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Strickland MR, Rau MJ, Summers B, Basore K, Wulf J, Jiang H, Chen Y, Ulrich JD, Randolph GJ, Zhang R, Fitzpatrick JAJ, Cashikar AG, Holtzman DM. Apolipoprotein E secreted by astrocytes forms antiparallel dimers in discoidal lipoproteins. Neuron 2024; 112:1100-1109.e5. [PMID: 38266643 PMCID: PMC10994765 DOI: 10.1016/j.neuron.2023.12.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 11/24/2023] [Accepted: 12/22/2023] [Indexed: 01/26/2024]
Abstract
The Apolipoprotein E gene (APOE) is of great interest due to its role as a risk factor for late-onset Alzheimer's disease. ApoE is secreted by astrocytes in the central nervous system in high-density lipoprotein (HDL)-like lipoproteins. Structural models of lipidated ApoE of high resolution could aid in a mechanistic understanding of how ApoE functions in health and disease. Using monoclonal Fab and F(ab')2 fragments, we characterize the structure of lipidated ApoE on astrocyte-secreted lipoproteins. Our results provide support for the "double-belt" model of ApoE in nascent discoidal HDL-like lipoproteins, where two ApoE proteins wrap around the nanodisc in an antiparallel conformation. We further show that lipidated, recombinant ApoE accurately models astrocyte-secreted ApoE lipoproteins. Cryogenic electron microscopy of recombinant lipidated ApoE further supports ApoE adopting antiparallel dimers in nascent discoidal lipoproteins.
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Affiliation(s)
| | - Michael J Rau
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Brock Summers
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Katherine Basore
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - John Wulf
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Hong Jiang
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Yun Chen
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Department of Pathology and Immunology, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Jason D Ulrich
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Hope Center for Neurological Disorders, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Knight Alzheimer's Disease Research Center, 4488 Forest Park Ave., St. Louis, MO 63108, USA
| | - Gwendalyn J Randolph
- Department of Pathology and Immunology, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Rui Zhang
- Department of Biochemistry and Molecular Biophysics, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - James A J Fitzpatrick
- Washington University Center for Cellular Imaging, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - Anil G Cashikar
- Hope Center for Neurological Disorders, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Department of Psychiatry, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Taylor Family institute for Innovative Psychiatric Research, 660 S. Euclid Ave., St. Louis, MO 63110, USA
| | - David M Holtzman
- Department of Neurology, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Hope Center for Neurological Disorders, 660 S. Euclid Ave., St. Louis, MO 63110, USA; Knight Alzheimer's Disease Research Center, 4488 Forest Park Ave., St. Louis, MO 63108, USA.
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2
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Waldie S, Sebastiani F, Moulin M, Del Giudice R, Paracini N, Roosen-Runge F, Gerelli Y, Prevost S, Voss JC, Darwish TA, Yepuri N, Pichler H, Maric S, Forsyth VT, Haertlein M, Cárdenas M. ApoE and ApoE Nascent-Like HDL Particles at Model Cellular Membranes: Effect of Protein Isoform and Membrane Composition. Front Chem 2021; 9:630152. [PMID: 33996741 PMCID: PMC8117676 DOI: 10.3389/fchem.2021.630152] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 03/30/2021] [Indexed: 11/13/2022] Open
Abstract
Apolipoprotein E (ApoE), an important mediator of lipid transportation in plasma and the nervous system, plays a large role in diseases such as atherosclerosis and Alzheimer's. The major allele variants ApoE3 and ApoE4 differ only by one amino acid. However, this difference has major consequences for the physiological behaviour of each variant. In this paper, we follow (i) the initial interaction of lipid-free ApoE variants with model membranes as a function of lipid saturation, (ii) the formation of reconstituted High-Density Lipoprotein-like particles (rHDL) and their structural characterisation, and (iii) the rHDL ability to exchange lipids with model membranes made of saturated lipids in the presence and absence of cholesterol [1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) with and without 20 mol% cholesterol]. Our neutron reflection results demonstrate that the protein variants interact differently with the model membranes, adopting different protein conformations. Moreover, the ApoE3 structure at the model membrane is sensitive to the level of lipid unsaturation. Small-angle neutron scattering shows that the ApoE containing lipid particles form elliptical disc-like structures, similar in shape but larger than nascent or discoidal HDL based on Apolipoprotein A1 (ApoA1). Neutron reflection shows that ApoE-rHDL do not remove cholesterol but rather exchange saturated lipids, as occurs in the brain. In contrast, ApoA1-containing particles remove and exchange lipids to a greater extent as occurs elsewhere in the body.
