Characterization of the N-linked oligosaccharides of megalin (gp330) from rat kidney

Megalin (gp 330) is a large cell surface receptor expressed on the apical surfaces of epithelial tissues, that mediates the binding and internalization of a number of structurally and functionally distinct ligands. In this paper we report the first detailed structural characterization of megalin-derived oligosaccharides. Using strategies based on mass spectrometric analysis, we have defined the structures of the N-glycans of megalin. The results reveal that megalin glycoprotein is heterogeneously glycosylated. The major N-glycans identified belong to the following two classes: high mannose structures and complex type structures, with complex structures being more abundant than high mannose structures. The major nonreducing epitopes in the complex-type glycans are: GlcNAc, Galβ1-4GlcNAc (LacNAc), NeuAcα2-6Galβ1-4GlcNAc (sialylated LacNAc), GalNAcβ1-4[NeuAcα2-3]Galβ1-4GlcNAc (Sda) and Galα1-3Galβ1-4GlcNAc. Most complex structures are characterized by the presence of (α1,6)-core fucosylation and the presence of a bisecting GlcNAc residu