Hen ovotransferrin

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... 

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.

Milk transferrin (lactoferrin51a b c also found in leukocytes), hen egg transferrin (ovotransferrin),52 52a and rabbit and human serum transferrin54 543 all have similar structures. Each Fe3+ is bonded to oxygen anions from two tyrosine side chains, an aspartate carboxy-late, an imidazole group, and the bound carbonate ion (Fig. 16-2B). 

Ibrahim, H.R. 1997. Insights into the structure-function relationships of ovalbumin, ovotransferrin, and lysozyme. In Hen Eggs Their Basic and Applied Science (T. Yamamoto, L.R. Juneja, H. Hatta, and M. Kim, eds), pp. 37-56. CRC Press, Boca Raton. 

The first crystallographic studies on transferrins date back more than 20 years (58), and crystals of various transferrins have since been reported. These include the diferric forms of rabbit (59) and human (60) serum transferrins, hen (61) and duck (62) ovotransferrins, human (63) and bovine (64) lactoferrins, and the apo- (iron free) forms of human lactoferrin (65) and duck ovotransferrin (62). In spite of all this activity, the crystals in many cases have proved difficult to handle, and the X-ray analyses quite challenging. A low-resolution analysis of rabbit serum transferrin in 1979 demonstrated the bilobal nature of the molecule (66), but it was not until 1987, with the publication of the structure of human lactoferrin (67), that full details of a transferrin... 

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. 

Human serum transferrin is an iron(m) tr ispoTt protein which gives up Fe + ions to bone marrow and placental tissues in preference to other cells such as liver cells the protein can bind two iron atoms per molecule but an anion such as HCOa" must be present for binding to occur. Vanadyl ion has been used (as an e.s.r. spin label) to show that the two metal-binding sites are non-equivalent and the same conclusion has been drawn from studies on the dissociation of labelled protein-bound iron. On the other hand, Harris and Aisen have obtained evidence from radiotracer experiments that the two sites are kinetically equivalent. The kinetics of iron(in) (in the form of ferric citrate) binding to the analogous apoprotein from hen s egg (apo-ovotransferrin) have been reported and the following minimum mechanistic scheme has been proposed ... 

Ovotransferrin, also known as ovoconalbumin or conalbumin (76 kDa, pf = 6.1), which in hens is identical with serum transferrin, shows antimicrobial effects. This protein coagulates at a lower temperature than ovalbumin (coagulation temperature is 53 °C) and forms complexes with divalent and trivalent metal ions. Complexes with iron can cause a pink discolouration of products containing egg white. 

---