The primary structure and glycosylation pattern of milk lactoferrins

The primary structures of human, bovine, buffalo, sheep, goat, pig, horse, donkey, dromedary and mouse milk lactoferrins (LFs) were compared. Overall, the amino acid sequence alignment reveals that these proteins share 46.11% sequence identity, suggesting that LFs represent a highly conserved family of proteins. Donkey and horse LFs are very closely related proteins, sharing over 98% sequence identity. Dromedary, horse and donkey LFs are the most closely related proteins to human LF with sequence identity in the 72-73% range. The amino acid sequences of LFs from sheep, goat, buffalo, and cow share over 91% sequence identity, suggesting another group of closely related proteins. As a whole, the comparison shows that the glycosylation composition of donkey LF is markedly different from human and bovine LFs, while it is closer to that of goat LF, the most relevant difference being the higher presence of N-glycolylneuraminic acid (Neu5Gc) in goat LF. In addition, it appears that the glycosylation site at Asn 476 is the most highly conserved among the species, followed by Asn at 281 and Asn 233, whereas donkey, horse and human LFs are characterized by three glycoslylation sites, two of which are conserved in all three species.