] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Revised: 07/26/2017] [Accepted: 08/28/2017] [Indexed: 12/17/2022] Open
Abstract
Rhodopsin is a G protein-coupled receptor found in the rod outer segments in the retina, which triggers a visual response under dim light conditions. Recently, a study of the late, microsecond-to-millisecond kinetics of photointermediates of the human and bovine rhodopsins in their native membranes revealed a complex, double-square mechanism of rhodopsin activation. In this kinetic scheme, the human rhodopsin exhibited more Schiff base deprotonation than bovine rhodopsin, which could arise from the ∼7% sequence difference between the two proteins, or from the difference between their membrane lipid environments. To differentiate between the effects of membrane and protein structure on the kinetics, the human and bovine rhodopsins were inserted into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine lipid nanodiscs and the kinetics of activation at 15°C and pH 8.7 was investigated by time-resolved absorption spectroscopy and global kinetic analysis. For both proteins, the kinetics in nanodiscs shows the characteristics observed in the native membranes, and is described by a multisquare model with Schiff base deprotonation at the lumirhodopsin I intermediate stage. The results indicate that the protein sequence controls the extent of Schiff base deprotonation and accumulation of intermediates, and thus plays the main role in the different activation kinetics observed between human and bovine rhodopsins. The membrane lipid does have a minor role by modulating the timing of the kinetics, with the nanodisc environment leading to an earlier Schiff base deprotonation.
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Affiliation(s)
- Istvan Szundi
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California
| | - Chie Funatogawa
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California
| | - Ying Guo
- Department of Chemistry, Yale University, New Haven, Connecticut
| | - Elsa C Y Yan
- Department of Chemistry, Yale University, New Haven, Connecticut
| | - David S Kliger
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California.
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Neale C, Herce HD, Pomès R, García AE. Can Specific Protein-Lipid Interactions Stabilize an Active State of the Beta 2 Adrenergic Receptor? Biophys J 2016; 109:1652-62. [PMID: 26488656 DOI: 10.1016/j.bpj.2015.08.028] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Revised: 08/21/2015] [Accepted: 08/24/2015] [Indexed: 11/16/2022] Open
Abstract
G-protein-coupled receptors are eukaryotic membrane proteins with broad biological and pharmacological relevance. Like all membrane-embedded proteins, their location and orientation are influenced by lipids, which can also impact protein function via specific interactions. Extensive simulations totaling 0.25 ms reveal a process in which phospholipids from the membrane's cytosolic leaflet enter the empty G-protein binding site of an activated β2 adrenergic receptor and form salt-bridge interactions that inhibit ionic lock formation and prolong active-state residency. Simulations of the receptor embedded in an anionic membrane show increased lipid binding, providing a molecular mechanism for the experimental observation that anionic lipids can enhance receptor activity. Conservation of the arginine component of the ionic lock among Rhodopsin-like G-protein-coupled receptors suggests that intracellular lipid ingression between receptor helices H6 and H7 may be a general mechanism for active-state stabilization.
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Affiliation(s)
- Chris Neale
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York
| | - Henry D Herce
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York
| | - Régis Pomès
- Molecular Structure and Function, The Hospital for Sick Children, Toronto, Ontario, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Angel E García
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York; Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York.
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Functional stability of rhodopsin in a bicelle system: evaluating G protein activation by rhodopsin in bicelles. Methods Mol Biol 2015; 1271:67-76. [PMID: 25697517 DOI: 10.1007/978-1-4939-2330-4_5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Rhodopsin is a prototypical member of the G protein-coupled receptors (GPCRs). This photoreceptor is responsible for initiating the visual signaling transduction cascade upon interaction with its heterotrimeric G protein, transducin (Gt), after light activation. Like all transmembrane proteins, rhodopsin is embedded within a phospholipid bilayer. Many studies have proposed that the membrane composition of this bilayer is an important factor for receptor function during the activation process. Here we describe the methods and assays used to evaluate the function of purified and reconstituted rhodopsin in bicelles.
