title: Functional divergence of a unique C-terminal domain of leucyl-tRNA synthetase to accommodate its splicing and aminoacylation roles.
abstract: Leucyl-tRNA synthetase (LeuRS) performs dual essential roles in group I intron RNA splicing as well as protein synthesis within the yeast mitochondria. Deletions of the C terminus differentially impact the two functions of the enzyme in splicing and aminoacylation in vivo. Herein, we determined that a fiveamino acid C-terminal deletion of LeuRS, which does not complement a null strain, can form a ternary complex with the bI4 intron and its maturase splicing partner. However, the complex fails to stimulate splicing activity. The x-ray co-crystal structure of LeuRS showed that a C-terminal extension of about 60 amino acids forms a discrete domain, which is unique among the LeuRSs and interacts with the corner of the L-shaped tRNALeu. Interestingly, deletion of the entire yeast mitochondrial LeuRS C-terminal domain enhanced its aminoacylation and amino acid editing activities. In striking contrast, deletion of the corresponding C-terminal domain of Escherichia coli LeuRS abolished aminoacylation of tRNALeu and also amino acid editing of mischarged tRNA molecules. These results suggest that the role of the leucine-specific C-terminal domain in tRNA recognition for aminoacylation and amino acid editing has adapted differentially and with surprisingly opposite effects. We propose that the secondary role of yeast mitochondrial LeuRS in RNA splicing has impacted the functional evolution of this critical C-terminal domain.
authors.affiliation: Department of Biochemistry, University of Illinois, Urbana, Illinois 61801-3732, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Hsu
authors.forename: Seung Bae
authors.initials: SB
authors.lastname: Rho
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Vannella
authors.forename: Susan A
authors.initials: SA
authors.lastname: Martinis
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D007935:Leucine-tRNA Ligase / Q000737:chemistry*; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012326:RNA Splicing; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000737:chemistry; D015003:Yeasts / Q000378:metabolism
chemical_list: D014764:Viral Proteins; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases; D007935:Leucine-tRNA Ligase