The Primary Structure of Hen Ovotransferrin

Abstract

Peptide sequences obtained from hen ovotransferrin are compared with the complete amino acid sequence of the protein deduced from a cDNA sequence (Jeltsch and Chambon, preceding paper). Of the 705 positions of the whole protein 605 can be matched by the peptide sequences. Some possible discrepancies between the two methods are pointed out. The two halves of the chain show marked similarities in their sequences with 37 identical residues. The positions of the 15 disulphide bridges are shown; there are 6 homologous bridges in each half of the molecule and 3 extra bridges which occur only in the C-terminal half. The terminal residues of the halfmolecule fragments obtained by limited proteolysis are identified. The two domains are joined by a 9-residue connecting peptide. Sequence variability has been found at 9 positions. The sequence of hen ovotransferrin IS compared with the partial sequence available for human transferrin. From this some tentative conclusions about the identities of the metal-binding residues and about the evolution of transferrin are reached.The iron-binding protein transferrin is present in all vertebrate species. The closely related protein lactoferrin (or lactotransferrin) appears to be restricted to mammals. The amino acid sequences of these proteins have been studied for many years in order to elucidate their structure, evolution and ironbinding properties. Brew and his colleagues [1,2] have determined about 80 % of the sequence of human serum transferrin and have discovered that the N-terminal and C-terminal halves of the chain have similar sequences, with about 40 identical residues. X-ray crystallography [3] and partial proteolysis experiments [4,5] show that each half of the chain folds up into a largely independent, compact domain which carries a specific metal-binding site. Since the domains can be isolated as single-chain fragments after partial proteolysis it can be inferred that the disulphide bridges are located within the domains, none passing between them. These data suggest that the present-day bilobar protein has evolved by gene duplication and subsequent fusion from a smaller ancestral protein, which apparently no longer exists. Partial sequence data on human lactoferrin show that this protein is homologous to transferrin and that it too possesses internal duplication of structure [6,7]. Lactoferrin may, thus, have arisen by a further duplication of the transferrin gene in the ancestors of the mammals.In birds expression of the transferrin gene in the oviduct, which is under steroid control, leads to the synthesis of ovotransferrin (conalbumin), which differs from serum transferrin only in the nature of the attached glycan [8,9]. The sequences of cysteic-acid-containing peptides from digests of performicacid-oxidized ovotransferrin have been determined [lo] ; 34 unique cysteic acid residues were identified and some of the disulphide bridges were characterized after pepsin digestion of the unoxidized protein. A 102-residue sequence, which includes the point of attachment of ...

Primary structure of the human melanoma-associated antigen p97 (melanotransferrin) deduced from the mRNA sequence.

“…Human transferrin also contains 2 extra cysteines unique to its N-terminal domain. The positions of most of the disulfides in human serum transferrin, lactotransferrin, and chicken transferrin have been determined directly (27,33,(35)(36)(37)(38), and one can thus predict the positions of seven disulfide bonds in each domain of p97.…”

Conformation Changes and Subsequent Gelation of Conalbumin by a Thiol Reagent

“…The native or 2-ME-reacted conalbumin was diluted 20 times with 0.1 M sodium phosphate, pH 8.0. The CD data in the 190"" 245 nm regions were expressed in terms of the mean molecular ellipticity [8]MRW, taking 111 as the mean residue weight calculated from the data of Williams et al 2 ) and in the 245"" 340 nm regions as ellipticity per mole of conalbumin, [8]. All of the CD spectra were corrected by subtracting the spectrum in the absence of the protein.…”

Effects of heating, autoclaving and ultra-high pressure on the solubility, immunoreactivity and structure of major allergens in egg

“…The OVT structure unfolded when heated to 55-60°C, and the secondary structure disappeared when heating to 70-80°C. Conversely, the allergenicity of OVT was enhanced under these conditions as the protein structure expanded and disulfide bonds fractured (Williams, Elleman, Kingston, Wilkins, & Kuhn, 1982).…”