Aggresome formation.

Bulk protein degradation in the cell is catalyzed by the ubiquitin-proteasome system (UPS). At the heart of the UPS is the proteasome, a large multisubunit tightly-regulated protease. The UPS performs key functions in protein quality control by monitoring and eliminating potentially toxic misfolded or damaged proteins. When the capacity of this protease system is exceeded, misfolded protein substrates aggregate and are assembled through an active and regulated process to form an aggresome. Aggresomes are dynamic structures, formed as a general response to an overload of improperly folded proteins. Assembly of aggresomes occurs at the centrosome, a perinuclear structure that also serves as a site for the recruitment and concentration of components of the UPS, including the proteasome, its regulators, and other proteins typically involved in protein quality control. Thus, in addition to other cellular activities, the centrosome may play a central role in protein quality control, sitting at the crossroads of protein folding, degradation, and aggregation.