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Phinney NZ, Huang X, Toombs JE, Brekken RA. Development of betabodies: the next generation of phosphatidylserine targeting agents. J Biol Chem 2024:107681. [PMID: 39159812 DOI: 10.1016/j.jbc.2024.107681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2024] [Revised: 06/09/2024] [Accepted: 08/02/2024] [Indexed: 08/21/2024] Open
Abstract
Externalized phosphatidylserine (PS) is a phospholipid and a selective marker of the tumor microenvironment (TME). It is exposed on the outer leaflet of the plasma membrane of tumor-associated endothelial cells, apoptotic tumor cells, and some viable tumor cells, where it functions in part to suppress immune responses by binding to PS receptors expressed on tumor-infiltrating myeloid cells. PS has been targeted with antibodies, such as bavituximab, that bind the phospholipid via a cofactor, β2-glycoprotein 1 (β2GP1); these antibodies showed excellent specificity for tumor vasculature and induce an immune stimulatory environment. We have advanced this concept by developing the next generation of PS targeting agent, a fusion protein (betabody) constructed by linking PS-binding domain V of β2GP1 to the Fc of an IgG2a. Betabodies bind to externalized PS with high affinity (∼1 nM), without the requirement of a co-factor and localize robustly to the TME. We demonstrate that betabodies are a direct PS-targeting agent that have the potential to be used as anti-tumor therapy, drug delivery vehicles, and tools for imaging the TME.
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Affiliation(s)
- Natalie Z Phinney
- Department of Surgery, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Hamon Center for Therapeutic Oncology Research, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Cancer Biology Graduate Program, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA
| | - Xianming Huang
- Hamon Center for Therapeutic Oncology Research, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Department of Pharmacology, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA
| | - Jason E Toombs
- Department of Surgery, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Hamon Center for Therapeutic Oncology Research, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA
| | - Rolf A Brekken
- Department of Surgery, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Hamon Center for Therapeutic Oncology Research, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Cancer Biology Graduate Program, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Department of Pharmacology, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA; Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX, 75390-8593, USA.
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Giannakopoulos B, Krilis SA. Domain 5 of Beta 2 glycoprotein I: Friend or foe in health? Context matters. Clin Immunol 2024; 265:110282. [PMID: 38917928 DOI: 10.1016/j.clim.2024.110282] [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: 06/14/2023] [Revised: 06/03/2024] [Accepted: 06/05/2024] [Indexed: 06/27/2024]
Abstract
Beta 2 glycoprotein I (β2GPI) is the major autoantigen in the antiphospholipid syndrome, an autoimmune disorder characterized by thrombotic and obstetric complications. The autoantibodies that target beta 2 glycoprotein I are pathogenic and contribute to disease pathogenesis. The β2GPI molecule is composed of 5 domains that are numbered 1 through to 5. Autoantibodies bind mainly to domain 1 whereas the majority of the biological functions of the β2GPI molecule in diverse processes such as apoptotic cell clearance, complement regulation, lipopolysaccharide clearance and anticoagulation have been localised to domain 5 and its unique biochemistry, reviewed in this article. The role of purified domain 5 peptide as a potential therapeutic agent in APS and ischemia reperfusion injury is discussed.
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Affiliation(s)
- Bill Giannakopoulos
- Faculty of Medicine and Health, University of New South Wales, St George and Sutherland Campus, Level 2, Pitney Building, Kogarah, Sydney, NSW 2217, Australia; Department of Rheumatology, St George Public Hospital, Kogarah, Sydney, 2217, Australia.
| | - Steven A Krilis
- Faculty of Medicine and Health, University of New South Wales, St George and Sutherland Campus, Level 2, Pitney Building, Kogarah, Sydney, NSW 2217, Australia; Department of Infectious Diseases, Immunology, and Sexual Health, St George Public Hospital, Kogarah, Sydney 2217, Australia.
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3
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Hasdemir HS, Pozzi N, Tajkhorshid E. Atomistic characterization of β2-glycoprotein I domain V interaction with anionic membranes. J Thromb Haemost 2024:S1538-7836(24)00427-6. [PMID: 39047943 DOI: 10.1016/j.jtha.2024.07.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 06/18/2024] [Accepted: 07/01/2024] [Indexed: 07/27/2024]
Abstract
BACKGROUND Interaction of β2-glycoprotein I (β2GPI) with anionic membranes is crucial in antiphospholipid syndrome (APS), implicating the role of its membrane-binding domain, domain V (DV). The mechanism of DV binding to anionic lipids is not fully understood. OBJECTIVES This study aimed to elucidate the molecular details of β2GPI DV binding to anionic membranes. METHODS We utilized molecular dynamics simulations to investigate the structural basis of anionic lipid recognition by DV. To corroborate the membrane-binding mode identified in the highly mobile membrane mimetic simulations, we conducted additional simulations using a full membrane model. RESULTS The study identified critical regions in DV, namely the lysine-rich loop and the hydrophobic loop, which are essential for membrane association via electrostatic and hydrophobic interactions, respectively. A novel lysine pair contributing to membrane binding was also discovered, providing new insights into β2GPI's membrane interaction. Simulations revealed 2 distinct binding modes of DV to the membrane, with mode 1 characterized by the insertion of the hydrophobic loop into the lipid bilayer, suggesting a dominant mechanism for membrane association. This interaction is pivotal for the pathogenesis of APS, as it facilitates the recognition of β2GPI by antiphospholipid antibodies. CONCLUSION The study advances our understanding of the molecular interactions between β2GPI's DV and anionic membranes, which are crucial for APS pathogenesis. It highlights the importance of specific regions in DV for membrane binding and reveals a predominant binding mode. These findings have significant implications for APS diagnostics and therapeutics, offering a deeper insight into the molecular basis of the syndrome.
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Affiliation(s)
- Hale S Hasdemir
- Theoretical and Computational Biophysics Group, NIH Resource for Macromolecular Modeling and Visualization, Beckman Institute for Advanced Science and Technology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA; Center for Biophysics and Computational Biology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Nicola Pozzi
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri, USA. https://www.twitter.com/LabPozzi
| | - Emad Tajkhorshid
- Theoretical and Computational Biophysics Group, NIH Resource for Macromolecular Modeling and Visualization, Beckman Institute for Advanced Science and Technology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA; Center for Biophysics and Computational Biology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA; Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.
