Ovotransferrin glycans

Occasionally, the branchings are incomplete and the formation of the N-acetyl-lactosamine residues is only started in outline, as in the glycans of ovotransferrin (see Fig. 15), ovalbumin (see Fig. 16), and ovomucoid (see Fig. 18). In other instances, glycan structures such as have just been described are enriched with supplementary monosaccharide residues for example, the occurrence of disialyl groups [a-NeuAc-(2—>8)-a-NeuAc], and of /3-Gal-(l- 3) residues linked to the terminal galactosyl residues, has been demonstrated in different tissues and cell membranes,114,115 and in calf-thymocyte membranes,118 respectively. 

Ouotransferrins. The peptide chain of hen ovotransferrin is identical to that of hen serotransferrin. However, both glycoproteins differ only by the structure of their glycans (see Figs. 16B,D). Two potential glycosylation sites have been identified... 

In contrast to sero- and lactotransferrins, glycans of ovotransferrins from avian egg-white contain a bisecting A-acetylglucosamine residue, like other glycoproteins from oviducts, such as ovomucoid and ovalbumin for instance (Fig. 16A-C). Like all of the avian egg glycoproteins, ovotransferrins are not fueosylated. 

Fig. 16. Primary structure of glycans from turkey ovotransferrin (A) [119,238], hen ovotransferrin (B) [239, 240], chicken embryo serum (C), and chicken serotransferrin (D)[241]. R, GlcNAc(Pl-4)GlcNAc(Pl-N)Asn. Glycans of transferrin from embryo hepatocytes secreted into culture medium are a-l,6-fucosylated.

Two structures [(53) and (54)1 are proposed for the unique glycan of hen egg-white ovotransferrin. A comparative study of this glycan with those of human serotransferrin and lactotransferrin reveals profound differences that could form the basis for the specificity of recognition of target cells by these glycoproteins. 

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