Common tetrasaccharide epitope NeuAc alpha 2-->3Gal beta 1-->3(Neu-Ac alpha 2-->6)GalNAc, presented by different carrier glycosylceramides or O-linked peptides, is recognized by different antibodies and ligands having distinct specificities.

A novel globo-series disialoganglioside, disialosyl galactosyl globoside (Structure 1 below), defined by new monoclonal antibody (mAb) RM2, was isolated and characterized as having terminal structure identical to that of ganglio-series ganglioside GD1 alpha (Structure 2) and a common mucin-type epitope (Structure 3) widely distributed in glycoproteins such as glycophorin A. While these three structures share a common nonreducing tetrasaccharide terminus, mAb RM2 showed strong specific reactivity only with Structure 1, not with Structures 2 or 3. Another mAb, QSH2, reacted strongly with Structure 3 but did not cross-react with Structures 1 or 2. Conformational molecular models based on minimum energy hard sphere exoanomeric calculations suggest that Structure 1 presents a unique surface topology distinct from that of Structures 2 or 3. Our findings suggest the novel concept that reactivity of a common carbohydrate epitope with different antibodies or ligands is highly dependent on the type of carrier glycosylceramide or carrier O-linked peptide. [formula: see text]