Eukaryotic Hsp40, also known as HDJ-1, and bacterial DnaJ belong to the Hsp40 or DnaJ family whose members have a J-domain and various combinations of additional conserved and nonconserved regions. E. coli DnaJ consists of two major functional regions. The N-terminal highly conserved 75-amino acid J-domain is mainly responsible for the interaction with DnaK (1). Members of the human and yeast Hsp40 family such as HDJ-1, HDJ-2 and YDJ-1 also have a conserved J domain at the N-terminus. The DnaJ COOH-terminal part containing Gly/Phe-rich, cysteine-rich and less conserved last COOH-terminal regions are involved in the substrate binding (2,3). The binding of DnaJ to DnaK is dependent on the ATP binding state of DnaK. DnaJ plays a key catalyst role in the chaperone reaction by stimulating the ATPase activity and activating the substrate binding of Hsp70. The binding of ATP to the ATPase domain of Hsp70 induces a conformational change in the substrate binding domain of Hsp70 which results in an increase in the on/off rate for a substrate polypeptide and a low binding affinity. Subsequent DnaJ-stimulated ATP-hydrolysis involves a further conformation change and conversion of Hsp70 to an ADP form which has a slow on/off rate and relatively high binding affinity for a substrate polypeptide. Recent data also demonstrates that isoforms of the anti-apoptotic protein BAG-1M and BAG-1S stimulate ATP hydrolysis of Hsc70 in an Hsp40-dependent manner through an acceleration of ADP-ATP exchange (4). Hsp40 co-chaperones are involved in nearly all aspects of protein synthesis and secretion because of their importance in Hsp70 function and they are also thought to have an intrinsic ability to bind and fold some misfolded proteins (5). Applications: Suitable for use in Western Blot. On a 15-well minigel system, 100ng of protein per lane should be sufficient when used in a colorimetric Western Blot. Storage and Stability: May be stored at 4C for short-term only. For long-term storage, aliquot to avoid repeated freezing and thawing and freeze at -70C. Stable for 6 months after receipt. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.