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8
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Coleman JA, Zhu X, Djajadi HR, Molday LL, Smith RS, Libby RT, John SWM, Molday RS. Phospholipid flippase ATP8A2 is required for normal visual and auditory function and photoreceptor and spiral ganglion cell survival. J Cell Sci 2014; 127:1138-49. [PMID: 24413176 DOI: 10.1242/jcs.145052] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
ATP8A2 is a P4-ATPase that is highly expressed in the retina, brain, spinal cord and testes. In the retina, ATP8A2 is localized in photoreceptors where it uses ATP to transport phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the exoplasmic to the cytoplasmic leaflet of membranes. Although mutations in ATP8A2 have been reported to cause mental retardation in humans and degeneration of spinal motor neurons in mice, the role of ATP8A2 in sensory systems has not been investigated. We have analyzed the retina and cochlea of ATP8A2-deficient mice to determine the role of ATP8A2 in visual and auditory systems. ATP8A2-deficient mice have shortened photoreceptor outer segments, a reduction in photoresponses and decreased photoreceptor viability. The ultrastructure and phagocytosis of the photoreceptor outer segment appeared normal, but the PS and PE compositions were altered and the rhodopsin content was decreased. The auditory brainstem response threshold was significantly higher and degeneration of spiral ganglion cells was apparent. Our studies indicate that ATP8A2 plays a crucial role in photoreceptor and spiral ganglion cell function and survival by maintaining phospholipid composition and contributing to vesicle trafficking.
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Affiliation(s)
- Jonathan A Coleman
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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9
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Mondal S, Khelashvili G, Johner N, Weinstein H. How the dynamic properties and functional mechanisms of GPCRs are modulated by their coupling to the membrane environment. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 796:55-74. [PMID: 24158801 DOI: 10.1007/978-94-007-7423-0_4] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Experimental observations of the dependence of function and organization of G protein-coupled receptors (GPCRs) on their lipid environment have stimulated new quantitative studies of the coupling between the proteins and the membrane. It is important to develop such a quantitative understanding at the molecular level because the effects of the coupling are seen to be physiologically and clinically significant. Here we review findings that offer insight into how membrane-GPCR coupling is connected to the structural characteristics of the GPCR, from sequence to 3D structural detail, and how this coupling is involved in the actions of ligands on the receptor. The application of a recently developed computational approach designed for quantitative evaluation of membrane remodeling and the energetics of membrane-protein interactions brings to light the importance of the radial asymmetry of the membrane-facing surface of GPCRs in their interaction with the surrounding membrane. As the radial asymmetry creates adjacencies of hydrophobic and polar residues at specific sites of the GPCR, the ability of membrane remodeling to achieve complete hydrophobic matching is limited, and the residual mismatch carries a significant energy cost. The adjacencies are shown to be affected by ligand-induced conformational changes. Thus, functionally important organization of GPCRs in the cell membrane can depend both on ligand-determined properties and on the lipid composition of various membrane regions with different remodeling capacities. That this functionally important reorganization can be driven by oligomerization patterns that reduce the energy cost of the residual mismatch, suggests a new perspective on GPCR dimerization and ligand-GPCR interactions. The relation between the modulatory effects on GPCRs from the binding of specific cell-membrane components, e.g., cholesterol, and those produced by the non-local energetics of hydrophobic mismatch are discussed in this context.
