tRNAGlu increases the affinity of glutamyl-tRNA synthetase for its inhibitor glutamyl-sulfamoyl-adenosine, an analogue of the aminoacylation reaction intermediate glutamyl-AMP: mechanistic and evolutionary implications

PLoS One. 2015 Apr 10;10(4):e0121043. doi: 10.1371/journal.pone.0121043. eCollection 2015.


For tRNA-dependent protein biosynthesis, amino acids are first activated by aminoacyl-tRNA synthetases (aaRSs) yielding the reaction intermediates aminoacyl-AMP (aa-AMP). Stable analogues of aa-AMP, such as aminoacyl-sulfamoyl-adenosines, inhibit their cognate aaRSs. Glutamyl-sulfamoyl-adenosine (Glu-AMS) is the best known inhibitor of Escherichia coli glutamyl-tRNA synthetase (GluRS). Thermodynamic parameters of the interactions between Glu-AMS and E. coli GluRS were measured in the presence and in the absence of tRNA by isothermal titration microcalorimetry. A significant entropic contribution for the interactions between Glu-AMS and GluRS in the absence of tRNA or in the presence of the cognate tRNAGlu or of the non-cognate tRNAPhe is indicated by the negative values of -TΔSb, and by the negative value of ΔCp. On the other hand, the large negative enthalpy is the dominant contribution to ΔGb in the absence of tRNA. The affinity of GluRS for Glu-AMS is not altered in the presence of the non-cognate tRNAPhe, but the dissociation constant Kd is decreased 50-fold in the presence of tRNAGlu; this result is consistent with molecular dynamics results indicating the presence of an H-bond between Glu-AMS and the 3'-OH oxygen of the 3'-terminal ribose of tRNAGlu in the Glu-AMS•GluRS•tRNAGlu complex. Glu-AMS being a very close structural analogue of Glu-AMP, its weak binding to free GluRS suggests that the unstable Glu-AMP reaction intermediate binds weakly to GluRS; these results could explain why all the known GluRSs evolved to activate glutamate only in the presence of tRNAGlu, the coupling of glutamate activation to its transfer to tRNA preventing unproductive cleavage of ATP.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine / analogs & derivatives*
  • Adenosine / chemistry*
  • Adenosine / metabolism
  • Adenosine Monophosphate / analogs & derivatives*
  • Adenosine Monophosphate / chemistry*
  • Adenosine Monophosphate / metabolism
  • Amino Acid Sequence
  • Aminoacylation
  • Binding Sites
  • Calorimetry
  • Escherichia coli / enzymology
  • Glutamate-tRNA Ligase / antagonists & inhibitors
  • Glutamate-tRNA Ligase / metabolism*
  • Glutamates / chemistry
  • Glutamates / metabolism*
  • Hydrogen Bonding
  • Kinetics
  • Molecular Docking Simulation
  • Molecular Sequence Data
  • Protein Structure, Tertiary
  • RNA, Transfer, Glu / metabolism*
  • Sequence Alignment
  • Temperature
  • Thermodynamics


  • 5'-O-(N-(glutamyl)sulfamoyl)adenosine
  • Glutamates
  • RNA, Transfer, Glu
  • Adenosine Monophosphate
  • Glutamate-tRNA Ligase
  • Adenosine

Grant support

This work was supported by grant #CG051791 to JL and grant #9988 to JAK from the Natural Sciences and Engineering Research Council of Canada (NSERC) (, and by the grant #PR-133605 to JL and RC from the Fonds de Recherche du Québec - Nature et Technologies, (FRQNT) ( The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.