Preliminary crystallographic analysis of a Fab specific for the O-antigen of Shigella flexneri cell surface lipopolysaccharide with and without bound saccharides.

The Fab of a monoclonal anti-carbohydrate antibody, SYA/J6 (IgG3, kappa, murine), raised against the O-polysaccharide antigen of the cell surface lipopolysaccharide of variant Y Shigella flexneri, a Gram negative bacterium, has been crystallized in the unliganded form and in complex with tri- and pentasaccharide antigens. The three crystal forms belong to the tetragonal space group P4(3)2(1)2, or P4(1)2(1)2, with very similar unit cell dimensions and an asymmetric unit that contains one molecule of about 50,000 Daltons, and a fourth crystal form belongs to monoclinic space group P2(1) that contains four molecules of Fab in an asymmetric unit. Whereas diffractions of these crystals on an area detector-rotating anode system extend to only about 3.5 A resolution, those measured using an imaging plate and synchrotron radiation at the Photon Factory facility extend to 2.5 A.