Crystallization and preliminary X-ray analysis of a recombinant Fab fragment in complex with 17β-­oestradiol

The recombinant Fab fragment of the anti-17β-oestradiol antibody 57-­2 has been a target for several protein-engineering experiments. A method for production, purification and crystallization of the Fab fragment alone (apo form) and in complex with the major female sex hormone 17β-oestradiol is reported here. Diffracting apo-form crystals were only obtained with microseeding; crystals of the Fab–steroid complex were produced by co-crystallization in the presence of oestradiol and cross-seeding with the apo-form crystals. The crystals were grown using vapour-diffusion methods with reservoir solutions containing 10–14% PEG 4000 or 8–12% PEG 8000 and Tris–HCl buffer at high pH (9.0–9.5). Both the apo and complex crystals belong to space group P2₁2₁2₁ and diffract to 2.0 Å resolution. High-resolution X-ray data sets suitable for structure determination were collected from flash-cooled crystals using 25% glycerol as the cryoprotectant.