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Wang L, Jiang H, Yin X, Liang T, Li G, Ding C, Yang M, Zhang L, Liu J, Xu Y. PHE1-based IgG-like antibody platform provides a novel strategy for enhanced T-cell immunotherapy. Front Immunol 2024; 15:1415834. [PMID: 38933272 PMCID: PMC11201533 DOI: 10.3389/fimmu.2024.1415834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Accepted: 05/24/2024] [Indexed: 06/28/2024] Open
Abstract
Introduction Bispecific antibodies (BsAbs) can simultaneously target two epitopes of different antigenic targets, bringing possibilities for diversity in antibody drug design and are promising tools for the treatment of cancers and other diseases. T-cell engaging bsAb is an important application of the bispecific antibody, which could promote T cell-mediated tumor cell killing by targeting tumor-associated antigen (TAA) and CD3 at the same time. Methods This study comprised antibodies purification, Elisa assay for antigen binding, cytotoxicity assays, T cell activation by flow cytometry in vitro and xenogenic tumor model in vivo. Results We present a novel bsAb platform named PHE-Ig technique to promote cognate heavy chain (HC)-light chain (LC) pairing by replacing the CH1/CL regions of different monoclonal antibodies (mAbs) with the natural A and B chains of PHE1 fragment of Integrin β2 based on the knob-in-hole (KIH) technology. We had also verified that PHE-Ig technology can be effectively used as a platform to synthesize different desired bsAbs for T-cell immunotherapy. Especially, BCMA×CD3 PHE-Ig bsAbs exhibited robust anti-multiple myeloma (MM) activity in vitro and in vivo. Discussion Moreover, PHE1 domain was further shortened with D14G and R41S mutations, named PHE-S, and the PHE-S-based BCMA×CD3 bsAbs also showed anti BCMA+ tumor effect in vitro and in vivo, bringing more possibilities for the development and optimization of different bsAbs. To sum up, PHE1-based IgG-like antibody platform for bsAb construction provides a novel strategy for enhanced T-cell immunotherapy.
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Affiliation(s)
- Lingbin Wang
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Haojie Jiang
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Xuying Yin
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Tingting Liang
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Guoming Li
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Chen Ding
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Mina Yang
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Lin Zhang
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Junling Liu
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Synvida Biotechnology Co., Ltd, Shanghai, China
| | - Yanyan Xu
- Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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Bouti P, Klein BJAM, Verkuijlen PJH, Schornagel K, van Alphen FPJ, Taris KKH, van den Biggelaar M, Hoogendijk AJ, van Bruggen R, Kuijpers TW, Matlung HL. SKAP2 acts downstream of CD11b/CD18 and regulates neutrophil effector function. Front Immunol 2024; 15:1344761. [PMID: 38487529 PMCID: PMC10937362 DOI: 10.3389/fimmu.2024.1344761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2023] [Accepted: 02/01/2024] [Indexed: 03/17/2024] Open
Abstract
Background The importance of CD11b/CD18 expression in neutrophil effector functions is well known. Beyond KINDLIN3 and TALIN1, which are involved in the induction of the high-affinity binding CD11b/CD18 conformation, the signaling pathways that orchestrate this response remain incompletely understood. Method We performed an unbiased screening method for protein selection by biotin identification (BioID) and investigated the KINDLIN3 interactome. We used liquid chromatography with tandem mass spectrometry as a powerful analytical tool. Generation of NB4 CD18, KINDLIN3, or SKAP2 knockout neutrophils was achieved using CRISPR-Cas9 technology, and the cells were examined for their effector function using flow cytometry, live cell imaging, microscopy, adhesion, or antibody-dependent cellular cytotoxicity (ADCC). Results Among the 325 proteins significantly enriched, we identified Src kinase-associated phosphoprotein 2 (SKAP2), a protein involved in actin polymerization and integrin-mediated outside-in signaling. CD18 immunoprecipitation in primary or NB4 neutrophils demonstrated the presence of SKAP2 in the CD11b/CD18 complex at a steady state. Under this condition, adhesion to plastic, ICAM-1, or fibronectin was observed in the absence of SKAP2, which could be abrogated by blocking the actin rearrangements with latrunculin B. Upon stimulation of NB4 SKAP2-deficient neutrophils, adhesion to fibronectin was enhanced whereas CD18 clustering was strongly reduced. This response corresponded with significantly impaired CD11b/CD18-dependent NADPH oxidase activity, phagocytosis, and cytotoxicity against tumor cells. Conclusion Our results suggest that SKAP2 has a dual role. It may restrict CD11b/CD18-mediated adhesion only under resting conditions, but its major contribution lies in the regulation of dynamic CD11b/CD18-mediated actin rearrangements and clustering as required for cellular effector functions of human neutrophils.
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Affiliation(s)
- Panagiota Bouti
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Bart J. A. M. Klein
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Paul J. H. Verkuijlen
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Karin Schornagel
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Floris P. J. van Alphen
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Kees-Karel H. Taris
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, Netherlands
- LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, Netherlands
| | - Maartje van den Biggelaar
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Arie J. Hoogendijk
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Robin van Bruggen
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
| | - Taco W. Kuijpers
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
- Department of Pediatric Immunology and Infectious Diseases, Emma Children’s Hospital, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands
| | - Hanke L. Matlung
- Department of Molecular Hematology Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center (UMC), University of Amsterdam, Amsterdam, Netherlands
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Santos-López J, de la Paz K, Fernández FJ, Vega MC. Structural biology of complement receptors. Front Immunol 2023; 14:1239146. [PMID: 37753090 PMCID: PMC10518620 DOI: 10.3389/fimmu.2023.1239146] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 08/16/2023] [Indexed: 09/28/2023] Open
Abstract
The complement system plays crucial roles in a wide breadth of immune and inflammatory processes and is frequently cited as an etiological or aggravating factor in many human diseases, from asthma to cancer. Complement receptors encompass at least eight proteins from four structural classes, orchestrating complement-mediated humoral and cellular effector responses and coordinating the complex cross-talk between innate and adaptive immunity. The progressive increase in understanding of the structural features of the main complement factors, activated proteolytic fragments, and their assemblies have spurred a renewed interest in deciphering their receptor complexes. In this review, we describe what is currently known about the structural biology of the complement receptors and their complexes with natural agonists and pharmacological antagonists. We highlight the fundamental concepts and the gray areas where issues and problems have been identified, including current research gaps. We seek to offer guidance into the structural biology of the complement system as structural information underlies fundamental and therapeutic research endeavors. Finally, we also indicate what we believe are potential developments in the field.
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Affiliation(s)
- Jorge Santos-López
- Centro de Investigaciones Biológicas Margarita Salas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Karla de la Paz
- Centro de Investigaciones Biológicas Margarita Salas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
- Research & Development, Abvance Biotech SL, Madrid, Spain
| | | | - M. Cristina Vega
- Centro de Investigaciones Biológicas Margarita Salas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
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Tvaroška I, Kozmon S, Kóňa J. Molecular Modeling Insights into the Structure and Behavior of Integrins: A Review. Cells 2023; 12:cells12020324. [PMID: 36672259 PMCID: PMC9856412 DOI: 10.3390/cells12020324] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 01/09/2023] [Accepted: 01/11/2023] [Indexed: 01/18/2023] Open
Abstract
Integrins are heterodimeric glycoproteins crucial to the physiology and pathology of many biological functions. As adhesion molecules, they mediate immune cell trafficking, migration, and immunological synapse formation during inflammation and cancer. The recognition of the vital roles of integrins in various diseases revealed their therapeutic potential. Despite the great effort in the last thirty years, up to now, only seven integrin-based drugs have entered the market. Recent progress in deciphering integrin functions, signaling, and interactions with ligands, along with advancement in rational drug design strategies, provide an opportunity to exploit their therapeutic potential and discover novel agents. This review will discuss the molecular modeling methods used in determining integrins' dynamic properties and in providing information toward understanding their properties and function at the atomic level. Then, we will survey the relevant contributions and the current understanding of integrin structure, activation, the binding of essential ligands, and the role of molecular modeling methods in the rational design of antagonists. We will emphasize the role played by molecular modeling methods in progress in these areas and the designing of integrin antagonists.
