The structural basis of the different affinities of two types of acidic N-glycosidic glycopeptides for concanavalin a—sepharose

Abstract

Affinity chromatography on lectins covalently bound to Sepharose has proved to be a useful tool for the fractionation and purification of glycopeptides and glycoproteins. The most commonly used lectin for this purpose has been concanavalin A. Studies on the binding of oligosaccharides and glycopeptides to this lectin have indicated that at least two nonsubstituted or 2-O-substituted ol-mannosyl residues are required [l] . Recent reports on the fractionation of glycopeptides from various source: on ;oncanavaIin A-Sepharose have shown that in addition to the neutral mannose-rich glycopeptides, some acidic N-glycosidic glycopeptides are bound by the lectin, whereas others are not [2-S]. Since the carbohydrate composition of both types of acidic glycopeptides is rather similar [3--S], the reason for the difference in affinity is not understood. The purpose of the present investigation was to study the structural basis of the separation of acidic N-glycosidic glycopeptides on concanavalin ASepharose. Glycopeptides with known (or partially known) structures were chromatographed on concanavalin A and fractions bound and not bound by the lectin were analyzed by methylation. It was found that glycopeptides possessing two peripheral NeuNAcGal-GlcNAc*-branches linked to the core pentasaccharide were bound by the lectin, whereas glycopeptides with three branches were not (the structures of these compounds are shown below). The different