Molecular and functional characterization of peptidoglycan recognition protein-L2 from Hexagrammos otakii (Ho-PGRP-L2) involved in innate immune response.

Peptidoglycan recognition proteins (PGRPs), a family of pattern recognition receptors, play diverse roles in antimicrobial defense. This study investigated the role of a long-type peptidoglycan recognition protein designated as Ho-PGRP-L2 in the antibacterial immune response of the economically important fish species Hexagrammos otakii. Ho-PGRP-L2 was successfully cloned and characterized, which possesses a signal peptide, a typical PGRP domain, and a Zn binding domain including four specific amino acid residues which were required for amidase activity. The qRT-PCR analysis revealed that Ho-PGRP-L2 was predominantly expressed in the liver, with very low levels in the other tissues. The recombinant Ho-PGRP-L2 protein (rHo-PGRP-L2) exhibited polysaccharide-binding, bacteria-binding, bacteria agglutinating, amidase, and antibacterial activities, indicating its function as a recognizer and effector within the antibacterial immune response. Additionally, rHo-PGRP-L2 enhanced phagocyte chemotaxis, indicating its role as an 'immune activator'. These findings indicated that Ho-PGRP-L2 of H. otakii was involved in host defense against bacterial infections, laying a foundation for developments in H. otakii aquaculture disease management.