Hsp110 Chaperones Control Client Fate Determination in the Hsp70–Hsp90 Chaperone System

Heat shock protein 70 (Hsp70) plays a central role in protein homeostasis and quality control in conjunction with other chaperone machines, including Hsp90. The Hsp110 chaperone Sse1 promotes Hsp90 activity in yeast, and functions as a nucleotide exchange factor (NEF) for cytosolic Hsp70, but the precise roles Sse1 plays in client maturation through the Hsp70–Hsp90 chaperone system are not fully understood. We find that upon pharmacological inhibition of Hsp90, a model protein kinase, Ste11ΔN, is rapidly degraded, whereas heterologously expressed glucocorticoid receptor (GR) remains stable. Hsp70 binding and nucleotide exchange by Sse1 was required for GR maturation and signaling through endogenous Ste11, as well as to promote Ste11ΔN degradation. Overexpression of another functional NEF partially compensated for loss of Sse1, whereas the paralog Sse2 fully restored GR maturation and Ste11ΔN degradation. Sse1 was required for ubiquitinylation of Ste11ΔN upon Hsp90 inhibition, providing a mechanistic explanation for its role in substrate degradation. Sse1/2 copurified with Hsp70 and other proteins comprising the “early-stage” Hsp90 complex, and was absent from “late-stage” Hsp90 complexes characterized by the presence of Sba1/p23. These findings support a model in which Hsp110 chaperones contribute significantly to the decision made by Hsp70 to fold or degrade a client protein.

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Roles of the nucleotide exchange factor and chaperone Hsp110 in cellular proteostasis and diseases of protein misfolding

Biological Chemistry ◽

10.1515/hsz-2018-0209 ◽

2018 ◽

Vol 399 (10) ◽

pp. 1215-1221 ◽

Cited By ~ 7

Author(s):

Unekwu M. Yakubu ◽

Kevin A. Morano

Keyword(s):

Heat Shock ◽

Heat Shock Protein ◽

Molecular Chaperones ◽

Protein Misfolding ◽

Recent Progress ◽

Cellular Protein ◽

Protein Homeostasis ◽

Nucleotide Exchange ◽

Exchange Factor ◽

Nucleotide Exchange Factor

Abstract Cellular protein homeostasis (proteostasis) is maintained by a broad network of proteins involved in synthesis, folding, triage, repair and degradation. Chief among these are molecular chaperones and their cofactors that act as powerful protein remodelers. The growing realization that many human pathologies are fundamentally diseases of protein misfolding (proteopathies) has generated interest in understanding how the proteostasis network impacts onset and progression of these diseases. In this minireview, we highlight recent progress in understanding the enigmatic Hsp110 class of heat shock protein that acts as both a potent nucleotide exchange factor to regulate activity of the foldase Hsp70, and as a passive chaperone capable of recognizing and binding cellular substrates on its own, and its integration into the proteostasis network.

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Disassembly of Tau fibrils by the human Hsp70 disaggregation machinery generates small seeding-competent species

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.013478 ◽

2020 ◽

Vol 295 (28) ◽

pp. 9676-9690 ◽

Cited By ~ 8

Author(s):

Eliana Nachman ◽

Anne S. Wentink ◽

Karine Madiona ◽

Luc Bousset ◽

Taxiarchis Katsinelos ◽

...

Keyword(s):

