Molecular cloning of a C-type lectin with two CRD domains from the banana shrimp Fenneropenaeus merguiensis: early gene up-regulation after Vibrio harveyi infection.

A diverse class of pattern-recognition proteins called lectins play important roles in shrimp innate immunity. A novel C-type lectin gene (FmLC) was cloned from the hepatopancreas of banana shrimp Fenneropenaeus merguiensis by means of PCR and 5' and 3' rapid amplification of cDNA ends (RACE). The full-length cDNA consists of 1118 bp with one 1002 bp open reading frame, encoding 333 amino acids. Its deduced amino acid sequence contains a putative signal peptide of 20 amino acids. FmLC contains two carbohydrate recognition domains, CRD1 and CRD2, that share only 30% identity with each other. The first CRD comprises a QPD motif with specificity for binding galactose and a single Ca(2+) binding site, while the second CRD consists of an EPN motif for a mannose-specific binding site. FmLC had a close evolutionary relationship to other dual-CRD lectins of penaeid shrimp. Expression results showed that transcripts of FmLC were detected only in the hepatopancreas, none was found in other tissues. After challenging either whole shrimp or hepatopancreas tissue fragments with Vibrioharveyi, the expression of FmLC was up-regulated. This indicates that FmLC is inducible and may be involved in a shrimp immune response to recognize potential bacterial pathogens.