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Affiliation(s)
- Igor Tvaroška
- Institute of Chemistry, Slovak Academy of Sciences, Dúbravska cesta 9, 845 38 Bratislava, Slovakia
- Correspondence:
| | - Stanislav Kozmon
- Institute of Chemistry, Slovak Academy of Sciences, Dúbravska cesta 9, 845 38 Bratislava, Slovakia
- Medical Vision o. z., Záhradnícka 4837/55, 821 08 Bratislava, Slovakia
| | - Juraj Kóňa
- Institute of Chemistry, Slovak Academy of Sciences, Dúbravska cesta 9, 845 38 Bratislava, Slovakia
- Medical Vision o. z., Záhradnícka 4837/55, 821 08 Bratislava, Slovakia
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Goldschmidt Gőz V, Duong KHY, Horváth D, Ferentzi K, Farkas V, Perczel A. Application of Sugar Amino Acids: Flow Chemistry Used for α/β‐Chimera Synthesis. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100943] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Viktória Goldschmidt Gőz
- MTA-ELTE Protein Modeling Research Group Eötvös Loránd Research Network (ELKH) ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
| | - Kim Hoang Yen Duong
- Laboratory of Structural Chemistry and Biology Institute of Chemistry ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
- Hevesy György PhD School of Chemistry Institute of Chemistry ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
| | - Dániel Horváth
- Laboratory of Structural Chemistry and Biology Institute of Chemistry ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
| | - Kristóf Ferentzi
- Laboratory of Structural Chemistry and Biology Institute of Chemistry ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
- Hevesy György PhD School of Chemistry Institute of Chemistry ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
| | - Viktor Farkas
- MTA-ELTE Protein Modeling Research Group Eötvös Loránd Research Network (ELKH) ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
| | - András Perczel
- MTA-ELTE Protein Modeling Research Group Eötvös Loránd Research Network (ELKH) ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
- Laboratory of Structural Chemistry and Biology Institute of Chemistry ELTE Eötvös Loránd University Pázmány P. stny. 1/A 1117 Budapest Hungary
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Dobson HE, Ruan S, Chang AE, Wicha MS, Li Q. Targeting cancer stem cells via integrin β4. Oncotarget 2021; 12:1850-1858. [PMID: 34504657 PMCID: PMC8416562 DOI: 10.18632/oncotarget.27977] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 05/13/2021] [Indexed: 12/12/2022] Open
Abstract
Integrins mediate cell-cell interactions and communication with the extracellular matrix (ECM). These transmembrane protein receptors allow binding between a cell and its surroundings, initiating a breadth of intracellular signaling resulting in proliferation, differentiation, survival, or migration. Such responses have made integrins an attractive target for cancer therapy. Self-renewing and highly tumorigenic cancer stem cells (CSCs) are most resistant to traditional radiation treatment and chemotherapy, and therefore may contribute directly to the metastasis and relapse of the disease. In both the 4T1 mouse metastatic mammary tumor model and SCC7 head and neck squamous cell carcinoma model, integrin β4 (ITGB4) was expressed on ALDHhigh 4T1 and SCC7 CSCs. Using two immunological approaches, we targeted ITGB4 through 1) ITGB4 protein-pulsed dendritic cell (ITGB4-DC) vaccination or 2) via anti-CD3/anit-ITGB4 bispecific antibody (ITGB4 BiAb)-armed T cell adoptive transfer. These two therapies reduced ITGB4-expressing CSCs and inhibited local tumor growth and lung metastasis through ITGB4 specific cellular and humoral immune responses. Additionally, the combination of anti-PD-L1 immunotherapy with our two ITGB4-targeted approaches significantly improved treatment efficacy. We also found increased concentrations of serum IFN-γ and IL-6 in the 4T1 and SCC7 models which may help define future directions of this ITGB4-targeted study. Together, these results emphasize ITGB4 as a practical CSC immunological target with possible therapeutic benefits across tumor types with high ITGB4 expression.
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Affiliation(s)
- Hannah E Dobson
- Rogel Cancer Center, University of Michigan, Ann Arbor, MI 48109, USA
| | - Shasha Ruan
- Rogel Cancer Center, University of Michigan, Ann Arbor, MI 48109, USA.,Department of Clinical Oncology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, China
| | - Alfred E Chang
- Rogel Cancer Center, University of Michigan, Ann Arbor, MI 48109, USA
| | - Max S Wicha
- Rogel Cancer Center, University of Michigan, Ann Arbor, MI 48109, USA
| | - Qiao Li
- Rogel Cancer Center, University of Michigan, Ann Arbor, MI 48109, USA
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7
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Mrugacz M, Bryl A, Falkowski M, Zorena K. Integrins: An Important Link between Angiogenesis, Inflammation and Eye Diseases. Cells 2021; 10:1703. [PMID: 34359873 PMCID: PMC8305893 DOI: 10.3390/cells10071703] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 07/02/2021] [Accepted: 07/04/2021] [Indexed: 12/25/2022] Open
Abstract
Integrins belong to a group of cell adhesion molecules (CAMs) which is a large group of membrane-bound proteins. They are responsible for cell attachment to the extracellular matrix (ECM) and signal transduction from the ECM to the cells. Integrins take part in many other biological activities, such as extravasation, cell-to-cell adhesion, migration, cytokine activation and release, and act as receptors for some viruses, including severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2). They play a pivotal role in cell proliferation, migration, apoptosis, tissue repair and are involved in the processes that are crucial to infection, inflammation and angiogenesis. Integrins have an important part in normal development and tissue homeostasis, and also in the development of pathological processes in the eye. This review presents the available evidence from human and animal research into integrin structure, classification, function and their role in inflammation, infection and angiogenesis in ocular diseases. Integrin receptors and ligands are clinically interesting and may be promising as new therapeutic targets in the treatment of some eye disorders.
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Affiliation(s)
- Małgorzata Mrugacz
- Department of Ophthalmology and Eye Rehabilitation, Medical University of Bialystok, 15-089 Bialystok, Poland;
| | - Anna Bryl
- Department of Ophthalmology and Eye Rehabilitation, Medical University of Bialystok, 15-089 Bialystok, Poland;
| | | | - Katarzyna Zorena
- Department of Immunobiology and Environmental Microbiology, Medical University of Gdansk, 80-211 Gdansk, Poland;
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Zhou D, Thinn AMM, Zhao Y, Wang Z, Zhu J. Structure of an extended β 3 integrin. Blood 2018; 132:962-972. [PMID: 30018079 PMCID: PMC6117741 DOI: 10.1182/blood-2018-01-829572] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 07/10/2018] [Indexed: 12/23/2022] Open
Abstract
Cells use adhesion receptor integrins to communicate with their surroundings. Integrin activation and cellular signaling are coupled with change from bent to extended conformation. β3 integrins, including αIIbβ3, which is essential for the function of platelets in hemostasis and thrombosis, and αVβ3, which plays multiple roles in diverse cell types, have been prototypes in understanding integrin structure and function. Despite extensive structural studies, a high-resolution integrin structure in an extended conformation remains to be determined. The human β3 Leu33Pro polymorphism, located at the PSI domain, defines human platelet-specific alloantigens 1a and 1b (HPA-1a/b), immune response to which is a cause of posttransfusion purpura and fetal/neonatal alloimmune thrombocytopenia. Leu33Pro substitution has also been suggested to be a risk factor for thrombosis. Here we report the crystal structure of the β3 headpiece in either Leu33 or Pro33 form, both of which reveal intermediate and fully extended conformations coexisting in 1 crystal. These were used to build high-resolution structures of full-length β3 integrin in the intermediate and fully extended states, agreeing well with the corresponding conformations observed by electron microscopy. Our structures reveal how β3 integrin becomes extended at its β-knee region and how the flexibility of β-leg domains is determined. In addition, our structures reveal conformational changes of the PSI and I-EGF1 domains upon β3 extension, which may affect the binding of conformation-dependent anti-HPA-1a alloantibodies. Our structural and functional data show that Leu33Pro substitution does not directly alter the conformation or ligand binding of β3 integrin.
