engleski

tRNA-dependent amino acid discrimination by yeast sery-tRNA synthetases

The ability of aminoacyl-tRNA synthetases to distinguish among similar amino acids is crucial for accurate translation of the genetic code. Saccharomyces cerevisiae seryl-tRNA synthetase (SerRS) employs tRNA-dependent recognition of its cognate amino acid serine (Lenhard, B. et al. (1997) J. Biol. Chem. 272, 1136-1141). Here we show that dimeric SerRS enzyme complexed with one molecule of tRNASer is more specific and more efficient in catalyzing seryl-adenylate formation than the apoenzyme alone. Sequence-specific tRNA:protein interactions enhance discrimination of the amino acid substrate by yeast SerRS and diminish the misactivation of the structurally similar noncognate threonine. This may proceed via a tRNA-induced conformational change in the enzyme’ s active site. The 3’ -terminal adenosine of tRNASer is not important in effecting the rearrangement of the serine binding site. Our results do not provide an indication for a readjustment of ATP binding in a tRNA-assisted manner. The stoichiometric analyses of the complexes between the enzyme and tRNASer revealed that two cognate tRNA molecules can be bound to dimeric SerRS, however with very different affinities.

tRNASer:SerRS complexes; tRNA-dependent amino acid recognition; amino acid selection; tRNA binding; covalent cross-linking

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