Ca2+: a stabilizing component of the transglutaminase activity of Gα(h) (Transglutaminase II)

초록

Galpha(h) (transglutaminase type II; tissue transglutaminase) is a bifunctional enzyme with transglutaminase (TGase) and guanosine triphosphatase (GTPase) activities.. The GTPase function of Galpha(h) is involved in hormonal signaling and cell growth while the TGase function plays an important role in apoptosis and in cross-linking extracellular and intracellular proteins. To analyze the regulation of these dual enzymatic activities we examined their calcium-dependence and thermal stability in enzymes from several cardiac sources (mouse heart, and normal, ischemic and dilated cardiomyopathic human hearts). The GTP binding activity of Galpha(h) was markedly inhibited by Ca2+ whereas the TGase activity was strongly stimulated, suggesting that Ca2+ acts as a regulator, switching Galpha(h) from a GTPase to a TGase. The TGase function of Galpha(h) of both mouse and human hearts was more thermostable in the presence of Ca2+.

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