A Novel Function of Escherichia coli Chaperone DnaJ

Molecular chaperones, protein-disulfide isomerases, and peptidyl prolyl cis-trans isomerases assist protein folding in both prokaryotes and eukaryotes. The DnaJ protein of Escherichia coli and the DnaJ-like proteins of eukaryotes are known as molecular chaperones and specific regulators of DnaK-like proteins and are involved in protein folding and renaturation after stress. In this study we show that DnaJ, like thioredoxin, protein-disulfide isomerase, and DsbA, possesses an active dithiol/disulfide group and catalyzes protein disulfide formation (oxidative renaturation of reduced RNase), reduction (reduction of insulin disulfides), and isomerization (refolding of randomly oxidized RNase). These results suggest that, in addition to its known function as a chaperone, DnaJ might be involved in controlling the redox state of cytoplasmic, membrane, or exported proteins.