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Correlating amino acid conservation with function in tyrosyl-tRNA synthetase
1Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, 71130, USA.
Journal of Molecular Biology
|October 12, 2000
Summary
The study reveals how Bacillus stearothermophilus tyrosyl-tRNA synthetase evolved its catalytic mechanism. Specific motifs like HIGH stabilize tyrosine activation, while others like Thr40, Lys82, and Arg86 stabilize both reaction steps.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Tyrosyl-tRNA synthetase (TyrRS) catalyzes tRNA(Tyr) aminoacylation in two steps: tyrosine activation and transfer.
- The class I conserved KMSKS motif is known to be involved only in the tyrosine activation step.
Purpose of the Study:
- To elucidate the evolutionary path of the catalytic mechanism in Bacillus stearothermophilus tyrosyl-tRNA synthetase.
- To investigate the roles of the HIGH motif, Thr40, Lys82, and Arg86 in TyrRS catalysis.
Main Methods:
- Sequence comparisons
- Mutational analyses
- Kinetic analyses
Main Results:
- The class I conserved HIGH motif is involved solely in the tyrosine activation step.
- Amino acids Thr40, Lys82, and Arg86 stabilize transition states for both activation and transfer steps.
- Stabilization of the first catalytic step preceded the second, supporting an evolutionary model.
Conclusions:
- The evolution of aminoacyl-tRNA synthetases likely involved the sequential acquisition of catalytic functions.
- Primordial aminoacyl-tRNA synthetases may have replaced an ancestral ribozyme for amino acid activation.