Characterization of a crustin-like peptide involved in shrimp immune response to bacteria and Enterocytozoon hepatopenaei (EHP) infection in Palaemon carinicauda

Crustins represent one type of antimicrobial peptides (AMPs) that are key components of the innate immune process of crustaceans. This study successfully identified a novel crustin-like peptide, EcCrustin2, in ridgetail white prawn, Palaemon carinicauda (formerly Exopalaemon carinicauda). EcCrustin2 was found to be 1082 bp in length, with a 378 bp open reading frame (ORF) encoding 125 amino acids. The deduced amino acid sequence of EcCrustin2 exhibited characteristics of crustins in crustacean, including a Cys-rich region at the N-terminus as well as a whey acidic protein domain at the C-terminus. Phylogenetic analysis revealed that the EcCrustin2 was first clustered with Type I crustins, then with other crustins. Expression of EcCrustin2 was mainly detected in immune tissues, including hemocytes, gill and stomach. The expression level of EcCrustin2 was also significantly up-regulated after being exposed to lipopolysaccharide (LPS), lipoteichoic acid (LTA), Vibrio parahaemolyticus and Staphylococcus aureus. EHP infection could also induce EcCrustin2 expression in P. carinicauda. Knockdown of EcCrustin2 with siRNA increased the mortality of V. parahaemolyticus challenged shrimp. Finally, the recombinant EcCrustin2 protein was obtained and demonstrated a wide spectrum of antibacterial activity in vitro. These results indicated that EcCrustin2 takes part in the immune response against bacteria and EHP infection.