Aminoacetylation Reaction Catalyzed by Leucyl-tRNA Synthetase Operates via a Self-Assisted Mechanism Using a Conserved Residue and the Aminoacyl Substrate

J Phys Chem B. 2016 May 19;120(19):4388-98. doi: 10.1021/acs.jpcb.6b02387. Epub 2016 May 10.


Leucyl-tRNA synthetase catalyzes attachment of leucine amino acid to its cognate tRNA. During the second, aminoacetylation, step of the reaction, the leucyl moiety is transferred from leucyl-adenylate to the terminal A76 adenosine of tRNA. In this work, we have investigated the aminoacetylation step catalyzed by leucyl-tRNA synthase, using ab initio quantum chemical/molecular mechanical hybrid potentials in conjunction with reaction-path-location algorithms and molecular dynamics free energy simulations. We have modeled reaction mechanisms arising from both crystallographic studies and computational work. We invoke various groups as potential proton acceptors-namely, the phosphate and leucyl amino groups of leucyl-adenylate, the A76 base of tRNA, and the Asp80 and Glu532 residues of the protein-and consider both metal-assisted and metal-free reactions. Free energy calculations indicate that both the phosphate group of leucyl adenylate and Glu532 are not strong bases. This agrees with the results of the quantum chemical/molecular mechanical reaction path calculations which give high free energy barriers for the studied pathways involving these groups. A self-assisted mechanism with the leucyl amino group and Asp80 as proton acceptors is the most likely. Furthermore, in this mechanism the presence of a metal ion coordinated by the phosphate group and Glu532 strongly activates the reaction.

MeSH terms

  • Acetylation
  • Biocatalysis
  • Crystallography, X-Ray
  • Escherichia coli / enzymology
  • Leucine-tRNA Ligase / chemistry
  • Leucine-tRNA Ligase / metabolism*
  • Metals / chemistry
  • Molecular Dynamics Simulation
  • Protein Structure, Tertiary
  • Quantum Theory
  • Substrate Specificity
  • Thermodynamics
  • Water / chemistry
  • Water / metabolism


  • Metals
  • Water
  • Leucine-tRNA Ligase