Cooperative Amyloid Fibre Binding and Disassembly by the Hsp70 disaggregase

Summary Although amyloid fibres are highly stable protein aggregates, a specific combination of human Hsp70 system chaperones can disassemble them, including fibres formed of α-synuclein, huntingtin or Tau. Disaggregation requires the ATPase activity of the constitutively expressed Hsp70, Hsc70, together with the J domain protein DNAJB1 and the nucleotide exchange factor Apg2. Recruitment and clustering of Hsc70 on the fibrils appear to be necessary for disassembly. Here we use atomic force microscopy (AFM) to show that segments of in vitro assembled α-synuclein fibrils are first coated with chaperones and then undergo bursts of rapid, unidirectional disassembly. Cryo-electron tomography reveals fibrils with regions of densely bound chaperones extending from the fibre surface, preferentially at one end of the fibre. Sub-stoichiometric amounts of Apg2 relative to Hsc70 dramatically increase recruitment of Hsc70 to the fibres, creating localised active zones that then undergo rapid disassembly at a rate of ∼4 subunits per second.