Apextrin from Ruditapes philippinarum functions as pattern recognition receptor and modulates NF-κB pathway

Apextrin belongs to ApeC-containing proteins (ACPs) and features a signal-peptide, an N-terminal membrane attack complex component/perforin (MACPF) domain, and a C-terminal ApeC domain. Recently, apextrin-like proteins were identified as pattern recognition receptor (PRR), which recognize the bacterial cell wall component and participate in innate immunity. Here, an apextrin ( Rpape ) was identified and characterized in Ruditapes philippinarum . Our results showed that Rpape mRNA was significantly induced under bacterial challenges. The Rpape recombinant protein exhibited a significant inhibitory effect on gram-positive bacteria ( Bacillus subtilis and Staphylococcus aureus ) and bound with Vibrio anguillarum, S. aureus and B. subtilis . We found Rpape protein positively activated the NF-κB signaling cascade and increased the activity of Nitric oxide (NO). This study revealed the immunity role of apextrin in R. philippinarum and provided a reference for further study on the role of apextrin in bivalves.