The structures of the galactose-containing sugar chains of ovalbumin.

Abstract

Structural studies of the sugar moieties of ovalbumin glycopeptides I and II were performed by using endo- fi-N-acetylglucosaminidase H. The oligosaccharide fraction liberated from glycopeptide I by the enzyme action consisted almost exclusively of a single compo- nent, whereas that from glycopeptide II was a mixture of two major components. These two components were successfully separated by concanavalin A-Sepharose column chromatography. The structures of these three oligosaccharides were determined by the combination of sequential exoglycosidase digestion, methylation analysis, acetolysis, and Smith degradation. Based on the results, the whole structure of the glycopeptide I was elucidated as Mane1 ---f G(Mancu1 + 3)Mancwl + 6[Gal/31-+ 4GlcNAcfil+ 4(GlcNAcPl+ 2)Manal-+ 3]- (GlcNAcfil --, 4)Manpl + 4GlcNAc/31 -+ 4GlcNAc -+ Asn. Glycopeptide II was shown to be a mixture of two major glycopeptides; Mancvl -+ 3Manal --+ 6[Galfll + 4GlcNAc/?l + 4(GlcNAc/?l + 2)Mancul + 3](GlcNAc/31 -+ 4)Man/31+ 4GlcNAcfil+ 4GlcNAc + Asn and Mancvl -+ G(Mana1 + 3)Mancul+ 6[GlcNAc/~?l + 4(GlcNA$l + 2)Mancul -+ 3](GlcNAc/il ---f 4)Manfil --+ 4GlcNAcPl -+ 4GlcNAc + Asn. The extreme resistance of the P-N- acetylglucosamine residue, linked at the C-4 position of the /%mannosyl residue, to periodate oxidation was observed, and the possible shielding effect by neigh- boring N-acetylglucosamine was discussed. Recent development of the techniques to study the heter- osaccharide chains have elucidated the structures of aspara- gine-linked sugar chains of many glycoproteins. Although several exceptional cases were reported, most of the established structures of asparagine-linked sugar chains can be classified into two major groups. The sugar chains, which fall into the so-called “high mannose type,” have a general structure of (Mann),,Mar$l ---f 4GlcNAc,81 + 4GlcNAc. Our recent studies of the structures of the sugar chains of ovalbumin (1) and thyroglobulin (2) indicated that Mann1 + 6(Mannl 3)Mancul 6(Mancul 3)ManBl -+ 4GlcNAc,B -+ 4GlcNAc + Asn may occur as a common core structure of the high mannose-type sugar chains. Another group, which is called “hetero type,” has a common core structure; Manal + 6(Mancul+ 3)Manpl-+ 4GlcNAc,Bl + 4GlcNAc -+ Asn, to which from two to four side chains composed of sialic acid, galactose, and N-acetylglucosamine