Structural assessment of the N-linked oligosaccharides of cell-CAM 105 by lectin-agarose affinity chromatography

The N-linked oligosaccharides of cell-CAM 105, a glycoprotein involved in the intercellular adhesion between rat hepatocytes, were studied by sequential lectin-agarose affinity chromatography of desialylated, [14C]-labelled glycopeptides. These glycopeptides were obtained by extensive pronase digestion followed by N-[14C]acetylation of the peptide moieties and desialylation by mild acid hydrolysis. Assuming that all glycopeptides were radiolabelled to the same specific radioactivity, Concanavalin A-Sepharose chromatography indicated that the majority of the glycans (84%) were of the complex-type of which approximately half were bi-antennary structures. The remainder of the glycans comprised oligomannose-type structures and/or incomplete bi-antennary structures. Pisum sativum lectin-agarose chromatography revealed that part of the bi-antennary glycans contained a fucose residue alpha(1-6)-linked to the N-acetylglucosamine which is attached to asparagine. Furthermore, the presence of tri-, and tetra- and/or tri'-antennary complex-type glycans was demonstrated by chromatography on immobilized Phaseolus vulgaris leukoagglutinating phytohemagglutinin and Aleuria aurantia lectin (AAL). AAL-agarose chromatography furthermore indicated the presence of alpha(1-3)-linked fucose in part of these glycopeptides, whereas no alpha(1-6)-linked fucose could be detected in these structures. The degree of beta-galactosylation of the complex-type glycans was investigated by chromatography on Ricinus communis agglutinin-agarose. The results indicated that only part of the bi-antennary glycans were completely beta-galactosylated. Similarly, at least three beta-galactose residues were present in only a part of the tri-, and tetra- and/or tri'-antennary glycans.