1
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Situ AJ, Kim J, An W, Kim C, Ulmer TS. Insight Into Pathological Integrin αIIbβ3 Activation From Safeguarding The Inactive State. J Mol Biol 2021; 433:166832. [PMID: 33539882 PMCID: PMC11025565 DOI: 10.1016/j.jmb.2021.166832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 01/01/2021] [Accepted: 01/12/2021] [Indexed: 11/20/2022]
Abstract
The inhibition of physiological activation pathways of the platelet adhesion receptor integrin αIIbβ3 may fail to prevent fatal thrombosis, suggesting that the receptor is at risk of activation by yet an unidentified pathway. Here, we report the discovery and characterization of a structural motif that safeguards the receptor by selectively destabilizing its inactive state. At the extracellular membrane border, an overpacked αIIb(W968)-β3(I693) contact prevents αIIb(Gly972) from optimally assembling the αIIbβ3 transmembrane complex, which maintains the inactive state. This destabilization of approximately 1.0 kcal/mol could be mitigated by hydrodynamic forces but not physiological agonists, thereby identifying hydrodynamic forces as pathological activation stimulus. As reproductive life spans are not generally limited by cardiovascular disease, it appears that the evolution of the safeguard was driven by fatal, hydrodynamic force-mediated integrin αIIbβ3 activation in the healthy cardiovascular system. The triggering of the safeguard solely by pathological stimuli achieves an effective increase of the free energy barrier between inactive and active receptor states without incurring an increased risk of bleeding. Thus, integrin αIIbβ3 has evolved an effective way to protect receptor functional states that indicates the availability of a mechanical activation pathway when hydrodynamic forces exceed physiological margins.
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Affiliation(s)
- Alan J Situ
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Jiyoon Kim
- Department of Life Sciences, Korea University, Seoul, Republic of Korea
| | - Woojin An
- Department of Biochemistry and Molecular Medicine, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA, USA
| | - Chungho Kim
- Department of Life Sciences, Korea University, Seoul, Republic of Korea.
| | - Tobias S Ulmer
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
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2
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Song G, Luo BH. Effects of the association of the α v β 8 lower legs on integrin ligand binding. J Cell Biochem 2021; 122:801-813. [PMID: 33619784 DOI: 10.1002/jcb.29912] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 02/08/2021] [Accepted: 02/10/2021] [Indexed: 12/18/2022]
Abstract
Many integrins transmit signals through global conformational changes. However, it is unclear whether integrin αv β8 adopts a similar mechanism during integrin activation and signaling on the cell surface. Here, we showed that disulfide-bonded mutants, which prevented integrin αv β8 lower leg dissociation, bound ligands with similar level as the wild-type protein, suggesting that αv β8 ligand binding did not require lower leg disassociation. We further showed that the N-glycosylation mutant at the interface between the β I and hybrid domains did not affect ligand binding, suggesting that the αv β8 open headpiece was not present on the cell surface. We proposed that αv β8 integrin may adopt only one state, that is, the extended conformation with a closed headpiece. Our results showed that two lower legs retained heterodimeric interfaces, and this association might be important for stabilizing integrin in the extended conformation. Therefore, αv β8 may not transmit bidirectional signals across the plasma membrane but instead may serve as an anchoring site with high affinity and high accessibility for extracellular ligands.
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Affiliation(s)
- Guannan Song
- Department of Life Science, University of Louisiana State University, Baton Rouge, Louisiana, USA
| | - Bing-Hao Luo
- Department of Life Science, University of Louisiana State University, Baton Rouge, Louisiana, USA
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3
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Tan SK, Fong KP, Polizzi NF, Sternisha A, Slusky JSG, Yoon K, DeGrado WF, Bennett JS. Modulating Integrin αIIbβ3 Activity through Mutagenesis of Allosterically Regulated Intersubunit Contacts. Biochemistry 2019; 58:3251-3259. [PMID: 31264850 DOI: 10.1021/acs.biochem.9b00430] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Integrin αIIbβ3, a transmembrane heterodimer, mediates platelet aggregation when it switches from an inactive to an active ligand-binding conformation following platelet stimulation. Central to regulating αIIbβ3 activity is the interaction between the αIIb and β3 extracellular stalks, which form a tight heterodimer in the inactive state and dissociate in the active state. Here, we demonstrate that alanine replacements of sensitive positions in the heterodimer stalk interface destabilize the inactive conformation sufficiently to cause constitutive αIIbβ3 activation. To determine the structural basis for this effect, we performed a structural bioinformatics analysis and found that perturbing intersubunit contacts with favorable interaction geometry through substitutions to alanine quantitatively accounted for the degree of constitutive αIIbβ3 activation. This mutational study directly assesses the relationship between favorable interaction geometry at mutation-sensitive positions and the functional activity of those mutants, giving rise to a simple model that highlights the importance of interaction geometry in contributing to the stability between protein-protein interactions.