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4
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Periodic bilayer organization in the complexes of Beta-2 Glycoprotein I with anionic lipid membranes. Colloids Surf B Biointerfaces 2021; 208:112118. [PMID: 34547703 DOI: 10.1016/j.colsurfb.2021.112118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 09/04/2021] [Accepted: 09/13/2021] [Indexed: 11/20/2022]
Abstract
β2 glycoprotein I (β2GPI) is a soluble protein that participates in blood coagulation, clearance of apoptotic bodies and generation of antigens in antiphospholipid syndrome among many other functions. We studied the aggregates formed by β2GPI with the anionic phospholipids palmitoyloleoylphosphatidyl glycerol, dimyristoylphosphatidyl glycerol, dipalmitoylphosphatidyl glycerol and cardiolipin using small angle X-ray scattering. The complexes obtained in a medium containing 0.01 M NaCl showed Bragg peaks up to the sixth order in a well-defined integer sequence indicating the presence of a lamellar stacking with a periodicity of 17.8 nm and with largely reduced membrane fluctuations. Modeling the complex signal allowed us to conclude that the coherence length was only two bilayers and that about 15% of the total surface was actually stacked. The space between bilayers allows accommodating an extended β2GPI molecule making a bridge between the interacting bilayers. The interactions between membranes mediated by β2GPI was favored when the membranes were in the liquid crystalline state.
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Smalley H, Rowe JM, Nieto F, Zeledon J, Pollard K, Tomich JM, Fleming SD. Beta2 glycoprotein I-derived therapeutic peptides induce sFlt-1 secretion to reduce melanoma vascularity and growth. Cancer Lett 2020; 495:66-75. [PMID: 32891714 PMCID: PMC7899169 DOI: 10.1016/j.canlet.2020.08.039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 07/11/2020] [Accepted: 08/31/2020] [Indexed: 12/15/2022]
Abstract
Melanoma, a form of skin cancer, is one of the most common cancers in young men and women. Tumors require angiogenesis to provide oxygen and nutrients for growth. Pro-angiogenic molecules such as VEGF and anti-angiogenic molecules such as sFlt-1 control angiogenesis. In addition, the serum protein, Beta2 Glycoprotein I (β2-GPI) induces or inhibits angiogenesis depending on conformation and concentration. β2-GPI binds to proteins and negatively charged phospholipids on hypoxic endothelial cells present in the tumor microenvironment. We hypothesized that peptides derived from the binding domain of β2-GPI would regulate angiogenesis and melanoma growth. In vitro analyses determined the peptides reduced endothelial cell migration and sFlt-1 secretion. In a syngeneic, immunocompetent mouse melanoma model, β2-GPI-derived peptides also reduced melanoma growth in a dose-dependent response with increased sFlt-1 and attenuated vascular markers compared to negative controls. Importantly, administration of peptide with sFlt-1 antibody resulted in tumor growth. These data demonstrate the therapeutic potential of novel β2-GPI-derived peptides to attenuate tumor growth and endothelial migration is sFlt-1 dependent.
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Affiliation(s)
- Haley Smalley
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - Jennifer M Rowe
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - Fernando Nieto
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - Jazmin Zeledon
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - Kellyn Pollard
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - John M Tomich
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS, 66506, USA
| | - Sherry D Fleming
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA.
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Ruben E, Planer W, Chinnaraj M, Chen Z, Zuo X, Pengo V, De Filippis V, Alluri RK, McCrae KR, Macor P, Tedesco F, Pozzi N. The J-elongated conformation of β 2-glycoprotein I predominates in solution: implications for our understanding of antiphospholipid syndrome. J Biol Chem 2020; 295:10794-10806. [PMID: 32518155 PMCID: PMC7397106 DOI: 10.1074/jbc.ra120.013939] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2020] [Revised: 06/06/2020] [Indexed: 01/07/2023] Open
Abstract
β2-Glycoprotein I (β2GPI) is an abundant plasma protein displaying phospholipid-binding properties. Because it binds phospholipids, it is a target of antiphospholipid antibodies (aPLs) in antiphospholipid syndrome (APS), a life-threatening autoimmune thrombotic disease. Indeed, aPLs prefer membrane-bound β2GPI to that in solution. β2GPI exists in two almost equally populated redox states: oxidized, in which all the disulfide bonds are formed, and reduced, in which one or more disulfide bonds are broken. Furthermore, β2GPI can adopt multiple conformations (i.e. J-elongated, S-twisted, and O-circular). While strong evidence indicates that the J-form is the structure bound to aPLs, which conformation exists and predominates in solution remains controversial, and so is the conformational pathway leading to the bound state. Here, we report that human recombinant β2GPI purified under native conditions is oxidized. Moreover, under physiological pH and salt concentrations, this oxidized form adopts a J-elongated, flexible conformation, not circular or twisted, in which the N-terminal domain I (DI) and the C-terminal domain V (DV) are exposed to the solvent. Consistent with this model, binding kinetics and mutagenesis experiments revealed that in solution the J-form interacts with negatively charged liposomes and with MBB2, a monoclonal anti-DI antibody that recapitulates most of the features of pathogenic aPLs. We conclude that the preferential binding of aPLs to phospholipid-bound β2GPI arises from the ability of its preexisting J-form to accumulate on the membranes, thereby offering an ideal environment for aPL binding. We propose that targeting the J-form of β2GPI provides a strategy to block pathogenic aPLs in APS.
