Characterization of Novel Carbohydrate Ligands for Serum Lectin Associated with Anti-tumor Activity

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Mannan-binding protein (MBP) is a C-type mammalian lectin specific for Man, GlcNAc, and Fuc. The serum MBP has a potent growth inhibitory activity to a human colorectal carcinoma cell line in vivo via a complement-independent mechanism. In this study, we isolated and characterized the carbohydrate ligands to MBP expressed on the SW1116 cells, which were assumed to be associated with the anti-tumor activity of MBP.1. Isolation and characterization of the MBP-ligand oligosaccharides.By MS analyses of the MBP-ligand oligosaccharides and their endo-β-galactosidase digested products in combination with1) The non-reducing terminal unit of the MBP-ligand oligosaccharides is mostly Lewis a/b, a substantial portion of which is carried on extended type 1 chains as multimeric Lewis a units.2) The core portion of the oligosaccharides consisted mostly of core fucosylated tetra-antennary N-glycans.3) The inner units are most likely to be dominated by type 2 chain and not fully fucosylated.The overal … More l charbohydrate structures of neutral and acidic MBP-ligands are very similar except for the non-reducing termini. The acidic ligands are capped with sialic acid to form sialyl Lewis a structure. The MBP-oligosaccharide ligands expressed on human colon carcinoma, SW1116, cells, were large N-glycans with a highly fucosylated polylactosamine-type structures. These structures were unique and distinct from other previously reported tumor specific carbohydrate antigens. MBP requires clusters of tandem repeats of the Lewis a epitope for the binding.2. Isolation and characterization of the glycoproteins carrying the MBP-ligand oligosaccharides of the characteristic structure.1) The cell surface MBP-ligand glycoproteins, which had been labeled with biotin, were isolated by MBP- and avidin-affinity columns. A 120 kDa band on SDS-PAGE under reducing conditions was detected as a major component. The protein lost most of the binding activity to MBP by N-glycanase digestion.2) The MBP-ligand glycoproteins isolated by AAL- and MBP-affinity columns from SW1116 cell lysates. Two major bands, 120kDa and 82kDa on SDS-PAGE under reducing conditions were identified as CD26 and CD98 heavy chain, respectively, by MS analysis. Less