Mechanism of discrimination of natural proteinogenic and nonproteinogenic amino acids in class IA aminoacyl-tRNA synthetases

Biluš, Mirna (2016) Mechanism of discrimination of natural proteinogenic and nonproteinogenic amino acids in class IA aminoacyl-tRNA synthetases. Doctoral thesis, Faculty of Science > Department of Chemistry.

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Abstract

Aminoacyl-tRNA synthetases catalyze binding of amino acids to the 3'-end of tRNA in a 2-step reaction: the first step is activation of amino acid with ATP to form aminoacyl-adenylate, and in the second step the activated amino acid is transferred to tRNA's 3'-end. Structural similarity of the amino acid substrates and the required accuracy of the aminoacylation reaction directed the development of proofreading mechanisms by aminoacyl-tRNA synthetases: proofreading may occur before or after amino acid transfer to tRNA. In this dissertation, discrimination mechanisms of a natural non-proteinogenic amino acid norvaline by Escherichia coli isoleucyland valyl-tRNA synthetase were explored. IleRS activates norvaline well and transfers it to tRNAIle, and the repair mechanisms may operate prior to or after transfer of norvaline to tRNAIle. As previously shown with valine, besides tRNA-independent, IleRS also exhibits tRNA-dependent pre-transfer editing to eliminate norvaline. The latter mechanism is distinctive for IleRS and its existence has not been proven in other aminoacyl-tRNA synthetases. Norvalin is 3-4 × more toxic than valine to an E. coli strain that contains IleRS with inactivated posttransfer editing. ValRS weakly activates norvaline, and the discrimination achieved in the first step of aminoacylation is high enough to sustain the accuracy of overall protein biosynthesis. Nevertheless, as activated norvaline is efficiently transferred to tRNAVal, ValRS can eliminate norvalyl-tRNAVal through post-transfer editing.

Item Type: Thesis (Doctoral thesis)
Keywords: isoleucyl-tRNA synthetase, valyl-tRNA synthetase, leucyl-tRNA synthetase, mistranslation, norvaline, proofreading
Supervisor: Gruić Sovulj, Ita
Date: 2016
Number of Pages: 142
Subjects: NATURAL SCIENCES > Biology > Biochemistry and Molecular Biology
Divisions: Faculty of Science > Department of Chemistry
Depositing User: Branka Maravic
Date Deposited: 16 Jan 2017 16:33
Last Modified: 16 Jan 2017 16:33
URI: http://digre.pmf.unizg.hr/id/eprint/5414

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