Endogenous TOM20 proximity labelling: a Swiss-knife for the study of mitochondrial proteins in human cells

The majority of mitochondrial proteins are encoded by the nuclear genome and must be imported into the mitochondria. There are two main paths for mitochondrial protein import: post-translational and co-translational import. Co-translational import couples the translation and the translocation of the mitochondrial proteins, alleviating the energy cost typically associated with the post-translational import relying on chaperone systems. The mitochondrial co-translational import mechanisms are still unclear with few actors identified but none have been described in mammals yet. We thus profiled the TOM20 proxisome using BioID, assuming that some of identified proteins could be molecular actors of the co-translational import in human cells. The obtained results showed a high enrichment of RNA binding proteins close to the TOM complex. However, for the few selected candidates, we could not demonstrate a role in the mitochondrial co-translational import process. Nonetheless, we were able to demonstrate a new mitochondrial localization for nuclear proteins. Besides, additional analyses revealed a negative correlation between the abundance of mitochondrial proteins and their reported half-life. This experimental approach is thus proposed to potentially characterize mitochondrial co-translational import effectors in human cells and to monitor protein entry inside mitochondria with a potential application in the prediction of mitochondrial protein half-life.