In a study published in Nucleic Acids Res, the team led by Prof. ZHOU Xiaolong and Prof. WANG Enduo from the Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology of the Chinese Academy of Sciences reported that N6-threonylcarbamoyladenosine at A37 (t6A37) in mitochondrial (mt) transfer RNAs (tRNAs) regulates mitochondrial translation speed and accuracy.
tRNAs have the most abundant post-transcriptional modifications, which are crucial for tRNA function and structure. t6A modification is a highly conserved modification, which is harbored in almost all ANN-decoding tRNAs at position 37. A previous work by this team has revealed the biochemical basis of t6A modification catalyzed by OSGEPL1. However, the roles of t6A modification in mammalian mitochondrial translation are still unclear.
In this study, the researchers constructed the OSGEPL1 knock out cell line in HEK293T. They found that deficiency of t6A modification specifically upregulated the level of N1-methyladenosine at A9 (m1A9) and N2-methylguanosine at G10 (m2G10) modifications in mt-tRNAThr and mt-tRNALys. The hypomodification of t6A also caused the reduction of aminoacylation in mt-tRNAThr and mt-tRNALys. The researchers further isolated the supercomplex of oxidative phosphorylation complex and analyzed the translational fidelity by the LC-MS/MS, which showed that t6A hypomodification caused the infidelity of mitochondrial translation due to the mispairing between U36 and the first position of near-cognate codons. The reduction in mitochondrial translation efficiency and fidelity caused the decrease of OXPHOS activity and change in mitochondrial structure in KO cells, accompanied with an activated mitochondrial unfold protein response. Moreover, the researchers constructed the Osgepl1 knock out mouse. They found that expression of mitochondrial DNA-encoded Mt-cox2 and Mt-cox3 in the cardiac of KO mice was significantly decreased. However, these changes influenced neither mitochondrial function nor the life span of KO mice in physical conditions.
This study found the crosstalk between t6A37 and m1A9, m2G10 biogenesis in mitochondrial tRNAs; systematically revealed the effects of t6A modification on mt-tRNA aminoacylation and elucidated the mechanism of mitochondrial translation infidelity caused by the deficiency of t6A modification. All these results significantly advanced our understanding of the biological function of mitochondrial tRNA modifications.