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Affiliation(s)
- Sarah Waldie
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden.,Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France
| | - Federica Sebastiani
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Martine Moulin
- Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France
| | - Rita Del Giudice
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Nicolò Paracini
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Felix Roosen-Runge
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
| | - Yuri Gerelli
- Institut Laue-Langevin, Grenoble, France.,Department of Life and Environmental Sciences, Marche Polytechnic University, Ancona, Italy
| | | | - John C Voss
- Department of Biochemistry and Molecular Medicine, University of California, Davis, Davis, CA, United States
| | - Tamim A Darwish
- National Deuteration Facility, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Nageshwar Yepuri
- National Deuteration Facility, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Harald Pichler
- Austrian Centre of Industrial Biotechnology, Graz, Austria.,Graz University of Technology, Institute of Molecular Biotechnology, NAWI Graz, BioTechMed Graz, Graz, Austria
| | | | - V Trevor Forsyth
- Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France.,Faculty of Natural Sciences, Keele University, Staffordshire, United Kingdom
| | - Michael Haertlein
- Institut Laue-Langevin, Grenoble, France.,Partnership for Structural Biology (PSB), Grenoble, France
| | - Marité Cárdenas
- Department of Biomedical Science and Biofilms-Research Center for Biointerfaces, Malmö University, Malmö, Sweden
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3
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Kober DL, Stuchell-Brereton MD, Kluender CE, Dean HB, Strickland MR, Steinberg DF, Nelson SS, Baban B, Holtzman DM, Frieden C, Alexander-Brett J, Roberson ED, Song Y, Brett TJ. Functional insights from biophysical study of TREM2 interactions with apoE and Aβ 1-42. Alzheimers Dement 2020; 17:10.1002/alz.12194. [PMID: 33090700 PMCID: PMC8026773 DOI: 10.1002/alz.12194] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 08/12/2020] [Accepted: 08/20/2020] [Indexed: 12/20/2022]
Abstract
INTRODUCTION Triggering receptor expressed on myeloid cells-2 (TREM2) is an immune receptor expressed on microglia that also can become soluble (sTREM2). How TREM2 engages different ligands remains poorly understood. METHODS We used comprehensive biolayer interferometry (BLI) analysis to investigate TREM2 and sTREM2 interactions with apolipoprotein E (apoE) and monomeric amyloid beta (Aβ) (mAβ42). RESULTS TREM2 engagement of apoE was protein mediated with little effect of lipidation, showing slight affinity differences between isoforms (E4 > E3 > E2). Another family member, TREML2, did not bind apoE. Disease-linked TREM2 variants within a "basic patch" minimally impact apoE binding. Instead, TREM2 uses a unique hydrophobic surface to bind apoE, which requires the apoE hinge region. TREM2 and sTREM2 directly bind mAβ42 and potently inhibit Aβ42 polymerization, suggesting a potential role for soluble sTREM2 in preventing AD pathogenesis. DISCUSSION These findings demonstrate that TREM2 has at least two ligand-binding surfaces that might be therapeutic targets and uncovers a potential function for sTREM2 in directly inhibiting Aβ polymerization.
