Identification of antigenic domains and peptides from VP15 of white spot syndrome virus and their antiviral effects in Marsupenaeus japonicus.

White spot syndrome virus (WSSV) is one of the most devastating pathogens in penaeid shrimp and can cause massive damage in shrimp aquaculture industries. Previously, the WSSV structural protein VP15 was identified as an antigenic reagent against WSSV infections. In this study, we truncated this protein into VP15(1-25), VP15(26-57), VP15(58-80), and VP15(1-25,58-80). The purified proteins from the E. coli expression system were assayed as potential protective agents in Kuruma shrimp (Marsupenaeus japonicus) using the prime-and-boost strategy. Among the four truncated constructs, VP15(26-57) provided a significant improvement in the shrimp survival rate after 20 days of viral infection. Subsequently, four peptides (KR11, SR11, SK10, and KK13) from VP15(26-57) were synthesized and applied in an in vivo assay. Our results showed that SR11 could significantly enhance the shrimp survival rate, as determined from the accumulated survival rate. Moreover, a multiligand binding protein with a role in the host immune response and a possible VP15-binding partner, MjgC1qR, from the host M. japonicus were employed to test its binding with the VP15 protein. GST pull-down assays revealed that MjgC1qR binds with VP15, VP15(26-57), and SR11. Taken together, we conclude that SR11 is a determinant antigenic peptide of VP15 conferring antiviral activity against WSSV.