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Crystal structures that suggest late development of genetic code components for differentiating aromatic side chains
Xiang-Lei Yang1, Francella J Otero, Robert J Skene
1Departments of Molecular Biology and Chemistry, The Scripps Research Institute, BCC-379, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Summary
The genetic code may have initially produced "statistical" proteins. Structural analysis of enzymes suggests that distinguishing tryptophan from tyrosine evolved late in the genetic code
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Early genetic codes may have produced
- statistical
- proteins, where similar amino acids occupied the same sequence positions.
Purpose of the Study:
- To investigate the evolutionary development of amino acid discrimination in the genetic code.
- To understand the structural basis for distinguishing aromatic amino acids, specifically tryptophan and tyrosine.
Main Methods:
- Crystal structures of human tryptophanyl-tRNA synthetase and a fragment of tyrosyl-tRNA synthetase were determined.
- Structure-based sequence alignments of approximately 45 orthologs for each enzyme were performed.
Main Results:
- Active sites of both enzymes were identified through structural analysis.
- Two critical positions in the enzymes responsible for amino acid discrimination were identified.
- Phylogenetic analyses suggested that tyrosine-tryptophan discrimination evolved late in the genetic code's development.
Conclusions:
- The structural and phylogenetic data indicate that the discrimination between tyrosine and tryptophan was a relatively late event in the evolution of the genetic code.
- This contrasts with the evolutionary timeline for the discrimination of many other amino acids.