A single-CRD C-type lectin from Haliotis discus hannai acts as pattern recognition receptor enhancing hemocytes opsonization.

C-type lectins (CTLs), as a member of the Ca2+-dependent carbohydrate recognition protein superfamily, play multiple roles in non-self recognition and the elimination of invading pathogens. In this study, a C-type lectin was identified and characterized from the Pacific abalone Haliotis discus hannai (designed as Hd Clec), and its open reading frame (ORF) encoded a polypeptide of 163 amino acids containing a typical signal peptide and only one carbohydrate-recognition domain (CRD). The deduced amino acid sequence of CRD in Hd Clec shared identities ranging from 22.4% to 39.8% with that of other identified CRDs of CTLs. A novel NPN motif was found in Ca2+-binding site 2 of Hd Clec. The mRNA transcripts of Hd Clec were detectable in all the examined tissues of non-stimulated abalones, with the highest expression in hepatopancreas (224.13-fold of that in gills). The expression of Hd Clec mRNA in hemocytes was significantly up-regulated after Vibrio harveyi challenge. Recombinant Hd Clec protein (r Hd Clec) could bind lipopolysaccharide (LPS) and peptidoglycan (PGN) in vitro in the presence of Ca2+. Coinciding with the PAMPs binding assay, r Hd Clec displayed broad agglutination activities towards Gram-negative bacteria V. splendidus , V. anguillarum , V. parahaemolyticus , V. harveyi , Escherichia coli , and Gram-positive bacteria Micrococcus luteus. Moreover, r Hd Clec could significantly elicit the chemotactic response of hemocytes in vitro. And the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by r Hd Clec. All these results showed that Hd Clec could function as pattern recognition receptors (PRRs) and further enhance the opsonization of hemocytes, which might play a crucial role in the innate immune responses of Pacific abalone. • A single-CRD C-type lectin (Hd CLec) with novel NPN motif was identified from abalone. • The mRNA of Hd CLec was significantly up-regulated post Vibrio harveyi challenge. • R Hd CLec displayed broad microbe agglutination spectrum. • R Hd CLec could elicit the chemotactic response of hemocytes in vitro. • R Hd CLec could function as an opsonin enhancing phagocytosis and encapsulation activities of hemocytes. [ABSTRACT FROM AUTHOR]