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Affiliation(s)
- Sayan Mondal
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, Room E-509, 1300 York Avenue, 10065, New York City, NY, USA
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11
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Inagaki S, Ghirlando R, White JF, Gvozdenovic-Jeremic J, Northup JK, Grisshammer R. Modulation of the interaction between neurotensin receptor NTS1 and Gq protein by lipid. J Mol Biol 2012; 417:95-111. [PMID: 22306739 DOI: 10.1016/j.jmb.2012.01.023] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Revised: 01/09/2012] [Accepted: 01/13/2012] [Indexed: 12/11/2022]
Abstract
Membrane lipids have been implicated to influence the activity of G-protein-coupled receptors (GPCRs). Almost all of our knowledge on the role of lipids on GPCR and G protein function comes from work on the visual pigment rhodopsin and its G protein transducin, which reside in a highly specialized membrane environment. Thus, insight gained from rhodopsin signaling may not be simply translated to other nonvisual GPCRs. Here, we investigated the effect of lipid head group charges on the signal transduction properties of the class A GPCR neurotensin (NT) receptor 1 (NTS1) under defined experimental conditions, using self-assembled phospholipid nanodiscs prepared with the zwitter-ionic lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), the negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG), or a POPC/POPG mixture. A combination of dynamic light scattering and sedimentation velocity showed that NTS1 was monomeric in POPC-, POPC/POPG-, and POPG-nanodiscs. Binding of the agonist NT to NTS1 occurred with similar affinities and was essentially unaffected by the phospholipid composition. In contrast, Gq protein coupling to NTS1 in various lipid nanodiscs was significantly different, and the apparent affinity of Gαq and Gβ(1)γ(1) to activated NTS1 increased with increasing POPG content. NTS1-catalyzed GDP/GTPγS nucleotide exchange at Gαq in the presence of Gβ(1)γ(1) and NT was crucially affected by the lipid type, with exchange rates higher by 1 or 2 orders of magnitude in POPC/POPG- and POPG-nanodiscs, respectively, compared to POPC-nanodiscs. Our data demonstrate that negatively charged lipids in the immediate vicinity of a nonvisual GPCR modulate the G-protein-coupling step.
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Affiliation(s)
- Sayaka Inagaki
- Membrane Protein Structure Function Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Department of Health and Human Services, Rockville, MD 20852, USA
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12
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Soubias O, Gawrisch K. The role of the lipid matrix for structure and function of the GPCR rhodopsin. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:234-40. [PMID: 21924236 DOI: 10.1016/j.bbamem.2011.08.034] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2011] [Revised: 08/30/2011] [Accepted: 08/30/2011] [Indexed: 01/20/2023]
Abstract
Photoactivation of rhodopsin in lipid bilayers results within milliseconds in a metarhodopsin I (MI)-metarhodopsin II (MII) equilibrium that is very sensitive to the lipid composition. It has been well established that lipid bilayers that are under negative curvature elastic stress from incorporation of lipids like phosphatidylethanolamines (PE) favor formation of MII, the rhodopsin photointermediate that is capable of activating G protein. Furthermore, formation of the MII state is favored by negatively charged lipids like phosphatidylserine and by lipids with longer hydrocarbon chains that yield bilayers with larger membrane hydrophobic thickness. Cholesterol and rhodopsin-rhodopsin interactions from crowding of rhodopsin molecules in lipid bilayers shift the MI-MII equilibrium towards MI. A variety of mechanisms seems to be responsible for the large, lipid-induced shifts between MI and MII: adjustment of the thickness of lipid bilayers to rhodopsin and adjustment of rhodopsin helicity to the thickness of bilayers, curvature elastic deformations in the lipid matrix surrounding the protein, direct interactions of PE headgroups and polyunsaturated hydrocarbon chains with rhodopsin, and direct or lipid-mediated interactions between rhodopsin molecules. This article is part of a Special Issue entitled: Membrane protein structure and function.
