Impact of non-proteinogenic amino acid norvaline and proteinogenic valine misincorporation on a secondary structure of a model peptide

ABSTRACT Norvaline is a straight-chain, hydrophobic, non-proteinogenic amino acid, isomeric with valine. Both amino acids can be misincorporated into proteins at isoleucine positions by isoleucyl-tRNA synthetase when the mechanisms of translation fidelity are impaired. Our previous study showed that proteome-wide substitution of isoleucine with norvaline resulted in higher toxicity in comparison to the proteome-wide substitution of isoleucine with valine. Although mistranslated proteins/peptides are considered to have non-native structures responsible for their toxicity, the observed difference in protein stability between norvaline and valine misincorporation has not yet been fully understood. To examine the observed effect, we choose the model peptide with three isoleucines in the native structure, introduced selected amino acids at isoleucine positions and applied molecular-dynamics simulations at different temperatures. The obtained results showed that norvaline has the highest destructive effect on the β-sheet structure and suggest that the higher toxicity of norvaline over valine is predominantly due to the misincorporation within the β-sheet secondary elements.