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Insights into the C-terminal domain of apolipoprotein E from chimera studies with apolipophorin III. Mol Cell Biochem 2023; 478:173-183. [PMID: 35763125 DOI: 10.1007/s11010-022-04497-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 06/01/2022] [Indexed: 01/17/2023]
Abstract
Apolipoprotein E3 (apoE) is a critical cholesterol transport protein in humans and is composed of two domains: a well characterized N-terminal (NT) domain that harbors the low-density lipoprotein LDL receptor, and a less understood C-terminal (CT) domain that is the site of protein oligomerization and initiation of lipid binding. To better understand the domain structure of apoE, the CT domain was fused to apolipophorin III (apoLp-III), a single-domain, monomeric apolipoprotein of insect origin, to yield a chimeric protein, apoLp-III/CT-apoE. Recombinant apoLp-III/CT-apoE maintained an overall helical content similar to that of the parent proteins, while chemical induced unfolding studies indicated that its structural integrity was not compromised. Analysis using 1-anilinonaphthalene-8-sulfonic acid (ANS), a sensitive fluorescent indicator of exposed hydrophobic sites and protein folding, demonstrated that whereas apoLp-III provided few ANS binding sites, apoLp-III/CT-apoE harbored an abundance of ANS binding sites. Thus, this indicated tertiary structure formation in CT-apoE when part of the chimera. Size-exclusion chromatography and chemical crosslinking analysis demonstrated that while apoLp-III is monomeric, the chimeric protein formed large oligomeric complexes, similar to native apoE3. Compared to apoLp-III, the chimera showed a two-fold enhancement in phospholipid vesicle solubilization rates and a significantly improved ability to bind to lipolyzed low-density lipoprotein, preventing the onset of lipoprotein aggregation at concentrations comparable to that of parent CT-apoE. These results confirm that high lipid binding and self-association sites are located in the CT domain of apoE, and that these properties can be transferred to an unrelated apolipoprotein, demonstrating that these properties operate independently from the NT domain.
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2
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Kim M, Bezprozvanny I. Differences in Recycling of Apolipoprotein E3 and E4-LDL Receptor Complexes-A Mechanistic Hypothesis. Int J Mol Sci 2021; 22:5030. [PMID: 34068576 PMCID: PMC8126166 DOI: 10.3390/ijms22095030] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 05/05/2021] [Accepted: 05/07/2021] [Indexed: 12/13/2022] Open
Abstract
Apolipoprotein E (ApoE) is a protein that plays an important role in the transport of fatty acids and cholesterol and in cellular signaling. On the surface of the cells, ApoE lipoparticles bind to low density lipoprotein receptors (LDLR) that mediate the uptake of the lipids and downstream signaling events. There are three alleles of the human ApoE gene. Presence of ApoE4 allele is a major risk factor for developing Alzheimer's disease (AD) and other disorders late in life, but the mechanisms responsible for biological differences between different ApoE isoforms are not well understood. We here propose that the differences between ApoE isoforms can be explained by differences in the pH-dependence of the association between ApoE3 and ApoE4 isoforms and LDL-A repeats of LDLR. As a result, the following endocytosis ApoE3-associated LDLRs are recycled back to the plasma membrane but ApoE4-containing LDLR complexes are trapped in late endosomes and targeted for degradation. The proposed mechanism is predicted to lead to a reduction in steady-state surface levels of LDLRs and impaired cellular signaling in ApoE4-expressing cells. We hope that this proposal will stimulate experimental research in this direction that allows the testing of our hypothesis.
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Affiliation(s)
- Meewhi Kim
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Ilya Bezprozvanny
- Department of Physiology, UT Southwestern Medical Center, Dallas, TX 75390, USA
- Laboratory of Molecular Neurodegeneration, Peter the Great St. Petersburg State Polytechnic University, 195251 St. Petersburg, Russia
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3
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The C-Terminus of Perilipin 3 Shows Distinct Lipid Binding at Phospholipid-Oil-Aqueous Interfaces. MEMBRANES 2021; 11:membranes11040265. [PMID: 33917451 PMCID: PMC8067514 DOI: 10.3390/membranes11040265] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/25/2021] [Accepted: 04/01/2021] [Indexed: 12/13/2022]
Abstract
Lipid droplets (LDs) are ubiquitously expressed organelles; the only intracellular organelles that contain a lipid monolayer rather than a bilayer. Proteins localize and bind to this monolayer as they do to intracellular lipid bilayers. The mechanism by which cytosolic LD binding proteins recognize, and bind, to this lipid interface remains poorly understood. Amphipathic α-helix bundles form a common motif that is shared between cytosolic LD binding proteins (e.g., perilipins 2, 3, and 5) and apolipoproteins, such as apoE and apoLp-III, found on lipoprotein particles. Here, we use pendant drop tensiometry to expand our previous work on the C-terminal α-helix bundle of perilipin 3 and the full-length protein. We measure the recruitment and insertion of perilipin 3 at mixed lipid monolayers at an aqueous-phospholipid-oil interface. We find that, compared to its C-terminus alone, the full-length perilipin 3 has a higher affinity for both a neat oil/aqueous interface and a phosphatidylcholine (PC) coated oil/aqueous interface. Both the full-length protein and the C-terminus show significantly more insertion into a fully unsaturated PC monolayer, contrary to our previous results at the air-aqueous interface. Additionally, the C-terminus shows a preference for lipid monolayers containing phosphatidylethanolamine (PE), whereas the full-length protein does not. These results strongly support a model whereby both the N-terminal 11-mer repeat region and C-terminal amphipathic α-helix bundle domains of perilipin 3 have distinct lipid binding, and potentially biological roles.
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4
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Roda AR, Montoliu-Gaya L, Villegas S. The Role of Apolipoprotein E Isoforms in Alzheimer's Disease. J Alzheimers Dis 2020; 68:459-471. [PMID: 30775980 DOI: 10.3233/jad-180740] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Alzheimer's disease (AD), the most common type of dementia worldwide, is characterized by high levels of amyloid-β (Aβ) peptide and hyperphosphorylated tau protein. Genetically, the ɛ4 allele of apolipoprotein E (ApoE) has been established as the major risk factor for developing late-onset AD (LOAD), the most common form of the disease. Although the role ApoE plays in AD is still not completely understood, a differential role of its isoforms has long been known. The current review compiles the involvement of ApoE isoforms in amyloid-β protein precursor transcription, Aβ aggregation and clearance, synaptic plasticity, neuroinflammation, lipid metabolism, mitochondrial function, and tau hyperphosphorylation. Due to the complexity of LOAD, an accurate description of the interdependence among all the related molecular mechanisms involved in the disease is needed for developing successful therapies.
