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Fung KYY, Ho TWW, Xu Z, Neculai D, Beauchemin CAA, Lee WL, Fairn GD. Apolipoprotein A1 and high-density lipoprotein limit low-density lipoprotein transcytosis by binding SR-B1. J Lipid Res 2024; 65:100530. [PMID: 38479648 PMCID: PMC11004410 DOI: 10.1016/j.jlr.2024.100530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Revised: 02/27/2024] [Accepted: 02/29/2024] [Indexed: 04/09/2024] Open
Abstract
Atherosclerosis results from the deposition and oxidation of LDL and immune cell infiltration in the sub-arterial space leading to arterial occlusion. Studies have shown that transcytosis transports circulating LDL across endothelial cells lining blood vessels. LDL transcytosis is initiated by binding to either scavenger receptor B1 (SR-B1) or activin A receptor-like kinase 1 on the apical side of endothelial cells leading to its transit and release on the basolateral side. HDL is thought to partly protect individuals from atherosclerosis due to its ability to remove excess cholesterol and act as an antioxidant. Apolipoprotein A1 (APOA1), an HDL constituent, can bind to SR-B1, raising the possibility that APOA1/HDL can compete with LDL for SR-B1 binding, thereby limiting LDL deposition in the sub-arterial space. To examine this possibility, we used in vitro approaches to quantify the internalization and transcytosis of fluorescent LDL in coronary endothelial cells. Using microscale thermophoresis and affinity capture, we find that SR-B1 and APOA1 interact and that binding is enhanced when using the cardioprotective variant of APOA1 termed Milano (APOA1-Milano). In male mice, transiently increasing the levels of HDL reduced the acute deposition of fluorescently labeled LDL in the atheroprone inner curvature of the aorta. Reduced LDL deposition was also observed when increasing circulating wild-type APOA1 or the APOA1-Milano variant, with a more robust inhibition from the APOA1-Milano. The results suggest that HDL may limit SR-B1-mediated LDL transcytosis and deposition, adding to the mechanisms by which it can act as an atheroprotective particle.
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Affiliation(s)
- Karen Y Y Fung
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada; Keenan Research Centre, St. Michael's Hospital, Unity Health Toronto, Toronto, Ontario, Canada
| | - Tse Wing Winnie Ho
- Keenan Research Centre, St. Michael's Hospital, Unity Health Toronto, Toronto, Ontario, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Zizhen Xu
- Department of Cell Biology, and Department of Pathology Sir Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Dante Neculai
- Department of Cell Biology, and Department of Pathology Sir Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Catherine A A Beauchemin
- Department of Physics, Toronto Metropolitan University, Toronto, Ontario, Canada; Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program, RIKEN, Wako, Saitama, Japan
| | - Warren L Lee
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada; Keenan Research Centre, St. Michael's Hospital, Unity Health Toronto, Toronto, Ontario, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada; Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada.
| | - Gregory D Fairn
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada; Keenan Research Centre, St. Michael's Hospital, Unity Health Toronto, Toronto, Ontario, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada; Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
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2
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Chanthamontri CK, Jordan DS, Wang W, Wu C, Lin Y, Brett TJ, Gross ML, Leung DW. The Ebola Viral Protein 35 N-Terminus Is a Parallel Tetramer. Biochemistry 2019; 58:657-664. [PMID: 30592210 DOI: 10.1021/acs.biochem.8b01154] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Members of Mononegavirales, the order that includes nonsegmented negative sense RNA viruses (NNSVs), encode a small number of multifunctional proteins. In members of the Filoviridae family, virus protein 35 (VP35) facilitates immune evasion and functions as an obligatory cofactor for viral RNA synthesis. VP35 functions in a manner orthologous to that of phosphoproteins from other NNSVs. Although the critical roles of Ebola viral VP35 (eVP35) in immune evasion and RNA synthesis are well-appreciated, a complete understanding of its organization and its role in carrying out its many functions has yet to be fully realized. In particular, we currently lack information about the role of the oligomerization domain within eVP35. To address this limitation, we report here an investigation of the oligomer structure of eVP35 using hybrid methods that include multiangle light scattering, small-angle X-ray scattering, and cross-linking coupled with mass spectrometry to determine the shape and orientation of the eVP35 oligomer. Our integrative results are consistent with a parallel tetramer in which the N-terminal regions that are required for RNA synthesis are all oriented in the same direction. Furthermore, these results define a framework for targeting the symmetric tetramer for structure-based antiviral discovery.
