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Burdick JP, Basi RS, Burns KS, Weers PMM. The role of C-terminal ionic residues in self-association of apolipoprotein A-I. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184098. [PMID: 36481181 DOI: 10.1016/j.bbamem.2022.184098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 11/15/2022] [Accepted: 11/27/2022] [Indexed: 12/12/2022]
Abstract
Apolipoprotein A-I (apoA-I) is the main protein of high-density lipoprotein and is comprised of a helical bundle domain and a C-terminal (CT) domain encompassing the last ~65 amino acid residues of the 243-residue protein. The CT domain contains three putative helices (helix 8, 9, and 10) and is critical for initiating lipid binding and harbors sites that mediate self-association of the lipid-free protein. Three lysine residues reside in helix-8 (K195, 206, 208), and three in helix-10 (K226, 238, 239). To determine the role of each CT lysine residue in apoA-I self-association, single, double and triple lysine to glutamine mutants were engineered via site-directed mutagenesis. Circular dichroism and chemical denaturation analysis revealed all mutants retained their structural integrity. Chemical crosslinking and size-exclusion chromatography showed a small effect on self-association when helix-8 lysine residues were changed into glutamine. In contrast, mutation of the three helix-10 lysine residues resulted in a predominantly monomeric protein and K226 was identified as a critical residue. When helix-10 glutamate residues 223, 234, or 235 were substituted with glutamine, reduced self-association was observed similar to that of the helix-10 lysine variants, suggesting ionic interactions between these residues. Thus, helix-10 is a critical part of apoA-I mediating self-association, and disruption of ionic interactions changes apoA-I from an oligomeric state into a monomer. Since the helix-10 triple mutant solubilized phospholipid vesicles at higher rates compared to wild-type apoA-I, this indicates monomeric apoA-I is more potent in lipid binding, presumably because helix-10 is fully accessible to interact with lipids.
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Affiliation(s)
- John P Burdick
- Department of Chemistry and Biochemistry, California State University Long Beach, CA 90840, USA
| | - Rohin S Basi
- Department of Chemistry and Biochemistry, California State University Long Beach, CA 90840, USA
| | - Kaitlyn S Burns
- 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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2
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Fadaei R, Davies SS. Oxidative modification of HDL by lipid aldehydes impacts HDL function. Arch Biochem Biophys 2022; 730:109397. [PMID: 36116503 PMCID: PMC9670862 DOI: 10.1016/j.abb.2022.109397] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Accepted: 09/12/2022] [Indexed: 11/21/2022]
Abstract
Reduced levels of high-density lipoprotein (HDL) cholesterol correlate with increased risk for atherosclerotic cardiovascular diseases and HDL performs functions including reverse cholesterol transport, inhibition of lipid peroxidation, and suppression of inflammation, that would appear critical for cardioprotection. However, several large clinical trials utilizing pharmacologic interventions that elevated HDL cholesterol levels failed to provide cardioprotection to at-risk individuals. The reasons for these unexpected results have only recently begun to be elucidated. HDL cholesterol levels and HDL function can be significantly discordant, so that elevating HDL cholesterol levels may not necessarily lead to increased functional capacity, particularly under conditions that cause HDL to become oxidatively modified, resulting in HDL dysfunction. Here we review evidence that oxidative modifications of HDL, including by reactive lipid aldehydes generated by lipid peroxidation, reduce HDL functionality and that dicarbonyl scavengers that protect HDL against lipid aldehyde modification are beneficial in pre-clinical models of atherosclerotic cardiovascular disease.
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Affiliation(s)
- Reza Fadaei
- Sleep Disorders Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran
| | - Sean S Davies
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA.
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3
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Hafiane A, Gianopoulos I, Sorci-Thomas MG, Daskalopoulou SS. Current models of apolipoprotein A-I lipidation by adenosine triphosphate binding cassette transporter A1. Curr Opin Lipidol 2022; 33:139-145. [PMID: 34581311 DOI: 10.1097/mol.0000000000000786] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW The primary cardioprotective function of high-density lipoprotein (HDL) is to remove excess cellular free cholesterol (FC) from peripheral tissues and deliver it to the liver. Here, we summarize recent research that examines apolipoprotein A-I (apoA-I) lipidation models by adenosine triphosphate binding cassette transporter A1 (ABCA1) and discuss its relevance in atherosclerotic cardiovascular disease (ASCVD). RECENT FINDINGS The first step in HDL formation involves the interaction between apoA-I and ABCA1, where ABCA1 mediates the removal of FC and phospholipids from lipid-laden macrophages to form discoidal nascent HDL (nHDL). However, there are currently no clear-cut systematic models that characterize HDL formation. A number of recent studies have investigated the importance of apoA-I C- and N-terminal domains required for optimal cholesterol efflux and nHDL production. Furthermore, functional ABCA1 is required for direct or indirect binding to apoA-I where ABCA1 dimer-monomer interconversion facilitates apoA-I lipidation from plasma membrane microdomains. Microparticles are also another lipid source for apoA-I solubilization into nHDL. SUMMARY ApoA-I and ABCA1 are key factors in macrophage-mediated cholesterol efflux and nHDL production. Understanding of the key steps in HDL formation may unlock the therapeutic potential of HDL and improve clinical management of ASCVD.
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Affiliation(s)
- Anouar Hafiane
- Division of Experimental Medicine, Department of Medicine, Faculty of Medicine, Research Institute of the McGill University Health Centre, McGill University, Montreal, Canada
| | - Ioanna Gianopoulos
- Division of Experimental Medicine, Department of Medicine, Faculty of Medicine, Research Institute of the McGill University Health Centre, McGill University, Montreal, Canada
| | - Mary G Sorci-Thomas
- Division of Endocrinology, Metabolism and Clinical Nutrition, Department of Medicine, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Stella S Daskalopoulou
- Division of Experimental Medicine, Department of Medicine, Faculty of Medicine, Research Institute of the McGill University Health Centre, McGill University, Montreal, Canada
- Division of Internal Medicine, Department of Medicine, Faculty of Medicine, McGill University Health Centre, McGill University Montreal, Montreal, Canada
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4
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Bedi S, Morris J, Shah A, Hart RC, Jerome WG, Aller SG, Tang C, Vaisar T, Bornfeldt KE, Segrest JP, Heinecke JW, Davidson WS. Conformational flexibility of apolipoprotein A-I amino- and carboxy-termini is necessary for lipid binding but not cholesterol efflux. J Lipid Res 2022; 63:100168. [PMID: 35051413 PMCID: PMC8953623 DOI: 10.1016/j.jlr.2022.100168] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 01/03/2022] [Accepted: 01/11/2022] [Indexed: 11/25/2022] Open
Abstract
Because of its critical role in HDL formation, significant efforts have been devoted to studying apolipoprotein A-I (APOA1) structural transitions in response to lipid binding. To assess the requirements for the conformational freedom of its termini during HDL particle formation, we generated three dimeric APOA1 molecules with their termini covalently joined in different combinations. The dimeric (d)-APOA1C-N mutant coupled the C-terminus of one APOA1 molecule to the N-terminus of a second with a short alanine linker, whereas the d-APOA1C-C and d-APOA1N-N mutants coupled the C-termini and the N-termini of two APOA1 molecules, respectively, using introduced cysteine residues to form disulfide linkages. We then tested the ability of these constructs to generate reconstituted HDL by detergent-assisted and spontaneous phospholipid microsolubilization methods. Using cholate dialysis, we demonstrate WT and all APOA1 mutants generated reconstituted HDL particles of similar sizes, morphologies, compositions, and abilities to activate lecithin:cholesterol acyltransferase. Unlike WT, however, the mutants were incapable of spontaneously solubilizing short chain phospholipids into discoidal particles. We found lipid-free d-APOA1C-N and d-APOA1N-N retained most of WT APOA1's ability to promote cholesterol efflux via the ATP binding cassette transporter A1, whereas d-APOA1C-C exhibited impaired cholesterol efflux. Our data support the double belt model for a lipid-bound APOA1 structure in nascent HDL particles and refute other postulated arrangements like the "double super helix." Furthermore, we conclude the conformational freedom of both the N- and C-termini of APOA1 is important in spontaneous microsolubilization of bulk phospholipid but is not critical for ABCA1-mediated cholesterol efflux.
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Affiliation(s)
- Shimpi Bedi
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH, USA
| | - Jamie Morris
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH, USA
| | - Amy Shah
- Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Rachel C Hart
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - W Gray Jerome
- Department of Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Stephen G Aller
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Chongren Tang
- Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA
| | - Tomas Vaisar
- Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA
| | - Karin E Bornfeldt
- Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA
| | - Jere P Segrest
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Jay W Heinecke
- Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA
| | - W Sean Davidson
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH, USA.
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5
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First eight residues of apolipoprotein A-I mediate the C-terminus control of helical bundle unfolding and its lipidation. PLoS One 2020; 15:e0221915. [PMID: 31945064 PMCID: PMC6964839 DOI: 10.1371/journal.pone.0221915] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Accepted: 12/30/2019] [Indexed: 11/23/2022] Open
Abstract
The crystal structure of a C-terminal deletion of apolipoprotein A-I (apoA1) shows a large helical bundle structure in the amino half of the protein, from residues 8 to 115. Using site directed mutagenesis, guanidine or thermal denaturation, cell free liposome clearance, and cellular ABCA1-mediated cholesterol efflux assays, we demonstrate that apoA1 lipidation can occur when the thermodynamic barrier to this bundle unfolding is lowered. The absence of the C-terminus renders the bundle harder to unfold resulting in loss of apoA1 lipidation that can be reversed by point mutations, such as Trp8Ala, and by truncations as short as 8 residues in the amino terminus, both of which facilitate helical bundle unfolding. Locking the bundle via a disulfide bond leads to loss of apoA1 lipidation. We propose a model in which the C-terminus acts on the N-terminus to destabilize this helical bundle. Upon lipid binding to the C-terminus, Trp8 is displaced from its interaction with Phe57, Arg61, Leu64, Val67, Phe71, and Trp72 to destabilize the bundle. However, when the C-terminus is deleted, Trp8 cannot be displaced, the bundle cannot unfold, and apoA1 cannot be lipidated.
