The nature and importance of the inter‐ε chain disulfide bonds in human IgE

Abstract

IgE antibodies are best known for their pathological role in allergy. The class‐specific effector sites are located in the ε chains; these form covalent dimers via two cystine residues (Cys²⁴¹ and Cys³²⁸) linking opposite C_ε2 domains. The nature and biological significance of the inter‐ε chain disulfide‐bond arrangement is unresolved. For structural and functional analysis site‐specific mutations were introduced into the C_ε2 domain of recombinant human IgE. The introduction of an additional cyanogen bromide cleavage site (His²⁴⁶ → Met) facilitated the identification of parallel disulfide bond pairing. This linkage was also confirmed for myeloma IgE PS by sequence determination of disulfide‐linked C₂ dimers. Substitution of Cys²⁴¹ and Cys³²⁸ by Ser does not destroy receptor binding, but reductive alkylation, or the replacement of Cys³²⁸ by Met, leads to loss of activity. This shows that covalent dimerization is not essential for IgE/receptor interaction and points to the importance of the structural integrity of the site surrounding Cys³²⁸, visualized in a new model of human Fcε.