Milk contains several proteins and peptides of interest for human health that have been investigated for decades. Among these proteins, lactoferrin has drawn considerable attention due to its implication in immune, antioxidant response, and inflammatory activities and its capability to fight against pathogenic microorganisms.
Lactoferrin was first identified in 1939 in bovine milk and was isolated in 1960 from both human and bovine milk (Sørensen, 1939, Johanson, 1960, Montreuil et al., 1960, Berlutti et al., 2011). It is a non-haem iron-binding protein that is part of the transferrin protein family along with serum transferrin, ovotransferrin, melanotransferrin and the inhibitor of carbonic anhydrase (Gonzalez-Chavez et al., 2009).
At the structural level lactoferrin is an 80-kDa glycoprotein composed of about 690 amino acid residues. The molecule is folded into two lobes (N-lobe residues 1-333 and C-lobe residues 345-691 in human lactoferrin) which are connected by a peptide that forms a 3-turn alpha-helix as illustrated in Figure 1. Each lobe of lactoferrin is divided in 2 domains (as seen in Figure 1; N1-N2 and C1-C2) and binds one Fe3+ ion (Berlutti et al., 2011).
From a chemical point of view, lactoferrin has the ability to chelate reversibly two Fe3+ ions per molecule. This reaction is characterized by the high affinity between lactoferrin and ferric ions as the binding can occur in pH as low as 3, while other transferrin-family proteins have lower affinity (iron release occurs at pH 5.5) (Berlutti et al., 2011). Lactoferrin can also bind other metal ions (Cu, Zn, Mn) but with lower affinities (Berlutti et al., 2011).