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Affiliation(s)
- Chamnongsak Ken Chanthamontri
- Department of Chemistry , Washington University in St. Louis , Box 1134, One Brookings Drive , St. Louis , Missouri 63130 , United States
| | - David S Jordan
- Department of Pathology and Immunology , Washington University School of Medicine in St. Louis , St. Louis , Missouri 63110 , United States
| | - Wenjie Wang
- Department of Pathology and Immunology , Washington University School of Medicine in St. Louis , St. Louis , Missouri 63110 , United States
| | - Chao Wu
- Department of Pathology and Immunology , Washington University School of Medicine in St. Louis , St. Louis , Missouri 63110 , United States
| | - Yanchun Lin
- Department of Chemistry , Washington University in St. Louis , Box 1134, One Brookings Drive , St. Louis , Missouri 63130 , United States
| | - Tom J Brett
- Department of Medicine , Washington University School of Medicine in St. Louis , St. Louis , Missouri 63110 , United States
| | - Michael L Gross
- Department of Chemistry , Washington University in St. Louis , Box 1134, One Brookings Drive , St. Louis , Missouri 63130 , United States
| | - Daisy W Leung
- Department of Pathology and Immunology , Washington University School of Medicine in St. Louis , St. Louis , Missouri 63110 , United States
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3
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Lee MH, Appleton KM, El-Shewy HM, Sorci-Thomas MG, Thomas MJ, Lopes-Virella MF, Luttrell LM, Hammad SM, Klein RL. S1P in HDL promotes interaction between SR-BI and S1PR1 and activates S1PR1-mediated biological functions: calcium flux and S1PR1 internalization. J Lipid Res 2016; 58:325-338. [PMID: 27881715 DOI: 10.1194/jlr.m070706] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 11/10/2016] [Indexed: 01/01/2023] Open
Abstract
HDL normally transports about 50-70% of plasma sphingosine 1-phosphate (S1P), and the S1P in HDL reportedly mediates several HDL-associated biological effects and signaling pathways. The HDL receptor, SR-BI, as well as the cell surface receptors for S1P (S1PRs) may be involved partially and/or completely in these HDL-induced processes. Here we investigate the nature of the HDL-stimulated interaction between the HDL receptor, SR-BI, and S1PR1 using a protein-fragment complementation assay and confocal microscopy. In both primary rat aortic vascular smooth muscle cells and HEK293 cells, the S1P content in HDL particles increased intracellular calcium concentration, which was mediated by S1PR1. Mechanistic studies performed in HEK293 cells showed that incubation of cells with HDL led to an increase in the physical interaction between the SR-BI and S1PR1 receptors that mainly occurred on the plasma membrane. Model recombinant HDL (rHDL) particles formed in vitro with S1P incorporated into the particle initiated the internalization of S1PR1, whereas rHDL without supplemented S1P did not, suggesting that S1P transported in HDL can selectively activate S1PR1. In conclusion, these data suggest that S1P in HDL stimulates the transient interaction between SR-BI and S1PRs that can activate S1PRs and induce an elevation in intracellular calcium concentration.
