Protein synthesis and its fidelity rely upon the aminoacyl-tRNA synthetases. Leucyl-tRNA synthetase (LeuRS), isoleucyl-tRNA synthetase (IleRS), and valyl-tRNA synthetase (ValRS) have evolved a discrete editing domain called CP1 that hydrolyzes the respective incorrectly misaminoacylated noncognate amino acids. Although active CP1 domain fragments have been isolated for IleRS and ValRS, previous reports suggested that the LeuRS CP1 domain required idiosyncratic adaptations to confer editing activity independent of the full-length enzyme. Herein, characterization of a series of rationally designed Escherichia coli LeuRS fragments showed that the β-strands, which link the CP1 domain to the aminoacylation core of LeuRS, are required for editing of mischarged tRNALeu. Hydrolytic activity was also enhanced by inclusion of short flexible peptides that have been called "hinges" at the end of both LeuRS β-strands. We propose that these long β-strand extensions of the LeuRS CP1 domain interact specifically with the tRNA for post-transfer editing of misaminoacylated amino acids.
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