Abstract:
Peptidoglycan recognition proteins (PGRPs) are a widely studied group of pattern recognition receptors
found in invertebrate as well as vertebrate lineages, and are involved in bacterial pathogen sensing.
However, in addition to this principal role, they can also function in multiple host defense processes,
including cell phagocytosis and hydrolysis of peptidoglycans (PGNs). In this study, a novel invertebrate
short-type PGRP was identified in disk abalone (Haliotis discus discus) designated as AbPGRP. The
complete coding sequence of AbPGRP was 534 bp, encoding a 178-amino acid protein with a predicted
molecular mass of 20 kDa. The AbPGRP gene had a bipartite arrangement consisting of two exons
separated by a single intron. Homology analysis revealed that AbPGRP shares conserved features,
including amino acid residues critical for substrate and ion binding as well as for its amidase activity,
with homologs of other species. Phylogenetic analysis of AbPGRP revealed that it likely evolved from a
common ancestor of invertebrates, having significant homology with other molluscan PGRPs. Recombinant AbPGRP exhibited detectable, dose-dependent PGN-hydrolyzing activity with the presence of
Zn2þ, and strong antibacterial activity against Vibrio tapetis, consistent with the functional properties
previously reported for PGRPs in other mollusks. Moreover, AbPGRP transcription was induced upon
treatment of healthy abalones with bacterial peptidoglycan and lipopolysaccharide, although the
expression profiles differed with treatment, suggesting a capacity for discriminating between bacterial
pathogens through molecular pattern recognition. Collectively, the findings of this study indicate that
AbPGRP is a true homolog of invertebrate PGRPs and likely plays an indispensable role in host immunity.
