Abstract
Hsp90 is a key mediator in the folding process of a growing number of client proteins. The molecular chaperone cooperates with many co-chaperones and partner proteins to fulfill its task. In Saccharomyces cerevisiae, several co-chaperones of Hsp90 interact with Hsp90 via a tetratricopeptide repeat (TPR) domain. Here we show that one of these proteins, Cns1, binds both to Hsp90 and to the yeast Hsp70 protein Ssa1 with comparable affinities. This is reminiscent of Sti1, another TPR-containing co-chaperone. Unlike Sti1, Cns1 exhibits no influence on the ATPase of Hsp90. However, it activates the ATPase of Ssa1 up to 30-fold by accelerating the rate-limiting ATP hydrolysis step. This stimulating effect is mediated by the N-terminal TPR-containing part of Cns1, whereas the C-terminal part showed no effect. Competition experiments allow the conclusion that Hsp90 and Ssa1 compete for binding to the single TPR domain of Cns1. Taken together, Cns1 is a potent cochaperone of Ssa1. Our findings highlight the importance of the regulation of Hsp70 function in the context of the Hsp90 chaperone cycle.
Highlights
Hsp901 is an abundant molecular chaperone in the cytosol even under nonstress conditions
CD spectroscopy confirmed that Cns1 and the respective constructs are folded proteins, with a high ␣ helix content in the full-length protein (Fig. 2A and Table I) and the N-terminal construct
We show that Cns1 from S. cerevisiae is a novel tetratricopeptide repeat (TPR)-containing modulator of the yeast Hsp70 ATPase activity
Summary
Hsp901 is an abundant molecular chaperone in the cytosol even under nonstress conditions. In contrast to Hsp, which is involved in a wide variety of functions including folding of nascent polypeptide chains (4 – 6), Hsp seems to be a more specialized folding factor (6 –10) It cooperates with a still increasing number of co-chaperones. Some of these partner proteins exhibit chaperone function on their own, such as Cdc (11), the large prolyl isomerases, and p23 (12, 13) Another partner protein, Sti (stress-inducible protein 1), inhibits the ATPase of yeast Hsp as a noncompetitive inhibitor (14, 15). In contrast to other co-chaperones containing a TPR domain, Cns is essential in yeast (4, 23, 25–28). Cns fragment from amino acid 218 to 385; DTT, dithiothreitol; CS, citrate synthase; SPR, surface plasmon resonance; TPR, tetratricopeptide repeat; Ssa1-SBD, substrate-binding domain of Ssa; RU, resonance units; PPIase, peptidyl-prolyl cis/trans-isomerase; SEC, size ex-
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.
