The hsp70 chaperone machine performs many diverse roles in the cell, including folding of nascent proteins, translocation of polypeptides across organelle membranes, coordinating responses to stress, and targeting selected proteins for degradation. DnaJ is a member of the hsp40 family of molecular chaperones, which is also called the J-protein family, the members of which regulate the activity of hsp70s. DnaJ (hsp40) binds to DnaK (hsp70) and stimulates its ATPase activity, generating the ADP-bound state of DnaK, which interacts stably with the polypeptide substrate [1]. Besides stimulating the ATPase activity of DnaK through its J-domain, DnaJ also associates with unfolded polypeptide chains and prevents their aggregation [2].

DnaJ consists of an N-terminal conserved domain (called 'J' domain) of about 70 amino acid residues, a glycine and phenylalanine-rich domain ('G/F' domain), a central cysteine rich domain (CR-type zinc finger) containing four repeats of a CXXCXGXG motif which can coordinate two zinc atom and a C-terminal domain (CTD) [3].

This entry represents the central cysteine-rich (CR) domain of DnaJ proteins. This central cysteine rich domain (CR-type zinc finger) has an overall V-shaped extended beta-hairpin topology and contains four repeats of the motif CXXCXGXG where X is any amino acid. The isolated cysteine rich domain folds in zinc dependent fashion. Each set of two repeats binds one unit of zinc. Although this domain has been implicated in substrate binding, no evidence of specific interaction between the isolated DnaJ cysteine rich domain and various hydrophobic peptides has been found [4].

1. Folding of newly translated proteins in vivo: the role of molecular chaperones. Annu. Rev. Biochem. 70, 603-47
2. cis-Effect of DnaJ on DnaK in ternary complexes with chimeric DnaK/DnaJ-binding peptides. FEBS Lett. 563, 146-50
3. The J-protein family: modulating protein assembly, disassembly and translocation. EMBO Rep. 5, 567-71
4. Solution structure of the cysteine-rich domain of the Escherichia coli chaperone protein DnaJ. J. Mol. Biol. 300, 805-18

The hsp70 chaperone machine performs many diverse roles in the cell, including folding of nascent
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