Heat shock protein 70 (Hsp70) is a molecular chaperone that plays a central role in protein quality control (PQC). Hsp70 is considered a "triage chaperone" because it is important in protein folding, while it also blocks aggregation and targets misfolded proteins for degradation by the ubiquitin proteasome system (UPS) and the chaperone-mediated autophagy (CMA) pathway. How does Hsp70 "decide" if a protein can be folded? What molecular and structural mechanisms link Hsp70 to the various fates of its protein substrates? These questions are essential to our understanding of how cells maintain protein homeostasis (i.e. proteostasis). Based on the findings obtained in the first funding cycle (2008-present), we have developed a model in which the dwell time of a substrate in the Hsp70 complex might be one factor that contributes to whether a protein is ultimately folded or degraded. This model emerged from experiments in which we used high throughput screening (HTS) to uncover new chemical probes that "tune" the ATPase activity of Hsp70. Using these molecules, we showed that inhibiting ATP turnover favored degradation of multiple Hsp70 substrates, such as tau and polyglutamine (polyQ) expanded huntingtin (polyQ-Htt) and androgen receptor (polyQ-AR), while stimulating activity led to substrate accumulation and proteotoxicity. Because ATP turnover in Hsp70 is allosterically linked to substrate affinity, we now hypothesize that prolonged interactions with Hsp70 may be a molecular "trigger" that favors recruitment of UPS components. In the proposed work, we will explore this idea in the following specific aims: (1) develop a suite of chemical probes and point mutants that trap Hsp70 in either its tight or loose affinity forms, (2) explore the role of substrate affinity in stabilization of te unfolded model proteins, tau and polyQ-Htt, and (3) understand how Hsp70 discriminates between normal AR and misfolded, polyQ-AR. From these studies, we expect to better understand how Hsp70 makes key triage decisions. This study is significant because Hsp70 has been linked to many protein-misfolding diseases, including neurodegenerative disorders. Thus, the proposed studies will clarify the logic of Hsp70-mediated PQC and, perhaps, suggest new methods for treating these diseases. This work is innovative because we will use a comprehensive chemical biology approach, combining new chemical probes with point mutants and cell-based models of disease to explore fundamental mechanisms of PQC.

Public Health Relevance

Neurodegenerative disorders, including Huntington's disease (HD), are devastating, progressive diseases that have no known cure. These diseases are thought to involve an imbalance in protein quality control (PQC) that allows accumulation of misfolded protein. The proposed work explores whether the heat shock protein 70 (Hsp70) could be an under-explored therapeutic target for HD and other protein misfolding diseases.

National Institute of Health (NIH)
Research Project (R01)
Project #
Application #
Study Section
Macromolecular Structure and Function B Study Section (MSFB)
Program Officer
Sutherland, Margaret L
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California San Francisco
Schools of Medicine
San Francisco
United States
Zip Code
Connarn, Jamie N; Assimon, Victoria A; Reed, Rebecca A et al. (2014) The molecular chaperone Hsp70 activates protein phosphatase 5 (PP5) by binding the tetratricopeptide repeat (TPR) domain. J Biol Chem 289:2908-17
Walter, Gladis M; Raveh, Avi; Mok, Sue-Ann et al. (2014) High-throughput screen of natural product extracts in a yeast model of polyglutamine proteotoxicity. Chem Biol Drug Des 83:440-9
Pratt, William B; Morishima, Yoshihiro; Gestwicki, Jason E et al. (2014) A model in which heat shock protein 90 targets protein-folding clefts: rationale for a new approach to neuroprotective treatment of protein folding diseases. Exp Biol Med (Maywood) 239:1405-13
Rauch, Jennifer N; Gestwicki, Jason E (2014) Binding of human nucleotide exchange factors to heat shock protein 70 (Hsp70) generates functionally distinct complexes in vitro. J Biol Chem 289:1402-14
Assimon, Victoria A; Gillies, Anne T; Rauch, Jennifer N et al. (2013) Hsp70 protein complexes as drug targets. Curr Pharm Des 19:404-17
Miyata, Yoshinari; Li, Xiaokai; Lee, Hsiu-Fang et al. (2013) Synthesis and initial evaluation of YM-08, a blood-brain barrier permeable derivative of the heat shock protein 70 (Hsp70) inhibitor MKT-077, which reduces tau levels. ACS Chem Neurosci 4:930-9
Cesa, Laura C; Patury, Srikanth; Komiyama, Tomoko et al. (2013) Inhibitors of difficult protein-protein interactions identified by high-throughput screening of multiprotein complexes. ACS Chem Biol 8:1988-97
Zuiderweg, Erik R P; Bertelsen, Eric B; Rousaki, Aikaterini et al. (2013) Allostery in the Hsp70 chaperone proteins. Top Curr Chem 328:99-153
Zuiderweg, Erik R P; Bagai, Ireena; Rossi, Paolo et al. (2013) EZ-ASSIGN, a program for exhaustive NMR chemical shift assignments of large proteins from complete or incomplete triple-resonance data. J Biomol NMR 57:179-91
Rauch, Jennifer N; Nie, Jing; Buchholz, Tonia J et al. (2013) Development of a capillary electrophoresis platform for identifying inhibitors of protein-protein interactions. Anal Chem 85:9824-31

Showing the most recent 10 out of 36 publications