Monoclonal antibodies that block cell adhesion in Polysphondylium pallidum: reaction with L-fucose, a terminal sugar in cell-surface glycoproteins.

By permethylation analysis the linkages of L-fucose and D-mannose in the oligosaccharide residues of cell surface glycoproteins of Polysphondylium pallidum were determined. Mannose was found in terminal positions, in 1,2-, 1,3- and 1,6-intra-chain linkages, and at branch points. Fucose was exclusively located at nonreducing ends. Fab of a monoclonal antibody, mAb 293, has been previously shown to inhibit cell adhesion in P. pallidum completely. Binding of this antibody to glycoprotein was blocked by L-fucose, and at very high concentrations also by D-mannose. The dissociation constant for the antibody-fucose complex was Kd = 70 microM, which was two orders of magnitude higher than estimated for the natural oligosaccharide. Antibody-glycoprotein complexes dissociated in the presence of 100 mM L-fucose with a half-time of about 56 s. The blockage by L-fucose is taken as evidence that the adhesion-blocking antibody binds to oligosaccharide end groups containing L-fucose as the terminal sugar.