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Zaman K, Breitman A, Malik I, Fortenberry YM. Positive Allosteric Modulation of Antithrombin's Inhibitory Activity by RNA Aptamers. Nucleic Acid Ther 2023; 33:277-286. [PMID: 37093131 DOI: 10.1089/nat.2022.0047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2023] Open
Abstract
The leading cause of death in adults in the United States is cardiovascular disease, with mortality and morbidity mainly attributed to thromboembolism. Heparin is the most common therapy used for treating venous and arterial thrombosis. Heparin effectively accelerates the inhibition of coagulation proteases thrombin and factor Xa through the serine protease inhibitor (serpin) antithrombin (AT). Heparin is an essential therapeutic anticoagulant because of its effectiveness and the availability of protamine sulfate as an antidote. However, heparin therapy has several limitations. Thus, new anticoagulants, including direct thrombin inhibitors (ie, argatroban) and low-molecular-weight heparins (ie, fondaparinux), are used to treat some thromboembolic disorders. We developed and characterized a family of novel RNA-based aptamers that bind AT using two novel selection schemes. One of the aptamers, AT-16, accelerates factor Xa inhibition by AT in the absence of heparin. AT-16's effect on thrombin inhibition by AT is less effective compared to factor Xa. AT-16 induces a conformational change in AT that is different from that induced by heparin. This study demonstrates that an AT-specific RNA aptamer, AT-16, exhibits a positive allosteric modulator effect on AT's inhibition of factor Xa.
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Affiliation(s)
- Khalequz Zaman
- Biology Department, Case Western Reserve University, Cleveland, Ohio, USA
| | - Adi Breitman
- Biology Department, Case Western Reserve University, Cleveland, Ohio, USA
| | - Isa Malik
- Biology Department, Case Western Reserve University, Cleveland, Ohio, USA
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2
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Izaguirre G, Swanson R, Roth R, Gettins PGW, Olson ST. Paramount Importance of Core Conformational Changes for Heparin Allosteric Activation of Antithrombin. Biochemistry 2021; 60:1201-1213. [PMID: 33822598 PMCID: PMC10921935 DOI: 10.1021/acs.biochem.1c00128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Antithrombin is unique among serpin family protein protease inhibitors with respect to the major reactive center loop (RCL) and core conformational changes that mediate allosteric activation of its anticoagulant function by heparin. A critical role for expulsion of the RCL hinge from a native stabilizing interaction with the hydrophobic core in the activation mechanism has been proposed from reports that antithrombin variants that block this change through engineered disulfide bonds block activation. However, the sufficiency of core conformational changes for activation without expulsion of the RCL from the core is suggested by variants that are activated without the need for heparin and retain the native RCL-core interaction. To resolve these apparently conflicting findings, we engineered variants in which disulfides designed to block the RCL conformational change were combined with constitutively activating mutations. Our findings demonstrate that while a reversible constitutive activation can be engineered in variants that retain the native RCL-core interaction, engineered disulfides that lock the RCL native conformation can also block heparin allosteric activation. Such findings support a three-state allosteric activation model in which constitutive activating mutations stabilize an intermediate-activated state wherein core conformational changes and a major activation have occurred without the release of the RCL from the core but with a necessary repositioning of the RCL to allow productive engagement with an exosite. Rigid disulfide bonds that lock the RCL native conformation block heparin activation by preventing both RCL repositioning in the intermediate-activated state and the release of the RCL from the core in the fully activated state.
