Effect of high hydrostatic pressure on the conformation of beta-lactoglobulin A as assessed by proteolytic peptide profiling

Upon pressure treatment of beta-lactoglobulin (beta-Lg), unfolding and exposure of some hydrophobic areas occur. Pressure-treated beta-lactoglobulin A was hydrolysed by specific enzymes (trypsin, chymotrypsin and a protease from Bacillus licheniformis) at ambient pressure in order to identify solvent exposed sites. Treatment at 150 MPa did not significantly affect the rate of hydrolysis, nor the resulting peptide profile, compared to hydrolysis of un-pressurized beta-Lg. However, treatment at 300 or 450 MPa increased the rate of hydrolysis 5-10 times and certain peptides occurred in relatively higher abundance in the peptide profiles. Two of these peptides were formed by cleavage in the beta-strands D and G of beta-Lg, indicating that these strands were partly detached from the beta-barrel upon pressure treatment of beta-Lg at or above 300 MPa. Peptides formed by cleavage of sites close to the Cys66-Cys160 disulfide bond were relatively more abundant in the hydrolysates from native beta-Lg than following pressure treatment, suggesting that these sites were hidden at the contact interfaces in pressure-induced oligomers. (C) 2002 Elsevier Science Ltd. All rights reserved.