Redox regulation of transglutaminase 2 activity

Abstract

Transglutaminase 2 (TG2) in the extracellular matrix is largely inactive but is transiently activated upon certain types of inflammation and cell injury. The enzymatic activity of extracellular TG2 thus appears to be tightly regulated. As TG2 is known to be sensitive to changes in the redox environment, inactivation through oxidation presents a plausible mechanism. Using mass spectrometry, we have identified a redox-sensitive cysteine triad consisting of Cys230, Cys370, and Cys371 that is involved in oxidative inactivation of TG2. Within this triad, Cys370 was found to participate in disulfide bonds with both Cys230 and its neighbor, Cys 371. Notably, Ca2+ was found to protect against formation of these disulfide bonds. To investigate the role of each cysteine residue, we created alanine mutants and found that Cys230 appears to promote oxidation and inactivation of TG2 by facilitating formation of Cys 370-Cys371 through formation of the Cys 230-Cys370 disulfide bond. Although vicinal disulfide pairs are found in several transglutaminase isoforms, Cys230 is unique for TG2, suggesting that this residue acts as an isoformspecific redox sensor. Our findings suggest that oxidation is likely to influence the amount of active TG2 present in the extracellular environment. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.