Structural basis of nonnatural amino acid recognition by an engineered aminoacyl-tRNA synthetase for genetic code expansion

Proc Natl Acad Sci U S A. 2005 Feb 1;102(5):1366-71. doi: 10.1073/pnas.0407039102. Epub 2005 Jan 25.


The genetic code in a eukaryotic system has been expanded by the engineering of Escherichia coli tyrosyl-tRNA synthetase (TyrRS) with the Y37V and Q195C mutations (37V195C), which specifically recognize 3-iodo-L-tyrosine rather than L-tyrosine. In the present study, we determined the 3-iodo-L-tyrosine- and L-tyrosine-bound structures of the 37V195C mutant of the E. coli TyrRS catalytic domain at 2.0-A resolution. The gamma-methyl group of Val-37 and the sulfur atom of Cys-195 make van der Waals contacts with the iodine atom of 3-iodo-L-tyrosine. The Val-37 and Cys-195 side chains are rigidly fixed by the neighboring residues forming the hydrophobic core of the TyrRS. The major roles of the two mutations are different for the 3-iodo-L-tyrosine-selective recognition in the first step of the aminoacylation reaction (the amino acid activation step): the Y37V mutation eliminates the fatal steric repulsion with the iodine atom, and the Q195C mutation reduces the L-tyrosine misrecognition. The structure of the 37V195C mutant TyrRS complexed with an L-tyrosyladenylate analogue was also solved, indicating that the 3-iodo-L-tyrosine and L-tyrosine side chains are similarly discriminated in the second step (the aminoacyl transfer step). These results demonstrate that the amino acid-binding pocket on the 37V195C mutant is optimized for specific 3-iodo-L-tyrosine recognition.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Amino Acids / metabolism*
  • Crystallography, X-Ray
  • Escherichia coli / enzymology
  • Genetic Code*
  • Genetic Engineering
  • Hydrogen Bonding
  • Models, Molecular
  • Monoiodotyrosine / chemistry
  • Monoiodotyrosine / metabolism
  • Mutagenesis, Site-Directed
  • Protein Structure, Secondary
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Substrate Specificity
  • Tyrosine-tRNA Ligase / chemistry
  • Tyrosine-tRNA Ligase / genetics*
  • Tyrosine-tRNA Ligase / metabolism*


  • Amino Acids
  • Recombinant Proteins
  • Tyrosine-tRNA Ligase
  • Monoiodotyrosine

Associated data

  • PDB/1VBN
  • PDB/1WQ3
  • PDB/1WQ4