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Affiliation(s)
- Daniel L. Kober
- Molecular Microbiology and Microbial Pathogenesis Program, Washington University School of Medicine, St. Louis, Missouri 63110
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Melissa D. Stuchell-Brereton
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Colin E. Kluender
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
- Biochemistry, Biophysics, and Structural Biology Program, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Hunter B. Dean
- Center for Neurodegeneration and Experimental Therapeutics, Alzheimer’s Disease Center, Departments of Neurology and Neurobiology, University of Alabama at Birmingham, AL 35294
- Department of Biomedical Engineering, University of Alabama at Birmingham, AL 35294
| | - Michael R. Strickland
- Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Deborah F. Steinberg
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Samantha S. Nelson
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Berevan Baban
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
| | - David M. Holtzman
- Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110
- Charles F. and Joanne Knight Alzheimer’s Disease Research Center, Washington University School of Medicine, St. Louis, Missouri 63110
- Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Carl Frieden
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
- Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Jennifer Alexander-Brett
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Erik D. Roberson
- Center for Neurodegeneration and Experimental Therapeutics, Alzheimer’s Disease Center, Departments of Neurology and Neurobiology, University of Alabama at Birmingham, AL 35294
| | - Yuhua Song
- Department of Biomedical Engineering, University of Alabama at Birmingham, AL 35294
| | - Tom J. Brett
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
- Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, Missouri 63110
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110
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4
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Shelby M, Gilbile D, Grant T, Bauer W, Segelke B, He W, Evans A, Crespo N, Fischer P, Pakendorf T, Hennicke V, Hunter M, Batyuk A, Barthelmess M, Meents A, Kuhl T, Frank M, Coleman M. Crystallization of ApoA1 and ApoE4 nanolipoprotein particles and initial XFEL-based structural studies. CRYSTALS 2020; 10. [PMID: 35686136 PMCID: PMC9175823 DOI: 10.3390/cryst10100886] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nanolipoprotein particles (NLPs), also called “nanodiscs”, are discoidal particles with a patch of lipid bilayer corralled by apolipoproteins. NLPs have long been of interest due to both their utility as membrane-model systems into which membrane proteins can be inserted and solubilized and their physiological role in lipid and cholesterol transport via HDL and LDL maturation, which are important for human health. Serial femtosecond crystallography (SFX) at X-ray free electron lasers (XFELs) is a powerful approach for structural biology of membrane proteins, which are traditionally difficult to crystallize as large single crystals capable of producing high-quality diffraction suitable for structure determination. To facilitate understanding of the specific role of two apolipoprotein/lipid complexes, ApoA1 and ApoE4, in lipid binding and HDL/LDL particle maturation dynamics and develop new SFX methods involving NLP membrane protein encapsulation, we have prepared and crystallized homogeneous populations of ApoA1 and ApoE4 NLPs. Crystallization of empty NLPs yields semi-ordered objects that appear crystalline and give highly anisotropic and diffuse X-ray diffraction, similar in characteristics to fiber diffraction. Several unit cell parameters were approximately determined for both NLPs from these measurements. Thus, low-background, sample conservative methods of delivery are critical. Here we implemented a fixed target sample delivery scheme utilizing the Roadrunner fast-scanning system and ultra-thin polymer/graphene support films, providing a low-volume, low-background approach to membrane protein SFX. This study represents initial steps in obtaining structural information for ApoA1 and ApoE4 NLPs and developing this system as a supporting scaffold for future structural studies of membrane proteins crystalized in a native lipid environment.