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Affiliation(s)
- Dongwen Zhou
- Blood Research Institute, BloodCenter of Wisconsin, part of Versiti, Milwaukee, WI
| | - Aye Myat Myat Thinn
- Blood Research Institute, BloodCenter of Wisconsin, part of Versiti, Milwaukee, WI
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI; and
| | - Yan Zhao
- Blood Research Institute, BloodCenter of Wisconsin, part of Versiti, Milwaukee, WI
- Department of Physiology, School of Basic Medical Science, Shanghai University of Traditional Chinese Medicine, Shanghai, China
| | - Zhengli Wang
- Blood Research Institute, BloodCenter of Wisconsin, part of Versiti, Milwaukee, WI
| | - Jieqing Zhu
- Blood Research Institute, BloodCenter of Wisconsin, part of Versiti, Milwaukee, WI
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI; and
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Pagani G, Pereira JPV, Stoldt VR, Beck A, Scharf RE, Gohlke H. The human platelet antigen-1b (Pro 33) variant of α IIbβ 3 allosterically shifts the dynamic conformational equilibrium of this integrin toward the active state. J Biol Chem 2018; 293:4830-4844. [PMID: 29462793 DOI: 10.1074/jbc.ra118.002149] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 02/08/2018] [Indexed: 11/06/2022] Open
Abstract
Integrins are heterodimeric cell-adhesion receptors comprising α and β subunits that transmit signals allosterically in both directions across the membrane by binding to intra- and extracellular components. The human platelet antigen-1 (HPA-1) polymorphism in αIIbβ3 arises from a Leu → Pro exchange at residue 33 in the genu of the β3 subunit, resulting in Leu33 (HPA-1a) or Pro33 (HPA-1b) isoforms. Although clinical investigations have provided conflicting results, some studies have suggested that Pro33 platelets exhibit increased thrombogenicity. Under flow-dynamic conditions, the Pro33 variant displays prothrombotic properties, characterized by increased platelet adhesion, aggregate/thrombus formation, and outside-in signaling. However, the molecular events underlying this prothrombotic phenotype have remained elusive. As residue 33 is located >80 Å away from extracellular binding sites or transmembrane domains, we hypothesized that the Leu → Pro exchange allosterically shifts the dynamic conformational equilibrium of αIIbβ3 toward an active state. Multiple microsecond-long, all-atom molecular dynamics simulations of the ectodomain of the Leu33 and Pro33 isoforms provided evidence that the Leu → Pro exchange weakens interdomain interactions at the genu and alters the structural dynamics of the integrin to a more unbent and splayed state. Using FRET analysis of fluorescent proteins fused with αIIbβ3 in transfected HEK293 cells, we found that the Pro33 variant in its resting state displays a lower energy transfer than the Leu33 isoform. This finding indicated a larger spatial separation of the cytoplasmic tails in the Pro33 variant. Together, our results indicate that the Leu → Pro exchange allosterically shifts the dynamic conformational equilibrium of αIIbβ3 to a structural state closer to the active one, promoting the fully active state and fostering the prothrombotic phenotype of Pro33 platelets.
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Affiliation(s)
- Giulia Pagani
- Institute for Pharmaceutical and Medicinal Chemistry, 40225 Düsseldorf, Germany
| | - Joana P V Pereira
- Division of Experimental and Clinical Hemostasis, Hemotherapy and Transfusion Medicine, Institute of Transplantation Diagnostics and Cell Therapeutics, Heinrich Heine University Medical Center, 40225 Düsseldorf, Germany
| | - Volker R Stoldt
- Division of Experimental and Clinical Hemostasis, Hemotherapy and Transfusion Medicine, Institute of Transplantation Diagnostics and Cell Therapeutics, Heinrich Heine University Medical Center, 40225 Düsseldorf, Germany
| | - Andreas Beck
- Institute of Informatics, 40225 Düsseldorf, Germany
| | - Rüdiger E Scharf
- Division of Experimental and Clinical Hemostasis, Hemotherapy and Transfusion Medicine, Institute of Transplantation Diagnostics and Cell Therapeutics, Heinrich Heine University Medical Center, 40225 Düsseldorf, Germany; Biological Medical Research Center, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - Holger Gohlke
- Institute for Pharmaceutical and Medicinal Chemistry, 40225 Düsseldorf, Germany; John von Neumann Institute for Computing (NIC), Jülich Supercomputing Centre (JSC), and Institute for Complex Systems-Structural Biochemistry (ICS 6), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
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Li J, Su Y, Xia W, Qin Y, Humphries MJ, Vestweber D, Cabañas C, Lu C, Springer TA. Conformational equilibria and intrinsic affinities define integrin activation. EMBO J 2017; 36:629-645. [PMID: 28122868 PMCID: PMC5331762 DOI: 10.15252/embj.201695803] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 12/12/2016] [Accepted: 12/15/2016] [Indexed: 11/25/2022] Open
Abstract
We show that the three conformational states of integrin α5β1 have discrete free energies and define activation by measuring intrinsic affinities for ligand of each state and the equilibria linking them. The 5,000-fold higher affinity of the extended-open state than the bent-closed and extended-closed states demonstrates profound regulation of affinity. Free energy requirements for activation are defined with protein fragments and intact α5β1 On the surface of K562 cells, α5β1 is 99.8% bent-closed. Stabilization of the bent conformation by integrin transmembrane and cytoplasmic domains must be overcome by cellular energy input to stabilize extension. Following extension, headpiece opening is energetically favored. N-glycans and leg domains in each subunit that connect the ligand-binding head to the membrane repel or crowd one another and regulate conformational equilibria in favor of headpiece opening. The results suggest new principles for regulating signaling in the large class of receptors built from extracellular domains in tandem with single-span transmembrane domains.
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Affiliation(s)
- Jing Li
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Yang Su
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Wei Xia
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Yan Qin
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Martin J Humphries
- Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Manchester, UK
| | | | - Carlos Cabañas
- Centro de Biología Molecular Severo Ochoa (CSIC-UAM) and Departamento de Microbiología I Facultad de Medicina UCM, Madrid, Spain
| | - Chafen Lu
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
| | - Timothy A Springer
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
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11
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Xu XP, Kim E, Swift M, Smith JW, Volkmann N, Hanein D. Three-Dimensional Structures of Full-Length, Membrane-Embedded Human α(IIb)β(3) Integrin Complexes. Biophys J 2016; 110:798-809. [PMID: 26910421 DOI: 10.1016/j.bpj.2016.01.016] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 12/08/2015] [Accepted: 01/13/2016] [Indexed: 10/22/2022] Open
Abstract
Integrins are bidirectional, allosteric transmembrane receptors that play a central role in hemostasis and arterial thrombosis. Using cryo-electron microscopy, multireference single-particle reconstruction methods, and statistics-based computational fitting approaches, we determined three-dimensional structures of human integrin αIIbβ3 embedded in a lipid bilayer (nanodiscs) while bound to domains of the cytosolic regulator talin and to extracellular ligands. We also determined the conformations of integrin in solution by itself to localize the membrane and the talin-binding site. To our knowledge, our data provide unprecedented three-dimensional information about the conformational states of intact, full-length integrin within membrane bilayers under near-physiological conditions and in the presence of cytosolic activators and extracellular ligands. We show that αIIbβ3 integrins exist in a conformational equilibrium clustered around four main states. These conformations range from a compact bent nodule to two partially extended intermediate conformers and finally to a fully upright state. In the presence of nanodiscs and the two ligands, the equilibrium is significantly shifted toward the upright conformation. In this conformation, the receptor extends ∼20 nm upward from the membrane. There are no observable contacts between the two subunits other than those in the headpiece near the ligand-binding pocket, and the α- and β-subunits are well separated with their cytoplasmic tails ∼8 nm apart. Our results indicate that extension of the ectodomain is possible without separating the legs or extending the hybrid domain, and that the ligand-binding pocket is not occluded by the membrane in any conformations of the equilibrium. Further, they suggest that integrin activation may be influenced by equilibrium shifts.
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Affiliation(s)
- Xiao-Ping Xu
- Bioinformatics and Structural Biology Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California
| | - Eldar Kim
- Bioinformatics and Structural Biology Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California
| | - Mark Swift
- Bioinformatics and Structural Biology Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California
| | - Jeffrey W Smith
- Infectious Disease Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California
| | - Niels Volkmann
- Bioinformatics and Structural Biology Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California.
| | - Dorit Hanein
- Bioinformatics and Structural Biology Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California.
