Preparation of Neoglycolipids for Structure and Function Assignments of Oligosaccharides

Abstract

One of the great challenges in modern cell biology has been to understand whether oligosaccharides with the diverse monosaccharide sequences that occur N- and O-glycosidically linked to proteins have roles as recognition structures. To assess the function of an individual oligosaccharide sequence, it is necessary to study it in isolation from other oligosaccharides that occur on a glycoprotein. Historically, indirect methods have been used, for example deglycosylation of the proteins by chemical or enzymatic means, inhibition or modification of glycosylation during biosynthesis and site-directed mutagenesis to delete specific glycosylation sites followed by monitoring of the bioactivities of the apoproteins in question. Chemical and enzymatic methods are well developed to release oligosaccharides from glycoproteins, and inhibition experiments with these oligosaccharides may be performed. But typically the oligosaccharides are obtained in small amounts as complex mixtures that are difficult to purify, and they generally have relatively poor inhibitory properties because of the loss of multivalency following their removal from the carrier protein; so relatively large amounts (often prohibitive) are required for inhibition. Neoglycolipid technology was developed (1–4) to fulfill the urgent need for a microprocedure for direct binding studies with oligosaccharides by methods adaptable to any type of oligosaccharide, pure or mixed, derived from natural or synthetic sources, thus allowing evaluation of the individual oligosaccharide sequences as antigens or as ligands for carbohydrate-binding proteins. The details of the development, chemistry and analytical aspects as well as biological applications have been reviewed recently (5, 6).