Import of mitochondrial precursor proteins into mitochondria of semi-intact yeast cells.

Mitochondria import hundreds of different precursor proteins from the cytosol and direct each of these to its specific mitochondrial subcompartment. The import routes and mechanisms by which precursors are transported into the outer membrane, the intermembrane space (IMS), the inner membrane and the matrix have been characterized in depth by use of very powerful in vitro assays. In the 'classical' import assays, radiolabeled precursor proteins are incubated with isolated mitochondria and the protein uptake is monitored by one or more of the following observations: intramitochondrial processing, resistance to externally added proteases, or the formation of disulfide bonds.

The ER-SURF pathway uses ER-mitochondria contact sites for protein targeting to mitochondria.

Most mitochondrial proteins are synthesized on cytosolic ribosomes and imported into mitochondria in a post-translational reaction. Mitochondrial precursor proteins which use the ER-SURF pathway employ the surface of the endoplasmic reticulum (ER) as an important sorting platform. How they reach the mitochondrial import machinery from the ER is not known.

The Orf9b protein of SARS-CoV-2 modulates mitochondrial protein biogenesis.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) expresses high amounts of the protein Orf9b to target the mitochondrial outer membrane protein Tom70. Tom70 serves as an import receptor for mitochondrial precursors and, independently of this function, is critical for the cellular antiviral response. Previous studies suggested that Orf9b interferes with Tom70-mediated antiviral signaling, but its implication for mitochondrial biogenesis is unknown.

The metabolite-controlled ubiquitin conjugase Ubc8 promotes mitochondrial protein import.

Mitochondria play a key role in cellular energy metabolism. Transitions between glycolytic and respiratory conditions induce considerable adaptations of the cellular proteome. These metabolism-dependent changes are particularly pronounced for the protein composition of mitochondria.

The chaperone-binding activity of the mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress.

Most mitochondrial proteins are synthesized as precursors in the cytosol and post-translationally transported into mitochondria. The mitochondrial surface protein Tom70 acts at the interface of the cytosol and mitochondria. In vitro import experiments identified Tom70 as targeting receptor, particularly for hydrophobic carriers.