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Affiliation(s)
- Sophia K Tan
- Department of Pharmaceutical Chemistry , University of California, San Francisco , San Francisco , California 94158 , United States
| | - Karen P Fong
- Hematology-Oncology Division , University of Pennsylvania School of Medicine , Philadelphia , Pennsylvania 19104 , United States
| | - Nicholas F Polizzi
- Department of Pharmaceutical Chemistry , University of California, San Francisco , San Francisco , California 94158 , United States
| | - Alex Sternisha
- Hematology-Oncology Division , University of Pennsylvania School of Medicine , Philadelphia , Pennsylvania 19104 , United States
| | - Joanna S G Slusky
- Department of Molecular Biosciences and Center for Computational Biology , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Kyungchul Yoon
- Hematology-Oncology Division , University of Pennsylvania School of Medicine , Philadelphia , Pennsylvania 19104 , United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California, San Francisco , San Francisco , California 94158 , United States
| | - Joel S Bennett
- Hematology-Oncology Division , University of Pennsylvania School of Medicine , Philadelphia , Pennsylvania 19104 , United States
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4
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Hu P, Luo B. The interface between the EGF1 and EGF2 domains is critical in integrin affinity regulation. J Cell Biochem 2018; 119:7264-7273. [DOI: 10.1002/jcb.26921] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Accepted: 04/04/2018] [Indexed: 02/02/2023]
Affiliation(s)
- Ping Hu
- Department of Biological SciencesLouisiana State UniversityBaton RougeLouisiana
- Department of Biomedical EngineeringUniversity of VirginiaCharlottesvilleVirginia
| | - Bing‐Hao Luo
- Department of Biological SciencesLouisiana State UniversityBaton RougeLouisiana
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5
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MT4-MMP deficiency increases patrolling monocyte recruitment to early lesions and accelerates atherosclerosis. Nat Commun 2018; 9:910. [PMID: 29500407 PMCID: PMC5834547 DOI: 10.1038/s41467-018-03351-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Accepted: 02/07/2018] [Indexed: 12/16/2022] Open
Abstract
Matrix metalloproteinases are involved in vascular remodeling. Little is known about their immune regulatory role in atherosclerosis. Here we show that mice deficient for MT4-MMP have increased adherence of macrophages to inflamed peritonea, and larger lipid deposits and macrophage burden in atherosclerotic plaques. We also demonstrate that MT4-MMP deficiency results in higher numbers of patrolling monocytes crawling and adhered to inflamed endothelia, and the accumulation of Mafb+ apoptosis inhibitor of macrophage (AIM)+ macrophages at incipient atherosclerotic lesions in mice. Functionally, MT4-MMP-null Mafb+AIM+ peritoneal macrophages express higher AIM and scavenger receptor CD36, are more resistant to apoptosis, and bind acLDL avidly, all of which contribute to atherosclerosis. CCR5 inhibition alleviates these effects by hindering the enhanced recruitment of MT4-MMP-null patrolling monocytes to early atherosclerotic lesions, thus blocking Mafb+AIM+ macrophage accumulation and atherosclerosis acceleration. Our results suggest that MT4-MMP targeting may constitute a novel strategy to boost patrolling monocyte activity in early inflammation.
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6
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Hu P, Luo BH. Integrin αv
β8
Adopts a High Affinity State for Soluble Ligands Under Physiological Conditions. J Cell Biochem 2017; 118:2044-2052. [DOI: 10.1002/jcb.25780] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 11/01/2016] [Indexed: 11/12/2022]
Affiliation(s)
- Ping Hu
- Department of Biological Sciences; Louisiana State University; Baton Rouge Louisiana
| | - Bing-Hao Luo
- Department of Biological Sciences; Louisiana State University; Baton Rouge Louisiana
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7
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Schmidt T, Ye F, Situ AJ, An W, Ginsberg MH, Ulmer TS. A Conserved Ectodomain-Transmembrane Domain Linker Motif Tunes the Allosteric Regulation of Cell Surface Receptors. J Biol Chem 2016; 291:17536-46. [PMID: 27365391 PMCID: PMC5016151 DOI: 10.1074/jbc.m116.733683] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 06/09/2016] [Indexed: 11/06/2022] Open
Abstract
In many families of cell surface receptors, a single transmembrane (TM) α-helix separates ecto- and cytosolic domains. A defined coupling of ecto- and TM domains must be essential to allosteric receptor regulation but remains little understood. Here, we characterize the linker structure, dynamics, and resulting ecto-TM domain coupling of integrin αIIb in model constructs and relate it to other integrin α subunits by mutagenesis. Cellular integrin activation assays subsequently validate the findings in intact receptors. Our results indicate a flexible yet carefully tuned ecto-TM coupling that modulates the signaling threshold of integrin receptors. Interestingly, a proline at the N-terminal TM helix border, termed NBP, is critical to linker flexibility in integrins. NBP is further predicted in 21% of human single-pass TM proteins and validated in cytokine receptors by the TM domain structure of the cytokine receptor common subunit β and its P441A-substituted variant. Thus, NBP is a conserved uncoupling motif of the ecto-TM domain transition and the degree of ecto-TM domain coupling represents an important parameter in the allosteric regulation of diverse cell surface receptors.
