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Type II Metacaspases Atmc4 And Atmc9 OfArabidopsis ThalianaCleave Substrates After Arginine And Lysine

Dominique Vercammen, Brigitte van de Cotte, Geert De Jaeger, Dominique Eeckhout, Peter Casteels, Klaas Vandepoele, Isabel Vandenberghe, Jozef Van Beeumen, Dirk Inzé, Frank Van Breusegem

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Nine potential caspase counterparts, designated metacaspases, were identified in theArabidopsis thalianagenome. Sequence analysis revealed two types of metacaspases, one with (type I) and one without (type II) a proline- or glutamine-rich N-terminal extension, possibly representing a prodomain. Production of recombinantArabidopsistype II metacaspases inEscherichia coliresulted in cysteine-dependent autocatalytic processing of the proform into large and small subunits, in analogy to animal caspases. A detailed biochemical characterization with a broad range of synthetic oligopeptides and several protease inhibitors of purified recombinant proteins of both metacaspase 4 and 9 showed that both metacaspases are arginine/lysine-specific cysteine proteases and did not cleave caspase-specific synthetic substrates. These findings suggest that type II metacaspases are not directly responsible for earlier reported caspase-like activities in plants.