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Affiliation(s)
- Eliza Ruben
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri, USA
| | - William Planer
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri, USA
| | - Mathivanan Chinnaraj
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri, USA
| | - Zhiwei Chen
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri, USA
| | - Xiaobing Zuo
- X-Ray Science Division, Argonne National Laboratory, Argonne, Illinois, USA
| | - Vittorio Pengo
- Thrombosis Research Laboratory, Department of Cardiac Thoracic and Vascular Sciences, and Public Health, University of Padova, Padova, Italy,Arianna Foundation on Anticoagulation, Bologna, Italy
| | - Vincenzo De Filippis
- Department of Pharmaceutical & Pharmacological Sciences, University of Padua, Padua, Italy
| | - Ravi K. Alluri
- Department of Cellular and Molecular Medicine, Cleveland Clinic, Cleveland, Ohio, USA
| | - Keith R. McCrae
- Department of Cellular and Molecular Medicine, Cleveland Clinic, Cleveland, Ohio, USA
| | - Paolo Macor
- Department of Life Sciences, University of Trieste, Trieste, Italy
| | - Francesco Tedesco
- Istituto Auxologico Italiano, IRCCS, Laboratory of Immuno-Rheumatology, Milan, Italy
| | - Nicola Pozzi
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri, USA,For correspondence: Nicola Pozzi,
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Mutants of β2-glycoprotein I: Their features and potent applications. Best Pract Res Clin Rheumatol 2018; 32:572-590. [DOI: 10.1016/j.berh.2019.01.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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Ağar Ç, de Groot P, Marquart JA, Meijers J. Evolutionary conservation of the lipopolysaccharide binding site of β2-glycoprotein I. Thromb Haemost 2017; 106:1069-75. [DOI: 10.1160/th11-05-0333] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 08/01/2011] [Indexed: 11/05/2022]
Abstract
Summaryβ2-Glycoprotein I (β2GPI) is a highly abundant plasma protein and the major antigen for autoantibodies in the antiphospholipid syndrome. Recently, we have described a novel function of β2GPI as scavenger of lipopolysaccharide (LPS). With this in mind we investigated the conservation of β2GPI in vertebrates and set out to identify the binding site of LPS within β2GPI. The genome sequences of 42 species were surveyed. Surface plasmon resonance (SPR) was performed with peptides to characterise the binding site of β2GPI for LPS. β2GPI could be identified in most tested vertebrates with a high overall amino acid homology of 80% or more in mammals. SPR revealed that a synthesised peptide (LAFWKTDA) from domain V of β2GPI was able to compete for binding of β2GPI to LPS. The AFWKTDA sequence was completely conserved in all mammals. The peptide containing the LPS binding site attenuated the inhibition by β2GPI in a cellular model of LPS-induced tissue factor expression. Other important sites, such as the binding site for anionic phospholipids and the antiphospholipid antibody binding epitope, were also preserved. β2GPI is highly conserved across the animal kingdom, which suggests that the function of β2GPI may be more important than anticipated.
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Krilis SA, Giannakopoulos B. Laboratory methods to detect antiphospholipid antibodies. HEMATOLOGY. AMERICAN SOCIETY OF HEMATOLOGY. EDUCATION PROGRAM 2014; 2014:321-328. [PMID: 25696873 DOI: 10.1182/asheducation-2014.1.321] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This chapter reviews several important themes pertaining to the antiphospholipid syndrome (APS), including a description of the clinical features, a discussion of the main autoantigen, beta 2-glycoprotein I (β2GPI), and insights into the characteristics of the pathogenic anti-β2GPI autoantibodies. Evidence-based considerations for when to test for APS are explored, along with the clinical significance of patients testing positive on multiple APS assays, so-called triple positivity. A detailed review of recently published laboratory guidelines for the detection of lupus anticoagulant and the solid-phase anticardiolipin and anti-β2GPI ELISAs is undertaken. Finally, a brief review of nonclassification criteria laboratory assays with potential future diagnostic utility is presented.
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Affiliation(s)
- Steven A Krilis
- Department of Infectious Diseases, Immunology, and Sexual Health and Department of Medicine, St George Clinical School, University of New South Wales, Kogarah, New South Wales, Australia
| | - Bill Giannakopoulos
- Department of Infectious Diseases, Immunology, and Sexual Health and Department of Rheumatology, St George Hospital, Kogarah, New South Wales, Australia; and Department of Medicine, St George Clinical School, University of New South Wales, Kogarah, New South Wales, Australia
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Abstract
β(2)glycoprotein I (β(2)GPI) is the major antigen in the antiphospholipid syndrome. It has been shown that β(2)GPI can adapt to different conformations, a circular, a S-shaped and a J-shaped conformation. In literature anticoagulant properties of β(2)GPI have been indicated, though there is no consensus on how β(2)GPI exerts a certain action. This article will first review existing data on the conformation of β(2)GPI. In addition, we will investigate whether the conformation of β(2)GPI plays a role in in the proposed anticoagulant activity of β(2)GPI. We investigated the effect of native β(2)GPI and phospholipid-bound β(2)GPI on thrombin generation (TG). Native β(2)GPI was found to have no significant effect on the TG regardless of the concentration of tissue factor. On the contrary, β(2)GPI preincubated with phospholipids significantly inhibited TG triggered with low TF concentration, suggesting an effect on the intrinsic pathway. This indicates that native β(2)GPI in circulation obtains its anticoagulant activity in the presence of anionic phospholipids such as activated blood cells thereby serving as an inhibitory modulator in hemostasis.
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Reed JH, Clancy RM, Purcell AW, Kim MY, Gordon TP, Buyon JP. β2-glycoprotein I and protection from anti-SSA/Ro60-associated cardiac manifestations of neonatal lupus. THE JOURNAL OF IMMUNOLOGY 2011; 187:520-6. [PMID: 21602492 DOI: 10.4049/jimmunol.1100122] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
One mechanism to molecularly explain the strong association of maternal anti-Ro60 Abs with cardiac disease in neonatal lupus (NL) is that these Abs initiate injury by binding to apoptotic cardiomyocytes in the fetal heart. Previous studies have demonstrated that β(2)-glycoprotein I (β(2)GPI) interacts with Ro60 on the surface of apoptotic Jurkat cells and prevents binding of anti-Ro60 IgG. Accordingly, the current study was initiated to test two complementary hypotheses, as follows: 1) competition between β(2)GPI and maternal anti-Ro60 Abs for binding apoptotic induced surface-translocated Ro60 occurs on human fetal cardiomyocytes; and 2) circulating levels of β(2)GPI influence injury in anti-Ro60-exposed fetuses. Initial flow cytometry experiments conducted on apoptotic human fetal cardiomyocytes demonstrated dose-dependent binding of β(2)GPI. In competitive inhibition experiments, β(2)GPI prevented opsonization of apoptotic cardiomyocytes by maternal anti-Ro60 IgG. ELISA was used to quantify β(2)GPI in umbilical cord blood from 97 neonates exposed to anti-Ro60 Abs, 53 with cardiac NL and 44 with no cardiac disease. β(2)GPI levels were significantly lower in neonates with cardiac NL. Plasmin-mediated cleavage of β(2)GPI prevented binding to Ro60 and promoted the formation of pathogenic anti-Ro60 IgG-apoptotic cardiomyocyte complexes. In aggregate these data suggest that intact β(2)GPI in the fetal circulation may be a novel cardioprotective factor in anti-Ro60-exposed pregnancies.
