Structural analysist of N-glycans from gull egg white glycoproteins and egg yolk IgG

摘要

We previously showed that the expression of (Galα1-4Gal)-bearing glycoproteins among birds is related to their phylogeny. However, precise structures of (Galα1-4Gal)-containing N-glycans were only known for pigeon egg white glycoproteins and IgG. To compare structural features of (Galα1-4Gal)-containing N-glycans from other species, we analyzed N-glycans of gull egg white (GEW)-glycoproteins, ovomucoid, and ovotransferrin, and gull egg yolk IgG by HPLC, mass spectrometry (MS), and MS/MS analyses. GEW-glycoproteins included neutral, monosialyl, and disialyl N-glycans, and some of them contained Galα1-4Gal sequences. Bi-, tri-, and tetra-antennary oligosaccharides that lacked bisecting GlcNAc were the major core structures, and incomplete α-galactosylation and sialylation as well as the presence of diLacNAc on the branches generated microheterogeneity of the N-glycan structures. Moreover, unlike pigeon egg white glycoproteins, the major sialylation in GEW-glycoproteins is α2,3-, but not α2,6-linked sialic acids (NeuAc). In addition to the complex-type oligosaccharide, hybrid-type oligosaccharides that lack bisecting GlcNAc were also abundant in GEW-glycoproteins. Gull egg yolk IgG also contained Galα1-4Galβ1-4GlcNAcβ1- sequences, but unlike pigeon IgG, no Galα1-4Galβ1-4Galβ1-4GlcNAcβ1- sequence was detected. Bi- and tri-antennary complex-type oligosaccharides with bisecting GlcNAc and with core fucosylation as well as high-mannose-type oligosaccharides were the major structures in gull IgG. Our data indicated that some N-glycans from both GEW-glycoproteins and gull IgG contain the Galα1-4Galβ1-4GlcNAcβ1- sequence, but the ratio of α-Gal-capped residues to non-α-Gal-capped residues in the nonreducing termini of N-glycans is much lower than that in those of pigeon glycoproteins.