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Richard B, Swanson R, Izaguirre G, Olson ST. Cooperative Interactions of Three Hotspot Heparin Binding Residues Are Critical for Allosteric Activation of Antithrombin by Heparin. Biochemistry 2018; 57:2211-2226. [PMID: 29561141 DOI: 10.1021/acs.biochem.8b00216] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Heparin allosterically activates the anticoagulant serpin, antithrombin, by binding through a sequence-specific pentasaccharide and inducing activating conformational changes in the protein. Three basic residues of antithrombin, Lys114, Lys125, and Arg129, have been shown to be hotspots for binding the pentasaccharide, but the molecular basis for such hotspot binding has been unclear. To determine whether this results from cooperative interactions, we analyzed the effects of single, double, and triple mutations of the hotspot residues on pentasaccharide binding and activation of antithrombin. Double-mutant cycles revealed that the contribution of each residue to pentasaccharide binding energy was progressively reduced when one or both of the other residues were mutated, indicating strong coupling between each pair of residues that was dependent on the third residue and reflective of the three residues acting as a cooperative unit. Rapid kinetic studies showed that the hotspot residue mutations progressively abrogated the ability of the pentasaccharide to bind productively to native antithrombin and to conformationally activate the serpin by engaging the hotspot residues in an induced-fit interaction. Examination of the antithrombin-pentasaccharide complex structure revealed that the hotspot residues form two adjoining binding pockets for critical sulfates of the pentasaccharide that structurally link these residues. Together, these findings demonstrate that cooperative interactions of Lys114, Lys125, and Arg129 are critical for the productive induced-fit binding of the heparin pentasaccharide to antithrombin that allosterically activates the anticoagulant function of the serpin.
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Affiliation(s)
- Benjamin Richard
- Center for Molecular Biology of Oral Diseases and Department of Periodontics , University of Illinois at Chicago , Chicago , Illinois 60612 , United States
| | - Richard Swanson
- Center for Molecular Biology of Oral Diseases and Department of Periodontics , University of Illinois at Chicago , Chicago , Illinois 60612 , United States
| | - Gonzalo Izaguirre
- Center for Molecular Biology of Oral Diseases and Department of Periodontics , University of Illinois at Chicago , Chicago , Illinois 60612 , United States
| | - Steven T Olson
- Center for Molecular Biology of Oral Diseases and Department of Periodontics , University of Illinois at Chicago , Chicago , Illinois 60612 , United States
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Arantes PR, Pérez-Sánchez H, Verli H. Antithrombin conformational modulation by D-myo-inositol 3,4,5,6-tetrakisphosphate (TMI), a novel scaffold for the development of antithrombotic agents. J Biomol Struct Dyn 2017; 36:4045-4056. [DOI: 10.1080/07391102.2017.1407259] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Pablo Ricardo Arantes
- Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves 9500, CP 15005, Porto Alegre 91500-970, RS, Brazil
| | - Horacio Pérez-Sánchez
- Bioinformatics and High Performance Computing Research Group (BIO-HPC), Computer Engineering Department, Universidad Católica de Murcia (UCAM), Murcia, Spain
| | - Hugo Verli
- Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves 9500, CP 15005, Porto Alegre 91500-970, RS, Brazil
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5
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Inhibitory serpins. New insights into their folding, polymerization, regulation and clearance. Biochem J 2017; 473:2273-93. [PMID: 27470592 DOI: 10.1042/bcj20160014] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 03/31/2016] [Indexed: 12/20/2022]
Abstract
Serpins are a widely distributed family of high molecular mass protein proteinase inhibitors that can inhibit both serine and cysteine proteinases by a remarkable mechanism-based kinetic trapping of an acyl or thioacyl enzyme intermediate that involves massive conformational transformation. The trapping is based on distortion of the proteinase in the complex, with energy derived from the unique metastability of the active serpin. Serpins are the favoured inhibitors for regulation of proteinases in complex proteolytic cascades, such as are involved in blood coagulation, fibrinolysis and complement activation, by virtue of the ability to modulate their specificity and reactivity. Given their prominence as inhibitors, much work has been carried out to understand not only the mechanism of inhibition, but how it is fine-tuned, both spatially and temporally. The metastability of the active state raises the question of how serpins fold, whereas the misfolding of some serpin variants that leads to polymerization and pathologies of liver disease, emphysema and dementia makes it clinically important to understand how such polymerization might occur. Finally, since binding of serpins and their proteinase complexes, particularly plasminogen activator inhibitor-1 (PAI-1), to the clearance and signalling receptor LRP1 (low density lipoprotein receptor-related protein 1), may affect pathways linked to cell migration, angiogenesis, and tumour progression, it is important to understand the nature and specificity of binding. The current state of understanding of these areas is addressed here.
