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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.