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Generation of mutated variants of the human form of the MHC class I-related receptor, FcRn, with increased affinity for mouse immunoglobulin G

Generation of mutated variants of the human form of the MHC class I-related receptor, FcRn, with increased affinity for mouse immunoglobulin G
Generation of mutated variants of the human form of the MHC class I-related receptor, FcRn, with increased affinity for mouse immunoglobulin G

Much data support the concept that the MHC class I-related receptor FcRn serves to regulate immunoglobulin G (IgG) concentrations in serum and other diverse body sites in both rodents and humans. Previous studies have indicated that the human ortholog of FcRn is endowed with unexpectedly high stringency in binding specificity for IgGs. In contrast to mouse FcRn, which binds promiscuously to IgGs across species, human FcRn does not bind to mouse IgG1 or IgG2a, and interacts weakly with mouse IgG2b. Here, we investigate the molecular basis for this high-level specificity. We have systematically mutated human FcRn residues to the corresponding mouse FcRn residues in the regions that encompass the FcRn-IgG interaction site. Notably, mutation of the poorly conserved residue Leu137 of human FcRn to glutamic acid (L137E) generates a human FcRn mutant that binds to mouse IgG1 and mouse IgG2a with equilibrium dissociation constants of 13.2 μM and 14.4 μM, respectively. From earlier high-resolution structural analyses of the rat FcRn-rat Fc complex, residue 137 of human FcRn is predicted to contact residue 436 of IgG, which can be either His436 (mouse IgG1, mouse IgG2a) or Tyr436 (human IgG1, mouse IgG2b). The simplest interpretation of our data for the L137E mutant is therefore that replacement of the Leu137-Tyr436 (human) by the Glu137-His436 (mouse) pair generates a receptor that can bind to mouse IgG1 and mouse IgG2a. The L137E mutation reduces the affinity of human FcRn for human IgG1 by about twofold, consistent with the introduction of a less favorable Glu137-Tyr436 interaction. However, the analysis of the effects of other mutations on the binding to different IgGs indicates that the contribution to binding of the interaction of FcRn residue 137 with IgG residue 436 can vary. This suggests the existence of distinct docking topologies that are accompanied by variations in contacts between these two residues for different FcRn-IgG pairs. Our observations are of direct relevance to understanding the molecular nature of the human FcRn-IgG interaction. In turn, understanding human FcRn function has significance for the optimization of the serum half-lives of therapeutic and prophylactic antibodies.

Immunoglobulin G, Neonatal Fc receptor FcRn, Serum half-life, Site-directed mutagenesis, Surface plasmon resonance
0022-2836
901-913
Zhou, Jinchun
373ef03a-4fb7-4022-98c2-7332251c5c30
Johnson, James E.
03994d4a-13f9-4af3-8d4a-2cd3cc6a5fe5
Ghetie, Victor
b7b50946-2bd9-4896-b841-6bbfba8237c2
Ober, Raimund J.
31f4d47f-fb49-44f5-8ff6-87fc4aff3d36
Ward, E. Sally
b31c0877-8abe-485f-b800-244a9d3cd6cc
Zhou, Jinchun
373ef03a-4fb7-4022-98c2-7332251c5c30
Johnson, James E.
03994d4a-13f9-4af3-8d4a-2cd3cc6a5fe5
Ghetie, Victor
b7b50946-2bd9-4896-b841-6bbfba8237c2
Ober, Raimund J.
31f4d47f-fb49-44f5-8ff6-87fc4aff3d36
Ward, E. Sally
b31c0877-8abe-485f-b800-244a9d3cd6cc

Zhou, Jinchun, Johnson, James E., Ghetie, Victor, Ober, Raimund J. and Ward, E. Sally (2003) Generation of mutated variants of the human form of the MHC class I-related receptor, FcRn, with increased affinity for mouse immunoglobulin G. Journal of Molecular Biology, 332 (4), 901-913. (doi:10.1016/S0022-2836(03)00952-5).

Record type: Article

Abstract

Much data support the concept that the MHC class I-related receptor FcRn serves to regulate immunoglobulin G (IgG) concentrations in serum and other diverse body sites in both rodents and humans. Previous studies have indicated that the human ortholog of FcRn is endowed with unexpectedly high stringency in binding specificity for IgGs. In contrast to mouse FcRn, which binds promiscuously to IgGs across species, human FcRn does not bind to mouse IgG1 or IgG2a, and interacts weakly with mouse IgG2b. Here, we investigate the molecular basis for this high-level specificity. We have systematically mutated human FcRn residues to the corresponding mouse FcRn residues in the regions that encompass the FcRn-IgG interaction site. Notably, mutation of the poorly conserved residue Leu137 of human FcRn to glutamic acid (L137E) generates a human FcRn mutant that binds to mouse IgG1 and mouse IgG2a with equilibrium dissociation constants of 13.2 μM and 14.4 μM, respectively. From earlier high-resolution structural analyses of the rat FcRn-rat Fc complex, residue 137 of human FcRn is predicted to contact residue 436 of IgG, which can be either His436 (mouse IgG1, mouse IgG2a) or Tyr436 (human IgG1, mouse IgG2b). The simplest interpretation of our data for the L137E mutant is therefore that replacement of the Leu137-Tyr436 (human) by the Glu137-His436 (mouse) pair generates a receptor that can bind to mouse IgG1 and mouse IgG2a. The L137E mutation reduces the affinity of human FcRn for human IgG1 by about twofold, consistent with the introduction of a less favorable Glu137-Tyr436 interaction. However, the analysis of the effects of other mutations on the binding to different IgGs indicates that the contribution to binding of the interaction of FcRn residue 137 with IgG residue 436 can vary. This suggests the existence of distinct docking topologies that are accompanied by variations in contacts between these two residues for different FcRn-IgG pairs. Our observations are of direct relevance to understanding the molecular nature of the human FcRn-IgG interaction. In turn, understanding human FcRn function has significance for the optimization of the serum half-lives of therapeutic and prophylactic antibodies.

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More information

Accepted/In Press date: 17 July 2003
e-pub ahead of print date: 6 September 2003
Published date: 26 September 2003
Keywords: Immunoglobulin G, Neonatal Fc receptor FcRn, Serum half-life, Site-directed mutagenesis, Surface plasmon resonance

Identifiers

Local EPrints ID: 424076
URI: http://eprints.soton.ac.uk/id/eprint/424076
ISSN: 0022-2836
PURE UUID: 272a565b-2fb6-4d8f-9d45-770c9b2a2c1a
ORCID for Raimund J. Ober: ORCID iD orcid.org/0000-0002-1290-7430
ORCID for E. Sally Ward: ORCID iD orcid.org/0000-0003-3232-7238

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Date deposited: 04 Oct 2018 16:30
Last modified: 18 Mar 2024 03:48

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Contributors

Author: Jinchun Zhou
Author: James E. Johnson
Author: Victor Ghetie
Author: Raimund J. Ober ORCID iD
Author: E. Sally Ward ORCID iD

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