Molecular insights into MytiCTL1: A C-type lectin from Mytilus coruscus with potential roles in immunity and feeding

The present study identified and characterized a C-type lectin from Mytilus coruscus , designated MytiCTL1. The full-length cDNA of MytiCTL1 is 791 bp, containing a canonical carbohydrate recognition domain (CRD). Multiple sequence alignment and phylogenetic analyses revealed that MytiCTL1 is closely related to MRC. MytiCTL1 was predominantly expressed in gill tissue, with specific localization to the frontal zone, a region composed of ciliated epithelial cells at the anterior tips of the gill filaments. Transcription of MytiCTL1 was transiently upregulated upon challenge with Vibrio alginolyticus and Staphylococcus aureus . In contrast, expression was significantly decreased under starvation, but was significantly induced after feeding resumed. Functional analyses revealed that recombinant MytiCTL1 protein (rMytiCTL1) exhibits hemagglutinating and carbohydrate-binding activities, along with broad-spectrum bacterial binding, growth inhibition, and agglutination capacities. With the exception of S. aureus , rMytiCTL1 significantly agglutinated and inhibited all tested bacterial species. These findings indicate that MytiCTL1 functions as a pattern recognition receptor (PRR) capable of identifying pathogen-associated molecular patterns (PAMPs), binding to bacteria, inducing agglutination and directly inhibiting bacterial growth, confirming its essential role in immune recognition and defense in mussels. Additionally, rMytiCTL1 exhibited specific agglutination activity toward N. closterium , Isochrysis zhanjiangensis and Platymonas helgolandica . Pre-incubation of these microalgae with rMytiCTL1 led to a significant reduction in their ingestion rates by mussels. These observations indicate that MytiCTL1 also plays a critical role in the recognition of microalgal particles. Overall, this study highlights the multifunctional properties of lectins and provides new perspectives on their biological roles in shellfish. These findings offer promising molecular targets for optimizing feed formulations and preventing bacterial diseases, ultimately improving survival rates in M. coruscus aquaculture.