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12
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Structural flexibility at a major conserved antibody target on hepatitis C virus E2 antigen. Proc Natl Acad Sci U S A 2016; 113:12768-12773. [PMID: 27791120 DOI: 10.1073/pnas.1609780113] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Hepatitis C virus (HCV) is a major cause of liver disease, affecting over 2% of the world's population. The HCV envelope glycoproteins E1 and E2 mediate viral entry, with E2 being the main target of neutralizing antibody responses. Structural investigations of E2 have produced templates for vaccine design, including the conserved CD81 receptor-binding site (CD81bs) that is a key target of broadly neutralizing antibodies (bNAbs). Unfortunately, immunization with recombinant E2 and E1E2 rarely elicits sufficient levels of bNAbs for protection. To understand the challenges for eliciting bNAb responses against the CD81bs, we investigated the E2 CD81bs by electron microscopy (EM), hydrogen-deuterium exchange (HDX), molecular dynamics (MD), and calorimetry. By EM, we observed that HCV1, a bNAb recognizing the N-terminal region of the CD81bs, bound a soluble E2 core construct from multiple angles of approach, suggesting components of the CD81bs are flexible. HDX of multiple E2 constructs consistently indicated the entire CD81bs was flexible relative to the rest of the E2 protein, which was further confirmed by MD simulations. However, E2 has a high melting temperature of 84.8 °C, which is more akin to proteins from thermophilic organisms. Thus, recombinant E2 is a highly stable protein overall, but with an exceptionally flexible CD81bs. Such flexibility may promote induction of nonneutralizing antibodies over bNAbs to E2 CD81bs, underscoring the necessity of rigidifying this antigenic region as a target for rational vaccine design.
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13
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Leukocyte integrin αLβ2 headpiece structures: The αI domain, the pocket for the internal ligand, and concerted movements of its loops. Proc Natl Acad Sci U S A 2016; 113:2940-5. [PMID: 26936951 DOI: 10.1073/pnas.1601379113] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
High-resolution crystal structures of the headpiece of lymphocyte function-associated antigen-1 (integrin αLβ2) reveal how the αI domain interacts with its platform formed by the α-subunit β-propeller and β-subunit βI domains. The αLβ2 structures compared with αXβ2 structures show that the αI domain, tethered through its N-linker and a disulfide to a stable β-ribbon pillar near the center of the platform, can undergo remarkable pivoting and tilting motions that appear buffered by N-glycan decorations that differ between αL and αX subunits. Rerefined β2 integrin structures reveal details including pyroglutamic acid at the β2 N terminus and bending within the EGF1 domain. Allostery is relayed to the αI domain by an internal ligand that binds to a pocket at the interface between the β-propeller and βI domains. Marked differences between the αL and αX subunit β-propeller domains concentrate near the binding pocket and αI domain interfaces. Remarkably, movement in allostery in the βI domain of specificity determining loop 1 (SDL1) causes concerted movement of SDL2 and thereby tightens the binding pocket for the internal ligand.
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14
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Deller MC, Kong L, Rupp B. Protein stability: a crystallographer's perspective. ACTA CRYSTALLOGRAPHICA SECTION F-STRUCTURAL BIOLOGY COMMUNICATIONS 2016; 72:72-95. [PMID: 26841758 PMCID: PMC4741188 DOI: 10.1107/s2053230x15024619] [Citation(s) in RCA: 140] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Accepted: 12/21/2015] [Indexed: 12/18/2022]
Abstract
Protein stability is a topic of major interest for the biotechnology, pharmaceutical and food industries, in addition to being a daily consideration for academic researchers studying proteins. An understanding of protein stability is essential for optimizing the expression, purification, formulation, storage and structural studies of proteins. In this review, discussion will focus on factors affecting protein stability, on a somewhat practical level, particularly from the view of a protein crystallographer. The differences between protein conformational stability and protein compositional stability will be discussed, along with a brief introduction to key methods useful for analyzing protein stability. Finally, tactics for addressing protein-stability issues during protein expression, purification and crystallization will be discussed.
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Affiliation(s)
- Marc C Deller
- Stanford ChEM-H, Macromolecular Structure Knowledge Center, Stanford University, Shriram Center, 443 Via Ortega, Room 097, MC5082, Stanford, CA 94305-4125, USA
| | - Leopold Kong
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health (NIH), Building 8, Room 1A03, 8 Center Drive, Bethesda, MD 20814, USA
| | - Bernhard Rupp
- Department of Forensic Crystallography, k.-k. Hofkristallamt, 91 Audrey Place, Vista, CA 92084, USA
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15
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Dai A, Ye F, Taylor DW, Hu G, Ginsberg MH, Taylor KA. The Structure of a Full-length Membrane-embedded Integrin Bound to a Physiological Ligand. J Biol Chem 2015; 290:27168-27175. [PMID: 26391523 DOI: 10.1074/jbc.m115.682377] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Indexed: 11/06/2022] Open
Abstract
Increased ligand binding to integrin ("activation") underpins many biological processes, such as leukocyte trafficking, cell migration, host-pathogen interaction, and hemostasis. Integrins exist in several conformations, ranging from compact and bent to extended and open. However, the exact conformation of membrane-embedded, full-length integrin bound to its physiological macromolecular ligand is still unclear. Integrin αIIbβ3, the most abundant integrin in platelets, has been a prototype for integrin activation studies. Using negative stain electron microscopy and nanodisc-embedding to provide a membrane-like environment, we visualized the conformation of full-length αIIbβ3 in both a Mn(2+)-activated, ligand-free state and a Mn(2+)-activated, fibrin-bound state. Activated but ligand-free integrins exist mainly in the compact conformation, whereas fibrin-bound αIIbβ3 predominantly exists in a fully extended, headpiece open conformation. Our results show that membrane-embedded, full-length integrin adopts an extended and open conformation when bound to its physiological macromolecular ligand.
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Affiliation(s)
- Aguang Dai
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4380 and
| | - Feng Ye
- Department of Hematology and Oncology, University of California at San Diego, La Jolla, California 92093-0726
| | - Dianne W Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4380 and
| | - Guiqing Hu
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4380 and
| | - Mark H Ginsberg
- Department of Hematology and Oncology, University of California at San Diego, La Jolla, California 92093-0726
| | - Kenneth A Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4380 and.
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16
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Nguyen PQT, Luu TT, Bai Y, Nguyen GKT, Pervushin K, Tam JP. Allotides: Proline-Rich Cystine Knot α-Amylase Inhibitors from Allamanda cathartica. JOURNAL OF NATURAL PRODUCTS 2015; 78:695-704. [PMID: 25832441 DOI: 10.1021/np500866c] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Cystine knot α-amylase inhibitors belong to a knottin family of peptidyl inhibitors of 30-32 residues and contain two to four prolines. Thus far, only four members of the group of cystine knot α-amylase inhibitors have been characterized. Herein, the discovery and characterization of five cystine knot α-amylase inhibitors, allotides C1-C5 (Ac1-Ac5) (1-5), from the medicinal plant Allamanda cathartica are reported using both proteomic and genomic methods. Proteomic analysis showed that 1-5 are 30 amino acids in length with three or four proline residues. NMR determination of 4 revealed that it has two cis- and one trans-proline residues and adopts two equally populated conformations in solution. Determination of disulfide connectivity of 2 by differential S-reduction and S-alkylation provided clues of its unfolding process. Genomic analysis showed that allotide precursors contain a three-domain arrangement commonly found in plant cystine knot peptides with conserved residues flanking the processing sites of the mature allotide domain. This work expands the number of known cystine knot α-amylase inhibitors and furthers the understanding of both the structural and biological diversity of this type of knottin family.
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Affiliation(s)
- Phuong Q T Nguyen
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Thuy T Luu
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Yang Bai
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Giang K T Nguyen
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Konstantin Pervushin
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - James P Tam
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
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17
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Abstract
Integrin α5β1 binds to an Arg-Gly-Asp (RGD) motif in its ligand fibronectin. We report high-resolution crystal structures of a four-domain α5β1 headpiece fragment, alone or with RGD peptides soaked into crystals, and RGD peptide affinity measurements. The headpiece crystallizes in a closed conformation essentially identical to that seen previously for α5β1 complexed with a Fab that allosterically inhibits ligand binding by stabilizing the closed conformation. Soaking experiments show that binding of cyclic RGD peptide with 20-fold higher affinity than a linear RGD peptide induces conformational change in the β1-subunit βI domain to a state that is intermediate between closed (low affinity) and open (high affinity). In contrast, binding of a linear RGD peptide induces no shape shifting. However, linear peptide binding induces shape shifting when Ca(2+) is depleted during soaking. Ca(2+) bound to the adjacent to metal ion-dependent adhesion site (ADMIDAS), at the locus of shape shifting, moves and decreases in occupancy, correlating with an increase in affinity for RGD measured when Ca(2+) is depleted. The results directly demonstrate that Ca(2+) binding to the ADMIDAS stabilizes integrins in the low-affinity, closed conformation. Comparisons in affinity between four-domain and six-domain headpiece constructs suggest that flexible integrin leg domains contribute to conformational equilibria. High-resolution views of the hybrid domain interface with the plexin-semaphorin-integrin (PSI) domain in different orientations show a ball-and-socket joint with a hybrid domain Arg side chain that rocks in a PSI domain socket lined with carbonyl oxygens.
