UCSF

Heat Shock Protein 90 (Hsp90) is a highly conserved molecular chaperone necessary for eukaryotic life. This member of the cellular folding machinery has been extensively studied in recent years due to its intimate link to fundamental biological pathways that govern cellular homeostasis and disease.

Hsp90 undergoes large ATP dependant conformational changes that are necessary for client maturation in vivo. Though much progress had been made in building a model for a functional cycle of Hsp90, the fundamental question of how Hsp90 functions to re-model clients remained unclear.

Several forms of Hsp90 can be found throughout evolution with most higher eukaryotes having four homologs: two in the cytosol (Hsp90α, Hsp90β), one in the endoplasmic reticulum (GRP94) and one in the mitochondria (TRAP1).

Though not extensively studied at the time, I set out to investigate the structure and function of TRAP1, originally inspired by the balance between a higher eukaryotic Hsp90 and a simplified Hsp90 being most similar to the bacterial Hsp90 (bHsp90). With the latter comes the advantage of a more simple system where the large number of cochaperones identified for Hsp90α/β are not known to be required for client interactions with TRAP. Further, unique biology and disease links of TRAP1 were emerging with in vivo data showing that TRAP1 had unique ties to cellular homeostasis through interactions with client protein cyclophilin D (CypD), the master regulator of the mitochondrial permeability transition pore (mtPTP) and thus necrotic cell death.

Through this work I developed several biochemical/biophysical assays and strategies for working with TRAP1 in vitro, and through collaboration elucidated both shared and unique aspects of Hsp90 mechanism. Importantly, this work has provided a new hypothesis for Hsp90 mechanism of action with client proteins, which contributes a new model for the productive use of ATP hydrolysis for client re-modeling.