Human immunoglobulin E flexes between acutely bent and extended conformations.

IgE molecules associate with the FcɛRIα receptor in an acutely bent conformation where the Cɛ2 domains fold over the Cɛ3-Cɛ4 domains. A new study demonstrates that IgE can exist in an extended conformation with a Cɛ2 domain capable of flipping from side to side, suggesting a level of structural flexibility that could functionally impact allergen recognition.