Partial characterization of the oligosaccharides of mouse thymocyte Thy-1 glycoprotein

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Abstract
Four glycopeptides (I, IIA, IIB, III) with different oligosaccharide structures were isolated from purified mouse thymocyte Thy-1 glycoprotein. The glycoprotein was digested with Pronase, and the glycopeptide fraction was isolated by gel filtration and acetylated with [3H]acetic anhydride. The different glycan structures were separated by affinity chromatography on concanavalin A-Sepharose 4B and lentil-Sepharose 4B. Size determinations of intact and exoglycosidase- and endoglycosidase-digested glycopeptides were performed by gel filtration on Bio-Gel P-6, calibrated with glycopeptides of known structure. On the basis of these experiments and on the behavior of the glycopeptides on the lectin columns, the following structures of the oligosaccharide chains were proposed: I, triantennary complex-type with terminal fucose; IIA, biantennary ''complex-type'' without fucose; IIB, biantennary complex-type with fucose; and III, a mixture of high-mannose chains containing either 5 or 6 mannose residues (.apprx. 50% of each). Amino acid analysis of the glycopeptides showed that the predominant oligosaccharide at glycosylation-site Asn-23 was of high-mannose type, whereas the other 2 sites (Asn-75 and Asn-99) were glycosylated with complex-type chains. Both these sites were variably glycosylated. The major glycans linked to Asn-75 were of structures I and IIB, whereas all 3 complex-type chains were represented at Asn-99. The previously reported carbohydrate heterogeneity of thymocyte Thy-1 glycoprotein was presented.