Interaction of the Small GTPase Cdc42 with Arginine Kinase Restricts White Spot Syndrome Virus in Shrimp.

Many types of small GTPases are widely expressed in eukaryotes and have different functions. As a crucial member of the Rho GTPase family, Cdc42 serves a number of functions, such as regulating cell growth, migration, and cell movement. Several RNA viruses employ Cdc42-hijacking tactics in their target cell entry processes. However, the function of Cdc42 in shrimp antiviral immunity is not clear. In this study, we identified a Cdc42 protein in the kuruma shrimp () and named it Cdc42. Cdc42 was upregulated in shrimp challenged by white spot syndrome virus (WSSV). The knockdown of Cdc42 and injection of Cdc42 inhibitors increased the proliferation of WSSV. Further experiments determined that Cdc42 interacted with an arginine kinase (AK). By analyzing the binding activity and enzyme activity of AK and its mutant, ΔAK, we found that AK could enhance the replication of WSSV in shrimp. AK interacted with the envelope protein VP26 of WSSV. An inhibitor of AK activity, quercetin, could impair the function of AK in WSSV replication. Further study demonstrated that the binding of Cdc42 and AK depends on Cys of AK and suppresses the WSSV replication-promoting effect of AK. By interacting with the active site of AK and suppressing its enzyme activity, Cdc42 inhibits WSSV replication in shrimp. Our results demonstrate a new function of Cdc42 in the cellular defense against viral infection in addition to the regulation of actin and phagocytosis, which has been reported in previous studies. The interaction of Cdc42 with arginine kinase plays a crucial role in the host defense against WSSV infection. This study identifies a new mechanism of Cdc42 in innate immunity and enriches the knowledge of the antiviral innate immunity of invertebrates.