title: Structural plasticity of an aminoacyl-tRNA synthetase active site.
abstract: 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 alpha8-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.
authors.affiliation: Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Turner
authors.forename: James
authors.initials: J
authors.lastname: Graziano
authors.forename: Glen
authors.initials: G
authors.lastname: Spraggon
authors.forename: Peter G
authors.initials: PG
authors.lastname: Schultz
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D017017:Methanococcus / Q000201:enzymology / Q000235:genetics; D008958:Models, Molecular; D016296:Mutagenesis; D009281:Naphthalenes / Q000378:metabolism; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D014448:Tyrosine-tRNA Ligase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C473369:3-(2-naphthyl)alanine; D009281:Naphthalenes; D011994:Recombinant Proteins; C060302:4-bromophenylalanine; D010649:Phenylalanine; D014448:Tyrosine-tRNA Ligase; D000409:Alanine