Evidence for interactions between the 30 kDa N- and 50 kDa C-terminal tryptic fragments of human lactotransferrin.
Gel filtration of a mild tryptic digest of diferric human lactotransferrin carried out in presence of 10% (v/v) acetic acid led to the isolation of two fragments, an N-terminal tryptic fragment having an Mr of 30,000 and a C-terminal tryptic fragment having an Mr of 50,000 [Legrand, Mazurier, Montreuil & Spik (1984) Biochim. Biophys. Acta 787, 90-96]. Both fragments possess a degree of organization lower than that of the native protein, as shown by the decrease of about 30% of the alpha-helical content observed by c.d. The two fragments are able to re-associate in neutral solutions, as shown by the isolation, by gel chromatography, of a re-associated 80 kDa N,C-tryptic complex having the chromatographic behaviour of the native lactotransferrin. Computer-based comparison of the measured c.d. spectrum of the mixture of N-tryptic and C-tryptic fragments (molar ratio 1:1) with the spectrum calculated by assuming one molecule of each fragment, shows that the alpha-helix content of lactotransferrin is restored. These results strongly suggest the existence of non-covalent and reversible interactions between the two lobes of lactotransferrin. In addition it was demonstrated that short peptide segments (residues 19-24, 45-58 and 264-276) are involved in the secondary-structure modifications referred to above.
D000596:Amino Acids / Q000378:metabolism; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D006020:Glycopeptides / Q000378:metabolism; D006801:Humans; D007781:Lactoferrin / Q000378:metabolism*; D007782:Lactoglobulins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011487:Protein Conformation
D000596:Amino Acids; D006020:Glycopeptides; D007782:Lactoglobulins; D010446:Peptide Fragments; D007781:Lactoferrin