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J. Biol. Chem., Vol. 279, Issue 34, 35320-35325, August 20, 2004

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The Importance of Lys-352 of Human Immunoglobulin E in FcRII/CD23 Recognition^*

Ian Sayers, Jonathan E. M. Housden¶, Alan C. Spivey||, and Birgit A. Helm¶**

From the ^¶Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, the Division of Therapeutics and Molecular Medicine, Queens Medical Centre, Nottingham NG7 2UH, and the ^||Department of Chemistry, Imperial College, South Kensington Campus, London SW7 2AZ, United Kingdom

The interaction of immunoglobulin E (IgE) with its low affinity receptor (FcRII/CD23) plays a central role in the initiation and regulation of type I hypersensitivity responses. We have previously identified the importance of amino acid residues in the A-B loop of the C3 domain of human IgE and implicated a region close to the glycosylation site at asparagine 371 as contributing to IgE-CD23 interaction. These residues were now targeted by site-directed mutagenesis. The IgE-CD23 interaction was assessed by semiquantitative flow cytometry. Replacement of the entire C3 A-B loop (residues 341–356) with the homologous rat IgE sequence resulted in complete loss of human CD23 recognition, as did replacement of residues 346–353, indicating that class-specific effector residue(s) are contained within these eight amino acids. Lysine 352 within the A-B loop was identified as contributing directly to human CD23 interaction. Mutation to the rodent homologue glycine or glutamate resulted in a significant reduction in binding compared with native IgE, whereas conservative substitution with arginine effected a small, but statistically significant, enhancement of CD23 binding. Mutation of the C3 glycosylation site at asparagine 371 to threonine or glutamine did not significantly affect CD23 recognition. Our results yield new insights into the structural basis of the hIgE-CD23 interaction and hold promise for the rational design of drugs that can manipulate IgE-mediated regulation of the allergic response.

Received for publication, April 26, 2004 , and in revised form, June 14, 2004.

^* This work was supported by grants from the Biotechnology and Biological Sciences Research Council, the Medical Research Council, and The Wellcome Trust. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Both authors contributed equally to this work.

^** To whom correspondence should be addressed. Tel.: 44-114-2824375; Fax: 44-114-2795495; E-mail: B.Helm{at}sheffield.ac.uk.

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