A C-type lectin (PvCTL2) from Penaeus vannamei participates in antibacterial immune response to Vibrio parahaemolyticus

C-type lectin is a type of calcium-dependent sugar recognition protein, which plays an important role in recognizing invading microorganisms as non-self and assists in the clearance of pathogenic microorganisms. In this study, a C-type lectin homolog was identified from Penaeus vannamei (PvCTL2) using RACE-PCR method and functionally characterized in detail. The open reading frame (ORF) of PvCTL2 was 1143 bp, encoding 380 amino acids, which contained a conservative carbohydrate recognition domain (CRD) and a low-density lipoprotein receptor (LDLR) domain A. The predicted molecular weight was 41.79 kDa and the theoretical isoelectric point was 6.27. PvCTL2 was relatively high expressed in muscle, intestine, heart, nerve, and hepatopancreas, and Vibrio parahaemolyticus challenge could significantly upregulate the expression level of PvCTL2 in muscle. Agglutination test of recombinant protein of PvCTL2 in vitro showed that rPvCTL2 was a Ca2+-dependent C-type lectin, which could agglutinate five types of bacteria, including Gram-negative bacteria and fungi, as well as bind different concentrations of monosaccharides. RNAi-based silencing of PvCTL2 gene resulted in significantly higher mortality rate when shrimp was challenged with Vibrio parahaemolyticus, and the median lethal time was significantly shorter than the control. These results suggested that PvCTL2 could be involved in the immune response against bacterial challenge and contributed to non-self recognition as a pattern recognition receptor in the innate immune system of shrimp P. vannamei.