Expression and functional characterization of three peptidoglycan recognition proteins, PGRP-L1, PGRP-L2 and PGRP-S in snakehead (Channa argus)

• Two long-type PGRP and one short PGRP, named as CaPGRP-L1, -L2 and -S were identified from snakehead. • CaPGRP-L1, -L2 showed high expression in the intestine and liver, while CaPGRP-S was abundant in the gill. • Three snakehead PGRPs demonstrated PGN-binding activity, amidase activity and antibacterial activity . • Three snakehead PGRPs are involved in NF-κB signaling. Peptidoglycan recognition proteins (PGRPs) are evolutionarily conserved pattern recognition receptors critical for antibacterial immunity across vertebrates and invertebrates. In this study, two long-type (CaPGRP-L1, -L2) and one short-type (CaPGRP-S) PGRP genes were identified in snakehead ( Channa argus ), an economically important aquaculture species. Sequence analysis revealed that all three PGRPs contain a conserved Zn²⁺-binding site (composed of two His, one Tyr, and one Cys), essential for amidase activity. Tissue distribution profiling showed distinct expression patterns, with high transcript levels detected in liver, intestine or gill. Functional assays demonstrated that recombinant CaPGRP-L1, -L2, and -S bound peptidoglycan (PGN), displayed Zn²⁺-dependent amidase activity, and inhibited Aeromonas hydrophila infection. Furthermore, three PGRPs activated NF-κB promoter reporter plasmid in a dose-dependent manner, while NF-κB subunits c-Rel and p65 upregulated the transcriptional activity of CaPGRP-L1, -L2, and -S luciferase promoters, suggesting that snakehead PGRPs are involved in NF-κB signaling. Collectively, this study has explored the function of snakehead PGRPs, and deepens our understanding on innate immune mechanisms in fish, which should provide a theoretical foundation for the application of snakehead PGRPs in preventing and controlling diseases in aquaculture.