A molluscan calreticulin ortholog from Haliotis discus discus: Molecular characterization and transcriptional evidence for its role in host immunity

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

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.

Two novel calreticulin-related molecules with microbial binding and phagocytosis enhancing capacity in the half-smooth tongue sole, Cynoglossus semilaevis

Calreticulin (CRT) is highly conserved chaperone located in the endoplasmic reticulum. It plays important roles in innate immunity. Although various immune-related functions of CRT have been reported in vertebrates and invertebrates, information on the potential functions of teleost CRT is very limited. In the present study, we characterized two calreticulin-related molecules from tongue sole (Cynoglossus semilaevis), calreticulin-like1 and calreticulin-like2 (CsCRTL1 and CsCRTL2). CsCRTL1and CsCRTL2 contain signature CRT motifs that are highly conserved in different species. CsCRTL1and CsCRTL2 were expressed in liver, head kidney, brain, spleen, heart, muscle, skin, intestine and gills. The expression levels of CsCRTL1and CsCRTL2 were highest in liver and spleen, respectively. After stimulation by Vibrio anguillarum and Streptococcus agalactiae, CsCRTL1 and CsCRTL2 were significantly up-regulated. The expression patterns depended on the tissue type, pathogen type, and infection time. The recombinant proteins rCsCRTL1and rCsCRTL2 bound to different pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and to different bacteria, such as Gram-negative bacteria V. anguillarum and Gram-positive bacteria Staphylococcus aureus. Moreover, rCsCRTL1and rCsCRTL2 significantly enhanced the killing of V. anguillarum by tongue sole macrophages. Our results indicate that CsCRTL1and CsCRTL2 play important roles in antibacterial immunity of tongue sole.

Identification and characterization of a novel calreticulin involved in the immune response of the Zhikong scallop, Chlamys farreri

Calreticulin (CRT) is a multifunctional calcium-binding chaperone shared among vertebrates and invertebrates. In this study, a novel CRT (CfCRT) was identified in the Zhikong scallop Chlamys farreri by rapid amplification of cDNA ends. The full-length cDNA was composed of 1345 bp, which included a 1158 bp open reading frame, a 25 bp 5'-untranslated region (UTR) and a 162 bp 3'-UTR. The predicted molecular mass of CfCRT was 44.8 kDa. CfCRT contained three highly conserved domains (N-, P- and C-domains) essential to the function of CRT. BLAST analysis revealed significant sequence similarity (73%-92%) with CRT proteins from other mollusks. The mRNA transcripts of CfCRT were present in all the tested tissues of Zhikong scallops, with the higher expression level in the hemocytes and mantle. After stimulation by Vibrio anguillarum, the mRNA transcript of CfCRT in hemocytes was significantly upregulated. Recombinant plasmid pBCRT was successfully expressed in Escherichia coli BL21 (DE3). The recombinant (r)CfCRT protein could bind to the surface of several bacteria including the Gram-negative bacteria V. anguillarum, E. coli, and the Gram-positive bacterium Staphylococcus aureus. Moreover, rCfCRT was able to suppress their growth significantly. These results indicate that CfCRT might act as an immune effector in Zhikong scallop innate immunity.