Identification of a beta-lactoglobulin lactosylation site.
Thermal treatment of milk leads to non-enzymatic glycosylation of proteins through Maillard reaction. Free NH2 groups of basic amino acids react with the reducing carbonyl group of lactose forming the so-called Amadori products. Electrospray mass spectrometry analysis shows that beta-lactoglobulin (beta-LG), the major whey protein, undergoes lactosylation under industrial thermal treatment. In order to investigate the specificity of reactive sites for lactose binding the analysis of trypsin hydrolysates of beta-LG isolated from different industrial milks was performed. Results demonstrate that Lys-100 is a preferential lactosylation site of beta-LG during industrial milk treatment. These results were confirmed by an analysis of the three-dimensional model of the protein which showed that Lys-100 had the highest solvent accessibility and proximity to another amino group making Lys-100 the best candidate to lactosylation. Lys-47, previously identified by other authors, showed a good proximity to another Lys residue, but an intermediate level of exposition to solvent.
Fogliano
V
V
Dipartimento di Scienza degli Alimenti, Università di Napoli 'Federico II', Parco Gussone, 80055 Portici, Naples, Italy. fogliano@uniroma2.it
Monti
S M
SM
Visconti
A
A
Randazzo
G
G
Facchiano
A M
AM
Colonna
G
G
Ritieni
A
A
D000595:Amino Acid Sequence; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D006031:Glycosylation; D006358:Hot Temperature; D007782:Lactoglobulins / Q000737:chemistry*; D007785:Lactose / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism; D015416:Maillard Reaction; D013058:Mass Spectrometry; D008894:Milk Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis; D014357:Trypsin / Q000378:metabolism
D007782:Lactoglobulins; D008894:Milk Proteins; D010446:Peptide Fragments; D014357:Trypsin; D007785:Lactose; D008239:Lysine