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18
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Abstract
It has been known for many decades that cell surface, soluble-secreted, and extracellular matrix proteins are generally rich in disulfide bonds, but only more recently has the functional diversity of disulfide bonding in extracellular proteins been appreciated. In addition to the classic mechanisms by which disulfide bonds enhance protein thermodynamic stability, disulfides in certain configurations contribute particular mechanical properties to proteins that sense and respond to tensile forces. Disulfides may help warp protein folds for the evolution of new functions, or they may fasten aggregation-prone flaps of polypeptide to protein surfaces to prevent fibrilization or oligomerization. Disulfides can also be used to package and secure macromolecular cargo for intercellular transport. A series of case studies illustrating diverse biophysical roles of disulfide bonding are reviewed, with a focus on proteins functioning in the extracellular environment.
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Affiliation(s)
- Deborah Fass
- Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
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19
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20
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The leucocyte β2 (CD18) integrins: the structure, functional regulation and signalling properties. Biosci Rep 2012; 32:241-69. [PMID: 22458844 DOI: 10.1042/bsr20110101] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted β2 integrins comprise four members, namely αLβ2, αMβ2, αXβ2 and αDβ2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.
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21
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Integrin inside-out signaling and the immunological synapse. Curr Opin Cell Biol 2011; 24:107-15. [PMID: 22129583 DOI: 10.1016/j.ceb.2011.10.004] [Citation(s) in RCA: 291] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Accepted: 10/19/2011] [Indexed: 11/22/2022]
Abstract
Integrins dynamically equilibrate between three conformational states on cell surfaces. A bent conformation has a closed headpiece. Two extended conformations contain either a closed or an open headpiece. Headpiece opening involves hybrid domain swing-out and a 70 Å separation at the integrin knees, which is conveyed by allostery from the hybrid-proximal end of the βI domain to a 3 Å rearrangement of the ligand-binding site at the opposite end of the βI domain. Both bent-closed and extended-closed integrins have low affinity, whereas extended-open integrin affinity is 10(3) to 10(4) higher. Integrin-mediated adhesion requires the extended-open conformation, which in physiological contexts is stabilized by post-ligand binding events. Integrins thus discriminate between substrate-bound and soluble ligands. Analysis of LFA-1-ICAM-1 interactions in the immunological synapse suggests that bond lifetimes are on the order of seconds, which is consistent with high affinity interactions subjected to cytoskeletal forces that increase the dissociation rate. LFA-1 βI domain antagonists abrogate function in the immunological synapse, further supporting a critical role for high affinity LFA-1.
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22
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Schürpf T, Springer TA. Regulation of integrin affinity on cell surfaces. EMBO J 2011; 30:4712-27. [PMID: 21946563 DOI: 10.1038/emboj.2011.333] [Citation(s) in RCA: 134] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Accepted: 08/22/2011] [Indexed: 11/09/2022] Open
Abstract
Lymphocyte activation triggers adhesiveness of lymphocyte function-associated antigen-1 (LFA-1; integrin α(L)β(2)) for intercellular adhesion molecules (ICAMs) on endothelia or antigen-presenting cells. Whether the activation signal, after transmission through multiple domains to the ligand-binding αI domain, results in affinity changes for ligand has been hotly debated. Here, we present the first comprehensive measurements of LFA-1 affinities on T lymphocytes for ICAM-1 under a broad array of activating conditions. Only a modest increase in affinity for soluble ligand was detected after activation by chemokine or T-cell receptor ligation, conditions that primed LFA-1 and robustly induced lymphocyte adhesion to ICAM-1 substrates. By stabilizing well-defined LFA-1 conformations by Fab, we demonstrate the absolute requirement of the open LFA-1 headpiece for adhesiveness and high affinity. Interaction of primed LFA-1 with immobilized but not soluble ICAM-1 triggers energy-dependent affinity maturation of LFA-1 to an adhesive, high affinity state. Our results lend support to the traction or translational motion dependence of integrin activation.
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Affiliation(s)
- Thomas Schürpf
- Department of Pathology, Harvard Medical School, Immune Disease Institute and Children's Hospital, Boston, MA, USA
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23
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Eng ET, Smagghe BJ, Walz T, Springer TA. Intact alphaIIbbeta3 integrin is extended after activation as measured by solution X-ray scattering and electron microscopy. J Biol Chem 2011; 286:35218-26. [PMID: 21832081 DOI: 10.1074/jbc.m111.275107] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Integrins are bidirectional signaling molecules on the cell surface that have fundamental roles in regulating cell behavior and contribute to cell migration and adhesion. Understanding of the mechanism of integrin signaling and activation has been advanced with truncated ectodomain preparations; however, the nature of conformational change in the full-length intact integrin molecule remains an active area of research. Here we used small angle x-ray scattering and electron microscopy to study detergent-solubilized, intact platelet integrin α(IIb)β(3). In the resting state, the intact α(IIb)β(3) adopted a compact, bent conformation. Upon activation with Mn(2+), the average integrin extension increased. Further activation by addition of ligand led to stabilization of the extended state and opening of the headpiece. The observed extension and conformational rearrangement upon activation are consistent with the extension and headpiece opening model of integrin activation.
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Affiliation(s)
- Edward T Eng
- Immune Disease Institute, Children's Hospital Boston, and Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA
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24
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Molecular dynamics simulations of forced unbending of integrin α(v)β₃. PLoS Comput Biol 2011; 7:e1001086. [PMID: 21379327 PMCID: PMC3040657 DOI: 10.1371/journal.pcbi.1001086] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Accepted: 01/18/2011] [Indexed: 11/24/2022] Open
Abstract
Integrins may undergo large conformational changes during activation, but the dynamic processes and pathways remain poorly understood. We used molecular dynamics to simulate forced unbending of a complete integrin αVβ3 ectodomain in both unliganded and liganded forms. Pulling the head of the integrin readily induced changes in the integrin from a bent to an extended conformation. Pulling at a cyclic RGD ligand bound to the integrin head also extended the integrin, suggesting that force can activate integrins. Interactions at the interfaces between the hybrid and β tail domains and between the hybrid and epidermal growth factor 4 domains formed the major energy barrier along the unbending pathway, which could be overcome spontaneously in ∼1 µs to yield a partially-extended conformation that tended to rebend. By comparison, a fully-extended conformation was stable. A newly-formed coordination between the αV Asp457 and the α-genu metal ion might contribute to the stability of the fully-extended conformation. These results reveal the dynamic processes and pathways of integrin conformational changes with atomic details and provide new insights into the structural mechanisms of integrin activation. Proteins can regulate their functions via conformational changes. One example is integrins, which are transmembrane receptors mediating cell-cell and cell-matrix adhesions. Inactive integrins may assume a bent conformation with low affinities for ligands unable to support adhesions. Intracellular or extracellular stimuli induce large scale changes from the bent to an extended conformation, resulting in active integrins with high affinities for ligands to mediate strong adhesions. We used molecular dynamics simulations to reveal the dynamics and pathways of integrin unbending in atomic details. Critical interactions in this process were identified. This study not only sheds light on the structural mechanisms of integrin activation, but also exemplifies allosteric regulations of protein functions.
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Abstract
Natural killer (NK) cells are innate immune cells that express members of the leukocyte β2 integrin family in humans and mice. These CD11/CD18 heterodimers play critical roles in leukocyte trafficking, immune synapse formation, and costimulation. The cell-surface expression of one of these integrins, CD11b/CD18, is also recognized as a major marker of mouse NK-cell maturation, but its function on NK cells has been largely ignored. Using N-ethyl-N-nitrosourea (ENU) mutagenesis, we generated a mouse carrying an A → T transverse mutation in the Itgb2 gene, resulting in a mutation that prevented the cell-surface expression of CD18 and its associated CD11a, CD11b, and CD11c proteins. We show that β2 integrin-deficient NK cells have a hyporesponsive phenotype in vitro, and present an alteration of their in vivo developmental program characterized by a selective accumulation of c-kit(+) cells. NK-cell missing-self recognition was partially altered in vivo, whereas the early immune response to mouse cytomegalovirus (MCMV) infection occurred normally in CD18-deficient mice. Therefore, β2 integrins are required for optimal NK-cell maturation, but this deficiency is partial and can be bypassed during MCMV infection, highlighting the robustness of antiviral protective responses.
