Two tyrosine residues outside the editing active site in Giardia lamblia leucyl-tRNA synthetase are essential for the post-transfer editing

Leucyl-tRNA synthetase (LeuRS) is responsible for the Leu-tRNALeu synthesis. The connective peptide 1 (CP1) domain inserted into the Rossmann nucleotide binding fold possesses editing active site to hydrolyze the mischarged tRNALeu with noncognate amino acid, then to ensure high fidelity of protein synthesis. A few co-crystal structures of LeuRS with tRNALeu in different conformations revealed that tRNALeu 3′ end shuttled between synthetic and editing active sites dynamically with direct and specific interaction with the CP1 domain. Here, we reported that Y515 and Y520 outside the editing active site of CP1 domain of Giardia lamblia LeuRS (GlLeuRS) are crucial for post-transfer editing by influencing the binding affinity with mischarged tRNALeu. Mutations on Y515 and Y520 also decreased tRNALeu charging activity to various extents but had no effect on leucine activation. Our results gave some biochemical knowledge about interaction of tRNALeu 3′ end with the CP1 domain in archaeal/eukaryotic LeuRS.