A novel Gal(β1-4)Gal(β1-4)Fuc(α1-6)-core modification attached to the proximal N-acetylglucosamine of keyhole limpet haemocyanin (KLH) N-glycans

KLH (keyhole limpet haemocyanin), the oxygen-carrying molecule of the marine snail Megathura crenulata, is often used as an adjuvant or as a hapten carrier for immunizations with peptides, oligosaccharides or other low-molecular-mass organic compounds. KLH exhibits several carbohydrate determinants, at least some of which are immunogenic: it shares an antigenic Fuc(alpha 1-3) GalNAc- determinant with schistosomes and contains unique Gal( beta 1-6)Man- structural motifs on its N-glycans. This study reveals the presence of N-glycans with unusual +/-Gal(beta 1-4)Gal(beta 1-4) Fuc- units (alpha 1-6)-linked to the reducing end N-acetylglucosamine residue. The following novel structures of KLH N-glycans were deduced by linkage analysis, exoglycosidase digestion, matrix-assisted laser-desorption ionization-tandem MS and nano-LC-ESI-IT-MS (where LC stands for liquid chromatography, ESI for electrospray ionization and IT for ion trap): Man(alpha 1-6) [+/- Man (alpha 1-3)]Man(beta 1-4)GlcNAc(beta 1-4)[Gal(beta 1-4)Fuc(alpha 1-6)]GlcNAc and Man(alpha 1-6)Man (beta 1-4)GlcNAc(beta 1-4) [Gal ( 1-4)Gal(p 1-4) Fuc(alpha 1-6)]GlcNAc. The Gal(beta 1-4)Fuc- and Gal(beta 1-4)Gal(beta 1-4)Fuc- core modifications are expected to be immunogenic, similar to other non-mammalian-type core modifications, and to contribute to the immunostimulatory properties of KLH.