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26
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Rosano C, Rocco M. Solution properties of full-length integrin alpha(IIb)beta3 refined models suggest environment-dependent induction of alternative bent /extended resting states. FEBS J 2010; 277:3190-202. [PMID: 20584077 DOI: 10.1111/j.1742-4658.2010.07724.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The recently published novel integrin alpha(IIb)beta(3) ectodomain crystallographic structure and NMR structures of its transmembrane/cytoplasmic segments were employed to refine previously developed molecular models. Alternative complete alpha(IIb)beta(3) models were built and evaluated, and their shape was compared with EM maps and their computed hydrodynamic/conformational properties were compared with the available experimental data. A partially extended/closed model, or a mixture of bent/closed and extended/closed conformations, are both compatible with the results of a recent small-angle neutron scattering study of Triton X-100-solubilized resting alpha(IIb)beta(3), while new electron microscopy evidence of nanodiscs-embedded alpha(IIb)beta(3) supports the bent/closed resting form. However, only an extended/closed model matches well the hydrodynamics of either octyl-glucoside-solubilized or nanodiscs-embedded resting alpha(IIb)beta(3), suggesting that different solubilization strategies and substrate interactions might operate a conformational selection between alternative, stable states. Furthermore, extended/open models are required to match the electron tomography map and the hydrodynamics following the priming-induced beta(3) hybrid domain swing-out, but without immediate full tail separation. Importantly, both extension and opening transitions can occur by pivoting at the recently identified beta(3) hinge point, which does not appear to be freely flexible. The structure and mechanism of action of integrins thus seem to depend on discrete transitions and to be more tightly coupled to the local environment than previously thought.
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Affiliation(s)
- Camillo Rosano
- Nanobiotecnologie, Istituto Nazionale per la Ricerca sul Cancro (IST), Genova, Italy
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27
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Yu T, Wu X, Gupta KB, Kucik DF. Affinity, lateral mobility, and clustering contribute independently to beta 2-integrin-mediated adhesion. Am J Physiol Cell Physiol 2010; 299:C399-410. [PMID: 20445173 DOI: 10.1152/ajpcell.00039.2009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Affinity changes and avidity modulation both contribute to activation of beta(2)-integrin-mediated adhesion, an essential, early step in inflammation. Avidity modulation, defined as an increase in adhesiveness independent of integrin conformational changes, might be due to integrin clustering, motion, or both. Increased integrin diffusion upon leukocyte activation has been demonstrated, but whether it is proadhesive in itself, or just constitutes a mechanism for integrin clustering, remains unclear. To understand the proadhesive effects of integrin affinity changes, clustering, and motion, an experimental system was devised to separate them. Clustering and integrin motion together were induced by cytochalasin D (CD) without inducing high-affinity; integrin motion could then be frozen by fixation; and high affinity was induced independently by Mn(2+). Adhesion was equivalent for fixed and unfixed cells except following pretreatment with CD or Mn(2+), which increased adhesion for both. However, fixed cells were less adhesive than unfixed cells after CD, even though integrin clustering was similar. A simple explanation is that CD induces both clustering and integrin motion, fixation then stops motion on fixed cells, but integrins continue to diffuse on unfixed cells, increasing the kinetics of integrin/ICAM-1 interactions to enhance adhesion. Affinity changes are then independent of, and additive to, avidity effects.
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Affiliation(s)
- Tao Yu
- Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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28
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Askari JA, Tynan CJ, Webb SED, Martin-Fernandez ML, Ballestrem C, Humphries MJ. Focal adhesions are sites of integrin extension. ACTA ACUST UNITED AC 2010; 188:891-903. [PMID: 20231384 PMCID: PMC2845069 DOI: 10.1083/jcb.200907174] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
FRET experiments model integrin conformation changes in adherent cells. Integrins undergo global conformational changes that specify their activation state. Current models portray the inactive receptor in a bent conformation that upon activation converts to a fully extended form in which the integrin subunit leg regions are separated to enable ligand binding and subsequent signaling. To test the applicability of this model in adherent cells, we used a fluorescent resonance energy transfer (FRET)–based approach, in combination with engineered integrin mutants and monoclonal antibody reporters, to image integrin α5β1 conformation. We find that restricting leg separation causes the integrin to adopt a bent conformation that is unable to respond to agonists and mediate cell spreading. By measuring FRET between labeled α5β1 and the cell membrane, we find extended receptors are enriched in focal adhesions compared with adjacent regions of the plasma membrane. These results demonstrate definitely that major quaternary rearrangements of β1-integrin subunits occur in adherent cells and that conversion from a bent to extended form takes place at focal adhesions.
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Affiliation(s)
- Janet A Askari
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, England, UK
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29
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Xue ZH, Zhao CQ, Chua GL, Tan SW, Tang XY, Wong SC, Tan SM. Integrin alphaMbeta2 clustering triggers phosphorylation and activation of protein kinase C delta that regulates transcription factor Foxp1 expression in monocytes. THE JOURNAL OF IMMUNOLOGY 2010; 184:3697-709. [PMID: 20190138 DOI: 10.4049/jimmunol.0903316] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Integrins are type I membrane and heterodimeric (alphabeta) cell adhesion receptors. Intracellular signals triggered by ligand-bound integrins are important for cell growth, differentiation, and migration. Integrin alpha(M)beta(2) plays key roles in myeloid cell adhesion, phagocytosis, and degranulation. In this study, we show that protein kinase C (PKC) delta is involved in alpha(M)beta(2) signaling. In human monocytic U937 cells and peripheral blood monocytes, alpha(M)beta(2) clustering induced PKCdelta translocation to the plasma membrane, followed by Tyr(311) phosphorylation and activation of PKCdelta by the src family kinases Hck and Lyn. Interestingly, alpha(M)beta(2)-induced PKCdelta Tyr(311) phosphorylation was not mediated by the tyrosine kinase Syk, which is a well reported kinase in beta(2) integrin signaling. Analysis of the beta(2) cytoplasmic tail showed that the sequence Asn(727)-Ser(734) is important in alpha(M)beta(2)-induced PKCdelta Tyr(311) phosphorylation. It has been shown that alpha(M)beta(2) clustering regulates the expression the transcription factor Foxp1 that has a role in monocyte differentiation. We show that Foxp1 expression was reduced in monocytes that were allowed to adhere to human microvascular endothelial cells. However, the expression of Foxp1 was not affected in monocytes that were treated with PKCdelta-targeting small interfering RNA, suggesting that PKCdelta regulates Foxp1 expression. These results demonstrate a role of PKCdelta in alpha(M)beta(2)-mediated Foxp1 regulation in monocytes.
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Affiliation(s)
- Zhi-Hong Xue
- Division of Molecular and Cell Biology, School of Biological Sciences, Nanyang Technological University, Singapore
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30
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Montresor A, Bolomini-Vittori M, Simon SI, Rigo A, Vinante F, Laudanna C. Comparative analysis of normal versus CLL B-lymphocytes reveals patient-specific variability in signaling mechanisms controlling LFA-1 activation by chemokines. Cancer Res 2010; 69:9281-90. [PMID: 19934331 DOI: 10.1158/0008-5472.can-09-2009] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Activation of lymphocyte function-associated antigen-1 (LFA-1) by chemokines is fine-tuned by inside-out signaling mechanisms responsible for integrin-mediated adhesion modulation. In the present study, we investigated the possibility of qualitative variability of signaling mechanisms controlling LFA-1 activation in chronic lymphocytic leukemia (CLL) cells. We pursued a multiplexed comparative analysis of the role of the recently described chemokine-triggered rho-signaling module in human normal versus CLL B-lymphocytes. We found that the rho-module of LFA-1 affinity triggering is functionally conserved in normal B-lymphocytes. In contrast, in malignant B-lymphocytes isolated from patients with B-CLL, the role of the rho-module was not maintained, showing remarkable differences and variability. Specifically, RhoA and phospholipase D1 were crucially involved in LFA-1 affinity triggering by CXCL12 in all analyzed patients. In contrast, Rac1 and CDC42 involvement displayed a consistent patient-by-patient variability, with a group of patients showing LFA-1 affinity modulation totally independent of Rac1 and CDC42 signaling activity. Finally, phosphatidylinositol-4-phosphate 5-kinase isoform 1gamma (PIP5KC) was found without any regulatory role in all patients. The data imply that the neoplastic progression may completely bypass the regulatory role of Rac1, CDC42, and PIP5KC, and show a profound divergence in the signaling mechanisms controlling integrin activation in normal versus neoplastic lymphocytes, suggesting that patients with CLL can be more accurately evaluated on the basis of the analysis of signaling mechanisms controlling integrin activation. Our findings could potentially affect the diagnosis, prognosis, and therapy of CLL disorders.