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Affiliation(s)
- Thomas Schmidt
- From the Department of Biochemistry & Molecular Biology and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Feng Ye
- the Department of Medicine, University of California San Diego, La Jolla, California 92093, and
| | - Alan J Situ
- From the Department of Biochemistry & Molecular Biology and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Woojin An
- the Department of Biochemistry & Molecular Biology and Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California 90033
| | - Mark H Ginsberg
- the Department of Medicine, University of California San Diego, La Jolla, California 92093, and
| | - Tobias S Ulmer
- From the Department of Biochemistry & Molecular Biology and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033,
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8
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Integrin αIIbβ3 transmembrane domain separation mediates bi-directional signaling across the plasma membrane. PLoS One 2015; 10:e0116208. [PMID: 25617834 PMCID: PMC4305291 DOI: 10.1371/journal.pone.0116208] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Accepted: 12/06/2014] [Indexed: 11/19/2022] Open
Abstract
Integrins play an essential role in hemostasis, thrombosis, and cell migration, and they transmit bidirectional signals. Transmembrane/cytoplasmic domains are hypothesized to associate in the resting integrins; whereas, ligand binding and intracellular activating signals induce transmembrane domain separation. However, how this conformational change affects integrin outside-in signaling and whether the α subunit cytoplasmic domain is important for this signaling remain elusive. Using Chinese Hamster Ovary (CHO) cells that stably expressed different integrin αIIbβ3 constructs, we discovered that an αIIb cytoplasmic domain truncation led to integrin activation but not defective outside-in signaling. In contrast, preventing transmembrane domain separation abolished both inside-out and outside-in signaling regardless of removing the αIIb cytoplasmic tail. Truncation of the αIIb cytoplasmic tail did not obviously affect adhesion-induced outside-in signaling. Our research revealed that transmembrane domain separation is a downstream conformational change after the cytoplasmic domain dissociation in inside-out activation and indispensable for ligand-induced outside-in signaling. The result implicates that the β TM helix rearrangement after dissociation is essential for integrin transmembrane signaling. Furthermore, we discovered that the PI3K/Akt pathway is not essential for cell spreading but spreading-induced Erk1/2 activation is PI3K dependent implicating requirement of the kinase for cell survival in outside-in signaling.
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9
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Eble JA, de Rezende FF. Redox-relevant aspects of the extracellular matrix and its cellular contacts via integrins. Antioxid Redox Signal 2014; 20:1977-93. [PMID: 24040997 PMCID: PMC3993061 DOI: 10.1089/ars.2013.5294] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Revised: 08/29/2013] [Accepted: 09/16/2013] [Indexed: 12/30/2022]
Abstract
SIGNIFICANCE The extracellular matrix (ECM) fulfills essential functions in multicellular organisms. It provides the mechanical scaffold and environmental cues to cells. Upon cell attachment, the ECM signals into the cells. In this process, reactive oxygen species (ROS) are physiologically used as signalizing molecules. RECENT ADVANCES ECM attachment influences the ROS-production of cells. In turn, ROS affect the production, assembly and turnover of the ECM during wound healing and matrix remodeling. Pathological changes of ROS levels lead to excess ECM production and increased tissue contraction in fibrotic disorders and desmoplastic tumors. Integrins are cell adhesion molecules which mediate cell adhesion and force transmission between cells and the ECM. They have been identified as a target of redox-regulation by ROS. Cysteine-based redox-modifications, together with structural data, highlighted particular regions within integrin heterodimers that may be subject to redox-dependent conformational changes along with an alteration of integrin binding activity. CRITICAL ISSUES In a molecular model, a long-range disulfide-bridge within the integrin β-subunit and disulfide bridges within the genu and calf-2 domains of the integrin α-subunit may control the transition between the bent/inactive and upright/active conformation of the integrin ectodomain. These thiol-based intramolecular cross-linkages occur in the stalk domain of both integrin subunits, whereas the ligand-binding integrin headpiece is apparently unaffected by redox-regulation. FUTURE DIRECTIONS Redox-regulation of the integrin activation state may explain the effect of ROS in physiological processes. A deeper understanding of the underlying mechanism may open new prospects for the treatment of fibrotic disorders.
