Activation of transglutaminase in mu-calpain null erythrocytes.
Intracellular transglutaminases (protein-glutamine: amine gamma-glutamyltransferase, EC 2.3.2.13) are calcium-dependent thiol enzymes that catalyze the covalent cross-linking of proteins, including those in the erythrocyte membrane. Several studies suggest that the activation of some transglutaminases is positively regulated by the calcium-dependent cysteine protease, mu-calpain. Using mu-calpain null (Capn1(-/-)) mouse erythrocytes, we demonstrate that the activation of soluble as well as membrane-bound forms of transglutaminase (TG2) in mouse erythrocytes was independent of mu-calpain. Also, the absence of mu-calpain or any detectable cysteine protease did not affect the transglutaminase activity in the erythrocyte lysate. Our studies also identify physiological substrates of mu-calpain in the erythrocyte membrane and show that their cleavage has no discernible effect on the transglutaminase mediated cross-linking of membrane proteins. Taken together, these data suggest the existence of a calpain-independent mechanism for the activation of transglutaminase 2 by calcium ions in the mouse erythrocytes and presumably also in non-erythroid cells.[1]References
- Activation of transglutaminase in mu-calpain null erythrocytes. O'Neill, G.M., Prasanna Murthy, S.N., Lorand, L., Khanna, R., Liu, S.C., Hanspal, M., Hanada, T., Chishti, A.H. Biochem. Biophys. Res. Commun. (2003) [Pubmed]
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