A macin family antimicrobial peptide from Atrina pectinata exhibiting dual functions in direct bactericidal activity...

Antimicrobial peptides (AMPs) are key effectors of innate immunity in invertebrates. In this study, a novel macin family AMP (designated ApMacin) was identified and functionally characterized from the economically important bivalve Atrina pectinata. The open reading frame of ApMacin encodes a 100-amino acid polypeptide containing a conserved Macin domain and eight cysteine residues forming four disulfide bonds. ApMacin transcripts were constitutively expressed in multiple tissues, with highest levels in gills, and were significantly upregulated in hemocytes, hepatopancreas, and gills following Vibrio parahaemolyticus challenge. Recombinant ApMacin (rApMacin) exhibited broad-spectrum binding activity to various pathogen-associated molecular patterns (PAMPs), including LPS, PGN, glucan, and chitin. rApMacin showed direct bacteriostatic and bactericidal activities against both Gram-positive (Micrococcus luteus) and Gram-negative (Vibrio anguillarum) bacteria, and significantly inhibited E. coli biofilm formation in a dose-dependent manner. Furthermore, rApMacin modulated hemocyte immune functions by enhancing chemotaxis while suppressing phagocytosis, reactive oxygen species (ROS) production. In vivo knockdown of ApMacin via RNA interference significantly impaired bacterial clearance, resulting in higher bacterial loads in hemocytes following V. parahaemolyticus infection. These findings demonstrate that ApMacin functions as a multifunctional AMP with both direct antimicrobial activity and immunomodulatory properties, contributing to the innate immune defense of A. pectinata against bacterial pathogens.