Chaperones and proteases--guardians of protein integrity in eukaryotic organelles.

Organelles like mitochondria, chloroplasts, or the endoplasmic reticulum are essential subcompartments of eukaryotic cells that fulfill important metabolic tasks. Organellar protein homeostasis is maintained by a combination of specific protein biogenesis processes and protein quality control (PQC) mechanisms that together guarantee the functional state of the organelle. According to their endosymbiontic origin, mitochondria and chloroplasts contain internal PQC systems that consist of a cooperative network of molecular chaperones and proteases. In contrast, the endoplasmic reticulum employs the main cytosolic degradation machinery, the proteasome, for the removal of damaged or misfolded proteins. Here we present and discuss recent experimental insights into the molecular mechanisms underlying organellar PQC processes.