Centre for Immune Regulation, Institute of Immunology, University of Oslo, Oslo, Norway.
J Biol Chem. 2010 Aug 13;285(33):25402-9. doi: 10.1074/jbc.M109.097162. Epub 2010 Jun 14.
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 Cys(230), Cys(370), and Cys(371) that is involved in oxidative inactivation of TG2. Within this triad, Cys(370) was found to participate in disulfide bonds with both Cys(230) and its neighbor, Cys(371). Notably, Ca(2+) 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 Cys(230) appears to promote oxidation and inactivation of TG2 by facilitating formation of Cys(370)-Cys(371) through formation of the Cys(230)-Cys(370) disulfide bond. Although vicinal disulfide pairs are found in several transglutaminase isoforms, Cys(230) is unique for TG2, suggesting that this residue acts as an isoform-specific redox sensor. Our findings suggest that oxidation is likely to influence the amount of active TG2 present in the extracellular environment.
细胞外基质中的转谷氨酰胺酶 2（TG2）在很大程度上是无活性的，但在某些类型的炎症和细胞损伤时会短暂激活。因此，细胞外 TG2 的酶活性似乎受到严格调控。由于已知 TG2 对氧化还原环境的变化敏感，通过氧化失活是一种合理的机制。我们使用质谱法鉴定了一个由半胱氨酸 230、370 和 371 组成的氧化还原敏感半胱氨酸三肽，该三肽参与了 TG2 的氧化失活。在这个三肽中，半胱氨酸 370 被发现与半胱氨酸 230 和其相邻的半胱氨酸 371 形成二硫键。值得注意的是，Ca2+ 被发现可以防止这些二硫键的形成。为了研究每个半胱氨酸残基的作用，我们创建了丙氨酸突变体，发现半胱氨酸 230 似乎通过形成半胱氨酸 230-半胱氨酸 370 二硫键来促进半胱氨酸 370-半胱氨酸 371 的形成，从而促进 TG2 的氧化和失活。尽管几个转谷氨酰胺酶同工型中都发现了毗邻的二硫键对，但半胱氨酸 230 是 TG2 所特有的，这表明该残基作为同工型特异性的氧化还原传感器发挥作用。我们的发现表明，氧化可能会影响细胞外环境中活性 TG2 的含量。