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Affiliation(s)
- Joanne H Reed
- Division of Rheumatology, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA.
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Matsuura E, Shen L, Matsunami Y, Quan N, Makarova M, Geske FJ, Boisen M, Yasuda S, Kobayashi K, Lopez LR. Pathophysiology of β2-glycoprotein I in antiphospholipid syndrome. Lupus 2010; 19:379-84. [DOI: 10.1177/0961203310361352] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Since β2-glycoprotein I (β2GPI) was described as the major antigenic target for antiphospholipid antibodies, many studies have focused their attention to the physiological role of β2GPI and anti-β2GPI antibodies on autoimmune-mediated thrombosis. Studies reporting the physiological role of β2GPI have been numerous, but the exact mechanism of action(s) has yet to be completely determined. β2GPI’s epitopes for anti-β2GPI autoantibodies have been characterized, however, not all of the heterogeneous anti-β2GPI antibodies are pathogenic. The pathophysiologic role of β2GPI has been reported in the fields of coagulation, fibrinolysis, angiogenesis, and atherosclerosis. Our understanding of the impact of β2GPI, its metabolites and autoantibodies to β2GPI on these physiological functions may contribute to the development of better therapeutic strategies to treat and prevent autoimmune-mediated atherothrombotic vascular disease. Lupus (2010) 19, 379—384.
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Affiliation(s)
- E. Matsuura
- Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama 700-8558, Japan,
| | - L. Shen
- Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama 700-8558, Japan
| | - Y. Matsunami
- Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama 700-8558, Japan
| | - N. Quan
- Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama 700-8558, Japan
| | - M. Makarova
- Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama 700-8558, Japan
| | - FJ Geske
- Corgenix Inc, Broomfield, CO, USA
| | | | - S. Yasuda
- Department of Medicine , Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan
| | - K. Kobayashi
- Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama 700-8558, Japan
| | - LR Lopez
- Corgenix Inc, Broomfield, CO, USA
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Bu C, Gao L, Xie W, Zhang J, He Y, Cai G, McCrae KR. beta2-glycoprotein i is a cofactor for tissue plasminogen activator-mediated plasminogen activation. ACTA ACUST UNITED AC 2009; 60:559-68. [PMID: 19180513 DOI: 10.1002/art.24262] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
OBJECTIVE Regulation of the conversion of plasminogen to plasmin by tissue plasminogen activator (tPA) is critical in the control of fibrin deposition. While several plasminogen activators have been described, soluble plasma cofactors that stimulate fibrinolysis have not been characterized. The purpose of this study was to investigate the effects of beta(2)-glycoprotein I (beta(2)GPI), an abundant plasma glycoprotein, on tPA-mediated plasminogen activation. METHODS The effect of beta(2)GPI on tPA-mediated activation of plasminogen was assessed using amidolytic assays, a fibrin gel, and plasma clots. Binding of beta(2)GPI to tPA and plasminogen was determined in parallel. The effects of IgG fractions and anti-beta(2)GPI antibodies from patients with antiphospholipid syndrome (APS) on tPA-mediated plasminogen activation were also measured. RESULTS Beta(2)-glycoprotein I stimulated tPA-dependent plasminogen activation in the fluid phase and within a fibrin gel. The beta(2)GPI region responsible for stimulating tPA activity was shown to be at least partly contained within beta(2)GPI domain V. In addition, beta(2)GPI bound tPA with high affinity (K(d) approximately 20 nM), stimulated tPA amidolytic activity, and caused an overall 20-fold increase in the catalytic efficiency (K(cat)/K(m)) of tPA-mediated conversion of Glu-plasminogen to plasmin. Moreover, depletion of beta(2)GPI from plasma led to diminished rates of clot lysis, with restoration of normal lysis rates following beta(2)GPI repletion. Stimulation of tPA-mediated plasminogen activity by beta(2)GPI was inhibited by monoclonal anti-beta(2)GPI antibodies as well as by anti-beta(2)GPI antibodies from patients with APS. CONCLUSION These findings suggest that beta(2)GPI may be an endogenous regulator of fibrinolysis. Impairment of beta(2)GPI-stimulated fibrinolysis by anti-beta(2)GPI antibodies may contribute to the development of thrombosis in patients with APS.
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Affiliation(s)
- Chunya Bu
- Tsinghua University, Shenzhen, China
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Rahgozar S, Giannakopoulos B, Yan X, Wei J, Cheng Qi J, Gemmell R, Krilis SA. Beta2-glycoprotein I protects thrombin from inhibition by heparin cofactor II: Potentiation of this effect in the presence of anti-β2-glycoprotein I autoantibodies. ACTA ACUST UNITED AC 2008; 58:1146-55. [DOI: 10.1002/art.23387] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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15
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Chapter 8 Interactions of Phospholipid Binding Proteins with Negatively Charged Membranes. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/s1554-4516(08)00208-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Sakai T, Balasubramanian K, Maiti S, Halder JB, Schroit AJ. Plasmin-cleaved beta-2-glycoprotein 1 is an inhibitor of angiogenesis. THE AMERICAN JOURNAL OF PATHOLOGY 2007; 171:1659-69. [PMID: 17872974 PMCID: PMC2043526 DOI: 10.2353/ajpath.2007.070146] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
beta-2-Glycoprotein 1, an abundant plasma glycoprotein, binds anionic cell surfaces and functions as a regulator of thrombosis. Here, we show that cleavage of the kringle domain at Lys317/Thr318 switches its function to a regulator of angiogenesis. In vitro, the cleaved protein specifically inhibited the proliferation and migration of endothelial cells. The protein was without effect on preformed endothelial cell tubes. In vivo, the cleaved protein inhibited neovascularization into subcutaneously implanted Matrigel and Gelfoam sponge implants and the growth of orthotopically injected tumors. Collectively, these data indicate that plasmin-cleaved beta-2-glycoprotein 1 is a potent antiangiogenic and antitumor molecule of potential therapeutic significance.