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Affiliation(s)
- Alejandro R Roda
- Protein Design and Immunotherapy Group, Departament de Bioquímica i Biologia Molecular, Facultat de Biociències, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - Laia Montoliu-Gaya
- Protein Design and Immunotherapy Group, Departament de Bioquímica i Biologia Molecular, Facultat de Biociències, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain.,Department of Clinical Chemistry and Transfusion Medicine, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden
| | - Sandra Villegas
- Protein Design and Immunotherapy Group, Departament de Bioquímica i Biologia Molecular, Facultat de Biociències, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
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5
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Fukuda R, Saito M, Shibukawa S, Sumino A, Nakano M, Murakami T. Urea-Assisted Reconstitution of Discoidal High-Density Lipoprotein. Biochemistry 2020; 59:1455-1464. [DOI: 10.1021/acs.biochem.0c00075] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Ryosuke Fukuda
- Department of Biotechnology, Graduate School of Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan
| | - Mio Saito
- Department of Biotechnology, Graduate School of Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan
| | - Shiori Shibukawa
- Department of Pharmaceutical Engineering, Faculty of Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan
| | - Ayumi Sumino
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa 920-1192, Japan
- Institute for Frontier Science Initiative, Kanazawa University, Kanazawa 920-1192, Japan
| | - Minoru Nakano
- Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Toyama 930-0194, Japan
| | - Tatsuya Murakami
- Department of Biotechnology, Graduate School of Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan
- Department of Pharmaceutical Engineering, Faculty of Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan
- Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University Institute for Advanced Study (KUIAS), Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
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6
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Petros AM, Korepanova A, Jakob CG, Qiu W, Panchal SC, Wang J, Dietrich JD, Brewer JT, Pohlki F, Kling A, Wilcox K, Lakics V, Bahnassawy L, Reinhardt P, Partha SK, Bodelle PM, Lake M, Charych EI, Stoll VS, Sun C, Mohler EG. Fragment-Based Discovery of an Apolipoprotein E4 (apoE4) Stabilizer. J Med Chem 2019; 62:4120-4130. [PMID: 30933499 DOI: 10.1021/acs.jmedchem.9b00178] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Apolipoprotein E is a 299-residue lipid carrier protein produced in both the liver and the brain. The protein has three major isoforms denoted apoE2, apoE3, and apoE4 which differ at positions 112 and 158 and which occur at different frequencies in the human population. Genome-wide association studies indicate that the possession of two apoE4 alleles is a strong genetic risk factor for late-onset Alzheimer's disease (LOAD). In an attempt to identify a small molecule stabilizer of apoE4 function that may have utility as a therapy for Alzheimer's disease, we carried out an NMR-based fragment screen on the N-terminal domain of apoE4 and identified a benzyl amidine based fragment binder. In addition to NMR, binding was characterized using various other biophysical techniques, and a crystal structure of the bound core was obtained. Core elaboration ultimately yielded a compound that showed activity in an IL-6 and IL-8 cytokine release assay.
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Affiliation(s)
- Andrew M Petros
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Alla Korepanova
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Clarissa G Jakob
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Wei Qiu
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Sanjay C Panchal
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Jie Wang
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Justin D Dietrich
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Jason T Brewer
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Frauke Pohlki
- Neuroscience Research , AbbVie Deutschland GmbH & Co. KG , Knollstrasse , 67061 Ludwigshafen , Germany
| | - Andreas Kling
- Neuroscience Research , AbbVie Deutschland GmbH & Co. KG , Knollstrasse , 67061 Ludwigshafen , Germany
| | - Kyle Wilcox
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Viktor Lakics
- Neuroscience Research , AbbVie Deutschland GmbH & Co. KG , Knollstrasse , 67061 Ludwigshafen , Germany
| | - Lamiaa Bahnassawy
- Neuroscience Research , AbbVie Deutschland GmbH & Co. KG , Knollstrasse , 67061 Ludwigshafen , Germany
| | - Peter Reinhardt
- Neuroscience Research , AbbVie Deutschland GmbH & Co. KG , Knollstrasse , 67061 Ludwigshafen , Germany
| | - Sarathy Karunan Partha
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Pierre M Bodelle
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Marc Lake
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Erik I Charych
- AbbVie Neuroscience Research , 200 Sydney Street , Cambridge , Massachusetts 02139 , United States
| | - Vincent S Stoll
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Chaohong Sun
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
| | - Eric G Mohler
- Research & Development , AbbVie , 1 North Waukegan Road , North Chicago , Illinois 60064 , United States
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7
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Lek MT, Cruz S, Ibe NU, Beck WHJ, Bielicki JK, Weers PMM, Narayanaswami V. Swapping the N- and C-terminal domains of human apolipoprotein E3 and AI reveals insights into their structure/activity relationship. PLoS One 2017. [PMID: 28644829 PMCID: PMC5482431 DOI: 10.1371/journal.pone.0178346] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Apolipoprotein (apo) E3 and apoAI are exchangeable apolipoproteins that play a dominant role in regulating plasma lipoprotein metabolism. ApoE3 (299 residues) is composed of an N-terminal (NT) domain bearing a 4-helix bundle and a C-terminal (CT) domain bearing a series of amphipathic α-helices. ApoAI (243 residues) also comprises a highly helical NT domain and a less structured CT tail. The objective of this study was to understand their structural and functional role by generating domain swapped chimeras: apoE3-NT/apoAI-CT and apoAI-NT/apoE-CT. The bacterially overexpressed chimeras were purified by affinity chromatography and their identity confirmed by immunoblotting and mass spectrometry. Their α-helical content was comparable to that of the parent proteins. ApoE3-NT/apoAI-CT retained the denaturation profile of apoE3 NT domain, with apoAI CT tail eliciting a relatively unstructured state; its lipid binding ability improved dramatically compared to apoE3 indicative of a significant role of apoAI CT tail in lipid binding interaction. The LDL receptor interaction and ability to promote ABCA1-mediated cholesterol efflux of apoE3-NT/apoAI-CT was comparable to that of apoE3. In contrast, apoAI-NT/apoE-CT elicited an unfolding pattern and lipid binding ability that were similar to that of apoAI. As expected, DMPC/apoAI-NT/apoE-CT discoidal particles did not elicit LDLr binding ability, and promoted SR-B1 mediated cellular uptake of lipids to a limited extent. However, apoAI-NT/apoE-CT displayed an enhanced ability to promote cholesterol efflux compared to apoAI, indicative of a significant role for apoE CT domain in mediating this function. Together, these results indicate that the functional attributes of apoAI and apoE3 can be conferred on each other and that NT-CT domain interactions significantly modulate their structure and function.