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Liu D, Ji L, Zhao M, Wang Y, Guo Y, Li L, Zhang D, Xu L, Pan B, Su J, Xiang S, Pennathur S, Li J, Gao J, Liu P, Willard B, Zheng L. Lysine glycation of apolipoprotein A-I impairs its anti-inflammatory function in type 2 diabetes mellitus. J Mol Cell Cardiol 2018; 122:47-57. [PMID: 30092227 DOI: 10.1016/j.yjmcc.2018.08.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 07/22/2018] [Accepted: 08/01/2018] [Indexed: 12/16/2022]
Abstract
Apolipoprotein A-I (apoA-I), the major protein compontent of high-density lipoprotein (HDL), exerts many anti-atherogenic functions. This study aimed to reveal whether nonenzymatic glycation of specific sites of apoA-I impaired its anti-inflammatory effects in type 2 diabetes mellitus (T2DM). LC-MS/MS was used to analyze the specific sites and the extent of apoA-I glycation either modified by glucose in vitro or isolated from T2DM patients. Cytokine release in THP-1 monocyte-derived macrophages was tested by ELISA. Activation of NF-kappa B pathway was detected by western blot. The binding affinity of apoA-I to THP-1 cells was measured using 125I-labeled apoA-I. We identified seven specific lysine (Lys, K) residues of apoA-I (K12, K23, K40, K96, K106, K107 and K238) that were susceptible to be glycated either in vitro or in vivo. Glycation of apoA-I impaired its abilities to inhibit the release of TNF-α and IL-1β against lipopolysaccharide (LPS) in THP-1 cells. Besides, the glycation levels of these seven K sites in apoA-I were inversely correlated with its anti-inflammatory abilities. Furthermore, glycated apoA-I had a lower affinity to THP-1 cells than native apoA-I had. We generated mutant apoA-I (K107E, M-apoA-I) with a substitution of glutamic acid (Glu, E) for lysine at the 107th site, and found that compared to wild type apoA-I (WT-apoA-I), M-apoA-I decreased its anti-inflammatory effects in THP-1 cells. We also modeled the location of these seven K residues on apoA-I which allowed us to infer the conformational alteration of glycated apoA-I and HDL. In summary, glycation of these seven K residues altered the conformation of apoA-I and consequently impaired the protective effects of apoA-I, which may partly account for the increased risk of cardiovascular disease (CVD) in diabetic subjects.
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Affiliation(s)
- Donghui Liu
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China; Department of Cardiology, the Affiliated Cardiovascular Hospital of Xiamen University, Medical College of Xiamen University, Xiamen, Fujian 361004, China
| | - Liang Ji
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China
| | - Mingming Zhao
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China
| | - Yang Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Yansong Guo
- Department of Cardiovascular Medicine, Fujian Provincial Hospital, Fuzhou, China
| | - Ling Li
- Proteomics Laboratory, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Dongmei Zhang
- Proteomics Laboratory, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Liang Xu
- Department of Cardiology, the First Affiliated Hospital of Fujian Medical University, Fujian 350005, China
| | - Bing Pan
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China
| | - Jinzi Su
- Department of Cardiology, the First Affiliated Hospital of Fujian Medical University, Fujian 350005, China
| | - Song Xiang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, 294 Taiyuan Road, Shanghai 200031, China
| | | | - Jingxuan Li
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China
| | - Jianing Gao
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China
| | - Pingsheng Liu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Belinda Willard
- Proteomics Laboratory, Cleveland Clinic, Cleveland, OH 44195, USA.
| | - Lemin Zheng
- The Institute of Cardiovascular Sciences, Institute of Systems Biomedicine, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, Key Laboratory of Cardiovascular Molecular Biology and Regulatory Peptides, Ministry of Health, Beijing Key Laboratory of Cardiovascular Receptors Research, Peking University Health Science Center, 100191 Beijing, China.
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7
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Fuentes LA, Beck WHJ, Tsujita M, Weers PMM. Charged Residues in the C-Terminal Domain of Apolipoprotein A-I Modulate Oligomerization. Biochemistry 2018; 57:2200-2210. [PMID: 29578333 DOI: 10.1021/acs.biochem.7b01052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Charged residues of the C-terminal domain of human apolipoprotein A-I (apoA-I) were targeted by site-directed mutagenesis. A series of mutant proteins was engineered in which lysine residues (Lys 195, 206, 208, 226, 238, and 239) or glutamate residues (Glu 234 and 235) were replaced by glutamine. The amino acid substitutions did not result in changes in secondary structure content or protein stability. Cross-linking and size-exclusion chromatography showed that the mutations resulted in reduced self-association, generating a predominantly monomeric apoA-I when five or six lysine residues were substituted. The rate of phosphatidylcholine vesicle solubilization was enhanced for all variants, with approximately a threefold rate enhancement for apoA-I lacking Lys 206, 208, 238, and 239, or Glu 234 and 235. Single or double mutations did not change the ability to protect lipolyzed low density lipoprotein from aggregation, but variants lacking >4 lysine residues were less effective in preventing lipoprotein aggregation. ApoA-I mediated cellular lipid efflux from wild-type mice macrophage foam cells was decreased for the variant with five lysine mutations. However, this protein was more effective in releasing cellular phosphatidylcholine and sphingomyelin from Abca1-null mice macrophage foam cells. This suggests that the mutations caused changes in the interaction with ABCA1 transporters and that membrane microsolubilization was primarily responsible for lipid efflux in cells lacking ABCA1. Taken together, this study indicates that ionic interactions in the C-terminal domain of apoA-I favor self-association and that monomeric apoA-I is more active in solubilizing phospholipid bilayers.
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Affiliation(s)
- Lukas A Fuentes
- Department of Chemistry and Biochemistry , California State University Long Beach , Long Beach , California 90840 , United States
| | - Wendy H J Beck
- Department of Chemistry and Biochemistry , California State University Long Beach , Long Beach , California 90840 , United States
| | - Maki Tsujita
- Department of Biochemistry , Nagoya City University Graduate School of Medical Sciences , Aichi 467-8601 , Japan
| | - Paul M M Weers
- Department of Chemistry and Biochemistry , California State University Long Beach , Long Beach , California 90840 , United States
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8
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Expression of the C-terminal domain of human apolipoprotein A-I using a chimeric apolipoprotein. Protein Expr Purif 2017. [PMID: 28624493 DOI: 10.1016/j.pep.2017.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Human apolipoprotein A-I (apoA-I) is the most abundant protein in high-density lipoprotein, an anti-atherogenic lipid-protein complex responsible for reverse cholesterol transport. The protein is composed of an N-terminal helix bundle domain, and a small C-terminal (CT) domain. To facilitate study of CT-apoA-I, a novel strategy was employed to produce this small domain in a bacterial expression system. A protein construct was designed of insect apolipophorin III (apoLp-III) and residues 179-243 of apoA-I, with a unique methionine residue positioned between the two proteins and an N-terminal His-tag to facilitate purification. The chimera was expressed in E. coli, purified by Ni-affinity chromatography, and cleaved by cyanogen bromide. SDS-PAGE revealed the presence of three proteins with masses of 7 kDa (CT-apoA-I), 18 kDa (apoLp-III), and a minor 26 kDa band of uncleaved chimera. The digest was reloaded on the Ni-affinity column to bind apoLp-III and uncleaved chimera, while CT-apoA-I was washed from the column and collected. Alternatively, CT-apoA-I was isolated from the digest by reversed-phase HPLC. CT-apoA-I was α-helical, highly effective in solubilizing phospholipid vesicles and disaggregating LPS micelles. However, CT-apoA-I was less active compared to full-length apoA-I in protecting lipolyzed low density lipoproteins from aggregating, and disrupting phosphatidylglycerol bilayer vesicles. Thus the novel expression system produced mg quantities of functional CT-apoA-I, facilitating structural and functional studies of this critical domain of apoA-I.
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9
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Horn JVC, Ellena RA, Tran JJ, Beck WHJ, Narayanaswami V, Weers PMM. Transfer of C-terminal residues of human apolipoprotein A-I to insect apolipophorin III creates a two-domain chimeric protein with enhanced lipid binding activity. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1317-1325. [PMID: 28434970 DOI: 10.1016/j.bbamem.2017.04.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 04/14/2017] [Accepted: 04/19/2017] [Indexed: 01/11/2023]
Abstract
Apolipophorin III (apoLp-III) is an insect apolipoprotein (18kDa) that comprises a single five-helix bundle domain. In contrast, human apolipoprotein A-I (apoA-I) is a 28kDa two-domain protein: an α-helical N-terminal domain (residues 1-189) and a less structured C-terminal domain (residues 190-243). To better understand the apolipoprotein domain organization, a novel chimeric protein was engineered by attaching residues 179 to 243 of apoA-I to the C-terminal end of apoLp-III. The apoLp-III/apoA-I chimera was successfully expressed and purified in E. coli. Western blot analysis and mass spectrometry confirmed the presence of the C-terminal domain of apoA-I within the chimera. While parent apoLp-III did not self-associate, the chimera formed oligomers similar to apoA-I. The chimera displayed a lower α-helical content, but the stability remained similar compared to apoLp-III, consistent with the addition of a less structured domain. The chimera was able to solubilize phospholipid vesicles at a significantly higher rate compared to apoLp-III, approaching that of apoA-I. The chimera was more effective in protecting phospholipase C-treated low density lipoprotein from aggregation compared to apoLp-III. In addition, binding interaction of the chimera with phosphatidylglycerol vesicles and lipopolysaccharides was considerably improved compared to apoLp-III. Thus, addition of the C-terminal domain of apoA-I to apoLp-III created a two-domain protein, with self-association, lipid and lipopolysaccharide binding properties similar to apoA-I. The apoA-I like behavior of the chimera indicate that these properties are independent from residues residing in the N-terminal domain of apoA-I, and that they can be transferred from apoA-I to apoLp-III.
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Affiliation(s)
- James V C Horn
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, United States
| | - Rachel A Ellena
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, United States
| | - Jesse J Tran
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, United States
| | - Wendy H J Beck
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, United States
| | - Vasanthy Narayanaswami
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, United States
| | - Paul M M Weers
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, United States.
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10
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Mei X, Liu M, Herscovitz H, Atkinson D. Probing the C-terminal domain of lipid-free apoA-I demonstrates the vital role of the H10B sequence repeat in HDL formation. J Lipid Res 2016; 57:1507-17. [PMID: 27317763 DOI: 10.1194/jlr.m068874] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Indexed: 12/23/2022] Open
Abstract
apoA-I plays important structural and functional roles in reverse cholesterol transport. We have described the molecular structure of the N-terminal domain, Δ(185-243) by X-ray crystallography. To understand the role of the C-terminal domain, constructs with sequential elongation of Δ(185-243), by increments of 11-residue sequence repeats were studied and compared with Δ(185-243) and WT apoA-I. Constructs up to residue 230 showed progressively decreased percent α-helix with similar numbers of helical residues, similar detergent and lipid binding affinity, and exposed hydrophobic surface. These observations suggest that the C-terminal domain is unstructured with the exception of the last 11-residue repeat (H10B). Similar monomer-dimer equilibrium suggests that the H10B region is responsible for nonspecific aggregation. Cholesterol efflux progressively increased with elongation up to ∼60% of full-length apoA-I in the absence of the H10B. In summary, the sequential repeats in the C-terminal domain are probably unstructured with the exception of H10B. This segment appears to be responsible for initiation of lipid binding and aggregation, as well as cholesterol efflux, and thus plays a vital role during HDL formation. Based on these observations and the Δ(185-243) crystal structure, we propose a lipid-free apoA-I structural model in solution and update the mechanism of HDL biogenesis.