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31
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Structure of an integrin with an alphaI domain, complement receptor type 4. EMBO J 2009; 29:666-79. [PMID: 20033057 DOI: 10.1038/emboj.2009.367] [Citation(s) in RCA: 142] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 11/05/2009] [Indexed: 11/08/2022] Open
Abstract
We report the structure of an integrin with an alphaI domain, alpha(X)beta(2), the complement receptor type 4. It was earlier expected that a fixed orientation between the alphaI domain and the beta-propeller domain in which it is inserted would be required for allosteric signal transmission. However, the alphaI domain is highly flexible, enabling two betaI domain conformational states to couple to three alphaI domain states, and greater accessibility for ligand recognition. Although alpha(X)beta(2) is bent similarly to integrins that lack alphaI domains, the terminal domains of the alpha- and beta-legs, calf-2 and beta-tail, are oriented differently than in alphaI-less integrins. Linkers extending to the transmembrane domains are unstructured. Previous mutations in the beta(2)-tail domain support the importance of extension, rather than a deadbolt, in integrin activation. The locations of further activating mutations and antibody epitopes show the critical role of extension, and conversion from the closed to the open headpiece conformation, in integrin activation. Differences among 10 molecules in crystal lattices provide unprecedented information on interdomain flexibility important for modelling integrin extension and activation.
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32
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Abstract
Integrins are a ubiquitous family of non-covalently associated alpha/beta transmembrane heterodimers linking extracellular ligands to intracellular signaling pathways [1] [Cell, 2002; 110: 673]. Platelets contain five integrins, three beta1 integrins that mediate platelet adhesion to the matrix proteins collagen, fibronectin and laminin, and the beta3 integrins alphavbeta3 and alphaIIbbeta3 [2] [J Clin Invest, 2005; 115: 3363]. While there are only several hundred alphavbeta3 molecules per platelet, alphavbeta3 mediates platelet adhesion to osteopontin and vitronectin in vitro [3] [J Biol Chem, 1997; 272: 8137]; whether this occurs in vivo remains unknown. By contrast, the 80,000 alphaIIbbeta3 molecules on agonist-stimulated platelets bind fibrinogen, von Willebrand factor, and fibronectin, mediating platelet aggregation when the bound proteins crosslink adjacent platelets [2] [J Clin Invest, 2005; 115: 3363]. Although platelet integrins are poised to shift from resting to active conformations, tight regulation of their activity is essential to prevent the formation of intravascular thrombi. This review focuses on the structure and function of the intensively studied beta3 integrins, in particular alphaIIbbeta3, but reference will be made to other integrins where relevant.
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Affiliation(s)
- J S Bennett
- Hematology-Oncology Division, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
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33
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Lau TL, Kim C, Ginsberg MH, Ulmer TS. The structure of the integrin alphaIIbbeta3 transmembrane complex explains integrin transmembrane signalling. EMBO J 2009; 28:1351-61. [PMID: 19279667 PMCID: PMC2683045 DOI: 10.1038/emboj.2009.63] [Citation(s) in RCA: 272] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Accepted: 02/18/2009] [Indexed: 12/16/2022] Open
Abstract
Heterodimeric integrin adhesion receptors regulate cell migration, survival and differentiation in metazoa by communicating signals bi-directionally across the plasma membrane. Protein engineering and mutagenesis studies have suggested that the dissociation of a complex formed by the single-pass transmembrane (TM) segments of the alpha and beta subunits is central to these signalling events. Here, we report the structure of the integrin alphaIIbbeta3 TM complex, structure-based site-directed mutagenesis and lipid embedding estimates to reveal the structural event that underlies the transition from associated to dissociated states, that is, TM signalling. The complex is stabilized by glycine-packing mediated TM helix crossing within the extracellular membrane leaflet, and by unique hydrophobic and electrostatic bridges in the intracellular leaflet that mediate an unusual, asymmetric association of the 24- and 29-residue alphaIIb and beta3 TM helices. The structurally unique, highly conserved integrin alphaIIbbeta3 TM complex rationalizes bi-directional signalling and represents the first structure of a heterodimeric TM receptor complex.
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Affiliation(s)
- Tong-Lay Lau
- Department of Biochemistry and Molecular Biology, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Chungho Kim
- Department of Medicine, University of California San Diego, La Jolla, CA, USA
| | - Mark H Ginsberg
- Department of Medicine, University of California San Diego, La Jolla, CA, USA
| | - Tobias S Ulmer
- Department of Biochemistry and Molecular Biology, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
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34
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Vanhoorelbeke K, De Meyer SF, Pareyn I, Melchior C, Plançon S, Margue C, Pradier O, Fondu P, Kieffer N, Springer TA, Deckmyn H. The novel S527F mutation in the integrin beta3 chain induces a high affinity alphaIIbbeta3 receptor by hindering adoption of the bent conformation. J Biol Chem 2009; 284:14914-20. [PMID: 19329429 DOI: 10.1074/jbc.m809167200] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Three heterozygous mutations were identified in the genes encoding platelet integrin receptor alphaIIbbeta3 in a patient with an ill defined platelet disorder: one in the beta3 gene (S527F) and two in the alphaIIb gene (R512W and L841M). Five stable Chinese hamster ovary cell lines were constructed expressing recombinant alphaIIbbeta3 receptors bearing the individual R512W, L841M, or S527F mutation; both the R512W and L841M mutations; or all three mutations. All receptors were expressed on the cell surface, and mutations R512W and L841M had no effect on integrin function. Interestingly, the beta3 S527F mutation produced a constitutively active receptor. Indeed, both fibrinogen and the ligand-mimetic antibody PAC-1 bound to non-activated alphaIIbbeta3 receptors carrying the S527F mutation, indicating that the conformation of this receptor was altered and corresponded to the high affinity ligand binding state. In addition, the conformational change induced by S527F was evident from basal anti-ligand-induced binding site antibody binding to the receptor. A molecular model bearing this mutation was constructed based on the crystal structure of alphaIIbbeta3 and revealed that the S527F mutation, situated in the third integrin epidermal growth factor-like (I-EGF3) domain, hindered the alphaIIbbeta3 receptor from adopting a wild type-like bent conformation. Movement of I-EGF3 into a cleft in the bent conformation may be hampered both by steric hindrance between Phe(527) in beta3 and the calf-1 domain in alphaIIb and by decreased flexibility between I-EGF2 and I-EGF3.
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Affiliation(s)
- Karen Vanhoorelbeke
- Laboratory for Thrombosis Research, Interdisciplinary Research Center, Katholieke Universiteit Leuven Campus Kortrijk, 8500 Kortrijk, Belgium.
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35
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Askari JA, Buckley PA, Mould AP, Humphries MJ. Linking integrin conformation to function. J Cell Sci 2009; 122:165-70. [PMID: 19118208 DOI: 10.1242/jcs.018556] [Citation(s) in RCA: 236] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Integrins are alphabeta heterodimeric adhesion receptors that relay signals bidirectionally across the plasma membrane between the extracellular matrix and cell-surface ligands, and cytoskeletal and signalling effectors. The physical and chemical signals that are controlled by integrins are essential for intercellular communication and underpin all aspects of metazoan existence. To mediate such diverse functions, integrins exhibit structural diversity, flexibility and dynamism. Conformational changes, as opposed to surface expression or clustering, are central to the regulation of receptor function. In recent years, there has been intense interest in determining the three-dimensional structure of integrins, and analysing the shape changes that underpin the interconversion between functional states. Considering the central importance of the integrin signalling nexus, it is perhaps no surprise that obtaining this information has been difficult, and the answers gained so far have been complicated. In this Commentary, we pose some of the key remaining questions that surround integrin structure-function relationships and review the evidence that supports the current models.
