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

Doblas, Laura; Hagglund, Per M.; Fuentes-Lemus, Eduardo; Davies, Michael J.


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 13-casein. Ubiquitin and 13-casein were oxidized using a rose Bengal/visible light/O2 system, or by the enzyme tyrosinase. The oxidized proteins were incubated with glutathione or 13-lactoglobulin (non-oxidized, but unfolded by treatment at 70 degrees 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 13-casein reacts efficiently with the thermally unfolded 13-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.

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Título según WOS: ID WOS:000913240100006 Not found in local WOS DB
Volumen: 733
Editorial: Elsevier Science Inc.
Fecha de publicación: 2023


Notas: ISI