1
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Labus J, Tang K, Henklein P, Krüger U, Hofmann A, Hondke S, Wöltje K, Freund C, Lucka L, Danker K. The α 1 integrin cytoplasmic tail interacts with phosphoinositides and interferes with Akt activation. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184257. [PMID: 37992949 DOI: 10.1016/j.bbamem.2023.184257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Revised: 11/03/2023] [Accepted: 11/14/2023] [Indexed: 11/24/2023]
Abstract
Integrin α1β1 is an adhesion receptor that binds to collagen and laminin. It regulates cell adhesion, cytoskeletal organization, and migration. The cytoplasmic tail of the α1 subunit consists of 15 amino acids and contains six positively charged lysine residues. In this study, we present evidence that the α1 integrin cytoplasmic tail (α1CT) directly associates with phosphoinositides, preferentially with phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). Since the association was disrupted by calcium, magnesium and phosphate ions, this interaction appears to be in ionic nature. Here, the peptide-lipid interaction was driven by the conserved KIGFFKR motif. The exchange of both two potential phospholipid-binding lysines for glycines in the KIGFFKR motif increased α1β1 integrin-specific adhesion and F-actin cytoskeleton formation compared to cells expressing the unmodified α1 subunit, whereas only mutation of the second lysine at position 1171 increased levels of constitutively active α1β1 integrins on the cell surface. In addition, enhanced focal adhesion formation and increased phosphorylation of focal adhesion kinase, but decreased phosphorylation of AKT was observed in these cells. We conclude that the KIGFFKR motif, and in particular lysine1171 is involved in the dynamic regulation of α1β1 integrin activity and that the interaction of α1CT with phosphoinositides may contribute to this process.
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Affiliation(s)
- Josephine Labus
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany; Hannover Medical School, Department of Cellular Neurophysiology, 30625 Hannover, Germany.
| | - Kerstin Tang
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany; Senate Department for Higher Education and Research, Health, Long-Term Care and Gender Equality, Sector Pharmaceuticals and Medical Devices, Oranienstraße 106, 10969 Berlin, Germany.
| | - Petra Henklein
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany.
| | - Ulrike Krüger
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany; BIH Core Facility Genomik, Charité-Universitätsmedizin Berlin, CVK, Charitéplatz 1, 10117 Berlin, Germany.
| | - Andreas Hofmann
- Structural Chemistry Program, Griffith Institute for Drug Discovery, Griffith University, Brisbane, Queensland 4111, Australia; Dept of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, Victoria 3010, Australia; NRZ-Authent, Max-Rubner-Institut, Bundesforschungsinstitut für Ernährung und Lebensmittel, E.-C.-Baumann-Str. 20, 95326 Kulmbach, Germany.
| | - Sylvia Hondke
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany
| | - Kerstin Wöltje
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany; Charité-Universitätsmedizin Berlin, Med. Klinik m.S. Infektiologie & Pneumologie, Augustenburger Platz 1, 13353 Berlin, Germany.
| | - Christian Freund
- Institute of Chemistry and Biochemistry, Freie Universität Berlin, Thielallee 63, 14195 Berlin, Germany.
| | - Lothar Lucka
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany.
| | - Kerstin Danker
- Institute for Biochemistry, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany.
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2
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Situ AJ, Ulmer TS. Comparison of Integrin αIIbβ3 Transmembrane Association in Vesicles and Bicelles. Biochemistry 2023. [PMID: 37279176 DOI: 10.1021/acs.biochem.3c00177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Membrane proteins are commonly reconstituted in membrane mimics exhibiting discontinuous lipid bilayers. In contrast, the continuous membranes of cells are conceptually best represented by large unilamellar vesicles (LUVs). Here, we compared the thermodynamic stability of the integrin αIIbβ3 transmembrane (TM) complex between vesicles and bicelles to assess the consequence of this simplification. In LUVs, we further evaluated the strength of the αIIb(G972S)-β3(V700T) interaction that corresponds to the hydrogen bond interaction postulated for β2 integrins. An upper limit of 0.9 kcal/mol was estimated for superior TM complex stabilization in LUVs relative to bicelles. Compared to the αIIbβ3 TM complex stability in LUVs of 5.6 ± 0.2 kcal/mol, this limit is modest, indicating that bicelles performed well relative to LUVs. The implementation of β3(V700T) alleviated αIIb(G972S) destabilization by 0.4 ± 0.2 kcal/mol in confirmation of relatively weak hydrogen bonding. Interestingly, the hydrogen bond adjusts the TM complex stability to a level that is not achievable by merely varying the residue corresponding to αIIb(Gly972).
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Affiliation(s)
- Alan J Situ
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
| | - Tobias S Ulmer
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
- Department of Biochemistry and Molecular Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
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3
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Wang Z, Zhu J. Structural determinants of the integrin transmembrane domain required for bidirectional signal transmission across the cell membrane. J Biol Chem 2021; 297:101318. [PMID: 34678312 PMCID: PMC8569584 DOI: 10.1016/j.jbc.2021.101318] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 10/12/2021] [Accepted: 10/18/2021] [Indexed: 11/26/2022] Open
Abstract
Studying the tight activity regulation of platelet-specific integrin αIIbβ3 is foundational and paramount to our understanding of integrin structure and activation. αIIbβ3 is essential for the aggregation and adhesion function of platelets in hemostasis and thrombosis. Structural and mutagenesis studies have previously revealed the critical role of αIIbβ3 transmembrane (TM) association in maintaining the inactive state. Gain-of-function TM mutations were identified and shown to destabilize the TM association leading to integrin activation. Studies using isolated TM peptides have suggested an altered membrane embedding of the β3 TM α-helix coupled with αIIbβ3 activation. However, controversies remain as to whether and how the TM α-helices change their topologies in the context of full-length integrin in native cell membrane. In this study, we utilized proline scanning mutagenesis and cysteine scanning accessibility assays to analyze the structure and function correlation of the αIIbβ3 TM domain. Our identification of loss-of-function proline mutations in the TM domain suggests the requirement of a continuous TM α-helical structure in transmitting activation signals bidirectionally across the cell membrane, characterized by the inside-out activation for ligand binding and the outside-in signaling for cell spreading. Similar results were found for αLβ2 and α5β1 TM domains, suggesting a generalizable mechanism. We also detected a topology change of β3 TM α-helix within the cell membrane, but only under conditions of cell adhesion and the absence of αIIb association. Our data demonstrate the importance of studying the structure and function of the integrin TM domain in the native cell membrane.
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Affiliation(s)
- Zhengli Wang
- Blood Research Institute, Versiti, Milwaukee, Wisconsin, USA
| | - Jieqing Zhu
- Blood Research Institute, Versiti, Milwaukee, Wisconsin, USA; Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
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4
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Isothermal Titration Calorimetry of Membrane Proteins. Methods Mol Biol 2021. [PMID: 33877623 DOI: 10.1007/978-1-0716-1394-8_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
The ability to quantify protein-protein interactions without adding labels to protein has made isothermal titration calorimetry (ITC) a preferred technique to study proteins in aqueous solution. Here, we describe the application of ITC to the study of protein-protein interactions in membrane mimics using the association of integrin αIIb and β3 transmembrane domains in phospholipid bicelles as an example. A higher conceptual and experimental effort compared to water-soluble proteins is required for membrane proteins and rewarded with rare thermodynamic insight into this central class of proteins.
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5
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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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6
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Lietha D, Izard T. Roles of Membrane Domains in Integrin-Mediated Cell Adhesion. Int J Mol Sci 2020; 21:ijms21155531. [PMID: 32752284 PMCID: PMC7432473 DOI: 10.3390/ijms21155531] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/29/2020] [Accepted: 07/31/2020] [Indexed: 12/13/2022] Open
Abstract
The composition and organization of the plasma membrane play important functional and regulatory roles in integrin signaling, which direct many physiological and pathological processes, such as development, wound healing, immunity, thrombosis, and cancer metastasis. Membranes are comprised of regions that are thick or thin owing to spontaneous partitioning of long-chain saturated lipids from short-chain polyunsaturated lipids into domains defined as ordered and liquid-disorder domains, respectively. Liquid-ordered domains are typically 100 nm in diameter and sometimes referred to as lipid rafts. We posit that integrin β senses membrane thickness and that mechanical force on the membrane regulates integrin activation through membrane thinning. This review examines what we know about the nature and mechanism of the interaction of integrins with the plasma membrane and its effects on regulating integrins and its binding partners.
