Serotransferrin structure

Chasteen, D, (1977) Human serotransferrins structure and function. Coord. Chem, Revs. 22 1-36. 

Conalbumin comprises 3-16% of the egg-white from various species of birds. It is structurally related to plasma serotransferrin, the polypeptide chain being coded by the same structural gene [27], but the carbohydrate moiety being different (see section 3.1.3). Because of the close relationship of these two proteins, the name ouotransferrin is now used in place of conalbumin. 

Important variations of the plasma serotransferrin concentration are observed in physiological and pathological situations. They are often accompanied by dramatic modifications of glycan primary structure (see section 3.2). 

Structural comparison of the iron binding sites of N-lobe of rabbit serotransferrin, human lactotransferrin and... 

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... 

Contrary to serotransferrin receptors, little is known about the structure, physicochemical properties and gene expression of lactotransferrin receptors. Their main characteristics, which are totally different from those of serotransferrin receptors, can be summarized as follows ... 

Fig. 6. Primary structure of serotransferrin diantennary glycans from human (A,B) [211-213], cow (A,B) [119, 214], rabbit (A) [103], sheep (A) [119,215], marsupial (kangaroo, opossum, wallaby) (A) [119,216], Primary structure of human serotransferrin triantennary glycans (C,D) [119-217],...

Fig. 7. Primary structure of the glycans from mouse serotransferrin [119,218,219],...

Fig. 8. Primary structures of the glycans from rat serotransferrin (A,B,C)[221] and from rat mammary gland transferrin (D) [67]. R, GlcNAc(pl-4)[Fuc(al-6)]o- GlcNAc(P-N)Asn.

Fig. 9. Primary structure of the four glycans identified in the three horse serotransferrin variants [113,114,119, 222,223], R, GlcNAc(Pl-4)GlcNAc(pi-N)Asn.

Fig, )0. Primary structure of glycans from fish serotransferrins. A, Carp big-head (Aristichthys nobilis) [224] B, pike Esox lucius)[225]. R, GlcNAc(pl-4)GlcNAc(pl-N)Asn. 

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.

Human seminal transferrin. Human seminal transferrin (MM 80kDa) contains 6.1% sugars. The primary structure of the major N-linked glycan is identical to that of the serotransferrin diantennary glycan of Fig. 6A [247]. 

Fig. 18. Primary structure of tetra- and pentaantennary glycans from human serotransferrin secreted into culture medium of human hepatocarcinoma cell line Hep G2. The a-l,3-linked fucose residue is conjugated to the GlcNAc of one of the antennae [261]. R, GlcNAc(pi )[Fuc(al-6)]o iGlcNAc(p-N)Asn.

CDG-type II syndrome [265,268] is a separate variant since it is characterized by a severe decrease in the activity of A-acetylglucosaminyltransferase II (UDP-GlcNAc a6-D-mannoside (3-l,2-A-acetylglucosaminyltransferase). As a consequence, the serotransferrin isoforms contain two truncated monoantennary glycans of which the primary structures are described in Fig. 19. 

Fig. 19. Primary structure of the glycan from human serotransferrin isolated from a patient with carbohydrate-deficient syndrome (CDG) type II [265,268], R, GIcNAc(pi-4)GIcNAc(pi-N)Asn.

As mentioned above (see section 2.2.1), the three-dimensional structure of the peptide chains of rabbit serotransferrin, of human and bovine lactotransferrins and of ovotrans-... 

As mentioned above. X-ray diffraction of transferrin furnishes little information on the 3D-structure of the glycans and the images we have today remain largely speculative since they result from molecular modelling studies. We have represented in Fig. 21 the 3D-structure, determined by molecular modelling on the basis of X-ray diffraction data of rabbit serotransferrin [276] and of human lactotransferrin [89,92]. In rabbit serotransferrin, the single glycan linked to the peptide chain is immobilized into only... 

Fig. 21. Molecular modelling (A,B) of rabbit serotransferrin glycan and (C) of human lactotransferrin [192, 210,275] (A) 3D structure of rabbit serotransferrin (B) interaction of rabbit serotransferrin glycan in a broken-wing conformation with a peptide segment (amino acids 254 to 271) in an a-helix conformation, 7,7, Al-acetylneuraminic acid residues (see Fig. 6A). (C) 3D structure of human lactotransferrin. Arrows indicate the position of glycans.

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