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Affiliation(s)
- M.L. Shelby
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
| | - D. Gilbile
- Department of Chemical Engineering, University of California at Davis, Davis, CA, USA
| | - T.D. Grant
- Department of Structural Biology, Jacobs School of Medicine and Biomedical Sciences, SUNY University at Buffalo, Buffalo, NY, USA
- Hauptman-Woodward Medical Research Institute, Buffalo, NY, USA
| | - W.J. Bauer
- Hauptman-Woodward Medical Research Institute, Buffalo, NY, USA
| | - B. Segelke
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
| | - W. He
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
| | - A.C. Evans
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
- Department of Chemical Engineering, University of California at Davis, Davis, CA, USA
| | - N. Crespo
- Department of Structural Biology, Jacobs School of Medicine and Biomedical Sciences, SUNY University at Buffalo, Buffalo, NY, USA
- Hauptman-Woodward Medical Research Institute, Buffalo, NY, USA
| | - P. Fischer
- Center for Free-Electron Laser Science, Hamburg, Germany
| | - T. Pakendorf
- Center for Free-Electron Laser Science, Hamburg, Germany
| | - V. Hennicke
- Center for Free-Electron Laser Science, Hamburg, Germany
| | - M.S. Hunter
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California, USA
| | - A. Batyuk
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California, USA
| | - M. Barthelmess
- Center for Free-Electron Laser Science, Hamburg, Germany
| | - A. Meents
- Center for Free-Electron Laser Science, Hamburg, Germany
| | - T.L. Kuhl
- Department of Chemical Engineering, University of California at Davis, Davis, CA, USA
| | - M. Frank
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
- Department of Chemical Engineering, University of California at Davis, Davis, CA, USA
- Correspondence: ; Tel: +1-925-423-7687 or ; Tel: 1-925-423-5068
| | - M.A. Coleman
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
- Department of Chemical Engineering, University of California at Davis, Davis, CA, USA
- Correspondence: ; Tel: +1-925-423-7687 or ; Tel: 1-925-423-5068
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5
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The Genetic Variability of APOE in Different Human Populations and Its Implications for Longevity. Genes (Basel) 2019; 10:genes10030222. [PMID: 30884759 PMCID: PMC6471373 DOI: 10.3390/genes10030222] [Citation(s) in RCA: 85] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 03/01/2019] [Accepted: 03/12/2019] [Indexed: 12/11/2022] Open
Abstract
Human longevity is a complex phenotype resulting from the combinations of context-dependent gene-environment interactions that require analysis as a dynamic process in a cohesive ecological and evolutionary framework. Genome-wide association (GWAS) and whole-genome sequencing (WGS) studies on centenarians pointed toward the inclusion of the apolipoprotein E (APOE) polymorphisms ε2 and ε4, as implicated in the attainment of extreme longevity, which refers to their effect in age-related Alzheimer's disease (AD) and cardiovascular disease (CVD). In this case, the available literature on APOE and its involvement in longevity is described according to an anthropological and population genetics perspective. This aims to highlight the evolutionary history of this gene, how its participation in several biological pathways relates to human longevity, and which evolutionary dynamics may have shaped the distribution of APOE haplotypes across the globe. Its potential adaptive role will be described along with implications for the study of longevity in different human groups. This review also presents an updated overview of the worldwide distribution of APOE alleles based on modern day data from public databases and ancient DNA samples retrieved from literature in the attempt to understand the spatial and temporal frame in which present-day patterns of APOE variation evolved.
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6
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Varkey J, Mizuno N, Hegde BG, Cheng N, Steven AC, Langen R. α-Synuclein oligomers with broken helical conformation form lipoprotein nanoparticles. J Biol Chem 2013; 288:17620-30. [PMID: 23609437 DOI: 10.1074/jbc.m113.476697] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
α-Synuclein (αS) is a membrane-binding protein with sequence similarity to apolipoproteins and other lipid-carrying proteins, which are capable of forming lipid-containing nanoparticles, sometimes referred to as "discs." Previously, it has been unclear whether αS also possesses this property. Using cryo-electron microscopy and light scattering, we found that αS can remodel phosphatidylglycerol vesicles into nanoparticles whose shape (ellipsoidal) and dimensions (in the 7-10-nm range) resemble those formed by apolipoproteins. The molar ratio of αS to lipid in nanoparticles is ∼1:20, and αS is oligomeric (including trimers and tetramers). Similar nanoparticles form when αS is added to vesicles of mitochondrial lipids. This observation suggests a mechanism for the previously reported disruption of mitochondrial membranes by αS. Circular dichroism and four-pulse double electron electron resonance experiments revealed that in nanoparticles αS assumes a broken helical conformation distinct from the extended helical conformation adopted when αS is bound to intact vesicles or membrane tubules. We also observed αS-dependent tubule and nanoparticle formation in the presence of oleic acid, implying that αS can interact with fatty acids and lipids in a similar manner. αS-related nanoparticles might play a role in lipid and fatty acid transport functions previously attributed to this protein.