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Affiliation(s)
- Daniel Lietha
- Cell Signaling and Adhesion Group, Structural and Chemical Biology, Margarita Salas Center for Biological Research (CIB-CSIC), E-28040 Madrid, Spain;
| | - Tina Izard
- Cell Adhesion Laboratory, Department of Integrative Structural and Computational Biology, The Scripps Research Institute, Jupiter, FL 33458, USA
- Correspondence:
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7
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Rohena C, Kalogriopoulos N, Rajapakse N, Roy S, Lopez-Sanchez I, Ablack J, Sahoo D, Ghosh P. GIV•Kindlin Interaction Is Required for Kindlin-Mediated Integrin Recognition and Activation. iScience 2020; 23:101209. [PMID: 32535026 PMCID: PMC7300163 DOI: 10.1016/j.isci.2020.101209] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Revised: 04/15/2020] [Accepted: 05/24/2020] [Indexed: 11/16/2022] Open
Abstract
Cells perceive and respond to the extracellular matrix via integrin receptors; their dysregulation has been implicated in inflammation and cancer metastasis. Here we show that a guanine nucleotide-exchange modulator of trimeric-GTPase Gαi, GIV (a.k.a Girdin), directly binds the integrin adaptor Kindlin-2. A non-canonical short linear motif within the C terminus of GIV binds Kindlin-2-FERM3 domain at a site that is distinct from the binding site for the canonical NPxY motif on the -integrin tail. Binding of GIV to Kindlin-2 allosterically enhances Kindlin-2's affinity for β1-integrin. Consequently, integrin activation and clustering are maximized, which augments cell adhesion, spreading, and invasion. Findings elucidate how the GIV•Kindlin-2 complex has a 2-fold impact: it allosterically synergizes integrin activation and enables β1-integrins to indirectly access and modulate trimeric GTPases via the complex. Furthermore, Cox proportional-hazard models on tumor transcriptomics provide trans-scale evidence of synergistic interactions between GIV•Kindlin-2•β1-integrin on time to progression to metastasis. GIV and Kindlin (K2), two integrin adaptors that promote metastasis, bind each other Binding of GIV or integrin to K2 allosterically enhances GIV•K2•integrin complexes Binding is required for the maximal recruitment of GIV and K2 to active integrins Binding facilitates integrin clustering, activation, tumor cell adhesion, invasion
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Affiliation(s)
- Cristina Rohena
- Department of Medicine, University of California San Diego, 9500 Gilman Drive (MC 0651), George E. Palade Bldg, Rm 239, La Jolla, CA 92093, USA
| | - Nicholas Kalogriopoulos
- Department of Medicine, University of California San Diego, 9500 Gilman Drive (MC 0651), George E. Palade Bldg, Rm 239, La Jolla, CA 92093, USA; Department of Cellular and Molecular Medicine, University of California San Diego, CA 92093, USA
| | - Navin Rajapakse
- Department of Cellular and Molecular Medicine, University of California San Diego, CA 92093, USA
| | - Suchismita Roy
- Department of Cellular and Molecular Medicine, University of California San Diego, CA 92093, USA
| | - Inmaculada Lopez-Sanchez
- Department of Medicine, University of California San Diego, 9500 Gilman Drive (MC 0651), George E. Palade Bldg, Rm 239, La Jolla, CA 92093, USA
| | - Jailal Ablack
- Department of Medicine, University of California San Diego, 9500 Gilman Drive (MC 0651), George E. Palade Bldg, Rm 239, La Jolla, CA 92093, USA
| | - Debashis Sahoo
- Department of Pediatrics, University of California San Diego, CA 92093, USA; Department of Computer Science and Engineering, Jacob's School of Engineering, University of California San Diego, CA 92093, USA; Rebecca and John Moore Comprehensive Cancer Center, University of California San Diego, CA 92093, USA
| | - Pradipta Ghosh
- Department of Medicine, University of California San Diego, 9500 Gilman Drive (MC 0651), George E. Palade Bldg, Rm 239, La Jolla, CA 92093, USA; Department of Cellular and Molecular Medicine, University of California San Diego, CA 92093, USA; Rebecca and John Moore Comprehensive Cancer Center, University of California San Diego, CA 92093, USA; Veterans Affairs Medical Center, 3350 La Jolla Village Drive, San Diego, CA 92161, USA.
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8
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Chill JH, Qasim A, Sher I, Gross R. NMR Perspectives of the KcsA Potassium Channel in the Membrane Environment. Isr J Chem 2019. [DOI: 10.1002/ijch.201900107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jordan H. Chill
- Department of ChemistryBar Ilan University Ramat Gan 52900 Israel
| | - Arwa Qasim
- Department of ChemistryBar Ilan University Ramat Gan 52900 Israel
| | - Inbal Sher
- Department of ChemistryBar Ilan University Ramat Gan 52900 Israel
| | - Renana Gross
- Department of ChemistryBar Ilan University Ramat Gan 52900 Israel
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9
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Abstract
Integrins are heterodimeric cell surface receptors ensuring the mechanical connection between cells and the extracellular matrix. In addition to the anchorage of cells to the extracellular matrix, these receptors have critical functions in intracellular signaling, but are also taking center stage in many physiological and pathological conditions. In this review, we provide some historical, structural, and physiological notes so that the diverse functions of these receptors can be appreciated and put into the context of the emerging field of mechanobiology. We propose that the exciting journey of the exploration of these receptors will continue for at least another new generation of researchers.
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Affiliation(s)
- Michael Bachmann
- Department of Cell Physiology and Metabolism, University of Geneva, Centre Médical Universitaire , Geneva , Switzerland ; and Faculty of Medicine and Health Technology, Tampere University, and Fimlab Laboratories , Tampere , Finland
| | - Sampo Kukkurainen
- Department of Cell Physiology and Metabolism, University of Geneva, Centre Médical Universitaire , Geneva , Switzerland ; and Faculty of Medicine and Health Technology, Tampere University, and Fimlab Laboratories , Tampere , Finland
| | - Vesa P Hytönen
- Department of Cell Physiology and Metabolism, University of Geneva, Centre Médical Universitaire , Geneva , Switzerland ; and Faculty of Medicine and Health Technology, Tampere University, and Fimlab Laboratories , Tampere , Finland
| | - Bernhard Wehrle-Haller
- Department of Cell Physiology and Metabolism, University of Geneva, Centre Médical Universitaire , Geneva , Switzerland ; and Faculty of Medicine and Health Technology, Tampere University, and Fimlab Laboratories , Tampere , Finland
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10
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Bibow S. Opportunities and Challenges of Backbone, Sidechain, and RDC Experiments to Study Membrane Protein Dynamics in a Detergent-Free Lipid Environment Using Solution State NMR. Front Mol Biosci 2019; 6:103. [PMID: 31709261 PMCID: PMC6823230 DOI: 10.3389/fmolb.2019.00103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 09/19/2019] [Indexed: 12/22/2022] Open
Abstract
Whereas solution state NMR provided a wealth of information on the dynamics landscape of soluble proteins, only few studies have investigated membrane protein dynamics in a detergent-free lipid environment. Recent developments of smaller nanodiscs and other lipid-scaffolding polymers, such as styrene maleic acid (SMA), however, open new and promising avenues to explore the function-dynamics relationship of membrane proteins as well as between membrane proteins and their surrounding lipid environment. Favorably sized lipid-bilayer nanodiscs, established membrane protein reconstitution protocols and sophisticated solution NMR relaxation methods probing dynamics over a wide range of timescales will eventually reveal unprecedented lipid-membrane protein interdependencies that allow us to explain things we have not been able to explain so far. In particular, methyl group dynamics resulting from CEST, CPMG, ZZ exchange, and RDC experiments are expected to provide new and surprising insights due to their proximity to lipids, their applicability in large 100+ kDa assemblies and their simple labeling due to the availability of commercial precursors. This review summarizes the recent developments of membrane protein dynamics with a special focus on membrane protein dynamics in lipid-bilayer nanodiscs. Opportunities and challenges of backbone, side chain and RDC dynamics applied to membrane proteins are discussed. Solution-state NMR and lipid nanodiscs bear great potential to change our molecular understanding of lipid-membrane protein interactions.
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Affiliation(s)
- Stefan Bibow
- Biozentrum, University of Basel, Basel, Switzerland
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11
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Topological analysis of the gp41 MPER on lipid bilayers relevant to the metastable HIV-1 envelope prefusion state. Proc Natl Acad Sci U S A 2019; 116:22556-22566. [PMID: 31624123 DOI: 10.1073/pnas.1912427116] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The membrane proximal external region (MPER) of HIV-1 envelope glycoprotein (gp) 41 is an attractive vaccine target for elicitation of broadly neutralizing antibodies (bNAbs) by vaccination. However, current details regarding the quaternary structural organization of the MPER within the native prefusion trimer [(gp120/41)3] are elusive and even contradictory, hindering rational MPER immunogen design. To better understand the structural topology of the MPER on the lipid bilayer, the adjacent transmembrane domain (TMD) was appended (MPER-TMD) and studied. Membrane insertion of the MPER-TMD was sensitive both to the TMD sequence and cytoplasmic residues. Antigen binding of MPER-specific bNAbs, in particular 10E8 and DH511.2_K3, was significantly impacted by the presence of the TMD. Furthermore, MPER-TMD assembly into 10-nm diameter nanodiscs revealed a heterogeneous membrane array comprised largely of monomers and dimers, as enumerated by bNAb Fab binding using single-particle electron microscopy analysis, arguing against preferential trimeric association of native MPER and TMD protein segments. Moreover, introduction of isoleucine mutations in the C-terminal heptad repeat to induce an extended MPER α-helical bundle structure yielded an antigenicity profile of cell surface-arrayed Env variants inconsistent with that found in the native prefusion state. In line with these observations, electron paramagnetic resonance analysis suggested that 10E8 inhibits viral membrane fusion by lifting the MPER N-terminal region out of the viral membrane, mandating the exposure of residues that would be occluded by MPER trimerization. Collectively, our data suggest that the MPER is not a stable trimer, but rather a dynamic segment adapted for structural changes accompanying fusion.
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12
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Tseng HY, Samarelli AV, Kammerer P, Scholze S, Ziegler T, Immler R, Zent R, Sperandio M, Sanders CR, Fässler R, Böttcher RT. LCP1 preferentially binds clasped αMβ2 integrin and attenuates leukocyte adhesion under flow. J Cell Sci 2018; 131:jcs.218214. [PMID: 30333137 DOI: 10.1242/jcs.218214] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 09/07/2018] [Indexed: 12/13/2022] Open
Abstract
Integrins are α/β heterodimers that interconvert between inactive and active states. In the active state the α/β cytoplasmic domains recruit integrin-activating proteins and separate the transmembrane and cytoplasmic (TMcyto) domains (unclasped TMcyto). Conversely, in the inactive state the α/β TMcyto domains bind integrin-inactivating proteins, resulting in the association of the TMcyto domains (clasped TMcyto). Here, we report the isolation of integrin cytoplasmic tail interactors using either lipid bicelle-incorporated integrin TMcyto domains (α5, αM, αIIb, β1, β2 and β3 integrin TMcyto) or a clasped, lipid bicelle-incorporated αMβ2 TMcyto. Among the proteins found to preferentially bind clasped rather than the isolated αM and β2 subunits was L-plastin (LCP1, also known as plastin-2), which binds to and maintains the inactive state of αMβ2 integrin in vivo and thereby regulates leukocyte adhesion to integrin ligands under flow. Our findings offer a global view on cytoplasmic proteins interacting with different integrins and provide evidence for the existence of conformation-specific integrin interactors.
