Abstract
Bovine lactoferrin (LF) has been shown to prevent adhesion to and invasion of mammalian cell lines by pathogenic bacteria, with evidence for direct bacterial binding by the milk glycoprotein. However, the glycosylation pattern of LF changes over the lactation cycle. In this study, we aim to investigate the effect that this variation has on the milk glycoprotein’s ability to interact with pathogens. Surface plasmon resonance technology was employed to compare the binding of LF from colostrum (early lactation) and mature milk (late lactation) to a panel of pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Cronobacter sakazakii, Streptococcus pneumoniae, Pseudomonas aeruginosa, Listeria monocytogenes and Salmonella typhimurium). Novel interactions with LF were identified for C. sakazakii, S. pneumoniae and P. aeruginosa with the highest binding ability observed for mature milk LF in all cases, with the exception of S. typhimurium. The difference in bacterial binding observed may be as a result of the varying glycosylation profiles. This work demonstrates the potential of LF as a functional food ingredient to prevent bacterial infection.
Highlights
Bovine milk lactoferrin (LF) is a single chain, iron-binding, glycosylated protein [1] present in the whey protein fraction of milk [2]
The associated glycan chains are composed of N-acetyl-glucosamine (GlcNAc), galactose (Gal), N-acetyl-galactosamine (GalNAc), fucose (Fuc), mannose (Man), N-acetyl-neuraminic acid (Neu5Ac) and N-glycolyl-neuraminic acid (Neu5Gc) and variation in the glycosylation pattern of LF has been described over the lactation cycle [7]
A greater degree of heterogeneity in glycan structure has been reported for LF from early lactation, with an abundance of high-mannose type glycans present on th glycoprotein in mature milk [7]
Summary
Bovine milk lactoferrin (LF) is a single chain, iron-binding, glycosylated protein [1] present in the whey protein fraction of milk [2] (http://www.uniprot.org/uniprot/B9VPZ5). Lactoferrin may have high-mannose type, complex type or hybrid type N-linked glycans attached. The associated glycan chains are composed of N-acetyl-glucosamine (GlcNAc), galactose (Gal), N-acetyl-galactosamine (GalNAc), fucose (Fuc), mannose (Man), N-acetyl-neuraminic acid (Neu5Ac) and N-glycolyl-neuraminic acid (Neu5Gc) (as previously reviewed [6]) and variation in the glycosylation pattern of LF has been described over the lactation cycle [7]. A greater degree of heterogeneity in glycan structure has been reported for LF from early lactation, with an abundance of high-mannose type glycans present on th glycoprotein in mature milk [7]. The glycan chains in mature milk LF are 65% oligomannose type, consisting of multiple isomers of high-mannose type glycans, containing five to nine mannose residues, 38% of the total mannose structures accounted for by Man8 [8]. Neu5Gc was shown to be present on bovine LF only in the initial days postpartum and the total sialic acid content decreased as lactation progressed [7]
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