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Biogenesis of glutaminyl-mt tRNAGln in human mitochondria
- Nagao, Asuteka, Suzuki, Takeo, Katoh, Takayuki, Sakaguchi, Yuriko, Suzuki, Tsutomu
- Proceedings of the National Academy of Sciences of the United States of America 2009 v.106 no.38 pp. 16209-16214
- binding capacity, biogenesis, glutamate-tRNA ligase, humans, mitochondria, mitochondrial genome, nuclear genome, protein synthesis, transfer RNA, translation (genetics)
- Mammalian mitochondrial (mt) tRNAs, which are required for mitochondrial protein synthesis, are all encoded in the mitochondrial genome, while mt aminoacyl-tRNA synthetases (aaRSs) are encoded in the nuclear genome. However, no mitochondrial homolog of glutaminyl-tRNA synthetase (GlnRS) has been identified in mammalian genomes, implying that Gln-tRNAGln is synthesized via an indirect pathway in the mammalian mitochondria. We demonstrate here that human mt glutamyl-tRNA synthetase (mtGluRS) efficiently misaminoacylates mt tRNAGln to form Glu-tRNAGln. In addition, we have identified a human homolog of the Glu-tRNAGln amidotransferase, the hGatCAB heterotrimer. When any of the hGatCAB subunits were inactivated by siRNA-mediated knock down in human cells, the Glu-charged form of tRNAGln accumulated and defects in respiration could be observed. We successfully reconstituted in vitro Gln-tRNAGln formation catalyzed by the recombinant mtGluRS and hGatCAB. The misaminoacylated form of tRNAGln has a weak binding affinity to the mt elongation factor Tu (mtEF-Tu), indicating that the misaminoacylated form of tRNAGln is rejected from the translational apparatus to maintain the accuracy of mitochondrial protein synthesis.