Conformational Flexibility in Immunoglobulin E-Fc3–4 Revealed in Multiple Crystal Forms

The structure of immunoglobulin E (IgE)-Fc3–4 has been solved in three new crystal forms, providing 13 snapshots of the Fc conformation and revealing a diverse range of open–closed motions among subunit chains and dimers. A more detailed analysis of the open-to-closed motion of IgE-Fc3–4 was possible with so many structures, and the new structures allow a more thorough examination of the flexibility of IgE-Fc and its implications for receptor binding. The existence of a hydrophobic pocket at the elbow region of the Fc appears to be conformation dependent and suggests a means of regulating the IgE-Fc conformation (and potentially receptor binding) with small molecules.