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Affiliation(s)
- Olivier Soubias
- Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
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Kaya AI, Thaker TM, Preininger AM, Iverson TM, Hamm HE. Coupling efficiency of rhodopsin and transducin in bicelles. Biochemistry 2011; 50:3193-203. [PMID: 21375271 DOI: 10.1021/bi200037j] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
G protein coupled receptors (GPCRs) can be activated by various extracellular stimuli, including hormones, peptides, odorants, neurotransmitters, nucleotides, or light. After activation, receptors interact with heterotrimeric G proteins and catalyze GDP release from the Gα subunit, the rate limiting step in G protein activation, to form a high affinity nucleotide-free GPCR-G protein complex. In vivo, subsequent GTP binding reduces affinity of the Gα protein for the activated receptor. In this study, we investigated the biochemical and structural characteristics of the prototypical GPCR, rhodopsin, and its signaling partner, transducin (G(t)), in bicelles to better understand the effects of membrane composition on high affinity complex formation, stability, and receptor mediated nucleotide release. Our results demonstrate that the high-affinity complex (rhodopsin-G(t)(empty)) forms more readily and has dramatically increased stability when rhodopsin is integrated into bicelles of a defined composition. We increased the half-life of functional complex to 1 week in the presence of negatively charged phospholipids. These data suggest that a membrane-like structure is an important contributor to the formation and stability of functional receptor-G protein complexes and can extend the range of studies that investigate properties of these complexes.
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Affiliation(s)
- Ali I Kaya
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600, United States
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14
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Subramaniam V, D'Ambruoso GD, Hall HK, Wysocki RJ, Brown MF, Saavedra SS. Reconstitution of rhodopsin into polymerizable planar supported lipid bilayers: influence of dienoyl monomer structure on photoactivation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:11067-75. [PMID: 18759470 PMCID: PMC2726791 DOI: 10.1021/la801835g] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
G-protein-coupled receptors (GPCRs) play key roles in cellular signal transduction and many are pharmacologically important targets for drug discovery. GPCRs can be reconstituted in planar supported lipid bilayers (PSLBs) with retention of activity, which has led to development of GPCR-based biosensors and biochips. However, PSLBs composed of natural lipids lack the high stability desired for many technological applications. One strategy is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how lipid polymerization affects GPCR structure and activity. Here we have investigated the photochemical activity of bovine rhodopsin (Rho), a model GPCR, reconstituted into PSLBs composed of lipids having one or two polymerizable dienoyl moieties located in different regions of the acyl chains. Plasmon waveguide resonance spectroscopy was used to compare the degree of Rho photoactivation in fluid and poly(lipid) PSLBs. The position of the dienoyl moiety was found to have a significant effect: polymerization near the glycerol backbone significantly attenuates Rho activity whereas polymerization near the acyl chain termini does not. Differences in cross-link density near the acyl chain termini also do not affect Rho activity. In unpolymerized PSLBs, an equimolar mixture of phosphatidylethanolamine and phosphatidylcholine (PC) lipids enhances activity relative to pure PC; however after polymerization, the enhancement is eliminated which is attributed to stabilization of the membrane lamellar phase. These results should provide guidance for the design of robust lipid bilayers functionalized with transmembrane proteins for use in membrane-based biochips and biosensors.
