Characterization and crystallization of a recombinant IgE Fab fragment in complex with the bovine β-lactoglobulin allergen

A D1 Fab fragment containing the allergen-binding variable domains of the IgE antibody was characterized by ESI FT–ICR mass spectrometry and crystallized with bovine β-lactoglobulin (BLG) using the hanging-drop vapour-diffusion method at 293 K. X-ray data suitable for structure determination were collected to 2.8 A resolution using synchrotron radiation. The crystal belonged to the orthorhombic space group P212121, with unit-cell parameters a = 67.0, b = 100.6, c = 168.1 A. The three-dimensional structure of the D1 Fab fragment–BLG complex will provide the first insight into IgE antibody–allergen interactions at the molecular level.