A novel C-type lectin gene with QPS and WND motifs in clam Meretrix meretrix

C-type lectins (CTLs), as a class of classical calcium-dependent pattern recognition receptors (PRRs), plays an essential role in immune recognition and defense. In this study, a novel CTLs (MmCTL5) was identified from clam Meretrix meretrix, and the full-length cDNA of MmCTL5 encoded a 127-amino acids carbohydrate-recognition domain (CRD). The characteristic motifs of the Ca²⁺-binding site of MmCTL5 were QPS and WND. The typical double-loop structure of MmCTL5 contained three disulfide bonds at the bottom. Significant expression of MmCTL5 in hemocytes and hepatopancreas. After stimulation by Vibrio splendidus, the expression levels of MmCTL5 increased by 6.2-fold at 12 h in hemocytes and 9.4-fold at 3 h in hepatopancreas, respectively. The recombinant MmCTL5 protein (rMmCTL5) could agglutinate two kinds of pathogenic Vibrio parahemolyticus. And the rMmCTL5 could bind to a variety of carbohydrates, including four kinds of monosaccharides and two kinds of disaccharides. These results suggested that MmCTL5, as a novel CTL, took an essential part in innate immune response of M. meretrix.