DnaJ proteins

Hence, although the specific numerical values reported for ATPase rates of stress-70 proteins show some variation, possibly attributable to differences in specific protein preparation and assay procedures utilized by different individuals, the consensus scheme that these data show is that in the absence of substrate peptide, the stress-70 proteins have a low basal ATPase rate, typically found to be 0.01-0.03 (mol ATP/mol stress-70 protein min). This can be enhanced severalfold either by binding of peptides or denatured proteins, or (as demonstrated by the effect of grpE and dnaJ proteins on dnaK) by the action of ancillary proteins. To the extent that the observations on HSC70 can be generalized to other members of the stress-70 protein family, peptide binding appears to relieve the attenuation of ATPase activity and allow it to proceed at the rate characteristic of the ATPase fragment of the protein alone. 

Caplan, A. J., and Douglas, M. G. (1991). Characterization of YDJ1 A yeast homologue of the bacterial dnaj protein, y. Cell Biol. 114, 609-621. 

Wickner, S. H. (1990). Three Escherichia coli heat shock proteins are required for PI plasmid DNA replication Formation of an active complex between E. coli DnaJ protein and the PI initiator protein. Proc. Nall. Acad. Sci. U.S.A. 87, 2690-2694. 

E. coli DnaJ protein Chaperone lEXK Cysp 2 CysL 49 Cysfi 2 Cys... 

The question of how DnaJ proteins interact with substrates and mediate their transfer onto Hsp70 partner proteins is not answered for any of the three classes of DnaJ proteins. Some DnaJ homologs have broad substrate specificity, such as E. coli DnaJ and yeast Ydjl, while others have more restricted substrate spectra. In particular the DnaJ proteins of class III may either bind a restricted number of substrates, such as the clathrin-specific auxilin or the kinesin light chain, or they may not bind substrates themselves but rather are positioned in close proximity to substrates. The latter seems to be the case for Dj 1A in the plasma membrane of E. coli (Clarke et al, 1997 Kelley and Georgopoulos, 1997a), Sec63 at the translocation pore in the ER (Corsi and Schekman, 1996 Rapoport et al., 1996), and cysteine string proteins on the surface of neurosecretory vesicles (Buchner and Bundersen, 1997). 

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