Redox‐regulated methionine oxidation of Arabidopsis thaliana glutathione transferase Phi9 induces H‐site flexibility
(2018) Protein Science — Vol. 28, n° 5, p. 56-67 (2018)
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- Glutathione transferase enzymes help plants to cope with biotic and abiotic stress. They mainly catalyze the conjugation of glutathione (GSH) onto xenobiotics, and some act as glutathione peroxidase. With X-ray crystallography, kinetics, and thermodynamics, we studied the impact of oxidation on Arabidopsis thaliana glutathione transferase Phi 9 (GSTF9). GSTF9 has no cysteine in its sequence, and it adopts a universal GST structural fold characterized by a typical conserved GSH-binding site (G-site) and a hydrophobic co-substrate-binding site (H-site). At elevated H2 O2 concentrations, methionine sulfur oxidation decreases its transferase activity. This oxidation increases the flexibility of the H-site loop, which is reflected in lower activities for hydrophobic substrates. Determination of the transition state thermodynamic parameters shows that upon oxidation an increased enthalpic penalty is counterbalanced by a more favourable entropic contribution. All in all, to guarantee functionality under oxidative stress conditions, GSTF9 employs a thermodynamic and structural compensatory mechanism and becomes substrate of methionine sulfoxide reductases, making it a redox-regulated enzyme.
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Tossounian, M.-A., Wahni, K., Van Molle, I., Vertommen, D., Astolfi Rosado, L., & Messens, J. (2018). Redox‐regulated methionine oxidation of Arabidopsis thaliana glutathione transferase Phi9 induces H‐site flexibility. Protein Science, 28(5), 56-67. https://doi.org/10.1002/pro.3440 (Original work published 2018)