C-terminal Domain of Leucyl-tRNA Synthetase from Pathogenic Candida albicans Recognizes Both tRNASer and tRNALeu [RNA]

December 16th, 2015 by Ji, Q.-Q., Fang, Z.-P., Ye, Q., Ruan, Z.-R., Zhou, X.-L., Wang, E.-D.

Leucyl-tRNA synthetase (LeuRS) is a multi-domain enzyme that catalyzes Leu-tRNALeu formation and is classified into bacterial and archaeal/eukaryotic types, with significant diversity in the C-terminal domain (CTD). CTDs of both bacterial and archaeal LeuRSs have been reported to recognize tRNALeu through different modes of interaction. In the human pathogen, Candida albicans, the cytoplasmic LeuRS (CaLeuRS) is distinguished by its capacity to recognize a uniquely evolved chimeric tRNASer [CatRNASer(CAG)] in addition to its cognate CatRNALeu, leading to CUG codon reassignment. Our previous study showed that eukaryotic but not archaeal LeuRSs recognize this peculiar tRNASer, suggesting the significance of their highly divergent CTDs in tRNASer recognition. The results of this study provided the first evidence of the indispensable function of eukaryotic LeuRS's CTD in recognizing non-cognate CatRNASer and cognate CatRNALeu. Three lysine residues were identified as involved in mediating enzyme-tRNA interaction in leucylation process: mutation of all three sites totally ablated the leucylation activity. The importance of the three lysine residues was further verified by gel mobility shift assays and complementation of a yeast leuS gene knockout strain.