Four crustins involved in antibacterial responses in Marsupenaeus japonicus.

Crustins are a family of cationic, cysteine-rich antimicrobial peptides with a whey acidic protein (WAP) domain in the C-terminal. They have diverse functions in antimicrobial immune responses. Four groups of crustins (crustins I, II, III, and IV) have been identified in crustaceans, but type I crustins have not been reported in penaeid shrimp until now. In this study, we identified four crustins in kuruma shrimp Marsupenaeus japonicus, and named them MjCrus I-2, 3, 4 and 5. These four crustins belong to type I crustins, which contain a signal peptide, cysteine-rich region at the N-terminus, and WAP domain at the C-terminus. Tissue distribution demonstrated that MjCrus I-2, 3 and 5 had high expression levels in hemocytes, gills and stomach. whereas MjCrus I-4 was distributed in all tissues detected. MjCrus I-2 to 5 showed different expression patterns in different tissues after Gram-positive bacterial (Staphylococcus aureus), Gram-negative bacterial (Vibrio anguillarum), and white spot syndrome virus (WSSV) challenge. The expression of MjCrus I-2 to 5 was upregulated by bacterial or WSSV challenge. The three crustins were recombinantly expressed in Escherichia coli, and the purified proteins showed few antimicrobial activities. Three MjCrus Is could bind to different bacteria. MjCrus I-2 and 3 showed different inhibitory abilities to secreted bacterial proteases. MjCrus I-4 could not inhibit bacterial proteases. After knockdown of MjCrus I-3, the bacterial scavenging ability to V. anguillarum was impaired. These results suggested that type I crustins played an important role in the innate immunity of shrimp.

A new group of anti-lipopolysaccharide factors from Marsupenaeus japonicus functions in antibacterial response.

Anti-lipopolysaccharide factors (ALFs) are a group of critical effector molecules with a broad spectrum of antimicrobial activities in crustaceans. Four groups of ALFs (A, B, C, and D) have been identified in peneaid shrimp. In the study, we identified a new group of ALFs (designated as MjALF-E) from Marsupenaeus japonicus. This new group (group E) included MjALF-E1 and E2. MjALF-E1 was highly expressed in hemocytes, heart, and intestine, whereas E2 was highly expressed in gills, stomach, and intestine. Expressions of both MjALF-E1 and E2 were upregulated by bacterial challenge. Synthesized LPS-binding domain peptides of MjALF-E1 and E2 strongly bind to bacterial cell wall components lipopolysaccharide (LPS) and peptidoglycan (PGN). The recombinant rMjALF-E2 showed relatively weak binding activity to LPS and PGN. Both synthesized peptides and rMjALF-E2 exhibited antimicrobial activity against Gram-negative bacteria, whereas rMjALF-E2 could promote the clearance of bacteria in vivo. After knockdown of MjALF-E2 and infection with Vibrio anguillarum, shrimp showed high and rapid mortality compared with GFPi shrimp. These results suggest that MjALF-Es serves a protective function against bacterial infection in shrimp.

A novel crustin from Marsupenaeus japonicus promotes hemocyte phagocytosis.

Crustins are cationic cysteine-rich antimicrobial peptides (AMPs) that contain multiple domains (glycine-rich, cysteine-rich, or proline-rich) at the N-terminus and whey acidic protein (WAP) domains at the C-terminus. Crustins have multiple functions, including protease inhibition and antimicrobial activity. Other functions of crustins need to be clarified. In this study, a novel crustin with a cysteine-rich region, and a single WAP domain, belonging to type I crustins, was identified in Marsupenaeus japonicus and designated as MjCru I-1. MjCru I-1 was expressed in various tissues. The expression of MjCru I-1 was upregulated in the hemocytes of shrimp challenged with bacteria. MjCru I-1 could bind to bacteria by binding to the cell wall molecules of the bacteria, such as lipopolysaccharide (LPS), peptidoglycan (PGN), and lipoteichoic acid (LTA). The synthesized WAP domain of MjCru I-1 but not synthesized Cys-rich domain has antibacterial and agglutinative activities. Scanning electron microscope assay showed that the bacterial cells treated with sMjCru I-1 appeared to be disrupted and cracked compared with those of the control samples. The knockdown of MjCru I-1 could reduce bacterial clearance and injection of MjCru I-1 could significantly increase the survival rate of shrimp infected with Vibrio anguillarum and Staphylococcus aureus compared with those of the control samples. Further study discovered that MjCru I-1 could increase the hemocyte phagocytosis against V. anguillarum and S. aureus. These results suggest that MjCru I-1 has dual functions, bactericidal and phagocytosis promoting activities, in the antibacterial immunity of shrimp.

Calnexin functions in antibacterial immunity of Marsupenaeus japonicus.

Calnexin (Cnx) is an endoplasmic reticulum membrane-bound lectin chaperone that comprises a dedicated maturation system with another lectin chaperone calreticulin (Crt). This maturation system is known as the Cnx/Crt cycle. The main functions of Cnx are Ca(2+) storage, glycoprotein folding, and quality control of synthesis. Recent studies have shown that Cnx is important in phagocytosis and in optimizing dendritic cell immunity. However, the functions of Cnx in invertebrate innate immunity remain unclear. In this research, we characterized Cnx in the kuruma shrimp Marsupenaeus japonicus (designated as MjCnx) and detected its function in shrimp immunity. The expression of MjCnx was upregulated in several tissues challenged with Vibrio anguillarum. Recombinant MjCnx could bind to bacteria by binding polysaccharides. MjCnx protein existed in the cytoplasm and on the membrane of hemocytes and was upregulated by bacterial challenge. The recombinant MjCnx enhanced the clearance of V. anguillarum in vivo, and the clearance effects were impaired after silencing MjCnx with RNA interference assay. Recombinant MjCnx promoted phagocytosis efficiency of hemocytes. These results suggest that MjCnx functions as one of the pattern recognition receptors and has crucial functions in shrimp antibacterial immunity.