Modulation of aminoacylation and editing properties of leucyl-tRNA synthetase by a conserved structural module [RNA]

March 27th, 2015 by Yan, W., Ye, Q., Tan, M., Chen, X., Eriani, G., Wang, E.-D.

A conserved structural module following the KMSKS catalytic loop exhibits α-α-β-α topology in class Ia and Ib aminoacyl-tRNA synthetases. However, the function of this domain has received little attention. Here, we describe the effect this module has on the aminoacylation and editing capacities of leucyl-tRNA synthetases (LeuRSs) by characterizing the key residues from various species. Mutation of highly conserved basic residues on the third α-helix of this domain impairs the affinity of LeuRS for the anticodon stem of tRNALeu, which decreases both aminoacylation and editing activities. Two glycine residues on this α-helix contribute to flexibility, leucine activation and editing of LeuRS from Escherichia coli (EcLeuRS). Acidic residues on the β-strand enhance the editing activity of EcLeuRS and sense the size of the tRNALeu D-loop. Incorporation of these residues stimulates the tRNA-dependent editing activity of the chimeric minimalist enzyme MmLeuRS fused with the connective polypeptide 1 (CP1) editing domain and leucine-specific domain of (LSD) from EcLeuRS. Together, these results reveal the stem contact (SC)-fold to be functional as well as a structural linker between the catalytic site and tRNA binding domain. Sequence comparison of the EcLeuRS SC-fold domain with editing-deficient enzymes suggests that key residues of this module have evolved an adaptive strategy to follow the editing functions of LeuRSs.