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Affiliation(s)
- Varuni Subramaniam
- Department of Chemistry, University of Arizona, Tucson, Arizona, 85721-0041
| | | | - H. K. Hall
- Department of Chemistry, University of Arizona, Tucson, Arizona, 85721-0041
| | - Ronald J. Wysocki
- Department of Chemistry, University of Arizona, Tucson, Arizona, 85721-0041
| | - Michael F. Brown
- Department of Chemistry, University of Arizona, Tucson, Arizona, 85721-0041
| | - S. Scott Saavedra
- Department of Chemistry, University of Arizona, Tucson, Arizona, 85721-0041
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15
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16
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Ritter E, Elgeti M, Hofmann KP, Bartl FJ. Deactivation and proton transfer in light-induced metarhodopsin II/metarhodopsin III conversion: a time-resolved fourier transform infrared spectroscopic study. J Biol Chem 2007; 282:10720-30. [PMID: 17287211 DOI: 10.1074/jbc.m610658200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Vertebrate rhodopsin shares with other retinal proteins the 11-cis-retinal chromophore and the light-induced 11-cis/trans isomerization triggering its activation pathway. However, only in rhodopsin the retinylidene Schiff base bond to the apoprotein is eventually hydrolyzed, making a complex regeneration pathway necessary. Metabolic regeneration cannot be short-cut, and light absorption in the active metarhodopsin (Meta) II intermediate causes anti/syn isomerization around the retinylidene linkage rather than reversed trans/cis isomerization. A new deactivating pathway is thereby triggered, which ends in the Meta III "retinal storage" product. Using time-resolved Fourier transform infrared spectroscopy, we show that the identified steps of receptor activation, including Schiff base deprotonation, protein structural changes, and proton uptake by the apoprotein, are all reversed. However, Schiff base reprotonation is much faster than the activating deprotonation, whereas the protein structural changes are slower. The final proton release occurs with pK approximately 4.5, similar to the pK of a free Glu residue and to the pK at which the isolated opsin apoprotein becomes active. A forced deprotonation, equivalent to the forced protonation in the activating pathway, which occurs against the unfavorable pH of the medium, is not observed. This explains properties of the final Meta III product, which displays much higher residual activity and is less stable than rhodopsin arising from regeneration with 11-cis-retinal. We propose that the anti/syn conversion can only induce a fast reorientation and distance change of the Schiff base but fails to build up the full set of dark ground state constraints, presumably involving the Glu(134)/Arg(135) cluster.
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Affiliation(s)
- Eglof Ritter
- Institut für Medizinische Physik und Biophysik, Charité, Universitätsmedizin Berlin, Charitéplatz 1, D-10098 Berlin
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17
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Kusnetzow AK, Altenbach C, Hubbell WL. Conformational states and dynamics of rhodopsin in micelles and bilayers. Biochemistry 2006; 45:5538-50. [PMID: 16634635 PMCID: PMC2739654 DOI: 10.1021/bi060101v] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitroxide sensors were placed in rhodopsin at sites 140, 227, 250, and 316 to monitor the dynamics and conformation of the receptor at the cytoplasmic surface in solutions of dodecyl maltoside (DM), digitonin, and phospholipid bilayers of two compositions. The EPR spectra reveal a remarkable similarity of rhodopsin structure and the activating conformational change in DM and bilayers, the hallmark of which is an outward tilt of transmembrane helix VI. This conformational change is blocked in solutions of digitonin, although changes in optical absorbance accompany activation, showing that absorbance and structural changes are not necessarily coupled. In DM and bilayers, the receptor is apparently in equilibrium between conformational substates whose populations are modulated by activation. Despite the general similarity in the two environments, the receptor conformations have increased flexibility in DM relative to bilayers. For the activated receptor in DM and bilayers, a pH-dependent conformational equilibrium is identified that may correspond to the optically characterized MII(a)()-MII(b)() equilibrium. No specific effects of headgroup composition on receptor conformation in lipid bilayers were found.
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Affiliation(s)
- Ana Karin Kusnetzow
- Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-7008, USA
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18
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Ces O, Mulet X. Physical coupling between lipids and proteins: a paradigm for cellular control. ACTA ACUST UNITED AC 2006. [DOI: 10.1002/sita.200500079] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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19
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Lee AG. Lipid-protein interactions in biological membranes: a structural perspective. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1612:1-40. [PMID: 12729927 DOI: 10.1016/s0005-2736(03)00056-7] [Citation(s) in RCA: 639] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Lipid molecules bound to membrane proteins are resolved in some high-resolution structures of membrane proteins. An analysis of these structures provides a framework within which to analyse the nature of lipid-protein interactions within membranes. Membrane proteins are surrounded by a shell or annulus of lipid molecules, equivalent to the solvent layer surrounding a water-soluble protein. The lipid bilayer extends right up to the membrane protein, with a uniform thickness around the protein. The surface of a membrane protein contains many shallow grooves and protrusions to which the fatty acyl chains of the surrounding lipids conform to provide tight packing into the membrane. An individual lipid molecule will remain in the annular shell around a protein for only a short period of time. Binding to the annular shell shows relatively little structural specificity. As well as the annular lipid, there is evidence for other lipid molecules bound between the transmembrane alpha-helices of the protein; these lipids are referred to as non-annular lipids. The average thickness of the hydrophobic domain of a membrane protein is about 29 A, with a few proteins having significantly smaller or greater thicknesses than the average. Hydrophobic mismatch between a membrane protein and the surrounding lipid bilayer generally leads to only small changes in membrane thickness. Possible adaptations in the protein to minimise mismatch include tilting of the helices and rotation of side chains at the ends of the helices. Packing of transmembrane alpha-helices is dependent on the chain length of the surrounding phospholipids. The function of membrane proteins is dependent on the thickness of the surrounding lipid bilayer, sometimes on the presence of specific, usually anionic, phospholipids, and sometimes on the phase of the phospholipid.