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Affiliation(s)
- Mi-Hye Lee
- Division of Endocrinology, Metabolism, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, SC
| | - Kathryn M Appleton
- Department of Pharmaceutical & Biomedical Sciences, College of Pharmacy, Medical University of South Carolina, Charleston, SC
| | - Hesham M El-Shewy
- Division of Endocrinology, Metabolism, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, SC
| | - Mary G Sorci-Thomas
- Division of Endocrinology, Metabolism, and Clinical Nutrition, Department of Medicine, Medical College of Wisconsin, Milwaukee, WI
| | - Michael J Thomas
- Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI
| | - Maria F Lopes-Virella
- Division of Endocrinology, Metabolism, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, SC.,Research Service, Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC
| | - Louis M Luttrell
- Division of Endocrinology, Metabolism, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, SC.,Department of Pharmaceutical & Biomedical Sciences, College of Pharmacy, Medical University of South Carolina, Charleston, SC.,Research Service, Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC
| | - Samar M Hammad
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC
| | - Richard L Klein
- Division of Endocrinology, Metabolism, and Medical Genetics, Department of Medicine, Medical University of South Carolina, Charleston, SC .,Research Service, Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC
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4
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Bisgaier CL, Ackermann R, Rea T, Rodrigueza WV, Hartman D. ApoA-IMilano phospholipid complex (ETC-216) infusion in human volunteers. Insights into the phenotypic characteristics of ApoA-IMilano carriers. Pharmacol Res 2016; 111:86-99. [DOI: 10.1016/j.phrs.2016.05.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2015] [Revised: 05/02/2016] [Accepted: 05/02/2016] [Indexed: 12/15/2022]
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5
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Pollard RD, Fulp B, Sorci-Thomas MG, Thomas MJ. High-Density Lipoprotein Biogenesis: Defining the Domains Involved in Human Apolipoprotein A-I Lipidation. Biochemistry 2016; 55:4971-81. [PMID: 27501467 DOI: 10.1021/acs.biochem.6b00347] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The first step in removing cholesterol from a cell is the ATP-binding cassette transporter 1 (ABCA1)-driven transfer of cholesterol to lipid-free or lipid-poor apolipoprotein A-I (apoA-I), which yields cholesterol-rich nascent high-density lipoprotein (nHDL) that then matures in plasma to spherical, cholesteryl ester-rich HDL. However, lipid-free apoA-I has a three-dimensional (3D) conformation that is significantly different from that of lipidated apoA-I on nHDL. By comparing the lipid-free apoA-I 3D conformation of apoA-I to that of 9-14 nm diameter nHDL, we formulated the hypothetical helical domain transitions that might drive particle formation. To test the hypothesis, ten apoA-I mutants were prepared that contained two strategically placed cysteines several of which could form intramolecular disulfide bonds and others that could not form these bonds. Mass spectrometry was used to identify amino acid sequence and intramolecular disulfide bond formation. Recombinant HDL (rHDL) formation was assessed with this group of apoA-I mutants. ABCA1-driven nHDL formation was measured in four mutants and wild-type apoA-I. The mutants contained cysteine substitutions in one of three regions: the N-terminus, amino acids 34 and 55 (E34C to S55C), central domain amino acids 104 and 162 (F104C to H162C), and the C-terminus, amino acids 200 and 233 (L200C to L233C). Mutants were studied in the locked form, with an intramolecular disulfide bond present, or unlocked form, with the cysteine thiol blocked by alkylation. Only small amounts of rHDL or nHDL were formed upon locking the central domain. We conclude that both the N- and C-terminal ends assist in the initial steps in lipid acquisition, but that opening of the central domain was essential for particle formation.