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Serpins in arthropod biology. Semin Cell Dev Biol 2016; 62:105-119. [PMID: 27603121 DOI: 10.1016/j.semcdb.2016.09.001] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 08/31/2016] [Accepted: 09/02/2016] [Indexed: 12/21/2022]
Abstract
Serpins are the largest known family of serine proteinase inhibitors and perform a variety of physiological functions in arthropods. Herein, we review the field of serpins in arthropod biology, providing an overview of current knowledge and topics of interest. Serpins regulate insect innate immunity via inhibition of serine proteinase cascades that initiate immune responses such as melanization and antimicrobial peptide production. In addition, several serpins with anti-pathogen activity are expressed as acute-phase serpins in insects upon infection. Parasitoid wasps can downregulate host serpin expression to modulate the host immune system. In addition, examples of serpin activity in development and reproduction in Drosophila have also been discovered. Serpins also function in host-pathogen interactions beyond immunity as constituents of venom in parasitoid wasps and saliva of blood-feeding ticks and mosquitoes. These serpins have distinct effects on immunosuppression and anticoagulation and are of interest for vaccine development. Lastly, the known structures of arthropod serpins are discussed, which represent the serpin inhibitory mechanism and provide a detailed overview of the process.
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Boulton S, Melacini G. Advances in NMR Methods To Map Allosteric Sites: From Models to Translation. Chem Rev 2016; 116:6267-304. [PMID: 27111288 DOI: 10.1021/acs.chemrev.5b00718] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The last five years have witnessed major developments in the understanding of the allosteric phenomenon, broadly defined as coupling between remote molecular sites. Such advances have been driven not only by new theoretical models and pharmacological applications of allostery, but also by progress in the experimental approaches designed to map allosteric sites and transitions. Among these techniques, NMR spectroscopy has played a major role given its unique near-atomic resolution and sensitivity to the dynamics that underlie allosteric couplings. Here, we highlight recent progress in the NMR methods tailored to investigate allostery with the goal of offering an overview of which NMR approaches are best suited for which allosterically relevant questions. The picture of the allosteric "NMR toolbox" is provided starting from one of the simplest models of allostery (i.e., the four-state thermodynamic cycle) and continuing to more complex multistate mechanisms. We also review how such an "NMR toolbox" has assisted the elucidation of the allosteric molecular basis for disease-related mutations and the discovery of novel leads for allosteric drugs. From this overview, it is clear that NMR plays a central role not only in experimentally validating transformative theories of allostery, but also in tapping the full translational potential of allosteric systems.
