Molecular characterization and functional analysis of Peptidoglycan recognition protein-L2 in Hexagrammos otakii

Peptidoglycan recognition proteins (PGRPs) belong to the pattern recognition receptors (PRRs), which are essential for sensing and defending against pathogenic microorganisms during innate immunity pathways. Although an increasing body of research indicates that the PGRP protein in fish has various biological functions such as antimicrobial activity, amidase activity, and the ability to regulate multiple signaling pathways, the molecular mechanisms by which PGRP contributes to the innate immune processes in fish remain relatively limited. In the present study, we have recombinantly expressed a long-type PGRP from fat greenling ( Hexagrammos otakii ) (HoPGRP-L2) and analyzed its molecular mechanism in the pathogen identification process. The open reading frame (ORF) of HoPGRP-L2 is 1449 bp in length that encodes for a peptide with 482 amino acids. As a PRR, HoPGRP-L2 has a typical PGRP domain that enables HoPGRP-L2 to recognize and conjugate to bacterial peptidoglycan (PGN) on the cell wall. We demonstrated that HoPGRP-L2 could bind to pathogenic microorganisms and promote the agglutination of them. Furthermore, HoPGRP-L2 was confirmed to possess zinc ion-dependent amidase activity and exhibited an effect on the growth inhibition of chosen bacteria. HoPGRP-L2 also prolongs the survival time in carp injected with Aeromonas hydrophila . Taken together, our results indicate that PGRP acts as a PRR involved in recognizing and eliminating pathogens during the innate immune response in Hexagrammos otakii .