The Disaggregation Activity of the Mitochondrial ClpB Homolog Hsp78 Maintains Hsp70 Function during Heat Stress

Janowsky, Birgit von; Major, Tamara; Knapp, Karin; Voos, Wolfgang

doi:10.1016/j.jmb.2006.01.008

Cited by 46 publications

(40 citation statements)

References 60 publications

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“…6A) (30). In fact, disaggregation of aggregated mtHsp70 required the mitochondrial ClpB homolog HSP78 (43). Secondly, and most importantly, some HSP70B expressed with an N-terminal intein/chitin binding domain was reproducibly converted to the active, CGE1-binding competent state when purified HEP2 was present during thiol-induced cleavage of the fusion protein (Fig.…”

Section: Discussionmentioning

confidence: 97%

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Willmund

Hinnenberger

Nick

et al. 2008

Journal of Biological Chemistry

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Previous efforts aimed at the biochemical characterization of chloroplast HSP70B were hampered by the observation that recombinant HSP70B was inactive, i.e. incompetent of interacting with its nucleotide exchange factor CGE1. In addition, because heterologously expressed mitochondrial Hsp70 was inactive unless coexpressed with the escort protein Hep1, we wondered whether homologs of Hep1 existed in the chloroplast. Data base searches revealed that algae and higher plants indeed encode at least two HEP homologs, one predicted to be targeted to mitochondria, the others to chloroplasts. Using Chlamydomonas reinhardtii as plant model organism we demonstrate that this alga encodes an HEP homolog (termed HEP2) that is localized to the stroma. HEP2 is expressed constitutively as a low abundance protein with an apparent molecular mass of ϳ21 kDa. In cell extracts HEP2 interacts with HSP70B in an ATP-dependent fashion. Coexpression of HSP70B with HEP2 in Escherichia coli yielded high levels of CGE1-binding competent HSP70B, which also displayed ATPase activity. Inactive HSP70B was more prone to proteolysis than active HSP70B. Although inactive HSP70B interacted with HEP2, it could not be activated. Active HSP70B remained active for 48 h in the absence of HEP2, suggesting that HEP2 was not involved in maintaining HSP70B in an active state. However, some HSP70B expressed as a fusion protein with an N-terminal extension was activated when HEP2 was present during cleavage of the fusion protein, suggesting that in vivo HEP2 might be required for de novo folding of HSP70B after transit peptide cleavage.

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Section: Discussionmentioning

confidence: 97%

Assistance for a Chaperone

Willmund

Hinnenberger

Nick

et al. 2008

Journal of Biological Chemistry

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“…ssc1-3 hsp78⌬ and ssc1-2 hsp78⌬ mutant strains also exhibit impaired protein import at the nonpermissive temperature. Conversely, the overexpression of Hsp78 in ssc1-3 cells substantially improves import activity, suggesting that Hsp78 can at least partially complement the functional roles played by Ssc1 (486). Interestingly, Ssc1 itself is subject to misfolding during stress, and Hsp78 is required for its resolubilization (486).…”

Section: Hsp78 the Mitochondrial Disaggregasementioning

confidence: 99%

“…Conversely, the overexpression of Hsp78 in ssc1-3 cells substantially improves import activity, suggesting that Hsp78 can at least partially complement the functional roles played by Ssc1 (486). Interestingly, Ssc1 itself is subject to misfolding during stress, and Hsp78 is required for its resolubilization (486). Therefore, it is possible that a major role of Hsp78 with regard to thermotolerance is to maintain Ssc1 in a soluble and functional state under stress conditions.…”

Section: Hsp78 the Mitochondrial Disaggregasementioning

confidence: 99%

Biology of the Heat Shock Response and Protein Chaperones: Budding Yeast (Saccharomyces cerevisiae) as a Model System

Verghese

Abrams

Wang

et al. 2012

Microbiol Mol Biol Rev

504

410

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SUMMARY The eukaryotic heat shock response is an ancient and highly conserved transcriptional program that results in the immediate synthesis of a battery of cytoprotective genes in the presence of thermal and other environmental stresses. Many of these genes encode molecular chaperones, powerful protein remodelers with the capacity to shield, fold, or unfold substrates in a context-dependent manner. The budding yeast Saccharomyces cerevisiae continues to be an invaluable model for driving the discovery of regulatory features of this fundamental stress response. In addition, budding yeast has been an outstanding model system to elucidate the cell biology of protein chaperones and their organization into functional networks. In this review, we evaluate our understanding of the multifaceted response to heat shock. In addition, the chaperone complement of the cytosol is compared to those of mitochondria and the endoplasmic reticulum, organelles with their own unique protein homeostasis milieus. Finally, we examine recent advances in the understanding of the roles of protein chaperones and the heat shock response in pathogenic fungi, which is being accelerated by the wealth of information gained for budding yeast.

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“…Thus, in the yeast cytoplasm, a large number of Hsp70-Hsp40 can collaborate with the ClpB-like (Hsp104) disaggregating co-chaperone to prevent the formation of misfolded species and even solubilizeresistant prions. Similarly, yeast mitochondria can use the unfolding abilities of Ssc1, which together with Mdj1 can collaborate with the ClpB homologue, Hsp78, at the active unfolding and disaggregation of potentially toxic misfolded protein conformers (von Janowsky et al 2006).…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Reactivation of protein aggregates by mortalin and Tid1—the human mitochondrial Hsp70 chaperone system

Iosefson

Sharon

Goloubinoff

et al. 2012

Cell Stress and Chaperones

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The mitochondrial 70-kDa heat shock protein (mtHsp70), also known in humans as mortalin, is a central component of the mitochondrial protein import motor and plays a key role in the folding of matrix-localized mitochondrial proteins. MtHsp70 is assisted by a member of the 40-kDa heat shock protein co-chaperone family named Tid1 and a nucleotide exchange factor. Whereas, yeast mtHsp70 has been extensively studied in the context of protein import in the mitochondria, and the bacterial 70-kDa heat shock protein was recently shown to act as an ATP-fuelled unfolding enzyme capable of detoxifying stably misfolded polypeptides into harmless natively refolded proteins, little is known about the molecular functions of the human mortalin in protein homeostasis. Here, we developed novel and efficient purification protocols for mortalin and the two spliced versions of Tid1, Tid1-S, and Tid1-L and showed that mortalin can mediate the in vitro ATP-dependent reactivation of stable-preformed heat-denatured model aggregates, with the assistance of Mge1 and either Tid1-L or Tid1-S co-chaperones or yeast Mdj1. Thus, in addition of being a central component of the protein import machinery, human mortalin together with Tid1, may serve as a protein disaggregating machine which, for lack of Hsp100/ClpB disaggregating co-chaperones, may carry alone the scavenging of toxic protein aggregates in stressed, diseased, or aging human mitochondria.

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The Disaggregation Activity of the Mitochondrial ClpB Homolog Hsp78 Maintains Hsp70 Function during Heat Stress

Cited by 46 publications

References 60 publications

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Biology of the Heat Shock Response and Protein Chaperones: Budding Yeast (Saccharomyces cerevisiae) as a Model System

Reactivation of protein aggregates by mortalin and Tid1—the human mitochondrial Hsp70 chaperone system

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