Small Heat Shock Proteins Potentiate Amyloid Dissolution by Protein Disaggregases from Yeast and Humans

Brandeis University, United States of America
PLoS Biology (Impact Factor: 9.34). 06/2012; 10(6):e1001346. DOI: 10.1371/journal.pbio.1001346
Source: PubMed


How small heat shock proteins (sHsps) might empower proteostasis networks to control beneficial prions or disassemble pathological amyloid is unknown. Here, we establish that yeast sHsps, Hsp26 and Hsp42, inhibit prionogenesis by the [PSI+] prion protein, Sup35, via distinct and synergistic mechanisms. Hsp42 prevents conformational rearrangements within molten oligomers that enable de novo prionogenesis and collaborates with Hsp70 to attenuate self-templating. By contrast, Hsp26 inhibits self-templating upon binding assembled prions. sHsp binding destabilizes Sup35 prions and promotes their disaggregation by Hsp104, Hsp70, and Hsp40. In yeast, Hsp26 or Hsp42 overexpression prevents [PSI+] induction, cures [PSI+], and potentiates [PSI+]-curing by Hsp104 overexpression. In vitro, sHsps enhance Hsp104-catalyzed disaggregation of pathological amyloid forms of α-synuclein and polyglutamine. Unexpectedly, in the absence of Hsp104, sHsps promote an unprecedented, gradual depolymerization of Sup35 prions by Hsp110, Hsp70, and Hsp40. This unanticipated amyloid-depolymerase activity is conserved from yeast to humans, which lack Hsp104 orthologues. A human sHsp, HspB5, stimulates depolymerization of α-synuclein amyloid by human Hsp110, Hsp70, and Hsp40. Thus, we elucidate a heretofore-unrecognized human amyloid-depolymerase system that could have applications in various neurodegenerative disorders.

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    • "NEFs then stimulate ADP release, enabling rebinding of ATP to Hsp70 with concomitant substrate release (Bukau and Horwich, 1998). However , when tested for the ability to disassemble amyloids in vitro, the human Hsp70 machinery disassembles a-Syn amyloids only slowly, over a timescale of weeks (Duennwald et al., 2012). The efficacy , and hence pathophysiological relevance, of cellular amyloid disaggregation activity therefore remains unclear. "
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    • "A systematic study of the interaction of several small Hsps (αB-crystallin, Hsp27, Hsp20, HspB8, and HspB2B3) showed that transient binding to the various forms of α-synuclein resulted in the inhibition of mature α-synuclein fibril formation [37]. Further, in vitro experiments showed that the small HSP, αB-crystallin (HspB5) can mediate the depolymerization of α-synuclein fibers with the help of other chaperones, including Hsp70 and its co-chaperones [38]. Moreover, in an in vitro system, mammalian Hsp110 can synergize Hsp70 to drive the catalytic disaggregation of α-synuclein amyloid fibrils [39]. "
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    • "But this implies that rather than preferably binding to i.e. apparently solely directed by the primary amino acid sequence. Whereas, ClpB proved to be an effective ATP-fuelled co-chaperone of DnaK at breaking down large preformed protein aggregates into soluble species that were amenable to further DnaK/DnaJ/GrpEmediated unfolding/refolding [52] [53], the Hsp110 chaperones, which are orthologous Hsp70-like proteins, are effective co-chaperones of the Hsp70s in the ATP-dependent disaggregation of large stable protein aggregates, such as stable luciferase aggregates following urea-unfolding, of a-synuclein fibrils and of aggregated polyglutamine repeats [55]. Remarkably, bacterial Hsp70 (DnaK) may also act as a catalytic polypeptide unfoldase enzyme, which can specifically bind stable misfolded luciferase monomers and, upon ATP hydrolysis, unfold them by a mechanism combining direct molecular clamping [56] and cooperative entropic pulling [20]. "
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