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Affiliation(s)
- Mark T. Lek
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, California, United States of America
| | - Siobanth Cruz
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, California, United States of America
| | - Nnejiuwa U. Ibe
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, California, United States of America
| | - Wendy H. J. Beck
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, California, United States of America
| | - John K. Bielicki
- Donner Laboratory, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America
| | - Paul M. M. Weers
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, California, United States of America
| | - Vasanthy Narayanaswami
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, California, United States of America
- * E-mail:
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8
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Dwivedi P, Rodriguez J, Ibe NU, Weers PMM. Deletion of the N- or C-Terminal Helix of Apolipophorin III To Create a Four-Helix Bundle Protein. Biochemistry 2016; 55:3607-15. [PMID: 27280697 DOI: 10.1021/acs.biochem.6b00381] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Apolipophorin III (apoLp-III) is an exchangeable apolipoprotein found in insects and plays an important function in lipid transport. The protein has an unusual five-helix bundle architecture, deviating from the common four-helix bundle motif. To understand the role of the additional helix in apoLp-III, the N-terminal or C-terminal helix was deleted to create a putative four-helix bundle protein. While the protein lacking helix-1 could be expressed in bacteria albeit at reduced yields, apoLp-III lacking helix-5 could not be produced. Mutational analysis by truncating helix-5 showed that a minimum segment of approximately one-third of the C-terminal helix is required for protein expression. The variant lacking helix-5 was produced by inserting a methionine residue between helix-4 and -5; subsequent cyanogenbromide cleavage generated the four-helix variant. Both N- and C-terminal helix deletion variants displayed significantly reduced helical content, protein stability, and tertiary structure. Despite the significantly altered structure, the variants were still fully functional. The rate of dimyristoylphosphatidylcholine vesicle solubilization was enhanced 4-5-fold compared to the wild-type protein, and the deletion variants were effective in binding to lipolyzed low density lipoprotein thereby preventing lipoprotein aggregation. These results show that the additional helix of apoLp-III is not essential for lipid binding but is required for proper folding to keep the protein into a stable conformation.
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Affiliation(s)
- Pankaj Dwivedi
- Department of Chemistry and Biochemistry, California State University , Long Beach, California 90840, United States
| | - Johana Rodriguez
- Department of Chemistry and Biochemistry, California State University , Long Beach, California 90840, United States
| | - Nnejiuwa U Ibe
- Department of Chemistry and Biochemistry, California State University , Long Beach, California 90840, United States
| | - Paul M M Weers
- Department of Chemistry and Biochemistry, California State University , Long Beach, California 90840, United States
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9
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Thistle J, Martinon D, Weers PMM. Helix 1 tryptophan variants in Galleria mellonella apolipophorin III. Chem Phys Lipids 2015; 193:18-23. [PMID: 26462904 DOI: 10.1016/j.chemphyslip.2015.10.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Revised: 09/21/2015] [Accepted: 10/05/2015] [Indexed: 01/19/2023]
Abstract
Apolipophorin III (apoLp-III) from Galleria mellonella is a critical apolipoprotein aiding in lipid transport and has gained considerable interest for a role in innate immunity. Both functions are likely related and form the rationale to gain a more detailed understanding of the lipid binding properties of this insect apolipoprotein. Tryptophan residues were introduced at positions 16, 20 or 24, all in helix 1 as it may play a critical role in the initial steps of lipid binding. Steady-state fluorescence analysis showed that each tryptophan displayed unique properties, indicating different environments both in lipid-free as in lipid-bound states, and demonstrating potential for use in lipid binding analysis. While α-helical contents of wild-type and the tryptophan variant proteins were similar, W20- and W24-apoLp-III displayed increased protein stability. These variants were significantly slower in their ability to convert phosphatidylcholine vesicles into discoidal lipoproteins, which was employed as a measure for lipid binding. In contrast, W16-apoLp-III displayed decreased protein stability but an order of magnitude higher rate of discoidal lipoprotein formation. This demonstrates an inverse correlation between protein stability and the ability to convert vesicles in discoidal lipoproteins. The most stable W20-apoLp-III variant displayed comprised LDL binding capabilities, indicating a partial loss of function. Thus, there is a delicate balance between helix bundle stability and the ability to bind lipids, and helix 1 may play a critical role in this process.
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Affiliation(s)
- Jake Thistle
- Department of Chemistry and Biochemistry, California State University Long Beach, CA 90840, USA
| | - Daisy Martinon
- Department of Chemistry and Biochemistry, California State University Long Beach, CA 90840, USA
| | - Paul M M Weers
- Department of Chemistry and Biochemistry, California State University Long Beach, CA 90840, USA.
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10
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Meyers NL, Larsson M, Olivecrona G, Small DM. A Pressure-dependent Model for the Regulation of Lipoprotein Lipase by Apolipoprotein C-II. J Biol Chem 2015; 290:18029-18044. [PMID: 26026161 DOI: 10.1074/jbc.m114.629865] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Indexed: 12/31/2022] Open
Abstract
Apolipoprotein C-II (apoC-II) is the co-factor for lipoprotein lipase (LPL) at the surface of triacylglycerol-rich lipoproteins. LPL hydrolyzes triacylglycerol, which increases local surface pressure as surface area decreases and amphipathic products transiently accumulate at the lipoprotein surface. To understand how apoC-II adapts to these pressure changes, we characterized the behavior of apoC-II at multiple lipid/water interfaces. ApoC-II adsorption to a triacylglycerol/water interface resulted in large increases in surface pressure. ApoC-II was exchangeable at this interface and desorbed on interfacial compressions. These compressions increase surface pressure and mimic the action of LPL. Analysis of gradual compressions showed that apoC-II undergoes a two-step desorption, which indicates that lipid-bound apoC-II can exhibit at least two conformations. We characterized apoC-II at phospholipid/triacylglycerol/water interfaces, which more closely mimic lipoprotein surfaces. ApoC-II had a large exclusion pressure, similar to that of apoC-I and apoC-III. However, apoC-II desorbed at retention pressures higher than those seen with the other apoCs. This suggests that it is unlikely that apoC-I and apoC-III inhibit LPL via displacement of apoC-II from the lipoprotein surface. Upon rapid compressions and re-expansions, re-adsorption of apoC-II increased pressure by lower amounts than its initial adsorption. This indicates that apoC-II removed phospholipid from the interface upon desorption. These results suggest that apoC-II regulates the activity of LPL in a pressure-dependent manner. ApoC-II is provided as a component of triacylglycerol-rich lipoproteins and is the co-factor for LPL as pressure increases. Above its retention pressure, apoC-II desorbs and removes phospholipid. This triggers release of LPL from lipoproteins.