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Affiliation(s)
- Taro Sakai
- The Department of Cancer Biology, The University of Texas, M. D. Anderson Cancer Center, Houston, TX, USA
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17
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Rahgozar S, Yang Q, Giannakopoulos B, Yan X, Miyakis S, Krilis SA. Beta2-glycoprotein I binds thrombin via exosite I and exosite II: anti-beta2-glycoprotein I antibodies potentiate the inhibitory effect of beta2-glycoprotein I on thrombin-mediated factor XIa generation. ACTA ACUST UNITED AC 2007; 56:605-13. [PMID: 17265495 DOI: 10.1002/art.22367] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
OBJECTIVE Beta(2)-glycoprotein I (beta(2)GPI) is a dominant antigenic target in antiphospholipid syndrome (APS). Beta(2)-glycoprotein I may bind to factor XI and serve a physiologic function as a regulator of factor XI activation by thrombin. We undertook this study to investigate the possible interactions of beta(2)GPI with thrombin in beta(2)GPI-regulated factor XI activation by thrombin and to evaluate the effect of anti-beta(2)GPI antibodies on this system. METHODS The beta(2)GPI interaction with thrombin was investigated in direct and competitive assays using beta(2)GPI domain mutants and thrombin-binding exosite oligonucleotides. Beta(2)-glycoprotein I inhibition of thrombin-mediated factor XI activation was assessed in the presence of 8 anti-beta(2)GPI monoclonal antibodies (mAb) directed against domain I. RESULTS Domain V of beta(2)GPI was involved in direct binding to thrombin, and exosite I and exosite II on thrombin took part in this interaction. Anti-beta(2)GPI mAb produced a >70% inhibition of thrombin-mediated factor XI activation in the presence of beta(2)GPI. CONCLUSION We demonstrate that beta(2)GPI interacts with thrombin exosites I and II. This novel finding necessitates a reinterpretation of previous studies from which the detection of anti-human thrombin antibodies in APS has been reported. We also show that anti-beta(2)GPI antibodies potentiate the inhibitory effect of beta(2)GPI on thrombin-mediated factor XIa generation.
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Affiliation(s)
- Soheila Rahgozar
- St George Hospital, University of New South Wales, Sydney, New South Wales, Australia
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18
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Beecken WDC, Engl T, Ringel EM, Camphausen K, Michaelis M, Jonas D, Folkman J, Shing Y, Blaheta RA. An endogenous inhibitor of angiogenesis derived from a transitional cell carcinoma: clipped beta2-glycoprotein-I. Ann Surg Oncol 2006; 13:1241-51. [PMID: 16955386 DOI: 10.1245/s10434-006-9009-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Accepted: 12/13/2005] [Indexed: 11/18/2022]
Abstract
BACKGROUND Invasive cell carcinoma of the bladder often develops after complete transurethral excision of superficial transitional cell carcinoma. It has been postulated that primary tumors release angiogenesis-blocking proteins which suppress distant metastases. We have identified an endogenous protein which might be responsible for tumor dormancy. METHODS A transitional cell carcinoma cell line was developed (UMUC-3i) which inhibits the growth of a tumor implant at a distant site in SCID mice. Conditioned media of UMUC-3i cultured cells was first pooled and then fractioned, and the capacity of individual components to block endothelial cell growth was tested. The protein fraction responsible for blocking endothelial cell growth was identified by N-terminal amino acid sequencing as well as by mass-spectrometry. The effects of the purified protein in preventing endothelial cell proliferation and tube formation in an in vitro angiogenesis assay was investigated. RESULTS The plasma protein beta(2)-glycoprotein-I (beta(2)gpI) was isolated and identified from conditioned medium of UMUC-3i cultured cells. Based on the in vitro angiogenesis assay, beta(2)gpI strongly inhibited endothelial cell growth and tube formation, whereby the inhibitory activity corresponded to the clipped version of beta(2)gpI (cbeta(2)gpI). Clipping was induced by adding plasmin at a molar ratio 1:15 (plasmin:substrate). Further analysis indicated that cbeta(2)gpI effects were mediated by annexin II surface receptors expressed on endothelial cells. CONCLUSIONS cbeta2gpI may be involved in blocking angiogenic processes and bladder cancer progression. In this case, cbeta2gpI may be a promising tool in bladder cancer therapy.
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MESH Headings
- Angiogenesis Inhibitors/therapeutic use
- Animals
- Annexin A2/metabolism
- Carcinoma, Transitional Cell/blood supply
- Carcinoma, Transitional Cell/metabolism
- Carcinoma, Transitional Cell/therapy
- Cell Proliferation
- Cells, Cultured
- Culture Media, Conditioned/pharmacology
- Electrophoresis, Polyacrylamide Gel
- Endothelium, Vascular/cytology
- Endothelium, Vascular/metabolism
- Fibrinolysin/metabolism
- Glycoproteins/isolation & purification
- Glycoproteins/metabolism
- Humans
- Immunoblotting
- Mass Spectrometry
- Mice
- Mice, SCID
- Neovascularization, Pathologic/metabolism
- Neovascularization, Pathologic/prevention & control
- Umbilical Veins/cytology
- Umbilical Veins/metabolism
- Urinary Bladder Neoplasms/blood supply
- Urinary Bladder Neoplasms/metabolism
- Urinary Bladder Neoplasms/therapy
- beta 2-Glycoprotein I
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19
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Atsumi T, Amengual O, Yasuda S, Matsuura E, Koike T. Research around beta 2-glycoprotein I: a major target for antiphospholipid antibodies. Autoimmunity 2005; 38:377-81. [PMID: 16227153 DOI: 10.1080/08916930500124312] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Beta2-glycoprotein I (beta2GPI), a phospholipid-binding protein, is one of the major target antigens for antiphospholipid antibodies (aPL) found in patients with antiphospholipid syndrome (APS). Thrombophilic disorders in APS patients are strongly associated with aPL, and their pathogenic properties depend on the presence of beta2GPI. Procoagulant cell stimulation by aPL, via beta2GPI, is one of the most plausible mechanisms of thrombosis in APS, and p38 mitogen activated protein kinase (MAPK) pathway plays a crucial role in such activation. beta2GPI is proteolytically cleaved in domain V by activated factor X or plasmin, leading to the generation of the nicked form of beta2GPI. Recently, increasing attention is focused on the role of nicked-beta2GPI as a regulator of extrinsic fibrinolysis pathway.
