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Aminoacyl-tRNA (also aa-tRNA or charged tRNA) is tRNA to which its cognated amino acid is chemically bonded (charged). The aa-tRNA, along with some elongation factors, deliver the amino acid to the ribosome for incorporation into the polypeptide chain that is being produced.^[1] A specific cognate amino acid is charged or aminoacylated to each tRNA by aminoacyl tRNA synthetase. This matching is crucial, since it ensures that only the particular amino acid matching the anticodon of the tRNA, and in turn matching the codon of the mRNA, is used in protein synthesis.

Due to the degeneracy of the genetic code, multiple tRNAs will have the same amino acid but different codons. These different tRNAs are called isoacceptors. Under certain circumstances, non-cognate amino acids will be charged, resulting in mischarged or misaminoacylated tRNA. These mischarged tRNAs must be hydrolyzed in order to prevent incorrect protein synthesis.

Synthesis

Aminoacyl-tRNA is produced in two steps. First is the adenylation of the amino acid, which forms aminoacyl-AMP:

amino acid + ATP ↔ aminoacyl-AMP + PP_i

Second, the amino acid residue is transferred to the tRNA:

aminoacyl-AMP + tRNA ↔ aminoacyl-tRNA + AMP

The net reaction is:

amino acid + ATP + tRNA ↔ aminoacyl-tRNA + AMP + PP_i

The net reaction is energetically favourable only because the pyrophosphate is hydrolysed; that reaction is highly energetically favourable and drives the other reactions. All of these reactions take place inside the aminoacyl-tRNA synthetase specific for that tRNA.

Hydrolysis

The different aa-tRNAs have varying pseudo-first-order rate constants for the hydrolysis of the ester bond between amino acid and tRNA.^[2] In general, proline aa-tRNA is found to be the least stable while the steric hindrance of the methyl group on the β carbon of isoleucine and valine tend to stabilize their aa-tRNAs. Increased ionic strength resulting from sodium, potassium, and magnesium salts has been shown to destabilize the aa-tRNA bond. Increased pH also destabilizes the bond and changes the ionization of the α carbon amino group of the amino acid. The charged amino group can destabilize the aa-tRNA bond via the inductive effect. The elongation factor EF-Tu has been shown to stabilize the bond.^[3]

Drug targeting

Certain drugs like tetracycline prevent the aminoacyl-tRNA from binding to the ribosomal subunit in prokaryotes.

References

^ Berg J, Tymoczko JL, Stryer L (2006). Biochemistry (6th ed. ed.). San Francisco: W. H. Freeman. ISBN 0-7167-8724-5. CS1 maint: Extra text (link)
^ Hentzen, Daniele; et al. (1972). "Relation between aminoacyl-tRNA stability and the fixed amino acid". Biochmica et Biophysica Acta 281: 228–232. doi:10.1016/0005-2787(72)90174-8.
^ Pinck, M; Francis S (1974). "On the chemical reactivity of aminoacyl-tRNA ester bond I, II, III". Biochimie 56: 383–390. doi:10.1016/s0300-9084(74)80146-x.

UpToDate Contents

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English Journal

Rapid detection of exon 2-deleted AIMP2 mutation as a potential biomarker for lung cancer by molecular beacons.

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Biosensors & bioelectronics.Biosens Bioelectron.2013 Aug 15;46:142-9. doi: 10.1016/j.bios.2013.02.037. Epub 2013 Mar 6.
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The Structure of FemXWv in Complex with a Peptidyl-RNA Conjugate: Mechanism of Aminoacyl Transfer from Ala-tRNA(Ala) to Peptidoglycan Precursors.

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Angewandte Chemie (International ed. in English).Angew Chem Int Ed Engl.2013 Jul 8;52(28):7278-81. doi: 10.1002/anie.201301411. Epub 2013 Jun 6.
To gain insight into the catalytic mechanism of non-ribosomal amino acid transferases, peptidyl-RNA conjugates were synthesized for co-crystallization with FemXWv of Weissella viridescens, which transfers L-Ala from Ala-tRNA(Ala) to the peptidoglycan precursor UDP-MurNAc-pentapeptide. The structure
PMID 23744707

The mechanistic and evolutionary aspects of the 2[prime]- and 3[prime]-OH paradigm in biosynthetic machinery.

Safro M, Klipcan L.AbstractBACKGROUND: The translation machinery underlies a multitude of biological processes within the cell. The design and implementation of the modern translation apparatus on even the simplest course of action is extremely complex, and involves different RNA and protein factors. According to the "RNA world" idea, the critical link in the translation machinery may be assigned to an adaptor tRNA molecule. Its exceptional functional and structural characteristics are of primary importance in understanding the evolutionary relationships among all these macromolecular components.
Biology direct.Biol Direct.2013 Jul 8;8(1):17. [Epub ahead of print]
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Japanese Journal

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★リンクテーブル★

リンク元	「リボソーム」「アミノアシルtRNA」
拡張検索	「aminoacyl-tRNA synthetase」「aminoacyl-tRNA binding site」
関連記事	「tRNA」「tRNAs」