Uncovering a region of heat shock protein 90 important for client binding in E. coli and chaperone function in yeast

The heat shock protein 90 (Hsp90) family of heat shock proteins is an abundantly expressed and highly conserved family of ATP-dependent molecular chaperones. Hsp90 facilitates remodeling and activation of hundreds of proteins. In this study, we developed a screen to identify Hsp90-defective mutants in E. coli. The mutations obtained define a region incorporating residues from the middle and C-terminal domains of E. coli Hsp90. The mutant proteins are defective in chaperone activity and client binding in vitro. We constructed homologous mutations in S. cerevisiae Hsp82 and identified several that caused defects in chaperone activity in vivo and in vitro. However, the Hsp82 mutant proteins were less severely defective in client binding to a model substrate than the corresponding E. coli mutant proteins. Our results identify a region in Hsp90 important for client binding in E. coli Hsp90 and suggest an evolutionary divergence in the mechanism of client interaction by bacterial and yeast Hsp90.