Determination of the efficacy of using a serine protease gene as a DNA vaccine to protect against Vibrio parahaemolyticus infection in Litopenaeus vannamei

Serine proteases are proteolytic enzymes that exhibit biological roles in many biological systems. Previously, a Vibrio parahaemolyticus serine protease was reported to be a virulence factor. Here, the serine protease gene of V. parahaemolyticus was investigated as a DNA vaccine against V. parahaemolyticus in Litopenaeus vannamei. The serine protease gene was mutated to replace the conserved residues His82, Asp131 and Ser231 with Gly, Asp and Pro, respectively. Then, a pcDNA3.1 vector to express mutVpSP (mutant serine protease) was constructed for in vitro and in vivo DNA vaccine investigation. In vivo mutVpSP transcriptional analysis revealed expression in various immunized white shrimp tissues, such as hemocytes, hepatopancreas, stomach, intestine, gills, and muscle. The efficiency of prevention of V. parahaemolyticus infection was investigated in vaccinated shrimp, and the lowest cumulative mortality percentage was 30%, while the control shrimp had a 60% cumulative mortality rate. The immune system was stimulated in shrimp vaccinated with the DNA vaccine. The mRNA expression of the shrimp immune-responsive genes phenoloxidase, peroxinectin and C-type lectin was significantly upregulated. Additionally, the humoral and cellular immune responses, including the PO, phagocytic, and encapsulation activities and nodule formation, were elevated. These results suggested that the serine protease could be a V. parahaemolyticus virulence determinant and that this DNA vaccine could be applied as an effective vaccine candidate for control of acute hepatopancreatic necrosis disease syndrome (AHPND) in shrimp.

Effects of the interaction between a clip domain serine protease and a white spot syndrome virus protein on phenoloxidase activity

Clip domain serine proteinases participate in invertebrate innate immunity by acting as crucial enzymes in the signaling cascade involved in shrimp immunity. To functionally characterize its role in Fenneropenaeus merguiensis, FmclipSP cDNA was cloned and characterized. The FmclipSP gene comprised 1353 bp with an open reading frame of 1110 bp and encoded 369 amino acids. The protein contained clip and serine protease domains. FmClipSP mRNA is highly expressed in hemocytes, and its expression was significantly upregulated by bacterial or viral pathogen challenge. Furthermore, FmClipSP recombinant protein (rFmClipSP) was produced and possessed protease activity, stimulating prophenoloxidase activity. Additionally, rFmClipSP exhibited antibacterial activity against pathogens and nonpathogens. ELISA results demonstrated the binding ability of rFmClipSP to a recombinant protein of VP28 (rVP28). Interestingly, the binding significantly inhibited prophenoloxidase activity. Altogether, we partially characterized the function of FmclipSP and demonstrated its association with VP28. This study indicates the importance of clipSP as a component of F. merguiensis innate immunity. However, the role of clipSP in crustaceans remains unclear and requires further investigation.