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Affiliation(s)
- Hui-Yuan Tseng
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany
| | - Anna V Samarelli
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany
| | - Patricia Kammerer
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany
| | - Sarah Scholze
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany
| | - Tilman Ziegler
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany
| | - Roland Immler
- Walter Brendel Center for Experimental Medicine, Ludwig-Maximilians-University, 81377 Munich, Germany
| | - Roy Zent
- Division of Nephrology, Department of Medicine, Vanderbilt University, Nashville, 37232 Tennessee, USA.,Department of Medicine, Veterans Affairs Medical Center, Nashville, 37232 Tennessee, USA
| | - Markus Sperandio
- Walter Brendel Center for Experimental Medicine, Ludwig-Maximilians-University, 81377 Munich, Germany
| | - Charles R Sanders
- Department of Biochemistry, Center for Structural Biology, and Institute of Chemical Biology, Vanderbilt University School of Medicine, Nashville, 37232 Tennessee, USA
| | - Reinhard Fässler
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Munich Heart Alliance, 80802 Munich, Germany
| | - Ralph T Böttcher
- Department of Molecular Medicine, Max Planck Institute for Biochemistry, 82152 Martinsried, Germany .,DZHK (German Centre for Cardiovascular Research), partner site Munich Heart Alliance, 80802 Munich, Germany
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13
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Intramembrane ionic protein-lipid interaction regulates integrin structure and function. PLoS Biol 2018; 16:e2006525. [PMID: 30427828 PMCID: PMC6261646 DOI: 10.1371/journal.pbio.2006525] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 11/28/2018] [Accepted: 10/29/2018] [Indexed: 11/24/2022] Open
Abstract
Protein transmembrane domains (TMDs) are generally hydrophobic, but our bioinformatics analysis shows that many TMDs contain basic residues at terminal regions. Physiological functions of these membrane-snorkeling basic residues are largely unclear. Here, we show that a membrane-snorkeling Lys residue in integrin αLβ2 (also known as lymphocyte function-associated antigen 1 [LFA-1]) regulates transmembrane heterodimer formation and integrin adhesion through ionic interplay with acidic phospholipids and calcium ions (Ca2+) in T cells. The amino group of the conserved Lys ionically interacts with the phosphate group of acidic phospholipids to stabilize αLβ2 transmembrane association, thus keeping the integrin at low-affinity conformation. Intracellular Ca2+ uses its charge to directly disrupt this ionic interaction, leading to the transmembrane separation and the subsequent extracellular domain extension to increase adhesion activity. This Ca2+-mediated regulation is independent on the canonical Ca2+ signaling or integrin inside-out signaling. Our work therefore showcases the importance of intramembrane ionic protein–lipid interaction and provides a new mechanism of integrin activation. Integrin αLβ2 is the major integrin in T cells and plays a vital role in regulating T-cell activation, adhesion, and migration. The transmembrane association of αL and β2 is crucial for maintaining the integrin at low-affinity conformation. Here, we find that the conserved basic residue (K702) in the transmembrane domain of β2 contributes to transmembrane association through ternary ionic interaction with acidic phospholipid and αL cytoplasmic residue. Upon T-cell activation, influxed calcium ions (Ca2+) can directly disrupt the ionic K702–lipid interaction through its positive charges, which leads to transmembrane separation and subsequent extracellular domain extension to switch αLβ2 to high-affinity conformation. This Ca2+-mediated regulation is through the modulation of the ionic Lys–lipid interaction but not through the canonical Ca2+ signaling or integrin inside-out signaling. Our study thus reports a new regulatory mechanism of integrin activation and showcases the importance of intramembrane ionic protein–lipid interaction. This finding might have general relevance, as bioinformatics analysis shows the presence of membrane-snorkeling basic residue is a common feature of transmembrane proteins.
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14
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Kot EF, Arseniev AS, Mineev KS. Behavior of Most Widely Spread Lipids in Isotropic Bicelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:8302-8313. [PMID: 29924628 DOI: 10.1021/acs.langmuir.8b01454] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Isotropic bicelles are a widely used membrane mimetic for structural studies of membrane proteins and their transmembrane domains. Simple and cheap in preparation, they contain a patch of lipid bilayer that reproduces the native environment of membrane proteins. Despite the obvious power of bicelles in reproducing the various kinds of environments, the vast majority of structural studies employ the single lipid/detergent system. On the other hand, even if the alternative bicelle composition is used, the properties of mixtures are not characterized, and the mere presence of lipid bilayer and discoidal shape of bicelle particles is not confirmed. Here we present an extensive investigation of various bicellar mixtures and describe the behavior of bicelles with lipids other than classical DMPC, namely sphingomyelins (SM), phosphatidylethanolamines (PE), phosphatidylglycerols (PG), phosphatidylserines (PS), and cholesterol. These lipids are rarely used in modern structural biology, but can help a lot in understanding the influence of the membrane composition on the properties of both integral and peripheral membrane proteins. Additionally, the ability of diheptanoylphosphatidylcholine (DH7PC) to serve as a rim-forming agent was investigated. We followed the phase transitions as revealed by 31P NMR and size of particles measured by 1H NMR diffusion as the criteria of the proper morphology and structure of bicelles. As an outcome, we state that SM exclusively, and PG/PS in mixtures with zwitterionic lipids can form small isotropic bicelles, which reproduce the key features of lipid behavior in bilayers. Mixtures, containing exclusively the anionic lipids, fail to reveal the lipid phase transition and do not follow the size predicted for the ideal bicelle particles. PE and DH7PC are the unwanted components of bicellar mixtures, and cholesterol can be added to bicelles, however, with certain precautions. In combination with our several most recent works, this study provides a practical guide for the preparation of small isotropic bicelles.
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Affiliation(s)
- E F Kot
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10 , Moscow 117997, Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , Dolgoprudnyi 141700 , Russian Federation
| | - A S Arseniev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10 , Moscow 117997, Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , Dolgoprudnyi 141700 , Russian Federation
| | - K S Mineev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10 , Moscow 117997, Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , Dolgoprudnyi 141700 , Russian Federation
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15
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Gomes KAGG, Dos Santos DM, Santos VM, Piló-Veloso D, Mundim HM, Rodrigues LV, Lião LM, Verly RM, de Lima ME, Resende JM. NMR structures in different membrane environments of three ocellatin peptides isolated from Leptodactylus labyrinthicus. Peptides 2018; 103:72-83. [PMID: 29596881 DOI: 10.1016/j.peptides.2018.03.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 03/21/2018] [Accepted: 03/23/2018] [Indexed: 10/17/2022]
Abstract
The peptides ocellatin-LB1, -LB2 and -F1 have previously been isolated from anurans of the Leptodactylus genus and the sequences are identical from residue 1-22, which correspond to ocellatin-LB1 sequence (GVVDILKGAAKDIAGHLASKVM-NH2), whereas ocellatin-LB2 carries an extra N and ocellatin-F1 extra NKL residues at their C-termini. These peptides showed different spectra of activities and biophysical investigations indicated a direct correlation between membrane-disruptive properties and antimicrobial activities, i.e. ocellatin-F1 > ocellatin-LB1 > ocellatin-LB2. To better characterize their membrane interactions, we report here the detailed three-dimensional NMR structures of these peptides in TFE-d2:H2O (60:40) and in the presence of zwitterionic DPC-d38 and anionic SDS-d25 micellar solutions. Although the three peptides showed significant helical contents in the three mimetic environments, structural differences were noticed. When the structures of the three peptides in the presence of DPC-d38 micelles are compared to each other, a more pronounced curvature is observed for ocellatin-F1 and the bent helix, with the concave face composed mostly of hydrophobic residues, is consistent with the micellar curvature and the amphipathic nature of the molecule. Interestingly, an almost linear helical segment was observed for ocellatin-F1 in the presence of SDS-d25 micelles and the conformational differences in the two micellar environments are possibly related to the presence of the extra Lys residue near the peptide C-terminus, which increases the affinity of ocellatin-F1 to anionic membranes in comparison with ocellatin-LB1 and -LB2, as proved by isothermal titration calorimetry. To our knowledge, this work reports for the first time the three-dimensional structures of ocellatin peptides.
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Affiliation(s)
- Karla A G G Gomes
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, P.O. Box 486, 31270-901 Belo Horizonte, MG, Brazil; Instituto de Engenharia, Ciência e Tecnologia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 39440-000 Janaúba, MG, Brazil
| | - Daniel M Dos Santos
- Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, P.O. Box 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Virgílio M Santos
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, P.O. Box 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Dorila Piló-Veloso
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, P.O. Box 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Higor M Mundim
- Instituto de Química, Universidade Federal de Goiás, Av. Esperança, s/n, Campus Samambaia, 74690-900 Goiânia, GO, Brazil
| | - Leticia V Rodrigues
- Instituto de Química, Universidade Federal de Goiás, Av. Esperança, s/n, Campus Samambaia, 74690-900 Goiânia, GO, Brazil
| | - Luciano M Lião
- Instituto de Química, Universidade Federal de Goiás, Av. Esperança, s/n, Campus Samambaia, 74690-900 Goiânia, GO, Brazil
| | - Rodrigo M Verly
- Departamento de Química, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 39100-000 Diamantina, MG, Brazil
| | - Maria Elena de Lima
- Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, P.O. Box 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Jarbas M Resende
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, P.O. Box 486, 31270-901 Belo Horizonte, MG, Brazil.
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16
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Pettersson P, Ye W, Jakob M, Tannert F, Klösgen RB, Mäler L. Structure and dynamics of plant TatA in micelles and lipid bilayers studied by solution NMR. FEBS J 2018; 285:1886-1906. [PMID: 29654717 DOI: 10.1111/febs.14452] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Revised: 03/09/2018] [Accepted: 03/27/2018] [Indexed: 12/21/2022]
Abstract
The twin-arginine translocase (Tat) transports folded proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. In Gram-negative bacteria and chloroplasts, the translocon consists of three subunits, TatA, TatB, and TatC, of which TatA is responsible for the actual membrane translocation of the substrate. Herein we report on the structure, dynamics, and lipid interactions of a fully functional C-terminally truncated 'core TatA' from Arabidopsis thaliana using solution-state NMR. Our results show that TatA consists of a short N-terminal transmembrane helix (TMH), a short connecting linker (hinge) and a long region with propensity to form an amphiphilic helix (APH). The dynamics of TatA were characterized using 15 N relaxation NMR in combination with model-free analysis. The TMH has order parameters characteristic of a well-structured helix, the hinge is somewhat less rigid, while the APH has lower order parameters indicating structural flexibility. The TMH is short with a surprisingly low protection from solvent, and only the first part of the APH is protected to some extent. In order to uncover possible differences in TatA's structure and dynamics in detergent compared to in a lipid bilayer, fast-tumbling bicelles and large unilamellar vesicles were used. Results indicate that the helicity of TatA increases in both the TMH and APH in the presence of lipids, and that the N-terminal part of the TMH is significantly more rigid. The results indicate that plant TatA has a significant structural plasticity and a capability to adapt to local environments.
