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Garrigues RJ, Garrison MP, Garcia BL. The Crystal Structure of the Michaelis-Menten Complex of C1 Esterase Inhibitor and C1s Reveals Novel Insights into Complement Regulation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2024; 213:718-729. [PMID: 38995166 PMCID: PMC11333171 DOI: 10.4049/jimmunol.2400194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2024] [Accepted: 06/13/2024] [Indexed: 07/13/2024]
Abstract
The ancient arm of innate immunity known as the complement system is a blood proteolytic cascade involving dozens of membrane-bound and solution-phase components. Although many of these components serve as regulatory molecules to facilitate controlled activation of the cascade, C1 esterase inhibitor (C1-INH) is the sole canonical complement regulator belonging to a superfamily of covalent inhibitors known as serine protease inhibitors (SERPINs). In addition to its namesake role in complement regulation, C1-INH also regulates proteases of the coagulation, fibrinolysis, and contact pathways. Despite this, the structural basis for C1-INH recognition of its target proteases has remained elusive. In this study, we present the crystal structure of the Michaelis-Menten (M-M) complex of the catalytic domain of complement component C1s and the SERPIN domain of C1-INH at a limiting resolution of 3.94 Å. Analysis of the structure revealed that nearly half of the protein/protein interface is formed by residues outside of the C1-INH reactive center loop. The contribution of these residues to the affinity of the M-M complex was validated by site-directed mutagenesis using surface plasmon resonance. Parallel analysis confirmed that C1-INH-interfacing residues on C1s surface loops distal from the active site also drive affinity of the M-M complex. Detailed structural comparisons revealed differences in substrate recognition by C1s compared with C1-INH recognition and highlight the importance of exosite interactions across broader SERPIN/protease systems. Collectively, this study improves our understanding of how C1-INH regulates the classical pathway of complement, and it sheds new light on how SERPINs recognize their cognate protease targets.
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Affiliation(s)
- Ryan J Garrigues
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC
| | - Matthew P Garrison
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC
| | - Brandon L Garcia
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC
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Antithrombin and Its Role in Host Defense and Inflammation. Int J Mol Sci 2021; 22:ijms22084283. [PMID: 33924175 PMCID: PMC8074369 DOI: 10.3390/ijms22084283] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 04/13/2021] [Accepted: 04/15/2021] [Indexed: 12/12/2022] Open
Abstract
Antithrombin (AT) is a natural anticoagulant that interacts with activated proteases of the coagulation system and with heparan sulfate proteoglycans (HSPG) on the surface of cells. The protein, which is synthesized in the liver, is also essential to confer the effects of therapeutic heparin. However, AT levels drop in systemic inflammatory diseases. The reason for this decline is consumption by the coagulation system but also by immunological processes. Aside from the primarily known anticoagulant effects, AT elicits distinct anti-inflammatory signaling responses. It binds to structures of the glycocalyx (syndecan-4) and further modulates the inflammatory response of endothelial cells and leukocytes by interacting with surface receptors. Additionally, AT exerts direct antimicrobial effects: depending on AT glycosylation it can bind to and perforate bacterial cell walls. Peptide fragments derived from proteolytic degradation of AT exert antibacterial properties. Despite these promising characteristics, therapeutic supplementation in inflammatory conditions has not proven to be effective in randomized control trials. Nevertheless, new insights provided by subgroup analyses and retrospective trials suggest that a recommendation be made to identify the patient population that would benefit most from AT substitution. Recent experiment findings place the role of various AT isoforms in the spotlight. This review provides an overview of new insights into a supposedly well-known molecule.
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Rezaie AR, Giri H. Anticoagulant and signaling functions of antithrombin. J Thromb Haemost 2020; 18:3142-3153. [PMID: 32780936 PMCID: PMC7855051 DOI: 10.1111/jth.15052] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Revised: 07/25/2020] [Accepted: 08/04/2020] [Indexed: 12/19/2022]
Abstract
Antithrombin (AT) is a major plasma glycoprotein of the serpin superfamily that regulates the proteolytic activity of the procoagulant proteases of both intrinsic and extrinsic pathways. Two important structural features that participate in the regulatory function of AT include a mobile reactive center loop that binds to active site of coagulation proteases, trapping them in the form of inactive covalent complexes, and a basic D-helix that binds to therapeutic heparins and heparan sulfate proteoglycans (HSPGs) on vascular endothelial cells. The binding of D-helix of AT by therapeutic heparins promotes the reactivity of the serpin with coagulation proteases by several orders of magnitude by both a conformational activation of the serpin and a template (bridging) mechanism. In addition to its essential anticoagulant function, AT elicits a potent anti-inflammatory signaling response when it binds to distinct vascular endothelial cell HSPGs, thereby inducing prostacyclin synthesis. Syndecans-4 has been found as a specific membrane-bound HSPG receptor on endothelial cells that relays the signaling effect of AT to the relevant second messenger molecules in the signal transduction pathways inside the cell. However, following cleavage by coagulation proteases and/or by spontaneous conversion to a latent form, AT loses both its anti-inflammatory activity and high-affinity interaction with heparin and HSPGs. Interestingly, these low-affinity heparin conformers of AT elicit potent proapoptotic and antiangiogenic activities by also binding to specific HSPGs by unknown mechanisms. This review article will summarize current knowledge about mechanisms through which different conformers of AT exert their serine protease inhibitory and intracellular signaling functions in these biological pathways.