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Affiliation(s)
- Stephen Boulton
- Department of Chemistry and Chemical Biology Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main St. W., Hamilton L8S 4M1, Canada
| | - Giuseppe Melacini
- Department of Chemistry and Chemical Biology Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main St. W., Hamilton L8S 4M1, Canada
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Jin Y, Yegneswaran S, Gu JM, Gritzan U, Schönfeld DL, Paz P, Patel C, Dittmer F, Strerath M, Bringmann P, Kauser K, Myles T, Murphy JE, Hermiston TW. Identification and function probing of an antithrombin IIIβ conformation-specific antibody. J Thromb Haemost 2016; 14:356-65. [PMID: 26581031 DOI: 10.1111/jth.13198] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Indexed: 11/30/2022]
Abstract
UNLABELLED ESSENTIALS: Antithrombin III (AT)β binds heparin with higher affinity than ATα. A conformation-specific antibody against ATβ, TPP2009, was made to investigate ATβ in hemostasis. TPP2009 bound specifically to heparin-ATβ and greatly reduced the anticoagulant effect of AT. This antibody was effective in elucidating the importance of ATβ in hemostasis. BACKGROUND Antithrombin III (AT)β is an isoform of AT that lacks the post-translational carbohydrate modification at Asn135. This isoform binds heparin with greater affinity than ATα, and has been shown to target antithrombotic function to the extracellular vascular endothelial injury site. OBJECTIVES To characterize a conformation-specific antibody against ATβ and begin to investigate the role of ATβ in maintaining hemostasis. METHODS Surface plasmon resonance (SPR), antigen binding and functional assays were conducted to characterize the mode of action of antibodies generated against heparin-bound ATβ (ATβ*H) by the use of phage display. RESULTS SPR and binding studies showed that one of the antibodies, TPP2009, bound specifically to ATβ*H and glycosaminoglycan-associated ATβ on endothelial cells. In diluted prothrombin and activated factor X (FXa)-induced clotting assays, TPP2009 dose-dependently reduced the anticoagulant effect of heparin in non-hemophilic and FVIII-deficient human plasma, with half-maximal effective concentrations (EC50 ) of 10.5 nm and 4.7 nm, respectively. In AT-deficient human plasma, TPP2009 dose-dependently inhibited the effects of exogenously added ATβ and heparin. In purified systems with ATβ and pentasaccharide, TPP2009 restored > 91% of FXa activity. TPP2009 dose-dependently reversed the effects of heparin in rabbit (EC50 , 25.7 nm) and cynomolgus monkey (EC50 , 21.5 nm) plasma, but not in mouse plasma. TPP2009 was also effective in partially restoring FXa activity in rabbit and cynomolgus monkey plasma treated with FVIII function-neutralizing antibodies. CONCLUSIONS TPP2009 specifically targets a unique conformational epitope on ATβ*H and blocks ATβ-mediated anticoagulation. It effectively promotes coagulation in plasma, indicating the importance of ATβ in hemostasis.
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Affiliation(s)
- Y Jin
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - S Yegneswaran
- Hematology Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - J-M Gu
- Hematology Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - U Gritzan
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, Cologne, Germany
| | - D L Schönfeld
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, Wuppertal, Germany
| | - P Paz
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - C Patel
- Hematology Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - F Dittmer
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, Cologne, Germany
| | - M Strerath
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, Wuppertal, Germany
| | - P Bringmann
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - K Kauser
- Hematology Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - T Myles
- Hematology Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - J E Murphy
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
| | - T W Hermiston
- Global Biologics Research, Bayer HealthCare Pharmaceuticals, San Francisco, CA, USA
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9
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Roth R, Swanson R, Izaguirre G, Bock SC, Gettins PGW, Olson ST. Saturation Mutagenesis of the Antithrombin Reactive Center Loop P14 Residue Supports a Three-step Mechanism of Heparin Allosteric Activation Involving Intermediate and Fully Activated States. J Biol Chem 2015; 290:28020-28036. [PMID: 26359493 DOI: 10.1074/jbc.m115.678839] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Indexed: 11/06/2022] Open
Abstract
Past studies have suggested that a key feature of the mechanism of heparin allosteric activation of the anticoagulant serpin, antithrombin, is the release of the reactive center loop P14 residue from a native state stabilizing interaction with the hydrophobic core. However, more recent studies have indicated that this structural change plays a secondary role in the activation mechanism. To clarify this role, we expressed and characterized 15 antithrombin P14 variants. The variants exhibited basal reactivities with factors Xa and IXa, heparin affinities and thermal stabilities that were dramatically altered from wild type, consistent with the P14 mutations perturbing native state stability and shifting an allosteric equilibrium between native and activated states. Rapid kinetic studies confirmed that limiting rate constants for heparin allosteric activation of the mutants were altered in conjunction with the observed shifts of the allosteric equilibrium. However, correlations of the P14 mutations' effects on parameters reflecting the allosteric activation state of the serpin were inconsistent with a two-state model of allosteric activation and suggested multiple activated states. Together, these findings support a minimal three-state model of allosteric activation in which the P14 mutations perturb equilibria involving distinct native, intermediate, and fully activated states wherein the P14 residue retains an interaction with the hydrophobic core in the intermediate state but is released from the core in the fully activated state, and the bulk of allosteric activation has occurred in the intermediate.
