Gly56 in the synthetic site of isoleucyl‐tRNA synthetase confers specificity and maintains communication with the editing site

Abstract

Isoleucyl‐tRNA synthetase (IleRS) links isoleucine to cognate tRNA via the Ile‐AMP intermediate. Non‐cognate valine is often mistakenly recognized as the IleRS substrate; therefore, to maintain the accuracy of translation, IleRS hydrolyzes Val‐AMP within the synthetic site (pre‐transfer editing). As this activity is not efficient enough, Val‐tRNAIle is formed and hydrolyzed in the distant post‐transfer editing site. A strictly conserved synthetic site residue Gly56 was previously shown to safeguard Ile‐to‐Val discrimination during aminoacyl (aa)‐AMP formation. Here, we show that the Gly56Ala variant lost its specificity in pre‐transfer editing, confirming that this residue ensures the selectivity of all synthetic site reactions. Moreover, we found that the Gly56Ala mutation affects IleRS interaction with aa‐tRNA likely by disturbing tRNA‐dependent communication between the two active sites.