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Affiliation(s)
- Jobin Varkey
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California 90033, USA
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7
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Zhang L, Tong H, Garewal M, Ren G. Optimized negative-staining electron microscopy for lipoprotein studies. Biochim Biophys Acta Gen Subj 2012; 1830:2150-9. [PMID: 23032862 DOI: 10.1016/j.bbagen.2012.09.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2012] [Revised: 09/20/2012] [Accepted: 09/23/2012] [Indexed: 12/16/2022]
Abstract
BACKGROUND Negative-staining (NS), a rapid, simple and conventional technique of electron microscopy (EM), has been commonly used to initially study the morphology and structure of proteins for half a century. Certain NS protocols however can cause artifacts, especially for structurally flexible or lipid-related proteins, such as lipoproteins. Lipoproteins were often observed in the form of rouleau as lipoprotein particles appeared to be stacked together by conventional NS protocols. The flexible components of lipoproteins, i.e. lipids and amphipathic apolipoproteins, resulted in the lipoprotein structure being sensitive to the NS sample preparation parameters, such as operational procedures, salt concentrations, and the staining reagents. SCOPE OF REVIEW The most popular NS protocols that have been used to examine lipoprotein morphology and structure were reviewed. MAJOR CONCLUSIONS The comparisons show that an optimized NS (OpNS) protocol can eliminate the rouleau artifacts of lipoproteins, and that the lipoproteins are similar in size and shape as statistically measured from two EM methods, OpNS and cryo-electron microscopy (cryo-EM). OpNS is a high-throughput, high-contrast and high-resolution (near 1nm, but rarely better than 1nm) method which has been used to discover the mechanics of a small protein, 53kDa cholesterol ester transfer protein (CETP), and the structure of an individual particle of a single protein by individual-particle electron tomography (IPET), i.e. a 14Å-resolution IgG antibody three-dimensional map. GENERAL SIGNIFICANCE It is suggested that OpNS can be used as a general protocol to study the structure of proteins, especially highly dynamic proteins with equilibrium-fluctuating structures.
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Affiliation(s)
- Lei Zhang
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
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8
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Zhang L, Song J, Newhouse Y, Zhang S, Weisgraber KH, Ren G. An optimized negative-staining protocol of electron microscopy for apoE4 POPC lipoprotein. J Lipid Res 2009; 51:1228-36. [PMID: 19965615 PMCID: PMC2853450 DOI: 10.1194/jlr.d002493] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Apolipoprotein E (apoE), one of the major protein components of lipoproteins in the peripheral and central nervous systems, regulates cholesterol metabolism through its interaction with members of the low density lipoprotein receptor family. One key to understanding apoE function is determining the structure of lipid-bound forms of apoE. Negative-staining (NS) electron microscopy (EM) is an easy and rapid approach for studying the structure and morphology of lipid-bound forms of apoE. However, an artifact of using the conventional NS protocol is that the apoE•phospholipid particles form rouleaux. In this study, we used cryo-electron microscopy (cryo-EM) to examine apoE4•palmitoyl-oleoylphosphatidylcholine (POPC) particles in a frozen-hydrated native state. By comparing the particle sizes and shapes produced by different NS protocols to those produced by cryo-EM, we propose an optimized protocol to examine apoE4•POPC particles. Statistical analysis demonstrated that the particle sizes differ by less than 5% between the optimized protocol and the cryo-EM method, with similar shapes. The high contrast and fine detail of particle images produced using this optimized protocol lend themselves to the structural study of lipid-bound forms of apoE.
