Complement is Activated by Elevated IgG3 Hexameric Platforms and Deposits C4b Onto Distinct Antibody Domains

Overview

Journal Nat Commun

Specialty Biology

Date 2023 Jul 7

PMID 37419978

Authors

Leoni Abendstein

Douwe J Dijkstra

Rayman T N Tjokrodirijo

Peter A Van Veelen

Leendert A Trouw

Paul J Hensbergen

Thomas H Sharp

Affiliations

Soon will be listed here.

Abstract

IgG3 is unique among the IgG subclasses due to its extended hinge, allotypic diversity and enhanced effector functions, including highly efficient pathogen neutralisation and complement activation. It is also underrepresented as an immunotherapeutic candidate, partly due to a lack of structural information. Here, we use cryoEM to solve structures of antigen-bound IgG3 alone and in complex with complement components. These structures reveal a propensity for IgG3-Fab clustering, which is possible due to the IgG3-specific flexible upper hinge region and may maximise pathogen neutralisation by forming high-density antibody arrays. IgG3 forms elevated hexameric Fc platforms that extend above the protein corona to maximise binding to receptors and the complement C1 complex, which here adopts a unique protease conformation that may precede C1 activation. Mass spectrometry reveals that C1 deposits C4b directly onto specific IgG3 residues proximal to the Fab domains. Structural analysis shows this to be caused by the height of the C1-IgG3 complex. Together, these data provide structural insights into the role of the unique IgG3 extended hinge, which will aid the development and design of upcoming immunotherapeutics based on IgG3.

Citing Articles

Acquired drivers of C3 glomerulopathy.

Welsh S, Zhang Y, Smith R Clin Kidney J. 2025; 18(3):sfaf022.

PMID: 40052168 PMC: 11883229. DOI: 10.1093/ckj/sfaf022.

Complement factor H targeting antibody GT103 in refractory non-small cell lung cancer: a phase 1b dose escalation trial.

Clarke J, Simon G, Mamdani H, Gu L, Herndon 2nd J, Stinchcombe T Nat Commun. 2025; 16(1):93.

PMID: 39747856 PMC: 11695982. DOI: 10.1038/s41467-024-55092-2.

Streamlining segmentation of cryo-electron tomography datasets with Ais.

Last M, Abendstein L, Voortman L, Sharp T Elife. 2024; 13.

PMID: 39704648 PMC: 11661790. DOI: 10.7554/eLife.98552.

Underappreciated layers of antibody-mediated immune synapse architecture and dynamics.

Goldberg B, Ackerman M mBio. 2024; 16(1):e0190024.

PMID: 39660921 PMC: 11708040. DOI: 10.1128/mbio.01900-24.

Complement activation by IgG subclasses is governed by their ability to oligomerize upon antigen binding.

Frischauf N, Strasser J, Borg E, Labrijn A, Beurskens F, Preiner J Proc Natl Acad Sci U S A. 2024; 121(44):e2406192121.

PMID: 39436656 PMC: 11536094. DOI: 10.1073/pnas.2406192121.

References

Roux K, Strelets L, Michaelsen T . Flexibility of human IgG subclasses. J Immunol. 1997; 159(7):3372-82. View

Campbell R, DODDS A, Porter R . The binding of human complement component C4 to antibody-antigen aggregates. Biochem J. 1980; 189(1):67-80. PMC: 1161918. DOI: 10.1042/bj1890067. View

Venkatraman Girija U, Gingras A, Marshall J, Panchal R, Sheikh M, Harper J . Structural basis of the C1q/C1s interaction and its central role in assembly of the C1 complex of complement activation. Proc Natl Acad Sci U S A. 2013; 110(34):13916-20. PMC: 3752233. DOI: 10.1073/pnas.1311113110. View

Vidarsson G, Dekkers G, Rispens T . IgG subclasses and allotypes: from structure to effector functions. Front Immunol. 2014; 5:520. PMC: 4202688. DOI: 10.3389/fimmu.2014.00520. View

Michaelsen T, Aase A, Westby C, Sandlie I . Enhancement of complement activation and cytolysis of human IgG3 by deletion of hinge exons. Scand J Immunol. 1990; 32(5):517-28. DOI: 10.1111/j.1365-3083.1990.tb03192.x. View