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Affiliation(s)
- Ricquita D Pollard
- Section on Molecular Medicine, Department of Internal Medicine, Wake Forest School of Medicine , Winston-Salem, North Carolina 27101, United States
| | - Brian Fulp
- Department of Biochemistry, Wake Forest School of Medicine , Winston-Salem, North Carolina 27101, United States
| | - Mary G Sorci-Thomas
- Departments of Medicine, Division of Endocrinology, Pharmacology and Toxicology, and Blood Research Institute, BloodCenter of Wisconsin, Medical College of Wisconsin , Milwaukee, Wisconsin 53226, United States
| | - Michael J Thomas
- Department of Pharmacology and Toxicology, Medical College of Wisconsin , 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, United States
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6
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Gogonea V. Structural Insights into High Density Lipoprotein: Old Models and New Facts. Front Pharmacol 2016; 6:318. [PMID: 26793109 PMCID: PMC4709926 DOI: 10.3389/fphar.2015.00318] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Accepted: 12/22/2015] [Indexed: 11/13/2022] Open
Abstract
The physiological link between circulating high density lipoprotein (HDL) levels and cardiovascular disease is well-documented, albeit its intricacies are not well-understood. An improved appreciation of HDL function and overall role in vascular health and disease requires at its foundation a better understanding of the lipoprotein's molecular structure, its formation, and its process of maturation through interactions with various plasma enzymes and cell receptors that intervene along the pathway of reverse cholesterol transport. This review focuses on summarizing recent developments in the field of lipid free apoA-I and HDL structure, with emphasis on new insights revealed by newly published nascent and spherical HDL models constructed by combining low resolution structures obtained from small angle neutron scattering (SANS) with contrast variation and geometrical constraints derived from hydrogen-deuterium exchange (HDX), crosslinking mass spectrometry, electron microscopy, Förster resonance energy transfer, and electron spin resonance. Recently published low resolution structures of nascent and spherical HDL obtained from SANS with contrast variation and isotopic labeling of apolipoprotein A-I (apoA-I) will be critically reviewed and discussed in terms of how they accommodate existing biophysical structural data from alternative approaches. The new low resolution structures revealed and also provided some answers to long standing questions concerning lipid organization and particle maturation of lipoproteins. The review will discuss the merits of newly proposed SANS based all atom models for nascent and spherical HDL, and compare them with accepted models. Finally, naturally occurring and bioengineered mutations in apoA-I, and their impact on HDL phenotype, are reviewed and discuss together with new therapeutics employed for restoring HDL function.
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Affiliation(s)
- Valentin Gogonea
- Department of Chemistry, Cleveland State UniversityCleveland, OH, USA; Departments of Cellular and Molecular Medicine and the Center for Cardiovascular Diagnostics and Prevention, Cleveland ClinicCleveland, OH, USA
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7
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Pollard RD, Blesso CN, Zabalawi M, Fulp B, Gerelus M, Zhu X, Lyons EW, Nuradin N, Francone OL, Li XA, Sahoo D, Thomas MJ, Sorci-Thomas MG. Procollagen C-endopeptidase Enhancer Protein 2 (PCPE2) Reduces Atherosclerosis in Mice by Enhancing Scavenger Receptor Class B1 (SR-BI)-mediated High-density Lipoprotein (HDL)-Cholesteryl Ester Uptake. J Biol Chem 2015; 290:15496-15511. [PMID: 25947382 DOI: 10.1074/jbc.m115.646240] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Indexed: 01/28/2023] Open
Abstract
Studies in human populations have shown a significant correlation between procollagen C-endopeptidase enhancer protein 2 (PCPE2) single nucleotide polymorphisms and plasma HDL cholesterol concentrations. PCPE2, a 52-kDa glycoprotein located in the extracellular matrix, enhances the cleavage of C-terminal procollagen by bone morphogenetic protein 1 (BMP1). Our studies here focused on investigating the basis for the elevated concentration of enlarged plasma HDL in PCPE2-deficient mice to determine whether they protected against diet-induced atherosclerosis. PCPE2-deficient mice were crossed with LDL receptor-deficient mice to obtain LDLr(-/-), PCPE2(-/-) mice, which had elevated HDL levels compared with LDLr(-/-) mice with similar LDL concentrations. We found that LDLr(-/-), PCPE2(-/-) mice had significantly more neutral lipid and CD68+ infiltration in the aortic root than LDLr(-/-) mice. Surprisingly, in light of their elevated HDL levels, the extent of aortic lipid deposition in LDLr(-/-), PCPE2(-/-) mice was similar to that reported for LDLr(-/-), apoA-I(-/-) mice, which lack any apoA-I/HDL. Furthermore, LDLr(-/-), PCPE2(-/-) mice had reduced HDL apoA-I fractional clearance and macrophage to fecal reverse cholesterol transport rates compared with LDLr(-/-) mice, despite a 2-fold increase in liver SR-BI expression. PCPE2 was shown to enhance SR-BI function by increasing the rate of HDL-associated cholesteryl ester uptake, possibly by optimizing SR-BI localization and/or conformation. We conclude that PCPE2 is atheroprotective and an important component of the reverse cholesterol transport HDL system.
