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The C-Ala Domain Brings Together Editing and Aminoacylation Functions on One tRNA

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Science  07 Aug 2009:
Vol. 325, Issue 5941, pp. 744-747
DOI: 10.1126/science.1174343

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Transfer RNA Fix

Accurate protein synthesis requires that transfer RNAs (tRNAs) must be acylated with the correct amino acid. Mistranslation of serine or glycine for alanine apparently presents a particular challenge and is corrected by an editing domain of alanyl-tRNA synthetases (AlaRSs). Guo et al. (p. 744) now show that aside from the aminoacylation and editing domains, a third domain, C-Ala, plays a key role in AlaRS function. It forms a nucleic acid–binding motif that promotes binding of both aminoacylation and editing domains to tRNAAla. The coupling of these two functions was likely important in the evolution of AlaRSs.

Abstract

Protein synthesis involves the accurate attachment of amino acids to their matching transfer RNA (tRNA) molecules. Mistranslating the amino acids serine or glycine for alanine is prevented by the function of independent but collaborative aminoacylation and editing domains of alanyl-tRNA synthetases (AlaRSs). We show that the C-Ala domain plays a key role in AlaRS function. The C-Ala domain is universally tethered to the editing domain both in AlaRS and in many homologous free-standing editing proteins. Crystal structure and functional analyses showed that C-Ala forms an ancient single-stranded nucleic acid binding motif that promotes cooperative binding of both aminoacylation and editing domains to tRNAAla. In addition, C-Ala may have played an essential role in the evolution of AlaRSs by coupling aminoacylation to editing to prevent mistranslation.

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