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Affiliation(s)
- A G Lee
- Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Bassett Crescent East, SO16 7PX, Southampton, UK.
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20
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Wang Y, Botelho AV, Martinez GV, Brown MF. Electrostatic properties of membrane lipids coupled to metarhodopsin II formation in visual transduction. J Am Chem Soc 2002; 124:7690-701. [PMID: 12083922 DOI: 10.1021/ja0200488] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Changes in lipid composition have recently been shown to exert appreciable influences on the activities of membrane-bound proteins and peptides. We tested the hypothesis that the conformational states of rhodopsin linked to visual signal transduction are related to biophysical properties of the membrane lipid bilayer. For bovine rhodopsin, the meta I-meta II conformational transition was studied in egg phosphatidylcholine (PC) recombinants versus the native rod outer segment (ROS) membranes by means of flash photolysis. Formation of metarhodopsin II was observed by the change in absorbance at 478 nm after a single actinic flash was delivered to the sample. The meta I/meta II ratio was investigated as a function of both temperature and pH. The data clearly demonstrated thermodynamic reversibility of the transition for both the egg PC recombinants and the native ROS membranes. A significant shift of the apparent pK(a) for the acid-base equilibrium to lower values was evident in the egg PC recombinant, with little meta II produced under physiological conditions. Calculations of the membrane surface pH using a Poisson-Boltzmann model suggested the free energies of the meta I and meta II states were significantly affected by electrostatic properties of the bilayer lipids. In the ROS membranes, phosphatidylserine (PS) is needed for full formation of meta II, in combination with phosphatidylethanolamine (PE) and polyunsaturated docosahexaenoic acid (DHA; 22:6omega3) chains. We propose that the PS surface potential leads to an accumulation of hydronium ions, H(3)O(+), in the electrical double layer, which drive the reaction together with the large negative spontaneous curvature (H(0)) conferred by PE plus DHA chains. The elastic stress/strain of the bilayer arises from an interplay of the approximately zero H(0) from PS and the negative H(0) due to the PE headgroups and polyunsaturated chains. The lipid influences are further explained in terms of matching of the bilayer spontaneous curvature to the curvature at the lipid/rhodopsin interface, as formulated by the Helfrich bending energy. These new findings guide current ideas as to how bilayer properties govern the conformational energetics of integral membrane proteins. Moreover, they yield knowledge of how membrane lipid-protein interactions involving acidic phospholipids such as PS and neutral polyunsaturated DHA chains are implicated in key biological functions such as vision.
