Hsp90 directly interacts, in vitro, with amyloid structures and modulates their assembly and disassembly.

BACKGROUND: The 90kDa heat shock protein (Hsp90) participates in regulating the homeostasis of cellular proteins and was considered one of the key chaperones involved in the control and regulation of amyloid deposits. Hsp90 interacts with the amyloid protein tau through tau aggregation-prone regions, including the VQIVYK hexapeptide motif. This hexapeptide, which self-aggregates, forming amyloid fibrils, is widely used to model amyloid formation mechanisms. Despite evidence showing that Hsp90 interacts directly with Ac-VQIVYK-NH2, its role in the hexapeptide fibrillation process and its binding to peptide structures have not yet been determined. METHODS: Various biochemical and biophysical techniques, including ultracentrifugation, spectrophotometry, spectrofluorimetry, and electron microscopy, were employed to assess the effects of Hsp90 on Ac-VQIVYK-NH2 assembly and disassembly processes. RESULTS: At sub-stoichiometric concentrations, Hsp90 bound directly to Ac-VQIVYK-NH2 amyloid structures in vitro, with each Hsp90 dimer interacting with an amyloid structure made of around 50 hexapeptide subunits. Hsp90 inhibited Ac-VQIVYK-NH2 assembly by increasing the critical concentrations of Ac-VQIVYK-NH2 required for assembly. Hsp90 also inhibited the disassembly of Ac-VQIVYK-NH2 amyloid fibrils and promoted their rescue. CONCLUSIONS: A model explaining the dual effect of Hsp90 on the Ac-VQIVYK-NH2 amyloid fibrillation process has been proposed. GENERAL SIGNIFICANCE: These in vitro results provide new insights into the possible roles of molecular chaperones in modulating amyloid structures by limiting the spread of toxic species.