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Affiliation(s)
- Xiaohu Mei
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - Minjing Liu
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - Haya Herscovitz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
| | - David Atkinson
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
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11
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Salminen A, Åström P, Metso J, Soliymani R, Salo T, Jauhiainen M, Pussinen PJ, Sorsa T. Matrix metalloproteinase 8 degrades apolipoprotein A-I and reduces its cholesterol efflux capacity. FASEB J 2014; 29:1435-45. [PMID: 25550459 DOI: 10.1096/fj.14-262956] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2014] [Accepted: 11/29/2014] [Indexed: 11/11/2022]
Abstract
Various cell types in atherosclerotic lesions express matrix metalloproteinase (MMP)-8. We investigated whether MMP-8 affects the structure and antiatherogenic function of apolipoprotein (apo) A-I, the main protein component of HDL particles. Furthermore, we studied serum lipid profiles and cholesterol efflux capacity in MMP-8-deficient mouse model. Incubation of apoA-I (28 kDa) with activated MMP-8 yielded 22 kDa and 25 kDa apoA-I fragments. Mass spectrometric analyses revealed that apoA-I was cleaved at its carboxyl-terminal part. Treatment of apoA-I and HDL with MMP-8 resulted in significant reduction (up to 84%, P < 0.001) in their ability to facilitate cholesterol efflux from cholesterol-loaded THP-1 macrophages. The cleavage of apoA-I by MMP-8 and the reduction in its cholesterol efflux capacity was inhibited by doxycycline. MMP-8-deficient mice had significantly lower serum triglyceride (TG) levels (P = 0.003) and larger HDL particles compared with wild-type (WT) mice. However, no differences were observed in the apoA-I levels or serum cholesterol efflux capacities between the mouse groups. Proteolytic modification of apoA-I by MMP-8 may impair the first steps of reverse cholesterol transport, leading to increased accumulation of cholesterol in the vessel walls. Eventually, inhibition of MMPs by doxycycline may reduce the risk for atherosclerotic vascular diseases.
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Affiliation(s)
- Aino Salminen
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Pirjo Åström
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Jari Metso
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Rabah Soliymani
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Tuula Salo
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Matti Jauhiainen
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Pirkko J Pussinen
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
| | - Timo Sorsa
- *Institute of Dentistry, University of Helsinki, Helsinki, Finland; Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland; Department of Diagnostics and Oral Medicine, Institute of Dentistry, and Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; National Institute for Health and Welfare, Public Health Genomics Unit, Biomedicum, Helsinki, Finland; Meilahti Clinical Proteomics Core Unit, Department of Biochemistry and Developmental Biology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Finland; and Division of Periodontology, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden
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12
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A novel ApoA-I truncation (ApoA-IMytilene) associated with decreased ApoA-I production. Atherosclerosis 2014; 235:470-6. [DOI: 10.1016/j.atherosclerosis.2014.05.935] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 05/16/2014] [Accepted: 05/20/2014] [Indexed: 11/23/2022]
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13
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Gao D, Willard B, Podrez EA. Analysis of covalent modifications of proteins by oxidized phospholipids using a novel method of peptide enrichment. Anal Chem 2014; 86:1254-62. [PMID: 24350680 DOI: 10.1021/ac4035949] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Free radical-induced oxidation of phospholipids contributes significantly to pathologies associated with inflammation and oxidative stress. Detection of covalent interaction between oxidized phospholipids (oxPL) and proteins by LC-MS/MS could provide valuable information about the molecular mechanisms of oxPL effects. However, such studies are very limited because of significant challenges in detection of the comparatively low levels of oxPL-protein adducts in complex biological systems. Current approaches have several limitations, most important of which is the inability to detect protein modifications by naturally occurring oxPL. We now report, for the first time, an enrichment method that can be applied to the global analysis of protein adducts with various naturally occurring oxPL in relevant biological systems. This method exploits intrinsic properties of peptides modified by oxPL, allowing highly efficient enrichment of oxPL-modified peptides from biological samples. Very low levels of oxPL-protein adducts (<2 ppm) were detected using this enrichment method in combination with LC-MS/MS. We applied the method to several model systems, including oxidation of high density lipoprotein (HDL) and interaction of human platelets with a specific oxPL, and demonstrated its extremely high efficiency and productivity. We report multiple new modifications of apolipoproteins in HDL and proteins in human platelets.
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Affiliation(s)
- Detao Gao
- Department of Molecular Cardiology, Cleveland Clinic, Lerner Research Institute , Cleveland, Ohio 44195, United States
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14
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Leman LJ, Maryanoff BE, Ghadiri MR. Molecules that mimic apolipoprotein A-I: potential agents for treating atherosclerosis. J Med Chem 2013; 57:2169-96. [PMID: 24168751 DOI: 10.1021/jm4005847] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Certain amphipathic α-helical peptides can functionally mimic many of the properties of full-length apolipoproteins, thereby offering an approach to modulate high-density lipoprotein (HDL) for combating atherosclerosis. In this Perspective, we summarize the key findings and advances over the past 25 years in the development of peptides that mimic apolipoproteins, especially apolipoprotein A-I (apoA-I). This assemblage of information provides a reasonably clear picture of the state of the art in the apolipoprotein mimetic field, an appreciation of the potential for such agents in pharmacotherapy, and a sense of the opportunities for optimizing the functional properties of HDL.
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Affiliation(s)
- Luke J Leman
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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15
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Shao B. Site-specific oxidation of apolipoprotein A-I impairs cholesterol export by ABCA1, a key cardioprotective function of HDL. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:490-501. [PMID: 22178192 DOI: 10.1016/j.bbalip.2011.11.011] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 11/18/2011] [Accepted: 11/20/2011] [Indexed: 12/11/2022]
Abstract
The mechanisms that deprive HDL of its cardioprotective properties are poorly understood. One potential pathway involves oxidative damage of HDL proteins by myeloperoxidase (MPO) a heme enzyme secreted by human artery wall macrophages. Mass spectrometric analysis demonstrated that levels of 3-chlorotyrosine and 3-nitrotyrosine - two characteristic products of MPO - are elevated in HDL isolated from patients with established cardiovascular disease. When apolipoprotein A-I (apoA-I), the major HDL protein, is oxidized by MPO, its ability to promote cellular cholesterol efflux by the membrane-associated ATP-binding cassette transporter A1 (ABCA1) pathway is diminished. Biochemical studies revealed that oxidation of specific tyrosine and methionine residues in apoA-I contributes to this loss of ABCA1 activity. Another potential mechanism for generating dysfunctional HDL involves covalent modification of apoA-I by reactive carbonyls, which have been implicated in atherogenesis and diabetic vascular disease. Indeed, modification of apoA-I by malondialdehyde (MDA) or acrolein also markedly impaired the lipoprotein's ability to promote cellular cholesterol efflux by the ABCA1 pathway. Tandem mass spectrometric analyses revealed that these reactive carbonyls target specific Lys residues in the C-terminus of apoA-I. Importantly, immunochemical analyses showed that levels of MDA-protein adducts are elevated in HDL isolated from human atherosclerotic lesions. Also, apoA-I co-localized with acrolein adducts in such lesions. Thus, lipid peroxidation products might specifically modify HDL in vivo. Our observations support the hypotheses that MPO and reactive carbonyls might generate dysfunctional HDL in humans. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).
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Affiliation(s)
- Baohai Shao
- Division of Metabolism, Endocrinology and Nutrition, Diabetes and Obesity Center of Excellence, Department of Medicine, University of Washington, Seattle, WA 98109, USA.
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16
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Lyssenko NN, Hata M, Dhanasekaran P, Nickel M, Nguyen D, Chetty PS, Saito H, Lund-Katz S, Phillips MC. Influence of C-terminal α-helix hydrophobicity and aromatic amino acid content on apolipoprotein A-I functionality. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:456-63. [PMID: 21840419 DOI: 10.1016/j.bbalip.2011.07.020] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 06/30/2011] [Accepted: 07/29/2011] [Indexed: 11/17/2022]
Abstract
The apoA-I molecule adopts a two-domain tertiary structure and the properties of these domains modulate the ability to form HDL particles. Thus, human apoA-I differs from mouse apoA-I in that it can form smaller HDL particles; the C-terminal α-helix is important in this process and human apoA-I is unusual in containing aromatic amino acids in the non-polar face of this amphipathic α-helix. To understand the influence of these aromatic amino acids and the associated high hydrophobicity, apoA-I variants were engineered in which aliphatic amino acids were substituted with or without causing a decrease in overall hydrophobicity. The variants human apoA-I (F225L/F229A/Y236A) and apoA-I (F225L/F229L/A232L/Y236L) were compared to wild-type (WT) apoA-I for their abilities to (1) solubilize phospholipid vesicles and form HDL particles of different sizes, and (2) mediate cellular cholesterol efflux and create nascent HDL particles via ABCA1. The loss of aromatic residues and concomitant decrease in hydrophobicity in apoA-I (F225L/F229A/Y236A) has no effect on protein stability, but reduces by a factor of about three the catalytic efficiencies (V(max)/K(m)) of vesicle solubilization and cholesterol efflux; also, relatively large HDL particles are formed. With apoA-I (F225L/F229L/A232L/Y236L) where the hydrophobicity is restored by the presence of only leucine residues in the helix non-polar face, the catalytic efficiencies of vesicle solubilization and cholesterol efflux are similar to those of WT apoA-I; this variant forms smaller HDL particles. Overall, the results show that the hydrophobicity of the non-polar face of the C-terminal amphipathic α-helix plays a critical role in determining apoA-I functionality but aromatic amino acids are not required. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).
