A Short-Type Peptidoglycan Recognition Protein From Atrina pectinata (ApPGRP) Exhibits Dual Functions in Pattern Recognition and Antibacterial Defense

Abstract

Peptidoglycan recognition proteins (PGRPs) could serve as key pattern recognition receptors (PRRs) in the innate immune systems of invertebrates. In this study, a short PGRP, designated as ApPGRP, was identified and functionally characterized from the mollusk Atrina pectinata to investigate its roles in immunity. The ApPGRP gene was cloned and found to encode a protein of 314 amino acids. ApPGRP shares 55.6–76.1% sequence identity with other PGRPs and is phylogenetically most closely related to the PGRP from Mimachlamys nobilis. In healthy A. pectinata, ApPGRP mRNA was constitutively expressed in all examined tissues, with the highest level in hepatopancreas. Its expression was significantly up-regulated following bacterial challenge. Recombinant ApPGRP (rApPGRP) exhibited binding ability to peptidoglycan (PGN), chitin, glucan, and zymosan, but not LPS. In vitro, rApPGRP demonstrated potent agglutination capabilities against E. coli and M. luteus. rApPGRP demonstrated Zn²⁺-dependent amidase activity, enabling the catalytic cleavage of PGN. Additionally, rApPGRP displayed direct antibacterial activity against E. coli and V. anguillarum and was capable of inhibiting E. coli biofilm formation in the presence of Zn²⁺. These findings suggest that ApPGRP contributes to the innate immune response of A. pectinata through pathogen recognition, agglutination, and bacterial clearance.