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Orlandi C, Deredge D, Ray K, Gohain N, Tolbert W, DeVico AL, Wintrode P, Pazgier M, Lewis GK. Antigen-Induced Allosteric Changes in a Human IgG1 Fc Increase Low-Affinity Fcγ Receptor Binding. Structure 2020; 28:516-527.e5. [PMID: 32209433 DOI: 10.1016/j.str.2020.03.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 02/07/2020] [Accepted: 03/05/2020] [Indexed: 11/15/2022]
Abstract
Antibody structure couples adaptive and innate immunity via Fab (antigen binding) and Fc (effector) domains that are connected by unique hinge regions. Because antibodies harbor two or more Fab domains, they are capable of crosslinking multi-determinant antigens, which is required for Fc-dependent functions through associative interactions with effector ligands, including C1q and cell surface Fc receptors. The modular nature of antibodies, with distal ligand binding sites for antigen and Fc-ligands, is reminiscent of allosteric proteins, suggesting that allosteric interactions might contribute to Fc-mediated effector functions. This hypothesis has been pursued for over 40 years and remains unresolved. Here, we provide evidence that allosteric interactions between Fab and Fc triggered by antigen binding modulate binding of Fc to low-affinity Fc receptors (FcγR) for a human IgG1. This work opens the path to further dissection of the relative roles of allosteric and associative interactions in Fc-mediated effector functions.
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Affiliation(s)
- Chiara Orlandi
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA
| | - Daniel Deredge
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Krishanu Ray
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA
| | - Neelakshi Gohain
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA
| | - William Tolbert
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA
| | - Anthony L DeVico
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA
| | - Patrick Wintrode
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Marzena Pazgier
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA
| | - George K Lewis
- Division of Vaccine Research, The Institute of Human Virology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA.
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Diebolder CA, Beurskens FJ, de Jong RN, Koning RI, Strumane K, Lindorfer MA, Voorhorst M, Ugurlar D, Rosati S, Heck AJR, van de Winkel JGJ, Wilson IA, Koster AJ, Taylor RP, Saphire EO, Burton DR, Schuurman J, Gros P, Parren PWHI. Complement is activated by IgG hexamers assembled at the cell surface. Science 2014; 343:1260-3. [PMID: 24626930 DOI: 10.1126/science.1248943] [Citation(s) in RCA: 531] [Impact Index Per Article: 53.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Complement activation by antibodies bound to pathogens, tumors, and self antigens is a critical feature of natural immune defense, a number of disease processes, and immunotherapies. How antibodies activate the complement cascade, however, is poorly understood. We found that specific noncovalent interactions between Fc segments of immunoglobulin G (IgG) antibodies resulted in the formation of ordered antibody hexamers after antigen binding on cells. These hexamers recruited and activated C1, the first component of complement, thereby triggering the complement cascade. The interactions between neighboring Fc segments could be manipulated to block, reconstitute, and enhance complement activation and killing of target cells, using all four human IgG subclasses. We offer a general model for understanding antibody-mediated complement activation and the design of antibody therapeutics with enhanced efficacy.
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Affiliation(s)
- Christoph A Diebolder
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, 3584 CH Utrecht, Netherlands
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Svehag SE. A solid-phase radioimmunoassay for C1q-binding immune complexes. I. Delta IgG as indicator molecule. Scand J Immunol 1975; 4:687-97. [PMID: 1198070 DOI: 10.1111/j.1365-3083.1975.tb02677.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A solid-phase radioimmunoassay for detection of circulating C1q-binding immune complexes (IC) or heat-aggregated IgG (delta IgG) is described. Purified human C1q protein was adsorbed to a fixed area of polystyrene tube surface for 1 hr at 22 degrees C, pH 7.3, mu 0.15. Binding of delta IgG or IC to solid-phase C1q at 22 degrees C progressed over several hours and was enhanced at low mu (0.05). Heating of C1q (56 degrees C for 30 min) reduced the binding by 85%-90%. Binding of IC or delta IgG was retained after several weeks' storage of solid-phase C1q at 4 degrees C. Detection of 2-5 ng delta IgG and less than 50 ng IC (in antibody excess) was achieved in competitive binding or inhibition tests with [125I]delta IgG. Preliminary testing of 48 human sera indicated the usefulness of the assay for detection of IC in patient sera.
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