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Affiliation(s)
- Tatsuya Atsumi
- Department of Medicine II, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
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20
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Yasuda S, Atsumi T, Ieko M, Koike T. Beta2-glycoprotein I, anti-beta2-glycoprotein I, and fibrinolysis. Thromb Res 2005; 114:461-5. [PMID: 15507279 DOI: 10.1016/j.thromres.2004.07.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2004] [Revised: 07/25/2004] [Accepted: 07/29/2004] [Indexed: 11/24/2022]
Abstract
Beta2-glycoprotein-I (beta2GPI) is a phospholipid-binding plasma protein that consists of five homologous domains. Domain V is distinguished from others by bearing a positively charged lysine cluster and hydrophobic extra C-terminal loop. Beta2GPI has been known as a natural anticoagulant regulator. Beta2GPI exerts anticoagulant activity by inhibition of phospholipid-dependent coagulation reactions such as prothrombinase, tenase, and factor XII activation. It also binds factor XI and inhibits its activation. On the other hand, beta2GPI inhibits anticoagulant activity of activated protein C. According to the data from knockout mice, beta2GPI may contribute to thrombin generation in vivo. Phospholipid-bound beta2GPI is one of the major target antigens for antiphospholipid antibodies present in patients with antiphospholipid syndrome (APS). Binding of pathogenic anti-beta2GPI antibodies increases the affinity of beta2GPI to the cell surface and disrupts the coagulation/fibrinolysis balance on the cell surface. These pathogenic antibodies activate endothelial cells via signal transduction events in the presence of beta2GPI. Impaired fibrinolysis has been reported in patients with APS. Using a newly developed chromogenic assay, we demonstrated lower activity of intrinsic fibrinolysis in euglobulin fractions from APS patients. Addition of monoclonal anti-beta2GPI antibodies with beta2GPI also decreased fibrinolytic activity in this assay system. beta2GPI is proteolytically cleaved by plasmin in domain V (nicked beta2GPI) and becomes unable to bind to phospholipids, reducing antigenicity against antiphospholipid antibodies. This cleavage occurs in patients with increased fibrinolysis turnover. Nicked beta2GPI binds to plasminogen and suppresses plasmin generation in the presence of fibrin, plasminogen, and tissue plasminogen activator (tPA). Thus, nicked beta2GPI plays a role in the extrinsic fibrinolysis via a negative feedback pathway loop.
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Affiliation(s)
- Shinsuke Yasuda
- Department of Medicine II, Hokkaido University Graduate School of Medicine, N15 W7, Kita-ku, Sapporo 060-8638, Japan.
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21
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Shi T, Giannakopoulos B, Iverson GM, Cockerill KA, Linnik MD, Krilis SA. Domain V of β2-Glycoprotein I Binds Factor XI/XIa and Is Cleaved at Lys317-Thr318. J Biol Chem 2005; 280:907-12. [PMID: 15522884 DOI: 10.1074/jbc.m410291200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The fifth domain (DV) of beta2-glycoprotein I (beta2GPI) is important for binding a number of ligands including phospholipids and factor XI (FXI). Beta2GPI is proteolytically cleaved in DV by plasmin but not by thrombin, VIIa, tissue plasminogen activator, or uPA. Following proteolytic cleavage of DV by plasmin, beta2GPI retains binding to FXI but not to phospholipids. Native beta2GPI, but not cleaved beta2GPI, inhibits activation of FXI by thrombin and factor XIIa, attenuating a positive feedback mechanism for additional thrombin generation. In this report, we have defined the FXI/FXIa binding site on beta2GPI using site-directed mutagenesis. We show that the positively charged residues Lys284, Lys286, and Lys287 in DV are essential for the interaction of beta2GPI with FXI/FXIa. We also demonstrate that FXIa proteolytically cleaves beta2GPI at Lys317-Thr318 in DV. Thus, FXIa cleavage of beta2GPI in vivo during thrombus formation may accelerate FXI activation by decreasing the inhibitory effect of beta2GPI.
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Affiliation(s)
- Tong Shi
- Department of Medicine, Department of Immunology, Allergy & Infectious Diseases, St. George Hospital, University of New South Wales, Sydney, New South Wales 2217, Australia
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22
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Cockerill KA, Linnik MD, Iverson GM. Detection and characterization of B cell epitopes on β2-glycoprotein I. Clin Immunol 2004; 112:129-35. [PMID: 15240155 DOI: 10.1016/j.clim.2004.02.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Accepted: 02/27/2004] [Indexed: 11/17/2022]
Abstract
Autoantibodies in antiphospholipid syndrome react predominantly with the plasma protein beta2-glycoprotein I (beta2GPI). Work by a large number of investigators has led to considerable progress in detecting and understanding beta2GPI reactivity with autoantibodies. Characterization of B cell epitopes on beta2GPI has benefited from an appreciation of its interactions with anionic phospholipids and a variety of microplate surfaces. In particular, autoantibodies to beta2GPI are of sufficiently low affinity to require high concentrations of antigen for detectable reactivity. Moreover, some microplate surfaces do not support the proper orientation of beta2GPI to allow display of epitopes in a manner accessible to autoantibodies. These concepts have helped to explain previous notions that exposure of cryptic beta2GPI epitopes may require interactions with anionic surfaces. Finally, we review evidence identifying a dominant B cell epitope that is partially defined by residues Gly40 and Arg43 on the amino terminal domain of beta2GPI.
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23
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Miyakis S, Robertson SA, Krilis SA. Beta-2 glycoprotein I and its role in antiphospholipid syndrome—lessons from knockout mice. Clin Immunol 2004; 112:136-43. [PMID: 15240156 DOI: 10.1016/j.clim.2004.02.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Accepted: 02/27/2004] [Indexed: 10/26/2022]
Abstract
The antiphospholipid syndrome is characterized by the presence in serum of autoantibodies against beta2GPI. Although the role of beta2GPI in the pathogenesis of antiphospholipid antibody syndrome (APS) is well recognized, its exact physiological functions still remain undisclosed. Several interactions of beta2GPI with components of the coagulation cascade have been proposed, resulting in both procoagulant and anticoagulant effects. Additionally, beta2GPI has been implicated in the mechanism of recurrent fetal loss entailed in APS. Recently, using a homologous recombination approach, reproduction of mice homozygous for deletion of the beta2GPI gene has been feasible. beta2GPI knockout mice offer a valuable tool for revealing the physiological role of the protein. These mice show decreased in vitro ability for thrombin generation. Furthermore, although mice lacking beta2GPI are fertile, the success of early pregnancy is moderately compromised and functional beta2GPI is believed necessary for optimal implantation and placental morphogenesis.
