The crystal structure of IgE Fc reveals an asymmetrically bent conformation

The distinguishing structural feature of immunoglobulin E (IgE), the antibody responsible for allergic hypersensitivity, is the Cepsilon2 domain pair that replaces the hinge region of IgG. The crystal structure of the IgE Fc (constant fragment) at a 2.6-Angstrom resolution has revealed these domains. They display a distinctive, disulfide-linked Ig domain interface and are folded back asymmetrically onto the Cepsilon3 and Cepsilon4 domains, which causes an acute bend in the IgE molecule. The structure implies that a substantial conformational change involving Cepsilon2 must accompany binding to the mast cell receptor FcepsilonRI. This may be the basis of the exceptionally slow dissociation rate of the IgE-FcepsilonRI complex and, thus, of the ability of IgE to cause persistent allergic sensitization of mast cells.