Chaperoning the Chaperone: A Role for the Co-chaperone Cpr7 in Modulating Hsp90 Function in Saccharomyces cerevisiae

摘要

Heat-shock protein 90 ([Hsp90][1]) of Saccharomyces cerevisiae is an abundant essential eukaryotic molecular chaperone involved in the activation and stabilization of client proteins, including several transcription factors and oncogenic kinases. [Hsp90][1] undergoes a complex series of conformational changes and interacts with partner co-chaperones such as [Sba1][2], [Cpr6][3], [Cpr7][4], and [Cns1][5] as it binds and hydrolyzes ATP. In the absence of nucleotide, [Hsp90][1] is dimerized only at the carboxy-terminus. In the presence of ATP, [Hsp90][1] also dimerizes at the amino-terminus, creating a binding site for [Sba1][2]. Truncation of a charged linker region of yeast [Hsp90][1] ([Hsp82][1]Δlinker) was known to disrupt the ability of [Hsp82][1] to undergo amino-terminal dimerization and bind [Sba1][2]. We found that yeast expressing [Hsp82][1]Δlinker constructs exhibited a specific synthetic lethal phenotype in cells lacking [CPR7][4] . The isolated tetratricopeptide repeat domain of [Cpr7][4] was both necessary and sufficient for growth in those strains. [Cpr6][3] and [Cpr7][4] stably bound the carboxy-terminus of wild-type [Hsp82][1] only in the presence of nonhydrolyzable ATP and formed an [Hsp82][1]–[Cpr6][3]–[Cpr7][4] ternary complex. However, in cells expressing [Hsp82][1]Δlinker or lacking [CPR7][4] , [Cpr6][3] was able to bind [Hsp82][1] in the presence or absence of nucleotide. Overexpression of [CNS1][5] , but not of other co-chaperones, in [cpr7][4] cells restored nucleotide-dependent [Hsp82][1]–[Cpr6][3] interaction. Together, our results suggest that the in vivo functions of [Cpr7][4] include modulating [Hsp90][1] conformational changes, mediating proper signaling of the nucleotide-bound state to the carboxy-terminus of [Hsp82][1], or regulating [Hsp82][1]–[Cpr6][3] interaction. [1]: http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000006161 [2]: http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000001600 [3]: http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000004206 [4]: http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000003793 [5]: http://www.yeastgenome.org/cgi-bin/locus.fpl?dbid=S000000359