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Affiliation(s)
- Lei Zhang
- Department of Applied Physics, Xi'an Jiaotong University, Xi'an 710049, China
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9
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Hatters DM, Voss JC, Budamagunta MS, Newhouse YN, Weisgraber KH. Insight on the molecular envelope of lipid-bound apolipoprotein E from electron paramagnetic resonance spectroscopy. J Mol Biol 2008; 386:261-71. [PMID: 19124026 DOI: 10.1016/j.jmb.2008.12.040] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2008] [Revised: 12/04/2008] [Accepted: 12/10/2008] [Indexed: 10/21/2022]
Abstract
Although a high-resolution X-ray structure for the N-terminal domain of apolipoprotein E (apoE) in the lipid-free state has been solved, our knowledge of the structure of full-length apoE in a lipid-bound state is limited to an X-ray model fitting a molecular envelope at 10-A resolution. To add molecular detail to the molecular envelope, we used cysteine mutagenesis to incorporate spin labels for analysis with electron paramagnetic resonance (EPR) spectroscopy. Twelve cysteine residues were introduced singly and in pairs at unique locations throughout apoE4 and labeled with an EPR spin probe. The labeled apoE4 was combined with dipalmitoylphosphatidylcholine, the particles were purified, and spectra were determined for 24 combinations (single and double) of the cysteine mutants. Data on the conformation, mobility, distance, and surface exposure of regions revealed by the cysteine probes were modeled into the molecular envelope of apoE bound to dipalmitoylphosphatidylcholine that had been determined by X-ray analysis. This EPR model of apoE in a native lipid-bound state validates the structural model derived from X-ray analysis and provides additional insight into apoE structure-function relationships.
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Affiliation(s)
- Danny M Hatters
- Gladstone Institutes of Cardiovascular and Neurological Diseases, 1650 Owens Street, San Francisco, CA 94158, USA
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10
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Blanchette CD, Law R, Benner WH, Pesavento JB, Cappuccio JA, Walsworth V, Kuhn EA, Corzett M, Chromy BA, Segelke BW, Coleman MA, Bench G, Hoeprich PD, Sulchek TA. Quantifying size distributions of nanolipoprotein particles with single-particle analysis and molecular dynamic simulations. J Lipid Res 2008; 49:1420-30. [PMID: 18403317 DOI: 10.1194/jlr.m700586-jlr200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Self-assembly of purified apolipoproteins and phospholipids results in the formation of nanometer-sized lipoprotein complexes, referred to as nanolipoprotein particles (NLPs). These bilayer constructs are fully soluble in aqueous environments and hold great promise as a model system to aid in solubilizing membrane proteins. Size variability in the self-assembly process has been recognized for some time, yet limited studies have been conducted to examine this phenomenon. Understanding the source of this heterogeneity may lead to methods to mitigate heterogeneity or to control NLP size, which may be important for tailoring NLPs for specific membrane proteins. Here, we have used atomic force microscopy, ion mobility spectrometry, and transmission electron microscopy to quantify NLP size distributions on the single-particle scale, specifically focusing on assemblies with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and a recombinant apolipoprotein E variant containing the N-terminal 22 kDa fragment (E422k). Four discrete sizes of E422k/DMPC NLPs were identified by all three techniques, with diameters centered at approximately 14.5, 19, 23.5, and 28 nm. Computer simulations suggest that these sizes are related to the structure and number of E422k lipoproteins surrounding the NLPs and particles with an odd number of lipoproteins are consistent with the double-belt model, in which at least one lipoprotein adopts a hairpin structure.