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Affiliation(s)
- Pontus Pettersson
- Department of Biochemistry and Biophysics, Stockholm University, Sweden
| | - Weihua Ye
- Department of Biochemistry and Biophysics, Stockholm University, Sweden
| | - Mario Jakob
- Institut für Biologie, Institutsbereich Pflanzenphysiologie, Martin-Luther University, Halle, Germany
| | - Franzisca Tannert
- Institut für Biologie, Institutsbereich Pflanzenphysiologie, Martin-Luther University, Halle, Germany
| | - Ralf Bernd Klösgen
- Institut für Biologie, Institutsbereich Pflanzenphysiologie, Martin-Luther University, Halle, Germany
| | - Lena Mäler
- Department of Biochemistry and Biophysics, Stockholm University, Sweden
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17
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Sun H, Lagarrigue F, Gingras AR, Fan Z, Ley K, Ginsberg MH. Transmission of integrin β7 transmembrane domain topology enables gut lymphoid tissue development. J Cell Biol 2018. [PMID: 29535192 PMCID: PMC5881498 DOI: 10.1083/jcb.201707055] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Sun et al. establish the importance of transmission of changes in β-integrin transmembrane domain (TMD) topology in physiological integrin affinity modulation and biological function. Introduction of a flexible kink in the β7 integrin TMD blocks talin-mediated agonist-induced α4β7 integrin activation and function in gut lymphoid tissue development. Integrin activation regulates adhesion, extracellular matrix assembly, and cell migration, thereby playing an indispensable role in development and in many pathological processes. A proline mutation in the central integrin β3 transmembrane domain (TMD) creates a flexible kink that uncouples the topology of the inner half of the TMD from the outer half. In this study, using leukocyte integrin α4β7, which enables development of gut-associated lymphoid tissue (GALT), we examined the biological effect of such a proline mutation and report that it impairs agonist-induced talin-mediated activation of integrin α4β7, thereby inhibiting rolling lymphocyte arrest, a key step in transmigration. Furthermore, the α4β7(L721P) mutation blocks lymphocyte homing to and development of the GALT. These studies show that impairing the ability of an integrin β TMD to transmit talin-induced TMD topology inhibits agonist-induced physiological integrin activation and biological function in development.
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Affiliation(s)
- Hao Sun
- Department of Medicine, University of California, San Diego, La Jolla, CA
| | | | | | - Zhichao Fan
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA
| | - Klaus Ley
- Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA
| | - Mark H Ginsberg
- Department of Medicine, University of California, San Diego, La Jolla, CA
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18
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Situ AJ, Kang SM, Frey BB, An W, Kim C, Ulmer TS. Membrane Anchoring of α-Helical Proteins: Role of Tryptophan. J Phys Chem B 2018; 122:1185-1194. [PMID: 29323921 PMCID: PMC11025564 DOI: 10.1021/acs.jpcb.7b11227] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The function of membrane proteins relies on a defined orientation of protein relative to lipid. In apparent correlation to protein anchoring, tryptophan residues are enriched in the lipid headgroup region. To characterize the thermodynamic and structural basis of this relationship in α-helical membrane proteins, we examined the role of three conserved tryptophans in the folding of the heterodimeric integrin αIIbβ3 transmembrane (TM) complex in phospholipid bicelles and mammalian membranes. In the homogenous lipid environment of bicelles, tryptophan was replaceable by residues of distinct polarities. The appropriate polarity was guided by the electrostatic potential of the tryptophan surrounding, suggesting that tryptophan can complement diverse environments by adjusting the orientation of its anisotropic side chain to achieve site-specific anchoring. As a sole membrane anchor, tryptophan made a contribution of 0.4 kcal/mol to TM complex stability in bicelles. In membranes, it proved more difficult to replace tryptophan even by tyrosine, indicating a superior capacity to interact with heterogeneous lipids of biological membranes. Interestingly, at intracellular TM helix ends, where integrin activation is initiated, sequence motifs that interact with lipids via opposing polarity patterns were found to restrict TM helix orientations beyond tryptophan anchoring. In contrast to bicelles, phenylalanine became the least accepted substitute in membranes, demonstrating an increased role of the hydrophobic effect. Altogether, our study implicates a wide amphiphilic range of tryptophan, membrane complexity, and the hydrophobic effect to be important factors in tryptophan membrane anchoring.
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Affiliation(s)
- Alan J Situ
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , 1501 San Pablo Street, Los Angeles, California 90033, United States
| | - So-Min Kang
- Department of Life Sciences, Korea University , 145 Anam-Ro, Seongbuk-Gu, Seoul 136-701, South Korea
| | - Benjamin B Frey
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , 1501 San Pablo Street, Los Angeles, California 90033, United States
| | - Woojin An
- Department of Biochemistry & Molecular Medicine and Norris Comprehensive Cancer Center, University of Southern California , Los Angeles, California 90033, United States
| | - Chungho Kim
- Department of Life Sciences, Korea University , 145 Anam-Ro, Seongbuk-Gu, Seoul 136-701, South Korea
| | - Tobias S Ulmer
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , 1501 San Pablo Street, Los Angeles, California 90033, United States
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19
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β 1-Integrin-Mediated Adhesion Is Lipid-Bilayer Dependent. Biophys J 2017; 113:1080-1092. [PMID: 28877491 DOI: 10.1016/j.bpj.2017.07.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 06/19/2017] [Accepted: 07/13/2017] [Indexed: 11/21/2022] Open
Abstract
Integrin-mediated adhesion is a central feature of cellular adhesion, locomotion, and endothelial cell mechanobiology. Although integrins are known to be transmembrane proteins, little is known about the role of membrane biophysics and dynamics in integrin adhesion. We treated human aortic endothelial cells with exogenous amphiphiles, shown previously in model membranes, and computationally, to affect bilayer thickness and lipid phase separation, and subsequently measured single-integrin-molecule adhesion kinetics using an optical trap, and diffusion using fluorescence correlation spectroscopy. Benzyl alcohol (BA) partitions to liquid-disordered (Ld) domains, thins them, and causes the greatest increase in hydrophobic mismatch between liquid-ordered (Lo) and Ld domains among the three amphiphiles, leading to domain separation. In human aortic endothelial cells, BA increased β1-integrin-Arg-Gly-Asp-peptide affinity by 18% with a transition from single to double valency, consistent with a doubling of the molecular brightness of mCherry-tagged β1-integrins measured using fluorescence correlation spectroscopy. Accordingly, BA caused an increase in the size of focal-adhesion-kinase/paxillin-positive peripheral adhesions and reduced migration speeds as measured using wound-healing assays. Vitamin E, which thickens Lo domains and disperses them by lowering edge energy on domain boundaries, left integrin affinity unchanged but reduced binding probability, leading to smaller focal adhesions and equivalent migration speed relative to untreated cells. Vitamin E reversed the BA-induced decrease in migration speed. Triton X-100 also thickens Lo domains, but partitions to both lipid phases and left unchanged binding kinetics, focal adhesion sizes, and migration speed. These results demonstrate that only the amphiphile that thinned Ld lipid domains increased β1-integrin-Arg-Gly-Asp-peptide affinity and valency, thus implicating Ld domains in modulation of integrin adhesion, nascent adhesion formation, and cell migration.
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20
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Smrt ST, Draney AW, Singaram I, Lorieau JL. Structure and Dynamics of Membrane Proteins and Membrane Associated Proteins with Native Bicelles from Eukaryotic Tissues. Biochemistry 2017; 56:5318-5327. [PMID: 28915027 DOI: 10.1021/acs.biochem.7b00575] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Sean T. Smrt
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, United States
| | - Adrian W. Draney
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, United States
| | - Indira Singaram
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, United States
| | - Justin L. Lorieau
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, United States
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21
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Liebau J, Ye W, Mäler L. Characterization of fast-tumbling isotropic bicelles by PFG diffusion NMR. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2017; 55:395-404. [PMID: 26662467 DOI: 10.1002/mrc.4399] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Revised: 11/12/2015] [Accepted: 11/17/2015] [Indexed: 06/05/2023]
Abstract
Small isotropic bicelles are versatile membrane mimetics, which, in contrast to micelles, provide a lipid bilayer and are at the same time suitable for solution-state NMR studies. The lipid composition of the bilayer is flexible allowing for incorporation of various head groups and acyl chain types. In bicelles, lipids are solubilized by detergents, which are localized in the rim of the disk-shaped lipid bilayer. Bicelles have been characterized by a broad array of biophysical methods, pulsed-field gradient NMR (PFG NMR) being one of them. PFG NMR can readily be used to measure diffusion coefficients of macromolecules. It is thus employed to characterize bicelle size and morphology. Even more importantly, PFG NMR can be used to study the degree of protein association to membranes. Here, we present the advances that have been made in producing small, fast-tumbling isotropic bicelles from a variety of lipids and detergents, together with insights on the morphology of such mixtures gained from PFG NMR. Furthermore, we review approaches to study protein-membrane interaction by PFG NMR. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Jobst Liebau
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Weihua Ye
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Lena Mäler
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
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22
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Expression, Purification, and Monitoring of Conformational Changes of hCB2 TMH67H8 in Different Membrane-Mimetic Lipid Mixtures Using Circular Dichroism and NMR Techniques. MEMBRANES 2017; 7:membranes7010010. [PMID: 28218648 PMCID: PMC5371971 DOI: 10.3390/membranes7010010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 01/26/2017] [Accepted: 02/06/2017] [Indexed: 12/13/2022]
Abstract
This work was intended to develop self-assembly lipids for incorporating G-protein coupled receptors (GPCRs) in order to improve the success rate for nuclear magnetic resonance spectroscopy (NMR) structural elucidation. We hereby report the expression and purification of uniformly 15N-labeled human cannabinoid receptor-2 domain in insect cell media. The domain was refolded by screening several membrane mimetic environments. Different q ratios of isotropic bicelles were screened for solubilizing transmembrane helix 6, 7 and 8 (TMH67H8). As the concentration of dimyristoylphosphocholine (DMPC) was increased such that the q ratio was between 0.16 and 0.42, there was less crowding in the cross peaks with increasing q ratio. In bicelles of q = 0.42, the maximum number of cross peaks were obtained and the cross peaks were uniformly dispersed. The receptor domain in bicelles beyond q = 0.42 resulted in peak crowding. These studies demonstrate that GPCRs folding especially in bicelles is protein-specific and requires the right mix of the longer chain and shorter chain lipids to provide the right environment for proper folding. These findings will allow further development of novel membrane mimetics to provide greater diversity of lipid mixtures than those currently being employed for GPCR stability and folding, which are critical for both X-ray and NMR studies of GPCRs.
