The oncofetal J28 epitope involves fucosylated O-linked oligosaccharide structures of the fetoacinar pancreatic protein

The fetoacinar pancreatic protein (FAP), characterized by themAb J28, is an oncofetal form of bile salt dependent lipase(BSDL), the expression of which is related to pancreatic differentiationand neoplastic processes. Because the J28 epitope, recognizedby imAb J28, is suggested to be dependent upon carbohydrates,we have attempted to gain information about the structure ofthis epitope. Indeed, treatment of FAP with sodium periodateabolished the reactivity of the protein to mAb J28, which demonstratesthe implication of oligosaccharides in the structure of theJ28 epitope. FAP offers both O-linked and N-linked carbohydratestructures, of which, as we have determined, one is involved.Peptides obtained after cyanogen bromide cleavage were desialylatedthen separated by affinity chromatography on an immobilizedpeanut agglutinin agarose column. The peptide retained on thiscolumn carried out the reactivity with the mAb J28. Althoughsome differences in amino acid analysis were observed, the N-terminalsequence of this peptide correlates with that of the C-terminalpart of the enzyme. Carbohydrate analysis of the peptide bearingthe J28 epitope revealed fucose, galactose, N-acetylgalactosamine,N-acetylglucosamine, and N-acetylneuraminic acid. The competitionobserved between mAb J28 and Ulex europaeus I lectin for bindingto the J28 epitope suggested that fucose residue a (1–2)linked to a galactose residue was implicated in the structureof the J28 epitope. Alternatively, the loss of the mAb J28 reactivityupon treatment of FAP either with bovine kidney or bovine epididymisfucosidase was observed indicating that fucose residues linkedat the