A comparative study of the asparagine-linked oligosaccharides on siglec-5,siglec-7 and siglec-8, expressed in a CHO cell line, and their contribution to ligand recognition

The siglecs (sialic acid-binding immunoglobulin-like lectins) mediate siali c acid-dependent cellular interactions and may in some cases signal through SH2-binding domains. In addition to the previously characterized siglecs, sialoadhesin, CD22, CD33 and myelin-associated glycoprotein, several new on es, siglec-5, siglec-7 and siglec-8, have recently been cloned. Although th ese novel receptors have generated considerable interest as therapeutic tar gets because of their expression pattern on immune cells, very little is kn own about how their lectin activity is regulated. Previous studies with sia loadhesin, CD22 and CD33 have shown that siglec glycosylation has significa nt effects on binding. To determine any differences in the glycan compositi on of siglec-5, siglec-7 and siglec-8 that may modify their function, we re leased and characterized the N-linked oligosaccharide distribution in these three glycoproteins. The glycan pools from siglec-5 and siglec-7 contained a larger proportion of sialylated and core-fucosylated biantennary, triant ennary and tetra-antennary oligosaccharides, whereas the carbohydrate mixtu re released from siglec-8 is noticeably less sialylated and is more abundan t in 'high-mannose'-type glycans. In addition, we show that, in contrast wi th CD22 and CD33, mutating the conserved potentially N-linked glycosylation site in the first domain has no effect on binding mediated by siglec-5 or siglec-7.