Leucyl-tRNA synthetase from the hyperthermophilic bacterium Aquifex aeolicus recognizes minihelices.
Aminoacylation of the minihelix mimicking the amino acid acceptor arm of tRNA has been demonstrated in more than 10 aminoacyl-tRNA synthetase systems. Although Escherichia coli or Homo sapiens cytoplasmic leucyl-tRNA synthetase (LeuRS) is unable to charge the cognate minihelix or microhelix, we show here that minihelix(Leu) is efficiently charged by Aquifex aeolicus synthetase, the only known heterodimeric LeuRS (alpha beta-LeuRS). Aminoacylation of minihelices is strongly dependent on the presence of the A73 identity nucleotide and greatly stimulated by destabilization of the first base pair as reported for the E. coli isoleucyl-tRNA synthetase and methionyl-tRNA synthetase systems. In the E. coli LeuRS system, the anticodon of tRNA(Leu) is not important for recognition by the synthetase. However, the addition of RNA helices that mimic the anticodon domain stimulates minihelix(Leu) charging by alpha beta-LeuRS, indicating possible domain-domain communication within alpha beta-LeuRS. The leucine-specific domain of alpha beta-LeuRS is responsible for minihelix recognition. To ensure accurate translation of the genetic code, LeuRS functions to hydrolyze misactivated amino acids (pretransfer editing) and misaminoacylated tRNA (posttransfer editing). In contrast to tRNA(Leu), minihelix(Leu) is unable to induce posttransfer editing even upon the addition of the anticodon domain of tRNA. Therefore, the context of tRNA is crucial for the editing of mischarged products. However, the minihelix(Leu) cannot be misaminoacylated, perhaps because of the tRNA-independent pretransfer editing activity of alpha beta-LeuRS.
Xu
Min-Gang
MG
State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, The Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China.
Zhao
Ming-Wei
MW
Wang
En-Duo
ED
D000255:Adenosine Triphosphate / Q000737:chemistry; D001419:Bacteria / Q000201:enzymology*; D001483:Base Sequence; D003062:Codon; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D006868:Hydrolysis; D007935:Leucine-tRNA Ligase / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D014176:Protein Biosynthesis; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays
D003062:Codon; D012313:RNA; D000255:Adenosine Triphosphate; D007935:Leucine-tRNA Ligase