IDENTIFICATION OF A BETA-LACTOGLOBULIN LACTOSYLATION SITE

Thermal treatment of milk leads to non-enzymatic glycosylation of prot eins through Maillard reaction. Free NH2 groups of basic amino acids r eact 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 lactos ylation under industrial thermal treatment. In order to investigate th e specificity of reactive sites for lactose binding the analysis of tr ypsin hydrolysates of beta-LG isolated from different industrial milks was performed. Results demonstrate that Lys-100 is a preferential lac tosylation site of beta-LG during industrial milk treatment. These res ults were confirmed by an analysis of the three-dimensional model of t he protein which showed that Lys-100 had the highest solvent accessibi lity and proximity to another amino group making Lys-100 the best cand idate 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. (C) 1998 Elsevier Science B.V. All rig hts reserved.