title: Domain-domain communication for tRNA aminoacylation: the importance of covalent connectivity.
abstract: Aminoacyl-tRNA synthetases form complexes with tRNA to catalyze transfer of activated amino acids to the 3' end of tRNA. The tRNA synthetase complexes are roughly divided into the activation and tRNA-binding domains of synthetases, which interact with the acceptor and anticodon ends of tRNAs, respectively. Efficient aminoacylation of tRNA by Escherichia coli cysteinyl-tRNA synthetase (CysRS) requires both domains, although the pathways for the long-range domain-domain communication are not well understood. Previous studies show that dissection of tRNA(Cys) into acceptor and anticodon helices seriously reduces the efficiency of aminoacylation, suggesting that communication requires covalent continuity of the tRNA backbone. Here we tested if communication requires the continuity of the synthetase backbone. Two N-terminal fragments and one C-terminal fragment of E. coli CysRS were generated. While the N-terminal fragments were active in adenylate synthesis, they were severely defective in the catalytic efficiency and specificity of tRNA aminoacylation. Conversely, although the C-terminal fragment was not catalytically active, it was able to bind and discriminate tRNA. However, addition of the C-terminal fragment to an N-terminal fragment in trans did not improve the aminoacylation efficiency of the N-terminal fragment to the level of the full-length enzyme. These results emphasize the importance of covalent continuity of both CysRS and tRNA(Cys) for efficient tRNA aminoacylation, and highlight the energetic costs of constraining the tRNA synthetase complex for domain-domain communication. Importantly, this study also provides new insights into the existence of several natural "split" synthetases that are now identified from genomic sequencing projects.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, 233 South 10 Street, BLSB 220, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Chun-Mei
authors.initials: CM
authors.lastname: Zhang
authors.forename: Ya-Ming
authors.initials: YM
authors.lastname: Hou
mesh_terms: D000249:Adenosine Monophosphate / Q000031:analogs & derivatives / Q000096:biosynthesis; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D003545:Cysteine / Q000031:analogs & derivatives / Q000096:biosynthesis; D004734:Energy Metabolism / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012350:RNA, Transfer, Cys / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D046249:Transfer RNA Aminoacylation / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; D010446:Peptide Fragments; D012350:RNA, Transfer, Cys; D000249:Adenosine Monophosphate; D000604:Amino Acyl-tRNA Synthetases; C019975:cysteinyl-tRNA synthetase; D003545:Cysteine