Functional characterization of a canonical C-type lectin from Mytilus coruscus: Roles in innate immunity and feeding processes

C-type lectins (CTLs) play crucial roles in immune defense and feeding regulation, serving as key mediators of pathogen recognition and nutrient uptake in invertebrates. Although previous studies have demonstrated the involvement of CTLs in the immune response of Mytilus coruscus , their role in feeding regulation remains unclear. In this study, we identified a C-type lectin, designated MytiCTL17A , from M. coruscus and investigated its dual function in immune defense and feeding behavior. The purified recombinant MytiCTL17A binds to LPS and PGN. Additionally, it binds to both Gram-positive and Gram-negative bacteria, promoting bacterial agglutination. Notably, this agglutination can be inhibited by PAMPs. These findings confirm that rMytiCTL17A functions as a pattern recognition receptor (PRR), recognizing PAMPs, binding to bacteria, and promoting their agglutination, thereby playing a role in immune defense. Additionally, rMytiCTL17A also exhibits direct antibacterial activity. In feeding experiments, rMytiCTL17A can bind to microalgae and reduce the feeding rate of M. coruscus , indicating its involvement in the feeding process. Moreover, rMytiCTL17A can recognize carbohydrates (D-Man, D-Gal, Glu, Mal, and Suc) on the surface of microalgae and induce microalgal agglutination. Notably, this agglutination can be inhibited by D-Man, demonstrating its dependence on carbohydrate recognition. Thus, rMytiCTL17A also participates in feeding by recognizing microalgae through specific carbohydrates. This study highlights the multifunctionality of rMytiCTL17A and provides new insights into the roles of C-type lectins in bivalves, with potential implications for aquaculture in terms of enhancing disease resistance and feeding efficiency.