Abstract
DnaK, the Escherichia coli hsp70 protein, interacts with DnaJ, a protein cofactor that appears to be involved in presenting protein substrates to DnaK. The yeast DnaJ homolog, YDJ1, has also been shown to interact with yeast hsp70, although the function of this interaction is unknown. In the present study, we investigated the interaction of YDJ1 with both yeast and bovine brain hsp70. We found that, in the presence of ATP, where hsp70 is normally monomeric, YDJ1 induced almost all of the yeast and bovine brain hsp70 to form large polymers, which are readily sedimentable. These polymers were much larger than the dimers and trimers of hsp70, which normally form in the presence of ADP. YDJ1 appeared to be acting catalytically since very little YDJ1 copolymerized with the hsp70, and maximum polymerization occurred at low ratios of YDJ1 to hsp70. The polymerization required ATP and was completely reversed when ATP was replaced by ADP. These data suggest that, in the presence of ATP, YDJ1 may present one hsp70 to another just as under other conditions DnaJ is able to present protein substrates to DnaK.
Highlights
Our laboratory (Greene and Eisenberg, 1990; Prasad et al, 1994b; Greene et al, 1995) has previously characterized the effect of nucleotides on the interaction of brain hsp70 with clathrin and peptide substrates
In agreement with the observations of Cyr et al (1992), we found that the yeast DnaJ homolog, YDJ1, activates the ATPase activity of the yeast hsp70, SSA1; in addition, we found that it activates the ATPase activity of bovine brain hsp70
This latter observation establishes that yeast YDJ1 interacts with yeast SSA1 and with brain hsp70
Summary
Our laboratory (Greene and Eisenberg, 1990; Prasad et al, 1994b; Greene et al, 1995) has previously characterized the effect of nucleotides on the interaction of brain hsp with clathrin and peptide substrates. In addition to DnaJ, there appears to be a number of other cofactors that are involved in presenting protein substrates to hsp. Of the various cofactors that present proteins to hsp, DnaJ is interesting because, like hsp, it consists of a large family of proteins present in many different cell organelles. This has been most clearly demonstrated in yeast. Rather than YDJ1 presenting these substrates to hsp, it appeared to be interfering with their binding to hsp70 This suggests that the effect of DnaJ and its homologs may be different for different substrates
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