Goers J, Porter R . The assembly of early components of complement on antibody-antigen aggregates and on antibody-coated erythrocytes. Biochem J. 1978; 175(2):675-84. PMC: 1186118. DOI: 10.1042/bj1750675. View

Kapur R, Einarsdottir H, Vidarsson G . IgG-effector functions: "the good, the bad and the ugly". Immunol Lett. 2014; 160(2):139-44. DOI: 10.1016/j.imlet.2014.01.015. View

Bruhns P, Iannascoli B, England P, Mancardi D, Fernandez N, Jorieux S . Specificity and affinity of human Fcgamma receptors and their polymorphic variants for human IgG subclasses. Blood. 2008; 113(16):3716-25. DOI: 10.1182/blood-2008-09-179754. View

Spiteri V, Goodall M, Doutch J, Rambo R, Gor J, Perkins S . Solution structures of human myeloma IgG3 antibody reveal extended Fab and Fc regions relative to the other IgG subclasses. J Biol Chem. 2021; 297(3):100995. PMC: 8371214. DOI: 10.1016/j.jbc.2021.100995. View

10.

Wilkinson I, Hale G . Systematic analysis of the varied designs of 819 therapeutic antibodies and Fc fusion proteins assigned international nonproprietary names. MAbs. 2022; 14(1):2123299. PMC: 9481088. DOI: 10.1080/19420862.2022.2123299. View

11.

Schiele F, van Ryn J, Canada K, Newsome C, Sepulveda E, Park J . A specific antidote for dabigatran: functional and structural characterization. Blood. 2013; 121(18):3554-62. DOI: 10.1182/blood-2012-11-468207. View

12.

de Taeye S, Bentlage A, Mebius M, Meesters J, Lissenberg-Thunnissen S, Falck D . FcγR Binding and ADCC Activity of Human IgG Allotypes. Front Immunol. 2020; 11:740. PMC: 7218058. DOI: 10.3389/fimmu.2020.00740. View

13.

Kidmose R, Laursen N, Dobo J, Kjaer T, Sirotkina S, Yatime L . Structural basis for activation of the complement system by component C4 cleavage. Proc Natl Acad Sci U S A. 2012; 109(38):15425-30. PMC: 3458355. DOI: 10.1073/pnas.1208031109. View

14.

Roux K, Strelets L, Brekke O, Sandlie I, Michaelsen T . Comparisons of the ability of human IgG3 hinge mutants, IgM, IgE, and IgA2, to form small immune complexes: a role for flexibility and geometry. J Immunol. 1998; 161(8):4083-90. View

15.

Sharp T, Faas F, Koster A, Gros P . Imaging complement by phase-plate cryo-electron tomography from initiation to pore formation. J Struct Biol. 2016; 197(2):155-162. DOI: 10.1016/j.jsb.2016.09.008. View

16.

Chu T, Crowley A, Backes I, Chang C, Tay M, Broge T . Hinge length contributes to the phagocytic activity of HIV-specific IgG1 and IgG3 antibodies. PLoS Pathog. 2020; 16(2):e1008083. PMC: 7058349. DOI: 10.1371/journal.ppat.1008083. View

17.

Liu F, Rijkers D, Post H, Heck A . Proteome-wide profiling of protein assemblies by cross-linking mass spectrometry. Nat Methods. 2015; 12(12):1179-84. DOI: 10.1038/nmeth.3603. View

18.

Hagen W, Wan W, Briggs J . Implementation of a cryo-electron tomography tilt-scheme optimized for high resolution subtomogram averaging. J Struct Biol. 2016; 197(2):191-198. PMC: 5287356. DOI: 10.1016/j.jsb.2016.06.007. View

19.

Pettersen E, Goddard T, Huang C, Couch G, Greenblatt D, Meng E . UCSF Chimera--a visualization system for exploratory research and analysis. J Comput Chem. 2004; 25(13):1605-12. DOI: 10.1002/jcc.20084. View

20.

Iudin A, Korir P, Somasundharam S, Weyand S, Cattavitello C, Fonseca N . EMPIAR: the Electron Microscopy Public Image Archive. Nucleic Acids Res. 2022; 51(D1):D1503-D1511. PMC: 9825465. DOI: 10.1093/nar/gkac1062. View