Molecular chaperones DnaK/DnaJ

Thomas JG, Baneyx F (1996) Protein folding in the cytoplasm of Escherichia coli requirements for the DnaK-DnaJ-GrpE and GroEL-GroES molecular chaperone machines. Mol Microbiol 21 1185-1196... 

The GroES-GroEL system, DnaK-DnaJ-GrpE system, and ClpB are representative molecular chaperones in bacterial cells. These chaperones were previously reported to be regulated by sigma32 (RpoH), a bacterial sigma factor. We described the involvement of these chaperones in the process of acetic acid fermentation by acetic acid bacteria. 

Many of the chaperones double as heat shock-proteins (Hsp). When a cell is put under stress that can cause proteins to denature, such as too high a temperature, it produces heat-shock proteins. Their names are abbreviated to Hsp plus their subunit molecular mass in kDa. Hsp70, for example, is a ubiquitous heat-shock protein in eukaryotes. It is known in E. coli as DnaK for historical reasons because it was first discovered from a supposed role in DNA replication. Hsp70 is also important in protein trafficking and the conveying of proteins across membranes, because the denatured state is important in these processes. In protein biosynthesis, the unfolded state of the nascent polypeptide chain is passed on to DnaK, which maintains it in an extended form. The chain, under the influence of ATP and co-chaperones such as DnaJ and GrpE, is handed over to GroEL. 

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