Characterization of a Novel C-type Lectin against OsHV-1 infection in Scapharca broughtonii

As important pattern recognition receptors (PRRs), most C-type lectins (CTLs) are a class of Ca2+-dependent carbohydrate-binding proteins that are found to be involved in non-self-recognition and antiviral process. In this study, a new CTL, named SbCTL, was identified from ark clams, Scapharca broughtonii. The amino acid sequence of SbCTL consisted of a predicted CRD (carbohydrate recognition domain) structural domain (including 102 amino acid residues). The amino acid sequence of SbCTL shared 28 % - 39 % similarity with other CTLs. There were two potential Ca2+ binding sites in SbCTL. The expression of SbCTL mRNA was detected in all selected tissues, with the highest expression in the gills. Expression of SbCTL mRNA increased significantly (p < 0.05) and total vibrio content increased significantly (p < 0.05) in ark clam infected with OsHV-1 at 72 h post-infection. The binding activities of recombinant SbCTL (rSbCTL) to various PAMPs with or without Ca2+ were analyzed by ELISA, rSbCTL showed especially high binding activity to LPS in a Ca2+-independent manner. rSbCTL also functioned on sheltering ark clams from OsHV-1 infection in vivo, there were less mortality occurred in the rSbCTL treated group than the control. In all, it suggests that SbCTL, could served a critical role in the immune response against intruders in ark clams.