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.

Download full-text


Available from: James Shorter
  • Source
    • "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. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Intracellular amyloid fibrils linked to neurodegenerative disease typically accumulate in an age-related manner, suggesting inherent cellular capacity for counteracting amyloid formation in early life. Metazoan molecular chaperones assist native folding and block polymerization of amyloidogenic proteins, preempting amyloid fibril formation. Chaperone capacity for amyloid disassembly, however, is unclear. Here, we show that a specific combination of human Hsp70 disaggregase-associated chaperone components efficiently disassembles alpha-synuclein amyloid fibrils characteristic of Parkinson’s disease in vitro. Specifically, the Hsc70 chaperone, the class B J-protein DNAJB1, and an Hsp110 family nucleotide exchange factor (NEF) provide ATP-dependent activity that disassembles amyloids within minutes via combined fibril fragmentation and depolymerization. This ultimately generates non-toxic alpha-synuclein monomers. Concerted, rapid interaction cycles of all three chaperone components with fibrils generate the power stroke required for disassembly. This identifies a powerful human Hsp70 disaggregase activity that efficiently disassembles amyloid fibrils and points to crucial yet undefined biology underlying amyloid-based diseases.
    Full-text · Article · Sep 2015 · Molecular cell
  • Source
    • "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]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: By virtue of their general ability to bind (hold) translocating or unfolding polypeptides otherwise doomed to aggregate, molecular chaperones are commonly dubbed "holdases". Yet, chaperones also carry physiological functions that do not necessitate prevention of aggregation, such as altering the native states of proteins, as in the disassembly of SNARE complexes and clathrin coats. To carry such physiological functions, major members of the Hsp70, Hsp110, Hsp100, and Hsp60/CCT chaperone families act as catalytic unfolding enzymes or unfoldases that drive iterative cycles of protein binding, unfolding/pulling, and release. One unfoldase chaperone may thus successively convert many misfolded or alternatively folded polypeptide substrates into transiently unfolded intermediates, which, once released, can spontaneously refold into low-affinity native products. Whereas during stress, a large excess of non-catalytic chaperones in holding mode may optimally prevent protein aggregation, after the stress, catalytic disaggregases and unfoldases may act as nanomachines that use the energy of ATP hydrolysis to repair proteins with compromised conformations. Thus, holding and catalytic unfolding chaperones can act as primary cellular defenses against the formation of early misfolded and aggregated proteotoxic conformers in order to avert or retard the onset of degenerative protein conformational diseases.
    Full-text · Article · Apr 2014 · Cellular and Molecular Life Sciences CMLS
  • Source
    • "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]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Stress-denatured or de novo synthesized and translocated unfolded polypeptides can spontaneously reach their native state without assistance of other proteins. Yet, the pathway to native folding is complex, stress-sensitive and prone to errors. Toxic misfolded and aggregated conformers may accumulate in cells and lead to degenerative diseases. Members of the canonical conserved families of molecular chaperones, Hsp100s, Hsp70/110/40s, Hsp60/CCTs, the small Hsps and probably also Hsp90s, can recognize and bind with high affinity, abnormally exposed hydrophobic surfaces on misfolded and aggregated polypeptides. Binding to Hsp100, Hsp70, Hsp110, Hsp40, Hsp60, CCTs and Trigger factor may cause partial unfolding of the misfolded polypeptide substrates, and ATP hydrolysis can induce further unfolding and release from the chaperone, leading to spontaneous refolding into native proteins with low-affinity for the chaperones. Hence, specific chaperones act as catalytic polypeptide unfolding isomerases, rerouting cytotoxic misfolded and aggregated polypeptides back onto their physiological native refolding pathway, thus averting the onset of protein conformational diseases.
    Full-text · Article · May 2013 · FEBS letters
Show more