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Affiliation(s)
- Nicholas N Lyssenko
- Lipid Research Group, Gastroenterology, Hepatology and Nutrition Division, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4318, USA
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17
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Shao B, Heinecke JW. Impact of HDL oxidation by the myeloperoxidase system on sterol efflux by the ABCA1 pathway. J Proteomics 2011; 74:2289-99. [PMID: 21501700 DOI: 10.1016/j.jprot.2011.04.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 03/30/2011] [Accepted: 04/02/2011] [Indexed: 12/15/2022]
Abstract
Protein oxidation by phagocytic white blood cells is implicated in tissue injury during inflammation. One important target might be high-density lipoprotein (HDL), which protects against atherosclerosis by removing excess cholesterol from artery wall macrophages. In the human artery wall, cholesterol-laden macrophages are a rich source of myeloperoxidase (MPO), which uses hydrogen peroxide for oxidative reactions in the extracellular milieu. Levels of two characteristic products of MPO-chlorotyrosine and nitrotyrosine-are markedly elevated in HDL from human atherosclerotic lesions. Here, we describe how MPO-dependent chlorination impairs the ability of apolipoprotein A-I (apoA-I), HDL's major protein, to transport cholesterol by the ATP-binding cassette transporter A1 (ABCA1) pathway. Faulty interactions between apoA-I and ABCA1 are involved. Tandem mass spectrometry and investigations of mutated forms of apoA-I demonstrate that tyrosine residues in apoA-I are chlorinated in a site-specific manner by chloramine intermediates on suitably juxtaposed lysine residues. Plasma HDL isolated from subjects with coronary artery disease (CAD) also contains higher levels of chlorinated and nitrated tyrosine residues than HDL from healthy subjects. Thus, the presence of chlorinated HDL might serve as a marker of CAD risk. Because HDL damaged by MPO in vitro becomes dysfunctional, inhibiting MPO in vivo might be cardioprotective.
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Affiliation(s)
- Baohai Shao
- Division of Metabolism, Endocrinology and Nutrition, Diabetes and Obesity Center of Excellence, Department of Medicine, University of Washington, Seattle, WA 98109, USA.
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18
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Abstract
Cholesterol is of vital importance for the human body. It is a constituent for most biological membranes, it is needed for the formation of bile salts, and it is the precursor for steroid hormones and vitamin D. However, the presence of excess cholesterol in cells, and in particular in macrophages in the arterial vessel wall, might be harmful. The accumulation of cholesterol in arteries can lead to atherosclerosis, and in turn, to other cardiovascular diseases. The route that is primarily thought to be responsible for the disposal of cholesterol is called reverse cholesterol transport (RCT). Therefore, RCT is seen as an interesting target for the development of drugs aimed at the prevention of atherosclerosis. Research on RCT has taken off in recent years. In this review, the classical concepts about RCT are discussed, together with new insights about this topic.
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19
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Weers PMM, Patel AB, Wan LCP, Guigard E, Kay CM, Hafiane A, McPherson R, Marcel YL, Kiss RS. Novel N-terminal mutation of human apolipoprotein A-I reduces self-association and impairs LCAT activation. J Lipid Res 2010; 52:35-44. [PMID: 20884842 PMCID: PMC2999918 DOI: 10.1194/jlr.m007500] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We have identified a novel mutation in apoA-I (serine 36 to alanine; S36A) in a human subject with severe hypoalphalipoproteinemia. The mutation is located in the N-terminal region of the protein, which has been implicated in several functions, including lipid binding and lecithin:cholesterol acyltransferase (LCAT) activity. In the present study, the S36A protein was produced recombinantly and characterized both structurally and functionally. While the helical content of the mutant protein was lower compared with wild-type (WT) apoA-I, it retained its helical character. The protein stability, measured as the resistance to guanidine-induced denaturation, decreased significantly. Interestingly, native gel electrophoresis, cross-linking, and sedimentation equilibrium analysis showed that the S36A mutant was primarily present as a monomer, notably different from the WT protein, which showed considerable oligomeric forms. Although the ability of S36A apoA-I to solubilize phosphatidylcholine vesicles and bind to lipoprotein surfaces was not altered, a significantly impaired LCAT activation compared with the WT protein was observed. These results implicate a region around S36 in apoA-I self-association, independent of the intact C terminus. Furthermore, the region around S36 in the N-terminus of human apoA-I is necessary for LCAT activation.
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Affiliation(s)
- Paul M M Weers
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA, USA
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20
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Vedhachalam C, Chetty PS, Nickel M, Dhanasekaran P, Lund-Katz S, Rothblat GH, Phillips MC. Influence of apolipoprotein (Apo) A-I structure on nascent high density lipoprotein (HDL) particle size distribution. J Biol Chem 2010; 285:31965-73. [PMID: 20679346 DOI: 10.1074/jbc.m110.126292] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The principal protein of high density lipoprotein (HDL), apolipoprotein (apo) A-I, in the lipid-free state contains two tertiary structure domains comprising an N-terminal helix bundle and a less organized C-terminal domain. It is not known how the properties of these domains modulate the formation and size distribution of apoA-I-containing nascent HDL particles created by ATP-binding cassette transporter A1 (ABCA1)-mediated efflux of cellular phospholipid and cholesterol. To address this issue, proteins corresponding to the two domains of human apoA-I (residues 1-189 and 190-243) and mouse apoA-I (residues 1-186 and 187-240) together with some human/mouse domain hybrids were examined for their abilities to form HDL particles when incubated with either ABCA1-expressing cells or phospholipid multilamellar vesicles. Incubation of human apoA-I with cells gave rise to two sizes of HDL particles (hydrodynamic diameter, 8 and 10 nm), and removal or disruption of the C-terminal domain eliminated the formation of the smaller particle. Variations in apoA-I domain structure and physical properties exerted similar effects on the rates of formation and sizes of HDL particles created by either spontaneous solubilization of phospholipid multilamellar vesicles or the ABCA1-mediated efflux of cellular lipids. It follows that the sizes of nascent HDL particles are determined at the point at which cellular phospholipid and cholesterol are solubilized by apoA-I; apparently, this is the rate-determining step in the overall ABCA1-mediated cellular lipid efflux process. The stability of the apoA-I N-terminal helix bundle domain and the hydrophobicity of the C-terminal domain are important determinants of both nascent HDL particle size and their rate of formation.
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Affiliation(s)
- Charulatha Vedhachalam
- Lipid Research Group, Gastroenterology, Hepatology, and Nutrition Division, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA
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21
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Fukuda M, Nakano M, Miyazaki M, Handa T. Thermodynamic and Kinetic Stability of Discoidal High-Density Lipoprotein Formation from Phosphatidylcholine/Apolipoprotein A-I Mixture. J Phys Chem B 2010; 114:8228-34. [DOI: 10.1021/jp101071t] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Masakazu Fukuda
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501
| | - Minoru Nakano
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501
| | - Masakazu Miyazaki
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501
| | - Tetsurou Handa
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501
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22
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Shao B, Pennathur S, Pagani I, Oda MN, Witztum JL, Oram JF, Heinecke JW. Modifying apolipoprotein A-I by malondialdehyde, but not by an array of other reactive carbonyls, blocks cholesterol efflux by the ABCA1 pathway. J Biol Chem 2010; 285:18473-84. [PMID: 20378541 DOI: 10.1074/jbc.m110.118182] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Dysfunctional high density lipoprotein (HDL) is implicated in the pathogenesis of cardiovascular disease, but the underlying pathways remain poorly understood. One potential mechanism involves covalent modification by reactive carbonyls of apolipoprotein A-I (apoA-I), the major HDL protein. We therefore determined whether carbonyls resulting from lipid peroxidation (malondialdehyde (MDA) and hydroxynonenal) or carbohydrate oxidation (glycolaldehyde, glyoxal, and methylglyoxal) covalently modify lipid-free apoA-I and inhibit its ability to promote cellular cholesterol efflux by the ABCA1 pathway. MDA markedly impaired the ABCA1 activity of apoA-I. In striking contrast, none of the other four carbonyls were effective. Liquid chromatography-electrospray ionization-tandem mass spectrometry of MDA-modified apoA-I revealed that Lys residues at specific sites had been modified. The chief adducts were MDA-Lys and a Lys-MDA-Lys cross-link. Lys residues in the C terminus of apoA-I were targeted for cross-linking in high yield, and this process may hinder the interaction of apoA-I with lipids and ABCA1, two key steps in reverse cholesterol transport. Moreover, levels of MDA-protein adducts were elevated in HDL isolated from human atherosclerotic lesions, suggesting that lipid peroxidation might render HDL dysfunctional in vivo. Taken together, our observations indicate that MDA damages apoA-I by a pathway that generates lysine adducts at specific sites on the protein. Such damage may facilitate the formation of macrophage foam cells by impairing cholesterol efflux by the ABCA1 pathway.
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Affiliation(s)
- Baohai Shao
- Department of Medicine, University of Washington, Seattle, Washington 98195, USA.
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23
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Kono M, Tanaka T, Tanaka M, Vedhachalam C, Chetty PS, Nguyen D, Dhanasekaran P, Lund-Katz S, Phillips MC, Saito H. Disruption of the C-terminal helix by single amino acid deletion is directly responsible for impaired cholesterol efflux ability of apolipoprotein A-I Nichinan. J Lipid Res 2009; 51:809-18. [PMID: 19805625 DOI: 10.1194/jlr.m002113] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Apolipoprotein A-I (apoA-I) Nichinan, a naturally occurring variant with DeltaE235 in the C terminus, is associated with low plasma HDL levels. Here, we investigated the tertiary structure, lipid-binding properties, and ability to induce cellular cholesterol efflux of apoA-I Nichinan and its C-terminal peptide. Thermal and chemical denaturation experiments demonstrated that the DeltaE235 mutation decreased the protein stability compared with wild type (WT). ApoA-I Nichinan exhibited capabilities to bind to or solubilize lipid vesicles that are intermediate to that of WT and a L230P/L233P/Y236P variant in which the C-terminal alpha-helix folding is completely disrupted and forms relatively larger and unstable discoidal complexes, indicating that perturbation of the C-terminal alpha-helical structure by the DeltaE235 mutation leads to reduced lipid binding. Supporting this, apoA-I 209-241/DeltaE235 peptide showed significantly decreased ability to form alpha-helix both in the lipid-free and lipid-bound states, and reduced efficiency to solubilize vesicles. In addition, both apoA-I Nichinan and its C-terminal peptide exhibited reduced activity in ABCA1-mediated cellular cholesterol efflux. Thus, the disruption of the ability of the C-terminal region to form alpha-helix caused by the E235 deletion appears to be the important determinant of impaired lipid binding and cholesterol efflux ability and, consequently, the low plasma HDL levels of apoA-I Nichinan probands.
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Affiliation(s)
- Momoe Kono
- Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe, Japan
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24
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Narayanaswami V, Kiss RS, Weers PMM. The helix bundle: a reversible lipid binding motif. Comp Biochem Physiol A Mol Integr Physiol 2009; 155:123-33. [PMID: 19770066 DOI: 10.1016/j.cbpa.2009.09.009] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2009] [Revised: 09/09/2009] [Accepted: 09/11/2009] [Indexed: 01/01/2023]
Abstract
Apolipoproteins are the protein components of lipoproteins that have the innate ability to inter convert between a lipid-free and a lipid-bound form in a facile manner, a remarkable property conferred by the helix bundle motif. Composed of a series of four or five amphipathic alpha-helices that fold to form a helix bundle, this motif allows the en face orientation of the hydrophobic faces of the alpha-helices in the protein interior in the lipid-free state. A conformational switch then permits helix-helix interactions to be substituted by helix-lipid interactions upon lipid binding interaction. This review compares the apolipoprotein high-resolution structures and the factors that trigger this switch in insect apolipophorin III and the mammalian apolipoproteins, apolipoprotein E and apolipoprotein A-I, pointing out the commonalities and key differences in the mode of lipid interaction. Further insights into the lipid-bound conformation of apolipoproteins are required to fully understand their functional role under physiological conditions.
