Metabolic Synthesis of Clickable Glutathione for Chemoselective Detection of Glutathionylation

Glutathionylation involves reversible protein cysteine modification that regulates the function of numerous proteins in response to redox stimuli, thereby altering cellular processes. Herein we developed a selective and versatile approach to identifying glutathionylation by using a mutant of glutathione synthetase (GS). GS wildtype catalyzes coupling of gamma Glu-Cys to Gly to form glutathione. We generated a GS mutant that catalyzes azido-Ala in place of Gly with high catalytic efficiency and selectivity. Transfection of this GS mutant (F152A/S151G) and incubation of azido-Ala in cells efficiently afford the azide-containing glutathione derivative, gamma Glu-Cys-azido-Ala. Upon H2O2 treatment, clickable glutathione allowed for selective and sensitive detection of glutathionylated proteins by Western blotting or fluorescence after click reaction with biotin-alkyne or rhodamine-alkyne. This approach affords the efficient metabolic tagging of intracellular glutathione with small clickable functionality, providing a versatile handle for characterizing glutathionylation.