Abstract
The aminoacyl-tRNA synthetases (aaRSs) are well established as the translators of the genetic code, because their products, the aminoacyl-tRNAs, read codons to translate messenger RNAs into proteins. Consequently, deleterious errors by the aaRSs can be transferred into the proteome via misacylated tRNAs. Nevertheless, many microorganisms use an indirect pathway to produce Asn-tRNAAsn via Asp-tRNAAsn. This intermediate is produced by a non-discriminating aspartyl-tRNA synthetase (ND-AspRS) that has retained its ability to also generate Asp-tRNAAsp. Here we report the discovery that ND-AspRS and its discriminating counterpart, AspRS, are also capable of specifically producing Glu-tRNAGlu, without producing misacylated tRNAs like Glu-tRNAAsn, Glu-tRNAAsp, or Asp-tRNAGlu, thus maintaining the fidelity of the genetic code. Consequently, bacterial AspRSs have glutamyl-tRNA synthetase-like activity that does not contaminate the proteome via amino acid misincorporation.
Highlights
The fidelity of protein translation depends on the accurate pairing of cognate tRNAs to their cognate amino acids
The ligation of the amino acid to its tRNA is catalyzed by a highly specific group of enzymes known as the aminoacyl-tRNA synthetases [1,2,3]
The non-discriminating form, ND-Aspartyl-tRNA synthetase (AspRS), is found in many bacteria and archaea and some organelles; this enzyme cannot differentiate between tRNAAsp and tRNAAsn and aminoacylates both with aspartate to generate Asp-tRNAAsp and the misacylated Asp-tRNAAsn, respectively (Figure 1B) [14,15,16,17]
Summary
The fidelity of protein translation depends on the accurate pairing of cognate tRNAs to their cognate amino acids. The ligation of the amino acid to its tRNA is catalyzed by a highly specific group of enzymes known as the aminoacyl-tRNA synthetases (aaRSs) [1,2,3]. Under normal conditions, these enzymes maintain high accuracy and specificity in selecting their cognate amino acid and tRNA substrates. Aspartyl-tRNA synthetase (AspRS) is an exception to the rule of one aaRS per amino acid/tRNA pair. This enzyme is found in two general forms, discriminating and non-discriminating, based on divergent tRNA specificities.
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