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Affiliation(s)
- Vasanthy Narayanaswami
- Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach CA 90840, USA
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25
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Abstract
PURPOSE OF REVIEW The lipid efflux pathway is important for both HDL formation and the reverse cholesterol transport pathway. This review is focused on recent findings on the mechanism of lipid efflux and its regulation, particularly in macrophages. RECENT FINDINGS Significant progress has been made on understanding the sequence of events that accompany the interaction of apolipoproteins A-I with cell surface ATP-binding cassette transporter A1 and its subsequent lipidation. Continued research on the regulation of ATP-binding cassette transporter A1 and ATP-binding cassette transporter G1 expression and traffic has also generated new paradigms for the control of lipid efflux from macrophages and its contribution to reverse cholesterol transport. In addition, the mobilization of cholesteryl esters from lipid droplets represents a new step in the control of cholesterol efflux. SUMMARY The synergy between lipid transporters is a work in progress, but its importance in reverse cholesterol transport is clear. The regulation of efflux implies both the regulation of relevant transporters and the cellular trafficking of cholesterol.
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Affiliation(s)
- Yves L Marcel
- Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
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26
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Gonzalez MC, Toledo JD, Tricerri MA, Garda HA. The central type Y amphipathic α-helices of apolipoprotein AI are involved in the mobilization of intracellular cholesterol depots. Arch Biochem Biophys 2008; 473:34-41. [DOI: 10.1016/j.abb.2008.02.021] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2008] [Revised: 02/14/2008] [Accepted: 02/16/2008] [Indexed: 01/14/2023]
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27
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Hassan HH, Denis M, Lee DYD, Iatan I, Nyholt D, Ruel I, Krimbou L, Genest J. Identification of an ABCA1-dependent phospholipid-rich plasma membrane apolipoprotein A-I binding site for nascent HDL formation: implications for current models of HDL biogenesis. J Lipid Res 2007; 48:2428-42. [PMID: 17656736 DOI: 10.1194/jlr.m700206-jlr200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
It is well accepted that both apolipoprotein A-I (apoA-I) and ABCA1 play crucial roles in HDL biogenesis and in the human atheroprotective system. However, the nature and specifics of apoA-I/ABCA1 interactions remain poorly understood. Here, we present evidence for a new cellular apoA-I binding site having a 9-fold higher capacity to bind apoA-I compared with the ABCA1 site in fibroblasts stimulated with 22-(R)-hydroxycholesterol/9-cis-retinoic acid. This new cellular apoA-I binding site was designated "high-capacity binding site" (HCBS). Glyburide drastically reduced (125)I-apoA-I binding to the HCBS, whereas (125)I-apoA-I showed no significant binding to the HCBS in ABCA1 mutant (Q597R) fibroblasts. Furthermore, reconstituted HDL exhibited reduced affinity for the HCBS. Deletion of the C-terminal region of apoA-I (Delta187-243) drastically reduced the binding of apoA-I to the HCBS. Interestingly, overexpressing various levels of ABCA1 in BHK cells promoted the formation of the HCBS. The majority of the HCBS was localized to the plasma membrane (PM) and was not associated with membrane raft domains. Importantly, treatment of cells with phosphatidylcholine-specific phospholipase C, but not sphingomyelinase, concomitantly reduced the binding of (125)I-apoA-I to the HCBS, apoA-I-mediated cholesterol efflux, and the formation of nascent apoA-I-containing particles. Together, these data suggest that a functional ABCA1 leads to the formation of a major lipid-containing site for the binding and the lipidation of apoA-I at the PM. Our results provide a biochemical basis for the HDL biogenesis pathway that involves both ABCA1 and the HCBS, supporting a two binding site model for ABCA1-mediated nascent HDL genesis.
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Affiliation(s)
- Houssein Hajj Hassan
- Cardiovascular Genetics Laboratory, Cardiology Division, McGill University Health Centre/Royal Victoria Hospital, Montréal, Québec, Canada
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Vedhachalam C, Ghering AB, Davidson WS, Lund-Katz S, Rothblat GH, Phillips MC. ABCA1-induced cell surface binding sites for ApoA-I. Arterioscler Thromb Vasc Biol 2007; 27:1603-9. [PMID: 17478755 DOI: 10.1161/atvbaha.107.145789] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
OBJECTIVE The purpose of this study was to understand the interactions of apoA-I with cells expressing ABCA1. METHODS AND RESULTS The binding of wild-type (WT) and mutant forms of human apoA-I to mouse J774 macrophages was examined. Analysis of total binding at 37 degrees C of 125I-WT apoA-I to the cells and specifically to ABCA1, as determined by covalent cross-linking, revealed saturable high affinity binding in both cases. Determination of the level of cell-surface expression of ABCA1 showed that only about 10% of the apoA-I associated with the cell surface was bound directly to ABCA1. Furthermore, when 125I -apoA-I was cross-linked to ABCA1-upregulated cells and examined by SDS-PAGE, the major (approximately 90%) band migrated as monomeric apoA-I. In contrast to WT apoA-I, the C-terminal deletion mutants delta190 to 243 and delta223 to 243 that have reduced lipid affinity, exhibited marked reductions (50 and 70%, respectively) in their abilities to bind to the surface of ABCA1-upregulated cells. However, these C-terminal deletion mutants cross-linked to ABCA1 as effectively as WT apoA-I. CONCLUSIONS This study demonstrates that ABCA1 activity creates 2 types of high affinity apoA-I binding sites at the cell surface. The low capacity site formed by direct apoA-I/ABCA1 interaction functions in a regulatory role, whereas the much higher capacity site generated by apoA-I/lipid interactions functions in the assembly of nascent HDL particles.
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Affiliation(s)
- Charulatha Vedhachalam
- Division of GI/Nutrition, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4318, USA
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29
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Garda HA. Structure–function relationships in human apolipoprotein A-I: role of a central helix pair. ACTA ACUST UNITED AC 2007. [DOI: 10.2217/17460875.2.1.95] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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30
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Zhu X, Wu G, Zeng W, Xue H, Chen B. Cysteine mutants of human apolipoprotein A-I: a study of secondary structural and functional properties. J Lipid Res 2005; 46:1303-11. [PMID: 15805548 DOI: 10.1194/jlr.m400401-jlr200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Apolipoprotein A-I(Milano) (A-I(M)) (R173C), a natural mutant of human apolipoprotein A-I (apoA-I), and five other cysteine variants of apoA-I at residues 52 (S52C), 74 (N74C), 107 (K107C), 129 (G129C), and 195 (K195C) were generated. Cysteine residues were incorporated in each of the various helices at the same helical wheel position as for the substitution in A-I(M). The secondary structural properties of the monomeric mutants, their abilities to bind lipid and to promote cholesterol efflux from THP-1 macrophages, and the possibility of antiperoxidation were investigated. Results showed that the alpha helical contents of all of the cysteine mutants were similar to that of wild-type apoA-I (wtapoA-I). The cysteine variant of A-I(M) at residue 173 [A-I(M)(R173C)] exhibited weakened structural stability, whereas A-I(G129C) a more stable structure than wtapoA-I. A-I(G129C) and A-I(K195C) exhibited significantly impaired capabilities to bind lipid compared with wtapoA-I. A-I(K107C) possessed a higher capacity to promote cholesterol efflux from macrophages than wtapoA-I, and A-I(M)(R173C) and A-I(K195C) exhibited an impaired efflux capability. Neither A-I(M)(R173C) nor any other cysteine mutant could resist oxidation against lipoxygenase. In summary, in spite of the similar mutant position on the helix, these variants exhibited different structural features or biological activities, suggesting the potential influence of the local environment of mutations on the whole polypeptide chain.
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Affiliation(s)
- Xuewei Zhu
- Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China 100005
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31
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Li L, Chen J, Mishra VK, Kurtz JA, Cao D, Klon AE, Harvey SC, Anantharamaiah GM, Segrest JP. Double belt structure of discoidal high density lipoproteins: molecular basis for size heterogeneity. J Mol Biol 2004; 343:1293-311. [PMID: 15491614 DOI: 10.1016/j.jmb.2004.09.017] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2004] [Revised: 08/24/2004] [Accepted: 09/10/2004] [Indexed: 10/26/2022]
Abstract
We recently proposed an all-atom model for apolipoprotein (apo) A-I in discoidal high-density lipoprotein in which two monomers form stacked antiparallel helical rings rotationally aligned by interhelical salt-bridges. The model can be derived a priori from the geometry of a planar bilayer disc that constrains the hydrophobic face of a continuous amphipathic alpha helix in lipid-associated apoA-I to a plane inside of an alpha-helical torus. This constrains each apoA-I monomer to a novel conformation, that of a slightly unwound, curved, planar amphipathic alpha 11/3 helix (three turns per 11 residues). Using non-denaturing gradient gel electrophoresis, we show that dimyristoylphosphocholine discs containing two apoA-I form five distinct particles with maximal Stokes diameters of 98 A (R2-1), 106 A (R2-2), 110 A (R2-3), 114 A (R2-4) and 120 A (R2-5). Further, we show that the Stokes diameters of R2-1 and R2-2 are independent of the N-terminal 43 residues (the flexible domain) of apoA-I, while the flexible domain is necessary and sufficient for the formation of the three larger complexes. On the basis of these results, the conformation of apoA-I on the R2-2 disc can be modeled accurately as an amphipathic helical double belt extending the full length of the lipid-associating domain with N and C-terminal ends in direct contact. The smallest of the discs, R2-1, models as the R2-2 conformation with an antiparallel 15-18 residue pairwise segment of helixes hinged off the disc edge. The conformations of full-length apoA-I on the flexible domain-dependent discs (R2-3, R2-4 and R2-5) model as the R2-2 conformation extended on the disc edge by one, two or three of the 11-residue tandem amphipathic helical repeats (termed G1, G2 and G3), respectively, contained within the flexible domain. Although we consider these results to favor the double belt model, the topographically very similar hairpin-belt model cannot be ruled out entirely.
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Affiliation(s)
- Ling Li
- Department of Medicine, UAB Medical Center, Birmingham, AL 35294, USA.