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Affiliation(s)
- Johannes A. Eble
- Institute for Physiological Chemistry and Pathobiochemistry, University of Münster, Münster, Germany
- Excellence Cluster Cardio-Pulmonary System, Center for Molecular Medicine, Vascular Matrix Biology, Frankfurt University Hospital, Frankfurt/Main, Germany
| | - Flávia Figueiredo de Rezende
- Institute for Physiological Chemistry and Pathobiochemistry, University of Münster, Münster, Germany
- Excellence Cluster Cardio-Pulmonary System, Center for Molecular Medicine, Vascular Matrix Biology, Frankfurt University Hospital, Frankfurt/Main, Germany
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10
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Raborn J, Fu T, Wu X, Xiu Z, Li G, Luo BH. Variation in one residue associated with the metal ion-dependent adhesion site regulates αIIbβ3 integrin ligand binding affinity. PLoS One 2013; 8:e76793. [PMID: 24116162 PMCID: PMC3792891 DOI: 10.1371/journal.pone.0076793] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 08/29/2013] [Indexed: 01/06/2023] Open
Abstract
The Asp of the RGD motif of the ligand coordinates with the β I domain metal ion dependent adhesion site (MIDAS) divalent cation, emphasizing the importance of the MIDAS in ligand binding. There appears to be two distinct groups of integrins that differ in their ligand binding affinity and adhesion ability. These differences may be due to a specific residue associated with the MIDAS, particularly the β3 residue Ala252 and corresponding Ala in the β1 integrin compared to the analogous Asp residue in the β2 and β7 integrins. Interestingly, mutations in the adjacent to MIDAS (ADMIDAS) of integrins α4β7 and αLβ2 increased the binding and adhesion abilities compared to the wild-type, while the same mutations in the α2β1, α5β1, αVβ3, and αIIbβ3 integrins demonstrated decreased ligand binding and adhesion. We introduced a mutation in the αIIbβ3 to convert this MIDAS associated Ala252 to Asp. By combination of this mutant with mutations of one or two ADMIDAS residues, we studied the effects of this residue on ligand binding and adhesion. Then, we performed molecular dynamics simulations on the wild-type and mutant αIIbβ3 integrin β I domains, and investigated the dynamics of metal ion binding sites in different integrin-RGD complexes. We found that the tendency of calculated binding free energies was in excellent agreement with the experimental results, suggesting that the variation in this MIDAS associated residue accounts for the differences in ligand binding and adhesion among different integrins, and it accounts for the conflicting results of ADMIDAS mutations within different integrins. This study sheds more light on the role of the MIDAS associated residue pertaining to ligand binding and adhesion and suggests that this residue may play a pivotal role in integrin-mediated cell rolling and firm adhesion.
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Affiliation(s)
- Joel Raborn
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, United States of America
- University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States of America
| | - Ting Fu
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, PR China
- Department of Bioscience and Biotechnology, Dalian University of Technology, Dalian, PR China
- Graduate University of the Chinese Academy of Sciences, Beijing, P. R. China
| | - Xue Wu
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, PR China
- Department of Bioscience and Biotechnology, Dalian University of Technology, Dalian, PR China
| | - Zhilong Xiu
- Department of Bioscience and Biotechnology, Dalian University of Technology, Dalian, PR China
| | - Guohui Li
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, PR China
- * E-mail: (GL); (BL)
| | - Bing-Hao Luo
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, United States of America
- * E-mail: (GL); (BL)
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11
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Abstract
Integrins are heterodimeric cell adhesion molecules that are important in many biological functions, such as cell migration, proliferation, differentiation, and survival. They can transmit bi-directional signals across the plasma membrane. Inside-out activating signal from some cell surface receptors bound with soluble agonists triggers integrins conformational change leading to high affinity for extracellular ligands. Then binding of ligands to integrins results in outside-in signaling, leading to formation of focal adhesion complex at the integrin cytoplasmic tail and activation of downstream signal pathways. This bi-directional signaling is essential for rapid response of cell to surrounding environmental changes. During this process, the conformational change of integrin extracellular and transmembrane/cytoplasmic domains is particularly important. In this review, we will summarize recent progress in both inside-out and outside-in signaling with specific focus on the mechanism how integrins transmit bi-directional signals through transmembrane/cytoplasmic domains.
