Proteolysis of bovine beta-lactoglobulin during thermal treatment in subdenaturing conditions highlights some structural features of the temperature-modified protein and yields fragments with low immunoreactivity.
Bovine beta-lactoglobulin was hydrolyzed with trypsin or chymotrypsin in the course of heat treatment at 55, 60 and 65 degrees C at neutral pH. At these temperatures beta-lactoglobulin undergoes significant but reversible structural changes. In the conditions used in the present study, beta-lactoglobulin was virtually insensitive to proteolysis by either enzyme at room temperature, but underwent extensive proteolysis when either protease was present during the heat treatment. High-temperature proteolysis occurs in a progressive manner. Mass spectrometry analysis of some large-sized breakdown intermediates formed in the early steps of hydrolysis indicated that both enzymes effectively hydrolyzed some regions of beta-lactoglobulin that were transiently exposed during the physical treatments and that were not accessible in the native protein. The immunochemical properties of the products of beta-lactoglobulin hydrolysis were assessed by using various beta-lactoglobulin-specific antibodies, and most epitopic sites were no longer present after attack of the partially unfolded protein by the two proteases.
Iametti
Stefania
S
Dipartimento di Scienze Molecolari Agroalimentari, University of Milan, Italy.
Rasmussen
Patrizia
P
Frøkiaer
Hanne
H
Ferranti
Pasquale
P
Addeo
Francesco
F
Bonomi
Francesco
F
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000502:physiology*; D004795:Enzyme Stability; D006868:Hydrolysis; D007782:Lactoglobulins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D010446:Peptide Fragments / Q000276:immunology*; D011489:Protein Denaturation; D011817:Rabbits; D013696:Temperature
D007782:Lactoglobulins; D010446:Peptide Fragments; D010450:Endopeptidases