N-Glycan Structures of Pigeon IgG A MAJOR SERUM GLYCOPROTEIN CONTAINING Galα1–4Gal TERMINI

Abstract We had shown previously that all major glycoproteins of pigeon egg white contain Galα1–4Gal epitopes (Suzuki, N., Khoo, K. H., Chen, H. C., Johnson, J. R., and Lee, Y. C. (2001) J. Biol. Chem. 276, 23221–23229). We now report that Galα1–4Gal-bearing glycoproteins are also present in pigeon serum, lymphocytes, and liver, as probed by Western blot with Griffonia simplicifolia-I lectin (specific for terminal α-Gal) and anti-P1 (specific for Galα1–4Galβ1–4GlcNAcβ1–) monoclonal antibody. One of the major glycoproteins from pigeon plasma was identified as IgG (also known as IgY), which has Galα1–4Gal in its heavy chains. High pressure liquid chromatography, mass spectrometric (MS), and MS/MS analyses revealed that N-glycans of pigeon serum IgG included (i) high mannose-type (33.3%), (ii) disialylated biantennary complex-type (19.2%), and (iii) α-galactosylated complex-type N-glycans (47.5%). Bi- and tri-antennary oligosaccharides with bisecting GlcNAc and α1–6 Fuc on the Asn-linked GlcNAc were abundant among N-glycans possessing terminal Galα1–4Gal sequences. Moreover, MS/MS analysis identified Galα1–4Galβ1–4Galβ1–4GlcNAc branch terminals, which are not found in pigeon egg white glycoproteins. An additional interesting aspect is that about two-thirds of high mannose-type N-glycans from pigeon IgG were monoglucosylated. Comparison of the N-glycan structures with chicken and quail IgG indicated that the presence of high mannose-type oligosaccharides may be a characteristic of these avian IgG.