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Affiliation(s)
- Craig D Blanchette
- Chemistry, Materials, and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
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11
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Peters-Libeu CA, Newhouse Y, Hall SC, Witkowska HE, Weisgraber KH. Apolipoprotein E*dipalmitoylphosphatidylcholine particles are ellipsoidal in solution. J Lipid Res 2007; 48:1035-44. [PMID: 17308333 DOI: 10.1194/jlr.m600545-jlr200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Apolipoprotein E (apoE) is a major protein component of cholesterol-transporting lipoprotein particles in the central nervous system and in plasma. Polymorphisms of apoE are associated with cardiovascular disease and with a predisposition to Alzheimer's disease and other forms of neurodegeneration. For full biological activity, apoE must be bound to a lipoprotein particle. Complexes of apoE and phospholipid mimic many of these activities. In contrast to a widely accepted discoidal model of apoA-I bound to dimyristoylphosphatidylcholine, which is based on solution studies, an X-ray diffraction study of apoE bound to dipalmitoylphosphatidylcholine (DPPC) indicated that apoE*DPPC particles are quasi-spheroidal and that the packing of the phospholipid core is similar to a micelle. Using small-angle X-ray scattering, we show that apoE*DPPC particles in solution are ellipsoidal and that the shape of the phospholipid core is compatible with a twisted-bilayer model. The proposed model is consistent with the results of mass spectrometric analysis of products of limited proteolysis. These revealed that the nonlipid-bound regions of apoE in the particle are consistent with an alpha-helical hairpin.
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Affiliation(s)
- Clare A Peters-Libeu
- Gladstone Institute of Neurological Disease, Biomolecular Resource Center Mass Spectrometry Facility, Department of Cell and Tissue Biology, University of California, San Francisco, CA 94158, USA
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Hatters DM, Peters-Libeu CA, Weisgraber KH. Apolipoprotein E structure: insights into function. Trends Biochem Sci 2006; 31:445-54. [PMID: 16820298 DOI: 10.1016/j.tibs.2006.06.008] [Citation(s) in RCA: 385] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2006] [Revised: 06/01/2006] [Accepted: 06/22/2006] [Indexed: 02/07/2023]
Abstract
Human apolipoprotein E (apoE) is a member of the family of soluble apolipoproteins. Through its interaction with members of the low-density lipoprotein receptor family, apoE has a key role in lipid transport both in the plasma and in the central nervous system. Its three common structural isoforms differentially affect the risk of developing atherosclerosis and neurodegenerative disorders, including Alzheimer's disease. Because the function of apoE is dictated by its structure, understanding the structural properties of apoE and its isoforms is required both to determine its role in disease and for the development of therapeutic strategies.
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Affiliation(s)
- Danny M Hatters
- Gladstone Institute of Neurological Disease and Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA
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Peters-Libeu CA, Newhouse Y, Hatters DM, Weisgraber KH. Model of biologically active apolipoprotein E bound to dipalmitoylphosphatidylcholine. J Biol Chem 2005; 281:1073-9. [PMID: 16278220 DOI: 10.1074/jbc.m510851200] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein (apo)E plays a critical role in cholesterol transport, through high affinity binding to the low density lipoprotein receptor. This interaction requires apoE to be associated with a lipoprotein particle. To determine the structure of biologically active apoE on a lipoprotein particle, we crystallized dipalmitoylphosphatidylcholine particles containing two apoE molecules and determined the molecular envelope of apoE at 10 Angstroms resolution. On the basis of the molecular envelope and supporting biochemical evidence, we propose a model in which each apoE molecule is folded into a helical hairpin with the binding region for the low density lipoprotein receptor at its apex.
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Affiliation(s)
- Clare A Peters-Libeu
- Gladstone Institute of Cardiovascular Disease and Gladstone Institute of Neurological Disease, San Francisco, CA 94158, USA
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