Evolutionarily conserved cysteines in plant cytosolic seryl-tRNA synthetase are important for its resistance to oxidation.

We have previously identified a unique disulfide bond in the crystal structure of Arabidopsis cytosolic seryl-tRNA synthetase involving cysteines evolutionarily conserved in all green plants. Here, we discovered that both cysteines are important for protein stability, but with opposite effects, and that their microenvironment may promote disulfide bond formation in oxidizing conditions. The crystal structure of the C244S mutant exhibited higher rigidity and an extensive network of noncovalent interactions correlating with its higher thermal stability. The activity of the wild type showed resistance to oxidation with H 2 O 2 , while activities of cysteine-to-serine mutants were impaired, indicating that the disulfide link may enable the protein to function under oxidative stress conditions which can be beneficial for an efficient plant stress response.