engleski

Distinctive mechanisms of amino acid selection in the synthetic and editing sites of tRNA synthetases

Amino acids are directed into protein synthesis by their coupling to the cognate tRNAs in the reactions catalyzed by corresponding aminoacyl- tRNA synthetases (aaRS). These enzymes may use editing to prevent accumulation of aa-tRNA mismatches. The prominent error-correction step is hydrolysis of misacylated tRNAs within a dedicated protein domain. Also, the near-cognate aminoacyl-adenylate intermediate may be proofread within the synthetic site. Using several class I aaRSs as model enzymes we tackle the mechanisms and evolution of amino acid discrimination and editing. We found that the synthetic and editing sites use distinct mechanisms to strengthen specificity. The synthetic site promotes specificity by enabling a 100-fold difference in the Km values for cognate and near-cognate amino acids. In contrast, the post-transfer editing site exclude the corresponding cognate aminoacyl- tRNA, with 103-fold specificity that arises from decreased rate of deacylation. This challenges a general perception in which the editing domain operates as a steric sieve.

editing ; aminoacyl-tRNA synthetases ; leucyl-tRNA synthetase ; norvaline

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