Oligomeric assembly is required for chaperone activity of the filamentous γ-prefoldin

Prefoldins (PFDs) are molecular chaperones with a distinctive jellyfish-shape that have a general role in denovo protein folding in Archaea and in the biogenesis of cytoskeleton proteins in eukaryotes. In general, PFDs are hetero-hexameric protein assemblies consisting of two and four subunits. However, a PFD variant called gamma-prefoldin (PFD), isolated from the hyperthermophilic archaeon Methanocaldococcusjannaschii, exhibits a unique filamentous structure that is composed of hundreds of monomeric subunits. In this study, we investigated the relationship between the morphology of the PFD filament and its ability to prevent protein aggregation. A chaperone assay demonstrated that PFD must be in a filamentous assembly for functional activity and the distal regions of the coiled-coils are required for binding of non-native proteins. Molecular dynamic simulations were used to model the interactions between insilico thermally denatured protein substrates and the coiled-coils of a PFD filament. During molecular dynamic simulations at 300 and 353K, each coiled-coil was highly flexible, enabling it to widen the central cavity of the filament to potentially capture various non-native proteins. Docking molecular dynamic simulations of PFD filaments with unfolded citrate synthase or insulin showed a size-dependence between the substrate and the number of interacting coiled-coils. To confirm this observation, we generated filaments containing specific numbers of subunits, and showed that between six and eight PFD subunits are required for chaperone activity to prevent citrate synthase from thermal aggregation. These results provide insights into structure-function relationships of oligomeric chaperones and illuminate the potential role of PFD in its native environment.