Molecular cloning and functional characterization of a short peptidoglycan recognition protein (HcPGRPS1) from the freshwater mussel, Hyriopsis cumingi

- In this study a short-form HcPGRPS1 was identified in Hyriopsis cumingi.
- The HcPGRPS1 exhibited a wide range of tissues distribution, and the gene was significantly up-regulated in tissues (gonad, nephridium, gill and foot) after LPS or PGN stimulation.
- The PGN binding activity, amidase activity and antibacterial activity of recombinant protein of HcPGRPS1 was experimentally revealed, which suggested its important roles in the innate immune defense against bacterial infections in mussel.

Peptidoglycan recognition proteins (PGRPs), which are evolutionarily conserved from invertebrates to vertebrates, function as pattern-recognition and effector molecules in innate immunity. In the present study, a short-form PGRP, designated as HcPGRPS1 was identified from freshwater mussel Hyriopsis cumingi. The deduced amino acid sequence of HcPGRPS1 is composed of 235 residues which contains a conserved PGRP domain at the C-terminus. Sequence analysis showed that HcPGRPS1 shared high identities with other known PGRPs. The mRNA of HcPGRPS1 is constitutively expressed in a wide range of all tested tissues, with highest expression level in hepatopancreas, and its expression in tissues (gonad, nephridium, gill and foot) was up-regulated significantly after LPS or PGN stimulation (P < 0.05). The recombinant protein of HcPGRPS1 exhibited binding activity and peptidoglycan-lytic amidase activity toward Lys-PGN from Staphylococcus aureus and DAP-PGN from Bacillus subtilis. Furthermore, recombinant HcPGRPS1 displayed strong antibacterial activity to both Gram-negative bacteria Escherichia coli, Aeromonas hydrophila, Aeromonas sobria and Gram-positive bacteria S. aureus in the presence of Zn2+. These results suggested that HcPGRPS1 plays a multifunctional role in the defense and protection mechanisms of mussel innate immunity against infections.