title: Split leucine-specific domain of leucyl-tRNA synthetase from the hyperthermophilic bacterium Aquifex aeolicus.
abstract: Leucyl-tRNA synthetase (LeuRS) from Aquifex aeolicus is the only known heterodimer synthetase. It is named LeuRS alphabeta;, and its alpha and beta subunits contain 634 and 289 residues, respectively. Like Thermus thermophilus LeuRS, LeuRS alphabeta has a large extra domain, the leucine-specific domain, inserted into the catalytic domain. The subunit split site is exactly in the middle of the leucine-specific domain and may have a unique function. Here, a series of mutants of LeuRS alphabeta consisting of either mutated alpha subunits and wild-type beta subunits or wild-type alpha subunits and mutated beta subunits were constructed and purified. ATP-PPi exchange and aminoacylation activities and the ability of the mutants to charge minihelix(Leu) were assayed. Interaction of the mutants with the tRNA was assessed by gel shift. Two peptides of eight and nine amino acid residues in the domain located in the alpha subunit were found to be essential for the enzyme's activity. We also showed that the domain in LeuRS alphabeta plays an important role in minihelix(Leu) recognition. Additionally, the domain was found to have little impact on the assembly of the heterodimer, to play a role in the thermal stability of the whole enzyme, and to interact with the cognate tRNA in the predicted manner.
authors.affiliation: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Graduate School of the Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031, People's Republic of China.
authors.forename: Jing-Jing
authors.initials: JJ
authors.lastname: Ma
authors.forename: Ming-Wei
authors.initials: MW
authors.lastname: Zhao
authors.forename: En-Duo
authors.initials: ED
authors.lastname: Wang
mesh_terms: D019943:Amino Acid Substitution; D001419:Bacteria / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000032:analysis*; D007935:Leucine-tRNA Ligase / Q000737:chemistry* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D007935:Leucine-tRNA Ligase; D007930:Leucine