The Human Chorionic Gonadotropin-β Arginine 68 to Glutamic Acid Substitution Fixes the Conformation of the C-Terminal Peptide

Charrel-Dennis, Marie and Terrazzini, Nadia and McBride, Jeffrey D. and Kaye, Paul and Martensen, Pia M. and Justesen, Just and Berger, Peter and Lapthorn, Adrian and Kelly, Charles and Roitt, Ivan M. and Delves, Peter J. and Lund, Torben (2005) ‘The Human Chorionic Gonadotropin-β Arginine 68 to Glutamic Acid Substitution Fixes the Conformation of the C-Terminal Peptide’, Molecular Endocrinology, 19(7).

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Official URL: http://dx.doi.org/10.1210/me.2004-0109

Abstract

Wild-type human chorionic gonadotropin (hCG) has been used as a contraceptive vaccine. However, extensive sequence homology with LH elicits production of cross-reactive antibodies. Substitution of arginine68 of the β-subunit (hCGβ) with glutamic acid (R68E) profoundly reduces the cross-reactivity while refocusing the immune response to the hCG β -specific C-terminal peptide (CTP). To investigate the molecular basis for this change in epitope usage, we immunized mice with a plasmid encoding a truncated hCG β-R68E chain lacking the CTP. The animals produced LH-cross-reactive antibodies, suggesting that the refocused immunogenicity of R68E is a consequence of epitope masking by a novel disposition of the CTP in the mutant rather than a structural change in the cross-reactive epitope region. This explanation was strongly supported by surface plasmon resonance analysis using a panel of anti-hCGβ-specific and anti-hCGβ/LH cross-reactive monoclonal antibodies (mAbs). Whereas the binding of the LH cross-reactive mAbs to hCGβ-R68E was eliminated, mAbs reacting with hCGβ-specific epitopes bound to hCGβ and hCGβ-R68E with identical affinities. In a separate series of experiments, we observed that LH cross-reactive epitopes were silent after immunization with a plasmid encoding a membrane form of hCGβ-R68E, as previously observed with the soluble mutant protein itself. In contrast, the plasmid encoding the soluble secreted form of hCGβ-R68E evoked LH cross-reactive antibodies, albeit of relatively low titer, suggesting that the handling and processing of the proteins produced by the two constructs differed.

Item Type: Article
Additional Information: Citation: Charrel-Dennis, M. et al. (2005) ‘The Human Chorionic Gonadotropin-β Arginine 68 to Glutamic Acid Substitution Fixes the Conformation of the C-Terminal Peptide’ Molecular Endocrinology 19 (7) 1803–1811.
Divisions: Schools > Health, Sports and Bioscience, School of
Depositing User: Mr Stephen Grace
Date Deposited: 05 Aug 2010 16:09
Last Modified: 27 Sep 2012 12:00
URI: http://hdl.handle.net/10552/936

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