Structural characterization of the oligosaccharides of a human monoclonal anti-lipopolysaccharide immunoglobulin M

The oligosaccharide side chains of a human anti-lipopolysaccharide IgMproduced by a human-human-mouse heterohybridoma were analyzed at each ofits five conserved N-glycosylation sites. This antibody also has apotential sixth N-glycosylation site in the variable region of its heavychain which is not glycosylated. The oligosaccharides were released bydigestion with various endo- and exoglycosidases and analyzed bymatrix-assisted laser desorption/ionization-time of flight massspectrometry and fluorophore-assisted carbohydrate electrophoresis. Theantibody has various complex- and hybrid-type oligosaccharide structures atAsn 171, various sialylated complex-type oligosaccharides at Asn 332 and395, and high-mannose-type oligosaccharides at Asn 402 and 563. Of note isthe presence in this human IgM of oligosaccharides containingN-glycolylneuraminic acid and N-acetylneuraminic acid in the ratio of 98:2as determined using anion- exchange chromatography. Furthermore, weobserved oligosaccharide structures containing Gal alpha (1,3)Gal that havenot been reported as components of human glycoproteins.