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Affiliation(s)
- Alireza R. Rezaie
- Cardiovascular Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
- Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104
| | - Hemant Giri
- Cardiovascular Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
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Scott BM, Sheffield WP. Engineering the serpin α 1 -antitrypsin: A diversity of goals and techniques. Protein Sci 2019; 29:856-871. [PMID: 31774589 DOI: 10.1002/pro.3794] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 11/19/2019] [Accepted: 11/19/2019] [Indexed: 12/19/2022]
Abstract
α1 -Antitrypsin (α1 -AT) serves as an archetypal example for the serine proteinase inhibitor (serpin) protein family and has been used as a scaffold for protein engineering for >35 years. Techniques used to engineer α1 -AT include targeted mutagenesis, protein fusions, phage display, glycoengineering, and consensus protein design. The goals of engineering have also been diverse, ranging from understanding serpin structure-function relationships, to the design of more potent or more specific proteinase inhibitors with potential therapeutic relevance. Here we summarize the history of these protein engineering efforts, describing the techniques applied to engineer α1 -AT, specific mutants of interest, and providing an appended catalog of the >200 α1 -AT mutants published to date.
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Affiliation(s)
- Benjamin M Scott
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland.,Biosystems and Biomaterials Division, National Institute of Standards and Technology, Gaithersburg, Maryland
| | - William P Sheffield
- Canadian Blood Services, Centre for Innovation, Hamilton, Ontario, Canada.,Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
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Papareddy P, Kalle M, Bhongir RKV, Mörgelin M, Malmsten M, Schmidtchen A. Antimicrobial effects of helix D-derived peptides of human antithrombin III. J Biol Chem 2014; 289:29790-800. [PMID: 25202017 DOI: 10.1074/jbc.m114.570465] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Antithrombin III (ATIII) is a key antiproteinase involved in blood coagulation. Previous investigations have shown that ATIII is degraded by Staphylococcus aureus V8 protease, leading to release of heparin binding fragments derived from its D helix. As heparin binding and antimicrobial activity of peptides frequently overlap, we here set out to explore possible antibacterial effects of intact and degraded ATIII. In contrast to intact ATIII, the results showed that extensive degradation of the molecule yielded fragments with antimicrobial activity. Correspondingly, the heparin-binding, helix D-derived, peptide FFFAKLNCRLYRKANKSSKLV (FFF21) of human ATIII, was found to be antimicrobial against particularly the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. Fluorescence microscopy and electron microscopy studies demonstrated that FFF21 binds to and permeabilizes bacterial membranes. Analogously, FFF21 was found to induce membrane leakage of model anionic liposomes. In vivo, FFF21 significantly reduced P. aeruginosa infection in mice. Additionally, FFF21 displayed anti-endotoxic effects in vitro. Taken together, our results suggest novel roles for ATIII-derived peptide fragments in host defense.
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Affiliation(s)
- Praveen Papareddy
- From the Division of Dermatology and Venereology, Department of Clinical Sciences, Lund University, Biomedical Center, Tornavägen 10, SE-221 84 Lund, Sweden, the Division of Infection Medicine, Department of Clinical Sciences, Lund University, Biomedical Center, Tornavägen 10, SE-221 84 Lund, Sweden,
| | - Martina Kalle
- From the Division of Dermatology and Venereology, Department of Clinical Sciences, Lund University, Biomedical Center, Tornavägen 10, SE-221 84 Lund, Sweden
| | - Ravi K V Bhongir
- the Division of Infection Medicine, Department of Clinical Sciences, Lund University, Biomedical Center, Tornavägen 10, SE-221 84 Lund, Sweden
| | - Matthias Mörgelin
- the Division of Infection Medicine, Department of Clinical Sciences, Lund University, Biomedical Center, Tornavägen 10, SE-221 84 Lund, Sweden
| | - Martin Malmsten
- the Department of Pharmacy, Uppsala University, SE-751 23, Uppsala, Sweden, and
| | - Artur Schmidtchen
- From the Division of Dermatology and Venereology, Department of Clinical Sciences, Lund University, Biomedical Center, Tornavägen 10, SE-221 84 Lund, Sweden, the LKCMedicine, Nanyang Technological University, 11 Mandalay Road, Singapore, 308232
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