Binding of modified fragments of the Shigella dysenteriae type 1 O-specific polysaccharide to monoclonal IgM 3707 E9 and docking of the immunodeterminant to its modeled Fv

The O-specific polysaccharide (O-SP) of Shigella dysenteriae type 1 has been shown by others to have the structure →3)-α-l-Rhap-(1⃗3)-α-l-Rhap-(1⃗2)-α-d-Galp-(1⃗3)-α-d-GlcpNAc-(1⃗. We have shown in the past that IgM 3707 E9, an anti S. dysenteriae type 1 O-SP monoclonal antibody, binds specifically to the -α-l-Rhap-(1⃗2)-α-d-Galp- determinant of the polysaccharide. In this report we show that determinant to have hydrogen bonds, necessary for binding to the antibody, involving positions 3, 4 and 6 of the galactopyranosyl residue. The hydroxyl groups of the rhamnopyranosyl moiety of the immunodeterminant appear not to partake in hydrogen-bond interactions with the antibody. A model is presented of the Fv of IgM 3707 E9 based on our previously established cDNA-sequence and two known, highly homologous immunoglobulin crystal structures. The methyl glycoside of the immunodeterminant α-l-rhamnopyranosyl-(1⃗2)-α-d-galactopyranose is docked to the combining area of the Fv.