Protein Homeostasis ◽

Nucleotide Exchange ◽

Cell Culture Model ◽

Nucleotide Exchange Factor ◽

Culture Model ◽

Class B ◽

The Cost ◽

Human Hsp70 ◽

Tau Fibrils

The accumulation of amyloid Tau aggregates is implicated in Alzheimer's disease (AD) and other tauopathies. Molecular chaperones are known to maintain protein homeostasis. Here, we show that an ATP-dependent human chaperone system disassembles Tau fibrils in vitro. We found that this function is mediated by the core chaperone HSC70, assisted by specific cochaperones, in particular class B J-domain proteins and a heat shock protein 110 (Hsp110)-type nucleotide exchange factor (NEF). The Hsp70 disaggregation machinery processed recombinant fibrils assembled from all six Tau isoforms as well as Sarkosyl-resistant Tau aggregates extracted from cell cultures and human AD brain tissues, demonstrating the ability of the Hsp70 machinery to recognize a broad range of Tau aggregates. However, the chaperone activity released monomeric and small oligomeric Tau species, which induced the aggregation of self-propagating Tau conformers in a Tau cell culture model. We conclude that the activity of the Hsp70 disaggregation machinery is a double-edged sword, as it eliminates Tau amyloids at the cost of generating new seeds.

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Deconstruction of the Ras switching cycle through saturation mutagenesis

eLife ◽

10.7554/elife.27810 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 38

Author(s):

Pradeep Bandaru ◽

Neel H Shah ◽

Moitrayee Bhattacharyya ◽

John P Barton ◽

Yasushi Kondo ◽

...

Keyword(s):

Mechanistic Explanation ◽

Biochemical Network ◽

Saturation Mutagenesis ◽

Evolutionary Analysis ◽

Nucleotide Exchange ◽

Ras Proteins ◽

Vertebrate Lineage ◽

Activating Mutations ◽

Nucleotide Exchange Factor ◽

High Conservation

Ras proteins are highly conserved signaling molecules that exhibit regulated, nucleotide-dependent switching between active and inactive states. The high conservation of Ras requires mechanistic explanation, especially given the general mutational tolerance of proteins. Here, we use deep mutational scanning, biochemical analysis and molecular simulations to understand constraints on Ras sequence. Ras exhibits global sensitivity to mutation when regulated by a GTPase activating protein and a nucleotide exchange factor. Removing the regulators shifts the distribution of mutational effects to be largely neutral, and reveals hotspots of activating mutations in residues that restrain Ras dynamics and promote the inactive state. Evolutionary analysis, combined with structural and mutational data, argue that Ras has co-evolved with its regulators in the vertebrate lineage. Overall, our results show that sequence conservation in Ras depends strongly on the biochemical network in which it operates, providing a framework for understanding the origin of global selection pressures on proteins.

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Hsp90 Quaternary Structures and the Chaperone Cycle: Highly Flexible Dimeric and Oligomeric Structures and Their Regulation by Co-Chaperones

Current Proteomics ◽

10.2174/1570164615666180522095147 ◽

2018 ◽

Vol 16 (1) ◽

pp. 5-11

Author(s):

Eléonore Lepvrier ◽

Daniel Thomas ◽

Cyrille Garnier

Keyword(s):

Conformational Changes ◽

Client Protein ◽

Key Players ◽

Hsp90 Activity ◽

Hsp90 Chaperone ◽

Client Proteins ◽

Quaternary Structures ◽

Chaperone Interactions ◽

High Flexibility ◽

Future Work

Proposed models of the function of Hsp90 are characterised by high flexibility of the dimeric state and conformational changes regulated by both nucleotide binding and hydrolysis, and by co-chaperone interactions. In addition to its dimeric state, Hsp90 self-associates upon particular stimuli. The Hsp90 dimer is the building block up to the hexamer that we named “cosy nest”, and the dodecamer results from the association of two hexamers. Oligomers exhibit chaperone activity, but their exact mechanism of action has not yet been determined. One of the best ways to elucidate how oligomers might operate is to study their interactions with co-chaperone proteins known to regulate the Hsp90 chaperone cycle, such as p23 and Aha1. In this review, we summarise recent results and conclude that Hsp90 oligomers are key players in the chaperone cycle. Crucible-shaped quaternary structures likely provide an ideal environment for client protein accommodation and folding, as is the case for other Hsp families. Confirmation of the involvement of Hsp90 oligomers in the chaperone cycle and a better understanding of their functionality will allow us to address some of the more enigmatic aspects of Hsp90 activity. Utilising this knowledge, future work will highlight how Hsp90 oligomers and co-chaperones cooperate to build the structures required to fold or refold numerous different client proteins.

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