Crystallization of the fab fragments of monoclonal anti-p-azophenylarsonate antibodies and their complexes with haptens.

We report on the preparation, crystallization, and preliminary x-ray crystallographic study of Fab fragments from monoclonal anti-p-azophenylarsonate antibodies. Several crystalline forms were obtained with the Fab fragment from the R19.9 monoclonal antibody as well as with the complex between the hapten p-aminobenzenearsonic acid and Fab R19.9. The crystals of this hapten-Fab complex are similar to but not always isomorphous with the native Fab crystals. All the native and complex crystals were obtained using polyethylene glycol 6000 as crystallizing agent. Some of these crystalline forms diffract to a 2-A resolution or beyond and are suitable for high resolution x-ray diffraction analysis. A possible interpretation of hapten binding to crystalline Fab fragments from R19.9 and from the R9.3 monoclonal anti-p-azophenylarsonate antibody, implying conformational changes, is discussed.