Chaperones and Proteases of Mitochondria: From Protein Folding and Degradation to Mitophagy

Abstract

In eukaryotic cells, mitochondria fulfill a multitude of essential functions. Under both normal and stress conditions, a complex system of molecular chaperones and protease enzymes is at work to maintain mitochondrial biogenesis and protein quality control (PQC), summarized as "mitochondrial protein homeostasis." Mitochondrial chaperones of the heat shock protein Hsp60 and Hsp70 families play main roles in the import and folding of nuclear-encoded polypeptides, representing the majority of the mitochondrial proteome. These enzymes together with chaperones of the Clp family prevent the accumulation of aggregated or superfluous polypeptides in a close cooperation with specific PQC proteases of the AAA+ (adenosine triphosphatases associated with diverse cellular activities) family. Recent evidence demonstrated the removal of terminally damaged mitochondria as a whole by a variation of autophagy, termed mitophagy, as an additional level of mitochondrial quality control. The details of mitochondrial protein homeostasis, comprising the functional contribution of this broad set of chaperones and proteases will be discussed here.