Cystamine and Disulfiram Inhibit Human Transglutaminase 2 via an Oxidative Mechanism

• Published in: Biochemistry (Easton) Vol. 57; no. 24; pp. 3359 - 3363
• Main Authors: Palanski, Brad A, Khosla, Chaitan
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.06.2018
• Subjects: Biocatalysis; Cystamine - chemistry; Cystamine - pharmacology; Disulfiram - chemistry; Disulfiram - pharmacology; Dose-Response Relationship, Drug; GTP-Binding Proteins - antagonists & inhibitors; GTP-Binding Proteins - metabolism; Humans; Kinetics; Molecular Structure; Oxidation-Reduction; Structure-Activity Relationship; Transglutaminases - antagonists & inhibitors; Transglutaminases - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/acs.biochem.8b00204

The catalytic activity of transglutaminase 2 (TG2), a ubiquitously expressed mammalian enzyme, is regulated by multiple post-translational mechanisms. Because elevated activity of TG2 in the extracellular matrix is associated with organ-specific diseases such as celiac disease and renal fibrosis, there is growing therapeutic interest in inhibitors of this enzyme. Cystamine, a symmetric disulfide compound, is one of the earliest reported TG2 inhibitors. Despite its widespread use as a tool compound to block TG2 activity in vitro and in vivo, its mechanism of action has remained unclear. Here, we demonstrate that cystamine irreversibly inhibits human TG2 (k inh/K i = 1.2 mM–1 min–1) via a mechanism fundamentally distinct from those proposed previously. Through mass spectrometric disulfide mapping and site-directed mutagenesis, we show that cystamine promotes the formation of a physiologically relevant disulfide bond between Cys370 and Cys371 that allosterically abrogates the catalytic activity of human TG2. This discovery led us to evaluate clinically useful thiol → disulfide oxidants for TG2 inhibitory activity. It is demonstrated that disulfiram, a relatively safe oral thiuram disulfide, is a fairly potent TG2 inhibitor (k inh/K i = 8.3 mM–1 min–1) and may therefore provide a practical tool for clinically validating this emerging therapeutic target in intestinal disorders such as celiac disease.