Structural plasticity of an aminoacyl-tRNA synthetase active site.
Recently, tRNA aminoacyl-tRNA synthetase pairs have been evolved that allow one to genetically encode a large array of unnatural amino acids in both prokaryotic and eukaryotic organisms. We have determined the crystal structures of two substrate-bound Methanococcus jannaschii tyrosyl aminoacyl-tRNA synthetases that charge the unnatural amino acids p-bromophenylalanine and 3-(2-naphthyl)alanine (NpAla). A comparison of these structures with the substrate-bound WT synthetase, as well as a mutant synthetase that charges p-acetylphenylalanine, shows that altered specificity is due to both side-chain and backbone rearrangements within the active site that modify hydrogen bonds and packing interactions with substrate, as well as disrupt the alpha(8)-helix, which spans the WT active site. The high degree of structural plasticity that is observed in these aminoacyl-tRNA synthetases is rarely found in other mutant enzymes with altered specificities and provides an explanation for the surprising adaptability of the genetic code to novel amino acids.[1]References
- Structural plasticity of an aminoacyl-tRNA synthetase active site. Turner, J.M., Graziano, J., Spraggon, G., Schultz, P.G. Proc. Natl. Acad. Sci. U.S.A. (2006) [Pubmed]
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