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Affiliation(s)
- Ricquita D Pollard
- Section of Molecular Medicine, Department of Internal Medicine and the Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101
| | - Christopher N Blesso
- Department of Nutritional Sciences, University of Connecticut, Storrs, Connecticut 06268
| | - Manal Zabalawi
- Section of Molecular Medicine, Department of Internal Medicine and the Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101
| | - Brian Fulp
- Section of Molecular Medicine, Department of Internal Medicine and the Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101
| | - Mark Gerelus
- Section of Molecular Medicine, Department of Internal Medicine and the Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101
| | - Xuewei Zhu
- Section of Molecular Medicine, Department of Internal Medicine and the Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101
| | - Erica W Lyons
- Section of Molecular Medicine, Department of Internal Medicine and the Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101
| | - Nebil Nuradin
- Department of Medicine and the Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Omar L Francone
- Shire Human Genetic Therapies, Lexington, Massachusetts 02421
| | - Xiang-An Li
- Department of Pediatrics, University of Kentucky, Lexington, Kentucky 40506
| | - Daisy Sahoo
- Department of Medicine and the Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Michael J Thomas
- Department of Medicine and the Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Mary G Sorci-Thomas
- Department of Medicine and the Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
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8
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Takahashi D, Dai H, Hiromasa Y, Krishnamoorthi R, Kanost MR. Self-association of an insect β-1,3-glucan recognition protein upon binding laminarin stimulates prophenoloxidase activation as an innate immune response. J Biol Chem 2014; 289:28399-410. [PMID: 25147183 DOI: 10.1074/jbc.m114.583971] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insect β-glucan recognition protein (βGRP), a pathogen recognition receptor for innate immune responses, detects β-1,3-glucan on fungal surfaces via its N-terminal carbohydrate-binding domain (N-βGRP) and triggers serine protease cascades for the activation of prophenoloxidase (pro-PO) or Toll pathways. Using biophysical and biochemical methods, we characterized the interaction of the N-terminal domain from Manduca sexta βGRP2 (N-βGRP2) with laminarin, a soluble form of β-1,3-glucan. We found that carbohydrate binding by N-βGRP2 induces the formation of two types of protein-carbohydrate complexes, depending on the molar ratio of carbohydrate to protein ([C]/[P]). Precipitation, analytical ultracentrifugation, and chemical cross-linking experiments have shown that an insoluble aggregate forms when the molar ratio of carbohydrate to protein is low ([C]/[P] ∼ 1). In contrast, a soluble complex, containing at least five N-βGRP2 molecules forms at a higher molar ratio of carbohydrate/protein ([C]/[P] >5). A hypothesis that this complex is assembled partly due to protein-protein interactions was supported by chemical cross-linking experiments combined with LC-MS/MS spectrometry analysis, which permitted identification of a specific intermolecular cross-link site between N-βGRP molecules in the soluble complex. The pro-PO activation in naive plasma was strongly stimulated by addition of the insoluble aggregates of N-βGRP2. The soluble complex with laminarin formed in the plasma also stimulated pro-PO activation, but at a lower level. Taken together, these results provide experimental evidence for novel mechanisms in which associations of βGRP with microbial polysaccharide promotes assembly of βGRP oligomers, which may form a platform needed to trigger the pro-PO pathway activation cascade.