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Affiliation(s)
- Ping Hu
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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12
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Zhang C, Liu J, Jiang X, Haydar N, Zhang C, Shan H, Zhu J. Modulation of integrin activation and signaling by α1/α1′-helix unbending at the junction. J Cell Sci 2013; 126:5735-47. [DOI: 10.1242/jcs.137828] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
How conformational signals initiated from one end of the integrin are transmitted to the other end remains elusive. At the ligand-binding βI domain, the α1/α1′-helix changes from a bent to a straightened α-helical conformation upon integrin headpiece opening. We demonstrated that a conserved glycine at the α1/α1′ junction is critical for maintaining the bent conformation of the α1/α1′-helix in the resting state. Mutations that facilitate α1/α1′-helix unbending rendered integrin constitutively active. However, mutations that block the α1/α1′-helix unbending abolished soluble ligand binding upon either outside or inside stimuli. Such mutations also blocked ligand-induced integrin extension from outside the cell, but had no effect on talin-induced integrin extension from inside the cell. In addition, integrin mediated cell spreading, F-actin stress fiber and focal adhesion formation, and focal adhesion kinase activation were also defective in these mutant integrins, although the cells still adhered to immobilized ligands at a reduced level. Our data establish the structural role of the α1/α1′ junction that allows relaxation of the α1/α1′-helix in the resting state and transmission of bidirectional conformational signals by helix unbending upon integrin activation.
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13
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Raborn J, Luo BH. Mutagenesis studies of the β I domain metal ion binding sites on integrin αVβ3 ligand binding affinity. J Cell Biochem 2012; 113:1190-7. [DOI: 10.1002/jcb.23448] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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14
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Wang W, Jiang Y, Wang C, Luo BH. Effects of the Association between the α-Subunit Thigh and the β-Subunit EGF2 Domains on Integrin Activation and Signaling. Biochemistry 2011; 50:9264-72. [DOI: 10.1021/bi200744g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Wei Wang
- Department of Biological Sciences,
202 Life Sciences
Building, Louisiana State University, Baton
Rouge, Louisiana 70803, United States
| | - Yan Jiang
- Department of Biological Sciences,
202 Life Sciences
Building, Louisiana State University, Baton
Rouge, Louisiana 70803, United States
| | - Chen Wang
- Department of Biological Sciences,
202 Life Sciences
Building, Louisiana State University, Baton
Rouge, Louisiana 70803, United States
| | - Bing-Hao Luo
- Department of Biological Sciences,
202 Life Sciences
Building, Louisiana State University, Baton
Rouge, Louisiana 70803, United States
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15
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Raborn J, Wang W, Luo BH. Regulation of integrin αIIbβ3 ligand binding and signaling by the metal ion binding sites in the β I domain. Biochemistry 2011; 50:2084-91. [PMID: 21309594 DOI: 10.1021/bi2000092] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The ability of αIIbβ3 to bind ligands and undergo outside-in signaling is regulated by three divalent cation binding sites in the β I domain. Specifically, the metal ion-dependent adhesion site (MIDAS) and the synergistic metal binding site (SyMBS) are thought to be required for ligand binding due to their synergy between Ca(2+) and Mg(2+). The adjacent to MIDAS (ADMIDAS) is an important ligand binding regulatory site that also acts as a critical link between the β I and hybrid domains for signaling. Mutations in this site have provided conflicting results for ligand binding and adhesion in different integrins. We have mutated the β3 SyMBS and ADMIDAS. The SyMBS mutant abolished ligand binding and outside-in signaling, but when an activating glycosylation mutation in the αIIb Calf 2 domain was introduced, the ligand binding affinity and signaling were restored. Thus, the SyMBS is important but not absolutely required for integrin bidirectional signaling. The ADMIDAS mutants showed reduced ligand binding affinity and abolished outside-in signaling, and the activating glycosylation mutation could fully restore integrin signaling of the ADMIDAS mutant. We propose that the ADMIDAS ion stabilizes the low-affinity state when the integrin headpiece is in the closed conformation, whereas it stabilizes the high-affinity state when the headpiece is in the open conformation with the swung-out hybrid domain.
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Affiliation(s)
- Joel Raborn
- Department of Biological Sciences, 202 Life Sciences Building, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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