Crystallization and preliminary crystallographic data for an antiprogesterone monoclonal antibody Fab' and steroid-Fab' complexes.

Crystals of an Fab' from an antiprogesterone monoclonal antibody (IgG1) have been grown from 1.5 M-ammonium sulfate, pH 5.5 to 8.5. The single crystals are hexagonal rods, space group P6222 (or P6422), with cell dimensions a = b = 135.2 A, and c = 124.2 A. Cocrystals of the Fab' with progesterone, pregnanedione and other related steroids have been grown. The complex crystals have different morphology but are isomorphous with the native crystals. A hydroxy-progesterone derivative obtained by substituting an iodo-benzoyl group at the 11 alpha-hydroxyl position looks promising as a suitable heavy-atom candidate in addition to other potential conventional heavy-atom derivatives. All crystals diffract to at least 2.8 A resolution and are suitable for high-resolution X-ray diffraction studies.