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23
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Lu Z, Mathew S, Chen J, Hadziselimovic A, Palamuttam R, Hudson BG, Fässler R, Pozzi A, Sanders CR, Zent R. Implications of the differing roles of the β1 and β3 transmembrane and cytoplasmic domains for integrin function. eLife 2016; 5. [PMID: 27929375 PMCID: PMC5207772 DOI: 10.7554/elife.18633] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 12/07/2016] [Indexed: 12/26/2022] Open
Abstract
Integrins are transmembrane receptors composed of α and β subunits. Although most integrins contain β1, canonical activation mechanisms are based on studies of the platelet integrin, αIIbβ3. Its inactive conformation is characterized by the association of the αIIb transmembrane and cytosolic domain (TM/CT) with a tilted β3 TM/CT that leads to activation when disrupted. We show significant structural differences between β1 and β3 TM/CT in bicelles. Moreover, the 'snorkeling' lysine at the TM/CT interface of β subunits, previously proposed to regulate αIIbβ3 activation by ion pairing with nearby lipids, plays opposite roles in β1 and β3 integrin function and in neither case is responsible for TM tilt. A range of affinities from almost no interaction to the relatively high avidity that characterizes αIIbβ3 is seen between various α subunits and β1 TM/CTs. The αIIbβ3-based canonical model for the roles of the TM/CT in integrin activation and function clearly does not extend to all mammalian integrins.
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Affiliation(s)
- Zhenwei Lu
- Department of Biochemistry, Vanderbilt University Medical Center, Nashville, United States
| | - Sijo Mathew
- Division of Nephrology, Department of Medicine, Vanderbilt Medical Center, Nashville, United States
| | - Jiang Chen
- Department of Biochemistry, Vanderbilt University Medical Center, Nashville, United States
| | - Arina Hadziselimovic
- Department of Biochemistry, Vanderbilt University Medical Center, Nashville, United States
| | - Riya Palamuttam
- Department of Biochemistry, Vanderbilt University Medical Center, Nashville, United States
| | - Billy G Hudson
- Department of Biochemistry, Vanderbilt University Medical Center, Nashville, United States.,Division of Nephrology, Department of Medicine, Vanderbilt Medical Center, Nashville, United States.,Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, United States.,Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, United States
| | - Reinhard Fässler
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Ambra Pozzi
- Division of Nephrology, Department of Medicine, Vanderbilt Medical Center, Nashville, United States.,Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, United States.,Veterans Affairs Hospital, Nashville, United States.,Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, United States
| | - Charles R Sanders
- Department of Biochemistry, Vanderbilt University Medical Center, Nashville, United States
| | - Roy Zent
- Division of Nephrology, Department of Medicine, Vanderbilt Medical Center, Nashville, United States.,Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, United States.,Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, United States.,Veterans Affairs Hospital, Nashville, United States
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24
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Schmidt T, Situ AJ, Ulmer TS. Direct Evaluation of Protein-Lipid Contacts Reveals Protein Membrane Immersion and Isotropic Bicelle Structure. J Phys Chem Lett 2016; 7:4420-4426. [PMID: 27776216 PMCID: PMC11027914 DOI: 10.1021/acs.jpclett.6b02159] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The solvation of membrane proteins by both lipids and water makes their membrane immersion difficult to predict and the choice of a membrane mimic challenging. To characterize protein-lipid contacts and bicelle membrane mimics, we examined protein-lipid cross-relaxation of integrin αIIb and β3(A711P) transmembrane helices in isotropic phospholipid bicelles (q = 0.5 and 0.7). Long-chain bicelle lipids dominated contacts with central helix segments, whereas both short- and long-chain lipids contacted the terminal turns of each helix in corroboration of the mixed bicelle model. The saturation transfer profiles from long-chain lipids directly established helix midpoints in the lipid bilayer. Lipid headgroups and water molecules engaged the side chains of buried serine and threonine in competition with intrahelical hydrogen bonding, illustrating that polar side chains seek the most favorable electrostatic contacts.
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Affiliation(s)
- Thomas Schmidt
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, 1501 San Pablo Street, Los Angeles, CA 90033, USA
- Present address: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Alan J. Situ
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, 1501 San Pablo Street, Los Angeles, CA 90033, USA
| | - Tobias S. Ulmer
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, 1501 San Pablo Street, Los Angeles, CA 90033, USA
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25
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Xu L, Xia M, Guo J, Sun X, Li H, Xu C, Gu X, Zhang H, Yi J, Fang Y, Xie H, Wang J, Shen Z, Xue B, Sun Y, Meckel T, Chen YH, Hu Z, Li Z, Xu C, Gong H, Liu W. Impairment on the lateral mobility induced by structural changes underlies the functional deficiency of the lupus-associated polymorphism FcγRIIB-T232. J Exp Med 2016; 213:2707-2727. [PMID: 27799621 PMCID: PMC5110019 DOI: 10.1084/jem.20160528] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 08/08/2016] [Accepted: 09/28/2016] [Indexed: 12/18/2022] Open
Abstract
Xu et al. show that the lupus-associated polymorphism FcγRIIB-T232 has structural changes of the TM domain that reduces lateral mobility and inhibitory functions. FcγRIIB functions to suppress the activation of immune cells. A single-nucleotide polymorphism in the transmembrane (TM) domain of FcγRIIB, FcγRIIB-T232, is associated with lupus. In this study, we investigated the pathogenic mechanism of FcγRIIB-T232 at both functional and structural levels. Our results showed that FcγRIIB-T232 exhibited significantly reduced lateral mobility compared with FcγRIIB-I232 and was significantly less enriched into the microclusters of immune complexes (ICs) after stimulation. However, if sufficient responding time is given for FcγRIIB-T232 to diffuse and interact with the ICs, FcγRIIB-T232 can restore its inhibitory function. Moreover, substituting the FcγRIIB-T232 TM domain with that of a fast floating CD86 molecule restored both the rapid mobility and the inhibitory function, which further corroborated the importance of fast mobility for FcγRIIB to function. Mechanistically, the crippled lateral mobility of FcγRIIB-T232 can be explained by the structural changes of the TM domain. Both atomistic simulations and nuclear magnetic resonance measurement indicated that the TM helix of FcγRIIB-T232 exhibited a more inclined orientation than that of FcγRIIB-I232, thus resulting in a longer region embedded in the membrane. Therefore, we conclude that the single-residue polymorphism T232 enforces the inclination of the TM domain and thereby reduces the lateral mobility and inhibitory functions of FcγRIIB.
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Affiliation(s)
- Liling Xu
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Mengdie Xia
- Ministry of Education Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Jun Guo
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiaolin Sun
- Department of Rheumatology and Immunology, Clinical Immunology Center, Peking University People's Hospital, Beijing 100044, China
| | - Hua Li
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Chenguang Xu
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Xiaomei Gu
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Haowen Zhang
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Junyang Yi
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yan Fang
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Hengyi Xie
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Jing Wang
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Zhixun Shen
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Boxin Xue
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Biodynamic Optical Imaging Center, School of Life Sciences, Peking University, Beijing 100871, China
| | - Yujie Sun
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Biodynamic Optical Imaging Center, School of Life Sciences, Peking University, Beijing 100871, China
| | - Tobias Meckel
- Membrane Dynamics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Ying-Hua Chen
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Zhibin Hu
- Department of Epidemiology, School of Public Health, Nanjing Medical University, Nanjing 211166, China
| | - Zhanguo Li
- Department of Rheumatology and Immunology, Clinical Immunology Center, Peking University People's Hospital, Beijing 100044, China
| | - Chenqi Xu
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China .,School of Life Science and Technology, ShanghaiTech University, Shanghai 200031, China
| | - Haipeng Gong
- Ministry of Education Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Wanli Liu
- Ministry of Education Key Laboratory of Protein Sciences, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Institute for Immunology, School of Life Sciences, Tsinghua University, Beijing 100084, China
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26
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Fast-tumbling bicelles constructed from native Escherichia coli lipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2097-2105. [DOI: 10.1016/j.bbamem.2016.06.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 06/09/2016] [Accepted: 06/10/2016] [Indexed: 11/20/2022]
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27
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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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28
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Bugge K, Lindorff-Larsen K, Kragelund BB. Understanding single-pass transmembrane receptor signaling from a structural viewpoint-what are we missing? FEBS J 2016; 283:4424-4451. [PMID: 27350538 DOI: 10.1111/febs.13793] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 06/10/2016] [Accepted: 06/27/2016] [Indexed: 11/30/2022]
Abstract
Single-pass transmembrane receptors are involved in essential processes of both physiological and pathological nature and represent more than 1300 proteins in the human genome. Despite the high biological relevance of these receptors, the mechanisms of the signal transductions they facilitate are incompletely understood. One major obstacle is the lack of structures of the transmembrane domains that connect the extracellular ligand-binding domains to the intracellular signaling platforms. Over a period of almost 20 years since the first structure was reported, only 21 of these receptors have become represented by a transmembrane domain structure. This scarceness stands in strong contrast to the significance of these transmembrane α-helices for receptor functionality. In this review, we explore the properties and qualities of the current set of structures, as well as the methodological difficulties associated with their characterization and the challenges left to be overcome. Without an increased and focused effort to bring this class of proteins on par with the remaining membrane protein field, a serious lag in their biological understanding looms. Design of pharmaceutical agents, prediction of mutational affects in relation to disease, and deciphering of functional mechanisms require high-resolution structural information, especially when dealing with a domain carrying so much functionality in so few residues.
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Affiliation(s)
- Katrine Bugge
- Department of Biology, Structural Biology and NMR Laboratory, University of Copenhagen, Denmark
| | - Kresten Lindorff-Larsen
- Department of Biology, Structural Biology and NMR Laboratory, University of Copenhagen, Denmark
| | - Birthe B Kragelund
- Department of Biology, Structural Biology and NMR Laboratory, University of Copenhagen, Denmark
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29
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The Rap1-RIAM-talin axis of integrin activation and blood cell function. Blood 2016; 128:479-87. [PMID: 27207789 DOI: 10.1182/blood-2015-12-638700] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 05/07/2016] [Indexed: 12/14/2022] Open
Abstract
Integrin adhesion receptors mediate the adhesion of blood cells, such as leukocytes, to other cells, such as endothelial cells. Integrins also are critical for anchorage of hematopoietic precursors to the extracellular matrix. Blood cells can dynamically regulate the affinities of integrins for their ligands ("activation"), an event central to their functions. Here we review recent progress in understanding the mechanisms of integrin activation with a focus on the functions of blood cells. We discuss how talin binding to the integrin β cytoplasmic domain, in conjunction with the plasma membrane, induces long-range allosteric rearrangements that lead to integrin activation. Second, we review our understanding of how signaling events, particularly those involving Rap1 small guanosine triphosphate (GTP)hydrolases, can regulate the talin-integrin interaction and resulting activation. Third, we review recent findings that highlight the role of the Rap1-GTP-interacting adapter molecule (RIAM), encoded by the APBB1IP gene, in leukocyte integrin activation and consequently in leukocyte trafficking.