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Affiliation(s)
- Ryan Roth
- Center for Molecular Biology of Oral Diseases and Departments of Periodontics
| | - Richard Swanson
- Center for Molecular Biology of Oral Diseases and Departments of Periodontics
| | - Gonzalo Izaguirre
- Center for Molecular Biology of Oral Diseases and Departments of Periodontics
| | - Susan C Bock
- Departments of Medicine and Bioengineering, University of Utah, Salt Lake City, Utah 84132
| | - Peter G W Gettins
- Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Steven T Olson
- Center for Molecular Biology of Oral Diseases and Departments of Periodontics.
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10
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Pomin VH, Mulloy B. Current structural biology of the heparin interactome. Curr Opin Struct Biol 2015; 34:17-25. [PMID: 26038285 DOI: 10.1016/j.sbi.2015.05.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Revised: 05/03/2015] [Accepted: 05/12/2015] [Indexed: 10/23/2022]
Abstract
Heparin is the best known therapeutically active carbohydrate. It can bind and regulate multiple functional proteins such as coagulation cofactors, chemokines, and growth factors. This versatility has led to the recently developed concept of the heparin interactome--a group of proteins that, as the name implies, interact with heparin. The heparin interactome is structurally and functionally diverse. Though natural ligands of this class of proteins may be any of the glycosaminoglycans however, their structural biology is generally studied using heparin as a model compound. NMR spectroscopy contributes significantly to structural investigations of the resultant complexes in solution. This review aims therefore at discussing the current status in structural biology of the molecular complexes formed between heparin and its protein partners through the current concept of the heparin interactome.
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Affiliation(s)
- Vitor H Pomin
- Program of Glycobiology, Institute of Medical Biochemistry Leopoldo de Meis, and University Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21941-913, Brazil.
| | - Barbara Mulloy
- Glycosciences Laboratory, Imperial College, Department of Medicine, Burlington Danes Building, Du Cane Road, London W12 0NN, UK.
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11
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Zhang X, Meekins DA, An C, Zolkiewski M, Battaile KP, Kanost MR, Lovell S, Michel K. Structural and inhibitory effects of hinge loop mutagenesis in serpin-2 from the malaria vector Anopheles gambiae. J Biol Chem 2014; 290:2946-56. [PMID: 25525260 DOI: 10.1074/jbc.m114.625665] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Serpin-2 (SRPN2) is a key negative regulator of the melanization response in the malaria vector Anopheles gambiae. SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9), which functions in a serine proteinase cascade culminating in the activation of prophenoloxidase and melanization. Silencing of SRPN2 in A. gambiae results in spontaneous melanization and decreased life span and is therefore a promising target for vector control. The previously determined structure of SRPN2 revealed a partial insertion of the hinge region of the reactive center loop (RCL) into β sheet A. This partial hinge insertion participates in heparin-linked activation in other serpins, notably antithrombin III. SRPN2 does not contain a heparin binding site, and any possible mechanistic function of the hinge insertion was previously unknown. To investigate the function of the SRPN2 hinge insertion, we developed three SRPN2 variants in which the hinge regions are either constitutively expelled or inserted and analyzed their structure, thermostability, and inhibitory activity. We determined that constitutive hinge expulsion resulted in a 2.7-fold increase in the rate of CLIPB9Xa inhibition, which is significantly lower than previous observations of allosteric serpin activation. Furthermore, we determined that stable insertion of the hinge region did not appreciably decrease the accessibility of the RCL to CLIPB9. Together, these results indicate that the partial hinge insertion in SRPN2 does not participate in the allosteric activation observed in other serpins and instead represents a molecular trade-off between RCL accessibility and efficient formation of an inhibitory complex with the cognate proteinase.
