Human chaperone activity directs 𝜶-Synuclein aggregation in biomolecular condensates

Biomolecular condensates formed by protein phase separation play a key role in cellular organization and homeostasis. Condensates recruit various client proteins and alter their activity or stability. Recently, amyloidogenic proteins, such as α-synuclein (aSyn), a pre-synaptic protein associated with Parkinson’s disease, were found to accumulate at condensate interfaces, which accelerates their aggregation. Molecular chaperones are part of the protein quality control system that functions to prevent protein misfolding and aggregation. However, whether chaperones can carry out their activity in condensates remains elusive. To address this question, we investigate the effects of the human chaperones Hsp70 and Hsc70, and a cochaperone on the aggregation of aSyn in model condensates made from peptide-based complex coacervates. All exhibit high affinity for the coacervate interface, further boosted by the presence of aSyn.  Moreover, ThT assays combined with fluorescence and electron microscopy showed that the chaperones retained their function on the surface of coacervates and could act as holdases to inhibit fibrillization of aSyn in coacervates. Based on this, we infer that chaperones may play a central role in surveilling the interfacial integrity of biomolecular condensates.