IDENTIFICATION OF ATTACHMENT SITES AND STRUCTURAL CLASSES OF ASPARAGINE-LINKED CARBOHYDRATES IN GLYCOPROTEINS

This chapter discusses identification of attachment sites and structural classes of asparagine-linked carbohydrates in glycoproteins. Glycosylation of specific asparagine (Asn) residues is one of the most common posttranslational modifications of proteins. However, its importance is just now becoming understood and widely appreciated. Current theories concerning the roles of Asn-linked oligosaccharides in modulating the biological activity of glycoproteins have been recently reviewed. The attachment-site Asn residues are with few exceptions present in an Asn-X-Ser/Thr consensus sequence in which “X” may be any amino acid except proline. In contrast to the peptide backbone of the protein, structural heterogeneity of the Asn-linked oligosaccharides is the rule rather than the exception. Glycoproteins commonly have several different structural classes of oligosaccharide attached (i.e., oligomannose, hybrid, or complex). Furthermore, each glycosylation site often has a heterogenous population of oligosaccharides of the same structural class, but differing in the number and type of sugar residues attached to the ends of the chains or antennae. The chapter describes two interrelated mass spectrometry-based strategies for: (1) identifying the attachment sites of Asn-linked sugars in glycoproteins and extent of glycosylation at each site, and (2) defining the compositions and molecular heterogeneity of carbohydrates at each specific attachment site in glycoproteins. © 1990, Elsevier Inc. All rights reserved.