Energy conversion of E. coli Hsp90 and yeast Hsp90
Final Report Abstract
The molecular chaperone Hsp90 is one of the most abundant proteins in unstressed eukaryotic cells. Hsp90 is involved in the folding and stabilization of several key regulatory proteins such as the tumor suppressor factor p53, stereoid hormone receptor and kinases. Its function is dependent on ATP binding and ATP hydrolysis. In the previous proposal, we developed the methodology to observe conformational changes of single yeast Hsp90 (yHsp90) molecules in real time. In addition, a single molecule triple FRET assay allowed us to correlate nucleotide binding with the large conformational changes of yHsp90. Here we successfully extended these studies in two directions. First, the yHsp90 system was compared to the E.coli Hsp90 (HtpG) system. We could show that the reaction cycle of HtpG is driven by a mechanical ratchet mechanism. This is in strong contrast to yHsp90, which is driven by thermal fluctuations. Therefore, we believe that the Hsp90 machinery has developed to a more flexible and less nucleotidecontrolled system during evolution. Second, we investigated the control of yHsp90 by cochaperones. Here we could reveal that the cochaperone p23 strengthens the coupling between ATP hydrolysis and the kinetic steps involved in the yHsp90 system, which results in a stronger directionality. Currently, we extend these studies to other cochaperones and client proteins in the framework of an ERC consolidator grant. We are convinced that such single molecule studies are not only important to understand the Hsp90 system, but also to gain molecular insights into ATP driven multi-component interactions in general.
Publications
- Four-colour FRET reveals directionality in the Hsp90 multicomponent machinery. Nature Communications 5:4192 (2014)
C. Ratzke, B. Hellenkamp, T. Hugel
(See online at https://doi.org/10.1038/ncomms5192)
