Transglutaminase 2 activity is enhanced via S-glutathionylation under oxidative stress conditions

Abstract

Transglutaminase 2 (TG2) is an enzyme that catalyzes, in a calcium-dependent manner, the incorporation of primary amino groups of various compounds into glutaminyl side-chains in protein substrates. It has been reported that TG2 is activated under oxidative stress conditions. Moreover, it has been suggested that reduction-oxidation (redox)-sensitive cysteinyl thiols of TG2 are involved in regulation of TG2 activity. Intracellular redox status can be detected by various protein thiol modifications. S-glutathionylation of proteins (PSSG) is a process in which mixed disulfide bonds are formed between cysteinyl thiols and glutathione. PSSG can be used to modulate target protein function and to protect proteins from irreversible oxidative damage. However, S-glutathionylation of TG2 and the resulting products effects on protein function have not been previously reported. In this study, TG2 is shown to undergo S-glutathionylation when purified TG2 is treated with oxidized glutathione (GSSG). In vitro enzymatic activity of S-glutathionylated TG2 (TG2-SG) was enhanced compared to that of the untreated control. Treatment of TG2-SG with various thiol-containing compounds resulted in deglutathionylation. HeLa cells cultured under oxidative stress conditions with a high ratio of GSSG to reduced glutathione (GSH) resulted in enhanced transamidation activity. The TG2 S-glutathionylation sites were identified by using mass spectrometry. The results indicate that TG2 can be S-glutathionylated under oxidative stress conditions and that S-glutathionylation of TG2 can result in enhancement of the transamidation activity of TG2.