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Affiliation(s)
- Nathan L Meyers
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Mikael Larsson
- Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-901 87 Umeå, Sweden; Department of Medicine, UCLA, Los Angeles, California 90095
| | - Gunilla Olivecrona
- Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-901 87 Umeå, Sweden
| | - Donald M Small
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118.
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11
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Meyers NL, Wang L, Gursky O, Small DM. Changes in helical content or net charge of apolipoprotein C-I alter its affinity for lipid/water interfaces. J Lipid Res 2013; 54:1927-38. [PMID: 23670531 DOI: 10.1194/jlr.m037531] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Amphipathic α-helices mediate binding of exchangeable apolipoproteins to lipoproteins. To probe the role of α-helical structure in protein-lipid interactions, we used oil-drop tensiometry to characterize the interfacial behavior of apolipoprotein C-I (apoC-I) variants at triolein/water (TO/W) and 1-palmitoyl-2-oleoylphosphatidylcholine/triolein/water (POPC/TO/W) interfaces. ApoC-I, the smallest apolipoprotein, has two amphipathic α-helices. Mutants had single Pro or Ala substitutions that resulted in large differences in helical content in solution and on phospholipids. The ability of apoC-I to bind TO/W and POPC/TO/W interfaces correlated strongly with α-helical propensity. On binding these interfaces, peptides with higher helical propensity increased surface pressure to a greater extent. Likewise, peptide exclusion pressure at POPC/TO/W interfaces increased with greater helical propensity. ApoC-I retention on TO/W and POPC/TO/W interfaces correlated strongly with phospholipid-bound helical content. On compression of these interfaces, peptides with higher helical content were ejected at higher pressures. Substitution of Arg for Pro in the N-terminal α-helix altered net charge and reduced apoC-I affinity for POPC/TO/W interfaces. Our results suggest that peptide-lipid interactions drive α-helix binding to and retention on lipoproteins. Point mutations in small apolipoproteins could significantly change α-helical propensity or charge, thereby disrupting protein-lipid interactions and preventing the proteins from regulating lipoprotein catabolism at high surface pressures.
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Affiliation(s)
- Nathan L Meyers
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA
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12
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Tran TN, Kim SH, Gallo C, Amaya M, Kyees J, Narayanaswami V. Biochemical and biophysical characterization of recombinant rat apolipoprotein E: similarities to human apolipoprotein E3. Arch Biochem Biophys 2012; 529:18-25. [PMID: 23103361 DOI: 10.1016/j.abb.2012.10.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 10/12/2012] [Accepted: 10/13/2012] [Indexed: 11/28/2022]
Abstract
Apolipoprotein E (apoE) is an anti-atherogenic protein that plays a critical role in maintaining plasma cholesterol and triglyceride homeostasis by virtue of its ability to act as a ligand for the low-density lipoprotein receptor (LDLr) family of proteins. In this study, we characterized the biochemical and biophysical features of recombinant rat apoE, in comparison with those of human apoE3. Rat apoE was overexpressed in Escherichia coli using a codon optimized system and purified by affinity chromatography. SDS-PAGE and RP-HPLC of rat apoE confirmed the purity, while immunoblot verified the identity and cross-reactivity with the LDLr-binding region of apoE3. The α-helical content was calculated to be ~45% by circular dichroism spectroscopy. The protein exists in a predominantly tetrameric form in lipid-free state. Chemical denaturation studies reveal that the unfolding pattern is biphasic with mid points of denaturation corresponding to 0.8 and 2.2 M guanidine hydrochloride, suggesting the presence of two domains. Rat apoE converts DMPC vesicles to smaller DMPC/apoE complexes with a first order rate constant of 0.12 min(-1). It has the ability to bind the LDLr and to heparin. Our studies indicate that although its sequence resembles apoE4, an isoform of apoE3, rat apoE displays the biophysical behavior of apoE3.
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Affiliation(s)
- Tuyen N Tran
- Department of Chemistry and Biochemistry, 1250 Bellflower Boulevard, California State University Long Beach, Long Beach, CA 90840, USA
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13
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Hauser PS, Narayanaswami V, Ryan RO. Apolipoprotein E: from lipid transport to neurobiology. Prog Lipid Res 2010; 50:62-74. [PMID: 20854843 DOI: 10.1016/j.plipres.2010.09.001] [Citation(s) in RCA: 222] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 09/04/2010] [Accepted: 09/12/2010] [Indexed: 12/17/2022]
Abstract
Apolipoprotein (apo) E has a storied history as a lipid transport protein. The integral association between cholesterol homeostasis and lipoprotein clearance from circulation are intimately related to apoE's function as a ligand for cell-surface receptors of the low-density lipoprotein receptor family. The receptor binding properties of apoE are strongly influenced by isoform specific amino acid differences as well as the lipidation state of the protein. As understanding of apoE as a structural component of circulating plasma lipoproteins has evolved, exciting developments in neurobiology have revitalized interest in apoE. The strong and enduring correlation between the apoE4 isoform and age of onset and increased risk of Alzheimer's disease has catapulted apoE to the forefront of neurobiology. Using genetic tools generated for study of apoE lipoprotein metabolism, transgenic "knock-in" and gene-disrupted mice are now favored models for study of its role in a variety of neurodegenerative diseases. Key structural knowledge of apoE and isoform-specific differences is driving research activity designed to elucidate how a single amino acid change can manifest such profoundly significant pathological consequences. This review describes apoE through a lens of structure-based knowledge that leads to hypotheses that attempt to explain the functions of apoE and isoform-specific effects relating to disease mechanism.