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Affiliation(s)
- Daisuke Takahashi
- From the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Huaien Dai
- From the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Yasuaki Hiromasa
- From the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Ramaswamy Krishnamoorthi
- From the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Michael R Kanost
- From the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
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9
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Pollard RD, Fulp B, Samuel MP, Sorci-Thomas MG, Thomas MJ. The conformation of lipid-free human apolipoprotein A-I in solution. Biochemistry 2013; 52:9470-81. [PMID: 24308268 DOI: 10.1021/bi401080k] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Apolipoprotein AI (apoA-I) is the principal acceptor of lipids from ATP-binding cassette transporter A1, a process that yields nascent high density lipoproteins. Analysis of lipidated apoA-I conformation yields a belt or twisted belt in which two strands of apoA-I lie antiparallel to one another. In contrast, biophysical studies have suggested that a part of lipid-free apoA-I was arranged in a four-helix bundle. To understand how lipid-free apoA-I opens from a bundle to a belt while accepting lipid it was necessary to have a more refined model for the conformation of lipid-free apoA-I. This study reports the conformation of lipid-free human apoA-I using lysine-to-lysine chemical cross-linking in conjunction with disulfide cross-linking achieved using selective cysteine mutations. After proteolysis, cross-linked peptides were verified by sequencing using tandem mass spectrometry. The resulting structure is compact with roughly four helical regions, amino acids 44-186, bundled together. C- and N-terminal ends, amino acids 1-43 and 187-243, respectively, are folded such that they lie close to one another. An unusual feature of the molecule is the high degree of connectivity of lysine40 with six other lysines, lysines that are close, for example, lysine59, to distant lysines, for example, lysine239, that are at the opposite end of the primary sequence. These results are compared and contrasted with other reported conformations for lipid-free human apoA-I and an NMR study of mouse apoA-I.
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Affiliation(s)
- Ricquita D Pollard
- Department of Biochemistry and ‡Department of Pathology, Section on Lipid Sciences, Wake Forest School of Medicine , Medical Center Blvd, Winston-Salem, North Carolina 27157-1016, United States
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10
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Abstract
PURPOSE OF REVIEW New therapeutic strategies are needed for the rapid stabilization of acute coronary syndrome (ACS) patients by treating nonculprit lesions. Reconstituted HDL (rHDL), which is apoA-I combined with phospholipids, is currently being tested in clinical trials for this purpose and is the subject of this review. RECENT FINDINGS At least four different formulations (SRC-rHDL, CSL-111, CSL-112 and ETC-216) have been tested in clinical trials. The various rHDL preparations have been shown to be effective in the rapid mobilization of excess cholesterol from cells and in regressing atherosclerotic plaques in animal models. Two of the rHDL agents, namely ETC-216 and CSL-111, have been shown to be effective after only a few treatments in reducing plaque volume in ACS patients, as assessed by intravascular ultrasound, but no clinical trials assessing clinical endpoints have yet been completed. SUMMARY rHDL is a promising new potential therapy for ACS patients, but much work remains to be done, and there are many unresolved questions. Progress in developing rHDL into a therapy will depend on improving our understanding of their mechanism of action, determining the optimum formulation and delivery and how to monitor rHDL therapy.