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Affiliation(s)
- Yin Wang
- Department of Physics, University of Arizona, Tucson, AZ 85721, USA
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21
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Degrip W, Rothschild K. Chapter 1 Structure and mechanism of vertebrate visual pigments. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s1383-8121(00)80004-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
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22
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Yuan C, Chen H, Anderson RE, Kuwata O, Ebrey TG. The unique lipid composition of gecko (Gekko Gekko) photoreceptor outer segment membranes. Comp Biochem Physiol B Biochem Mol Biol 1998; 120:785-9. [PMID: 9854823 DOI: 10.1016/s0305-0491(98)10079-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
This study investigated the lipid and fatty acid composition of gecko photoreceptor outer segment membranes which contain the P521 cone-type pigment. The lipids of gecko photoreceptor outer segment membranes were first extracted and separated by thin layer chromatography (TLC) and then analyzed by gas chromatography (GC). Our results show that gecko photoreceptor outer segment membranes contain less phosphatidylethanolamine (PE) and more phosphatidylcholine (PC) and phosphatidylserine (PS) compared with those of bovine and frog. The content of the polyunsaturated fatty acid, docosahexaenoic acid (DHA), in PC and PS is also the highest yet reported (55 and 63%, respectively). These lipid differences may provide some insight into the specific lipid requirements of cone-type pigments.
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Affiliation(s)
- C Yuan
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, USA
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23
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Brown MF. Chapter 8 Influence of Nonlamellar-Forming Lipids on Rhodopsin. CURRENT TOPICS IN MEMBRANES 1997. [DOI: 10.1016/s0070-2161(08)60212-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Abstract
A prevalent model for the function of rhodopsin centers on the metarhodopsin I (MI) to metarhodopsin II (MII) conformational transition as the triggering event for the visual process. Flash photolysis techniques enable one to determine the [MII]/[MI] ratio for rhodopsin in various recombinant membranes, and thus investigate the roles of the phospholipid head groups and the lipid acyl chains systematically. The results obtained to date clearly show that the pK for the acid-base MI-MII equilibrium of rhodopsin is modulated by the lipid environment. In bilayers of phosphatidylcholines the MI-MII equilibrium is shifted to the left; whereas in the native rod outer segment membranes it is shifted to the right, i.e., at neutral pH near physiological temperature. The lipid mixtures sufficient to yield full photochemical function of rhodopsin include a native-like head group composition, viz, comprising phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS), in combination with polyunsaturated docosahexaenoic acid (DHA; 22:6 omega 3) chains. Yet such a native-like lipid mixture is not necessary for the MI-MII conformational transition of rhodopsin; one can substitute other lipid compositions having similar properties. The MI-MII transition is favored by relatively small head groups which produce a condensed bilayer surface, viz, a comparatively small interfacial area as in the case of PE, together with bulky acyl chains such as DHA which prefer a relatively large cross sectional area. The resulting force imbalance across the layer gives rise to a curvature elastic stress of the lipid/water interface, such that the lipid mixtures yielding native-like behavior form reverse hexagonal (HII) phases at slightly higher temperatures. A relatively unstable membrane is needed: lipids tending to form the lamellar phase do not support full native-like photochemical function of rhodopsin. Thus chemically specific properties of the various lipids are not required, but rather average or material properties of the entire assembly, which may involve the curvature free energy of the membrane-lipid water interface. These findings reveal that the membrane lipid bilayer has a direct influence on the energetics of the conformational states of rhodopsin in visual excitation.
