Identification and characterization of a novel mannose-binding C-type lectin (PjLec2) in shrimp Penaeus japonicus

C-type lectins (CTLs) are important molecules involved in the innate immunity of invertebrates. In this investigation, we reported a novel CTL (designated as PjLec2) from the marine shrimp Penaeus japonicus (P. japonicus). The cDNA of PjLec2 is 669 bp in length with an open reading frame (ORF) of 477 bp. It encodes a protein of 159 amino acids (aa) containing a putative 18-aa signal peptide and a carbohydrate recognition domain (CRD). The CRD of PjLec2 possesses an EPN (Glu-Pro-Asn) motif which is putatively responsible for mannose recognition. Expression pattern analysis demonstrated that PjLec2 mRNA is exclusively expressed in hepatopancreas in P. japonicus. At protein level, PjLec2 is detected in hemolymph and hepatopancreas. Recombinant PjLec2 has a mannose binding activity and a strong agglutination activity against Gram-negative bacteria Vibrio alginolyticus (V. alginolyticus) and Aromonas hydrophila (A. hydrophila) in a calcium-dependent manner. In addition, the expression of PjLec2 is significantly upregulated at both mRNA and protein levels after challenging shrimp with A. hydrophila. Our results indicated that PjLec2 may play a fundamental role in the recognition of pathogenic bacteria in shrimp.