Proteasomes and molecular chaperones: cellular machinery responsible for folding and destruction of unfolded proteins.

Molecular chaperones recognize proteins of non-native structure, prevent them from irreversible intracellular aggregation, and then act with regulatory co-chaperones in the conversion of proteins to be properly folded and in a functional state. However, not every non-native protein is folded successfully. Those proteins that are not accurately folded/ refolded are then directed to the ubiquitin-proteasome system (UPS) for destruction. Both chaperones and proteasomes act jointly together for selective removal of proteins with aberrant structure so as to keep protein homeostasis in cells. Though the precise nature of the cooperative linkage between chaperone and UPS pathways remains largely elusive so far, accumulating evidence from in vivo and in vitro studies shed some light on the molecular mechanisms that link proteasomes and molecular chaperones. This review focuses on how unfolded proteins are handled by these two machineries.