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32
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Vedhachalam C, Liu L, Nickel M, Dhanasekaran P, Anantharamaiah GM, Lund-Katz S, Rothblat GH, Phillips MC. Influence of ApoA-I structure on the ABCA1-mediated efflux of cellular lipids. J Biol Chem 2004; 279:49931-9. [PMID: 15383537 DOI: 10.1074/jbc.m406924200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The influence of apolipoprotein (apo) A-I structure on ABCA1-mediated efflux of cellular unesterified (free) cholesterol (FC) and phospholipid (PL) is not well understood. To address this issue, we used a series of apoA-I mutants to examine the contributions of various domains in the molecule to ABCA1-mediated FC and PL efflux from mouse J774 macrophages and human skin fibroblasts. Irrespective of the cell type, deletion or disruption of the C-terminal lipid-binding domain of apoA-I drastically reduced the FC and PL efflux ( approximately 90%), indicating that the C-terminal amphipathic alpha-helix is required for high affinity microsolubilization of FC and PL. Deletion in the N-terminal region of apoA-I also reduced the lipid efflux ( approximately 30%) and increased the K(m) about 2-fold compared with wild type apoA-I, whereas deletion of the central domain (Delta123-166) had no effect on either K(m) or V(max). These results indicate that ABCA1-mediated lipid efflux is relatively insensitive to the organization of the apoA-I N-terminal helix-bundle domain. Alterations in apoA-I structure caused parallel changes in its ability to bind to a PL bilayer and to induce efflux of FC and PL. Overall, these results are consistent with a two-step model for ABCA1-mediated lipid efflux. In the first step, apoA-I binds to ABCA1 and hydrophobic alpha-helices in the C-terminal domain of apoA-I insert into the region of the perturbed PL bilayer created by the PL transport activity of ABCA1, thereby allowing the second step of lipidation of apoA-I and formation of nascent high density lipoprotein particles to occur.
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Affiliation(s)
- Charulatha Vedhachalam
- Division of GI/Nutrition, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA
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33
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Saito H, Dhanasekaran P, Nguyen D, Deridder E, Holvoet P, Lund-Katz S, Phillips MC. α-Helix Formation Is Required for High Affinity Binding of Human Apolipoprotein A-I to Lipids. J Biol Chem 2004; 279:20974-81. [PMID: 15020600 DOI: 10.1074/jbc.m402043200] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein (apo) A-I is thought to undergo a conformational change during lipid association that results in the transition of random coil to alpha-helix. Using a series of deletion mutants lacking different regions along the molecule, we examined the contribution of alpha-helix formation in apoA-I to the binding to egg phosphatidylcholine (PC) small unilamellar vesicles (SUV). Binding isotherms determined by gel filtration showed that apoA-I binds to SUV with high affinity and deletions in the C-terminal region markedly decrease the affinity. Circular dichroism measurements demonstrated that binding to SUV led to an increase in alpha-helix content, but the helix content was somewhat less than in reconstituted discoidal PC.apoA-I complexes for all apoA-I variants, suggesting that the helical structure of apoA-I on SUV is different from that in discs. Isothermal titration calorimetry showed that the binding of apoA-I to SUV is accompanied by a large exothermic heat and deletions in the C-terminal regions greatly decrease the heat. Analysis of the rate of release of heat on binding, as well as the kinetics of quenching of tryptophan fluorescence by brominated PC, indicated that the opening of the N-terminal helix bundle is a rate-limiting step in apoA-I binding to the SUV surface. Significantly, the correlation of thermodynamic parameters of binding with the increase in the number of helical residues revealed that the contribution of alpha-helix formation upon lipid binding to the enthalpy and the free energy of the binding of apoA-I is -1.1 and -0.04 kcal/mol per residue, respectively. These results indicate that alpha-helix formation, especially in the C-terminal regions, provides the energetic source for high affinity binding of apoA-I to lipids.
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Affiliation(s)
- Hiroyuki Saito
- Division of Gastroenterology and Nutrition, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Abramson Research Center, 3625 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA
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34
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Kockx M, Rye KA, Gaus K, Quinn CM, Wright J, Sloane T, Sviridov D, Fu Y, Sullivan D, Burnett JR, Rust S, Assmann G, Anantharamaiah GM, Palgunachari MN, Katz SL, Phillips MC, Dean RT, Jessup W, Kritharides L. Apolipoprotein A-I-stimulated apolipoprotein E secretion from human macrophages is independent of cholesterol efflux. J Biol Chem 2004; 279:25966-77. [PMID: 15066991 DOI: 10.1074/jbc.m401177200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein A-I (apoA-I)-mediated cholesterol efflux involves the binding of apoA-I to the plasma membrane via its C terminus and requires cellular ATP-binding cassette transporter (ABCA1) activity. ApoA-I also stimulates secretion of apolipoprotein E (apoE) from macrophage foam cells, although the mechanism of this process is not understood. In this study, we demonstrate that apoA-I stimulates secretion of apoE independently of both ABCA1-mediated cholesterol efflux and of lipid binding by its C terminus. Pulse-chase experiments using (35)S-labeled cellular apoE demonstrate that macrophage apoE exists in both relatively mobile (E(m)) and stable (E(s)) pools, that apoA-I diverts apoE from degradation to secretion, and that only a small proportion of apoA-I-mobilized apoE is derived from the cell surface. The structural requirements for induction of apoE secretion and cholesterol efflux are clearly dissociated, as C-terminal deletions in recombinant apoA-I reduce cholesterol efflux but increase apoE secretion, and deletion of central helices 5 and 6 decreases apoE secretion without perturbing cholesterol efflux. Moreover, a range of 11- and 22-mer alpha-helical peptides representing amphipathic alpha-helical segments of apoA-I stimulate apoE secretion whereas only the C-terminal alpha-helix (domains 220-241) stimulates cholesterol efflux. Other alpha-helix-containing apolipoproteins (apoA-II, apoA-IV, apoE2, apoE3, apoE4) also stimulate apoE secretion, implying a positive feedback autocrine loop for apoE secretion, although apoE4 is less effective. Finally, apoA-I stimulates apoE secretion normally from macrophages of two unrelated subjects with genetically confirmed Tangier Disease (mutations C733R and c.5220-5222delTCT; and mutations A1046D and c.4629-4630insA), despite severely inhibited cholesterol efflux. We conclude that apoA-I stimulates secretion of apoE independently of cholesterol efflux, and that this represents a novel, ABCA-1-independent, positive feedback pathway for stimulation of potentially anti-atherogenic apoE secretion by alpha-helix-containing molecules including apoA-I and apoE.
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Affiliation(s)
- Maaike Kockx
- Macrophage Biology Group, Centre for Vascular Research, University of New South Wales, Sydney 2052, Australia
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35
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Hersberger M, von Eckardstein A. Low high-density lipoprotein cholesterol: physiological background, clinical importance and drug treatment. Drugs 2004; 63:1907-45. [PMID: 12930163 DOI: 10.2165/00003495-200363180-00003] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Low high-density lipoprotein (HDL) cholesterol is an important risk factor for coronary heart disease (CHD). In vitro, HDL exerts several potentially anti-atherogenic activities. HDLs mediate the reverse cholesterol transport (RCT) from peripheral cells to the liver, inhibit oxidation of low-density lipoprotein (LDL), adhesion of monocytes to the endothelium, apoptosis of vascular endothelial and smooth muscle cells and platelet activation, and stimulate the endothelial secretion of vasoactive substances as well as smooth muscle cell proliferation. Hence, raising HDL-cholesterol levels has become an interesting target for anti-atherosclerotic drug therapy. Levels of HDL cholesterol and the composition of HDL subclasses in plasma are regulated by apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors and cellular transporters. The interplay of these factors leads to RCT and determines the composition and, thereby, the anti-atherogenic properties of HDL. Several inborn errors of metabolism, as well as genetic animal models, are characterised by both elevated HDL cholesterol and increased rather than decreased cardiovascular risk. These findings suggest that the mechanism of HDL modification rather than simply increasing HDL cholesterol determine the efficacy of anti-atherosclerotic drug therapy. In several controlled and prospective intervention studies, patients with low HDL cholesterol and additional risk factors benefited from treatment with fibric acid derivatives (fibrates) or HMG-CoA reductase inhibitors (statins). However, only in some trials was prevention of coronary events in patients with low HDL cholesterol and hypertriglyceridaemia related to an increase in HDL cholesterol. We discuss the clinical and metabolic effects of fibrates, statins, nicotinic acid and sex steroids, and present novel therapeutic strategies that show promise in modifying HDL metabolism. In conclusion, HDL-cholesterol levels increase only moderately after treatment with currently available drugs and do not necessarily correlate with the functionality of HDL. Therefore, the anti-atherosclerotic therapy of high-risk cardiovascular patients should currently be focused on the correction of other risk factors present besides low HDL cholesterol. However, modification of HDL metabolism and improvement of RCT remain an attractive target for the development of new regimens of anti-atherogenic drug therapy.
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Affiliation(s)
- Martin Hersberger
- Institute of Clinical Chemistry, University Hospital Zurich, Zurich, Switzerland
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36
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Denis M, Haidar B, Marcil M, Bouvier M, Krimbou L, Genest J. Molecular and cellular physiology of apolipoprotein A-I lipidation by the ATP-binding cassette transporter A1 (ABCA1). J Biol Chem 2003; 279:7384-94. [PMID: 14660648 DOI: 10.1074/jbc.m306963200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dynamics of ABCA1-mediated apoA-I lipidation were investigated in intact human fibroblasts induced with 22(R)-hydroxycholesterol and 9-cis-retinoic acid (stimulated cells). Specific binding parameters of (125)I-apoA-I to ABCA1 at 37 degrees C were determined: K(d) = 0.65 microg/ml, B(max) = 0.10 ng/microg cell protein. Lipid-free apoA-I inhibited the binding of (125)I-apoA-I to ABCA1 more efficiently than pre-beta(1)-LpA-I, reconstituted HDL particles r(LpA-I), or HDL(3) (IC(50) = 0.35 +/- 1.14, apoA-I; 1.69 +/- 1.07, pre-beta(1)-LpA-I; 17.91 +/- 1.39, r(LpA-I); and 48.15 +/- 1.72 microg/ml, HDL(3)). Treatment of intact cells with either phosphatidylcholine-specific phospholipase C or sphingomyelinase affected neither (125)I-apoA-I binding nor (125)I-apoA-I/ABCA1 cross-linking. We next investigated the dynamics of apoA-I lipidation by monitoring the kinetic of apoA-I dissociation from ABCA1. The dissociation of (125)I-apoA-I from normal cells at 37 degrees C was rapid (t((1/2)) = 1.4 +/- 0.66 h; n = 3) but almost completely inhibited at either 15 or 4 degrees C. A time course analysis of apoA-I-containing particles released during the dissociation period showed nascent apoA-I-phospholipid complexes that exhibited alpha-electrophoretic mobility with a particle size ranging from 9 to 20 nm (designated alpha-LpA-I-like particles), whereas lipid-free apoA-I incubated with ABCA1 mutant (Q597R) cells was unable to form such particles. These results demonstrate that: 1) the physical interaction of apoA-I with ABCA1 does not depend on membrane phosphatidylcholine or sphingomyelin; 2) the association of apoA-I with lipids reduces its ability to interact with ABCA1; and 3) the lipid translocase activity of ABCA1 generates alpha-LpA-I-like particles. This process plays in vivo a key role in HDL biogenesis.
