Hsp90: A means to an end.

The Hsp90 molecular chaperone is a key component of the protein homeostasis (proteostasis) system. Hsp90 likely serves as a gatekeeper in a cell's protein quality control decision tree since this chaperone is linked to nascent polypeptide folding, client maturation, metastable protein maintenance, and polypeptide degradation. Interestingly, how a client protein is directed through the decision process is unclear. Minimally, modifications to the amino-terminal ATP-binding domain of Hsp90 can favor client degradation. As this includes a common class of Hsp90 inhibitors that trigger the breakdown of clinically relevant factors, a better understanding of Hsp90's role in quality control is merited. Here, we explore how Hsp90 links to both polypeptide biogenesis and triage, the events that regulate the decision route, and how Hsp90's connections to proteolysis pathways are being exploited for the development of new therapeutics.