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Affiliation(s)
- Spiros Miyakis
- Department of Immunology, Allergy and Infectious Disease, St. George Hospital, University of New South Wales, Kogarah, NSW 2217, Australia
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24
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Shi T, Iverson GM, Qi JC, Cockerill KA, Linnik MD, Konecny P, Krilis SA. Beta 2-Glycoprotein I binds factor XI and inhibits its activation by thrombin and factor XIIa: loss of inhibition by clipped beta 2-glycoprotein I. Proc Natl Acad Sci U S A 2004; 101:3939-44. [PMID: 15007174 PMCID: PMC374348 DOI: 10.1073/pnas.0400281101] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Activation of factor XI (FXI) by thrombin in vivo plays a role in coagulation by providing an important positive feedback mechanism for additional thrombin generation. FXI is activated in vitro by thrombin, or FXIIa in the presence of dextran sulfate. In this report, we investigated the effect of beta(2)-glycoprotein I (beta(2)GPI) on the activation of FXI. beta(2)GPI bound FXI in vitro and inhibited its activation to FXIa by thrombin and FXIIa. The affinity of the interaction between beta(2)GPI and FXI was equivalent to the interaction between FXI and high molecular weight kininogen. Inhibition of FXI activation occurred with lower concentrations of beta(2)GPI than found in human plasma. Proteolytic clipping of beta(2)GPI by plasmin abolished its inhibition of FXI activation. The results suggest a mechanism of regulation whereby physiological concentrations of beta(2)GPI may attenuate thrombin generation in vivo by inhibition of FXI activation. Plasmin cleavage of beta(2)GPI provides a negative feedback that counteracts its inhibition of FXI activation.
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Affiliation(s)
- Tong Shi
- Department of Medicine, St. George Hospital, University of New South Wales, Kogarah 2217, Australia
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25
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Miyakis S, Giannakopoulos B, Krilis SA. Beta 2 glycoprotein I-function in health and disease. Thromb Res 2004; 114:335-46. [PMID: 15507263 DOI: 10.1016/j.thromres.2004.07.017] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2004] [Revised: 07/18/2004] [Accepted: 07/23/2004] [Indexed: 10/26/2022]
Abstract
Beta-2 glycoprotein I (beta2GPI) is the principal target of autoantibodies in the antiphospholipid syndrome (APS). It is abundant in human plasma and shares high homology between different mammalian species. Although the exact physiological function of beta2GPI has not been fully elucidated, several interactions have been described with other proteins and with negatively charged surfaces, such as anionic phospholipids, dextran and heparin. beta2GPI is involved in the coagulation pathway, exerting both procoagulant and anticoagulant activities. Plasma from beta2GPI-deficient mice exhibits impaired thrombin generation in vitro. Recently, it has been demonstrated that beta2GPI binds factor (F) XI in vitro at concentrations lower than those of the protein in human plasma, and this binding inhibits FXI activation to FXIa by thrombin and FXIIa. Proteolytic cleavage of the fifth domain of beta2GPI abolishes its inhibition of FXI activation and results in reduced ability of the cleaved beta2GPI to bind phospholipids. It retains its ability to bind FXI. In vivo activation of FXI by thrombin is thought to be an important mechanism by which coagulation is accelerated via components of the contact activation pathway. Thus beta2GPI may attenuate the contact activation pathway by inhibiting activation of FXI by thrombin. Moreover, because beta2GPI is the dominant autoantigen in patients with APS, dysregulation of this pathway by autoantibodies may be an important mechanism for thrombosis in patients with APS.
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Affiliation(s)
- Spiros Miyakis
- Department of Immunology, Allergy and Infectious Diseases, University of New South Wales, St. George Hospital, 2 South Street, Kogarah, NSW 2217, Australia
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26
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Gao PJ, Piao YF, Liu XD, Qu LK, Shi Y, Wang XC, Yang HY. Studies on specific interaction of beta-2-glycoprotein I with HBsAg. World J Gastroenterol 2003; 9:2114-6. [PMID: 12970918 PMCID: PMC4656686 DOI: 10.3748/wjg.v9.i9.2114] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To observe the binding activity of beta-2-glycoprotein I (β2GPI) to hepatitis B surface antigen (HBsAg) and the possible roles of β2GPI in hepatitis B virus (HBV) infection.
METHODS: The rationale of ELISA methods and ELISA-based research method and ligand-blotting technique were used to detect the specific interaction of β2GPI with HBsAg.
RESULTS: With the increase of rHBsAg, the binding of β2GPI to rHBsAg elevated, and these changes had statistic significance. When we added non-biotinlyated β2GPI, the OD value significantly decreased though they still were positively relevant to rHBsAg, suggesting non-biotinlyated β2GPI competed with biotinlyated β2GPI to saturate the binding sites on rHBsAg. Meanwhile BSA was used as negative control to substitute for rHBsAg coating the plates. The results indicated no interaction between β2GPI and BSA, suggesting the affinity of β2GPI to rHBsAg was specific. The ligand blotling indicated that β2GPI might bind to rHBsAg no matter whether it was under reduced condition or not.
CONCLUSION: The binding of β2GPI to HBsAg suggests that β2GPI may be a carrier of HBV and that β2GPI may play important roles in HBV infection.
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Affiliation(s)
- Pu-Jun Gao
- Department of Digestion, 1st Hospital affiliated to Jilin University, Changchun 130021, Jilin Province, China.
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27
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Reddel SW, Wang YX, Krilis SA. Anti-beta2-glycoprotein I autoantibodies require an antigen density threshold, consistent with divalent binding. Lupus 2003; 12:37-45. [PMID: 12587825 DOI: 10.1191/0961203303lu280oa] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Autoantibodies binding beta2-glycoprotein I (B2GPI) are an important finding in the antiphospholipid syndrome. While antibodies from mice or rabbits immunized with B2GPI readily bind B2GPI coated on a polystyrene microwell plate, anti-B2GPI autoantibodies only do so when using a modified microwell plate with a negatively charged surface. This study demonstrates that, for the detection of anti-B2GPI autoantibodies in an ELISA using modified plates, an antigen coating concentration threshold exists, such that minimal or no binding occurs below a certain coating concentration of antigen, even though antigen is easily demonstrable on the plate. This is consistent with the hypothesis that autoantibodies require divalent binding to B2GPI for detection, as sufficient antigen density for two protein molecules to be sufficiently close to enable divalent binding would only be expected to occur at higher coating concentrations. Several mutant forms of B2GPI developed for epitope determination experiments are shown to have decreased binding to microtitre plates compared to wild-type. If wild-type and mutants are assayed for antibody binding near the threshold a significant diminution in binding to mutants occurs that is the result of inadequate binding to the plate, but could be misinterpreted as the result of interruption of an epitope by the mutation.
