In this project, we have discovered a mitochondrial error-correction mechanism, which is vital for energy production in mammals. The study, “Editing activity for eliminating mischarged tRNAs is essential in mammalian mitochondria,” was published in the journal Nucleic Acids Research in 2018. We show for the first time that this mechanisms is central for protein quality control in mitochondria. We have also extensively investigated the roles of two poorly characterized mitochondrial proteins, GRPEL1 and GRPEL2, in protein homeostasis. We have found that of these similar proteins, GRPEL1 is the essential protein required in all cells, whereas GRPEL2 is a stress-regulated counterpart (Konovalova et al. Redox Biology 2018). Importantly, we show accordingly that mice lacking GRPEL1 do not survive development but GRPEL2 has an unexpected and interesting role as a new regulator of metabolism. Mice lacking GRPEL2 have abnormally functioning brown adipose tissue, which burns fat excessively, resulting in resistance to age- ja diet-induced obesity (submitted study). Our study has revealed new mechanisms of how mitochondrial protein homeostasis is involved in tissue-specific regulation of mitochondrial functions. These results are important for understanding the tissue-specificity of mitochondrial diseases, and in modifying mitochondrial metabolism for the benefit of human health.