A unique insert of leucyl-tRNA synthetase is required for aminoacylation and not amino acid editing.
Leucyl-tRNA synthetase (LeuRS) is a class I enzyme, which houses its aminoacylation active site in a canonical core that is defined by a Rossmann nucleotide binding fold. In addition, many LeuRSs bear a unique polypeptide insert comprised of about 50 amino acids located just upstream of the conserved KMSKS sequence. The role of this leucine-specific domain (LS-domain) remains undefined. We hypothesized that this domain may be important for substrate recognition in aminoacylation and/or amino acid editing. We carried out a series of deletion mutations and chimeric swaps within the leucine-specific domain of Escherichia coli. Our results support that the leucine-specific domain is critical for aminoacylation but not required for editing activity. Kinetic analysis determined that deletion of the LS-domain primarily impacts kcat. Because of its proximity to the aminoacylation active site, we propose that this domain interacts with the tRNA during amino acid activation and/or tRNA aminoacylation. Although the leucine-specific domain does not appear to be important to the editing complex, it remains possible that it aids the dynamic translocation process that moves tRNA from the aminoacylation to the editing complex.
Vu
Michael T
MT
Department of Biochemistry, Roger Adams Laboratory, University of Illinois at Urbana-Champaign, Box B4, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
Martinis
Susan A
SA
D000215:Acylation; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D007935:Leucine-tRNA Ligase / Q000378:metabolism*; D008969:Molecular Sequence Data; D017393:RNA Editing; D012356:RNA, Transfer, Leu / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D000596:Amino Acids; D012356:RNA, Transfer, Leu; D007935:Leucine-tRNA Ligase