The membrane‐proximal part of FcϵRIα contributes to human IgE and antibody binding – implications for a general structural motif in Fc receptors

FEBS Letters

Kricek, Franz¹  Nechansky, Andreas¹  Aschauer, Heinrich¹ 

[1] Novartis Forschungsinstitut GmbH, Brunnerstrasse 59, 1230 Vienna, Austria

关键词: Human high affinity IgE receptor;    IgE binding site;    Epitope mapping;    Alanine substitution mutagenesis;    Homology alignment;    FcϵRI;    human high affinity Fc receptor for IgE;    FcϵRIα;    α-subunit of the human high affinity Fc receptor for IgE;    hIgE;    human IgE;   

DOI  :  10.1016/S0014-5793(98)01558-0

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

The high affinity receptor for human IgE (FcϵRI) on tissue mast cells and blood basophils is responsible for immediate hypersensitivity reactions. Binding of human IgE (hIgE) to FcϵRI has been shown to be mediated via three independent regions in the extracellular part of the α-subunit of FcϵRI (ecFcϵRIα). By site-directed mutagenesis we investigated the contribution of amino acids within the ecFcϵRIα FG loop (residues Lys¹⁵⁴–Leu¹⁶⁵) to binding to hIgE and two monoclonal anti-FcϵRIα antibodies (15/1, 5H5/F8). The mutated receptors were expressed and secreted from eukaryotic cells as amino-terminal fusion to HSA. We show that the proposed loop region contributes partly to hIgE binding and that the epitope of mAb 15/1, which inhibits hIgE/FcϵRIα interaction, maps to this region whereby a single W156A mutation results in complete loss of mAb 15/1 binding. In contrast, hIgE binding is not affected by the W156A mutation indicating that different amino acid residues within the loop are recognized by the mAbs 15/1 and hIgE. MAb 5H5/F8 does not recognize a receptor mutant truncated to Ile¹⁷⁰. By screening a random dodecapeptide library displayed on bacterial flagella the epitope for mAb 5H5/F8 was mapped to P¹⁷³REKY¹⁷⁷ whereas one of the 15/1 binding clones displayed a peptide with an amino acid sequence homologous to Leu¹⁵⁸–Ile¹⁶⁷. Based on the epitopes identified for the inhibitory mAb 15/1 and the non-inhibitory mAb 5H5F8 and on binding data obtained with polyclonal antisera raised against two ecFcϵRIα peptides, we propose a structural element in the membrane proximal part of ecFcϵRIα which forms a 3D structure which might facilitate specific and efficient attachment of hIgE.

【 授权许可】

Unknown