tRNA AND AMINO ACID RECOGNITION BY CLASS II AMINOACYL-tRNA SYNTHETASES. Stephen Cusack, Anders Åberg, Anya Yaremchuk, Carmen Berthet, Laurence Seignovert, Reuben Leberman, Mikhail Tukalo, European Molecular Biology Laboratory (EMBL-Grenoble) -Grenoble Outstation, c/o ILL, 156X, 38042 Grenoble Cedéx 9, France
Similarities and differences in the modes of recognition of tRNAs and amino acids by their cognate aminoacyl-tRNA synthetases will be discussed with reference to crystal structures of substrate complexes of three Thermus thermophilus class II synthetases: seryl-, lysyl- and histidyl-tRNA synthetases.
New data at 2.8Å resolution collected at cryo temperature on the T. thermophilus seryl-tRNA synthetase-tRNAser complex co-crystallised with a seryl-adenylate analogue, reveals how the synthetase interacts with the acceptor stem of the cognate tRNAser. A novel hydrophobic interaction between Phe-262 in the motif 2 loop and bases U68 and C69 in the major groove of the tRNA discriminates pyrimidines from purines in these positions. The motif 2 loop is observed in two distinct conformations depending on which step of the aminoacylation reaction is in progress.
The crystal structure at 2.75Å resolution of T. thermophilus lysyl-tRNA synthetase complexed with E. coli tRNAlys reveals how the anti-codon 34-UUU-36 (where in this tRNA, the 34-U is modified to mnm5s2U) is specifically recognised by an N-terminal domain. The mode of recognition is rather similar to that observed in the closely related aspartyl-tRNA synthetase which however recognises the anti-codon 34-GUC-36.
The crystal structure of T. thermophilus histidyl-tRNA synthetase co-crystallised with histidine, determined by multiple isomorphous replacement at 2.7Å resolution, will be described.
Progress on the structure determination of the T.thermophilus prolyl- and asparaginyl-tRNA synthetases will be presented.