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Affiliation(s)
- Paul S Hauser
- Center for Prevention of Obesity, Cardiovascular Disease and Diabetes, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA
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14
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Koyama M, Tanaka M, Dhanasekaran P, Lund-Katz S, Phillips MC, Saito H. Interaction between the N- and C-terminal domains modulates the stability and lipid binding of apolipoprotein A-I. Biochemistry 2010; 48:2529-37. [PMID: 19239199 DOI: 10.1021/bi802317v] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The tertiary structures of human and mouse apolipoprotein A-I (apoA-I) are comprised of an N-terminal helix bundle and a separate C-terminal domain. To define the possible intramolecular interaction between the N- and the C-terminal domains, we examined the effects on protein stability and lipid-binding properties of exchanging either the C-terminal domain or helix between human and mouse apoA-I. Chemical denaturation experiments demonstrated that replacement of the C-terminal domain or helical segment in human apoA-I with the mouse counterparts largely destabilizes the N-terminal helix bundle. Removal of the C-terminal domain or alpha-helix in human apoA-I had a similar effect on the destabilization of the helix bundle against urea denaturation, indicating that the C-terminal helical segment mainly contributes to stabilizing the N-terminal helix bundle structure in the apoA-I molecule. Consistent with this, KI quenching experiments indicated that removal or replacement of the C-terminal domain or helix in human apoA-I causes Trp residues in the N-terminal domain to become exposed to solvent. Measurements of the heats of binding to egg phosphatidylcholine (PC) vesicles and the kinetics of solubilization of dimyristoyl PC vesicles demonstrated that the destabilized human N-terminal helix bundle can strongly interact with lipids without the hydrophobic C-terminal helix. In addition, site-specific labeling of the N- and C-terminal helices by acrylodan to probe the conformational stability and the spatial proximity of the two domains indicated that the C-terminal helix is located near the N-terminal helix bundle, leading to a relatively less solvent-exposed, more organized conformation of the C-terminal domain. Taken together, these results suggest that interaction between the N- and C-terminal tertiary structure domains in apoA-I modulates the stability and lipid-binding properties of the N-terminal helix bundle.
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Affiliation(s)
- Mao Koyama
- Department of Biophysical Chemistry, Kobe Pharmaceutical University, 4-19-1 Motoyamakitamachi, Higashinada-ku, Kobe 658-8558, Japan
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15
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Minagawa H, Gong JS, Jung CG, Watanabe A, Lund-Katz S, Phillips MC, Saito H, Michikawa M. Mechanism underlying apolipoprotein E (ApoE) isoform-dependent lipid efflux from neural cells in culture. J Neurosci Res 2009; 87:2498-508. [PMID: 19326444 PMCID: PMC3065888 DOI: 10.1002/jnr.22073] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We determined the molecular mechanisms underlying apolipoprotein E (ApoE)-isoform-dependent lipid efflux from neurons and ApoE-deficient astrocytes in culture. The ability of ApoE3 to induce lipid efflux was 2.5- to 3.9-fold greater than ApoE4. To explore the contributions of the amino- and carboxyl-terminal tertiary structure domains of ApoE to cellular lipid efflux, each domain was studied separately. The amino-terminal fragment of ApoE3 (22-kDa-ApoE3) induced lipid efflux greater than 22-kDa-ApoE4, whereas the common carboxyl-terminal fragment of ApoE induced very low levels of lipid efflux. Addition of segments of the carboxyl-terminal domain to 22-kDa-ApoE3 additively induced lipid efflux in a length-dependent manner; in contrast, this effect did not occur with ApoE4. This observation, coupled with the fact that introduction of the E255A mutation (which disrupts domain-domain interaction) into ApoE4 increases lipid efflux, indicates that interaction between the amino- and carboxyl-terminal domains in ApoE4 reduces the ability of this isoform to mediate lipid efflux from neural cells. Dimeric 22-kDa or intact ApoE3 induced higher lipid efflux than monomeric 22-kDa or intact ApoE3, respectively, indicating that dimerization of ApoE3 enhances the ability to release lipids. The adenosine triphosphate-binding cassette protein A1 (ABCA1) is involved in ApoE-induced lipid efflux. In conclusion, there are two major factors, intramolecular domain interaction and intermolecular dimerization, that cause ApoE-isoform-dependent lipid efflux from neural cells in culture.
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Affiliation(s)
- Hirohisa Minagawa
- Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Aichi, Japan
| | - Jiang-Sheng Gong
- Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Aichi, Japan
| | - Cha-Gyun Jung
- Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Aichi, Japan
| | - Atsushi Watanabe
- Department of Vascular Dementia, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Aichi, Japan
| | - Sissel Lund-Katz
- Lipid Research Group, Children’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Michael C. Phillips
- Lipid Research Group, Children’s Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Hiroyuki Saito
- Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe, Japan
| | - Makoto Michikawa
- Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Aichi, Japan
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16
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Elliott DA, Tsoi K, Holinkova S, Chan SL, Kim WS, Halliday GM, Rye KA, Garner B. Isoform-specific proteolysis of apolipoprotein-E in the brain. Neurobiol Aging 2009; 32:257-71. [PMID: 19278755 DOI: 10.1016/j.neurobiolaging.2009.02.006] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2008] [Revised: 02/01/2009] [Accepted: 02/03/2009] [Indexed: 11/19/2022]
Abstract
Apolipoprotein-E (apoE) plays important roles in neurobiology and the apoE4 isoform increases risk for Alzheimer's disease (AD). ApoE peptides are biologically active and may be produced in the brain. It is unclear if apoE proteolysis is dependent on isoform or AD status and this was addressed here. Hippocampus, frontal cortex, occipital lobe and cerebellum samples were homogenized into fractions that were soluble in Tris-buffered saline (TBS), Triton X-100 or guanidine hydrochloride and analysed for apoE fragmentation by Western blotting. Approximately 20% of apoE3 was detected as fragments and this was predominantly as a 25 kDa peptide in TBS-soluble fractions. The concentration of TBS-soluble apoE fragments was two- to three-fold higher in apoE3 compared to apoE4 subjects. This difference was observed in all areas of the brain examined and was not related to AD status. Cathepsin-D treatment generated apoE fragments that were very similar to those detected in brain, however, no apoE isoform-specific differences in susceptibility to cathepsin-D proteolysis were detected. This indicates that proteolytic processing of apoE to form soluble fragments in the human brain is dependent on apoE isoform but not AD status.