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30
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Chen VB, Wedell JR, Wenger RK, Ulrich EL, Markley JL. MolProbity for the masses-of data. JOURNAL OF BIOMOLECULAR NMR 2015; 63. [PMID: 26195077 PMCID: PMC4577456 DOI: 10.1007/s10858-015-9969-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
MolProbity is a powerful software program for validating structures of proteins and nucleic acids. Although MolProbity includes scripts for batch analysis of structures, because these scripts analyze structures one at a time, they are not well suited for the validation of a large dataset of structures. We have created a version of MolProbity (MolProbity-HTC) that circumvents these limitations and takes advantage of a high-throughput computing cluster by using the HTCondor software. MolProbity-HTC enables the longitudinal analysis of large sets of structures, such as those deposited in the PDB or generated through theoretical computation-tasks that would have been extremely time-consuming using previous versions of MolProbity. We have used MolProbity-HTC to validate the entire PDB, and have developed a new visual chart for the BioMagResBank website that enables users to easily ascertain the quality of each model in an NMR ensemble and to compare the quality of those models to the rest of the PDB.
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Affiliation(s)
- Vincent B Chen
- National Magnetic Resonance Facility at Madison, Biochemistry Department, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, 53706, USA
| | - Jonathan R Wedell
- BioMagResBank, Biochemistry Department, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, 53706, USA
| | - R Kent Wenger
- BioMagResBank, Biochemistry Department, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, 53706, USA
| | - Eldon L Ulrich
- BioMagResBank, Biochemistry Department, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, 53706, USA
| | - John L Markley
- National Magnetic Resonance Facility at Madison, Biochemistry Department, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, 53706, USA.
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31
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Kucharska I, Edrington TC, Liang B, Tamm LK. Optimizing nanodiscs and bicelles for solution NMR studies of two β-barrel membrane proteins. JOURNAL OF BIOMOLECULAR NMR 2015; 61:261-74. [PMID: 25869397 PMCID: PMC4397663 DOI: 10.1007/s10858-015-9905-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Accepted: 01/21/2015] [Indexed: 05/22/2023]
Abstract
Solution NMR spectroscopy has become a robust method to determine structures and explore the dynamics of integral membrane proteins. The vast majority of previous studies on membrane proteins by solution NMR have been conducted in lipid micelles. Contrary to the lipids that form a lipid bilayer in biological membranes, micellar lipids typically contain only a single hydrocarbon chain or two chains that are too short to form a bilayer. Therefore, there is a need to explore alternative more bilayer-like media to mimic the natural environment of membrane proteins. Lipid bicelles and lipid nanodiscs have emerged as two alternative membrane mimetics that are compatible with solution NMR spectroscopy. Here, we have conducted a comprehensive comparison of the physical and spectroscopic behavior of two outer membrane proteins from Pseudomonas aeruginosa, OprG and OprH, in lipid micelles, bicelles, and nanodiscs of five different sizes. Bicelles stabilized with a fraction of negatively charged lipids yielded spectra of almost comparable quality as in the best micellar solutions and the secondary structures were found to be almost indistinguishable in the two environments. Of the five nanodiscs tested, nanodiscs assembled from MSP1D1ΔH5 performed the best with both proteins in terms of sample stability and spectral resolution. Even in these optimal nanodiscs some broad signals from the membrane embedded barrel were severely overlapped with sharp signals from the flexible loops making their assignments difficult. A mutant OprH that had two of the flexible loops truncated yielded very promising spectra for further structural and dynamical analysis in MSP1D1ΔH5 nanodiscs.
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32
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A conserved amphipathic helix is required for membrane tubule formation by Yop1p. Proc Natl Acad Sci U S A 2015; 112:E639-48. [PMID: 25646439 DOI: 10.1073/pnas.1415882112] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The integral membrane proteins of the DP1 (deleted in polyposis) and reticulon families are responsible for maintaining the high membrane curvature required for both smooth endoplasmic reticulum (ER) tubules and the edges of ER sheets, and mutations in these proteins lead to motor neuron diseases, such as hereditary spastic paraplegia. Reticulon/DP1 proteins contain reticulon homology domains (RHDs) that have unusually long hydrophobic segments and are proposed to adopt intramembrane helical hairpins that stabilize membrane curvature. We have characterized the secondary structure and dynamics of the DP1 family protein produced from the YOP1 gene (Yop1p) and identified a C-terminal conserved amphipathic helix (APH) that, on its own, interacts strongly with negatively charged membranes and is necessary for membrane tubule formation. Analyses of DP1 and reticulon family members indicate that most, if not all, contain C-terminal sequences capable of forming APHs. Together, these results indicate that APHs play a previously unrecognized role in RHD membrane curvature stabilization.
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33
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Schmidt T, Suk JE, Ye F, Situ AJ, Mazumder P, Ginsberg MH, Ulmer TS. Annular anionic lipids stabilize the integrin αIIbβ3 transmembrane complex. J Biol Chem 2015; 290:8283-93. [PMID: 25632962 DOI: 10.1074/jbc.m114.623504] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cationic membrane-proximal amino acids determine the topology of membrane proteins by interacting with anionic lipids that are restricted to the intracellular membrane leaflet. This mechanism implies that anionic lipids interfere with electrostatic interactions of membrane proteins. The integrin αIIbβ3 transmembrane (TM) complex is stabilized by a membrane-proximal αIIb(Arg(995))-β3(Asp(723)) interaction; here, we examine the influence of anionic lipids on this complex. Anionic lipids compete for αIIb(Arg(995)) contacts with β3(Asp(723)) but paradoxically do not diminish the contribution of αIIb(Arg(995))-β3(Asp(723)) to TM complex stability. Overall, anionic lipids in annular positions stabilize the αIIbβ3 TM complex by up to 0.50 ± 0.02 kcal/mol relative to zwitterionic lipids in a headgroup structure-dependent manner. Comparatively, integrin receptor activation requires TM complex destabilization of 1.5 ± 0.2 kcal/mol, revealing a sizeable influence of lipid composition on TM complex stability. We implicate changes in lipid headgroup accessibility to small molecules (physical membrane characteristics) and specific but dynamic protein-lipid contacts in this TM helix-helix stabilization. Thus, anionic lipids in ubiquitous annular positions can benefit the stability of membrane proteins while leaving membrane-proximal electrostatic interactions intact.
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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 and
| | - Jae-Eun Suk
- From the Department of Biochemistry & Molecular Biology and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033 and
| | - Feng Ye
- the Department of Medicine, University of California San Diego, La Jolla, California 92093
| | - 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 and
| | - Parichita Mazumder
- From the Department of Biochemistry & Molecular Biology and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033 and
| | - Mark H Ginsberg
- the Department of Medicine, University of California San Diego, La Jolla, California 92093
| | - 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 and
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34
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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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35
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CW-EPR studies revealed different motional properties and oligomeric states of the integrin β1a transmembrane domain in detergent micelles or liposomes. Sci Rep 2015; 5:7848. [PMID: 25597475 PMCID: PMC4297981 DOI: 10.1038/srep07848] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 12/16/2014] [Indexed: 12/15/2022] Open
Abstract
Integrins are heterodimeric membrane proteins that regulate essential processes: cell migration, cell growth, extracellular matrix assembly and tumor metastasis. Each integrin α or β subunit contains a large extracellular domain, a single transmembrane (TM) domain, and a short cytoplasmic tail. The integrin TM domains are important for heterodimeric association and dissociation during the conversion from inactive to active states. Moreover, integrin clustering occurs by homo-oligomeric interactions between the TM helices. Here, the transmembrane and cytoplasmic (TMC) domains of integrin β1a were overexpressed, and the protein was purified in detergent micelles and/or reconstituted in liposomes. To investigate the TM domain conformational properties of integrin β1a, 26 consecutive single cysteine mutants were generated for site-directed spin labeling and continuous-wave electron paramagnetic resonance (CW-EPR) mobility and accessibility analyses. The mobility analysis identified two integrin β1a-TM regions with different motional properties in micelles and a non-continuous integrin β1a-TM helix with high immobility in liposomes. The accessibility analysis verified the TM range (Val737-Lys752) of the integrin β1a-TMC in micelles. Further mobility and accessibility comparisons of the integrin β1a-TMC domains in micelles or liposomes identified distinctively different oligomeric states of integrin β1a-TM, namely a monomer embedded in detergent micelles and leucine-zipper-like homo-oligomeric clusters in liposomes.
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36
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McCaffrey JE, James ZM, Thomas DD. Optimization of bicelle lipid composition and temperature for EPR spectroscopy of aligned membranes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 250:71-75. [PMID: 25514061 PMCID: PMC4286475 DOI: 10.1016/j.jmr.2014.09.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Revised: 09/24/2014] [Accepted: 09/29/2014] [Indexed: 06/04/2023]
Abstract
We have optimized the magnetic alignment of phospholipid bilayered micelles (bicelles) for EPR spectroscopy, by varying lipid composition and temperature. Bicelles have been extensively used in NMR spectroscopy for several decades, in order to obtain aligned samples in a near-native membrane environment and take advantage of the intrinsic sensitivity of magnetic resonance to molecular orientation. Recently, bicelles have also seen increasing use in EPR, which offers superior sensitivity and orientational resolution. However, the low magnetic field strength (less than 1 T) of most conventional EPR spectrometers results in homogeneously oriented bicelles only at a temperature well above physiological. To optimize bicelle composition for magnetic alignment at reduced temperature, we prepared bicelles containing varying ratios of saturated (DMPC) and unsaturated (POPC) phospholipids, using EPR spectra of a spin-labeled fatty acid to assess alignment as a function of lipid composition and temperature. Spectral analysis showed that bicelles containing an equimolar mixture of DMPC and POPC homogeneously align at 298 K, 20 K lower than conventional DMPC-only bicelles. It is now possible to perform EPR studies of membrane protein structure and dynamics in well-aligned bicelles at physiological temperatures and below.