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Affiliation(s)
- Maxime Denis
- Cardiovascular Genetics Laboratory, Cardiology Division, McGill University Health Center, Royal Victoria Hospital, Montréal, Québec H3A 1A1, Canada
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37
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Liu L, Bortnick AE, Nickel M, Dhanasekaran P, Subbaiah PV, Lund-Katz S, Rothblat GH, Phillips MC. Effects of apolipoprotein A-I on ATP-binding cassette transporter A1-mediated efflux of macrophage phospholipid and cholesterol: formation of nascent high density lipoprotein particles. J Biol Chem 2003; 278:42976-84. [PMID: 12928428 DOI: 10.1074/jbc.m308420200] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism of formation of high density lipoprotein (HDL) particles by the action of ATP-binding cassette transporter A1 (ABCA1) is not defined completely. To address this issue, we monitored efflux to apoA-I of phosphatidylcholine (PC), sphingomyelin (SM), and unesterified (free) cholesterol (FC) from J774 macrophages, in which ABCA1 is up-regulated, and investigated the nature of the particles formed. The various apoA-I/lipid particles appearing in the extracellular medium were separated by gel filtration chromatography. The presence of apoA-I in the extracellular medium led to the simultaneous formation of more than one type of poorly lipidated apoA-I-containing particle: there were 9- and 12-nm diameter particles containing approximately 3:1 and 1:1 phospholipid/FC (mol/mol), respectively, which were present together with 6-nm monomeric apoA-I. Removal of the C-terminal alpha-helix (residues 223-243) of apoA-I reduced phospholipid and FC efflux and prevented formation of the 9- and 12-nm HDL particles; the apoA-I variant formed larger particles that eluted in the void volume. FC loading of the J774 cells also led to the formation of larger apoA-I-containing particles that were highly enriched in FC. Besides creating HDL particles, ABCA1 mediated release of larger (20-450-nm diameter) FC-rich particles that were not involved in HDL formation and that are probably membrane vesicles. These particles contained 1:1 PC/SM in contrast to the HDL particles, which contained 2:1 PC/SM. This is consistent with lipid raft and non-raft plasma membrane domains being involved primarily in ABCA1-mediated vesicle release and nascent HDL formation, respectively.
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Affiliation(s)
- Lijuan Liu
- Gastrointestinal/Nutrition Division, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA
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38
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Burgess JW, Boucher J, Neville TAM, Rouillard P, Stamler C, Zachariah S, Sparks DL. Phosphatidylinositol promotes cholesterol transport and excretion. J Lipid Res 2003; 44:1355-63. [PMID: 12700341 DOI: 10.1194/jlr.m300062-jlr200] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Administration of phosphatidylinositol (PI) to New Zealand White rabbits increases HDL negative charge and stimulates reverse cholesterol transport. Intravenously administered PI (10 mg/kg) associated almost exclusively with the HDL fraction in rabbits. PI promoted an increase in the hepatic uptake of plasma free cholesterol (FC) and a 21-fold increase in the biliary secretion of plasma-derived cholesterol. PI also increased cholesterol excretion into the feces by 2.5-fold. PI directly affects cellular cholesterol metabolism. In cholesterol-loaded macrophages, PI stimulated cholesterol mass efflux to lipid-poor reconstituted HDL. PI was about half as effective as cAMP at stimulating efflux, and the effects of cAMP and PI were additive. In cultured HepG2 cells, PI-enriched HDL also enhanced FC uptake from HDL by 3-fold and decreased cellular cholesterol synthesis and esterification. PI enrichment had no effect on the selective uptake of cholesterol esters or on the internalization of HDL particles. PI-dependent metabolic events were efficiently blocked by inhibitors of protein kinase C and the inositol signaling cascade. The data suggest that HDL-PI acts via cell surface ATP binding cassette transporters and signaling pathways to regulate both cellular and intravascular cholesterol homeostasis.
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Affiliation(s)
- Jim W Burgess
- Liponex, Inc., 1740 Woodroffe Ave, Building 400, Ottawa, Ontario, Canada, K2G 3R8
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Yancey PG, Bortnick AE, Kellner-Weibel G, de la Llera-Moya M, Phillips MC, Rothblat GH. Importance of different pathways of cellular cholesterol efflux. Arterioscler Thromb Vasc Biol 2003; 23:712-9. [PMID: 12615688 DOI: 10.1161/01.atv.0000057572.97137.dd] [Citation(s) in RCA: 384] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The removal of excess free cholesterol from cells by HDL or its apolipoproteins is important for maintaining cellular cholesterol homeostasis. This process is most likely compromised in the atherosclerotic lesion because the development of atherosclerosis is associated with low HDL cholesterol. Multiple mechanisms for efflux of cell cholesterol exist. Efflux of free cholesterol via aqueous diffusion occurs with all cell types but is inefficient. Efflux of cholesterol is accelerated when scavenger receptor class-B type I (SR-BI) is present in the cell plasma membrane. Both diffusion-mediated and SR-BI-mediated efflux occur to phospholipid-containing acceptors (ie, HDL and lipidated apolipoproteins); in both cases, the flux of cholesterol is bidirectional, with the direction of net flux depending on the cholesterol gradient. The ATP-binding cassette transporter AI (ABCA1) mediates efflux of both cellular cholesterol and phospholipid. In contrast to SR-BI-mediated flux, efflux via ABCA1 is unidirectional, occurring to lipid-poor apolipoproteins. The relative importance of the SR-BI and ABCA1 efflux pathways in preventing the development of atherosclerotic plaque is not known but will depend on the expression levels of the two proteins and on the type of cholesterol acceptors available.
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Affiliation(s)
- Patricia G Yancey
- Division of Gastroenterology and Nutrition, Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4318, USA
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Marcel YL, Kiss RS. Structure-function relationships of apolipoprotein A-I: a flexible protein with dynamic lipid associations. Curr Opin Lipidol 2003; 14:151-7. [PMID: 12642783 DOI: 10.1097/00041433-200304000-00006] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
PURPOSE OF REVIEW Apolipoprotein A-I is the major structural protein of HDL. Its physicochemical properties maintain a delicate balance between maintenance of stable lipoproteins and the ability to associate with and dissociate from the lipid transported. Here we review the progress made in the last 2-3 years on the structure-function relationships of apolipoprotein A-I, including elements related to the ATP binding cassette transporter A1. RECENT FINDINGS Current evidence now supports the so-called 'belt' or 'hairpin' models for apolipoprotein A-I conformation when bound to discoidal lipoproteins. In-vivo expression of apolipoprotein A-I mutant proteins has shown that both the N- and C-terminal domains are important for lipid association as well as for the esterification reaction, particularly binding of cholesteryl esters and formation of mature alpha-migrating lipoproteins. This property is apparently quite distinct from the activation of the enzyme lecithin cholesterol acyl transferase, which requires interaction with the central helix 6. The interaction of apolipoprotein A-I with the ATP binding cassette transporter A1 has been shown to require the C-terminal domain, which is proposed to mediate the opening of the helix bundle formed by lipid-free or lipid-poor apolipoprotein A-I and allow its association with hydrophobic binding sites. SUMMARY Significant progress has been made in the understanding of the molecular mechanisms controlling the folding of apolipoprotein A-I and its interaction with lipids and various other protein factors involved in HDL metabolism.
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Affiliation(s)
- Yves L Marcel
- Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Room H460, 40 Ruskin Street, Ottawa, Ontario, Canada, K1Y 4W7.
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Lee M, Kovanen PT, Tedeschi G, Oungre E, Franceschini G, Calabresi L. Apolipoprotein composition and particle size affect HDL degradation by chymase: effect on cellular cholesterol efflux. J Lipid Res 2003; 44:539-46. [PMID: 12562834 DOI: 10.1194/jlr.m200420-jlr200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mast cell chymase, a chymotrypsin-like neutral protease, can proteolyze HDL3. Here we studied the ability of rat and human chymase to proteolyze discoidal pre beta-migrating reconstituted HDL particles (rHDLs) containing either apolipoprotein A-I (apoA-I) or apoA-II. Both chymases cleaved apoA-I in rHDL at identical sites, either at the N-terminus (Tyr18 or Phe33) or at the C-terminus (Phe225), so generating three major truncated polypeptides that remained bound to the rHDL. The cleavage sites were independent of the size of the rHDL particles, but small particles were more susceptible to degradation than bigger ones. Chymase-induced truncation of apoA-I yielded functionally compromised rHDL with reduced ability to promote cellular cholesterol efflux. In sharp contrast to apoA-I, apoA-II was resistant to degradation. However, when apoA-II was present in rHDL that also contained apoA-I, it was degraded by chymase. We conclude that chymase reduces the ability of apoA-I in discoidal rHDL particles to induce cholesterol efflux by cleaving off either its amino- or carboxy-terminal portion. This observation supports the concept that limited extracellular proteolysis of apoA-I is one pathophysiologic mechanism leading to the generation and maintenance of foam cells in atherosclerotic lesions.
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Affiliation(s)
- Miriam Lee
- Wihuri Research Institute, Helsinki, Finland
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Chroni A, Liu T, Gorshkova I, Kan HY, Uehara Y, Von Eckardstein A, Zannis VI. The central helices of ApoA-I can promote ATP-binding cassette transporter A1 (ABCA1)-mediated lipid efflux. Amino acid residues 220-231 of the wild-type ApoA-I are required for lipid efflux in vitro and high density lipoprotein formation in vivo. J Biol Chem 2003; 278:6719-30. [PMID: 12488454 DOI: 10.1074/jbc.m205232200] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have mapped the domains of lipid-free apoA-I that promote cAMP-dependent and cAMP-independent cholesterol and phospholipid efflux. The cAMP-dependent lipid efflux in J774 mouse macrophages was decreased by approximately 80-92% by apoA-I[delta(185-243)], only by 15% by apoA-I[delta(1-41)] or apoA-I[delta(1-59)], and was restored to 75-80% of the wild-type apoA-I control value by double deletion mutants apoA-I[delta(1-41)delta(185-243)] and apoA-I[delta(1-59)delta(185-243)]. Similar results were obtained in HEK293 cells transfected with an ATP-binding cassette transporter A1 (ABCA1) expression plasmid. The double deletion mutant of apoA-I had reduced thermal and chemical stability compared with wild-type apoA-I. Sequential carboxyl-terminal deletions showed that cAMP-dependent cholesterol efflux was diminished in all the mutants tested, except the apoA-I[delta(232-243)] which had normal cholesterol efflux. In cAMP-untreated or in mock-transfected cells, cholesterol efflux was not affected by the amino-terminal deletions, but decreased by 30-40% and 50-65% by the carboxyl-terminal and double deletions, respectively. After adenovirus-mediated gene transfer in apoA-I-deficient mice, wild-type apoA-I and apoA-I[delta(1-41)] formed spherical high density lipoprotein (HDL) particles, whereas apoA-I[delta(1-41)delta(185-243)] formed discoidal HDL. The findings suggest that although the central helices of apoA-I alone can promote ABCA1-mediated lipid efflux, residues 220-231 are necessary to allow functional interactions between the full-length apoA-I and ABCA1 that are required for lipid efflux and HDL biogenesis.
