Chaperones DnaK/DnaJ

Langer, T., Lu., C, Echols, H., Flanagan, J, Hayer, M.K., Hartl, F.-U. (1992). Successive action of Dnak, DnaJ, GroEL along the pathway of chaperone mediated protein folding. Nature 356, 683-689. 

Zolkiewski M (1999) ClpB cooperates with DnaK, DnaJ, and GrpE in suppressing protein aggregation. A novel multi-chaperone system from Escherichia coli. J Biol Chem 274 28083-28086... 

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. 

FIGURE 4-30 Chaperones in protein folding. The cyclic pathway by which chaperones bind and release polypeptides is illustrated for the . coli chaperone proteins DnaK and DnaJ, homologs of the eukaryotic chaperones Hsp70 and Hsp40. The chaperones do not actively promote the folding of the substrate protein, but instead prevent aggregation of unfolded peptides. For a population of polypeptides, some... 

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. 

Wickner, S., Hoskins, J., and McKenney, K. (1991a). Function of DnaJ and DnaK as chaperones in origin-specific DNA binding by RepA. Nature (London) 350, 165-167. 

Both ATP and extended polypeptides bind weakly to DnaK, and the ATP in the DnaK polypeptide ATP complex is hydrolyzed slowly to ADP and inorganic phosphate." " Co-chaperone DnaJ, which shares a largely a-helical structural motif with J-domains in various other proteins, binds to the complex." ... 

Recombinantly produced DnaK was utilized to characterize its APIase function enzymatically. Co-chaperones, such as DnaJ and GrpE in the presence of ATP might contribute to create the subsite specificity of DnaK. For oligopeptide substrates, the APIase function of DnaK does not require concomitant ATP hydrolysis. A functional overlap of a PPIase and an APIase, trigger factor and DnaK, respectively, could not be observed in an APIase and a standard PPIase assay [127]. Generally, PPIases fail to accelerate CTI of secondary amide peptide bonds in peptide substrates and folding intermediates [152]. 

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