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Affiliation(s)
- David A Elliott
- Prince of Wales Medical Research Institute, Randwick, NSW 2031, Australia
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17
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de Chaves EP, Narayanaswami V. Apolipoprotein E and cholesterol in aging and disease in the brain. ACTA ACUST UNITED AC 2008; 3:505-530. [PMID: 19649144 DOI: 10.2217/17460875.3.5.505] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Cholesterol can be detrimental or vital, and must be present in the right place at the right time and in the right amount. This is well known in the heart and the vascular system. However, in the CNS cholesterol is still an enigma, although several of its fundamental functions in the brain have been identified. Brain cholesterol has attracted additional attention owing to its close connection to ApoE, a key polymorphic transporter of extracellular cholesterol in humans. Indeed, both cholesterol and ApoE are so critical to fundamental activities of the brain, that the brain regulates their synthesis autonomously. Yet, similar control mechanisms of ApoE and cholesterol homeostasis may exist on either sides of the blood-brain barrier. One indication is that the APOE ε4 allele is associated with hypercholesterolemia and a proatherogenic profile on the vascular side and with increased risk of Alzheimer's disease on the CNS side. In this review, we draw attention to the association between cholesterol and ApoE in the aging and diseased brain, and to the behavior of the ApoE4 protein at the molecular level. The attempt to correlate in vivo and in vitro observations is challenging but crucial for developing future strategies to address ApoE-related aberrations in cholesterol metabolism selectively in the brain.
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18
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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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19
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Benjwal S, Jayaraman S, Gursky O. Role of secondary structure in protein-phospholipid surface interactions: reconstitution and denaturation of apolipoprotein C-I:DMPC complexes. Biochemistry 2007; 46:4184-94. [PMID: 17341095 PMCID: PMC2584444 DOI: 10.1021/bi062175c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Binding of protein to a phospholipid surface is commonly mediated by amphipathic alpha-helices. To understand the role of alpha-helical structure in protein-lipid interactions, we used discoidal lipoproteins reconstituted from dimyristoylphosphatidylcholine (DMPC) and human apolipoprotein C-I (apoC-I, 6 kDa) or its mutants containing single Pro substitutions along the sequence and differing in their alpha-helical content in solution (0-48%) and on DMPC (40-75%). Thermal denaturation revealed that lipoprotein stability correlates weakly with the protein helix content: proteins with higher alpha-helical content on DMPC may form more stable complexes. Lipoprotein reconstitution upon cooling from the heat-denatured state and DMPC clearance studies revealed that protein secondary structure in solution and on DMPC correlates strongly with the maximal temperature of lipoprotein reconstitution: more helical proteins can reconstitute lipoproteins at higher temperatures. Interestingly, at Tc = 24 degrees C of the DMPC gel-to-liquid crystal transition, the clearance rate is independent of the protein helical content. Consequently, if the packing defects at the phospholipid surface are readily available (e.g., at the lipid phase boundary), insertion of protein into these defects is independent of the secondary structure in solution. However, if hydrophobic defects are limited, protein binding and insertion are aided by other surface-bound proteins and depend on their helical propensity: the larger the propensity, the faster the binding and the broader its temperature range. This positive cooperativity in binding of alpha-helices to phospholipid surface, which may result from direct and/or lipid-mediated protein-protein interactions, may be important for lipoprotein metabolism and for protein-membrane binding.
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Affiliation(s)
- Sangeeta Benjwal
- Department of Physiology and Biophysics, Boston University School of Medicine, 715 Albany Street, Boston, Massachusetts 02118, USA
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20
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Hatters DM, Zhong N, Rutenber E, Weisgraber KH. Amino-terminal domain stability mediates apolipoprotein E aggregation into neurotoxic fibrils. J Mol Biol 2006; 361:932-44. [PMID: 16890957 DOI: 10.1016/j.jmb.2006.06.080] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Revised: 05/26/2006] [Accepted: 06/30/2006] [Indexed: 10/24/2022]
Abstract
The three isoforms of apolipoprotein (apo) E are strongly associated with different risks for Alzheimer's disease: apoE4>apoE3>apoE2. Here, we show at physiological salt concentrations and pH that native tetramers of apoE form soluble aggregates in vitro that bind the amyloid dyes thioflavin T and Congo red. However, unlike classic amyloid fibrils, the aggregates adopt an irregular protofilament-like morphology and are seemingly highly alpha-helical. The aggregates formed at substantially different rates (apoE4>apoE3>apoE2) and were significantly more toxic to cultured neuronal cells than the tetramer. Since the three isoforms have large differences in conformational stability that can influence aggregation and amyloid pathways, we tested the effects of mutations that increased or decreased stability. Decreasing the conformational stability of the amino-terminal domain of apoE increased aggregation rates and vice versa. Our findings provide a new perspective for an isoform-specific pathogenic role for apoE aggregation in which differences in the conformational stability of the amino-terminal domain mediate neurodegeneration.
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Affiliation(s)
- Danny M Hatters
- Gladstone Institute of Neurological Disease, 1650 Owens Street, San Francisco, CA 94158, USA
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21
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Stratman NC, Castle CK, Taylor BM, Epps DE, Melchior GW, Carter DB. Isoform-specific interactions of human apolipoprotein E to an intermediate conformation of human Alzheimer amyloid-beta peptide. Chem Phys Lipids 2005; 137:52-61. [PMID: 16140289 DOI: 10.1016/j.chemphyslip.2005.06.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2005] [Revised: 06/22/2005] [Accepted: 06/29/2005] [Indexed: 10/25/2022]
Abstract
Brain plaque deposits of amyloid-beta peptide (Abeta) is a pathological hallmark of Alzheimer's disease (AD) and apolipoprotein E (apoE) is thought to be involved in its deposition. One hypothesis for the role of apoE in the pathogenesis of AD is that apoE may be involved in deposition or clearance of Abeta by direct protein-to-protein interaction. Lipidated apoE4 bound preferentially to an intermediate aggregated form of Abeta and formed two- to three-fold more binding complexes than isoforms apoE2 or apoE3. The interaction was detected by a sandwich ELISA with capture antibodies specific for the N-terminus of apoE, whereas the interaction was not recognized with a C-terminal antibody. The observations indicate that the C-terminus of apoE4 interacts with the intermediate form of Abeta. The differential risk of AD related to apoE genotype may be the result of an enhanced capacity of apoE4 binding to an intermediate aggregated form of Abeta.
