Assembly chaperone Nas6 selectively destabilizes 26S proteasomes with defective regulatory particle-core particle interfaces

The 26S proteasome is a 66-subunit-chambered protease present in all eukaryotes that maintains organismal health by degrading unneeded or defective proteins. Defects in protea-some function or assembly are known to contribute to the development of various cancers, neurodegeneration, and dia-betes. During proteasome biogenesis, a family of evolutionarily conserved chaperones assembles a hexameric ring of AAA+ family ATPase subunits contained within the proteasomal regulatory particle (RP) and guide their docking onto the sur-face of the proteolytic core particle (CP). This RP-CP inter-action couples the substrate capture and unfolding process to proteolysis. We previously reported a mutation in the protea-some that promoted dissociation of the RP and CP by one of these chaperones, Nas6. However, the nature of the signal for Nas6-dependent proteasome disassembly and the generality of this postassembly proteasome quality control function for Nas6 remain unknown. Here, we use structure-guided mutagenesis and in vitro proteasome disassembly assays to demonstrate that Nas6 more broadly destabilizes 26S proteasomes with a defective RP-CP interface. We show that Nas6 can promote dissociation of mature proteasomes into RP and CP in cells harboring defects on either side of the RP-CP interface. This function is unique to Nas6 and independent from other known RP assembly chaperones. Further biochemical experiments suggest that Nas6 may exploit a weakened RP-CP interface to dissociate the RP from the CP. We propose that this post -assembly role of Nas6 may fulfill a quality control function in cells by promoting the recycling of functional subcomplexes contained within defective proteasomes.

Automated summary

The 26S proteasome is a protease that degrades unneeded or defective proteins in eukaryotes. The chaperone Nas6 can promote the dissociation of mature proteasomes into regulatory particle (RP) and core particle (CP) in cells with defects on either side of the RP-CP interface. This function of Nas6 may play a quality control role by promoting the recycling of functional subcomplexes in defective proteasomes.