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Affiliation(s)
- S W Reddel
- Faculty of Medicine and Department of Immunology, Allergy and Infectious Diseases, St George Hospital, University of New South Wales, Sydney, Australia
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28
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Arnout J, Vermylen J. Current status and implications of autoimmune antiphospholipid antibodies in relation to thrombotic disease. J Thromb Haemost 2003; 1:931-42. [PMID: 12871358 DOI: 10.1046/j.1538-7836.2003.00125.x] [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: 11/20/2022]
Abstract
This review briefly describes the development of the concepts of antiphospholipid antibody and of antiphospholipid syndrome. It focuses on the two main antigenic targets, beta2 glycoprotein I and prothrombin. An excessive production of natural antibodies rather than an immune response to exogenous antigen is proposed as pathogenetic for the development of these antibodies. The review attempts to explain how some of these antibodies are anticoagulant in vitro yet prothrombotic in vivo. The final section discusses when to test for such antibodies, how to test and how to consider treatment of patients with the antiphospholipid syndrome.
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Affiliation(s)
- J Arnout
- Center for Molecular and Vascular Biology, University of Leuven, Belgium
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29
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Guerin J, Sheng Y, Reddel S, Iverson GM, Chapman MG, Krilis SA. Heparin inhibits the binding of beta 2-glycoprotein I to phospholipids and promotes the plasmin-mediated inactivation of this blood protein. Elucidation of the consequences of the two biological events in patients with the anti-phospholipid syndrome. J Biol Chem 2002; 277:2644-9. [PMID: 11711550 DOI: 10.1074/jbc.m110176200] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The phospholipid-binding plasma protein beta2-glycoprotein I (beta2-GPI) is the primary antigen recognized by the circulating autoantibodies in patients with the "anti-phospholipid syndrome" (APS). Although heparin is routinely used in the treatment and prophylaxis of APS patients, the primary heparin-binding site within beta2-GPI has not been identified. More importantly, how heparin exerts its beneficial effects in vivo in APS patients has not been deduced at the molecular level. Using an expression/site-directed mutagenesis approach, we now show that the positively charged site that resides in the first domain of beta2-GPI is not the primary heparin-binding site. Rather it is the second positively charged site located within the fifth domain of the protein that also binds to phospholipids. Lys(284), Lys(286), and Lys(287) in this domain are essential for the interaction of beta2-GPI with heparin. These data indicate that beta2-GPI binds to heparin in a relatively specific manner even though the affinity for the interaction is rather low. Lys(317) resides in the center of the high affinity phospholipid-binding site. Surprisingly, heparin at concentrations that can be achieved in vivo during anticoagulation therapy greatly enhances the plasmin-mediated cleavage of the Lys(317)-Thr(318) site in beta2-GPI. Because the cleaved form cannot bind to phospholipids effectively, the combined actions of heparin and plasmin result in a diminished ability of beta2-GPI to recognize phospholipids. This, in turn, decreases the prothrombotic activity of the endogenous circulating anti-beta2-GPI antibodies in the patients. Thus, heparin exerts its beneficial effects in APS patients by at least two distinct mechanisms.
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Affiliation(s)
- Jan Guerin
- Department of Immunology, Division of Medicine, University of New South Wales, St. George Hospital, Sydney, New South Wales 2217, Australia
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Hoshino M, Hagihara Y, Nishii I, Yamazaki T, Kato H, Goto Y. Identification of the phospholipid-binding site of human beta(2)-glycoprotein I domain V by heteronuclear magnetic resonance. J Mol Biol 2000; 304:927-39. [PMID: 11124037 DOI: 10.1006/jmbi.2000.4243] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To understand the mechanism of the interaction between human beta(2)-glycoprotein I (beta(2)-GPI) and negatively charged phospholipids, we determined the three-dimensional solution structure of the fifth domain of beta(2)-GPI by heteronuclear multidimensional NMR. The results showed that the molecule is composed of well-defined four anti-parallel beta-strands and two short alpha-helices, as well as a long highly flexible loop. Backbone dynamic analysis demonstrated significant mobility of the flexible loop on a subnanosecond time scale. Structural modeling of the nicked fifth domain, in which the Lys317-Thr318 peptide bond was specifically cleaved, revealed the importance of this long C-terminal loop for the interaction between beta(2)-GPI and negatively charged phospholipids. A titration experiment with the anionic surfactant SDS showed that this highly mobile loop, as well as the short beta-hairpin between betaC and betaD strands, which is rich in positively charged residues, specifically interact with the surfactant. The mobile loop, together with the surrounding positively charged residues, probably construct the binding site for negatively charged phospholipids such as cardiolipin.
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Affiliation(s)
- M Hoshino
- Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, 565-0871, Japan
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31
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Affiliation(s)
- E Matsuura
- Department of Cell Chemistry, Institute of Cellular and Molecular Biology, Okayama University Medical School, Japan
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32
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Reddel SW, Krilis SA. Testing for and clinical significance of anticardiolipin antibodies. CLINICAL AND DIAGNOSTIC LABORATORY IMMUNOLOGY 1999; 6:775-82. [PMID: 10548562 PMCID: PMC95774 DOI: 10.1128/cdli.6.6.775-782.1999] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- S W Reddel
- The St. George Hospital, University of New South Wales, Sydney, Australia
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33
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Abstract
There is accumulating evidence showing that lupus anticoagulants (LA) are more strongly associated with thrombosis than anticardiolipin antibodies. In addition, indirect evidence has been presented indicating that beta2GPI-dependent LA are more strongly associated with thrombosis than prothrombin-dependent LA. From this, one may assume that anti-beta2GPI antibodies with LA activity are more pathogenic than anti-beta2GPI antibodies without LA activity. Therefore, it is of the utmost importance to understand the molecular basis on which some anti-beta2GPI antibodies behave as LA. In this presentation, the current knowledge on the interaction of beta2GPI with phospholipids and with anti-beta2GPI antibodies is reviewed and an integrated model for the anti-beta2GPI-dependent LA activity is proposed with implications for a pathogenic role of these particular antibodies.
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Affiliation(s)
- J Arnout
- Center for Molecular and Vascular Biology, University of Leuven, Belgium.
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