Quantitative NMR analysis of the mechanism and kinetics of chaperone Hsp104 action on amyloid-β42 aggregation and fibril formation

Authors

• A Ebrahim
• Z Wolfenson
• O Jean-Marie
• C Wahl
• LG Vezina
• WA Gahl
• C Toro

Abstract

Hsp104 is a unique disaggregase chaperone found in yeast, yet has been shown to function synergistically with mammalian chaperones, without displaying any overt toxicity and in turn, conferring increased stress tolerance. Additionally, Hsp104 is also the sole known chaperone to dissociate mature amyloid fibrils and help them convert back to native polypeptides. While the ability of Hsp104 to prevent and disaggregate fibrils is common knowledge, yet the pathway, mechanism, and kinetics associated with the activity still remains unanswered. To this end, I have used a combination of several biophysical techniques to probe the mechanism by which Hsp104 prevents fibrilization of amyloid β-42, which plays a central role in the onset and progression of Alzheimer's disease. Using a combination of Thioflavin T assays, nuclear magnetic resonance spectroscopic techniques, electron and atomic force microscopic techniques, we observe that Aβ42 aggregation occurs by a branching mechanism: an irreversible on-pathway leading to mature fibrils that entails primary and secondary nucleation and saturating elongation; and a reversible off-pathway to form nonfibrillar oligomers. Hsp104 binds reversibly with nanomolar affinity to sparsely populated Aβ42 nuclei, generated by primary and secondary nucleation, present in nanomolar concentrations, thereby completely inhibiting on-pathway fibril formation at substoichiometric ratios of Hsp104 to Aβ42 monomers. Hsp104 also impacts off-pathway oligomerization but to a much smaller degree, increasing the rate of off-pathway oligomerization.

Scientific Focus Area: Structural Biology

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