Mitochondrial Protein SLIRP Affects Biosynthesis of Cytochrome c Oxidase Subunits in HEK293T Cells.

Mitochondria carry out various vital roles in eukaryotic cells, including ATP energy synthesis, the regulation of apoptosis, Fe-S cluster formation, and the metabolism of fatty acids, amino acids, and nucleotides. Throughout evolution, mitochondria lost most of their ancestor's genome but kept the replication, transcription, and translation machinery. Protein biosynthesis in mitochondria is specialized in the production of highly hydrophobic proteins encoded by mitochondria. These proteins are components of oxidative phosphorylation chain complexes. The coordination of protein synthesis must be precise to ensure the correct assembly of nuclear-encoded subunits for these complexes. However, the regulatory mechanisms of mitochondrial translation in human cells are not yet fully understood. In this study, we examined the contribution of the SLIRP protein in regulating protein biosynthesis in mitochondria. Using a click-chemistry approach, we discovered that deletion of the SLIRP gene disturbs mitochondrial translation, leading to the dysfunction of complexes I and IV, but it has no significant effect on complexes III and V. We have shown that this protein interacts only with the small subunit of the mitochondrial ribosome, which may indicate its involvement in the regulation of the mitochondrial translation initiation stage.

Pentatricopeptide Protein PTCD2 Regulates COIII Translation in Mitochondria of the HeLa Cell Line.

Protein biosynthesis in mitochondria is tightly coupled with assembly of inner membrane complexes and therefore must be coordinated with cytosolic translation of the mRNAs corresponding to the subunits which are encoded in the nucleus. Molecular mechanisms underlying the regulation of mitochondrial translation remain unclear despite recent advances in structural biology. Until now, only one translational regulator of protein biosynthesis in mammalian mitochondria is known-protein TACO1, which regulates translation of COI mRNA. Here we describe the function of pentatricopeptide-containing protein PTCD2 as a translational regulator of another mitochondrially encoded subunit of cytochrome c oxidase-COIII in the HeLa cell line. Deletion of the PTCD2 gene leads to significant decrease in COIII translation efficiency and impairment in CIV activity. Additionally, we show that PTCD2 protein is partially co-sedimentates with associated mitochondrial ribosome and associates with mitochondrial ribosome proteins in pull-down assays. These data allow concluding that PTCD2 is a specific translational regulator of COIII which attracts the mRNA to the mitochondrial ribosome.