RRM
2006
Rustbelt RNA Meeting
RRM
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Talk abstracts
Abstract:
Protein synthesis requires the pairing of amino acids with tRNAs catalyzed by the aminoacyl-tRNA synthetases. The synthetases are highly specific, but errors in amino acid selection are occasionally made opening the door to inaccurate translation of the genetic code. The fidelity of protein synthesis is maintained by the editing activities of synthetases, which remove noncognate amino acids from tRNA before they can be delivered to the ribosome. While editing has been described in numerous synthetases, the reaction mechanism is unknown. To define the mechanism of editing, phenylalanyl-tRNA synthetase was used to investigate different models for hydrolysis of the noncognate product Tyr-tRNAPhe. Deprotonation of a water molecule by the highly conserved residue beta-His265, as proposed for threonyl-tRNA synthetase, was excluded since replacement of this and neighboring residues had little effect on editing activity. Model building suggested that instead of directly catalyzing hydrolysis, the role of the editing site is to discriminate and properly position non-cognate substrate for nucleophilic attack by water. In agreement with this model, replacement of certain editing site residues abolished substrate specificity but only reduced the catalytic efficiency of hydrolysis 2- to 10- fold. In contrast removal of the 3'-OH group of tRNAPhe severely impaired editing and revealed an essential function for this group in hydrolysis. The phenylalanyl-tRNA synthetase editing mechanism explains the discrepancy between the leucyl- and threonyl-tRNA synthetase models and provides a paradigm for synthetase editing.
References:
Jiqiang Ling, Hervé Roy and Michael Ibba. Mechanism of tRNA-dependent editing in translational quality control. Submitted.
Keywords: PheRS, editing mechanism, quality control
