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tRNA discrimination at the binding step by a class II aminoacyl-tRNA synthetase
1Department of Biochemistry, University of Vermont College of Medicine, Burlington 05405, USA.
Biochemistry
|October 16, 1999
Summary
Histidyl-tRNA synthetase distinguishes between correct and incorrect transfer RNAs (tRNAs) during protein synthesis. Key regions of the tRNA and enzyme interactions are crucial for this fidelity, ensuring accurate genetic code translation.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Aminoacyl-tRNA synthetases are essential enzymes for protein synthesis, responsible for attaching the correct amino acid to its corresponding transfer RNA (tRNA).
- Maintaining the fidelity of this aminoacylation process is critical for accurate translation of the genetic code.
- Escherichia coli histidyl-tRNA synthetase (HisRS) serves as a model system to study tRNA recognition mechanisms.
Purpose of the Study:
- To investigate the molecular basis of tRNA discrimination by Escherichia coli histidyl-tRNA synthetase at the binding level.
- To identify the specific regions of tRNA and the enzyme involved in cognate versus noncognate tRNA recognition.
- To elucidate the role of the anticodon and other tRNA elements in the fidelity of aminoacylation.
Main Methods:
- Competitive filter binding assays were employed to quantify the binding affinities of HisRS for cognate and noncognate tRNAs.
- Analytical ultracentrifugation (sedimentation velocity) was used to assess complex formation between HisRS and different tRNAs.
- Iodine footprinting experiments were performed to map the interaction sites of HisRS on tRNA.
Main Results:
- An adenylate analogue, HSA, enhanced discrimination against noncognate tRNA(Phe) and favored binding of cognate tRNA(His).
- A specific mutation (G405D) in the anticodon binding domain of HisRS altered tRNA binding properties, affecting discrimination.
- Footprinting data indicated that the anticodon and core regions of tRNA, along with specific enzyme domains, are critical for initial tRNA binding and discrimination.
Conclusions:
- The anticodon and core regions of tRNA, along with corresponding enzyme domains in HisRS, play significant roles in the initial binding discrimination between cognate and noncognate tRNAs.
- Nucleotides in the acceptor stem, particularly at position 73, appear to influence the reaction after initial tRNA binding.
- These findings contribute to understanding the intricate mechanisms ensuring the fidelity of protein synthesis.