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Affiliation(s)
- Jesse E McCaffrey
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - Zachary M James
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
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37
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Botelho SC, Enquist K, von Heijne G, Draheim RR. Differential repositioning of the second transmembrane helices from E. coli Tar and EnvZ upon moving the flanking aromatic residues. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:615-21. [PMID: 25445668 DOI: 10.1016/j.bbamem.2014.11.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Revised: 10/29/2014] [Accepted: 11/17/2014] [Indexed: 01/04/2023]
Abstract
Aromatic tuning, i.e. repositioning aromatic residues found at the cytoplasmic end of transmembrane (TM) domains within bacterial receptors, has been previously shown to modulate signal output from the aspartate chemoreceptor (Tar) and the major osmosensor EnvZ of Escherichia coli. In the case of Tar, changes in signal output consistent with the vertical position of the native Trp-Tyr aromatic tandem within TM2 were observed. In contrast, within EnvZ, where a Trp-Leu-Phe aromatic triplet was repositioned, the surface that the triplet resided upon was the major determinant governing signal output. However, these studies failed to determine whether moving the aromatic residues was sufficient to physically reposition the TM helix within a membrane. Recent coarse-grained molecular dynamics (CG-MD) simulations predicted displacement of Tar TM2 upon moving the aromatic residues at the cytoplasmic end of the helix. Here, we demonstrate that repositioning the Trp-Tyr tandem within Tar TM2 displaces the C-terminal boundary of the helix relative to the membrane. In a similar analysis of EnvZ, an abrupt initial displacement of TM2 was observed but no subsequent movement was seen, suggesting that the vertical position of TM2 is not governed by the location of the Trp-Leu-Phe triplet. Our results also provide another set of experimental data, i.e. the resistance of EnvZ TM2 to being displaced upon aromatic tuning, which could be useful for subsequent refinement of the initial CG-MD simulations. Finally, we discuss the limitations of these methodologies, how moving flanking aromatic residues might impact steady-state signal output and the potential to employ aromatic tuning in other bacterial membrane-spanning receptors.
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Affiliation(s)
- Salomé C Botelho
- Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden
| | - Karl Enquist
- Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden
| | - Gunnar von Heijne
- Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden
| | - Roger R Draheim
- Division of Pharmacy, Durham University, Queen's Campus, Stockton-on-Tees TS17 6BH, England, UK; Wolfson Research Institute for Health and Wellbeing, Durham University, Queen's Campus, Stockton-on-Tees, TS17 6BH, England, UK.
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38
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Situ AJ, Schmidt T, Mazumder P, Ulmer TS. Characterization of Membrane Protein Interactions by Isothermal Titration Calorimetry. J Mol Biol 2014; 426:3670-80. [DOI: 10.1016/j.jmb.2014.08.020] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/18/2014] [Accepted: 08/25/2014] [Indexed: 12/11/2022]
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39
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Provasi D, Negri A, Coller BS, Filizola M. Talin-driven inside-out activation mechanism of platelet αIIbβ3 integrin probed by multimicrosecond, all-atom molecular dynamics simulations. Proteins 2014; 82:3231-3240. [PMID: 24677266 DOI: 10.1002/prot.24540] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Revised: 02/06/2014] [Accepted: 02/10/2014] [Indexed: 01/20/2023]
Abstract
Platelet aggregation is the consequence of the binding of extracellular bivalent ligands such as fibrinogen and von Willebrand factor to the high affinity, active state of integrin αIIbβ3. This state is achieved through a so-called "inside-out" mechanism characterized by the membrane-assisted formation of a complex between the F2 and F3 subdomains of intracellular protein talin and the integrin β3 tail. Here, we present the results of multi-microsecond, all-atom molecular dynamics simulations carried on the complete transmembrane (TM) and C-terminal (CT) domains of αIIbβ3 integrin in an explicit lipid-water environment, and in the presence or absence of the talin-1 F2 and F3 subdomains. These large-scale simulations provide unprecedented molecular-level insights into the talin-driven inside-out activation of αIIbβ3 integrin. Specifically, they suggest a preferred conformation of the complete αIIbβ3 TM/CT domains in a lipid-water environment, and testable hypotheses of key intermolecular interactions between αIIbβ3 integrin and the F2/F3 domains of talin-1. Notably, not only do these simulations give support to a stable left-handed reverse turn conformation of the αIIb juxtamembrane motif rather than a helical turn, but they raise the question as to whether TM helix separation is required for talin-driven integrin activation.
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Affiliation(s)
- Davide Provasi
- Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, Box 1677, New York, New York 10029
| | - Ana Negri
- Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, Box 1677, New York, New York 10029
| | - Barry S Coller
- Allen and Frances Adler Laboratory of Blood and Vascular Biology, The Rockefeller University, 1230 York Avenue, Box 309, New York, New York 10065
| | - Marta Filizola
- Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, Box 1677, New York, New York 10029
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40
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Müller MA, Brunie L, Bächer AS, Kessler H, Gottschalk KE, Reuning U. Cytoplasmic salt bridge formation in integrin αvß3 stabilizes its inactive state affecting integrin-mediated cell biological effects. Cell Signal 2014; 26:2493-503. [PMID: 25041847 DOI: 10.1016/j.cellsig.2014.07.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Accepted: 07/09/2014] [Indexed: 02/01/2023]
Abstract
Heterodimeric integrin receptors are mediators of cell adhesion, motility, invasion, proliferation, and survival. By this, they are crucially involved in (tumor) cell biological behavior. Integrins trigger signals bidirectionally across cell membranes: by outside-in, following binding of protein ligands of the extracellular matrix, and by inside-out, where proteins are recruited to ß-integrin cytoplasmic tails resulting in conformational changes leading to increased integrin binding affinity and integrin activation. Computational modeling and experimental/mutational approaches imply that associations of integrin transmembrane domains stabilize the low-affinity integrin state. Moreover, a cytoplasmic interchain salt bridge is discussed to contribute to a tight clasp of the α/ß-membrane-proximal regions; however, its existence and physiological relevance for integrin activation are still a controversial issue. In order to further elucidate the functional role of salt bridge formation, we designed mutants of the tumor biologically relevant integrin αvß3 by mutually exchanging the salt bridge forming amino acid residues on each chain (αvR995D and ß3D723R). Following transfection of human ovarian cancer cells with different combinations of wild type and mutated integrin chains, we showed that loss of salt bridge formation strengthened αvß3-mediated adhesion to vitronectin, provoked recruitment of cytoskeletal proteins, such as talin, and induced integrin signaling, ultimately resulting in enhanced cell migration, proliferation, and activation of integrin-related signaling molecules. These data support the notion of a functional relevance of integrin cytoplasmic salt bridge disruption during integrin activation.
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Affiliation(s)
- Martina A Müller
- Clinical Research Unit, Dept. for Obstetrics & Gynecology, Technische Universitaet München, Munich, Germany
| | - Leonora Brunie
- Clinical Research Unit, Dept. for Obstetrics & Gynecology, Technische Universitaet München, Munich, Germany
| | - Anne-Sophie Bächer
- Clinical Research Unit, Dept. for Obstetrics & Gynecology, Technische Universitaet München, Munich, Germany
| | - Horst Kessler
- Institute for Advanced Study and Centre of Integrated Protein Science, Department Chemie, Technische Universitaet München, Garching, Germany; Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
| | | | - Ute Reuning
- Clinical Research Unit, Dept. for Obstetrics & Gynecology, Technische Universitaet München, Munich, Germany.
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41
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Virkki M, Boekel C, Illergård K, Peters C, Shu N, Tsirigos KD, Elofsson A, von Heijne G, Nilsson I. Large tilts in transmembrane helices can be induced during tertiary structure formation. J Mol Biol 2014; 426:2529-38. [PMID: 24793448 DOI: 10.1016/j.jmb.2014.04.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 04/19/2014] [Accepted: 04/22/2014] [Indexed: 10/25/2022]
Abstract
While early structural models of helix-bundle integral membrane proteins posited that the transmembrane α-helices [transmembrane helices (TMHs)] were orientated more or less perpendicular to the membrane plane, there is now ample evidence from high-resolution structures that many TMHs have significant tilt angles relative to the membrane. Here, we address the question whether the tilt is an intrinsic property of the TMH in question or if it is imparted on the TMH during folding of the protein. Using a glycosylation mapping technique, we show that four highly tilted helices found in multi-spanning membrane proteins all have much shorter membrane-embedded segments when inserted by themselves into the membrane than seen in the high-resolution structures. This suggests that tilting can be induced by tertiary packing interactions within the protein, subsequent to the initial membrane-insertion step.
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Affiliation(s)
- Minttu Virkki
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden
| | - Carolina Boekel
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
| | - Kristoffer Illergård
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden
| | - Christoph Peters
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden
| | - Nanjiang Shu
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden
| | - Konstantinos D Tsirigos
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden
| | - Arne Elofsson
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden
| | - Gunnar von Heijne
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden; Science for Life Laboratory, Stockholm University, SE-17177 Solna, Sweden.
| | - IngMarie Nilsson
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
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42
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Kalli AC, Campbell ID, Sansom MSP. Conformational changes in talin on binding to anionic phospholipid membranes facilitate signaling by integrin transmembrane helices. PLoS Comput Biol 2013; 9:e1003316. [PMID: 24204243 PMCID: PMC3814715 DOI: 10.1371/journal.pcbi.1003316] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2013] [Accepted: 09/19/2013] [Indexed: 01/01/2023] Open
Abstract
Integrins are heterodimeric (αβ) cell surface receptors that are activated to a high affinity state by the formation of a complex involving the α/β integrin transmembrane helix dimer, the head domain of talin (a cytoplasmic protein that links integrins to actin), and the membrane. The talin head domain contains four sub-domains (F0, F1, F2 and F3) with a long cationic loop inserted in the F1 domain. Here, we model the binding and interactions of the complete talin head domain with a phospholipid bilayer, using multiscale molecular dynamics simulations. The role of the inserted F1 loop, which is missing from the crystal structure of the talin head, PDB:3IVF, is explored. The results show that the talin head domain binds to the membrane predominantly via cationic regions on the F2 and F3 subdomains and the F1 loop. Upon binding, the intact talin head adopts a novel V-shaped conformation which optimizes its interactions with the membrane. Simulations of the complex of talin with the integrin α/β TM helix dimer in a membrane, show how this complex promotes a rearrangement, and eventual dissociation of, the integrin α and β transmembrane helices. A model for the talin-mediated integrin activation is proposed which describes how the mutual interplay of interactions between transmembrane helices, the cytoplasmic talin protein, and the lipid bilayer promotes integrin inside-out activation. Transmission of signals across the cell membrane is an essential process for all living organisms. Integrins are one example of cell surface receptors (αβ) which, uniquely, form a bidirectional signalling pathway across the membrane. Integrins are crucial for many cellular processes and play key roles in pathological defects such as cardiovascular diseases and cancer. They are activated to a high affinity state by the intracellular protein talin in a process known as ‘inside-out activation’. Despite their importance and the existence of functional and structural data, the mechanism by which talin activates integrin remains elusive. In this study we use a multi-scale computational approach, which combines coarse-grained and atomistic molecular dynamics simulations, to suggest how the formation of the complex between the talin head domain, the cell membrane and the integrin moves the integrin equilibrium towards an active state. Our results show that conformational changes within the talin head domains optimize its interactions with the cell membrane. Upon binding to the integrin, talin facilitates rearrangement of the integrin TM region thus promoting integrin activation. This study also provides a demonstration of the strengths of a computational multi-scale approach in studies of membrane interactions and receptor conformational changes and associated proteins that enable transmembrane signaling.
