Carbohydrate structures of recombinant soluble lamp-1 and leukosialin containing sialyl Le(x) terminus

Recombinant soluble lamp-1 and soluble leukosialin can be produced from CHO cells which express sialyl Le(x) structures after stable transfection of fucosyltransferase-III. It was shown previously that those soluble lamp-1 and leukosialin are potent inhibitors for E-selectin-mediated adhesion of human colonic tumor cells (Sawada, R.; Tsuboi, S.; Fukuda, M. J. Biol. Chem., 1994, 269, 1425). In the present study, we have determined the amount of the sialyl Le(x) structure present in recombinant, soluble lamp-1 and soluble leukosialin. CHO cells were metabolically labeled with [3H]-galactose and recombinant soluble lamp-1 and leukosialin were purified from the spent medium. Glycopeptides containing N-glycans derived from lamp-1 were fractionated by sequential lectin affinity chromatography. Similarly, O-glycans released from leukosialin were fractionated by Bio-Gel P-4 gel filtration. The terminal structures of carbohydrate chains were determined by sequential digestion with specific glycosidases. The results clearly indicate that soluble lamp-1 contains much more sialyl Le(x) structure than soluble leukosialin. Considering that soluble leukosialin and lamp-1 are almost equally effective as inhibitors for E-selectin-mediated adhesion, the results strongly suggest that densely clustered O-glycans are better presenters for E-selectin ligands than N-glycans.