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Affiliation(s)
- Angeliki Chroni
- Section of Molecular Genetics, Whitaker Cardiovascular Institute, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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Favari E, Bernini F, Tarugi P, Franceschini G, Calabresi L. The C-terminal domain of apolipoprotein A-I is involved in ABCA1-driven phospholipid and cholesterol efflux. Biochem Biophys Res Commun 2002; 299:801-5. [PMID: 12470649 DOI: 10.1016/s0006-291x(02)02745-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
ABCA1, a member of the ATP-binding cassette family, mediates the efflux of cellular lipids to free apolipoproteins, mainly apoA-I. The role of the C-terminal domain of apoA-I in this process has been evaluated by measuring the efflux capacity of a truncated form (apoA-I-(1-192)) versus intact apoA-I in different cellular models. In stimulated J774 macrophages, cholesterol efflux to apoA-I-(1-192) was remarkably lower than that to the intact apoA-I. The truncated apoA-I, lacking an important lipid-binding domain, was also significantly less efficient in removing phospholipids from stimulated macrophages. No difference was detected with stimulated Tangier fibroblasts that do not express functional ABCA1. The C-terminal domain of apoA-I is clearly involved in ABCA1-driven lipid efflux. Independent of the interaction with the cell surface, it may be the decreased ability of the truncated apoA-I to recruit membrane phospholipids that impairs its capacity to promote cell cholesterol efflux.
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Affiliation(s)
- Elda Favari
- Department of Pharmacological and Biological Sciences, and Applied Chemistry, University of Parma, Parco Area delle Scienze 27/A, 43100 Parma, Italy
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Panagotopulos SE, Witting SR, Horace EM, Hui DY, Maiorano JN, Davidson WS. The role of apolipoprotein A-I helix 10 in apolipoprotein-mediated cholesterol efflux via the ATP-binding cassette transporter ABCA1. J Biol Chem 2002; 277:39477-84. [PMID: 12181325 DOI: 10.1074/jbc.m207005200] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent studies of Tangier disease have shown that the ATP-binding cassette transporter A1 (ABCA1)/apolipoprotein A-I (apoA-I) interaction is critical for high density lipoprotein particle formation, apoA-I integrity, and proper reverse cholesterol transport. However, the specifics of this interaction are unknown. It has been suggested that amphipathic helices of apoA-I bind to a lipid domain created by the ABCA1 transporter. Alternatively, apoA-I may bind directly to ABCA1 itself. To better understand this interaction, we created several truncation mutants of apoA-I and then followed up with more specific point mutants and helix translocation mutants to identify and characterize the locations of apoA-I required for ABCA1-mediated cholesterol efflux. We found that deletion of residues 221-243 (helix 10) abolished ABCA1-mediated cholesterol efflux from cultured RAW mouse macrophages treated with 8-bromo-cAMP. Point mutations in helix 10 that affected the helical charge distribution reduced ABCA1-mediated cholesterol efflux versus the wild type. We noted a strong positive correlation between cholesterol efflux and the lipid binding characteristics of apoA-I when mutations were made in helix 10. However, there was no such correlation for helix translocations in other areas of the protein as long as helix 10 remained intact at the C terminus. From these observations, we propose an alternative model for apolipoprotein-mediated efflux.
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Affiliation(s)
- Stacey E Panagotopulos
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0529, USA
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Sviridov D, Miyazaki O, Theodore K, Hoang A, Fukamachi I, Nestel P. Delineation of the role of pre-beta 1-HDL in cholesterol efflux using isolated pre-beta 1-HDL. Arterioscler Thromb Vasc Biol 2002; 22:1482-8. [PMID: 12231570 DOI: 10.1161/01.atv.0000029120.44088.fe] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The role of pre-beta1-high density lipoprotein (pre-beta1-HDL) in cholesterol efflux was investigated by separating human plasma into purified pre-beta1-HDL and pre-beta1-HDL-deficient plasma by using a monoclonal antibody specifically reacting with pre-beta1-HDL. METHODS AND RESULTS When compared with whole plasma, pre-beta1-HDL-deficient plasma was equally efficient in promoting cholesterol efflux from human skin fibroblasts and THP-1 human macrophage cells. When added at the same apolipoprotein A-I concentration, pre-beta1-HDL was less effective than whole plasma in promoting cholesterol efflux from fibroblasts but equally effective in promoting cholesterol efflux from THP-1 cells. However, pre-beta1-HDL-deficient plasma reconstituted with 16% pre-beta1-HDL was more active than whole plasma, demonstrating that pre-beta1-HDL does promote cholesterol efflux actively. The amount of cellular cholesterol present in reisolated pre-beta1-HDL was 1.5- to 2-fold greater after incubation of the cells with whole plasma than after incubation of the cells with pre-beta1-HDL-deficient plasma or plasma treated with the anti-pre-beta1-HDL antibody. However, the anti-pre-beta1-HDL antibody did not inhibit cholesterol efflux. CONCLUSIONS We conclude that whereas pre-beta1-HDL is capable of taking up cellular cholesterol, its presence in plasma is not essential for cholesterol efflux, at least in vitro. Instead, pre-beta1-HDL may be the first product of apolipoprotein A-I lipidation during the formation of HDL but may not play a major role in transferring cellular cholesterol to HDL.
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MESH Headings
- Antibodies, Monoclonal/metabolism
- Antibodies, Monoclonal/pharmacology
- Biological Transport, Active/drug effects
- Biological Transport, Active/physiology
- Cells, Cultured
- Cholesterol/blood
- Cholesterol/metabolism
- Chromatography, Agarose
- Fibroblasts/metabolism
- High-Density Lipoproteins, Pre-beta
- Humans
- Lipoproteins, HDL/deficiency
- Lipoproteins, HDL/isolation & purification
- Lipoproteins, HDL/physiology
- Macrophages/metabolism
- Plasma/chemistry
- Plasma/immunology
- Plasma/metabolism
- Sepharose/analogs & derivatives
- Sepharose/metabolism
- Skin/cytology
- Time Factors
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Affiliation(s)
- Dmitri Sviridov
- Baker Medical Research Institute, Melbourne, Victoria, Australia.
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Burgess JW, Kiss RS, Zheng H, Zachariah S, Marcel YL. Trypsin-sensitive and lipid-containing sites of the macrophage extracellular matrix bind apolipoprotein A-I and participate in ABCA1-dependent cholesterol efflux. J Biol Chem 2002; 277:31318-26. [PMID: 12050168 DOI: 10.1074/jbc.m204200200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A unique property of the extracellular matrix of J774 and THP-1 cells has been identified, which contributes to the ability of these cells to promote cholesterol efflux. We demonstrate high level apolipoprotein (apo) A-I binding to macrophage cells (THP-1 and J774) and to their extracellular matrix (ECM). However, high level apoA-I binding is not observed on fibroblasts, HepG2 cells, or U937 cells (a macrophage cell line that does not efflux cholesterol to apoA-I or bind apoA-I on their respective ECM). Binding to the ECM of THP-1 or J774 macrophages depends on the presence of apoA-I C-terminal helices and is markedly reduced with a mutant lacking residues 187-243 (apoA-I Delta(187-243)), suggesting that the hydrophobic C terminus forms a hydrophobic interaction with the ECM. ApoA-I binding is lost upon trypsin treatment or with Triton X-100, a preparation method that de-lipidates the ECM. However, binding is recovered with re-lipidation, and is preserved with ECM prepared using cytochalasin B, which conserves the endogenous phospholipid levels of the ECM. We also demonstrate that specific cholesterol efflux to apoA-I is much reduced in cells released from their native ECM, but fully restored when ECM-depleted cells are added back to ECM in the presence of apoA-I. The apoA-I-mediated efflux is deficient in plated or suspension U937 macrophages, but is restored to high levels when the suspension U937 cells are reconstituted with the ECM of J774 cells. The ECM-dependent activity was much reduced in the presence of glyburide, indicating participation of ABCA1 (ATP-binding cassette transporter 1) in the efflux mechanism. These studies establish a novel binding site for apoA-I on the macrophage ECM that may function together with ABCA1 in promoting cholesterol efflux.
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Affiliation(s)
- Jim W Burgess
- Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ontario K1Y 4W7, Canada
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Sviridov D, Hoang A, Huang W, Sasaki J. Structure-function studies of apoA-I variants:site-directed mutagenesis and natural mutations. J Lipid Res 2002. [DOI: 10.1194/jlr.m100437-jlr200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Huang W, Ishii I, Zhang WY, Sonobe M, Kruth HS. PMA activation of macrophages alters macrophage metabolism of aggregated LDL. J Lipid Res 2002. [DOI: 10.1194/jlr.m100436-jlr200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Okon M, Frank PG, Marcel YL, Cushley RJ. Heteronuclear NMR studies of human serum apolipoprotein A-I. Part I. Secondary structure in lipid-mimetic solution. FEBS Lett 2002; 517:139-43. [PMID: 12062424 DOI: 10.1016/s0014-5793(02)02600-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The apolipoprotein A-I (apoA-I) solution structure in the presence of sodium dodecyl sulfate (SDS) was determined by combination of chemical shift index and torsion angle likelihood obtained from shift and sequence similarity methods. ApoA-I in lipid-mimetic solution is composed of alpha-helices (residues 8-32, 45-64, 67-77, 82-86, 90-97, 100-118, 122-140, 146-162, 167-205, 210-216 and 221-239), with 2-5 residue irregular segments between helical repeats, and the irregular segment 78-81 within helical repeat 2. ApoA-I is a monomer in the SDS complex and no evidence of interhelical interactions is found. Comparison of the apoA-I and apoA-I(1-186) [Okon et al., FEBS Lett. 487 (2001) 390-396] solution structures revealed that apoA-I undergoes a conformational change around Pro121.
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Affiliation(s)
- Mark Okon
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada.
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Experimental and computational studies of the interactions of amphipathic peptides with lipid surfaces. CURRENT TOPICS IN MEMBRANES 2002. [DOI: 10.1016/s1063-5823(02)52016-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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