The cysteine residue in beta-lactoglobulin reacts with oxidized tyrosine residues in beta-casein to give casein-lactoglobulin dimers.

Autor: Doblas L; Department of Biomedical Sciences, Panum Institute, Blegdamsvej 3, University of Copenhagen, Copenhagen, 2200, Denmark., Hägglund PM; Department of Biomedical Sciences, Panum Institute, Blegdamsvej 3, University of Copenhagen, Copenhagen, 2200, Denmark., Fuentes-Lemus E; Department of Biomedical Sciences, Panum Institute, Blegdamsvej 3, University of Copenhagen, Copenhagen, 2200, Denmark. Electronic address: eduardo.lemus@sund.ku.dk., Davies MJ; Department of Biomedical Sciences, Panum Institute, Blegdamsvej 3, University of Copenhagen, Copenhagen, 2200, Denmark. Electronic address: davies@sund.ku.dk.
Jazyk: angličtina
Zdroj: Archives of biochemistry and biophysics [Arch Biochem Biophys] 2023 Jan 01; Vol. 733, pp. 109482. Date of Electronic Publication: 2022 Nov 28.
DOI: 10.1016/j.abb.2022.109482
Abstrakt: 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/O 2 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.
(Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)
Databáze: MEDLINE
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