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Affiliation(s)
- Xin Zhang
- From the Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - David A Meekins
- From the Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - Chunju An
- From the Division of Biology, Kansas State University, Manhattan, Kansas 66506, the Department of Entomology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China
| | - Michal Zolkiewski
- the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Kevin P Battaile
- Industrial Macromolecular Crystallography Association Collaborative Access Team, Hauptman-Woodward Medical Research Institute, Advanced Photon Source Argonne National Laboratory, Argonne, Illinois 60439, and
| | - Michael R Kanost
- the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Scott Lovell
- the Protein Structure Laboratory, Del Shankel Structural Biology Center, University of Kansas, Lawrence, Kansas 66407
| | - Kristin Michel
- From the Division of Biology, Kansas State University, Manhattan, Kansas 66506,
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Izaguirre G, Aguila S, Qi L, Swanson R, Roth R, Rezaie AR, Gettins PGW, Olson ST. Conformational activation of antithrombin by heparin involves an altered exosite interaction with protease. J Biol Chem 2014; 289:34049-64. [PMID: 25331949 DOI: 10.1074/jbc.m114.611707] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Heparin allosterically activates antithrombin as an inhibitor of factors Xa and IXa by enhancing the initial Michaelis complex interaction of inhibitor with protease through exosites. Here, we investigate the mechanism of this enhancement by analyzing the effects of alanine mutations of six putative antithrombin exosite residues and three complementary protease exosite residues on antithrombin reactivity with these proteases in unactivated and heparin-activated states. Mutations of antithrombin Tyr(253) and His(319) exosite residues produced massive 10-200-fold losses in reactivity with factors Xa and IXa in both unactivated and heparin-activated states, indicating that these residues made critical attractive interactions with protease independent of heparin activation. By contrast, mutations of Asn(233), Arg(235), Glu(237), and Glu(255) exosite residues showed that these residues made both repulsive and attractive interactions with protease that depended on the activation state and whether the critical Tyr(253)/His(319) residues were mutated. Mutation of factor Xa Arg(143), Lys(148), and Arg(150) residues that interact with the exosite in the x-ray structure of the Michaelis complex confirmed the importance of all residues for heparin-activated antithrombin reactivity and Arg(150) for native serpin reactivity. These results demonstrate that the exosite is a key determinant of antithrombin reactivity with factors Xa and IXa in the native as well as the heparin-activated state and support a new model of allosteric activation we recently proposed in which a balance between attractive and repulsive exosite interactions in the native state is shifted to favor the attractive interactions in the activated state through core conformational changes induced by heparin binding.
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Affiliation(s)
- Gonzalo Izaguirre
- From the Department of Periodontics, Center for Molecular Biology of Oral Diseases and
| | - Sonia Aguila
- the Centro Regional de Hemodonación, University of Murcia, Murcia 30003, Spain, and
| | - Lixin Qi
- From the Department of Periodontics, Center for Molecular Biology of Oral Diseases and
| | - Richard Swanson
- From the Department of Periodontics, Center for Molecular Biology of Oral Diseases and
| | - Ryan Roth
- From the Department of Periodontics, Center for Molecular Biology of Oral Diseases and
| | - Alireza R Rezaie
- the Department of Biochemistry and Molecular Biology, St. Louis University, St. Louis, Missouri 63104
| | - Peter G W Gettins
- the Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois 60612
| | - Steven T Olson
- From the Department of Periodontics, Center for Molecular Biology of Oral Diseases and
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