Characterization of MytiGal: a galactose-binding lectin in the immune response of Mytilus coruscus – insights from sequence analysis, expression patterns, and bioactivities

Lectins are carbohydrate-binding proteins that function as pattern recognition receptors (PRRs) in animal innate immune system. Although invertebrates like mussels lack adaptive immune cells, they still mount pathogen-specific responses through rapidly recognition of pathogen-associated molecular patterns (PAMPs) by PRRs. Here, we identify and characterize a galactose-binding lectin from Mytilus coruscus, MytiGal, which belongs to the Mytilectin family. MytiGal features a β-trefoil fold with conserved carbohydrate-binding sites and shares significant homology with lectins in other marine bivalves. It is highly expressed in the foot, mantle, and hemocytes, and its expression is significantly upregulated following bacterial challenge. Functional assays using recombinant MytiGal revealed its capacity to bind carbohydrates, broad-spectrum antimicrobial activity, and bacterial binding and agglutination activities. Additionally, MytiGal enhanced hemocyte phagocytic activity and facilitated bacterial clearance both in vivo and in vitro. It also alleviated bacteria-induced vacuolation and activated the antibacterial autophagy of hemocytes by regulating the autophagy pathway and the TLR/NFκB signaling pathway. These findings suggest that MytiGal plays a critical role in the immune response of mussels via the activation of antibacterial autophagy and provide new insights into the immune recognition mechanisms in marine bivalves.