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22
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Pearson K, Tubb MR, Tanaka M, Zhang XQ, Tso P, Weinberg RB, Davidson WS. Specific Sequences in the N and C Termini of Apolipoprotein A-IV Modulate Its Conformation and Lipid Association. J Biol Chem 2005; 280:38576-82. [PMID: 16159879 DOI: 10.1074/jbc.m506802200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein (apoA-IV) is a 376-residue exchangeable apolipoprotein that may play a number of important roles in lipid metabolism, including chylomicron assembly, reverse cholesterol transport, and appetite regulation. In vivo, apoA-IV exists in both lipid-poor and lipid-associated forms, and the balance between these states may determine its function. We examined the structural elements that modulate apoA-IV lipid binding by producing a series of deletion mutants and determining their ability to interact with phospholipid liposomes. We found that the deletion of residues 333-343 strongly increased the lipid association rate versus native apoA-IV. Additional mutagenesis revealed that two phenylalanine residues at positions 334 and 335 mediated this lipid binding inhibitory effect. We also observed that residues 11-20 in the N terminus were required for the enhanced lipid affinity induced by deletion of the C-terminal sequence. We propose a structural model in which these sequences can modulate the conformation and lipid affinity of apoA-IV.
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Affiliation(s)
- Kevin Pearson
- Department of Pathology and Laboratory Medicine, The University of Cincinnati, Cincinnati, Ohio 45237-0507, USA
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23
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Hatters DM, Peters-Libeu CA, Weisgraber KH. Engineering conformational destabilization into mouse apolipoprotein E. A model for a unique property of human apolipoprotein E4. J Biol Chem 2005; 280:26477-82. [PMID: 15890642 DOI: 10.1074/jbc.m503910200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein (apo) E4 is a major risk factor for Alzheimer and cardiovascular diseases. ApoE4 differs from the two other common isoforms (apoE2 and apoE3) by its lower resistance to denaturation and greater propensity to form partially folded intermediates. As a first step to determine the importance of stability differences in vivo, we reengineered a partially humanized variant of the amino-terminal domain of mouse apoE (T61R mouse apoE) to acquire a destabilized conformation like that of apoE4. For this process, we determined the crystal structure of wild-type mouse apoE, which, like apoE4, forms a four-helix bundle, and identified two structural differences in the turn between helices 2 and 3 and in the middle of helix 3 as potentially destabilizing sites. Introducing mutations G83T and N113G at these sites destabilized the mouse apoE conformation. The mutant mouse apoE more rapidly remodeled phospholipid than T61R mouse apoE, which supports the hypothesis that a destabilized conformation promotes apoE4 lipid binding.
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Affiliation(s)
- Danny M Hatters
- Gladstone Institute of Neurological Disease, San Francisco, California 94158, USA
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24
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Raussens V, Drury J, Forte T, Choy N, Goormaghtigh E, Ruysschaert JM, Narayanaswami V. Orientation and mode of lipid-binding interaction of human apolipoprotein E C-terminal domain. Biochem J 2005; 387:747-54. [PMID: 15588256 PMCID: PMC1135005 DOI: 10.1042/bj20041536] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Revised: 12/02/2004] [Accepted: 12/10/2004] [Indexed: 11/17/2022]
Abstract
ApoE (apolipoprotein E) is an anti-atherogenic lipid transport protein that plays an integral role in lipoprotein metabolism and cholesterol homoeostasis. Lipid association educes critical functional features of apoE, mediating reduction in plasma and cellular cholesterol levels. The 10-kDa CT (C-terminal) domain of apoE facilitates helix-helix interactions in lipid-free state to promote apoE self-association and helix-lipid interactions during binding with lipoproteins, although the mode of lipid-binding interaction is not well understood. We investigated the mode of lipid-binding interaction and orientation of apoE CT domain on reconstituted lipoproteins. Isolated recombinant human apoE CT domain (residues 201-299) possesses a strong ability to interact with phospholipid vesicles, yielding lipoprotein particles with an apparent molecular mass of approximately 600 kDa, while retaining the overall alpha-helical content. Electron microscopy and non-denaturing PAGE analysis of DMPC (dimyristoylphosphatidylcholine)--apoE CT domain lipoprotein complexes revealed discoidal complexes with a diameter of approx. 17 nm. Cross-linking apoE CT domain on discoidal particles yielded dimeric species as the major product. Attenuated total reflectance Fourier transform IR spectroscopy of phospholipid-apoE CT domain complexes reveals that the helical axis is oriented perpendicular to fatty acyl chains of the phospholipid. Fluorescence quenching analysis of DMPC-apoE CT domain discoidal complexes by spin-labelled stearic acid indicated a relatively superficial location of the native tryptophan residues with respect to the plane of the phospholipid bilayer. Taken together, we propose that apoE CT domain interacts with phospholipid vesicles, forming a long extended helix that circumscribes the discoidal bilayer lipoprotein complex.
