The cysteine residue in beta-lactoglobulin reacts with oxidized tyrosine residues in beta-casein to give casein-lactoglobulin dimers
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Proteins are modified during milk processing and storage, with sidechain oxidation and crosslinking being major consequences. Despite the prevalence and importance of proteins in milk, and particularly caseins (∼80% of total content), the nature of the cross-links formed by oxidation, and their mechanisms of formation, are poorly characterized. In this study, we investigated the formation and stability of cross-links generated by the nucleophilic addition of Cys residues to quinones generated on oxidation of Tyr residues. The mechanisms and stability of these adducts was explored using ubiquitin as a model protein, and β-casein. Ubiquitin and β-casein were oxidized using a rose Bengal/visible light/O2 system, or by the enzyme tyrosinase. The oxidized proteins were incubated with glutathione or β-lactoglobulin (non-oxidized, but unfolded by treatment at 70 °C), before analysis by SDS-PAGE, immunoblotting and LC-MS. Our data indicate that Cys-quinone adducts are readily-formed, and are stable for >48 h. Thus, oxidized β-casein reacts efficiently with the thermally unfolded β-lactoglobulin, likely via Michael addition of the exposed Cys to a Tyr-derived quinone. These data provide a novel, and possibly general, mechanism of protein cross-link formation, and provides information of the stability of these species that have potential as markers of protein quality.
Original language | English |
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Article number | 109482 |
Journal | Archives of Biochemistry and Biophysics |
Volume | 733 |
Number of pages | 7 |
ISSN | 0003-9861 |
DOIs | |
Publication status | Published - 2023 |
Bibliographical note
Publisher Copyright:
© 2022 The Authors
- Beta-casein, Beta-lactoglobulin, Photosensitization, Protein cross-linking, Quinone, Thiol
Research areas
ID: 331788537