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Affiliation(s)
- Janet A Askari
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
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36
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Zhu J, Luo BH, Xiao T, Zhang C, Nishida N, Springer TA. Structure of a complete integrin ectodomain in a physiologic resting state and activation and deactivation by applied forces. Mol Cell 2009; 32:849-61. [PMID: 19111664 DOI: 10.1016/j.molcel.2008.11.018] [Citation(s) in RCA: 370] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2008] [Revised: 08/08/2008] [Accepted: 11/25/2008] [Indexed: 12/01/2022]
Abstract
The complete ectodomain of integrin alpha(IIb)beta(3) reveals a bent, closed, low-affinity conformation, the beta knee, and a mechanism for linking cytoskeleton attachment to high affinity for ligand. Ca and Mg ions in the recognition site, including the synergistic metal ion binding site (SyMBS), are loaded prior to ligand binding. Electrophilicity of the ligand-binding Mg ion is increased in the open conformation. The beta(3) knee passes between the beta(3)-PSI and alpha(IIb)-knob to bury the lower beta leg in a cleft, from which it is released for extension. Different integrin molecules in crystals and EM reveal breathing that appears on pathway to extension. Tensile force applied to the extended ligand-receptor complex stabilizes the closed, low-affinity conformation. By contrast, an additional lateral force applied to the beta subunit to mimic attachment to moving actin filaments stabilizes the open, high-affinity conformation. This mechanism propagates allostery over long distances and couples cytoskeleton attachment of integrins to their high-affinity state.
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Affiliation(s)
- Jianghai Zhu
- The Immune Disease Institute and Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
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37
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Rocco M, Rosano C, Weisel JW, Horita DA, Hantgan RR. Integrin conformational regulation: uncoupling extension/tail separation from changes in the head region by a multiresolution approach. Structure 2008; 16:954-64. [PMID: 18547527 DOI: 10.1016/j.str.2008.02.019] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Revised: 02/07/2008] [Accepted: 02/18/2008] [Indexed: 12/31/2022]
Abstract
Integrin-dependent adhesion and signaling are regulated by conformational changes whose details remain controversial. Crystallography revealed bent shapes for resting and primed integrin ectodomains, whereas large, ligand-induced rearrangements in other constructs suggested extension, "opening," and tail separation. We have used experimental/computed hydrodynamics to discriminate among different alpha(v)beta(3) and alpha(IIb)beta(3) atomic models built on X-ray, NMR, and EM data. In contrast with X-ray structures and EM maps, hydrodynamics indicate that resting integrins are already extended. Furthermore, the hydrodynamics of an alpha(v)beta(3) ectodomain-fibronectin fragment complex support opening via additional head region conformational changes (hybrid domain swing-out), but without tail separation. Likewise, frictional changes induced by priming agents in full-length alpha(IIb)beta(3) correlate well with the swing-out coupled to a simple transmembrane helix shift in an extended, electron tomography-based model. Extension and immediate tail separation are then uncoupled from head region rearrangements following activation, thus underscoring integrins' delicate, finely tuned plasticity.
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Affiliation(s)
- Mattia Rocco
- S.S. Biopolimeri e Proteomica, Istituto Nazionale per la Ricerca sul Cancro, IST c/o CBA, Genoa, Italy.
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Tang ML, Vararattanavech A, Tan SM. Urokinase-type plasminogen activator receptor induces conformational changes in the integrin alphaMbeta2 headpiece and reorientation of its transmembrane domains. J Biol Chem 2008; 283:25392-25403. [PMID: 18644795 DOI: 10.1074/jbc.m802311200] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The glycosylphosphatidylinositol-linked urokinase-type plasminogen activator receptor (uPAR) interacts with the heterodimer cell adhesion molecules integrins to modulate cell adhesion and migration. Devoid of a cytoplasmic domain, uPAR triggers intracellular signaling via its associated molecules that contain cytoplasmic domains. Interestingly, uPAR changes the ectodomain conformation of one of its partner molecules, integrin alpha(5)beta(1), and elicits cytoplasmic signaling. The separation or reorientation of integrin transmembrane domains and cytoplasmic tails are required for integrin outside-in signaling. However, there is a lack of direct evidence showing these conformational changes of an integrin that interacts with uPAR. In this investigation we used reporter monoclonal antibodies and fluorescence resonance energy transfer analyses to show conformational changes in the alpha(M)beta(2) headpiece and reorientation of its transmembrane domains when alpha(M)beta(2) interacts with uPAR.
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Affiliation(s)
- Man-Li Tang
- Division of Molecular and Cell Biology, School of Biological Sciences, Nanyang Technological University, 637551, Singapore
| | - Ardcharaporn Vararattanavech
- Division of Molecular and Cell Biology, School of Biological Sciences, Nanyang Technological University, 637551, Singapore
| | - Suet-Mien Tan
- Division of Molecular and Cell Biology, School of Biological Sciences, Nanyang Technological University, 637551, Singapore.
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39
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Tang XY, Li YF, Tan SM. Intercellular adhesion molecule-3 binding of integrin alphaL beta2 requires both extension and opening of the integrin headpiece. THE JOURNAL OF IMMUNOLOGY 2008; 180:4793-804. [PMID: 18354203 DOI: 10.4049/jimmunol.180.7.4793] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The leukocyte-restricted integrin alpha(L)beta(2) is required in immune processes such as leukocyte adhesion, migration, and immune synapse formation. Activation of alpha(L)beta(2) by conformational changes promotes alpha(L)beta(2) binding to its ligands, ICAMs. It was reported that different affinity states of alpha(L)beta(2) are required for binding ICAM-1 and ICAM-3. Recently, the bent, extended with a closed headpiece, and extended with open headpiece conformations of alpha(L)beta(2), was reported. To address the overall conformational requirements of alpha(L)beta(2) that allow selective binding of these ICAMs, we examined the adhesion properties of these alpha(L)beta(2) conformers. alpha(L)beta(2) with different conformations were generated by mutations, and verified by using a panel of reporter mAbs that detect alpha(L)beta(2) extension, hybrid domain movement, or I-like domain activation. We report a marked difference between extended alpha(L)beta(2) with closed and open headpieces in their adhesive properties to ICAM-1 and ICAM-3. Our data show that the extension of alpha(L)beta(2) alone is sufficient to mediate ICAM-1 adhesion. By contrast, an extended alpha(L)beta(2) with an open headpiece is required for ICAM-3 adhesion.
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Affiliation(s)
- Xiao-Yan Tang
- School of Biological Sciences, Nanyang Technological University, Singapore
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40
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Permissive transmembrane helix heterodimerization is required for the expression of a functional integrin. Biochem J 2008; 410:495-502. [DOI: 10.1042/bj20071218] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The current paradigm is that integrin is activated via inside-out signalling when its cytoplasmic tails and TMs (transmembrane helices) are separated by specific cytosolic protein(s). Perturbations of the helical interface between the α- and β-TMs of an integrin, as a result of mutations, affect its function. Previous studies have shown the requirement for specific pairing between integrin subunits by ectodomain-exchange analyses. It remains unknown whether permissive α/β-TM pairing of an integrin is also required for pairing specificity and the expression of a functionally regulated receptor. We performed scanning replacement of integrin β2-TM with a TM of other integrin β-subunits. With the exception of β4 substitution, others presented β2-integrins with modified phenotypes, either in their expression or ligand-binding properties. Subsequently, we adopted αLβ2 for follow-on experiments because its conformation and affinity-state transitions have been well defined as compared with other members of the β2-integrins. Replacement of β2- with β3-TM generated a chimaeric αLβ2 of an intermediate affinity that adhered to ICAM-1 (intercellular adhesion molecule 1) but not to ICAM-3 constitutively. Replacing αL-TM with αIIb-TM, forming a natural αIIb/β3-TM pair, reversed the phenotype of the chimaera to that of wild-type αLβ2. Interestingly, the replacement of αLβ2- with β3-TM showed neither an extended conformation nor the separation of its cytoplasmic tails, which are well-reported hallmarks of an activated αLβ2, as determined by reporter mAb (monoclonal antibody) KIM127 reactivity and FRET (fluorescence resonance energy transfer) measurements respectively. Collectively, our results suggest that TM pairing specificity is required for the expression of a functionally regulated integrin.
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