Peptidoglycan recognition protein of Solen grandis (SgPGRP-S1) mediates immune recognition and bacteria clearance

Peptidoglycan recognition proteins (PGRPs) are indispensable molecules in innate immunity due to their prominent function in sensing and eliminating invading microorganisms. In the present study, a short type PGRP from razor clam Solen grandis (SgPGRP-S1) was recombinantly expressed and purified to investigate its potential function in innate immunity. As a pattern recognition receptor, recombinant SgPGRP-S1 (rSgPGRP-S1) specifically bind Lys-type and Dap-type peptidoglycan in vitro, but not lipopolysaccharide or β-glucan. The peptidoglycan binding ability of rSgPGRP-S1 resulted in significant agglutination activity against Gram-negative Escherichia coli and Listonella anguillarum, as well as Gram-positive Micrococcus luteus. Furthermore, rSgPGRP-S1 was bactericidal, significantly suppressing the growth of both E. coli and Gram-positive Staphylococcus aureus. The protein also exhibited strong amidase activity and degraded bacterial peptidoglycan in the presence of Zn²⁺, suggesting amidase activity might contribute to SgPGRP-S1 antibacterial activity. These results indicate SgPGRP-S1 is multifunctional in innate immunity, mediating both immune recognition and bacteria elimination.