Molecular cloning and expression of caspase from white shrimp Penaeus merguiensis

Apoptosis is a fundamental cellular process that plays a critical role in normal development and tissue homeostasis, eliminating from an organism unwanted cells, including damaged and virus-infected cells. In order to investigate the significance of apoptosis in response to viral infections in crustacean, we have cloned a caspase gene (cap-3) from the white shrimp, Penaeus merguiensis infected with white spot syndrome virus (WSSV). The deduced amino acid sequence of the protein named CAP-3 was 320 amino acids in length and contained the highly conserved pentapeptide QACRG recognized as the active site of caspase. CAP-3 showed similarities to the insect caspase, Spodoptera frugiperda Sf caspase-1 and the caspases of Spodoptera littoralis, Bombyx mori, Drosophila melanogaster and Anopheles gambiae, which in turn belong to the group of human caspase-3, caspase-7 and CED-3. The recombinant CAP-3 protein prepared from Escherichia coli had enzymatic activity when assayed using a luminescent substrate specific for the cleavage target site for human caspase-3, implying that CAP-3 functioned as caspase-3. There was a high level of expression of this gene product in moribund shrimp infected with WSSV.