Identification of Caspase-cleavage site in the apoptosis suppressor protein P49 from the Spodoptera littoralis nucleopolyhedrovirus

The p49 gene from baculovirus Spodoptera lit-toralis nucleopolyhedrovirus (SlNPV) was able to suppress apoptosis of Sf9 cells induced by virus infection. Ectopically expressed P49 protein had the capacity to inhibit the activity of Caspases, being the executioner of apoptosis. Digestion of P49 with human Caspase or Bm-Caspase both yielded 10 and 40 kD fragments. Checking the sequence of P49, we found that the motif 91-TVTDG-95 of P49 was the sequence recog-nized by Caspases. The mutant of P49, Asp94Ala, could not be cut by both caspases and lost its caspases inhibition. Meanwhile, Thr91Ala mutant permitted the cleavage and partially retained its activity of caspases inhibition. We also found that P49 was a substrate of upstream initiator caspase and downstream effector Caspases, indicating that P49 was a broad specificity Caspase inhibitor.