SpgC1qR interacts with WSSV VP28 exhibiting antiviral activity.

Although human gC1qR is a multi-ligand binding protein with diverse biological functions, the functions of invertebrate gC1qR homologues remain largely unknown. In the present study, we characterized a novel gC1qR homologue, namely SpgC1qR, from mud crab Scylla paramamosain. SpgC1qR shared high identity and similar three-dimensional structure with human gC1qR. After challenge with White spot syndrome virus (WSSV), the transcripts of SpgC1qR were significantly increased, suggesting that SpgC1qR may be involved in antiviral immune response. To reveal the likely antiviral activity of SpgC1qR, the proliferation profile of WSSV in SpgC1qR-silenced crabs was examined. The result showed that knockdown of SpgC1qR by RNAi facilitated viral proliferation in vivo. This result was further confirmed by a SpgC1qR pre-incubation assay, in which pre-incubating WSSV particles with rSpgC1qR dramatically suppressed viral replication. Moreover, a GST pull-down assay revealed that SpgC1qR specifically bound to the viral envelope protein VP28. These findings clearly demonstrated that SpgC1qR specifically interacted with viral envelope protein VP28 and restricted WSSV replication, suggesting that it played a crucial role in anti-WSSV immune response of mud crab. This study provided new insights into the antiviral mechanism mediated by SpgC1qR and the biological functions of invertebrate gC1qR homologues.