Oligosaccharide microheterogeneity of the murine major histocompatibility antigens. Reproducible site-specific patterns of sialylation and branching in asparagine-linked oligosaccharides

The influence of peptide structure of endogenous cell-surface glycoproteins on the branching and sialylation of their asparagine-linked oligosaccharides was evaluated in a murine B cell lymphoma, AKTB-1b. This cell line simultaneously synthesizes two classes of major histocompatibility antigens that, within each class, share a high degree of amino acid sequence homology and possess potential N-linked glycosylation sites at invariant positions. [³H]Mannose-labeled oligosaccharides were released from each of 11 purified glycosylation sites by the almond peptide:N-glycosidase and analyzed by a variety of chromatographic procedures and glycosidase treatments. The data indicate: 1) a unique distribution of oligosaccharide structures is present at each glycosylation site; 2) each site-specific oligosaccharide pattern is highly reproducible, independent of the number of in vivo tumor passages. The heavy chain of the class I antigens, H-2K(k) and H-2D(k) contain two and three sites, respectively, in which biantennary structures predominate. However, each site varies with respect to the extent of sialylation and the proportions of more highly branched structures present. The class II antigens, I-A(k) and I-E(k), each contain an α-chain site toward the N terminus and a single β-chain site where the overall extent of sialylation is similar, yet the distributions of antennary structures are dramatically different for each. The α-chains of each class II antigen also contain a more C-terminal underglycosylated site where sialylation and branching are reduced to differing degrees depending upon the site. The influence of peptide structure on oligosaccharide microheterogeneity is manifest at two levels. First, the overall distributions of oligosaccharides at corresponding sites on structurally related glycoproteins are similar. Second, the specific 'fingerprint' of sialylation and branching patterns at a particular site are reproducibly unique. These data suggest that subtle changes in peptide structure are reflected in the extent of sialylation and branching of oligosaccharides found at corresponding glycosylation sites of structurally related glycoproteins.