PmSERPIN3 from black tiger shrimp Penaeus monodon is capable of controlling the proPO system

Serpin or serine proteinase inhibitor is a family of protease inhibitors that are involved in controlling the proteolytic cascade in various biological processes. In shrimp, several serpins have been identified but only a few have been characterized. Herein, the PmSERPIN3 gene identified from Penaeus monodon EST database was studied. By using the 5'- and 3'-Rapid Amplification of cDNA Ends (RACE) techniques, the full-length of PmSERPIN3 cDNA was obtained. The cDNA contained an open reading frame of 1233 bp encoding for 410 amino acid residue protein. Genome sequence analysis revealed that the PmSERPIN3 was an intronless gene. RT-PCR analysis revealed that it was constitutively expressed in all developmental stages, all shrimp tissues tested, and upon pathogen infections. The recombinant mature PmSERPIN3 protein (rPmSERPIN3) produced in Escherichia coli exhibited inhibitory activity against subtilisin. The rPmSERPIN3 also inhibited the shrimp prophenoloxidase system activation in vitro. Injecting the rPmSERPIN3 along with Vibrio harveyi into the shrimp decreased the clearance rate of bacteria in the hemolymph. Potentially, the PmSERPIN3 functions as a regulator of the proPO activating system.