Crystallization and preliminary X-ray diffraction analysis of two homologous antigen-binding fragments in complex with different carbohydrate antigens.
The antigen-binding fragments (Fab) of two murine monoclonal antibodies (mAb) S25-2 and S45-18, specific for carbohydrate epitopes in the lipopolysacchaide of the bacterial family Chlamydiaceae, have been crystallized in the presence and absence of synthetic oligosaccharides corresponding to their respective haptens. Crystals of both Fabs show different morphology depending on the presence of antigens. The sequence of mAb S45-18 was determined and shows a remarkable homology to that reported for mAb S25-2. These crystals offer an unparalleled opportunity to compare the structure and modes of binding of two homologous antibodies to similar but distinct carbohydrate epitopes.