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Affiliation(s)
- M F Brown
- Department of Chemistry, University of Arizona, Tucson 85721
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25
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Gibson NJ, Brown MF. Lipid headgroup and acyl chain composition modulate the MI-MII equilibrium of rhodopsin in recombinant membranes. Biochemistry 1993; 32:2438-54. [PMID: 8443184 DOI: 10.1021/bi00060a040] [Citation(s) in RCA: 133] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A current paradigm for visual function centers on the metarhodopsin I (MI) to metarhodopsin II (MII) conformational transition as the trigger for an intracellular enzyme cascade leading to excitation of the retinal rod. We investigated the influences of the membrane lipid composition on this key triggering event in visual signal transduction using flash photolysis techniques. Bovine rhodopsin was combined with various phospholipids to form membrane recombinants in which the lipid acyl chain composition was held constant at that of egg phosphatidylcholine (PC), while the identity of the lipid headgroups was varied. The ratio of MII/MI produced in these recombinants by an actinic flash at 28 degrees C was studied as a function of pH. The results were compared to the photochemical function observed for rhodopsin in native retinal rod outer segment (ROS) membranes, in total native ROS lipid recombinants, and in dimyristoylphosphatidylcholine (DMPC) recombinants. In membrane recombinants incorporating lipids derived from egg PC, as well as in the total ROS lipids control and the native ROS disk membranes, MI and MII were found to coexist in a pH-dependent, acid-base equilibrium on the millisecond time scale. The recombinants of rhodopsin with egg PC, either alone or in combination with egg PC-derived phosphatidylethanolamine (PE) or phosphatidylserine (PS), exhibited substantially reduced photochemical activity at pH 7.0. However, all recombinants comprising phospholipids with unsaturated acyl chains were capable of full native-like MII production at pH 5.0, confirming previous results [Gibson, N.J.. & Brown, M.F. (1990) Biochem. Biophys. Res. Commun. 169, 1028-1034]. It follows that energetic constraints on the MI and MII states imposed by egg PC-derived acyl chains can be offset by increased activity of H+ ions. The data reveal that the major effect of the membrane lipid composition is to alter the apparent pK for the MI-MII conformational equilibrium of rhodopsin [Gibson, N.J., & Brown, M.F. (1991) Biochem. Biophys. Res. Commun. 176, 915-921]. Recombinants containing only phosphocholine headgroups exhibited the lowest apparent pK values, whereas the presence of either 50 mol % PE or 15 mol % PS increased the apparent pK. The inability to obtain full native-like function in recombinants having egg PC-derived chains and a native-like headgroup composition indicates a significant role of the polyunsaturated docosahexaenoic acid (DHA) chains (22:6 omega 3) of the native retinal rod membrane lipids. Temperature studies of the MI-MII transition enabled an investigation of lipid influences on the thermodynamic parameters of a membrane protein conformational change linked directly to function.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- N J Gibson
- Department of Chemistry, University of Arizona, Tucson 85721
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26
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Cserhåti T, Szögyi M. Interaction of phospholipids with proteins and peptides. New advances III. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1993; 25:123-46. [PMID: 8444311 DOI: 10.1016/0020-711x(93)90001-u] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.
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Affiliation(s)
- T Cserhåti
- Central Research Institute for Chemistry, Hungarian Academy of Sciences, Budapest
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27
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Farahbakhsh ZT, Altenbach C, Hubbell WL. Spin labeled cysteines as sensors for protein-lipid interaction and conformation in rhodopsin. Photochem Photobiol 1992; 56:1019-33. [PMID: 1492127 DOI: 10.1111/j.1751-1097.1992.tb09725.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In stoichiometric amounts, the spin label N-tempoyl-(p-chloromercuribenzamide) reacts rapidly with one cysteine residue in membrane-bound bovine rhodopsin. This residue is distinct from the two reactive cysteines previously used as attachment sites for spectroscopic labels, and is on the external surface of the protein near the cytoplasmic membrane/aqueous interface. The spin-labeled side chain has revealed a light-induced conformational change in membrane-bound rhodopsin that is apparently not associated with protein aggregation. The changes are reversible upon the addition of 11-cis retinal, and the magnitude of the change is dependent on the identity of the phospholipid in the surrounding bilayer. Alteration of lipid composition has a much larger effect on bleached rhodopsin than rhodopsin itself, indicating that the former is more readily deformable in response to changes in bilayer properties. This is consistent with the loss of 11-cis retinal binding energy in opsin compared to rhodopsin. These results provide direct structural evidence that the conformation of a membrane protein can be modulated by the lipid properties.
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Affiliation(s)
- Z T Farahbakhsh
- Jules Stein Eye Institute, University of California, Los Angeles 90024-7008
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