Functional characterization of calreticulin in the antiviral response of Litopenaeus vannamei against white spot syndrome virus

Abstract

Calreticulin (CRT) is a highly conserved calcium-binding protein that participates in various biological processes such as calcium homeostasis, molecular chaperoning, and immune function. In the present study, the complete cDNA sequence of CRT (LvCRT) was cloned and characterized from Litopenaeus vannamei. The deduced amino acid sequence of LvCRT contained two conserved CRT family signatures, three conserved repeated CRT family motifs, and an HDEL motif, a signature sequence for endoplasmic reticulum retention. The highest mRNA expression of LvCRT was detected in the hepatopancreas of healthy shrimp. When the shrimp were challenged with white spot syndrome virus (WSSV), significantly upregulated expression of LvCRT was detected at 24 h post-injection (hpi). The recombinant protein of LvCRT (rLvCRT) was produced, and its functions were characterized. It could induce agglutination of all tested microorganisms, especially Vibrio parahaemolyticus, which could be inhibited by lipopolysaccharide (LPS) and N-acetyl neuraminic acid (NeuNAc). rLvCRT could bind not only to saccharides on microbial surfaces but also to the recombinant protein of C-type lectin (CTL) containing a low-density lipoprotein receptor domain from Litopenaeus vannamei (rLvLdlr). The rLvCRT-rLvLdlr complex could interact with a recombinant protein of WSSV (rVP28), impairing WSSV infection. These findings confirm that LvCRT plays a role in shrimp immunity. LvCRT might cooperate with other CTLs in antiviral activity by binding to WSSV to prevent the penetration of WSSV into the host cells.