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Affiliation(s)
- Brian R Krause
- aAlphaCore Pharma, Ann Arbor, Michigan bLipoprotein Metabolism Section, Cardiopulmonary Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
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11
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Gursky O, Jones MK, Mei X, Segrest JP, Atkinson D. Structural basis for distinct functions of the naturally occurring Cys mutants of human apolipoprotein A-I. J Lipid Res 2013; 54:3244-57. [PMID: 24038317 DOI: 10.1194/jlr.r037911] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
HDL removes cell cholesterol and protects against atherosclerosis. ApoA-I provides a flexible structural scaffold and an important functional ligand on the HDL surface. We propose structural models for apoA-I(Milano) (R173C) and apoA-I(Paris) (R151C) mutants that show high cardioprotection despite low HDL levels. Previous studies established that two apoA-I molecules encircle HDL in an antiparallel, helical double-belt conformation. Recently, we solved the atomic structure of lipid-free Δ(185-243)apoA-I and proposed a conformational ensemble for apoA-I(WT) on HDL. Here we modify this ensemble to understand how intermolecular disulfides involving C173 or C151 influence protein conformation. The double-belt conformations are modified by belt rotation, main-chain unhinging around Gly, and Pro-induced helical bending, and they are verified by comparison with previous experimental studies and by molecular dynamics simulations of apoA-I(Milano) homodimer. In our models, the molecular termini repack on various-sized HDL, while packing around helix-5 in apoA-I(WT), helix-6 in apoA-I(Paris), or helix-7 in apoA-I(Milano) homodimer is largely conserved. We propose how the disulfide-induced constraints alter the protein conformation and facilitate dissociation of the C-terminal segment from HDL to recruit additional lipid. Our models unify previous studies of apoA-I(Milano) and demonstrate how the mutational effects propagate to the molecular termini, altering their conformations, dynamics, and function.
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Affiliation(s)
- Olga Gursky
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118
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12
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Sorci-Thomas MG, Owen JS, Fulp B, Bhat S, Zhu X, Parks JS, Shah D, Jerome WG, Gerelus M, Zabalawi M, Thomas MJ. Nascent high density lipoproteins formed by ABCA1 resemble lipid rafts and are structurally organized by three apoA-I monomers. J Lipid Res 2012; 53:1890-909. [PMID: 22750655 PMCID: PMC3413229 DOI: 10.1194/jlr.m026674] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Revised: 06/29/2012] [Indexed: 12/29/2022] Open
Abstract
This report details the lipid composition of nascent HDL (nHDL) particles formed by the action of the ATP binding cassette transporter A1 (ABCA1) on apolipoprotein A-I (apoA-I). nHDL particles of different size (average diameters of ∼ 12, 10, 7.5, and <6 nm) and composition were purified by size-exclusion chromatography. Electron microscopy suggested that the nHDL were mostly spheroidal. The proportions of the principal nHDL lipids, free cholesterol, glycerophosphocholine, and sphingomyelin were similar to that of lipid rafts, suggesting that the lipid originated from a raft-like region of the cell. Smaller amounts of glucosylceramides, cholesteryl esters, and other glycerophospholipid classes were also present. The largest particles, ∼ 12 nm and 10 nm diameter, contained ∼ 43% free cholesterol, 2-3% cholesteryl ester, and three apoA-I molecules. Using chemical cross-linking chemistry combined with mass spectrometry, we found that three molecules of apoA-I in the ∼ 9-14 nm nHDL adopted a belt-like conformation. The smaller (7.5 nm diameter) spheroidal nHDL particles carried 30% free cholesterol and two molecules of apoA-I in a twisted, antiparallel, double-belt conformation. Overall, these new data offer fresh insights into the biogenesis and structural constraints involved in forming nascent HDL from ABCA1.
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Affiliation(s)
- Mary G Sorci-Thomas
- Department of Pathology, Section on Lipid Sciences, Wake Forest Baptist Medical Center, Winston-Salem, NC 27157, USA.
