Synthesis of disaccharide congeners of theTrichinella spiralisglycan and binding site mapping of two monoclonal antibodies

Abstract

The tetrasaccharide epitope, β-D-Tyvp(1[Formula: see text]3)β-D-GalNAcp(1[Formula: see text]4)[α-L-Fucp(1[Formula: see text]3)]β-D-GlcNAcp (1) is the major constituent of the N-glycan expressed on the cell surface of the parasite Trichinella spiralis. Two monoclonal antibodies (Mabs 9D4 and 18H1) that protect rats against infection by T. spiralis bind the terminal disaccharide epitope β-D-Tyvp(1[Formula: see text]3)β-D-GalNAcp conjugated to BSA. The syntheses of disaccharide congeners containing mono-deoxy, mono-methyl, as well as modifications to replace the acetamido group are reported. These target disaccharides were assayed for binding to the protective MAbs. For each antibody different clusters of three hydroxyl groups, that include C-2 and C-4 of tyvelose and for 18H1, the GalNAc acetamido group, provide the key polar interactions with the antibody binding sites. Mapping of the sites by functional group replacement revealed a similar pattern of recognition for the dideoxyhexose by the two MAbs while each recognizes distinct surfaces of the GalNAc residue. Consequently although both antibodies bury the 4-OH of tyvelose, the principal contact surface occurs on opposite sides of the 3,6-dideoxyhexose.Key words: β-tyveloside, 3,6-dideoxy-D-arabino-hexose, Trichinella carbohydrate antigen, antibody mapping, Trichinella spiralis, N-glycans, molecular recognition of carbohydrates, antigen topology, functional group replacement.