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Affiliation(s)
- Antreas C. Kalli
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Iain D. Campbell
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Mark S. P. Sansom
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
- * E-mail:
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43
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Ortega-Roldan JL, Ossa F, Schnell JR. Characterization of the human sigma-1 receptor chaperone domain structure and binding immunoglobulin protein (BiP) interactions. J Biol Chem 2013; 288:21448-21457. [PMID: 23760505 PMCID: PMC3774411 DOI: 10.1074/jbc.m113.450379] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 05/31/2013] [Indexed: 01/09/2023] Open
Abstract
The sigma-1 receptor (S1R) is a ligand-regulated membrane protein chaperone involved in the ER stress response. S1R activity is implicated in diseases of the central nervous system including amnesia, schizophrenia, depression, Alzheimer disease, and addiction. S1R has been shown previously to regulate the Hsp70 binding immunoglobulin protein (BiP) and the inositol triphosphate receptor calcium channel through a C-terminal domain. We have developed methods for bacterial expression and reconstitution of the chaperone domain of human S1R into detergent micelles that enable its study by solution NMR spectroscopy. The chaperone domain is found to contain a helix at the N terminus followed by a largely dynamic region and a structured, helical C-terminal region that encompasses a membrane associated domain containing four helices. The helical region at residues ∼198-206 is strongly amphipathic and proposed to anchor the chaperone domain to micelles and membranes. Three of the helices in the C-terminal region closely correspond to previously identified cholesterol and drug recognition sites. In addition, it is shown that the chaperone domain interacts with full-length BiP or the isolated nucleotide binding domain of BiP, but not the substrate binding domain, suggesting that the nucleotide binding domain is sufficient for S1R interactions.
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Affiliation(s)
| | - Felipe Ossa
- From the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Jason R Schnell
- From the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom.
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Lai C, Liu X, Tian C, Wu F. Integrin α1 has a long helix, extending from the transmembrane region to the cytoplasmic tail in detergent micelles. PLoS One 2013; 8:e62954. [PMID: 23646163 PMCID: PMC3639902 DOI: 10.1371/journal.pone.0062954] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 03/26/2013] [Indexed: 12/12/2022] Open
Abstract
Integrin proteins are very important adhesion receptors that mediate cell-cell and cell-extracellular matrix interactions. They play essential roles in cell signaling and the regulation of cellular shape, motility, and the cell cycle. Here, the transmembrane and cytoplasmic (TMC) domains of integrin α1 and β1 were over-expressed and purified in detergent micelles. The structure and backbone relaxations of α1-TMC in LDAO micelles were determined and analyzed using solution NMR. A long helix, extending from the transmembrane region to the cytoplasmic tail, was observed in α1-TMC. Structural comparisons of α1-TMC with reported αIIb-TMC domains indicated different conformations in the transmembrane regions and cytoplasmic tails. An NMR titration experiment indicated weak interactions between α1-TMC and β1-TMC through several α1-TMC residues located at its N-terminal juxta-transmembrane region and C-terminal extended helix region.
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Affiliation(s)
- Chaohua Lai
- Hefei National Laboratory for Physical Science at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Xiaoxi Liu
- Hefei National Laboratory for Physical Science at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Changlin Tian
- Hefei National Laboratory for Physical Science at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
- High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui, China
- * E-mail: (CT); (FW)
| | - Fangming Wu
- High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui, China
- * E-mail: (CT); (FW)
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45
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Localized lipid packing of transmembrane domains impedes integrin clustering. PLoS Comput Biol 2013; 9:e1002948. [PMID: 23516344 PMCID: PMC3597534 DOI: 10.1371/journal.pcbi.1002948] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Accepted: 01/11/2013] [Indexed: 12/12/2022] Open
Abstract
Integrin clustering plays a pivotal role in a host of cell functions. Hetero-dimeric integrin adhesion receptors regulate cell migration, survival, and differentiation by communicating signals bidirectionally across the plasma membrane. Thus far, crystallographic structures of integrin components are solved only separately, and for some integrin types. Also, the sequence of interactions that leads to signal transduction remains ambiguous. Particularly, it remains controversial whether the homo-dimerization of integrin transmembrane domains occurs following the integrin activation (i.e. when integrin ectodomain is stretched out) or if it regulates integrin clustering. This study employs molecular dynamics modeling approaches to address these questions in molecular details and sheds light on the crucial effect of the plasma membrane. Conducting a normal mode analysis of the intact αllbβ3 integrin, it is demonstrated that the ectodomain and transmembrane-cytoplasmic domains are connected via a membrane-proximal hinge region, thus merely transmembrane-cytoplasmic domains are modeled. By measuring the free energy change and force required to form integrin homo-oligomers, this study suggests that the β-subunit homo-oligomerization potentially regulates integrin clustering, as opposed to α-subunit, which appears to be a poor regulator for the clustering process. If α-subunits are to regulate the clustering they should overcome a high-energy barrier formed by a stable lipid pack around them. Finally, an outside-in activation-clustering scenario is speculated, explaining how further loading the already-active integrin affects its homo-oligomerization so that focal adhesions grow in size. Focal adhesions are complex, dynamic structures of multiple proteins that act as the cell's mechanical anchorage to its surrounding. Integrins are proteins linking the cell inner and outer environments, which act as a bridge that crosses the cell membrane. Integrins respond to mechanical loads exerted to them by changing their conformations. Several diseases, such as atherosclerosis and different types of cancer, are caused by altered function of integrins. Essential to the formation of focal adhesions is the process of integrin clustering. Bidirectional integrin signaling involves conformational changes in this protein, clustering, and finally the assembly of a large intracellular adhesion complex. Integrin clustering is defined as the interaction of integrins to form lateral assemblies that eventually lead to focal adhesion formation. The effect of the plasma membrane on formation of integrin clusters has been largely neglected in current literature; subsequently some apparently contradictory data has been reported by a number of researchers in the field. Using a molecular dynamics modeling approach, a computational method that simulates systems in a full-atomic scale, we probe the role of the plasma membrane in integrin clustering and hypothesize a clustering scenario that explains the relationship between integrin activation and focal adhesion growth.
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46
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Structural model for the protein-translocating element of the twin-arginine transport system. Proc Natl Acad Sci U S A 2013; 110:E1092-101. [PMID: 23471988 DOI: 10.1073/pnas.1219486110] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The twin-arginine translocase (Tat) carries out the remarkable process of translocating fully folded proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. Tat is required for bacterial pathogenesis and for photosynthesis in plants. TatA, the protein-translocating element of the Tat system, is a small transmembrane protein that assembles into ring-like oligomers of variable size. We have determined a structural model of the Escherichia coli TatA complex in detergent solution by NMR. TatA assembly is mediated entirely by the transmembrane helix. The amphipathic helix extends outwards from the ring of transmembrane helices, permitting assembly of complexes with variable subunit numbers. Transmembrane residue Gln8 points inward, resulting in a short hydrophobic pore in the center of the complex. Simulations of the TatA complex in lipid bilayers indicate that the short transmembrane domain distorts the membrane. This finding suggests that TatA facilitates protein transport by sensitizing the membrane to transient rupture.
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47
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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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48
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49
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Dürr UN, Gildenberg M, Ramamoorthy A. The magic of bicelles lights up membrane protein structure. Chem Rev 2012; 112:6054-74. [PMID: 22920148 PMCID: PMC3497859 DOI: 10.1021/cr300061w] [Citation(s) in RCA: 266] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Indexed: 12/12/2022]
Affiliation(s)
| | - Melissa Gildenberg
- Biophysics
and Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055,
United States
| | - Ayyalusamy Ramamoorthy
- Biophysics
and Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055,
United States
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50
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Kim C, Ye F, Hu X, Ginsberg MH. Talin activates integrins by altering the topology of the β transmembrane domain. ACTA ACUST UNITED AC 2012; 197:605-11. [PMID: 22641344 PMCID: PMC3365499 DOI: 10.1083/jcb.201112141] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Talin binding to the integrin β tail alters the β transmembrane domain’s topology, resulting in integrin activation. Talin binding to integrin β tails increases ligand binding affinity (activation). Changes in β transmembrane domain (TMD) topology that disrupt α–β TMD interactions are proposed to mediate integrin activation. In this paper, we used membrane-embedded integrin β3 TMDs bearing environmentally sensitive fluorophores at inner or outer membrane water interfaces to monitor talin-induced β3 TMD motion in model membranes. Talin binding to the β3 cytoplasmic domain increased amino acid side chain embedding at the inner and outer borders of the β3 TMD, indicating altered topology of the β3 TMD. Talin’s capacity to effect this change depended on its ability to bind to both the integrin β tail and the membrane. Introduction of a flexible hinge at the midpoint of the β3 TMD decoupled the talin-induced change in intracellular TMD topology from the extracellular side and blocked talin-induced activation of integrin αIIbβ3. Thus, we show that talin binding to the integrin β TMD alters the topology of the TMD, resulting in integrin activation.
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Affiliation(s)
- Chungho Kim
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
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