A Common Structural Unit in Asparagine-Oligosaccharides of Several Glycoproteins from Different Sources

Abstract

Abstract A new technique was developed to determine linkage position of glucosamine attached to asparagine. Treatment of asparagine-oligosaccharides with 1 m NaOH-1 m NaBH4 for 4 to 6 hours at 100° resulted in complete cleavage of the glucosamine-asparagine linkage with concomitant production of terminal glucosaminitol. Periodate oxidation, NaBH4 reduction, and hydrolysis of fragments thusly produced yielded different aminopolyols depending on the linkage positions. Reference glucosaminitol compounds bearing substituents 4 or 3 produced xylosaminitol and threosaminitol, respectively. Asparagine-oligosaccharides from chicken ovalbumin, α-amylase from Aspergillus oryzae, and pineapple bromelain all produced xylosaminitol by the described procedure, indicating the presence of a 1,4-linked glucosamine disaccharide unit. By the same technique, the penultimate glucosamine was found to be substituted by mannose at the 4 position. Methylation studies confirmed these data. On the basis of these results, it is proposed that O-β-d-Man-(1 → 4)-O-β-d-GluNAc-(1 → 4)-O-β-d-GlcNAc-Asn is the common structural unit in the asparagine oligosaccharides from these glycoproteins.