title: Lack of discrimination against non-proteinogenic amino acid norvaline by elongation factor Tu fromEscherichia coli.
abstract: The GTP-bound form of elongation factor Tu (EF-Tu) brings aminoacylated tRNAs (aa-tRNA) to the A-site of the ribosome. EF-Tu binds all cognate elongator aa-tRNAs with highly similar affinities, and its weaker or tighter binding of misacylated tRNAs may discourage their participation in translation. Norvaline (Nva) is a non-proteinogenic amino acid that is activated and transferred to tRNALeuby leucyl-tRNA synthetase (LeuRS). No notable accumulation of Nva-tRNALeuhas been observedin vitro, because of the efficient post-transfer hydrolytic editing activity of LeuRS. However, incorporation of norvaline into proteins in place of leucine does occur under certain conditionsin vivo. Here we show that EF-Tu binds Nva-tRNALeuand Leu-tRNALeuwith similar affinities, and that Nva-tRNALeuand Leu-tRNALeudissociate from EF-Tu at comparable rates. The inability of EF-Tu to discriminate against norvaline may have driven evolution of highly efficient LeuRS editing as the main quality control mechanism against misincorporation of norvaline into proteins.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia.
authors.forename: Nevena
authors.initials: N
authors.lastname: Cvetesic
authors.forename: Irena
authors.initials: I
authors.lastname: Akmacic
authors.forename: Ita
authors.initials: I
authors.lastname: Gruic-Sovulj
keywords: EF-Tu; aminoacyl-tRNA synthetases; leucyl-tRNA synthetase; mistranslation; non-proteinogenic amino acids; norvaline