Catalytic folding of the Cε3 domain by its high affinity receptor

The interaction of immunoglobulin E (IgE) with its cellular receptor FcεRIα is a central regulator of allergy. Structural studies have identified the third domain (Cε3) of the constant region of epsilon heavy chain as the receptor binding region. The isolated Cε3 domain is a “molten globule” that becomes structured upon binding of the FcεRIα ligand. In this study, fluorescence and nuclear magnetic resonance spectroscopies are used to characterise the role of soluble FcεRIα in the folding of the monomeric Cε3 domain of IgE. Soluble FcεRIα is shown to display characteristic properties of a catalyst for the folding of Cε3, with the rate of Cε3 folding being dependent on the concentration of the receptor.