Mass Spectrometry Unravels Disulfide Bond Formation as the Mechanism That Activates a Molecular Chaperone

The heat shock protein Hsp33 is a very potent molecular chaperone with a distinctive mode of functional regulation; its activity is redox-regulated. In its reduced form all six cysteinyl residues of Hsp33 are present as thiols, and Hsp33 displays no folding helper activity. Exposure of Hsp33 to oxid...

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Bibliographic Details
Published inThe Journal of biological chemistry Vol. 275; no. 25; pp. 18759 - 18766
Main Authors Barbirz, Stefanie, Jakob, Ursula, Glocker, Michael O.
Format Journal Article
LanguageEnglish
Published United States Elsevier Inc 23.06.2000
American Society for Biochemistry and Molecular Biology
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Summary:The heat shock protein Hsp33 is a very potent molecular chaperone with a distinctive mode of functional regulation; its activity is redox-regulated. In its reduced form all six cysteinyl residues of Hsp33 are present as thiols, and Hsp33 displays no folding helper activity. Exposure of Hsp33 to oxidizing conditions like H2O2, however, rapidly converts Hsp33 into an efficient molecular chaperone. Activated Hsp33 binds tightly to refolding intermediates of chemically denatured luciferase and suppresses efficiently their aggregation in vitro. Matrix-assisted laser desorption/ionization-mass spectrometry peptide mapping in combination with in vitro and on target protein chemical modification showed that this activation process of Hsp33 is accompanied by the formation of two intramolecular disulfide bonds within Hsp33: Cys232—S—S—Cys234 and Cys265—S–S—Cys268. Cys141, although not involved in disulfide bond formation, was found highly reactive toward chemical modifications. In contrast, Cys239is readily accessible under reducing conditions but becomes poorly accessible though still reduced when Hsp33 is in its active state. This indicates a significant conformational change during the activation process of Hsp33. Mass spectrometry, thus, unraveled a novel molecular mechanism by which alteration of the disulfide bond structure, as a result of changes in the cellular redox potential, results in the activation of a molecular chaperone.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M001089200