title: Heat-induced redistribution of disulfide bonds in milk proteins. 1. Bovine beta-lactoglobulin.
abstract: Changes in the structure and chemistry of beta-lactoglobulin (beta-LG) play an important role in the processing and functionality of milk products. In model beta-LG systems, there is evidence that the aggregates of heated beta-LG are held together by a mixture of intermolecular non-covalent association and heat-induced non-native disulfide bonds. Although a number of non-native disulfide bonds have been identified, little is known about the initial inter- and intramolecular disulfide bond rearrangements that occur as a result of heating. These interchange reactions were explored by examining the products of heat treatment to determine the novel disulfide bonds that form in the heated beta-LG aggregates. The native protein and heat-induced aggregates were hydrolyzed by trypsin, and the resulting peptides, before and after reduction with dithiothreitol, were separated by high-performance liquid chromatography and their identities confirmed by electrospray ionization mass spectrometry. Comparisons of these peptide patterns showed that some of the Cys160 was in the reduced form in heated beta-LG aggregates, indicating that the Cys160-Cys66 disulfide bond had been broken during heating. This finding suggests that disulfide bond interchange reactions between beta-LG non-native monomers, or polymers, and other proteins could occur largely via Cys160.
authors.affiliation: Fonterra Research Centre, Private Bag 11-029, Palmerston North, New Zealand. lawrie.creamer@fonterra.com
authors.forename: Lawrence K
authors.initials: LK
authors.lastname: Creamer
authors.forename: Annie
authors.initials: A
authors.lastname: Bienvenue
authors.forename: Hanna
authors.initials: H
authors.lastname: Nilsson
authors.forename: Marie
authors.initials: M
authors.lastname: Paulsson
authors.forename: Miriam
authors.initials: M
authors.lastname: van Wanroij
authors.forename: Edwin K
authors.initials: EK
authors.lastname: Lowe
authors.forename: Skelte G
authors.initials: SG
authors.lastname: Anema
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Boland
authors.forename: Rafael
authors.initials: R
authors.lastname: Jiménez-Flores
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000737:chemistry*; D006358:Hot Temperature; D006868:Hydrolysis; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism; D008894:Milk Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D021241:Spectrometry, Mass, Electrospray Ionization; D014357:Trypsin / Q000378:metabolism
chemical_list: D004220:Disulfides; D007782:Lactoglobulins; D008894:Milk Proteins; D010446:Peptide Fragments; D014357:Trypsin