tRNA-dependent amino acid discrimination by yeast seryl-tRNA synthetase.
The ability of aminoacyl-tRNA synthetases to distinguish between similar amino acids is crucial for accurate translation of the genetic code. Saccharomyces cerevisiae seryl-tRNA synthetase (SerRS) employs tRNA-dependent recognition of its cognate amino acid serine [Lenhard, B., Filipic, S., Landeka, I., Skrtic, I., Söll, D. & Weygand-Durasevic, I. (1997) J. Biol. Chem.272, 1136-1141]. Here we show that dimeric SerRS enzyme complexed with one molecule of tRNASer is more specific and more efficient in catalyzing seryl-adenylate formation than the apoenzyme alone. Sequence-specific tRNA-protein interactions enhance discrimination of the amino acid substrate by yeast SerRS and diminish the misactivation of the structurally similar noncognate threonine. This may proceed via a tRNA-induced conformational change in the enzyme's active site. The 3'-terminal adenosine of tRNASer is not important in effecting the rearrangement of the serine binding site. Our results do not provide an indication for a readjustment of ATP binding in a tRNA-assisted manner. The stoichiometric analyses of the complexes between the enzyme and tRNASer revealed that two cognate tRNA molecules can be bound to dimeric SerRS, however, with very different affinities.
Gruic-Sovulj
Ita
I
Department of Chemistry, Faculty of Science, University of Zagreb, Croatia.
Landeka
Irena
I
Söll
Dieter
D
Weygand-Durasevic
Ivana
I
D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D000596:Amino Acids / Q000737:chemistry* / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli; D046911:Macromolecular Substances; D011485:Protein Binding / Q000502:physiology; D012362:RNA, Transfer, Ser / Q000737:chemistry* / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D012714:Serine-tRNA Ligase / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity / Q000502:physiology; D013912:Threonine / Q000737:chemistry / Q000378:metabolism
D000596:Amino Acids; D046911:Macromolecular Substances; D012362:RNA, Transfer, Ser; D013912:Threonine; D012694:Serine; D000255:Adenosine Triphosphate; D012714:Serine-tRNA Ligase