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Li L, Li S, Jones MK, Segrest JP. Rotational and hinge dynamics of discoidal high density lipoproteins probed by interchain disulfide bond formation. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:481-9. [PMID: 22063273 DOI: 10.1016/j.bbalip.2011.10.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Revised: 10/10/2011] [Accepted: 10/13/2011] [Indexed: 11/30/2022]
Abstract
To develop a detailed double belt model for discoidal HDL, we previously scored inter-helical salt bridges between all possible registries of two stacked antiparallel amphipathic helical rings of apolipoprotein (apo) A-I. The top score was the antiparallel apposition of helix 5 with 5 followed closely by appositions of helix 5 with 4 and helix 5 with 6. The rationale for the current study is that, for each of the optimal scores, a pair of identical residues can be identified in juxtaposition directly on the contact edge between the two antiparallel helical belts of apoA-I. Further, these residues are always in the '9th position' in one of the eighteen 11-mer repeats that make up the lipid-associating domain of apoA-I. To illustrate our terminology, 129j (LL5/5) refers to the juxtaposition of the Cα atoms of G129 (in a '9th position') in the pairwise helix 5 domains. We reasoned that if identical residues in the double belt juxtapositions were mutated to a cysteine and kept under reducing conditions during disc formation, we would have a precise method for determining registration in discoidal HDL by formation of a disulfide-linked apoA-I homodimer. Using this approach, we conclude that 129j (LL5/5) is the major rotamer orientation for double belt HDL and propose that the small ubiquitous gap between the pairwise helix 5 portions of the double belt in larger HDL discoidal particles is significantly dynamic to hinge off the disc edge under certain conditions, e.g., in smaller particles or perhaps following binding of the enzyme LCAT. 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)
- Ling Li
- Department of Medicine and Atherosclerosis Research Unit, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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Sorci-Thomas MG, Zabalawi M, Bharadwaj MS, Wilhelm AJ, Owen JS, Asztalos BF, Bhat S, Thomas MJ. Dysfunctional HDL containing L159R ApoA-I leads to exacerbation of atherosclerosis in hyperlipidemic mice. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:502-12. [PMID: 21944998 DOI: 10.1016/j.bbalip.2011.08.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 08/20/2011] [Accepted: 08/31/2011] [Indexed: 11/16/2022]
Abstract
The mutation L159R apoA-I or apoA-I(L159R) (FIN) is a single amino acid substitution within the sixth helical repeat of apoA-I. It is associated with a dominant negative phenotype, displaying hypoalphaproteinemia and an increased risk for atherosclerosis in humans. Mice lacking both mouse apoA-I and LDL receptor (LDL(-/-), apoA-I(-/-)) (double knockout or DKO) were crossed>9 generations with mice transgenic for human FIN to obtain L159R apoA-I, LDLr(-/-), ApoA-I(-/-) (FIN-DKO) mice. A similar cross was also performed with human wild-type (WT) apoA-I (WT-DKO). In addition, FIN-DKO and WT-DKO were crossed to obtain WT/FIN-DKO mice. To determine the effects of the apoA-I mutations on atherosclerosis, groups of each genotype were fed either chow or an atherogenic diet for 12weeks. Interestingly, the production of dysfunctional HDL-like particles occurred in DKO and FIN-DKO mice. These particles were distinct with respect to size, and their enrichment in apoE and cholesterol esters. Two-dimensional gel electrophoresis indicated that particles found in the plasma of FIN-DKO mice migrated as large α(3)-HDL. Atherosclerosis analysis showed that FIN-DKO mice developed the greatest extent of aortic cholesterol accumulation compared to all other genotypes, including DKO mice which lack any apoA-I. Taken together these data suggest that the presence of large apoE enriched HDL particles containing apoA-I L159R lack the normal cholesterol efflux promoting properties of HDL, rendering them dysfunctional and pro-atherogenic. In conclusion, large HDL-like particles containing apoE and apoA-I(L159R) contribute rather than protect against atherosclerosis, possibly through defective efflux properties and their potential for aggregation at their site of interaction in the aorta. 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)
- Mary G Sorci-Thomas
- Department of Pathology, Section on Lipid Sciences, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA.
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