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Key Words
- apolipoprotein e
- cross-linking
- electron microscopy
- ir spectroscopy
- lipid-bound conformation
- lipoprotein-binding surface
- apoa-i, apolipoprotein a-i
- apoe, apolipoprotein e
- atr-ftir, attenuated total reflectance fourier transform ir
- ct, c-terminal
- dmpc, dimyristoylphosphatidylcholine
- dmpg, dimyristoylphosphatidylglycerol
- 5-dsa, 5-doxyl stearic acid
- 12-dsa, 12-doxyl stearic acid
- dss, disuccinimidyl suberate
- hdl, high-density lipoprotein
- ldl, low-density lipoprotein
- nt, n-terminal
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Affiliation(s)
- Vincent Raussens
- *Structure and Function of Biological Membranes, Université Libre de Bruxelles, CP-206/2, bd. Du Triomphe, B-1050 Brussels, Belgium
| | - Jessica Drury
- †Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, U.S.A
| | - Trudy M. Forte
- †Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, U.S.A
| | - Nicole Choy
- †Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, U.S.A
| | - Erik Goormaghtigh
- *Structure and Function of Biological Membranes, Université Libre de Bruxelles, CP-206/2, bd. Du Triomphe, B-1050 Brussels, Belgium
| | - Jean-Marie Ruysschaert
- *Structure and Function of Biological Membranes, Université Libre de Bruxelles, CP-206/2, bd. Du Triomphe, B-1050 Brussels, Belgium
| | - Vasanthy Narayanaswami
- †Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, U.S.A
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Saito H, Lund-Katz S, Phillips MC. Contributions of domain structure and lipid interaction to the functionality of exchangeable human apolipoproteins. Prog Lipid Res 2004; 43:350-80. [PMID: 15234552 DOI: 10.1016/j.plipres.2004.05.002] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Exchangeable apolipoproteins function in lipid transport as structural components of lipoprotein particles, cofactors for enzymes and ligands for cell-surface receptors. Recent findings with apoA-I and apoE suggest that the tertiary structures of these two members of the human exchangeable apolipoprotein gene family are related. Characteristically, these proteins contain a series of proline-punctuated, 11- or 22-amino acid, amphipathic alpha-helical repeats that can adopt a helix bundle conformation in the lipid-free state. The amino- and carboxyl-terminal regions form separate domains with the latter being primarily responsible for lipid binding. Interaction with lipid induces changes in the conformation of the amino-terminal domain leading to alterations in function; for example, opening of the amino-terminal four-helix bundle in apolipoprotein E upon lipid binding is associated with enhanced receptor-binding activity. The concept of a two-domain structure for the larger exchangeable apolipoproteins is providing new molecular insights into how these apolipoproteins interact with lipids and other proteins, such as receptors. The ways in which structural changes induced by lipid interaction modulate the functionality of these apolipoproteins are reviewed.
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Affiliation(s)
- Hiroyuki Saito
- Lipid Research Group, The Children's Hospital of Philadelphia, Abramson Research Center, Suite 1102, 3615 Civic Center Boulevard, University of Pennsylvania School of Medicine, Philadelphia, 19104-4318, USA
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26
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Saito H, Dhanasekaran P, Baldwin F, Weisgraber KH, Phillips MC, Lund-Katz S. Effects of polymorphism on the lipid interaction of human apolipoprotein E. J Biol Chem 2003; 278:40723-9. [PMID: 12917433 DOI: 10.1074/jbc.m304814200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ApoE exists as three common isoforms, apoE2, apoE3, and apoE4; apoE2 and apoE3 preferentially bind to high density lipoproteins, whereas apoE4 prefers very low density lipoproteins (VLDL). To understand the molecular basis for the different lipoprotein distributions of these isoforms in human plasma, we examined the lipid-binding properties of the apoE isoforms and some mutants using lipid emulsions. With both large (120 nm) and small (35 nm) emulsion particles, the binding affinity of apoE4 was much higher than that of apoE2 and apoE3, whereas the maximal binding capacities were similar among the three isoforms. The 22-kDa N-terminal fragment of apoE4 displayed a much higher binding capacity than did apoE2 and apoE3. The apoE4(E255A) mutant, which has no electrostatic interaction between Arg61 and Glu255, showed binding behavior similar to that of apoE3, indicating that N- and C-terminal domain interaction in apoE4 is responsible for its high affinity for lipid. In addition, the apoE3(P267A) mutant, which is postulated to contain a long alpha-helix in the C-terminal domain, had significantly decreased binding capacities for both sizes of emulsion particle, suggesting that the apoE4 preference for VLDL is not due to a stabilized long alpha-helical structure. Isothermal titration calorimetry measurements showed that there is no significant difference in thermodynamic parameters for emulsion binding among the apoE isoforms. However, fluorescence measurements of 8-anilino-1-naphthalenesulfonic acid binding to apoE indicated that apoE4 has more exposed hydrophobic surface compared with apoE3 mainly due to the different tertiary organization of the C-terminal domain. The less organized structure in the C-terminal domain of apoE4 leads to the higher affinity for lipid, contributing to its preferential association with VLDL. In fact, we found that apoE4 binds to VLDL with higher affinity compared with apoE3.
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Affiliation(s)
- Hiroyuki Saito
- National Institute of Health Sciences, Osaka Branch, Osaka 540-0006, Japan
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Kiss RS, Weers PMM, Narayanaswami V, Cohen J, Kay CM, Ryan RO. Structure-guided protein engineering modulates helix bundle exchangeable apolipoprotein properties. J Biol Chem 2003; 278:21952-9. [PMID: 12684504 DOI: 10.1074/jbc.m302676200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [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 major role in lipid metabolism by mediating cellular uptake of lipoprotein particles through interaction with members of the low density lipoprotein (LDL) receptor family. The primary region of apoE responsible for receptor binding has been limited to a cluster of basic amino acids between residues 134 and 150, located in the fourth helix of the N-terminal domain globular helix bundle structure. To investigate structural and functional requirements of this "receptor binding region" we engineered an apolipoprotein chimera wherein residues 131-151 of human apoE were substituted for residues 146-166 (helix 5) of Manduca sexta apolipophorin III (apoLp-III). Recombinant hybrid apolipoprotein was expressed in Escherichia coli, isolated, and characterized. Hybrid apolipoprotein and apoE3-N-terminal, but not apoLp-III, bound to heparin-Sepharose. Far UV circular dichroism spectroscopy revealed the presence of predominantly alpha-helix secondary structure, and stability studies revealed a urea denaturation midpoint of 1.05 m, similar to wild-type apoLp-III. Hybrid apolipoprotein-induced dimyristoylphosphatidylcholine (DMPC) bilayer vesicle solubilization activity was significantly enhanced compared with either parent protein, consistent with detection of solvent-exposed hydrophobic regions on the protein in fluorescent dye binding experiments. Unlike wild-type apoLp-III.DMPC complexes, disc particles bearing the hybrid apolipoprotein competed with 125ILDL for binding to the LDL receptor on cultured human skin fibroblasts. We conclude that a hybrid apolipoprotein containing a key receptor recognition element of apoE preserves the structural integrity of the parent protein while conferring a new biological activity, illustrating the potential of helix swapping to introduce desirable biological properties into unrelated or engineered apolipoproteins.
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Affiliation(s)
- Robert S Kiss
- Department of Biochemistry and Protein Engineering Network of Centers of Excellence, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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