Isolation and characterization of major glycoproteins of pigeon egg white: Ubiquitous presence of unique N-glycans containing Galα1-4Gal

Ovotransferrin (POT), two ovalbumins (POA(hi) and POA(lo)), and ovomucoid (POM) were isolated from pigeon egg white (PEW). Unlike their chicken egg white counterparts, PEW glycoproteins contain terminal Galα1-4Gal, as evidenced by GS-I lectin (specific for terminal α-Gal), anti-P₁ (Galα1-4Galα1-4GlcNAcβ1-3Galβ1-4Glcβ1-1Cer) monoclonal antibody, and P fimbriae on uropathogenic Escherichia coli (specific for Galα1-4Gal). Galα1-4Gal on PEW glycoproteins were found in N-glycans releasable by treatment with glycoamidase F. The respective contents of N-glycans in each glycoprotein were 3.5%, POT; 17%, POA(hi); and 31-37%, POM. POA(hi) has four N-glycosylation sites, in contrast to chicken ovalbumin, which has only one. High performance liquid chromatography analysis showed that N-glycans on POA(hi) were highly heterogeneous. Mass spectrometric analysis revealed that the major N-glycans were monosialylated tri-, tetra-, and penta-antennary oligosaccharides containing terminal Galα1-4Gal with or without bisecting N-acetylglucosamine. Oligosaccharide chains terminating in Galα1-4Gal are rare among N-glycans from the mammals and avians that have been studied, and our finding is the first predominant presence of (Galα1-4Gal)-terminated N-glycans.