Dual-targeted tRNA-dependent amidotransferase ensures both mitochondrial and chloroplastic Gln-tRNA ^Gln synthesis in plants

Abstract

Aminoacyl-tRNAs are generally formed by direct attachment of an amino acid to tRNAs by aminoacyl-tRNA synthetases, but Gln-tRNA is an exception to this rule. Gln-tRNA Gln is formed by this direct pathway in the eukaryotic cytosol and in protists or fungi mitochondria but is formed by an indirect transamidation pathway in most of bacteria, archaea, and chloroplasts. We show here that the formation of Gln-tRNA Gln is also achieved by the indirect pathway in plant mitochondria. The mitochondrial-encoded tRNA Gln , which is the only tRNA Gln present in mitochondria, is first charged with glutamate by a nondiscriminating GluRS, then is converted into Gln-tRNA Gln by a tRNA-dependent amidotransferase (AdT). The three subunits GatA, GatB, and GatC are imported into mitochondria and assemble into a functional GatCAB AdT. Moreover, the mitochondrial pathway of Gln-tRNA Gln formation is shared with chloroplasts as both the GluRS, and the three AdT subunits are dual-imported into mitochondria and chloroplasts.amidation ͉ aminoacylation ͉ GatCAB ͉ glutamyl-tRNA synthetase ͉ protein trafficking

Biogenesis of glutaminyl-mt tRNA Gln in human mitochondria

“…This discrepancy was solved by the finding that cyto GluRS is imported in mitochondria and glutamylates mt tRNA Gln , which is then subjected to Gln-tRNA Gln formation by GatFAB (9). In plants, mitochondrial Gln-tRNA Gln formation is achieved by the indirect pathway mediated by ND-GluRS and a GatCAB-type Glu-AdT, and both of these enzymes are also imported into chloroplasts (11). Therefore, the dual-targeted ND-GluRS and Glu-AdT ensure both mitochondrial and chloroplastic GlntRNA Gln formation in plants.…”

“…GatF is a fungi-specific subunit of Glu-AdT. In higher plants, dual targeted GluRS and GatCAB are responsible for both mitochondrial and chloroplastic Gln-tRNA Gln formation in the respective organelles (11). Thus, mitochondrial Gln-tRNA Gln formation is likely species-specific, which might make it difficult to predict what pathway and factors generate mitochon-drial Gln-tRNA Gln for mitochondrial translation in a given eukaryote.…”

Characterization of Gtf1p, the Connector Subunit of Yeast Mitochondrial tRNA-dependent Amidotransferase

“…is known to occur in prokaryotes and more recently has also been shown in eukaryotic organelles (3,5,6). In bacteria, the AdT reactions are catalyzed by the heterotrimeric enzyme encoded by the GatCAB operon (7,8).…”

Transfer RNA: A dancer between charging and mis-charging for protein biosynthesis

“…All known archaea (e.g., Methanothermobacter thermautotrophicus), most bacteria (e.g., Bacillus subtilis), chloroplast, and mitochondria lack GlnRS to synthesize the GlntRNA Gln [105][106][107][108]. Instead, in these organelles or organisms, GluRS is non-discriminating (ND-GluRS), which means that it can also recognize tRNA Gln other than its normal substrate tRNA Glu [109][110][111].…”